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ARPES results from bulk Fe1.08Te. (a) Constant energy contour acquired at hν = 65 eV by integrating the spectral weight in a 120 meV window around the Fermi energy. The purple dashed squares visualize the projected Fe1.08Te first and second bulk BZs with their high symmetry points (marked by small purple circles). The inset shows the LEED pattern used to determine the sample orientation (Ekin = 128 eV). (b) Photoemission intensity along the Γ¯1−M¯1−Γ¯2 directions and (c) the corresponding curvature plot. The solid red and green lines are the first principles calculations for the dispersion along Γ−M−X and Z − A − R, respectively. The calculations have been renormalized by a factor of ≈2 and shifted to align best with the experimental data. The light blue line indicates the Fermi level of the first principle calculations and the dashed black and white lines the Fermi level of the photoemission and curvature data, respectively. (d), (e) Photoemission intensity and curvature along the Γ¯1−M¯1−X¯1−Γ¯1 directions.
Source publication
The electronic structure of thin films of FeTe grown on Bi$_2$Te$_3$ is investigated using angle-resolved photoemission spectroscopy, scanning tunneling microscopy and first principles calculations. As a comparison, data from cleaved bulk \FeTe taken under the same experimental conditions is also presented. Due to the substrate and thin film symmet...
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Citations
... The ARPES Fermi surfaces and LEED patterns of the FeCh MLs [Fig. 2(a) and (e)] exhibit the characteristic 12-fold symmetric (kx, ky)-space pattern in line with the previously reported formation of three equally prominent 60-rotated tetragonal FeTe and FeSe island domains (D1, D2, and D3 hereafter) on the hexagonal Bi2Te3(0001) and Bi2Se3(0001) surface symmetry[14,17].Dark-field microscopy imaging inFig. 3(a)reveals D1, D2, and D3 domain widths in the range of 5 nm -100 nm, which we approximate by a normal distribution of (50 ± 20) nm. ...
FeTe monolayer islands situated on a topological insulator Bi2Te3 (0001) surface were recently reported to exhibit the opening of an energy gap below temperatures T ~ 6 K, which can be due to a superconducting phase transition. In this work, we present a magnetic field dependent transport study proving that this gap is indeed of superconducting origin. Upon cooling, several drops in resistance are observed in the temperature range between 6 K and 2 K, indicating multiple transitions. Using the Ginzburg-Landau theory, we show that the critical magnetic field of the dominant high-temperature transition at ~ 6 K is governed by orbital Cooper pair breaking in larger FeTe islands, large enough to exceed the superconductive coherence length\(\xi\). At smaller island sizes, transitions at lower temperatures < 6 K become more prominent, showing significantly increased critical fields dominated by paramagnetic pair breaking. The multiphase superconducting behavior is in line with an observed wide distribution of FeTe islands width 5 nm − 100 nm and seems to reflect disorder effects at the interface to Bi2Te3. The proof of local superconductivity makes the FeTe interface to the topological insulator Bi2Te3 substrate a potential host of topological superconductivity.
... Again we start our discussion in the decapped state prior to FeSe growth. Figure 4 [30] we comment here that the strong differences in In the energy range EB = 1.5-2.5 eV of figures 4(e) and (f), measured bands appear to be particularly broad and not well represented by our DFT calculations. Our ground state calculations do not contain any renormalization procedures, and the observed broadening might be captured e.g. by theory approaches including incoherent many-body excitations in Fe 3d states [31]. ...
... Closer to E F a camel-back shaped band appears at EB = 0.25 eV nearΓ, which we show in detail in the lower panels of figures 4(e) and (f). This band is often denoted as ω band and has been observed in FeSe/STO interfaces [32] but also in the Te-based counterpart FeTe/Bi 2 Te 3 [30] at comparable EBs. It is characteristic for the FeCh band structure [see e.g. ...
Enhanced superconductivity of FeSe in the 2D limit on oxide surfaces as well as the prediction of topological superconductivity at the interface to topological insulators makes the fabrication of Fe-chalcogenide monolayers a topic of current interest. So far superconductive properties of the latter are mostly studied by scanning tunneling spectroscopy, which can detect gaps in the local density of states as an indicator for Cooper pairing. Direct macroscopic transport properties, which can prove or falsify a true superconducting phase, are yet widely unexplored due to the difficulty to grow monolayer films with homogeneous material properties on a larger scale. Here we report on a promising route to fabricate micron-scale continuous carpets of monolayer thick FeSe on Bi 2 Se 3 topological insulators. In contrast to previous procedures based on ultraflat bulk Bi 2 Se 3 surfaces, we use molecular beam epitaxy grown Bi 2 Se 3 films with high step-edge densities (terrace widths 10–100 nm). We observe that step edges promote the almost strainless growth of coalescing FeSe domains without compromising the underlying Bi 2 Se 3 crystal structure.
... This results in a clean, uncontaminated, and atomically flat surface. 31 The cleaving procedure splits the sample along the weakly bound van der Waals gaps between the FeTe layers. This way, STM measurements were always performed on the topmost Te layer. ...
... Annealing the cleaved Fe 1+y Te crystal at 430 K for 30 min results in a clean Fe 1+y Te surface. 31 The surface corrugation and transition temperature T N of Fe 1+y Te are not affected by this mild annealing procedure as verified by the comparison of Fe 1.08 Te crystals before and after the process. This indicates that the intrinsic excess Fe amount y is not affected by the annealing procedure as well. ...
