Search

Thermal switching by applying magnetic field is one of the key technologies in thermal management in electronic devices. In low-temperature devices, superconductors can be used as a magneto-thermal-switching (MTS) materials due to the large change in carrier thermal conductivity by the superconducting transition. In this study, we measured the temperature (T) and magnetic field (H) dependences of thermal conductivity (κ) of Sn, Ta and V to enrich knowledge on MTS of type-Ⅰ and type-Ⅱ superconductors. From the data analyses, we found different trends of κ - H curves in type-Ⅰ and type-Ⅱ superconductors. The normalized κ - H curves of type-Ⅰ superconductors showed the similar behavior, which is solely governed by H c. However, the κ - H curves of type-Ⅱ superconductors were affected by the H c1 and H c2 , and its behavior greatly depends on the materials. In addition, we investigated the elemental composition of Sn and Ta to explore the origin of weak hysteresis in the κ - H curves and revealed the importance of impurity on the hysteresis of κ - H curves. [ABSTRACT FROM AUTHOR]

• We successfully prepared FeSe and a series of Fe 1- x Cu x Se 0.4 Te 0.6 (x = 0, 0.005, 0.01 and 0.015) single crystals and observed a linear relationship between the content of Cu and T c. By utilizing the strong suppression of superconducting transition temperature by Cu, a comparative system with FeSe was constructed to elucidate the physical origin of the second peak effect in FeSe 0.4 Te 0.6. • The substitution of Cu effectively weakens the normal state magnetic background signal, indicating a decrease in the content of the interstitial iron upon Cu substitution. Furthermore, this leads to a reduction in the second peak effect. Additionally, a significant reduction in the anisotropy of the critical current density is observed. • Studies on magnetic flux dynamics reveal that the reduction in interstitial iron caused by Cu doping leads to a decrease in the dynamic relaxation rate. Furthermore, the crossover between fast and slow magnetic flux relaxations is observed near the second peak effect. • Fitting of pinning force density and normalized critical current density curves for the series of single crystals indicates that even though the superconducting transition temperature is consistent, the types of pinning centers in Fe 1- x Cu x Se 0.4 Te 0.6 and FeSe are inconsistent, and a more complex pinning mode exists in Fe 1- x Cu x Se 0.4 Te 0.6. • The final fitting of the upper critical field for the FeSe and series of Fe 1- x Cu x Se 0.4 Te 0.6 (x = 0, 0.005, 0.01 and 0.015) single crystals revealed that the H c2 of the two types of crystals is limited by different mechanisms. This paper presents the preparation and comparative study of the superconducting properties and magnetic flux dynamics of FeSe and Fe 1- x Cu x Te 0.6 Se 0.4 (x = 0, 0.005, 0.01, 0.015) single crystals, with the aim of investigating the origin of the second peak in FeTe 0.6 Se 0.4. The Cu element significantly suppresses the superconducting transition temperature (T c) of Fe 1- x Cu x Te 0.6 Se 0.4 from 14.5 K at x = 0 to 9.23 K at x = 0.015, which is close to the 9 K of FeSe, while also suppressing the second peak effect. Additionally, the critical current density anisotropy (γ) is reduced. Dynamic relaxation rates (Q) indicate a crossover from rapid single-vortex pinning near the second peak to collective pinning, linking fast and slow magnetic flux relaxation with the second peak effect. By comparing the pinning properties of FeSe and Fe 1- x Cu x Te 0.6 Se 0.4 (x = 0, 0.005, 0.01, 0.015), it is found that the second peak effect is closely related to the transition from δ l - pinning to δT c - pinning in Fe 1- x Cu x Se 0.4 Te 0.6 (x = 0, 0.005, 0.01, 0.015). While surface pinning centers dominate in FeSe, the pinning in Fe 1- x Cu x Se 0.4 Te 0.6 (x = 0, 0.005, 0.01, 0.015) originates from the interaction between the core and normal centers. Furthermore, the electronic transport properties of the FeSe and Fe 1- x Cu x Se 0.4 Te 0.6 (x = 0, 0.005, 0.01, 0.015) series are also studied. Te substitution suppresses the nematic transition in FeSe, while Cu substitution suppresses the superconducting transition in Fe 1- x Cu x Se 0.4 Te 0.6 (x = 0, 0.005, 0.01, 0.015) and reduces the residual resistivity. Additionally, the upper critical field is reduced from 150 T in FeSe 0.4 Te 0.6 to 41 T in Fe 0.085 Cu 0.015 Se 0.4 Te 0.6 , but still higher than the 12.5 T observed in FeSe. [ABSTRACT FROM AUTHOR]

AeA Fe 4 As 4 (Ae = Ca, A = K; 1144) having a transition temperature of 35 K is a stoichiometric family of iron-based superconductors (FBS). Here, we present a detailed study of a high-pressure synthesis of CaKFe 4 As 4 bulks to investigate the impact of these conditions on the superconducting properties of the 1144 family. Additionally, these samples are also prepared by conventional synthesis method at ambient pressure (CSP) and studied the influence of impurities on the superconducting properties of CaKFe 4 As 4. Structural, microstructural, transport and magnetization measurements have been performed to reach the final conclusions. Interestingly, the high-pressure synthesis of the parent CaKFe 4 As 4 compound enhances the transition temperature (T c) by 2 K and the critical current density (J c) by one order of magnitude in the whole magnetic field range of 9 T than that of the 1144 bulks prepared by CSP. It suggests the improvement of the pinning centers and grain connections by the high-pressure synthesis approach. Interestingly, our results depict the superconducting onset transition temperature (T c onset ) of this stoichiometric 1144 family is robust with the presence of the common 122 (CaFe 2 As 2 or KFe 2 As 2) impurity phases, which is a different behavior compared to other FBS families. However, these impurity phases reduce the grain connections and lead to the phase separation during the formation of the superconducting (1144) phase. • Stoichiometric CaKFe 4 As 4 (1144) superconductor was prepared by high pressure synthesis method. • This novel approach has enhanced the superconducting properties and quality of the 1144 samples. • The onset superconducting transition is robust with the common impurity phases unlike other iron based superconductors. [ABSTRACT FROM AUTHOR]

