We have studied the electronic properties of ScS, a transition-metal monochalcogenide with rocksalt crystal structure, using magnetization, specific heat, transport, and muon spin rotation/relaxation ($μ$SR) measurements. All measurements confirm the bulk superconducting in ScS with a transition temperature of $T_{C}$ = 5.1(5) K. Specific heat together with transverse-field $μ$SR measurements indicate a full gap, while our zero-field $μ$SR study reveals the presence of spontaneous static or quasi-static magnetic fields emerging when entering the superconducting state. We discuss various possible microscopic origins of the observed time-reversal-symmetry breaking. As none of them can be readily reconciled with a conventional pairing mechanism, this introduces ScS as a novel candidate material for unconventional superconductivity.
Topological superconductors (SCs) are novel phases of matter with nontrivial bulk topology. They host at their boundaries and vortex cores zero-energy Majorana bound states, potentially useful in fault-tolerant quantum computation. Chiral SCs are particular examples of topological SCs with finite angular momentum Cooper pairs circulating around a unique chiral axis, thus spontaneously breaking time-reversal symmetry (TRS). They are rather scarce and usually feature triplet pairing: best studied examples in bulk materials are UPt3 and Sr2RuO4 proposed to be f-wave and p-wave SCs respectively, a…
Fermi surface effect on spontaneous breaking of time-reversal symmetry in unconventional superconducting films
我们提出了一种有助于稳定具有破缺时间反转对称性的超导态的机制，该机制被预测在d波超导膜中实现[A。B. Vorontsov，Phys. Rev. Lett. 102，177001（2009）]。在此超导相，时间反演对称性破缺伴随着沿膜表面的平移对称性的自发破缺。我们研究如何正常超导相边界的厚度-温度相图中的薄膜被修改取决于费米面形状。特别地，当费米面满足嵌套条件时，发现非均匀超导相基本上延伸到相图中的较小厚度区域。我们证明了这种费米表面效应使用正方形晶格紧束缚模型。
Elemental rhenium exhibiting type-II superconductivity has been previously reported to break time-reversal symmetry in the superconducting state. We have investigated an arc-melted sample of rhenium exhibiting type-I superconductivity. Low temperature zero-field muon-spin relaxation measurements indicate that time-reversal symmetry is preserved in the superconducting state. Muon diffusion is observed, which is due to quantum mechanical tunneling between interstitial sites. The normal state behavior is characterized by the conduction electrons screening the muons and thermal broadening, and is …
Evidence for broken time-reversal symmetry in the superconducting phase of URu$_2$Si$_2$
最近的实验和理论兴趣的超导相的重费米子材料URu $_2$ Si $_2$导致了一些建议，其中超导序参量打破时间反演对称性（TRS）。在这项研究中，我们测量了极性克尔效应（PKE）作为温度的函数的几个高品质的单晶URu $_2$ Si $_2$。我们发现一个发病的PKE低于超导转变，这是符合TRS打破序参量。这种效应似乎是独立的额外的，可能是外在的，PKE以上的隐藏阶跃在$T_{HO}=17.5$ K产生的，并包含以下的结构$T_c$暗示额外的物理在超导状态。
Bulk evidence for a time reversal symmetry broken superconducting state in URu2Si2
URu $_2$ Si $_2$被认为是一种手征\emph{d}波超导体，其库珀对波函数具有$k_z (k_x \pm ik_y)$时间反演对称破缺轨道分量，其中包含节点和节点线\cite{kasahara, kasahara2}。为了研究这种非常规状态的磁响应，通过大量的，热力学探针，我们测量了磁转矩$τ$在非常高的质量，良好的特性URu $_2$ Si $_2$单晶\cite{altarawneh,altarawneh2}在高磁场$H$和在非常低的温度$T$。URu $_2$ Si $_2$的磁化强度$M(H) \propto τ(H) /H$，在其超导状态下，并且对于从\emph{ab}平面的$15^{\circ}$内的角度，揭示了接近$H_{c2}$的$H$的符号的变化：从由涡旋的钉扎主导的明显的抗磁性响应到具有较小但“类顺磁性”滞后响应的状态，这意味着它与超导态有内在的联系。我们认为，这种异常的，角度依赖的行为是一个时间反转对称破缺超导状态的证据在URu $_2$ Si $_2$，虽然不一定是$k_z (k_x \pm ik_y)$状态。
