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Evolution of the charge density wave superstructure in ZrTe3 under pressure
Abstract
The material ZrTe3 is a well-known example of an incommensurate periodic lattice distortion (PLD) at low temperatures due to a charge density wave (CDW). Previous studies have found a sharp boundary as a function of pressure between CDW below 5 GPa and bulk superconductivity above this value. We present a study of low-temperature-high-pressure single crystal x-ray diffraction along with ab initio density functional theory calculations. The modulation vector qCDW is found to change smoothly with pressure until the PLD is lost. Fermi surface calculations reproduce these changes, but neither these nor the experimental crystal lattice structure show a particular step change at 5 GPa, thus leading to the conclusion that the CDW is lost accidentally by tipping the balance of CDW formation in the Fermi surface nesting that stabilizes it.
... Resistivity measurements on high-quality HfTe3 single crystals reveal pronounced anisotropic behaviors and obvious anomalies in both a(T) and c(T) but a very weak kink-like anomaly in b(T) at around 93 K [2]. In analog with the sister compound ZrTe3 [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], the transport anomaly at TCDW = 93 K has been ascribed to the formation of a CDW order within the ac-plane [6]. Since the c is about two orders of magnitude higher than a, the CDW should have a dominate 1D character along the -Te2-Te3-infinite chains. ...
... Intriguingly, we observed the emergence of an intrinsic filamentary SC in Ra(T) at T 4-5 K when the CDW of HfTe3 is suppressed completely by P 5 GPa, whereas no clear sign of SC is observed down to 1.4 K in Rb(T) and Rc(T), demonstrating an extraordinary case of Q1D SC rarely seen in real materials. We have analyzed the excess conductivity according to the theory of Aslamazov and Larkin (A-L) [21] and compared our results with those of ZrTe3 [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]22]. Finally, we discussed the observed Q1D SC in terms of the anisotropic FSs and the local pairs formed along the -Te2-Te3-chains parallel to the a-axis based on the first-principles electronic structure calculations. ...
... At ambient conditions, the cell volume of HfTe3 (228.70 Å 3 ) is about 1.35% smaller than that of ZrTe3 (231.83 Å 3 ), [8,20] which corresponds to the application of 0.84 GPa hydrostatic pressure on ZrTe3 given a compressibility of 0.016 GPa -1 [14]. At this pressure, it was found that the CDW transition of ZrTe3 is enhanced to ca. 100 K while the SC is suppressed completely [19,22], which are similar to the situations seen in HfTe3 at ambient pressure. ...
HfTe3 single crystal undergoes a charge-density-wave (CDW) transition at TCDW = 93 K without the appearance of superconductivity (SC) down to 50 mK at ambient pressure. Here, we determined its CDW vector q = 0.91(1) a* + 0.27(1) c* via low-temperature transimission electron microscope and then performed comprehensive high-pressure transport measurements along three major crystallographic axes. Our results indicate that the superconducting pairing starts to occur within the quasi-one-dimensional (Q1D) -Te2-Te3- chain at 4-5 K but the phase coherence between the superconducting chains cannot be realized along either the b- or c-axis down to at least 1.4 K, giving rise to an extremely anisotropic SC rarely seen in real materials. We have discussed the prominent Q1D SC in pressurized HfTe3 in terms of the anisotropic Fermi surfaces arising from the unidirectional Te-5px electronic states and the local pairs formed along the -Te2-Te3- chains based on the first-principles electronic structure calculations.
... [1][2][3][4] When the CDW order is suppressed by doping or pressure, a list of them can be tuned to superconductors. [5][6][7][8] In the temperature-doping (T -x) or temperature-pressure (T -p) phase diagram, sometimes a superconducting dome is observed on top of a CDW quantum critical point (QCP). [5][6][7][8] The reminiscent of this kind of phase diagram to that of the heavy-fermion and high-T c cuprate superconductors raises the possibility of unconventional superconductivity caused by CDW fluctuations. ...
... [5][6][7][8] In the temperature-doping (T -x) or temperature-pressure (T -p) phase diagram, sometimes a superconducting dome is observed on top of a CDW quantum critical point (QCP). [5][6][7][8] The reminiscent of this kind of phase diagram to that of the heavy-fermion and high-T c cuprate superconductors raises the possibility of unconventional superconductivity caused by CDW fluctuations. [5][6][7][8][9] ZrTe 3 is such a compound in which the CDW order and superconductivity compete and coexist. ...
... [5][6][7][8] The reminiscent of this kind of phase diagram to that of the heavy-fermion and high-T c cuprate superconductors raises the possibility of unconventional superconductivity caused by CDW fluctuations. [5][6][7][8][9] ZrTe 3 is such a compound in which the CDW order and superconductivity compete and coexist. [10] It belongs to a family of trichalcogenides MX 3 (M = Ti, Zr, Hf, U, Th, and X = S, Se, Te). ...
It was found that selenium doping can suppress the charge-density-wave (CDW) order and induce bulk superconductivity in ZrTe3. The observed superconducting dome suggests the existence of a CDW quantum critical point (QCP) in ZrTe3−x Sex near x ≈ 0.04. To elucidate the superconducting state near the CDW QCP, we measure the thermal conductivity of two ZrTe3−x Sex single crystals (x = 0.044 and 0.051) down to 80 mK. For both samples, the residual linear term κ 0/T at zero field is negligible, which is a clear evidence for nodeless superconducting gap. Furthermore, the field dependence of κ 0/T manifests a multigap behavior. These results demonstrate multiple nodeless superconducting gaps in ZrTe3−x Sex , which indicates conventional superconductivity despite of the existence of a CDW QCP.
... In each layer, 1-D chains along the b-direction spread in alignment along the a-direction [10,14,15]. Previous diffraction studies found a periodic lattice distortion in ZrTe3 [16][17][18][19][20]. Besides, a Kohn anomaly was observed by phonon measurements [14,16,21,22]. ...
