A newly discovered family of the Fe-based superconductors is isostructural with the so-called 122 family of Fe pnictides, but has a qualitatively different doping state. Early experiments indicate that superconductivity is nodeless, yet prerequisites for the $s_\pm$ nodeless state (generally believed to be realized in Fe superconductors) are missing. It is tempting to assign a $d-$ wave symmetry to the new materials, and it does seem at first glance that such a state may be nodeless. Yet a more careful analysis shows that it is not possible, given the particular 122 crystallography, and that the possible choice of admissible symmetries is severly limited: it is either a conventional single-sign $s_{+}$ state, or another $s_\pm$ state, different from the one believed to be present in other Fe-based superconductors.
We report superconducting properties of noncentrosymmetric superconductor LaPtGe which crystallizes in noncentrosymmetric $ α$-ThSi$ _{2} $ structure. The magnetization, resistivity and specific heat measurements confirm that LaPtGe is a type-II bulk superconductor with a transition temperature T$ _{c} $ = 3.05 $ \pm $ 0.05 K. Muon-spin relaxation/rotation measurements confirms that time reversal preserved in the superconducting ground state.
The noncentrosymmetric superconductor TaOs has been characterized using x-ray diffraction, resistivity, magnetization, and specific heat measurements. Magnetization and specific heat measurements show a bulk superconducting transition at 2.07 K. These measurements suggest that TaOs is a weakly coupled type-II superconductor. The electronic specific heat in the superconducting state can be explained by the single-gap BCS model, suggesting s-wave superconductivity in TaOs.
Increase of superconducting order parameter in the magnetic superconductor Dy0.6Y0.4Rh3.85Ru0.15B4 in a wide magnetic field range. Is it a further candidate in p-wave superconductors?
首次研究了磁性超导体Dy_（0.6）Y_（0.4）Rh_（3.85）Ru_（0.15）B_4的Andreev反射谱。结果表明，与传统的单线态超导体相比，外加磁场（最高可达0.7 Hc ~ 2）对超导体有很强的激励作用。对于某些接触获得的比率2Δ/kBTc \approx 4.0高于具有弱电子-声子相互作用的常规超导体的典型值3.52。在Dy_（0.6）Y_（0.4）Rh_（3.85）Ru_（0.15）B_4中，实现了三重态的超导配对机制。
Short review of the topical comprehension of the superconductor materials classes Cuprate High-Temperature Superconductors, other oxide superconductors, Iron-based Superconductors, Heavy-Fermion Superconductors, Nitride Superconductors, Organic and other Carbon-based Superconductors and Boride and Borocarbide Superconductors, featuring their present theoretical understanding and their aspects with respect to technical applications.
We have investigated the ternary noncentrosymmetric superconductors TaXSi (X=Re, Ru) by magnetization, resistivity, and specific heat measurements. The samples crystallize in orthorhombic TiFeSi structure having superconducting transition Tc = 5.32 K and 3.91 K, for TaReSi and TaRuSi respectively. Specific heat measurements indicated an s-wave nature of both materials with a moderately coupled nature. However, a low value of specific heat jump and the concave nature of the upper critical field suggests a nontrivial superconducting gap.