Energy dissipation from vortex motion, which appears as a resistivity of the mixed-state superconductor, limits the range of type II superconductors in low- and high-power electronics and optoelectronics. The level of dissipation increases with the development of the vortex motion phase from that of the thermally activated flux flow to that of the flux creep and finally to that of the flux flow. The vortex motion regimes depend on the balance between bias current-self-produced Lorentz force, accelerating vortices, and the pinning force, which, together with a magnetic drag force from pinned vortices, tends to stop the vortex motion. The current paper reports on energy dissipation in YBa2Cu3O7-δ (YBCO) devices provided with partially deoxygenated structures mutually interacting by magnetic force with one another. The shape of the structure and the magnetic interaction between the trapped and moving vortices, as well as the magnetic interaction between neighboring structures, can cause the appearance of voltage steps in the device's current–voltage characteristics observed in temperature range 0.94 ≥ T/Tc ≥ 0.98 (here, Tc = 91.4 K is the temperature of the superconducting transition in the YBCO material). Current findings demonstrate the potential of artificial structures to control vortex motion in a mixed-state YBCO superconductor by means of a temperature, bias current, and a specific configuration of the structure itself and a profile of the oxygen distribution in it. [ABSTRACT FROM AUTHOR]

The article discusses about the two-dimensional superconductivity at the surfaces of KTaO3. Topics including two-dimensional superconductivity gave birth to the second generation of oxide interface superconductors, how it exhibited a strong dependence on the surface plane of KTaO3 in contrast to others, and understanding the nature of these interfaces.

β-ThRhGe, the high-temperature polymorph of ThRhGe, is isostructural to the well-known ferromagnetic superconductor URhGe. However, contrary to URhGe, β-ThRhGe is nonmagnetic and undergoes an incomplete structural phase transition at 244 K, followed by a superconducting transition below 3.36 K. Here we show that the isovalent substitution of Ir for Rh leads to a strong enhancement of superconductivity by suppressing the structural transition. At x = 0.5, where the structural transition disappears, Tc reaches a maximum of 6.88 K. The enhancement of superconductivity is linked to the proximity to a structural quantum critical point at this Ir concentration, as suggested by the analysis of thermodynamic as well as resistivity data. First principles calculations indicate that the Ir doping has little effect on the electronic band dispersion near the Fermi level. β-ThRh1−xIrxGe thus provides an excellent platform to study the interplay between superconductivity and structural quantum criticality in actinide-containing compounds. [ABSTRACT FROM AUTHOR]

A film of high-temperature superconductor (HTSC) YBa2Cu3O7 has been grown on the (100) crystallographic plane of SrLaGaO4 crystal using pulse laser deposition. An X-ray diffraction (XRD) analysis has shown that this film is single-crystal, single-domain, and oriented in the (100) plane. The superconducting transition occurs at 88.8 K and has a width of 1.6 K. Measurements of the temperature dependence of electrical resistance in these films revealed a significant anisotropy of superconductivity in the (100) plane. Due to this specific feature, the critical superconducting-transition temperature, found by measuring the temperature dependence of resistance in the film plane oriented parallel to the CuO planes, exceeded the corresponding value obtained by the same measurement in the direction perpendicular to these planes by 2 K. In addition, it is revealed experimentally that the normal resistance in the former case is smaller than in the latter case by a factor of about 400. [ABSTRACT FROM AUTHOR]

Based on the spin-generalized Bogoliubov–de Gennes theory, we investigate the topological defect configurations in a mesoscopic superconducting square with spin–orbit (SO) interaction. The mixed even-parity d-wave and extended s-wave components can be obtained by suitable choice of the chemical potential in such a system. We find that several novel types of topological defect states can be generated in the presence of Rashba SO coupling when the external magnetic flux turns on. Unclosed domain-wall states carrying even or odd number of one-component vortices as well as double-quanta skyrmionic patterns can appear for different Rashba SO-coupling strengths. The next-nearest-neighbor hopping effect on the evolution of topological structures is further examined. A skyrmionic chain feature with one-component vortex–antivortex pairs can show up in the present mixed-pairing system. Our investigation may provide useful information for future experiments and shed new light on device designing. [ABSTRACT FROM AUTHOR]

Finite probability of creation of Cooper pairs in the normal state near the superconducting transition and their interaction with the remnant electrons cause superconducting fluctuation which eventually increase the conductivity in high-temperature superconductor. Based on the theory proposed by Aslamazov and Larkin, fluctuation phenomenon in GdBa 2 Cu 3 O 7 - δ superconductor has been studied close to the superconducting mean field transition temperature (T c mf) in presence of external magnetic field. Weakly first-order transition from normal to superconducting state has been observed as fluctuations near to T c mf (in the critical field region) is beyond 3D-XY-E scaling for both zero and finite fields. Following the novel approach of local pairs model, evolution process of fluctuating Cooper pairs (FCPs) obeying BCS theory from strongly coupled bosons (SCBs) which obey Bose–Einstein Condensation (BEC) theory in the temperature limit T c mf < T < T ∗ ( T ∗ is the temperature below which SCBs start to form) has been studied meticulously. The results indicate that pseudogap parameters Δ ∗ (T) shifted towards BCS phase from BEC state with decreasing temperature after exceeding the maximum critical size of the local pairs (28 Å) in the CuO 2 plane. The values of T pair (at which SCBs initiate to transform into FCPs) obtained from temperature-dependent study of Δ ∗ (T) decreases when magnetic field increases from zero to 4 T. Superconducting gap (Δ (0)) for all magnetic fields calculated from the local pairs model are within the BCS limit but the magnitudes reduce as the field escalates. [ABSTRACT FROM AUTHOR]

Junction resistance (RN) as a function of temperature (T) in bulk superconducting NdBa2Cu3O7-δ (NBCO) has been determined following the de Gennes (dG) and Ambegaokar–Baratoff (AB) theories. A convergence of RN (T) obtained by two theories is not impossible at a T which is below the critical temperature. Variation of RN (T) corresponding to the intergranular region is very sensitive to the T-dependence of the gap function (Δ). Moderate range of RN reveals that the junctions are SNS in nature. Within the framework of the dG theory, the influence of the correlation length (ξN) on RN has also been investigated. Also, a moderate junction resistance and nonlinear current–voltage (IV) together reveal that a resistive bulk pinning network may be existing near the superconducting phase transition region. [ABSTRACT FROM AUTHOR]

