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a Components of the magnetization vector, M T and M L , as a function of the angle for T70 K and H8 kOe. The direction of rotation is such that the conditions Hc,H CD, and H c proceed in that order. b M T vs M L polar graph of the same CW rotation of a full symbols together with the CCW rotation.
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We have measured the irreversible magnetization (Mi) of an ErBa2Cu3O7-delta single crystal with columnar defects (CD), using a technique based on sample rotation under a fixed magnetic field H. This method is valid for samples whose magnetization vector remains perpendicular to the sample surface over a wide angle range-which is the case for platel...
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... now focus on the high field range, where the crystal is in the mixed state. Figure 2a shows M L () and M T () for a rotation at 70 K and 8 kOe, where the angle independent background due to the holder has already been removed from M L . As the reversible magnetization of the superconductor ( 0 /32 2 2 )ln(H c2 /H)5G is negligible compared to M i , the response is dominated by vortex pinning. ...
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... mixed state. Figure 2a shows M L () and M T () for a rotation at 70 K and 8 kOe, where the angle independent background due to the holder has already been removed from M L . As the reversible magnetization of the superconductor ( 0 /32 2 2 )ln(H c2 /H)5G is negligible compared to M i , the response is dominated by vortex pinning. The curves in Fig. 2a sexhibit a rich structure, due to the combination of crystalline anisotropy, directional vortex pinning and geo- metrical effects. In order to extract useful information from them, we must first establish the relation between M i and the screening current J flowing through the ...
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... simplicity, we will analyze the case of a thin infinite strip of aspect ratio t/W1, that can rotate around its axis, which is perpendicular to H. Let us assume that the strip was originally ZFC at an angle and H was subse- quently applied the initial condition in Fig. 2a. If H is high enough we can consider 8 that a current density of uni- form modulus J c () flows over the whole volume. This J is parallel to the strip axis and it reverses sign at the plane that contains the axis and ...
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... now discuss what happens when the strip is rotated away from this initial state by a small angle . The result will depend on the direction of rotation. If n approaches H this corresponds to the angular ranges 90° to 180° and 270° to 360° in Fig. 2a, the normal component H will in- crease, thus inducing screening currents at the edges of the crystal in the same direction as those already flowing. Vorti- ces will then displace to satisfy the condition JJ c ( ) everywhere. If J c ( )J c () the new distri- bution will be analogous to the initial one, with JJ c ( ) everywhere and the ...
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... sample would rotate rigidly with it, a situation that has indeed been observed. [19][20][21] As we will show below, in the present case we have clear experi- mental evidence that the misorientation between the vortex direction and H due to this lag effect is negligible, so all this complication can be ignored. We now analyze the curves shown in Fig. 2. The measure- ment starts at 30° point A with n rotating away from H. Thus, J initially undergoes a flip until the reversed fully penetrated critical state is formed point B. From here the evolution of the system turns independent of the initial con- ditions and becomes two fold periodic. From point C ( 90°) to point E (180°) the ...
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... Fig. 2a the direction of rotation is such that the con- ditions Hc; HCD and Hc proceed in that order. We de- fine this as a clockwise CW rotation. In contrast, in a coun- terclockwise CCW rotation the alignment occurs when n is moving away from H. The consequences of this difference are described ...
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... Figure 2b the same CW data of Fig. 2a is shown in an M L vs M T polar graph full symbols, together with the CCW rotation under the same conditions open symbols. In both cases the initial behavior until the critical state is fully developed portion A, B in the CW and P, Q in the CCW and the subsequent 180°-periodic evolution in the critical state covering approximately two periods of 180°) are clearly distinguished. ...
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... Figure 2b the same CW data of Fig. 2a is shown in an M L vs M T polar graph full symbols, together with the CCW rotation under the same conditions open symbols. In both cases the initial behavior until the critical state is fully developed portion A, B in the CW and P, Q in the CCW and the subsequent 180°-periodic evolution in the critical state covering approximately two ...