The transition metal carbide superconductor Sc3CoC4 may represent a new benchmark system of quasi-1D superconducting behavior. We investigate the superconducting transition of a high-quality single crystalline sample by electrical transport experiments. Our data show that the superconductor goes through a complex dimensional crossover below the onset Tc of 4.5 K. First, a quasi-1D fluctuating superconducting state with finite resistance forms in the CoC4 ribbons which are embedded in a Sc matrix in this material. At lower temperature, the transversal Josephson or proximity coupling of neighbor…
High bias anomaly in YBa2Cu3O7/LaMnO_{3+delta}/YBa2Cu3O7 Superconductor/Ferromagnetic Insulator/Superconductor junctions: Evidence for a long-range superconducting proximity effect through the conduction band of a ferromagnetic insulator
研究了超导体/铁磁绝缘体/超导体（$_2$ O $_{7-x}$ /LaMnO $_{3+δ}$ /$_2$ O $_3$）隧道结的垂直输运特性.在一个大的偏置电压$V\sim 1$ V，我们观察到一个阶梯状的开始过电流，发生在超导转变温度$T<T_c$以下，很容易被磁场抑制。这种现象是由于非平衡电子通过Fowler-Nordheim隧穿过程注入到铁磁绝缘体导带中的一种新型的超导邻近效应。强非平衡布居的发生证实了在大偏压下的光子发射的检测。由于我们的铁磁绝缘体中的导带是强自旋极化的，所观察到的长程（20 nm）邻近效应为非传统的自旋三重态超导态提供了证据。
We analyze the presence of non-reciprocal critical currents, the so-called superconducting diode effect, in chiral superconductors within a generalized Ginzburg-Landau framework. After deriving its key symmetry conditions we illustrate the basic mechanism for two examples, the critical current in a thin film and a Josephson junction. The appearance of spontaneous edge currents and the energy bias for the formation of Josephson vortices play an essential part in establishing a splitting of the critical currents running in opposite directions. Eventually, this allows us to interpret a supercondu…
To decipher the mechanism of high temperature superconductivity, it is important to know how the superconducting pairing emerges from the unusual normal states of cuprate superconductors, including pseudogap, anomalous Fermi liquid and strange metal (SM). A long-standing issue under debate is how the superconducting pairing is formed and condensed in the SM phase because the superconducting transition temperature is the highest in this phase. Here, we report the first experimental observation of a pressure-induced crossover from two- to three-dimensional superconducting states in the optimally…
A strong superconducting diode effect (SDE) is revealed in a thin superconducting film periodically nanostructured with magnetic dots. The SDE is caused by the current-activated dissipation mitigated by vortex-antivortex pairs (VAPs), which periodically nucleate under the dots, move and annihilate in the superconductor - eventually driving the system to the high-resistive state. Inversing the polarity of the applied current destimulates the nucleation of VAPs, the system remains superconducting up to far larger currents, leading to the pronounced diodic response. Our dissipative Ginzburg-Landa…
Structural and electrical transport properties of superconducting Au{0.7}In{0.3} films: A random array of superconductor-normal metal-superconductor (SNS) Josephson junctions
The structural and superconducting properties of Au{0.7}In{0.3} films, grown by interdiffusion of alternating Au and In layers, have been studied. The films were found to consist of a uniform solid solution of Au{0.9}In{0.1}, with excess In precipitated in the form of In-rich grains of various Au-In phases (with distinct atomic compositions), including intermetallic compounds. As the temperature was lowered, these individual grains became superconducting at a particular transition temperature (Tc), determined primarily by the atomic composition of the grain, before a fully superconducting stat…
A superconductor with broken time reversal and inversion symmetry may exhibit nonreciprocal charge transport, including a nonreciprocal critical current, also known as superconducting diode effect. We report an intrinsic superconducting diode effect in a polar strontium titanate film. Differential resistance measurements reveal a superconducting state whose depairing current is polarity dependent. There is, however, no measurable deviation from Ohmic behavior, implying that this state does not arise from a bulk magnetochiral anisotropy. In the entire measurement range, the only deviation from …
The superconducting state is formed by the condensation of a large number of Cooper pairs. The normal state electronic properties can give significant influence on the superconducting state. For usual type-II superconductors, the vortices are cylinder like with a round cross-section. For many two dimensional superconductors, such as Cuprates, 2H-NbSe$_2$ etc., albeit the in-plane anisotropy, the vortices generally have a round shape. In this paper we report results based on the scanning tunneling microscopy/spectroscopy measurements on a newly discovered superconductor Ta$_4$Pd$_3$Te$_{16}$. T…