... This observation is consistent with the resistivity anisotropy in Fig. 1(b), supporting that the CDW order along the a-direction is developed in the sample. The fast Fourier transformation (FFT) of this topography, as shown in Fig. 2(b), also reveals a high-intensity spot along a*-direction that defines a wave vector of ~0.07a*, which agrees with that determined by bulk diffraction measurements [17,18,26]. ...
Impurity pinning has long been discussed to have a profound effect on the dynamics of an incommensurate charge density wave (CDW), which would otherwise slide through the lattice without resistance. Here we visualize the impurity pinning evolution of the CDW in ZrTe3 using the variable temperature scanning tunneling microscopy (STM). At low temperatures, we observe a quasi-1D incommensurate CDW modulation moderately correlated to the impurity positions, indicating a weak impurity pinning. As we raise the sample temperature, the CDW modulation gets progressively weakened and distorted, while the correlation with the impurities becomes stronger. Above the CDW transition temperature, short-range modulations persist with the phase almost all pinned by impurities. The evolution from weak to strong impurity pinning through the CDW transition can be understood as a result of losing phase rigidity.
... Bulk SC can be induced in ZrTe 3 by applying physical pressure, intercalation, doping, and disorder [36][37][38][39][40][41][42][43][44][45][46][47]. A pressure-induced re-entrant SC in ZrTe 3 implies a possible unconventional SC mechanism [36], while the ultralow-temperature thermal conductivity indicates multiple nodeless gaps in ZrTe 3−x Se x [44]. ...
Charge density waves (CDWs) with superconductivity, competing Fermi surface instabilities and collective orders, have captured much interest in two-dimensional van der Waals (vdW) materials. Understanding of CDW suppression mechanism, its connection to emerging superconducting state and electronic correlations provides opportunities for engineering the electronic properties of vdW heterostructures and thin film devices. Using combination of the thermal transport, X-ray photoemission spectroscopy, Raman measurements, and first-principle calculations, we observe an increase in electronic correlations of the conducting states as CDW is suppressed in ZrTe$_3$ with 5\% Cu and Ni intercalation in the vdW gap. As superconductivity emerges, intercalation brings decoupling of quasi-one-dimensional conduction electrons with phonons as a consequence of intercalation-induced lattice expansion but also a drastic increase in Zr$^{2+}$ at the expense of Zr$^{4+}$ metal atoms. These observation demonstrate the potential of atomic intercalates in vdW gap for ground state tuning but also illustrate the crucial role of Zr metal valence in formation of collective electronic orders.
... Bulk SC can be induced in ZrTe 3 by applying physical pressure, intercalation, doping, and disorder [36][37][38][39][40][41][42][43][44][45][46][47]. A pressure-induced reentrant SC in ZrTe 3 implies a possible unconventional SC mechanism [36], while the ultralowtemperature thermal conductivity indicates multiple nodeless gaps in ZrTe 3−x Se x [44]. ...
Charge density waves (CDWs) with superconductivity, competing Fermi surface instabilities, and collective orders have captured much interest in two-dimensional van der Waals (vdW) materials. Understanding the CDW suppression mechanism, its connection to the emerging superconducting state, and electronic correlations provides opportunities for engineering the electronic properties of vdW heterostructures and thin-film devices. Using a combination of the thermal transport, x-ray photoemission spectroscopy, Raman measurements, and first-principles calculations, we observe an increase in electronic correlations of the conducting states as the CDW is suppressed in ZrTe 3 with 5% Cu and Ni intercalation in the vdW gap. As superconductivity emerges, intercalation brings not only decoupling of quasi-one-dimensional conduction electrons with phonons as a consequence of intercalation-induced lattice expansion but also a drastic increase in Zr 2+ at the expense of Zr 4+ metal atoms. These observations not only demonstrate the potential of atomic intercalates in the vdW gap for ground-state tuning but also illustrate the crucial role of the Zr metal valence in the formation of collective electronic orders.
... 27,28 Below T CDW , ZrTe 3 shows a filamentary-to-bulk SC at T c $ 2 K with local pair fluctuations; the SC first condenses into filaments along the a-axis and then becomes phase coherent below 2 K. Bulk SC with an enhanced T c is observed by applying pressure, intercalation, substitution, and disorder with suppression of the CDW order. [29][30][31][32][33][34][35][36][37][38][39] Pressure-induced reentrant SC in ZrTe 3 implies the possible unconventional Cooper pairing mechanism, 29 yet the ultra-low-temperature thermal conductivity indicates multiple nodeless gaps in ZrTe 3Àx Se x . 36 ZrTe 3Àx Se x displays SC with the T c up to 4.4 K for x $0.04, ...
Two-dimensional transition metal trichalcogenides (TMTCs) feature covalently bonded metal-chalcogen layers separated by the van der Waals (vdW) gap. Similar to transition metal dichalcogenides (TMDCs), TMTCs often host charge density waves (CDWs) and superconductivity, but unlike TMDCs, atomic chains in the crystal structure give rise to quasi one-dimensional (quasi 1D) conduction. ZrTe3 features the CDW below TCDW = 63 K and filamentary superconductivity below 2 K that can be enhanced by pressure or chemical substitution. Here, we report the presence of mixed valent Zr²⁺ and Zr⁴⁺ atoms in ZrTe3 crystals that are reduced by doping in ZrTe3−xSex and Zr1−yHfyTe3. Superconductivity is enhanced via disorder in Te2-Te3 atomic chains that are associated with CDW formation. Hf substitution on the Zr atomic site enhances TCDW due to unperturbed Te2-Te3 chain periodicity and enhanced electron-phonon coupling. Weak electronic correlations in ZrTe3−xSex are likely governed by the lattice contraction effects.
... At first, it seems to fulfill a better nesting condition across the in-plane twodimensional Fermi surface, which can be finely tuned by compression [25]. As a result, the resistivity exhibits an enhancement across T*. ...
