scholarly journals Magnetic monopole mechanism for localized electron pairing in HTS

2021 ◽  
Author(s):  
Cristina Diamantini ◽  
Carlo Trugenberger ◽  
Valerii Vinokur
Keyword(s):  
High Temperature Superconductivity ◽  
Magnetic Monopoles ◽  
Real Space ◽  
Effective Field ◽  
Superconducting Transition ◽  
Infinite Cluster ◽  
Electron Pairing ◽  
Pseudogap Phase ◽  
Topological Quantum ◽  
A Charge

Abstract Recent effective field theory of high-temperature superconductivity (HTS) captures the universal features of HTS and the pseudogap phase and explains the underlying physics as a coexistence of a charge condensate with a condensate of dyons, particles carrying both magnetic and electric charges. Central to this picture are magnetic monopoles emerging in the proximity of the topological quantum superconductor-insulator transition (SIT) that dominates the HTS phase diagram. However, the mechanism responsible for spatially localized electron pairing, characteristic of HTS, remains elusive. Here we show that real-space, localized electron pairing is mediated by magnetic monopoles and occurs well above the superconducting transition temperature Tc. Localized electron pairing promotes the formation of superconducting granules connected by Josephson links. Global superconductivity sets in when these granules form an infinite cluster at Tc, which is estimated to fall in the range from hundred to thousand Kelvins. Our findings pave the way to tailoring materials with elevated superconducting transition temperatures.

Study of the Solid State Properties of an Organic Superconductor

1992 ◽  
Vol 247 ◽  
Author(s):  
Raul Fainchtein ◽  
S. T. D'arcangelo ◽  
S. S. Yangt ◽  
D. O. Cowant
Keyword(s):  
Density Wave ◽  
Sample Surface ◽  
Real Space ◽  
Organic Superconductor ◽  
Scanning Tunneling ◽  
Superconducting Transition ◽  
Tunneling Microscopy ◽  
Space Images ◽  
A Charge ◽  
Peculiar Behavior

ABSTRACTWe have synthesized cooper(I)di[bis(ethylenedithiolo)terathiafulvalene] bis(isothiocyanato), [(BEDT-TTF)2]+[Cu(NCS)2]using standard electrochemical methods. Single crystal samples of the compound were obtained and were found to have superconducting transition temperatures of 10.4 K, using DC conductivity measurements. [(BEDT-TTF)2+[Cu(NCS)2] shows a region between room temperature and 90 K which appears to be“semiconducting”To characterize the structure of the samples we used Scanning Tunneling Microscopy (STM). STM supplied real-space images of the sample surface in accordance to its electronic structure. Ravy observed diffuse streaks between Bragg spots in his X-ray data of [(BEDT-TTF)2+[Cu(NCS)2]−, which he attributes to a stacking fault at every fourth repetition of the anion in the crystal structure [1]. STM shows no evidence for such disorder in [−(BEDT-TTF)2]+[Cu(NCS)2]−of the type proposed, and in fact illustrates direct evidence to the contrary. An intensity modulation in the STM data supports the possibility of a charge density wave commensurate with the lattice. This interpretation is consistent with the calculated Fermi surface which allows nesting of the wave vector and may explain the peculiar behavior of the temperature dependency of the conductivity data in the normal region.

scholarly journals Inverse correlation between quasiparticle mass and Tc in a cuprate high-Tc superconductor

2016 ◽  
Vol 2 (3) ◽  
pp. e1501657 ◽  
Author(s):  
Carsten Putzke ◽  
Liam Malone ◽  
Sven Badoux ◽  
Baptiste Vignolle ◽  
David Vignolles ◽  
...  
Keyword(s):  
High Temperature Superconductivity ◽  
Inverse Correlation ◽  
Charge Order ◽  
Quantum Fluctuations ◽  
Quantum Oscillation ◽  
Strong Increase ◽  
Electron Mass ◽  
Superconducting Transition ◽  
Optimal Doping ◽  
A Charge

Close to a zero-temperature transition between ordered and disordered electronic phases, quantum fluctuations can lead to a strong enhancement of electron mass and to the emergence of competing phases such as superconductivity. A correlation between the existence of such a quantum phase transition and superconductivity is quite well established in some heavy fermion and iron-based superconductors, and there have been suggestions that high-temperature superconductivity in copper-oxide materials (cuprates) may also be driven by the same mechanism. Close to optimal doping, where the superconducting transition temperature Tc is maximal in cuprates, two different phases are known to compete with superconductivity: a poorly understood pseudogap phase and a charge-ordered phase. Recent experiments have shown a strong increase in quasiparticle mass m* in the cuprate YBa2Cu3O7-δ as optimal doping is approached, suggesting that quantum fluctuations of the charge-ordered phase may be responsible for the high-Tc superconductivity. We have tested the robustness of this correlation between m* and Tc by performing quantum oscillation studies on the stoichiometric compound YBa2Cu4O8 under hydrostatic pressure. In contrast to the results for YBa2Cu3O7-δ, we find that in YBa2Cu4O8, the mass decreases as Tc increases under pressure. This inverse correlation between m* and Tc suggests that quantum fluctuations of the charge order enhance m* but do not enhance Tc.