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... the CW and CCW curves in Fig. 2b are simi- lar rotated in 180° with respect to each other they also exhibit some differences. The most obvious one is that the peak at the CD direction dotted line is prominently seen in the CW rotation point D, while in the CCW rotation it is partially suppressed by the flip of M i . The flip starts at Hn, and ends at the angle F where ...
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... values of F are easily obtained from Fig. 3a, where M i is plotted as a function of for the same two sets of data CW and CCW of Fig. 2b. We observe here that the agreement between the CW and CCW data is excellent, thus they can complement each other to eliminate the blind region at low angles. Estimating F 25° for the CW rota- tion and F 30° for the CCW case, and using Eq. 8 we obtain H*370 and 540 Oe, respectively. We can check the consistency of these estimates in ...
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... This is also known as intrinsic pinning, since it immobilizes the vortices independently of impurities (which are extrinsic to the crystal). It was observed mainly in high anisotropy materials (mainly TlBaCuO [69,70,71], BSCO [72], and HgBaCuO [73]), but also in YBa 2 Cu 3 O 7−δ ( [26,49,50,51,52]) and other layered superconductors (for example Nb/Cu multilayers [74], organic superconductors [75], LSCO [76,77,78], and ErBaCuO [79]). YBa 2 Cu 3 O 7−δ is of particular interest for lock-in studies, since its low anisotropy allows one to observe the onset of lock-in far from T c , where critical fluctuations makes the analysis more difficult. ...
All the high-temperature superconductors have a layered structure. Mea- suring the anisotropy parameter of those systems by torque magnetometry is therefore a useful method to investigate their properties. In order to ex- tend the temperature and field domain accessible to our experimental torque setup, we built a new torque magnetometer that can be used in a 2 K cryostat equipped with a high-field superconducting magnet. Our measurements on the cuprate superconductor YBa2 Cu3 O7−δ show a slight temperture dependence of the anisotropy. The presence of multiple gaps has been proposed to explain the high critical temperatures of unconven- tional superconductors, and has also been linked to a temperature-dependent anisotropy. We observed the lock-in of the vortices in the same material. The lock-in evidences a transition from a three dimensional to two dimensional state. The intercalated iron selenides feature a coexistence of antiferromagnetic and superconducting phases at microscopic scales, as do some cuprates. In the iron-based superconductor Rbx Fe2−y Se2 , the anisotropy does not depend on temperature, but strongly depends on field. Measurements of crystals annealed just at the onset of phase separation between antiferromagnetic and non-antiferromagnetic phases confirm that the degree of homogeneity seems to control the quality of the superconductor. In the iron-based superconductor EuFe2−x Cox As2 , the superconductivity is reentrant due to the ordering of the large magnetic moments of the Eu atoms. Doping EuFe2 As2 with cobalt on the iron site suppresses the low field, low temperature antiferromagnetic phase of the Eu moments. This shows that the superconducting iron-arsenic layer interacts with the Eu moments.
Seit J. G. Bednorz und K. A. Müller 1986 entdeckten, dass Kupratverbindungen Supraleiter mit überraschend hohen kritischen Temperaturen sind, wurde eine grosse Anzahl Studien über diese Materialien durchgeführt. Den Mechanismus hinter dieser makroskopischen Ausprägung von quantenmechanischen Effekten zu verstehen, wird als eine der wichtigsten und schwierigsten Aufgaben in der Festkörperphysik und Materialwissenschaften betrachtet. Eine der vielen Techniken, die dabei eingesetzt wird, ist die Drehmomentmagnetometrie. Diese Methode wird verwendet, um das magnetische Moment einer Probe zu bestimmen, indem das Drehmoment gemessen wird, das sie in einem angelegten Magnetfeld erfährt. In dieser Dissertation wird die Entwicklung von verbesserten und flexibleren Sensoren für die Drehmomentmagnetometrie beschrieben, die hochempfindliche Studien magnetischer Phänomene erlauben, wie sie in der Hochtemperatursupraleitung auftreten. Zusätzlich wurde ein Programmpaket erstellt, das eine automatische Messwertaufnahme erlaubt. Die Struktur des magnetischen Flusses, der Kuprat-Einkristalle im gemischten Zustand durchdringt, konnte dank dieser Entwicklungen detailliert untersucht werden. Regionen der Feldrichtung, Feldstärke und Temperatur für drei verschiedene Flusskonfigurationen wurden bestimmt und erlaubten die Berichtigung einer früheren, fehlerhaften Messdateninterpretation. Since J. G. Bednorz and K. A. Müller discovered in 1986, that the cuprate compounds are superconductors with surprisingly high critical temperatures, a considerable number of studies has been performed on these materials. Elucidating the mechanism behind this macroscopic manifestation of quantum effects is still considered one of the most important and difficult problems in solid state physics and materials research. One of the many techniques employed is torque magnetometry, a method to measure the magnetic moment of a sample by the torque it experiences in an applied magnetic field. Within this thesis, improved and more flexible sensors for torque magnetometry have been developed, enabling highly sensitive studies of magnetic phenomena, such as those accompanying high temperature superconductivity. Furthermore, a software system for automated measurement taking was created. These developments allowed to investigate the magnetic flux structure penetrating cuprate single crystals in the intermediate state. The field angle, field magnitude and temperature regions were determined for three different flux configurations, allowing to revise a previously erroneous interpretation of data.