CsV3Sb5 is a newly discovered Z2 topological kagome metal showing the coexistence of a charge density wave (CDW)-like order at T* = 94 K and superconductivity (SC) at Tc = 2.5 K at ambient pressure. Here we study the interplay between CDW and SC in CsV3Sb5 via measurements of resistivity and magnetic susceptibility under hydrostatic pressures. We find that the CDW transition decreases with pressure and experience a subtle modification at Pc1 = 0.6-0.9 GPa before it vanishes completely at Pc2 = 2 GPa. Correspondingly, Tc(P) displays an unusual M-shaped double dome character with two maxima around Pc1 and Pc2, respectively, leading to a tripled enhancement of Tc to about 8 K at 2 GPa. The obtained temperature-pressure phase diagram resembles those of many unconventional superconductors, illustrating an intimated competition between CDW-like order and SC. The competition is found to be particularly strong for the intermediate pressure range Pc1 <= P <= Pc2 as evidenced by the broad superconducting transition and reduced superconducting volume fraction. This work not only demonstrates the potential to raise the Tc of the V-based kagome superconductors, but also offers more insights into the rich physics related to the electronic correlations in this novel family of topological kagome metals.
... Bulk SC emerges in ZrTe 3 when the CDW is quenched, e.g., at hydrostatic pressures above P c ¼ 5 GPa [10] or in disordered samples grown at high temperatures [21]. For the quenching of the CDW under pressure, two potential mechanisms have been discussed: disorder [22,23], or a rearrangement of band fillings in the multisheet FS leading to the loss of the CDW stability [24]. In either scenario it is reasonable to assume that the SC involves electrons in the q1D sheets of the FS that have been identified as driving the CDW [18][19][20] and which show strong electron-phonon coupling (EPC) to lowenergy vibrational modes [25,26]. ...
The charge density wave (CDW) in ZrTe 3 is quenched in samples with a small amount of Te isoelectronically substituted by Se. Using angle-resolved photoemission spectroscopy we observe subtle changes in the electronic band dispersions and Fermi surfaces upon Se substitution. The scattering rates are substantially increased, in particular for the large three-dimensional Fermi surface sheet. The quasi-one-dimensional band is unaffected by the substitution and still shows a gap at low temperature, which starts to open from room temperature. Long-range order is, however, absent in the electronic states as in the periodic lattice distortion. The competition between superconductivity and the CDW is thus linked to the suppression of long-range order of the CDW.
... Raman spectr oscopy studies suggest the occurrence of a structural phase transition accompanying the pressureinduced CDW to SC transition [15]. However, no such indication of a structural phase transition was observed from xray diffraction (XRD) measurements up to 6 GPa [16]. Despite these high pressure investigations, previous studies were limited to pressures below 12 GPa. ...
We report the superconductivity enhancement of ZrTe3 on compression up to 33 GPa. The superconducting transition occurs above 4.1 GPa and the superconducting temperature (TC) increases with pressure in further compression, reaching a maximum of 7.1 K at ~28 GPa. An anomalous change of superconducting temperature is seen in the compression above 21 GPa. No structural phase transition is observed in the whole compression up to 36 GPa, but a subtle change in structural parameter is seen between 17 - 19 GPa, which seems relevant to the anomalous increase in the superconducting temperature. First-principle calculations reveal that the density of states of the Fermi level increases with pressure which explains the enhancement of TC in ZrTe3 under compression.
Photocarrier dynamics of the ZrTe3 under pressure are investigated using optical pump-probe (OPOP) spectroscopy in combination with a diamond anvil cell. A prominent laser heating effect is manifested, characterized by significant changes in the profiles and an elongation of the echo period as the pump fluence is increased. Furthermore, this heating effect is found to be enhanced at pressures below 2 GPa, gradually diminishing until it completely disappears at 6 GPa. Additionally, the estimated sound velocity at high pressures indicates a rapid increase with pressure. This study not only assesses the potential application of ZrTe3 in the field of ultrafast optoelectronic devices but also provides fundamental understanding on the electron structural transition under pressure.
Various transition-metal trichalcogenides (TMTC) show unique electronic properties, such as metal-insulator transition, topological insulator, and even superconducting transition. Currently, almost all metallic TMTC compounds can show superconductivity either at ambient pressure or at high pressure. However, most TMTC compounds are semiconductors and even insulators. Does superconductivity exist in any non-metallic TMTC compound by artificial manipulation? In this work, the electronic behavior of highly insulating HfS3 has been manipulated in terms of pressure. HfS3 undergoes an insulator-to-semiconductor transition near 17 GPa with a band gap reduction of ∼1 eV. Optical absorption, Raman spectroscopy, and X-ray diffraction measurements provide consistent results, suggesting the structural origin of the electronic transition. Upon further compression, HfS3 becomes a superconductor without further structural transition. The superconducting transition occurs as early as 50.6 GPa, and the Tc reaches 8.1 K at 121 GPa, which sets a new record for TMTCs. This work reveals that all TMTCs may be superconductors and opens a new avenue to explore the abundant emergent phenomena in the TMTC material family.
Two-dimensional (2D) transition metal chalcogenides (TMCs) have lately attracted broad interest in advanced photonics field due to their tunable bandgap, high broadband absorption, and excellent nonlinear optical (NLO) performances. Among other TMCs, group-IV transition metal trichalcogenides (TMTs) are rarely investigated for the NLO applications. Zirconium tritelluride (ZrTe3) is a kind of group-IV TMTs that shows metallic behavior among TMTs materials. While several electrical properties of ZrTe3 have been studied recently, the research community is longing to explore NLO features of ZrTe3. Herein, by using open aperture Z-scan method, the NLO properties of ZrTe3-nanosheets are investigated. The admirable NLO characteristics of ZrTe3 are realized from the obtained highest nonlinear absorption coefficient value of −82.1 × 10³ in 1 µm and −13.05 × 10³ cm/GW in 1.5 µm. Moreover, broadband fiber optics ZrTe3-based saturable absorbers (SAs) are prepared for the first time by depositing 2D-ZrTe3 nanosheets on a side-polished fiber. Following integration of these ZrTe3-SAs into three distinct rare earth-doped fiber laser cavities, stable mode-locking pulses with pulse widths of 323 ps (1 µm), 751 fs (1.5 µm), and 1.2 ps (2 µm) are obtained, respectively. These findings indicate that the ZrTe3 can facilitate the exploration of 2D materials in nonlinear optics and ultrafast photonics applications.