We propose a superconducting instability where microscopic supercurrent loops form spontaneously within a unit cell at the superconducting transition temperature with only uniform, onsite and intra-orbital singlet pairing. As a result of the circulating currents time-reversal symmetry is spontaneously broken in the superconducting state. Using Ginzburg-Landau theory, we describe in detail how these currents emerge in a toy model. We discuss the crystallographic symmetry requirements to realize such a state and show that they are met by the Re6X (X=Zr, Hf, Ti) family of time-reversal symmetry b…
Direct visualization of sign reversal s^+- superconducting gaps in FeTe0.55Se0.45
在许多非常规超导体中，电子对是由排斥相互作用驱动的，这导致沿费米面（FS）或它们之间的超导带隙的符号反转。然而，测量这种符号变化并不容易和直接。众所周知，在具有符号反转带隙的超导体中，非磁性杂质可以破坏库珀对，导致超导态中的准粒子态密度。这些准粒子的驻波将相互干涉，导致携带相位信息的准粒子干涉（QPI）图案，该图案还反映了超导能隙结构。基于最近提出的缺陷束缚态QPI技术，我们探讨了该技术对典型铁基超导体FeTe $_{0.55}$ Se $_{0.45}$的适用性，该超导体的电子袋和空穴袋由波矢q_2=（0，π）连接，带隙值大致相等.研究发现，在负能量侧，当能量略低于能隙值时，相位参考量|g（q，-E）|\cos（θ_{q，+E}-θ_{q，-E}）随散射矢量q_2的增大而变负，振幅大大增强，而对应于电子-电子袋间散射的振幅（即q_3=（π，π））保持为正。这与s^+-配对能隙的理论预期非常一致，因此可以作为符号反转能隙的直接可视化。费米面结构和s^+配对能隙的理论计算也支持这一实验观察。
Broken time-reversal symmetry in superconducting Pr$_{1-x}$La$_{x}$Pt$_{4}$Ge$_{12}$
用比热、零场μ子自旋弛豫（$μ$ SR）和超导临界场测量方法系统地研究了填充方钴矿合金系列Pr $_{1-x}$ La $_{x}$ Pt $_{4}$ Ge $_{12}$的超导态。一个额外的不均匀的局部磁场，指示破缺的时间反转对称性（TRS），观察到在超导态的合金。对于$x \lesssim 0.5$，在明显低于超导转变温度$T_c$的温度$T_m$以下，断裂TRS相开始。对于$x \gtrsim 0.5$ $T_m \approx T_c$。局部场强随着$x \to 1$而减小，其中LaPt $_{4}$ Ge $_{12}$的特征在于常规配对。低临界场$H_{c1}(T)$的PrPt $_{4}$ Ge $_{12}$显示低于$T_q \sim T_m$的第二个二次温度区域的开始。上临界场$H_{c2}(T)$的测量表明多带超导性，和点间隙节点是一致的比热数据。在Pr $_{1-x}$ La $_{x}$ Pt $_{4}$ Ge $_{12}$中，在$T_c$处只观察到一个比热不连续，而在Pr Os $_{4}$ Sb $_{12}$中则观察到低于$T_c$的第二次跳跃。这些结果表明，超导电性的PrPt $_{4}$ Ge $_{12}$的特点是由一个复杂的序参量。
Time-Reversal Symmetry Breaking Superconducting State and Collective Modes in Kagome Superconductors
Capital Normal University（首都师范大学）；Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences（中国科学院大学理论科学研究所）；Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所北京凝聚态物理国家研究中心）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）；Institute of Theoretical Physics, Chinese Academy of Sciences（中国科学院理论物理研究所）
It has been shown [1] that many seemingly contradictory experimental findings concerning the superconducting state in Sr$_2$RuO$_4$ can be accounted for as resulting from the existence of an assumed tetra-critical point at near ambient pressure at which $d_{x^2-y^2}$ and $g_{xy(x^2-y^2)}$ superconducting states are degenerate. We perform both a Landau-Ginzburg and a microscopic mean-field analysis of the effect of spatially varying strain on such a state. In the presence of finite $xy$ shear strain, the superconducting state consists of two possible symmetry-related time-reversal symmetry (TRS…
Three-dimensional line-nodal superconductors exhibit nontrivial topology, which is protected by the time-reversal symmetry. Here we investigate four types of short-range interaction between the gapless line-nodal fermionic quasiparticles by carrying renormalization group analysis. We find that such interactions can induce the dynamical breaking of time-reversal symmetry, which alters the topology and might lead to six possible distinct superconducting states, distinguished by the group representations. After computing the susceptibilities for all the possible phase-transition instabilities, we…