A phonon of appropriate momentum k F will open a band gap at the Fermi energy E F . The gap within the electronic density-of-states (DOS), N (E F) , leads to a gain in electronic energy and a loss of elastic energy because of the gap-generating phonon. A BCS-like simulation shows that the energy gain is larger than the loss for temperatures below a certain transition temperature, T C . Here, it is shown that the energy count can be almost as favorable for gaps a little below or above E F . Such gaps can be generated by auxiliary phonons (or even spin- and charge-density waves) with k-vectors slightly different from k F . Gaps not too far from E F will add to the energy gain at the superconducting transition. In addition, a DOS-peak can appear at E F and thereby increase N (E F) and T C . A dip in the DOS below E F will result for temperatures below T C , which is similar to what often is observed in cuprate superconductors. The roles of spin waves and thermal disorders are discussed. [ABSTRACT FROM AUTHOR]

Pb 0.92 La 0.08 (Zr 0.52 Ti 0.48)O 3 /YBa 2 Cu 3 O 7-x (PLZT/YBCO) heterostructures with high c-axis epitaxial properties were prepared by PLD method. Hysteresis loops, photovoltaic effects, and current transfer properties of this structure were investigated. Hysteresis loop test results showed that residual polarization intensity of PLZT gradually decreases with decreasing temperature but coercivity field increases. I–V curve of PLZT/YBCO heterostructure in dark state was tested and found to have significant rectification characteristics, indicating the existence of potential barrier at interface of the heterostructure. UV illumination experiments showed that PLZT/YBCO heterostructure has clear photovoltaic effect, with both photovoltage and photocurrent decreasing as the temperature is decreased. Moreover, photovoltage and photocurrent display jump phenomenon when superconducting transition of YBCO occurs. Further analysis of jump phenomenon revealed that the difference of photovoltage with temperature before and after superconducting transition of YBCO is consistent with superconducting energy bandgap of YBCO. The opening of superconducting energy gap of YBCO lowers PLZT/YBCO interfacial potential barrier and promotes migration of photogenerated carriers, consequently increasing photovoltage and photocurrent. This work describes novel method to measure superconducting energy gap. [ABSTRACT FROM AUTHOR]

This paper reassesses the old dilemma "compact vs. extended phase" in the quantum theory of the rotator and the Josephson junction and the analogy of these two systems with a particle moving in a periodic potential. This dilemma is in fact the dilemma of whether the states with the phases φ and φ + 2π are distinguishable, or not. In the past it was widely accepted that in the Josephson junction these states are distinguishable, as in the case of a particle moving in a periodic potential. This paper argues that the states with the phases φ and φ + 2π are indistinguishable as in a pendulum (a particular example of the quantum rotator). However, this does not lead to revision of the conclusions of the conventional theory predicting the transition from the superconducting to the insulating state in the small Josephson junction. [ABSTRACT FROM AUTHOR]

At high pressure, the typical behavior of elements dictated by the periodic table—including oxidation numbers, stoichiometries in compounds, and reactivity, to name but a few—is altered dramatically. As pressure is applied, the energetic ordering of atomic orbitals shifts, allowing core orbitals to become chemically active, atypical electron configurations to occur, and in some cases, non-atom-centered orbitals to form in the interstices of solid structures. Strange stoichiometries, structures, and bonding motifs result. Crystal structure prediction tools, not burdened by preconceived notions about structural chemistry learned at atmospheric pressure, have been applied to great success to explore phase diagrams at high pressure, identifying novel structures in diverse chemical systems. Several of these phases have been subsequently synthesized. Experimentally, access to high-pressure regimes has been bolstered by advances in diamond anvil cell and dynamic compression techniques. The joint efforts of experiment and theory have led to startling successes stories in the realm of high-temperature superconductivity, identifying many novel phases—some of which have been synthesized—whose superconducting transition approaches room temperature. [ABSTRACT FROM AUTHOR]

The temperature dependence of AC susceptibility (ACS) has been measured for a very high-quality plate-like slightly overdoped YBCO single crystal for different frequencies and AC magnetic fields. Frequency dependence of the ACS is weak irrespective of the magnetic field orientation, but significant effects of field orientation with respect to the CuO2 planes and field magnitude on real and imaginary components of fundamental ACS are observed. We have found that the magnitude of the ratio of the loss peak to the full diamagnetic signal is slightly larger in perpendicular field than that in the parallel field arrangement. The height of the loss peak saturates as full penetration of magnetic field is achieved. This saturation is achieved at a lower field amplitude when HIIc. The peak temperature, Tp, in χ″ shifts to lower temperatures with increasing magnetic field amplitude for both HIIc and HIIab. The value of Tp depends on the orientation of the magnetic field with respect to the crystallographic axes, illustrating the anisotropy in the magnetic flux dynamics. The superconducting onset transition temperature obtained from the diamagnetic shielding component of the ACS, on the other hand, does not depend on the orientation of the magnetic field. The superconducting transition width increases weakly with increasing magnetic field; the rate of this increment is more prominent for HIIc case. The Cole–Cole plot [χ″(χ′)] shows qualitatively and quantitatively almost identical features for HIIc and HIIab, with small difference in the peak positions with respect to the orientation of the magnetic field and shielding current paths. The general features of χ″(χ′) imply that there is no flux creep for the range of frequencies and AC fields employed in this investigation. The maximum value of the loss peak and its position with respect to χ′ in the Cole–Cole plot are largely consistent with the Bean critical state model. Slightly increased peak value in comparison to the predicted peak value within the Bean critical state model is probably due to a weak field dependence of Jc. The results obtained here are compared with various theoretical models and experimental findings. Notable differences are highlighted and discussed in details in this study. [ABSTRACT FROM AUTHOR]