HfTe 3 single crystal undergoes a charge-density-wave (CDW) transition at T CDW = 93 K without the appearance of superconductivity (SC) down to 50 mK at ambient pressure. Here, we determined its CDW vector q = 0.91(1) a * + 0.27(1) c * via low-temperature transmission electron microscope and then performed comprehensive high-pressure transport measurements along three major crystallographic axes. Our results indicate that the superconducting pairing starts to occur within the quasi-one-dimensional (Q1D) -Te2-Te3- chain at 4–5 K but the phase coherence between the superconducting chains cannot be realized along either the b - or c- axis down to at least 1.4 K, giving rise to an extremely anisotropic SC rarely seen in real materials. We have discussed the prominent Q1D SC in pressurized HfTe 3 in terms of the anisotropic Fermi surfaces arising from the unidirectional Te-5p x electronic states and the local pairs formed along the -Te2-Te3- chains based on the first-principles electronic structure calculations.
Two-dimensional (2D) materials are at the forefront of current materials research due to their exciting and unique properties. 2D tellurides are emerging materials which are yet to be fully explored. To provide an overview of this emergent field, in this review, we discuss the structure, properties, synthesis methods, and applications of selected 2D tellurides, with stoichiometry of MxTey, and MxNyTez, (M, N are metal atoms). We present a summary of the latest advances in modeling, experimental synthesis, and characterization of 2D tellurides. Additionally, stress and strain-induced tunability of the physical properties have been reviewed, with a focus on the application of 2D tellurides in electronic, optoelectronic, and magnetic devices. We have discussed many emergent quantum properties of these materials. Finally, we conclude with a perspective on the future of 2D metal tellurides.
Impurity pinning has long been discussed to have a profound effect on the dynamics of an incommensurate charge density wave (CDW), which would otherwise slide through the lattice without resistance. Here, we visualize the impurity pinning evolution of the CDW in ZrTe3 using the variable temperature scanning tunneling microscopy. At low temperatures, we observe a quasi-1D incommensurate CDW modulation moderately correlated to the impurity positions, indicating a weak impurity pinning. As we raise the sample temperature, the CDW modulation gets progressively weakened and distorted, while the correlation with the impurities becomes stronger. Above the CDW transition temperature, short-range modulations persist with the phase almost all pinned by impurities. The evolution from weak to strong impurity pinning through the CDW transition can be understood as a result of losing phase rigidity.
The experimental determination of the superconducting transition requires the observation of the emergence of a zero-resistance and perfect diamagnetism state. Based on the close relationship between superconducting transition temperature ( ) and electron density of states (DOS), we take two typical superconducting materials Hg and ZrTe 3 as samples and calculate their DOS vs. temperature under different pressures by using the first-principle molecular dynamics simulations. According to the analysis of the calculation results, the main contributors that induce superconducting transitions are deduced by tracing the variation of partial density of states near . The microscopic mechanism of pressure induced increasing is further analyzed.
The strong in-plane anisotropy and quasi-1D electronic structures of transition-metal trichalcogenides (MX3; M = group IV or V transition metal; X = S, Se, or Te) have pronounced influence on moulding the properties of MX3 materials. In particular, the infinite trigonal MX6 prismatic chains running parallel to the b-axis are responsible for the manifestation of anisotropy in these materials. Several marvellous properties, such as inherent electronic, optical, electrical, magnetic, superconductivity, and charge density wave (CDW) transport properties, make transition-metal trichalcogenides (TMTCs) stand out from other 2D materials in the fields of nanoscience and materials science. In addition, with the assistance of pressure, temperature, and tensile strain, these materials and their exceptional properties can be tuned to a superior extent. The robust anisotropy and incommensurable properties make the MX3 family fit for accomplishing quite a lot of compelling applications in the areas of field effect transistors (FETs), solar and fuel cells, lithium-ion batteries, thermoelectricity, etc. In this review article, a precise audit of the distinctive crystal structures, static and dynamic properties, efficacious synthesis schemes, and enthralling applications of quasi-1D MX3 materials is made.
Crystalline and amorphous structures are two of the most common solid‐state phases. Crystals having orientational and periodic translation symmetries are usually both short‐range and long‐range ordered, while amorphous materials have no long‐range order. Short‐range ordered but long‐range disordered materials are generally categorized into amorphous phases. In contrast to the extensively studied crystalline and amorphous phases, the combination of short‐range disordered and long‐range ordered structures at the atomic level is extremely rare and so far has only been reported for solvated fullerenes under compression. Here, a report on the creation and investigation of a superconducting quasi‐1D material with long‐range ordered amorphous building blocks is presented. Using a diamond anvil cell, monocrystalline (TaSe4)2I is compressed and a system is created where the TaSe4 atomic chains are in amorphous state without breaking the orientational and periodic translation symmetries of the chain lattice. Strikingly, along with the amorphization of the atomic chains, the insulating (TaSe4)2I becomes a superconductor. The data provide critical insight into a new phase of solid‐state materials. The findings demonstrate a first ever case where superconductivity is hosted by a lattice with periodic but amorphous constituent atomic chains. Combination of long‐range ordered and short‐range disordered structures at the atomic level is demonstrated for a quasi‐1D linear chain compound. Under compression, the constituent atomic chains of the material are amorphized without breaking the orientational and periodic translation symmetries of the chain lattice. This lattice of amorphous atomic chains hosts a quantum condensate of Cooper pairs.