Crystal Growth of High Temperature Superconductors

MRS Bulletin ◽  
1988 ◽  
Vol 13 (10) ◽  
pp. 56-61 ◽  
Author(s):  
H.J. Scheel ◽  
F. Licci
Keyword(s):  
High Temperature ◽  
Critical Current Density ◽  
Single Crystals ◽  
Critical Current ◽  
Current Density ◽  
Large Scale ◽  
High Temperature Superconductivity ◽  
High Temperature Superconductors ◽  
Superconducting Transition ◽  
Theoretical Understanding

The discovery of high temperature superconductivity (HTSC) in oxide compounds has confronted materials scientists with many challenging problems. These include the preparation of ceramic samples with critical current density of about 106 A/cm2 at 77 K and sufficient mechanical strength for large-scale electrotechnical and magnetic applications and the preparation of epitaxial thin films of high structural perfection for electronic devices.The main interest in the growth of single crystals is for the study of physical phenomena, which will help achieve a theoretical understanding of HTSC. Theorists still do not agree on the fundamental mechanisms of HTSC, and there is a need for good data on relatively defect-free materials in order to test the many models. In addition, the study of the role of defects like twins, grain boundaries, and dislocations in single crystals is important for understanding such parameters as the critical current density. The study of HTSC with single crystals is also expected to be helpful for finding optimum materials for the various applications and hopefully achieving higher values of the superconducting transition temperature Tc than the current maximum of about 125 K. It seems unlikely at present that single crystals will be used in commercial devices, but this possibility cannot be ruled out as crystal size and quality improve.

scholarly journals Higher superconducting transition temperature by breaking the universal pressure relation

2019 ◽  
Vol 116 (6) ◽  
pp. 2004-2008 ◽  
Author(s):  
Liangzi Deng ◽  
Yongping Zheng ◽  
Zheng Wu ◽  
Shuyuan Huyan ◽  
Hung-Cheng Wu ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
High Temperature ◽  
Transition Temperature ◽  
Density Functional ◽  
High Temperature Superconductors ◽  
Density Functional Theory Calculations ◽  
Universal Relation ◽  
Superconducting Transition ◽  
Functional Theory ◽  
A Charge

By investigating the bulk superconducting state via dc magnetization measurements, we have discovered a common resurgence of the superconducting transition temperatures (Tcs) of the monolayer Bi2Sr2CuO6+δ(Bi2201) and bilayer Bi2Sr2CaCu2O8+δ(Bi2212) to beyond the maximum Tcs (Tc-maxs) predicted by the universal relation between Tcand doping (p) or pressure (P) at higher pressures. The Tcof underdoped Bi2201 initially increases from 9.6 K at ambient to a peak at 23 K at 26 GPa and then drops as expected from the universal Tc-P relation. However, at pressures above 40 GPa, Tcrises rapidly without any sign of saturation up to 30 K at 51 GPa. Similarly, the Tcfor the slightly overdoped Bi2212 increases after passing a broad valley between 20 and 36 GPa and reaches 90 K without any sign of saturation at 56 GPa. We have, therefore, attributed this Tcresurgence to a possible pressure-induced electronic transition in the cuprate compounds due to a charge transfer between the Cu 3dx2−y2and the O 2pbands projected from a hybrid bonding state, leading to an increase of the density of states at the Fermi level, in agreement with our density functional theory calculations. Similar Tc-P behavior has also been reported in the trilayer Br2Sr2Ca2Cu3O10+δ(Bi2223). These observations suggest that higher Tcs than those previously reported for the layered cuprate high-temperature superconductors can be achieved by breaking away from the universal Tc-P relation through the application of higher pressures.