In the present work, we investigated the influence of high hydrostatic pressure up to 11 kbar on the conductivity in the basal ab-plane of medium-doped with praseodymium (x≈0.23) single-crystal Y1-xPrxBa2Cu3O7-δ samples. It was determined that, in contrast to the pure YBa2Cu3O7-δsamples with the optimal oxygen content, the application of high pressure leads to the formation of phase separation in the basal plane of Y0.77Pr0.23Ba2Cu3O7-δ single crystals. Possible mechanisms of the effect of Pr doping and high pressure on the two-step resistive transition to the superconducting state are discussed. It was determined that in the normal state, the conductivity is metallic and is limited by phonons scattering (Bloch-Grüneisen regime) and defects. The fluctuation conductivity is considered within the Lorentz-Doniach model. Hydrostatic pressure, accompanied by a decrease in anisotropy, leads to a decrease in the residual and phonon resistances. Debye temperature and coherence length are independent of pressure. The applicability of the McMillan formula in the presence of significant anisotropy is discussed. [ABSTRACT FROM AUTHOR]

Exotic superconductivity that appears near the charge ordering instability has attracted significant interest since the beginning of superconducting study. The discovery of possible coexistence of charge ordering and superconductivity in cuprates and kagome metals has further fascinated researchers in recent years. In this review, we focus on the BEDT-TTF-based organic superconductor with β″-type molecular packing sequence, which shows the charge ordering transition in the very vicinity of superconducting transition, and summarize the experimental results reported up to the present. At the charge ordering temperature, ultrasonic measurement detects the softening of the crystal lattice, and 13C-NMR measurement shows an increase in nuclear spin-lattice relaxation rate divided by temperature 1/T1T. These results suggest that low-energy dynamics are activated near the charge ordering transition, leading us to invoke the charge-fluctuation mediated superconducting pairing mechanism. [ABSTRACT FROM AUTHOR]

A study of Berezinskii–Kosterlitz–Thouless transitions in clean, layered two-dimensional superconductors promises to provide insight into a host of novel phenomena like re-entrant vortex-dynamics, underlying unconventional metallic phases, and topological superconductivity. In this Letter, we report the study of charge carrier dynamics in a novel two-dimensional superconducting van der Waals heterostructure comprising of monolayer MoS2 and few-layer NbSe2 (∼ 15 nm). Using low-frequency conductance fluctuation spectroscopy, we show that the superconducting transition in the system is percolative. We present a phenomenological picture of different phases across the transition correlating with the evaluated noise. The analysis of the higher order statistics of fluctuation reveals non-Gaussian components around the transition indicative of long-range correlation in the system. [ABSTRACT FROM AUTHOR]

The recently discovered kagome superconductor CsV3Sb5 (Tc ≃ 2.5 K) has been found to host charge order as well as a non-trivial band topology, encompassing multiple Dirac points and probable surface states. Such a complex and phenomenologically rich system is, therefore, an ideal playground for observing unusual electronic phases. Here, we report anisotropic superconducting properties of CsV3Sb5 by means of transverse-field muon spin rotation (μSR) experiments. The fits of temperature dependences of in-plane and out-of-plane components of the magnetic penetration depth suggest that the superconducting order parameter may have a two-gap (s + s)-wave symmetry. The multiband nature of superconductivity could be further supported by the different temperature dependences of the anisotropic magnetic penetration depth γλ(T) and upper critical field γ B c 2 (T) . The relaxation rates obtained from zero field μSR experiments do not show noticeable change across the superconducting transition, indicating that superconductivity does not break time reversal symmetry. [ABSTRACT FROM AUTHOR]

Among other Fe-based superconductors, Fe(Se,Te) is particularly interesting because of the low structural anisotropy, large upper critical fields, low field dependence of the critical current density and low toxicity. It can also be grown as an epitaxial film on a metallic oriented substrate, making the fabrication of a Fe-based coated conductor (CC) possible. Less strict requirements on the template microstructure allow for the design of a simplified design compared to REBCO CCs. This design requires a buffer layer to promote the oriented growth of the superconducting film and avoid diffusion from the metallic template. In this work, CeO2 based buffer layers are prepared on single crystals via two chemical deposition techniques, metal organic decomposition (MOD) and polymer assisted deposition (PAD). With the design of a suitable thermal treatment, it is possible to obtain oriented buffers with large flat grains and low values of surface roughness. Fe(Se,Te) films are deposited on these templates via laser deposition, and excellent samples are obtained when a Fe(Se,Te) seed layer is used to favour chemical matching with the buffer: sharp superconducting transitions around 16 K and critical current densities exceeding 1 MA cm−2 at 4.2 K in self-field are observed. These results are the demonstration of the feasibility of a Fe-based CC architecture, with all the relative advantages concerning process simplification and cost reduction. [ABSTRACT FROM AUTHOR]

A hallmark of topological superconductivity is the non-Abelian statistics of Majorana bound states (MBS), its chargeless zero-energy emergent quasiparticles. The resulting fractionalization of a single electron, stored nonlocally as a two spatially-separated MBS, provides a powerful platform for implementing fault-tolerant topological quantum computing. However, despite intensive efforts, experimental support for MBS remains indirect and does not probe their non-Abelian statistics. Here we propose how to overcome this obstacle in mini-gate controlled planar Josephson junctions (JJs) and demonstrate non-Abelian statistics through MBS fusion, detected by charge sensing using a quantum point contact, based on dynamical simulations. The feasibility of preparing, manipulating, and fusing MBS in two-dimensional (2D) systems is supported in our experiments which demonstrate the gate control of topological transition and superconducting properties with five mini gates in InAs/Al-based JJs. While we focus on this well-established platform, where the topological superconductivity was already experimentally detected, our proposal to identify elusive non-Abelian statistics motivates also further MBS studies in other gate-controlled 2D systems. The current efforts to look for Majorana bound states (MBS) still cannot probe the hallmark property, the non-Abelian statistics. Here, the authors propose to realize non-Abelian statistics through MBS fusion in mini-gate controlled planar Josephson junctions. [ABSTRACT FROM AUTHOR]