Quasi-one-dimensional (1D)/two-dimensional (2D) ZrTe3 attracts intensive interests as a typical charge density wave (CDW)-bearing material physically. However, limited by high time consumption up to even weeks and less morphological controllability for conventional chemical vapor transport (CVT) synthesis of ZrTe3 bulks, it is highly desirable to develop feasible methods for fast and controlled ZrTe3 growth, while so far has not been demonstrated. In this work, we first demonstrated that ZrTe3 nanoribbons can be grown directly by a modified chemical vapor deposition (CVD) method. The growth time is significantly reduced to less than 90 min, and the size of ZrTe3 nanoribbons can be well tuned by controlling the growth time and growth temperature. Moreover, differing from most of the other transition metal trichalcogenides (TMTCs), we reveal that ZrTe3 nanoribbons exhibit a competing and synergistic magnetic property between its intrinsic diamagnetism and unexpected ferromagnetism, which can be interpreted by the structural imperfection and edge-states due to the reduced dimensionality. Such observable ferromagnetism might favor for exploring its spin-electronic applications.
We describe the low-frequency current fluctuations, i.e. electronic noise, in quasi-one-dimensional ZrTe3 van der Waals nanoribbons, which have recently attracted attention owing to their extraordinary high current carrying capacity. Whereas the low-frequency noise spectral density, SI/I², reveals 1/f behavior near room temperature, it is dominated by the Lorentzian bulges of the generation–recombination noise at low temperatures (I is the current and f is the frequency). Unexpectedly, the corner frequency of the observed Lorentzian peaks shows strong sensitivity to the applied source–drain bias. This dependence on electric field can be explained by the Frenkel–Poole effect in the scenario where the voltage drop happens predominantly on the defects, which block the quasi-1D conduction channels. We also have found that the activation energy of the characteristic frequencies of the G-R noise in quasi-1D ZrTe3 is defined primarily by the temperature dependence of the capture cross-section of the defects rather than by their energy position. These results are important for the application of quasi-1D van der Waals materials in ultimately downscaled electronics.
Layered 1T−TiSe2 has attracted much interest for the competition of charge density wave (CDW) and superconductivity in its bulk and even monolayer forms. Here we perform first-principles calculations of the electronic structure, phonon dispersion, and electron-phonon coupling of the Pb-intercalated 1T−TiSe2 in bulk and layered structures. Results show that upon the Pb atom intercalation, the CDW instability in 1T−TiSe2 can be effectively suppressed, accompanied by the removal of the imaginary phonon modes at qM. The Pb 6p orbitals occupy directly at the Fermi level. Both bulk and layered PbTiSe2 are phonon-mediated superconductors, with estimated superconducting temperature Tc to be ∼1.6–3.8 K. The main contribution to the electron-phonon coupling is from the vibrations of Pb and Se atoms and the superconductivity is mainly raised by Pb. The superconducting related physical quantities are found tunable by varying Pb content.
We experimentally investigate the thermoelectric power (Seebeck effect) of quasi-2D single crystals of titanium and zirconium trichalcogenides (TiS3, ZrS3, ZrSe3 and ZrTe3) under applied high pressure up to 10 GPa. Both sulphides were characterized by n-type semiconducting conduction in the whole pressure range investigated, and generally, showed moderate pressure responses of their electronic properties. Metallic ZrTe3 kept its p-type conduction under pressure and its Seebeck coefficient curve displayed a distinct crossover near 2 GPa. Semiconducting ZrSe3 demonstrated more remarkable responses to applied pressure, which included a multi-order gradual drop in its electrical resistance value up to 9 GPa and an n-p inversion of the dominant conduction type around 6 GPa. Furthermore, we found that a thermoelectric power factor of ZrSe3 may be greatly improved under high applied pressure, achieving a value of an order of 3.5 mW/(K2m) at 9.5 GPa. Thus, an appropriately strained p-type ZrSe3 with a dramatically reduced band gap value turns to be a promising thermoelectrics. One can anticipate that ZrSe3-ZrTe3 solid solutions, in which the addition of ZrTe3 should decrease the band gap value of ZrSe3 in a controlled manner, could also demonstrate high thermoelectric performance parameters. Reversibility and reproducibility of the pressure-driven changes in the electronic properties of ZrSe3 suggest that it has a potential for other industrial applications linked to cyclic stress loads, e.g., in n-p switches or control of p-n-p transistor elements.
The mechanism of emergent bulk superconductivity in transition metal intercalated ZrTe3 is investigated by studying the effect of Ni doping on the band structure and charge density wave (CDW). The study reports theoretical and experimental results in the range of Ni0.01ZrTe3 to Ni0.05ZrTe3. In the highest doped samples bulk superconductivity with Tc < TCDW is observed, while TCDW is strongly reduced. Relativistic ab-initio calculations reveal Ni incorporation occurs preferentially through intercalation in the van-der-Waals gap. Analysis of the structural and elec- tronic effects of intercalation, indicate buckling of the Te-sheets adjacent to the Ni site akin to a locally stabilised CDW-like lattice distortion. Experiments by low temperature x-ray diffraction, angle-resolved-photoemission spectroscopy (ARPES) as well as temperature dependent resistivity reveal the nearly unchanged persistence of the CDW into the regime of bulk superconductivity. The CDW gap is found to be unchanged in its extent in momentum space, with the gap size also unchanged or possibly slightly reduced on Ni intercalation. Both experimental observations suggest that superconductivity coexists with the CDW in NixZrTe3.
The charge density wave (CDW) in ZrTe3 is quenched in samples with small amount of Te iso-electronically substituted by Se. Using angle-resolved photoemission spectroscopy we observe subtle changes in the electronic band dispersions and Fermi surfaces on Se substitution. The scattering rates are substantially increased, in particular for the large three-dimensional Fermi surface sheet. The quasi-one-dimensional band is unaffected by the substitution and still shows a gap at low temperature, which starts to open from room temperature. The detailed temperature dependence reveals that the long-range order is absent in the electronic states as in the periodic lattice distortion. The competition between superconductivity and CDW is thus linked to the suppression of long-range order of the CDW.