The investigation of the magnetic phase transitions in the parent compounds of Fe-based superconductors is regarded essential for an understanding of the pairing mechanism in the related superconducting compounds. Even though the chemical and electronic properties of these materials are often strongly inhomogeneous on a nanometer length scale, studies of the magnetic phase transitions using spatially resolved experimental techniques are still scarce. Here, we present a real space spin-resolved scanning tunneling microscopy investigation of the surface of Fe 1+y Te single crystals with different excess Fe content, y, which are continuously driven through the magnetic phase transition. For Fe 1.08 Te, the transition into the low-temperature monoclinic phase is accompanied by the appearance of a chevron-patterned structural ordering due to the four 90° rotational domains of the monoclinic lattice. Each of the structural domains contains locally commensurate nanoscale diagonal double stripe antiferromagnetic spin order domains with π-phase slips accross domain boundaries. In the low-temperature phase of Fe 1.12 Te, on the other hand, the chevron pattern gets rather narrow and less well-defined, and an additional 90° rotated component of the spin-order with local plaquette order emerges. The simultaneous imaging of spin and structural order we show here gives valuable insights into the nature of the magneto-structural domains of Fe 1+y Te near the tricritical point, which presumably add to the understanding of the mechanism of superconductivity in the related Fe 1+y Te x Se 1−x material.
The interface between two-dimensional topological Dirac states and an s-wave superconductor is expected to support Majorana bound states that can be used for quantum computing applications. Realizing these novel states of matter and their applications requires control over superconductivity and spin-orbit coupling to achieve spin-momentum locked topological surface states which are simultaneously superconducting. While signatures of Majorana bound states have been observed in the magnetic vortex cores of bulk FeTe0.55 Se0.45 , inhomogeneity and disorder from doping makes these signatures unclear and inconsistent between vortices. Here we report superconductivity in monolayer FeTe1-y Sey (Fe(Te,Se)) grown on Bi2 Te3 by molecular beam epitaxy. Spin and angle resolved photoemission spectroscopy directly resolves the interfacial spin and electronic structure of Fe(Te,Se)/Bi2 Te3 heterostructures. We find that for y = 0.25 the Fe(Te,Se) electronic structure overlaps with the topological Bi2 Te3 interfacial states and the desired spin-momentum locking is not observed. In contrast, for y = 0.1 we find reduced inhomogeneity measured by scanning tunneling microscopy and a smaller Fe(Te,Se) Fermi surface with clear spin-momentum locking in the topological states. Hence, we demonstrate the Fe(Te,Se)/Bi2 Te3 system is a highly tunable platform for realizing Majorana bound states where reduced doping can improve characteristics important for Majorana interrogation and potential applications. This article is protected by copyright. All rights reserved.
We present an investigation on the controlled growth of epitaxial iron telluride films of multiple phases by molecular beam epitaxy. By optimizing the substrate temperature, we fabricate different phases of α-FeTe, β-FeTe, and FeTe2, respectively, whose crystalline morphologies are determined by means of in situ scanning tunneling microscopy/spectroscopy and ex situ scanning transmission electron microscopy. While both α- and β-FeTe films are metallic, we uncover a ∼185- and 65-mV semiconducting band gap for the (100) and (011) facets of FeTe2 film, respectively, with the former one being compatible with the first principles calculations. Moreover, for FeTe2, we observe reduced gaps with enhanced conductance in the vicinity of edge boundaries, which are dependent on the geometries of step orientation and possibly in correlation to the magnetic anisotropy with structural distortion. Our study provides insight into the controllable synthesis of Fe-Te compounds with variation of stoichiometries and surface terminations, which may generalize to other epitaxial Fe chalcogenide films.
How superconductivity emerges from antiferromagnetic ordering is an essential question for Fe-based superconductors. Here, we explore the effect of dimensionality on the interplay between antiferromagnetic ordering and superconductivity by investigating nanoribbons of single-layer FeTe1-xSe
x
films grown on SrTiO3(001) substrates by molecular beam epitaxy. Using scanning tunneling microscopy/spectroscopy, we find a one-dimensional (1D) superconducting channel 2 nm wide with a TC of 42 ± 4 K on the edge of FeTe1-xSe
x
(x < 0.1) ribbons, coexisting with a non-superconducting ribbon interior that remains bicollinear antiferromagnetically ordered. Density functional theory calculations indicate that both Se and the presence of the edge destabilize the bicollinear antiferromagnetic magnetic order, resulting in a paramagnetic region near the edge with strong local checkerboard fluctuations that is conducive to superconductivity. Our results represent the highest TC achieved in 1D superconductors and demonstrate an effective route toward stabilizing superconductivity in Fe-based superconductors at reduced dimensions.
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We studied the temperature dependence of the diagonal double-stripe spin order in one and two unit cell thick layers of FeTe grown on the topological insulator Bi_2Te_3 via spin-polarized scanning tunneling microscopy. The spin order persists up to temperatures which are higher than the transition temperature reported for bulk Fe_1+yTe with lowest possible excess Fe content y. The enhanced spin order stability is assigned to a strongly decreased y with respect to the lowest values achievable in bulk crystal growth, and effects due to the interface between the FeTe and the topological insulator.