The formation of Cooper pairs, a bound state of two electrons of opposite spin and momenta by exchange of a phonon, is a defining feature of conventional superconductivity. In the cuprate high temperature superconductors, even though the superconducting state also consists of Cooper pairs, the pairing mechanism remains intensely debated. Here, we investigate superconducting pairing in the Bi2Sr2CaCu2O8+δ (Bi2212) cuprate by employing spectral functions obtained from angle-resolved photoemission as input to the Bethe-Salpeter equation. Assuming Cooper pairing is driven by spin fluctuations, we construct the spin-fluctuation-mediated pairing interaction and use it to compute the eigenfunctions and eigenvalues of the Bethe-Salpeter equation for multiple Bi2212 samples. The leading d-wave eigenvalue increases as the temperature is decreased toward Tc, reaching a value of approximately 1 at the Tc corresponding to each doping value. This suggests that spin fluctuations can approximately account for Tc and mediate pairing in the cuprate superconductors. The pairing mechanism behind the Cooper pairs in unconventional superconductors has been debated since the discovery of the high-Tc cuprates. Here, using angle resolved photoemission spectroscopy data for Bi2212 applied to the Bethe-Salpeter equation, the authors suggest that a spin-mediated pairing interaction can account for the high superconducting temperature as well as play a dominant role in the Cooper pair formation. [ABSTRACT FROM AUTHOR]

Topological semimetals are three dimensional materials with symmetry-protected massless bulk excitations. As a special case, Weyl nodal-line semimetals are realized in materials having either no inversion or broken time-reversal symmetry and feature bulk nodal lines. The 111-family, including LaNiSi, LaPtSi and LaPtGe materials (all lacking inversion symmetry), belongs to this class. Here, by combining muon-spin rotation and relaxation with thermodynamic measurements, we find that these materials exhibit a fully-gapped superconducting ground state, while spontaneously breaking time-reversal symmetry at the superconducting transition. Since time-reversal symmetry is essential for protecting the normal-state topology, its breaking upon entering the superconducting state should remarkably result in a topological phase transition. By developing a minimal model for the normal-state band structure and assuming a purely spin-triplet pairing, we show that the superconducting properties across this family can be described accurately. Our results demonstrate that the 111 materials reported here provide an ideal test-bed for investigating the rich interplay between the exotic properties of Weyl nodal-line fermions and unconventional superconductivity. [ABSTRACT FROM AUTHOR]

The linear dependence on temperature of the resistivity in metals undergoing high‐temperature superconducting transition is a puzzle, which is generally attributed to non‐Fermi liquid behavior on a large range of temperature values. No particle and momentum conservation characterizes the 0 + 1 − d Sachdev–Ye–Kitaev model as a tractable non‐Fermi liquid starting paradigm, when extended to higher space dimensions. Due to the conformal symmetry breaking in the incoherent phase, Goldstone bosons arise, which provide energy diffusion in the lattice. The linear response to energy diffusion in the model is discussed, which is in principle charge neutral and non‐momentum conserving, and the temperature dependence of the thermal and electric conductivity in the incoherent prechaotic, intermediate temperature phase is obtained. [ABSTRACT FROM AUTHOR]

In our desire to give a new suggestion for H-based superconductors experiments we present a theoretical framework for understanding the impact of an applied electric field on pressured hydride superconductors. We study a material at pressure p, when it possesses insulator-superconductor transition, at the respective superconducting critical temperature T cr . The theory shows the applied electric field penetrates the material and forces the Cooper pairs to Bose condensate. If one applies an electric field and then increases the temperature, the theory predicts novel critical temperature T cr el higher than T cr . Therefore, the system has a higher superconducting critical temperature if we apply an electric field instead of increasing the pressure. The result shows that in the case of carbonaceous sulfur hydride at 234Gpa and near but below critical temperature T c = 283 K , applying a sufficiently strong electric field, we can bring the superconducting critical temperature close to 300 K. [ABSTRACT FROM AUTHOR]

We propose a novel platform for the creation and manipulation of Majorana zero modes consisting of a ferromagnetic metallic wire placed between conventional superconductors which are in proximity to ferromagnetic insulators. Our device relies on the interplay of applied supercurrents and exchange fields emerging from the ferromagnetic insulators. We assert that the proposed superconductor/ferromagnet heterostructures exhibit enhanced controllability, since topological superconductivity can be tuned apart from gate voltages applied on the ferromagnetic wire, also by manipulating the applied supercurrents and/or the magnetisation of the ferromagnetic insulators. [ABSTRACT FROM AUTHOR]

A scenario of shielding and stabilization of magnetic and electromagnetic fields in the measuring volume occupied by a superconducting flux qubit is considered. The qubit is used as an artificial macroscopic atom with discrete energy levels in a counter of single photons of the microwave range. It is shown that a decrease in the amplitude of variations of the external magnetic field inside the 3-layer hybrid cylindrical shield, composed of superconducting and ferromagnetic cylinders with the diameter-to-length ratio of 1:5, provides high stability of the magnetic field. The absolute value of the magnetic field at the sample location is determined mainly by the magnetic flux captured by the superconductor shields during their superconducting transition. Although the magnetic field stability is more important than the field itself for the photon counter, the paper also discusses experimental methods for reducing the absolute field value in the hybrid shield. [ABSTRACT FROM AUTHOR]