Charge density wave (CDW), the periodic modulation of the electronic charge density, will open a gap on the Fermi surface that commonly leads to decreased or vanishing conductivity. On the other hand superconductivity, a commonly believed competing order, features a Fermi surface gap that results in infinite conductivity. Here we report that superconductivity emerges upon Se doping in CDW conductor ZrTe3 when the long range CDW order is gradually suppressed. Superconducting critical temperature Tc(x) in ZrTe3-xSex (0 ≤ x ≤ 0.1) increases up to 4 K plateau for 0.04 ≤ x ≤ 0.07. Further increase in Se content results in diminishing Tc and filametary superconductivity. The CDW modes from Raman spectra are observed in x = 0.04 and 0.1 crystals, where signature of ZrTe3 CDW order in resistivity vanishes. The electronic-scattering for high Tc crystals is dominated by local CDW fluctuations at high temperatures, the resistivity is linear up to highest measured T = 300 K and contributes to substantial in-plane anisotropy.
The electronic band structure and Fermi surface of ZrTe3 was precisely determined by linearly polarized angle-resolved photoelectron spectroscopy. Several bands and a large part of the Fermi surface are found to be split by 100-200 meV into two parallel dispersions. Band structure calculations reveal that the splitting is due to a change of crystal structure near the surface. The agreement between calculation and experiment is enhanced by including the spin-orbit potential in the calculations, but the spin-orbit energy does not lead to a splitting of the bands. The dispersion of the highly nested small electron pocket that gives rise to the charge density wave is traceable even in the low-temperature gapped state, thus implying that the finite correlation length of the long-wavelength modulation leads to a smearing of the band back-folding.
A strong Kohn anomaly in ZrTe3 is identified in the mostly transverse acoustic phonon branch along the modulation vector q_{P} with polarization along the a;{*} direction. This soft mode freezes to zero frequency at the transition temperature T_{P}, and the temperature dependence of the frequency is strongly affected by fluctuation effects. Diffuse x-ray scattering of the incommensurate superstructure shows a power-law scaling of the intensity and the correlation length that is compatible with an order parameter of dimension n=2.
Superconductivity evolves as functions of pressure or doping from
charge-ordered phases in a variety of strongly correlated systems, suggesting
that there may be universal characteristics associated with the competition
between superconductivity and charge order in these materials. We present an
inelastic light (Raman) scattering study of the structural changes that precede
the pressure-tuned charge-density-wave (CDW) to superconductor transition in
one such system, ZrTe3. In certain phonon bands, we observe dramatic linewidth
reductions that accompany CDW formation, indicating that these phonons couple
strongly to the electronic degrees of freedom associated with the CDW. The same
phonon bands, which represent internal vibrations of ZrTe3 prismatic chains,
are suppressed at pressures above ~10 kbar, indicating a loss of long-range
order within the chains, specifically amongst intrachain Zr-Te bonds. These
results suggest a distinct structural mechanism for the observed
pressure-induced suppression of CDW formation and provide insights into the
origin of pressure-induced superconductivity in ZrTe3.
Layered ZrTe3 crystallizes in an unusual structure that consists of both quasi-one-dimensional and quasi-two-dimensional features, conducive to the formation of charge-density wave and superconductivity, respectively. Bulk superconductivity up to 4 K in single crystalline samples of layered ZrTe3 has been successfully induced through high growth temperature. This procedure induces atomic disorders at both the Zr and the Te1 sites, as evident from the x-ray-diffraction study. As a result, the charge-density wave is partially suppressed without chemical doping or pressurization. The observation helps to understand the peculiar superconductivity of ZrTe3 and suggests a new path for the induction of superconductivity in complicated compounds with competitive orderings.
The electron-phonon interaction is a major factor influencing the competition
between collective instabilities in correlated-electron materials, but its role
in driving high-temperature superconductivity in the cuprates remains poorly
understood. We have used high-resolution inelastic x-ray scattering to monitor
low-energy phonons in YBa$_2$Cu$_3$O$_{6.6}$ (superconducting $\bf T_c = 61$
K), which is close to a charge density wave (CDW) instability. Phonons in a
narrow range of momentum space around the CDW ordering vector exhibit extremely
large superconductivity-induced lineshape renormalizations. These results imply
that the electron-phonon interaction has sufficient strength to generate
various anomalies in electronic spectra, but does not contribute significantly
to Cooper pairing. In addition, a quasi-elastic "central peak" due to CDW
nanodomains is observed in a wide temperature range above and below $\bf T_c$,
suggesting that the gradual onset of a spatially inhomogeneous CDW domain state
with decreasing temperature is a generic feature of the underdoped cuprates.
We present the results of a combined experimental and theoretical study of the electronic structure of ZrTe3. ZrTe3 is a material that undergoes a transition to a charge density wave state at 63K and displays superconductivity below 2K. The results of photoemission measurements using synchrotron radiation as well as temperature dependent resistivity and thermopower data allow one to sketch a detailed experimental picture of the electronic structure at the Fermi level. High level TB-LMTO-ASA band structure calculations are used to analyze the bonding situation in ZrTe3 and to relate the physical properties of the crystal to the electronic structure. ZrTe3 is a layered material whose structure is built up from trigonal prismatic ZrTe3 chains with extensive TeTe interactions perpendicular to the chain direction. These TeTe interactions lead to wide bands in the direction perpendicular to the chains of trigonal prisms. Frozen phonon calculations indicate that the density of states at the Fermi level and the shape of the Fermi surface are strongly dependent on the TeTe interprism interactions. The complete computed Fermi surface consists of three independent envelopes: two sheet-like surfaces which are associated with the atoms of the Te2 group and a cylindrical section, the former one being responsible for the observed charge density wave properties of ZrTe3. The experimental and calculated nesting vectors for the charge density wave are in excellent agreement. A comparison of the band structures of ZrTe3 with those of the isostructural HfTe3 and ThTe3 reveals that HfTe3 should exhibit similar electronic properties as ZrTe3, whereas ThTe3 should be semimetallic. Based on the results of the frozen phonon calculations, we predict a strong pressure dependence of the physical properties of ZrTe3 and HfTe3.