We report a $μ$SR investigation of a non-centrosymmetric superconductor (LaNiC$_2$) in single crystal form. Compared to previous $μ$SR studies of non-centrosymmetric superconducting polycrystalline and powder samples, the unambiguous orientation of single crystals enables a simultaneous determination of the absolute value of the magnetic penetration depth and the vortex core size from measurements that probe the magnetic field distribution in the vortex state. The magnetic field dependence of these quantities unambiguously demonstrates the presence of two nodeless superconducting energy gaps. …
Infrared study of the spin reorientation transition and its reversal in the superconducting state in underdoped Ba$ _{1-x} $K$ _{x} $Fe$ _{2} $As$ _{2} $
用红外光谱研究了欠掺杂Ba $ _{1-x} $ K $ _{x} $ Fe $ _{2} $ As $ _{2} $超导态中从正交反铁磁（o-AF）到四元反铁磁（t-AF）的自旋重取向转变以及o-AF相的再进入。与预测的从单-$\mathbf{Q}$到双-$\mathbf{Q}$ AF结构的转变一致，我们发现在t-AF相中产生了明显的自旋密度波（SDW）。这种SDW的对破缺峰比o-AF态的对破缺峰获得了更多的低能谱权，这表明它与超导性的竞争更强。我们还观察到额外的声子模式，在t-AF阶段，这可能是由双$\mathbf{Q}$磁结构与两个Fe亚晶格表现出不同幅度的磁矩诱导的布里渊区折叠。
Sign reversal superconducting gaps revealed by phase referenced quasi-particle interference of impurity induced bound states in (Li$_{1-x}$Fe$_x$)OHFe$_{1-y}$Zn$_y$Se
通过测量Fe位上杂质附近微分电导的空间分布，获得了只有电子费米面的（Li $_{1-x}$ Fe $_x$）OHFe $_{1-y}$ Zn $_y$ Se超导体的准粒子干涉（QPI）花样.通过对这些图形进行傅里叶变换，我们研究了由折叠或杂化形成的两圈电子袋之间的散射特性。我们使用最近的理论方法[arXiv：1710.09089]，这是专门设计的杂质诱导的束缚态处理的数据。结果表明，两个电子袋上的超导能隙符号相反，这可以用相位参考QPI技术直接观察到，表明库珀对是由排斥相互作用引起的.我们的结果进一步表明，该方法也适用于多杂质的测量数据，这为非常规超导体的能隙函数的检测提供了一种简单可行的方法。
The topologically non-trivial band structure of A15 compounds has drawn attention owing to the possible realization of topological superconductivity. Here, we report a microscopic investigation of the superconducting ground state in A15 compound Ti$_{3}$X (X = Ir, Sb) by muon spectroscopy measurements. Zero field muon measurements have shown that time-reversal symmetry is preserved in these materials. Furthermore, specific heat and a transverse field muon spectroscopy measurement rule out any possibility to have a nodal or anisotropic superconducting gap, revealing a conventional s-wave nature…
Thermoelectric Signatures of Time-Reversal Symmetry Breaking States in Multiband Superconductors
我们发现，超导体与破缺的时间反演对称性有非常具体的磁和电响应不均匀加热。这种超导体的局部加热感应出具有对畴壁的存在和超导态的晶体各向异性敏感的轮廓的磁场。非稳态加热过程产生电场和不同带中的电荷不平衡。这些效应可以被测量并用于区分候选材料如Ba $_{1-x}$ K $_x$ Fe $_2$ As $_2$中的$s+is$和$s+id$超导态。
First-Order Topological FFLO Transition and Superconducting Diode Sign Reversal in Altermagnetic Nanowires
School of Sciences, Great Bay University（大湾大学理学院）；Department of Physics, The University of Hong Kong（香港大学物理系）；Hefei National Laboratory（合肥国家实验室）；School of Emerging Technology, University of Science and Technology of China（中国科学技术大学新兴技术学院）
研究交变磁纳米线中拓扑 FFLO 态，发现与零净磁化 d 波交变磁体接近的自旋轨道耦合纳米线，通过一阶相变实现该态，伴有超导二极管效应，金兹堡 - 朗道理论解释机制，提供无场途径并确定输运指纹。
There is considerable evidence that the superconducting state of Sr$_2$RuO$_4$ breaks time reversal symmetry. In the experiments showing time reversal symmetry breaking its onset temperature, $T_\text{TRSB}$, is generally found to match the critical temperature, $T_\text{c}$, within resolution. In combination with evidence for even parity, this result has led to consideration of a $d_{xz} \pm id_{yz}$ order parameter. The degeneracy of the two components of this order parameter is protected by symmetry, yielding $T_\text{TRSB} = T_\text{c}$, but it has a hard-to-explain horizontal line node at…