Structural stabilities of high‐pressure YMgHx phases (x=2−10,12,14$x = 2-10, 12, 14$, and 16) and their superconductivities are investigated by employing evolutionary‐algorithm‐based crystal search combined with first‐principles calculations. For predicted candidate structures of YMgHx, the convex hull and phonon analyses reveal seven stable and two metastable phases. For all the predicted phases, superconducting transition temperatures (Tc) are also predicted by using the McMillan formula. P4/mmm$P4/mmm$‐YMgH6 is found having Tc=76$T_\mathrm{c} = 76$ K at 300 GPa comparable to the boiling temperature of liquid nitrogen, and high‐Tc (≥77 K) being predicted for the H‐richer phases, P4/mmm$P4/mmm$‐YMgH8 (124 K at 300 GPa), Cmmm$Cmmm$‐YMgH12 (152 K at 250 GPa), and Fd3¯m$Fd\bar{3}m$‐YMgH12 (190 K at 200 GPa), which possess clathrate structures composed of H14, H18, H24, and H24 cages, respectively. To elucidate why the H‐rich phases attain high‐Tc, electronic and phonon band structures as well as electron–phonon coupling strength are analyzed based on Eliashberg spectral functions. The clathrate structures exhibit both a larger H‐driven electronic density of states at the Fermi level and a denser H‐driven phonon density of states, correlating with larger EPC constants. These structural and chemical bonding analyses reveal that the highest‐Tc phase Fd3¯m$Fd\bar{3}m$‐YMgH12 has H4 units formed in the sodalite cage. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of High Pressure Physics is the property of Chinese Journal of High Pressure Physics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We present a comprehensive analysis of the out-of-equilibrium Casimir pressure between two high- T c superconducting plates, each kept at a different temperature. Two interaction regimes can be distinguished. While the zero-point energy dominates in the near field, thermal effects become important at large interplate separations causing a drop in the force's magnitude compared with the usual thermal-equilibrium case. Our detailed calculations highlight the competing role played by propagating and evanescent modes. Moreover, as one of the plates undergoes the superconducting transition, we predict an abrupt change in the force for any plate distance, which has not been previously observed in other systems. The sensitivity of the dielectric function of the high- T c superconductors makes them ideal systems for a possible direct measurement of the out-of-equilibrium Casimir pressure. [ABSTRACT FROM AUTHOR]

AC-calorimetry was developed for a cubic-anvil-type pressure apparatus, which can explore the electromagnetic properties of matter over temperatures of 2–300 K and pressures of 0–15 GPa. This method was designed to observe the specific heat of fragile crystals that are difficult to mold into desired forms, such as β-Na0.33V2O5 and BaFe2S3. The calorimeter has two main components: a thermometer and a heater. We employed an AuFe (0.07 mol. %)-Chromel thermocouple and NiCr alloy foil/wire as the thermometer and heater, respectively. Using this calorimetry, we successfully observed the pressure dependencies of several transition temperatures in β-Na0.33V2O5 and the jump in the specific heat (ΔCac/T) at the superconducting transition in Pb-metal when under pressure. Meanwhile, the pressure dependencies of the observed ΔCac/T do not coincide with the literature, which may be attributed to the pressure dependence of the thermoelectric power for the AuFe-Chromel thermocouple at around 5 K. [ABSTRACT FROM AUTHOR]

Many of the world's leading manufacturers of magnetic resonance imagers (MRIs) pay considerable attention to reducing the consumption of liquid helium in modern magnetic MRI systems. This is primarily due to the significantly increasing price of liquid helium in recent years and the persistence of this tendency in the future, as well as the additional costs and difficulties associated with its delivery, storage, and use. For this reason, superconducting magnetic systems for MRIs that do not require liquid helium are being developed. One of the problems of helium-free magnetic systems is the increased risk of a transition from the superconducting state even with a short-term excess of the heat input over the cooler capacity, which is compensated in traditional systems by the liquid-helium evaporation. Along with the heat input due to the thermal conductivity of the cryostat and the supply elements, the eddy currents that arise in the conducting magnet structures during generation of an alternating magnetic field by the gradient MRI system are also a source of heat. Such an additional heat input was taken into account in this study when developing a gradient system for a helium-free MRI. This paper presents the calculation and modeling of a gradient system for a helium-free MRI. [ABSTRACT FROM AUTHOR]

Semiconducting group-VI-B transition metal dichalcogenides (TMDs) with the triangular prism crystal structure exhibit unique features. A particularly striking recent example is the observation of an Ising superconducting transition at high carrier densities induced through the field effect in an electric double layer transistor (EDLT). So far, this phenomenon has been accounted for by assuming that the original triangular prismatic bulk crystal structure is unaffected by the heavy doping. However, this assumption has not been verified so far, even though other crystal phases of these layered materials were shown to host Ising superconductivity as well. Here, we provide experimental evidence that the initial triangular prismatic crystal structure of the MoS2, which serves here as a representative member of the TMD family, is not altered during operation of the EDLT even when the carrier density is large enough to induce the superconducting transition. The latter is monitored via transport measurements, while the crystal structure is simultaneously examined in situ with micro-Raman spectroscopy at low temperature. [ABSTRACT FROM AUTHOR]

Semiconducting group-VI-B transition metal dichalcogenides (TMDs) with the triangular prism crystal structure exhibit unique features. A particularly striking recent example is the observation of an Ising superconducting transition at high carrier densities induced through the field effect in an electric double layer transistor (EDLT). So far, this phenomenon has been accounted for by assuming that the original triangular prismatic bulk crystal structure is unaffected by the heavy doping. However, this assumption has not been verified so far, even though other crystal phases of these layered materials were shown to host Ising superconductivity as well. Here, we provide experimental evidence that the initial triangular prismatic crystal structure of the MoS2, which serves here as a representative member of the TMD family, is not altered during operation of the EDLT even when the carrier density is large enough to induce the superconducting transition. The latter is monitored via transport measurements, while the crystal structure is simultaneously examined in situ with micro-Raman spectroscopy at low temperature. [ABSTRACT FROM AUTHOR]

Thermal anomalies in the temperature dependence of the heat capacity around the superconducting transition of a hole-doped superconductor, κ–(BEDT-TTF)4Hg2.89Br8, which is known as a dimer-Mott triangle lattice system are investigated by the ac modulation technique under external pressure. To detect the electronic phase transition under applied pressure conditions for a single crystal sample, we have improved resolution of the ac modulation technique. By tracking the appropriate frequency during the temperature scan measurement, we succeed in detecting the thermal anomaly with the applied pressure of 0.3 GPa where the electronic state is located in the crossover region of non-Fermi liquid to Fermi liquid. Application of the external magnetic fields of H = 2 and 6 T in the in-plane direction reveals that the superconductivity in this doped triangle lattice of molecular dimers is relatively stable against the magnetic field. [ABSTRACT FROM AUTHOR]