The magnetization behavior of the layered anisotropic high-Tc superconductor in the mixed state Hc1 < H < Hc2 has a feature that when the angle θ between the applied magnetic field H and the CuO plane (a-b plane) is less than a critical value (θ6≤θL), the vortex lattice is converted from three-dimensional structure into two-dimensional structure, forming a phenomenon so called the "lock-in" transition, where the flux lines are completely parallel to the a-b plane, and the vertical component of the magnetic induction B⊥ (perpendicular to the a-b plane) is consequently zero. So far, there have still existed the differences in the physical explanation of the lock-in phenomenon. For the lock-in phenomenon occurring in the region between the CuO planes, it can be considered to be caused by the transverse Meissner effect. However, for the one occurring in other extended correlated defect areas, such as twin boundaries in YBa2Cu3O7-δ (YBCO) crystal, this phenomenon is believed to be the results of the energy linearization of the vortices trapped in the defect channels. Many theoretical and experimental studies have revealed the existence of the lock-in behaviors related to the microstructure properties of the superconductor crystals. Therefore, the research of the lock-in transition behavior will be helpful to understand the intrinsic pinning properties of the layered anisotropic superconductors, and the phase transition process in the vortex system. In this paper, we systematically measure the magnetic torque signal in melt texture growth YBCO (MTG-YBCO) bulk and observe an abnormal lock-in transition behavior in the vortex system. The critical angle of the lock-in transition is found to be directly proportional to the strength of the magnetic field, which is contrary to the observations in the common cases. According to the framework of the Ginzburg-Landau theory and the kink structure model of the vortex line, we discuss the abnormal phenomenon, and propose that there is a type of extend-correlated defect structure, which is parallel to the a-b plane, in the MTG-YBCO crystal. The relationship between the critical angle of the lock-in transition to the temperature and the magnetic field is established theoretically, and the theoretical results coincide well with the torque measurements.
Neutron stars are astrophysical laboratories of many extremes of physics. Their rich phenomenology provides insights into the state and composition of matter at densities which cannot be reached in terrestrial experiments. Since the core of a mature neutron star is expected to be dominated by superfluid and superconducting components, observations also probe the dynamics of large-scale quantum condensates. The testing and understanding of the relevant theory tends to focus on the interface between the astrophysics phenomenology and nuclear physics. The connections with low-temperature experiments tend to be ignored. However, there has been dramatic progress in understanding laboratory condensates (from the different phases of superfluid helium to the entire range of superconductors and cold atom condensates). In this review, we provide an overview of these developments, compare and contrast the mathematical descriptions of laboratory condensates and neutron stars and summarise the current experimental state-of-the-art. This discussion suggests novel ways that we may make progress in understanding neutron star physics using low-temperature laboratory experiments.