We have shown that the superconducting transitions in ZrTe3 are successive from filamentary to bulk, based on experimental results obtained for a superconducting specific-heat anomaly and the anisotropic superconducting transition curve of resistivity. A small jumplike superconducting specific-heat anomaly with a large and widely extended tail was observed to closely follow the anisotropic zero-resistance transition. We concluded that the jumplike anomaly signifies the onset of the long-range order of Cooper pairs with the opening of a superconducting gap at TC, while the large and widely extended tail indicates behavior induced by Cooper pairs with a very short coherence length. As a limit for a very short coherence length, we propose local pairs with Bose characteristics. As a result, we can understand that the filamentary superconductivity is caused by the local pairs, and the large and widely extended tail is in a crossover region between superconductivity induced by local pairs and that induced by Cooper pairs. Based on a discussion about the origin of the change in the pair coupling from the starting of local pairing to Cooper pairing in ZrTe3, we conclude that “mixed bulk-filament superconductivity” results from unique electronic structural changes in the quasi-1D+3D (D, dimensional) Fermi surfaces after the CDW transition.
The concept that superconductivity competes with other orders in cuprate superconductors has become increasingly apparent,
but obtaining direct evidence with bulk-sensitive probes is challenging. We have used resonant soft x-ray scattering to identify
two-dimensional charge fluctuations with an incommensurate periodicity of ~3.2 lattice units in the copper-oxide planes of
the superconductors (Y,Nd)Ba2Cu3O6+x, with hole concentrations of 0.09 to 0.13 per planar Cu ion. The intensity and correlation length of the fluctuation signal
increase strongly upon cooling down to the superconducting transition temperature (Tc); further cooling below Tc abruptly reverses the divergence of the charge correlations. In combination with earlier observations of a large gap in the
spin excitation spectrum, these data indicate an incipient charge density wave instability that competes with superconductivity.
Superconductivity often emerges in the proximity of, or in competition with,
symmetry breaking ground states such as antiferromagnetism or charge density
waves (CDW)1-5. A number of materials in the cuprate family, which includes the
high-transition-temperature (high-Tc) superconductors, show spin and charge
density wave order5-7. Thus a fundamental question is to what extent these
ordered states exist for compositions close to optimal for superconductivity.
Here we use high-energy x-ray diffraction to show that a CDW develops at zero
field in the normal state of superconducting YBa2Cu3O6.67 (Tc = 67 K). Below
Tc, the application of a magnetic field suppresses superconductivity and
enhances the CDW. Hence, the CDW and superconductivity are competing orders in
this typical high-Tc superconductor, and high-Tc superconductivity can form
from a pre-existing CDW state. Our results explain observations of small Fermi
surface pockets8, negative Hall and Seebeck effect9,10 and the "Tc plateau"11
in this material when underdoped.
We report discovery of bulk superconductivity in Ni0.05ZrTe3 at Tc = 3.1 K,
obtained through Ni intercalation. Superconductivity coexists with charge
density wave (CDW) state with TCDW = 41 K. When compared to parent material
ZrTe3, filamentary superconducting transition is substantially increased
whereas TCDW was suppressed. The analysis of superconducting state indicates
that Ni0.05ZrTe3 is an intermediately coupled superconductor.
Scanning tunneling microscopy and spectroscopy measurements in the superconducting dichalcogenide 2H-NbS2 show a peculiar superconducting density of states with two well-defined features at 0.97 and 0.53 meV, located, respectively, above and below the value for the superconducting gap expected from the single band s-wave BCS model (Delta=1.76k_(B)T_(c)=0.9 meV). Both features have a continuous temperature evolution and disappear at T_(c)=5.7 K. Moreover, we observe the hexagonal vortex lattice with radially symmetric vortices and a well-developed localized state at the vortex cores. The sixfold star shape characteristic of the vortex lattice of the compound 2H-NbSe2 is, together with the charge density wave order, absent in 2H-NbS2.
Electrical resistivity and magnetic susceptibility of ZrTe3 were measured. The superconductivity below 2K is found not bulk but of filamentary.
The Fermi surface topology of the layered superconducting charge density wave compound ZrTe3is investigated by angle resolved photoelectron spectroscopy and density functional theory. The Fermi surface is dominated by bands originating from two perpendicular systems of quasi one-dimensional chains. Nesting and opening of a pseudogap at temperatures as high as 250 K are signatures of a Peierls transition in one of these chains. The nesting properties are also studied for high pressure simulated crystal structure.
This article reviews the static and dynamic properties of spontaneous
superstructures formed by electrons. Representations of such electronic
crystals are charge density waves and spin density waves in inorganic as well
as organic low dimensional materials. A special attention is paid to the
collective effects in pinning and sliding of these superstructures, and the
glassy properties at low temperature. Charge order and charge
disproportionation which occur in organic materials resulting from correlation
effects are analysed. Experiments under magnetic field, and more specifically
field-induced charge density waves are discussed. Properties of meso- and
nanostructures of charge density waves are also reviewed.
Because of inconsistencies in literature data, the crystal structure of ZrTe3was redetermined from single-crystal data and the electronic band structure was calculated using density functional theory in the local density approximation (LDA) and the linear muffin tin orbital method (LMTO). ZrTe3crystallizes in the monoclinic space groupP21/mwitha=589.8(1) pm,b=392.69(3) pm,c=1010.3(1) pm, andβ=97.81(1)° (Z=2) in the ZrSe3structure type (ωdata collection,Rw=1.88%). In the layer structure of ZrTe3almost linear homonuclear Te chains in [100] direction with alternating distances of 279.4(1) and 310.5(1) pm are observed. In addition to these, there are several other Te–Te distances below the sum of the radii of Te2−ions (370–380 pm). From the band structure calculations we found these homonuclear contacts to be responsible for the unexpected metallic conductivity of ZrTe3. The calculation of the Fermi surface revealed three branches. The one caused by the intersection ofEFwith bands of predominantly Te chain character shows an extended region of approximately parallel Fermi surface. The nesting vector, which lies in the range q→≈(0.95±0.05)a→*+(0.35±0.15)c→*, is in fair agreement with data from an electron diffraction study of ZrTe3, which has shown the presence of a charge density wave at a temperature of 63 K with the vector q→≈0.93a→*+0.33c→*.