Synthesis of the SmBa2Cu3O7–δ superconducting material by the standard solid-state reaction is reported. DC resistivity measurements were performed to analyse the conductivity excess close to the superconducting transition. The fluctuation analysis was performed by the method of logarithmic temperature derivative of the paraconductivity. A bulk Tc = 93.004 K was determined through the extrapolation of the genuinely critical regime, which is explained from the dynamical scaling theory. The correlations of the critical exponents with the dimensionality of the fluctuation system for each Gaussian regime were performed by using the Aslamazov–Larkin theory. From the analysis, the occurrence of Gaussian-like fluctuations associated to dimensional d = 3 and d = 2 pairing regimes and fluctuation developing in fractal topologies with d = 2.6 and d = 1.3 are established. The coherence length, the Ginzburg number, the jump in the specific heat δc at T = Tc, the penetration depth λ(0), the critical magnetic fields Bc1(T) and Bc2(T) and the critical current density Jc(0) were theoretically determined for this superconducting material. Results largely agree with experimental reports for RBa2Cu3O7–δ (R = Rare Earth elements) and YBa2Cu3O7–δ superconductors. [ABSTRACT FROM AUTHOR]

Synthesis of the SmBa2Cu3O7–δ superconducting material by the standard solid-state reaction is reported. DC resistivity measurements were performed to analyse the conductivity excess close to the superconducting transition. The fluctuation analysis was performed by the method of logarithmic temperature derivative of the paraconductivity. A bulk Tc = 93.004 K was determined through the extrapolation of the genuinely critical regime, which is explained from the dynamical scaling theory. The correlations of the critical exponents with the dimensionality of the fluctuation system for each Gaussian regime were performed by using the Aslamazov–Larkin theory. From the analysis, the occurrence of Gaussian-like fluctuations associated to dimensional d = 3 and d = 2 pairing regimes and fluctuation developing in fractal topologies with d = 2.6 and d = 1.3 are established. The coherence length, the Ginzburg number, the jump in the specific heat δc at T = Tc, the penetration depth λ(0), the critical magnetic fields Bc1(T) and Bc2(T) and the critical current density Jc(0) were theoretically determined for this superconducting material. Results largely agree with experimental reports for RBa2Cu3O7–δ (R = Rare Earth elements) and YBa2Cu3O7–δ superconductors. [ABSTRACT FROM AUTHOR]

Charge density wave (CDW) order is an emergent quantum phase that is characterized by periodic lattice distortion and charge density modulation, often present near superconducting transitions. Here, we uncover a novel inverted CDW state by using a femtosecond laser to coherently reverse the star-of-David lattice distortion in 1T-TaSe2. We track the signature of this novel CDW state using time- and angle-resolved photoemission spectroscopy and the time-dependent density functional theory to validate that it is associated with a unique lattice and charge arrangement never before realized. The dynamic electronic structure further reveals its novel properties that are characterized by an increased density of states near the Fermi level, high metallicity, and altered electron–phonon couplings. Our results demonstrate how ultrafast lasers can be used to create unique states in materials by manipulating charge-lattice orders and couplings. [ABSTRACT FROM AUTHOR]

The article discusses the findings of a study on the modification of transport and structural characteristics of SrTiO3 single crystals using high-power density excimer laser pulses. The researchers observed topographic modulation with segregated domains and found that the domain boundaries displayed different electrical properties. They also detected a superconducting phase transition below 180 mK in the irradiated crystals. The authors responded to a comment suggesting that the emergence of the superconducting state was due to the formation of low-oxidation state Ti-oxides at the surface of reduced SrTiO3, explaining that their experiments created a highly non-equilibrium situation with complex laser-matter interactions. They concluded that the primary change in elemental stoichiometric composition was an increased number of oxygen vacancies, contributing to the altered electronic properties of the irradiated crystals. The researchers also addressed other criticisms and provided evidence supporting their findings. [Extracted from the article]

The article presents a study that explores the spin-triplet superconductivity in K2Cr3As3. It mentions that spin-triplet superconductor can harbor Majorana bound states that can be used in topological quantum computing. It discusses about the spin susceptibility in the superconducting state as a bulk property.

A high-entropy-alloy-type (HEA-type) superconductor is new category of highly disordered superconductors. Therefore, finding brand-new superconducting characteristics in the HEA-type superconductors would open new avenue to investigate the relationship between structural disorder and superconductivity. Here, we report on the remarkable broadening of specific heat jump near a superconducting transition tempreature (T c) in transition-metal zirconides (Tr Zr2) with different mixing entropy (Î" S mix) at the Tr site. With increasing Î" S mix, the superconducting transition seen in specific heat became broader, whereas those seen in magnetization were commonly sharp. Therefore the broadening of specific heat jump would be related to the microscopic inhomogeneity of the formation of Cooper pairs behind the emergence of bulk superconductivity states. [ABSTRACT FROM AUTHOR]

We report the effect of the ab-plane magnetic field B up to 8 T on the resistivity ρ(T) and fluctuation conductivity σ′'(T) in YBa2Cu3O7-δ thin films. As expected, up to ∼ 2.5 T the magnetic field monotonously increases ρ, the width of the resistive transition, ΔTc, and coherence length along the c axis, ξC(0), but decreases both Tc and the range of superconducting (SC) fluctuations ΔTfl. The fluctuation conductivity exhibits a crossover at characteristic temperature T0 from the 3D Aslamasov-Larkin (AL) theory near Tc to the 2D fluctuation theory of Maki-Thompson (MT). However, at B = 3 T, the MT term is completely suppressed, and above T0 σ′'(T) is unexpectedly described by the fluctuation contribution of 2D AL, suggesting the formation of a 2D vortex lattice in the film under the action of a magnetic field. At the same time, ΔTf sharply increases by a factor of about 7, and ξC(0) demonstrates a very unusual dependence on Tc when B increases above 3 T. Our results demonstrate the possibility of the formation of a vortex state in YBCO and its evolution with increasing B. [ABSTRACT FROM AUTHOR]

A high-entropy-alloy-type (HEA-type) superconductor is new category of highly disordered superconductors. Therefore, finding brand-new superconducting characteristics in the HEA-type superconductors would open new avenue to investigate the relationship between structural disorder and superconductivity. Here, we report on the remarkable broadening of specific heat jump near a superconducting transition tempreature (T c) in transition-metal zirconides (Tr Zr2) with different mixing entropy (Î" S mix) at the Tr site. With increasing Î" S mix, the superconducting transition seen in specific heat became broader, whereas those seen in magnetization were commonly sharp. Therefore the broadening of specific heat jump would be related to the microscopic inhomogeneity of the formation of Cooper pairs behind the emergence of bulk superconductivity states. [ABSTRACT FROM AUTHOR]