The angular dependence of magnetization was measured in an optimally Co-doped BaFe2As2 single crystal, which is irradiated by 2.6 GeV uranium to introduce columnar defects (CDs). At low fields (H), we observe the irreversible magnetization Mirr insensitive to the angle θ around H ∥CDs. The field dependence of the angular range 2θL is proportional to 1/H, quite consistent with the expectation of the lock-in transition. This manifests the first observation of the fingerprint of the Bose glass phase in iron-based superconductors.
The theory of the critical states of a vortex lattice in type-II superconductors is examined without any assumptions about the relative perpendicularity of the local magnetic fields and circulating currents in the sample. Such a theory has made it possible to solve a number of problems for thin films of superconductors in an external magnetic field oriented perpendicular to their surface: a theory of the shaking effect is constructed for rectangular superconducting plates and the critical states in samples with anisotropic pinning of the flux lines as well as in the presence of an order-disorder phase transition in a vortex lattice are studied. In addition, the critical states in a long superconducting strip in an inclined magnetic field are investigated. Bibtex entry for this abstract Preferred format for this abstract (see Preferences) Find Similar Abstracts: Use: Authors Title Keywords (in text query field) Abstract Text Return: Query Results Return items starting with number Query Form Database: Astronomy Physics arXiv e-prints
Two Bi2Sr2CaCu2O8+delta single crystals were characterized, before and after irradiation with 200 MeV Ag ions under fluence of 5 × 1010 ions/cm2. Columnar defects were produced along the c-axis direction in one crystal, and in a direction tilted by an angle of 30° with respect to the c-axis for the other crystal. The 3D 2D vortex decoupling lines were significantly shifted to higher temperatures, after irradiation of the crystals, for magnetic fields smaller than the matching value BPhi ≈ 1 T. For B > 3 T the decoupling lines for the irradiated crystals tend smoothly to the same behavior observed in the original crystals, up to the maximum probed field of 5 T. Interestingly the vortex pinning by columnar defects was found to be almost independent of the applied magnetic field direction, as revealed by the width of magnetization loops.
Current-voltage (I-V) characteristics have been measured over a wide temperature range in a Bi1.8Pb0.2Sr2CaCu2O 8+δ single crystal with tilted columnar defects (CDs). This configuration was compared to a crystal irradiated along the c axis. Above 40 K and in the vortex solid state, angular measurements reveal a pronounced dip in the dissipation when a magnetic field is applied parallel to the CDs. At T≤40 K, the measured I-V characteristics showed that besides the persistence of the directional pinning at low temperatures, there is a shift from the CDs toward the c axis. Our samples showed, in the high temperature range (T ≥40 K) and for Bφ/10<H<Bφ (where Bφ is the matching field) applied parallel to the CDs, a three-dimensional Bose-glass transition with the same critical exponents as z′ = 5.3 ± 0.1 and υ′ = 1.1 ± 0.1 which are in very good agreement with numerical simulations. Our findings support the existence of the Bose-glass-to-liquid transition at TBG(μ0H) in the case of tilted columnar defects.
The cuprate superconductors have highly anisotropic, layered structures. This causes the flux lattice penetrating them in the intermediate state to undergo dramatic changes when the direction of the applied magnetic field approaches the CuO2 planes. We present highly sensitive torque measurements on tiny La2-xSrxCuO4 single crystals showing these regimes of vortex structure and their influence on the determination of the magnetic anisotropy parameter gamma . Systematic measurements of torque as a function of magnetic field magnitude and orientation at various temperatures below Tc made it possible to determine the conditions under which the structural changes occur, allowing a reliable determination of gamma . The values of gamma obtained for La2-xSrxCuO4 as a function of doping x , covering the whole doping regime (underdoped, optimally doped, and overdoped), are in good agreement with earlier results, indicating a flow toward quasi-two-dimensionality in the underdoped limit.
Penetration of magnetic flux into a rectangular platelet of superconducting Nb3Sn subject to an oblique magnetic field is studied by magneto-optical imaging. Flux patterns are observed for three distinct scenarios in which the final magnetic field vector is applied differently: (A) the vector has a fixed direction but its magnitude changes from zero to the final value, (B) first the perpendicular component is applied and then the in-plane component, and (C) vice versa. These scenarios lead to distinctly different final states that are consistent with theoretical predictions.