scholarly journals A Weyl-Z2 semimetal from holography

2021 ◽  
Vol 2021 (12) ◽  
Author(s):  
Xuanting Ji ◽  
Yan Liu ◽  
Ya-Wen Sun ◽  
Yun-Long Zhang
Keyword(s):  
Quantum Phase Transitions ◽  
Transport Coefficients ◽  
Effective Field ◽  
Anomalous Transport ◽  
Hall Conductivity ◽  
Chiral Anomaly ◽  
Transport Parameters ◽  
Strongly Coupled ◽  
Topological Quantum ◽  
Two Parameters

Abstract We present effective field theories for the weakly coupled Weyl-Z2 semimetal, as well as the holographic realization for the strongly coupled case. In both cases, the anomalous systems have both the chiral anomaly and the Z2 anomaly and possess topological quantum phase transitions from the Weyl-Z2 semimetal phases to partly or fully topological trivial phases. We find that the topological phase transition is characterized by the anomalous transport parameters, i.e. the anomalous Hall conductivity and the Z2 anomalous Hall conductivity. These two parameters are nonzero at the Weyl-Z2 semimetal phase and vanish at the topologically trivial phases. In the holographic case, the different behavior between the two anomalous transport coefficients is discussed. Our work reveals the novel phase structure of strongly interacting Weyl-Z2 semimetal with two pairs of nodes.

scholarly journals Translation-Invariant Bipolarons and Charge Density Waves in High-Temperature Superconductors

2021 ◽  
Vol 9 ◽  
Author(s):  
Victor D. Lakhno
Keyword(s):  
Charge Density ◽  
High Temperature Superconductors ◽  
Bose Condensate ◽  
Density Wave ◽  
Charge Density Waves ◽  
Superconducting Transition ◽  
Density Waves ◽  
Translation Invariant ◽  
Pseudogap Phase ◽  
Pair Density

A correlation is established between the theories of superconductivity based on the concept of charge density waves (CDWs) and the translation invariant (TI) bipolaron theory. It is shown that CDWs are originated from TI-bipolaron states in the pseudogap phase due to the Kohn anomaly and form a pair density wave (PDW) for wave vectors corresponding to nesting. Emerging in the pseudogap phase, CDWs coexist with superconductivity at temperatures below those of superconducting transition, while their wave amplitudes decrease as a Bose condensate is formed from TI bipolarons, vanishing at zero temperature.

scholarly journals Pressure-induced high-temperature superconductivity retained without pressure in FeSe single crystals

2021 ◽  
Vol 118 (28) ◽  
pp. e2108938118
Author(s):  
Liangzi Deng ◽  
Trevor Bontke ◽  
Rabin Dahal ◽  
Yu Xie ◽  
Bin Gao ◽  
...  
Keyword(s):  
High Temperature ◽  
High Temperature Superconductivity ◽  
Ambient Pressure ◽  
Superconducting Transition ◽  
Elastic Band ◽  
New Era ◽  
Ab Initio Simulations ◽  
Sustained Effort ◽  
Minimal Effort ◽  
Room Temperature Superconductivity

To raise the superconducting-transition temperature (Tc) has been the driving force for the long-sustained effort in superconductivity research. Recent progress in hydrides with Tcs up to 287 K under pressure of 267 GPa has heralded a new era of room temperature superconductivity (RTS) with immense technological promise. Indeed, RTS will lift the temperature barrier for the ubiquitous application of superconductivity. Unfortunately, formidable pressure is required to attain such high Tcs. The most effective relief to this impasse is to remove the pressure needed while retaining the pressure-induced Tc without pressure. Here, we show such a possibility in the pure and doped high-temperature superconductor (HTS) FeSe by retaining, at ambient pressure via pressure quenching (PQ), its Tc up to 37 K (quadrupling that of a pristine FeSe at ambient) and other pressure-induced phases. We have also observed that some phases remain stable without pressure at up to 300 K and for at least 7 d. The observations are in qualitative agreement with our ab initio simulations using the solid-state nudged elastic band (SSNEB) method. We strongly believe that the PQ technique developed here can be adapted to the RTS hydrides and other materials of value with minimal effort.

scholarly journals Универсальность поведения гистерезиса магнитосопротивления и его температурной эволюции для гранулярных высокотемпературных сверхпроводников Y-Ba-Cu-O

2021 ◽  
Vol 63 (7) ◽  
pp. 854
Author(s):  
С.В. Семенов ◽  
Д.А. Балаев ◽  
М.И. Петров
Keyword(s):  
External Field ◽  
High Temperature Superconductors ◽  
Magnetic Moments ◽  
Effective Field ◽  
Superconducting Transition ◽  
Hysteresis Width ◽  
Flux Compression ◽  
Three Samples ◽  
Order Of Magnitude ◽  
Intergrain Boundaries