Niobium diselenide (NbSe2) is a layered transition metal dichalcogenide with novel quantum phases at low temperatures (T) such as superconductivity and charge density wave order. While its electronic correlations and the interaction between electrons and other collective modes have been explored extensively, a detailed study of the transport behavior of photo-excited charge carriers still remains elusive. Here, we report a systematic investigation of the photoresponse generated in homogenous NbSe2 nano-flakes near the superconducting critical temperature (Tc). By combining scanning photocurrent microscopy and classic photoconductivity measurements, three distinctive mechanisms of the photoresponse are established, including the band bending at the NbSe2–metal junction, the perturbation of the superconducting state, and the photo-bolometric effect. Among them, the photo-induced phase transition from the superconducting to normal state results in an extremely large photocurrent, which is tunable by the bias voltage and is consistent with the observation via the electrical transport characterization. The photoresponsivity of our device reaches 42.3 A/W, and the response time is less than 2 μs at T = 3.8 K for an excitation in the visible wavelength, whose performance could be further improved by optimizing the device design and the experimental condition. Our result sheds light on ultrasensitive broadband photodetection with atomically thin NbSe2 and points to a potential means of probing the correlated electronic phases by exploring light–matter interactions. [ABSTRACT FROM AUTHOR]

Beyond a critical disorder, two-dimensional (2D) superconductors become insulating. In this Superconductor-Insulator Transition (SIT), the nature of the insulator is still controversial. Here, we present an extensive experimental study on insulating NbxSi1−x close to the SIT, as well as corresponding numerical simulations of the electrical conductivity. At low temperatures, we show that electronic transport is activated and dominated by charging energies. The sample thickness variation results in a large spread of activation temperatures, fine-tuned via disorder. We show numerically and experimentally that this originates from the localization length varying exponentially with thickness. At the lowest temperatures, there is an increase in activation energy related to the temperature at which this overactivated regime is observed. This relation, observed in many 2D systems shows that conduction is dominated by single charges that have to overcome the gap when entering superconducting grains. Despite extensive work on the superconductor-insulator transition in two-dimensional materials, the nature of the insulator is still debated. The authors report measurements and simulations of NbxSi1–x films, showing that conduction in the insulating state occurs by single charges hopping between superconducting grains. [ABSTRACT FROM AUTHOR]

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 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 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. [ABSTRACT FROM AUTHOR]

Herein, DC magnetization measurements of high‐quality single crystals of optimally doped YBa2Cu3O7−δ(YBCO) superconductor are reported on. The temperature and orientation dependence of the magnetic penetration depth λ(T,θ) for single‐crystal YBCO is estimated from the slope of the linear M(lnH) dependence in the London regime. The penetration depth is strongly anisotropic. Also, the electrical resistivity as a function of temperature in YBCO thin film deposited by laser ablation on the SrTiO3 substrate face is investigated around the superconducting transition region under various values of the magnetic field up to 14 T. In this work, based on the resistivity measurements, the upper critical magnetic field for both directions B∥c‐axis and B⊥c‐axis is determined with a DC weak transport current density by using 90% criteria of the normal‐state resistivity value. According to the relations Bc2∥c=ϕ02πξ∥2 and Bc2⊥c=ϕ02πξ∥ξ⊥, the coherence length ξ∥(0) and ξ⊥(0) is determined, where ϕ0 is the magnetic flux quantum. The anisotropy parameter is calculated and analyzed within the frame of Ginzburg–Landau theory. This result indicates that anisotropy is more evident in YBCO. [ABSTRACT FROM AUTHOR]

Almost all proposed configurations and practical achievements based on superconductor/ferromagnet (S/F) heterostrucutres focus on s-wave superconductors. However, several attempts targeted also high temperature superconductors, most of them using manganite ferromagnets LaXMnO3 (X: Ca or Sr) and Y1Ba2Cu3O7âˆ' x (YBCO). Here we propose a new ferromagnetic material that can be used with YBCO for the fabrication of S/F hybrid structures. We show that a ferromagnetic order can be induced in a thin layer (∼130 nm thickness) of CaRuO3 grown by pulsed laser deposition on epitaxial YBCO film. Detailed magnetic and structural investigations show that the observations of the weak ferromagnetism are consistent with the magnetic order induced by in-plane tensile strain of about 1.7% and the easy-magnetization axis forms an angle of ∼180Âş with the layer plane. The value of the Curie temperature T Curie estimated using the Curieâ€"Weiss law was 340 K. An unusual temperature dependence of the magnetic moment around the superconducting transition was observed in both field-cooled and zero-field-cooled configurations which is attributed to the paramagnetic Meissner effect. [ABSTRACT FROM AUTHOR]

Herein, DC magnetization measurements of high‐quality single crystals of optimally doped YBa2Cu3O7−δ(YBCO) superconductor are reported on. The temperature and orientation dependence of the magnetic penetration depth λ(T,θ) for single‐crystal YBCO is estimated from the slope of the linear M(lnH) dependence in the London regime. The penetration depth is strongly anisotropic. Also, the electrical resistivity as a function of temperature in YBCO thin film deposited by laser ablation on the SrTiO3 substrate face is investigated around the superconducting transition region under various values of the magnetic field up to 14 T. In this work, based on the resistivity measurements, the upper critical magnetic field for both directions B∥c‐axis and B⊥c‐axis is determined with a DC weak transport current density by using 90% criteria of the normal‐state resistivity value. According to the relations Bc2∥c=ϕ02πξ∥2 and Bc2⊥c=ϕ02πξ∥ξ⊥, the coherence length ξ∥(0) and ξ⊥(0) is determined, where ϕ0 is the magnetic flux quantum. The anisotropy parameter is calculated and analyzed within the frame of Ginzburg–Landau theory. This result indicates that anisotropy is more evident in YBCO. [ABSTRACT FROM AUTHOR]