We report on an intricate competition between charge density wave (CDW) formation and superconductivity under pressure up to 11 GPa in the low-dimensional conductor ZrTe3 . As pressure increases, the CDW transition temperature TCDW initially increases, then begins to decrease at 2 GPa and abruptly disappears near 5 GPa. On the other hand, while the superconducting transition temperature TC falls to below 1.2 K at ˜0.5GPa and is not observed at up to 5 GPa above 2.5 K, a superconducting transition emerges beginning at ˜5GPa and TC increases steeply up to 11 GPa. This is an observation of pressure-induced reentrant superconductivity. The results are discussed in terms of the change in the reduced area of the Fermi surface due to CDW formation.
Through detailed examination of the crystal structure and bonding conditions in the trichalcogenides, it has been possible to gain a deeper understanding of the band structure of these complex materials, and with this of their unusual electronic behavior. The character of the observed semimetallicity in TaSe3 and NbSe3 is much clarified. Each material in the group-V family is seen to achieve a very individually tailored band structure, enfolding the various structural and energy-level adjustments. The nonuniformity and the molecularization of these structures contrasts strongly with the dichalcogenide behavior. The structural, if not the electronic, dimensionality of the group-V trichalcogenides remains closer to two than to one. It is found that the periodic structural distortions developed by NbSe3 are probably more suited to a metal-metal bonding description than to the traditional Fermi surface determined instability of a charge-density wave. The field-induced sliding of these distortions can then be described in terms of cooperative bond flipping through a discommensurate superlattice. We examine in crystal chemical terms why this motion is so unusually weakly pinned to defects and impurities in NbSe3. In fact, the investigation shows that it will be very hard to find a material better suited to the realization of this phenomenon.
Angle-resolved photoemission spectroscopy of ZrTe3 has been performed from room temperature (T) down to 6 K (across TCDW=63 K) to study the charge-density-wave (CDW) fluctuation effects in a metallic CDW compound having Fermi surface (FS) sheets with differing dimensionality. While spectra on the three-dimensional (3D) FS show typical Fermi–Dirac functionlike T dependence, those along the quasi-one-dimensional (1D) FS show formation of a pseudogap, starting at a much higher T than TCDW. Simultaneously, a van-Hove singularity consisting of the quasi-1D FS intersecting the 3D FS shows an increase of coherence. This demonstrates the role of CDW fluctuations on the spectral function, and relation to the dimensionality of the states, in a metallic CDW system.
The exchange-correlation functionals of the generalized gradient approximation (GGA) are still the most used for the calculations of the geometry and electronic structure of solids. The PBE functional [ J. P. Perdew et al. Phys. Rev. Lett. 77 3865 (1996)], the most common of them, provides excellent results in many cases. However, very recently other GGA functionals have been proposed and compete in accuracy with the PBE functional, in particular for the structure of solids. We have tested these GGA functionals, as well as the local-density approximation (LDA) and TPSS (meta-GGA approximation) functionals, on a large set of solids using an accurate implementation of the Kohn-Sham equations, namely, the full-potential linearized augmented plane-wave and local orbitals method. Often these recently proposed GGA functionals lead to improvement over LDA and PBE, but unfortunately none of them can be considered as good for all investigated solids.
An electron microscope study of ZrTe3 shows that this material supports two modulations. One is unstable and lacks long-range order, and may be linked to compositional modulation. The second is associated with a phase transition already observed in the electrical and mechanical properties and may be attributed to the formation of a charge-density-wave normal to the metal atom chains.
The density functional theory (DFT) computation of electronic structure, total energy and other properties of materials, is a field in constant progress. In order to stay at the forefront of knowledge, a DFT software project can benefit enormously from widespread collaboration, if handled properly. Also, modern software engineering concepts can considerably ease its development. The ABINIT project relies upon these ideas: freedom of sources, reliability, portability, and self-documentation are emphasised, in the development of a sophisticated plane-wave pseudopotential code.We describe ABINITv3.0, distributed under the GNU General Public License. The list of ABINITv3.0 capabilities is presented, as well as the different software techniques that have been used until now: PERL scripts and CPP directives treat a unique set of FORTRAN90 source files to generate sequential (or parallel) object code for many different platforms; more than 200 automated tests secure existing capabilities; strict coding rules are followed; the documentation is extensive, including online help files, tutorials, and HTML-formatted sources.
A scheme that reduces the calculations of ground-state properties of systems of interacting particles exactly to the solution of single-particle Hartree-type equations has obvious advantages. It is not surprising, then, that the density functional formalism, which provides a way of doing this, has received much attention in the past two decades. The quality of the energy surfaces calculated using a simple local-density approximation for exchange and correlation exceeds by far the original expectations. In this work, the authors survey the formalism and some of its applications (in particular to atoms and small molecules) and discuss the reasons for the successes and failures of the local-density approximation and some of its modifications.
We report the coexistence of bulk superconductivity with T(c)=3.8 K and charge density wave (CDW) in Cu intercalated quasi-two-dimensional crystals of ZrTe(3). The Cu intercalation results in the expansion of the unit cell orthogonal to the Zr-Zr metal chains and partial filling of CDW energy gap. We present anisotropic parameters of the superconducting state. We also show that the contribution of CDW to the scattering mechanism is anisotropic in the a-b plane. The dominant scattering mechanism in the normal state for both ZrTe(3) and Cu(0.05)ZrTe(3) along the b axis is the electron-electron umklapp scattering.
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