The work is devoted to the establishment of regularities in the behavior of the magnetoresistance hysteresis R(H) of granular high-temperature superconductors (HTS) of the yttrium system. We carried out a comparative study of the magnetotransport properties of granular HTSC samples, which have (i) approximately the same magnetic properties and temperatures of the onset of the superconducting transition (90.5–93.5 K, which characterizes HTS grains) and (ii) different values of the transport critical current JC (which characterizes the intergrain boundaries). Despite the significant scatter in the JC values (more than an order of magnitude) of the three samples studied, a universal behavior of the magnetoresistance hysteresis was found, apparently inherent in all granular Y-Ba-Cu-O. The R(H) hysteresis is very wide, and in a sufficiently large interval of the external field, the dependence of the hysteresis width of the magnetoresistance H on the field Hdec (external field H = Hdec for a decreasing hysteresis branch) is close to a linear function: H ≈ Hdec. This behavior is observed for the entire temperature range of realization of the superconducting state (the studies were carried out at temperatures of 77–88 K and 4.2 K). The explanation of the obtained result is based on the concept of consideration the effective field in the intergrain boundaries. This effective field is the superposition of the external field and the field induced by the magnetic moments of the grains. The field induced by the grains, in turn, is significantly enhanced in the region of intergrain boundaries due to the effect of the magnetic flux compression (the length of the intergrain boundaries is several orders of magnitude smaller than the size of the HTS grains). The above is confirmed from the analysis of the R(H) hysteresis for a composite HTS sample based on Y-Ba-Cu-O and CuO, in which the length of the intergranular boundaries is purposefully increased, as a result, the effect of the flux compression is less pronounced, and the hysteresis R(H) narrows.

scholarly journals Search for non-Abelian Majorana braiding statistics in superconductors

2020 ◽  
Author(s):  
Carlo Beenakker
Keyword(s):  
Quantum Information ◽  
Parameter Space ◽  
Quantum Information Processing ◽  
Fusion Rule ◽  
Real Space ◽  
Edge Mode ◽  
Zero Modes ◽  
Topological Superconductors ◽  
Topological Quantum ◽  
Basic Concepts

This is a tutorial review of methods to braid non-Abelian anyons (Majorana zero-modes) in topological superconductors. That ``Holy Grail'' of topological quantum information processing has not yet been reached in the laboratory, but there now exists a variety of platforms in which one can search for the Majorana braiding statistics. After an introduction to the basic concepts of braiding we discuss how one might be able to braid immobile Majorana zero-modes, bound to the end points of a nanowire, by performing the exchange in parameter space, rather than in real space. We explain how Coulomb interaction can be used to both control and read out the braiding operation, even though Majorana zero-modes are charge neutral. We ask whether the fusion rule might provide for an easier pathway towards the demonstration of non-Abelian statistics. In the final part we discuss an approach to braiding in real space, rather than parameter space, using vortices injected into a chiral Majorana edge mode as ``flying qubits''.

scholarly journals Gate-controlled BCS-BEC crossover in a two-dimensional superconductor

Science ◽  
2021 ◽  
Vol 372 (6538) ◽  
pp. 190-195 ◽  
Author(s):  
Yuji Nakagawa ◽  
Yuichi Kasahara ◽  
Takuya Nomoto ◽  
Ryotaro Arita ◽  
Tsutomu Nojima ◽  
...  
Keyword(s):  
Carrier Density ◽  
Zirconium Nitride ◽  
Einstein Condensation ◽  
Two Dimensional ◽  
Superconducting Transition ◽  
Pseudogap Phase ◽  
Fermion Systems ◽  
Fermi Temperature ◽  
Crossover Behavior ◽  
Bose Einstein

Bardeen-Cooper-Schrieffer (BCS) superfluidity and Bose-Einstein condensation (BEC) are the two extreme limits of the ground state of the paired fermion systems. We report crossover behavior from the BCS limit to the BEC limit realized by varying carrier density in a two-dimensional superconductor, electron-doped zirconium nitride chloride. The phase diagram, established by simultaneous measurements of resistivity and tunneling spectra under ionic gating, demonstrates a pseudogap phase in the low-doping regime. The ratio of the superconducting transition temperature and Fermi temperature in the low–carrier density limit is consistent with the theoretical upper bound expected in the BCS-BEC crossover regime. These results indicate that the gate-doped semiconductor provides an ideal platform for the two-dimensional BCS-BEC crossover without added complexities present in other solid-state systems.

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