An external magnetic field is needed to drive a nanowire in proximity to an s-wave superconductor into a topological regime which supports Majorana end states. However, a magnetic field generally suppresses the proximity superconducting gap induced on the nanowire. In recent experiments using InSb nanowires coupled to Al, the induced proximity gap vanishes at magnetic fields B~1T. This results in a small superconducting gap on the wire and a narrow topological regime which is proportional to the strength of the magnetic field. In this work, we show that by placing nanowires in proximity to rec…
The unique nonreciprocal responses of superconductors, which stem from the Cooper pairs' quantum condensation, have been attracting attention. Recently, theories of the second-order nonlinear response in noncentrosymmetric superconductors were formulated based on the Bogoliubov-de Gennes theory. In this paper, we study the mechanism and condition for second-order optical responses of time-reversal symmetric superconductors. The numerical results show the characteristic photocurrent and second harmonic generation in the superconducting state. However, the superconductivity-induced nonlinear opt…
Double-stage continuous-discontinuous superconducting phase transition in the Pauli paramagnetic limit of a 3D superconductor: the URu$%_{2}$Si$_{2}$ case
在重费米子化合物URu $_{2}$ Si $% _{2}$的混合超导（SC）态中观察到的de-Haas van-Alphen振荡的急剧抑制证实了在3D顺磁限制的超导体中由波动模糊的窄的双级SC相变的理论预测。二阶过渡到非均匀（FFLO）状态，然后通过一阶过渡到均匀的SC状态，通过使用非微扰的方法获得的预测的情况下，也被发现是一致的，最近的热导率测量上进行的这种材料。
Copper oxide superconductors have continually fascinated the communities of condensed matter physics and material sciences because they host the highest ambient-pressure superconducting transition temperature (Tc) and mysterious physics. Searching for the universal correlation between the superconducting state and its normal state or neighboring ground state is believed to be an effective way for finding clues to elucidate the underlying mechanism of the superconductivity. One of the common pictures for the copper oxide superconductors is that a well-behaved metallic phase will present after t…
A unique platform for investigating the correlation between the antiferromagnetic (AFM) and superconducting (SC) states in high temperature superconductors is created by the discovery of alkaline iron selenide superconductors which are composed of an AFM insulating phase and a SC phase separated spatially. Our previous studies showed that pressure can fully suppress the superconductivity of ambient-pressure superconducting phase (SC-I) and AFM order simultaneously, then induce another superconducting phase (SC-II) at higher pressure. Consequently, the connection between the two superconducting…
This paper reviews the highlights of a 4-years-long research project supported by the Japanese Government to explore new superconducting materials and relevant functional materials. The project found several tens of new superconductors by examining ~1000 materials, each of which was chosen by Japanese team member experts with a background in solid state chemistry. This review summarizes the major achievements of the project in newly found superconducting materials, and the wire and tape fabrication of iron-based superconductors. It is a unique feature of this review to incorporate a list of ~7…
Parameters dependent superconducting transition temperature in high temperature superconductors
School of Physics and Astronomy, Beijing Normal University（北京师范大学物理与天文学院）；Key Laboratory of Multiscale Spin Physics(Ministry of Education), Beijing Normal University（北京师范大学多尺度自旋物理教育部重点实验室）；New Cornerstone Science Laboratory, Department of Physics, School of Science, Westlake University（西湖大学理学院物理学系新基石科学实验室）；Institute for Theoretical Sciences, Westlake University（西湖大学理论科学研究院）；Key Laboratory for Quantum Materials of Zhejiang Province, School of Science, Westlake University（西湖大学理学院浙江省量子材料重点实验室）；Institute of Natural Sciences, Westlake Institute for Advanced Study（西湖高等研究院自然科学研究院）
The properties of the noncentrosymmetric superconductor ($α$-$\textit{Mn}$ structure) Nb$_{0.5}$Os$_{0.5}$ is investigated using resistivity, magnetization, specific heat, and muon spin relaxation and rotation ($μ$SR) measurements. These measurements suggest that Nb$_{0.5}$Os$_{0.5}$ is a weakly coupled ($λ_{e-ph}$ $\sim$ 0.53) type-II superconductor ($κ_{GL}$ $\approx$ 61) having a bulk superconducting transition temperature $T_c$ = 3.07 K. The specific heat data in the superconductive regime fits well with the single-gap BCS model indicating nodeless s-wave superconductivity in Nb$_{0.5}$Os$…
