顺磁自旋三重态超导体UTe$_2$因其奇异的超导特性（包括极高的上临界场和可能的手性超导态）而备受关注。近期，UTe$_2$的超洁净单晶已可获得，因此对这些晶体的测量对于阐明其本征超导性质至关重要。在此，我们报告了这些高质量单晶在低场下的热力学临界场$H_{\ m c}$、下临界场$H_{\ m c1}$和上临界场$H_{\ m c2}$。通过比较$H_{\ m c1}$和$H_{\ m c2}$的各向异性，我们发现磁场沿$b$轴和$c$轴时的实验$H_{\ m c1}$值出现异常增强，表现出不寻常的低温上翘。我们提出强Ising型铁磁涨落对涡旋线能量的影响，作为$H_{\ m c1}$各向异性增强的起源。
英文摘要：
The paramagnetic spin-triplet superconductor UTe$_2$ has attracted significant attention because of its exotic superconducting properties including an extremely high upper critical field and possible chiral superconducting states. Recently, ultraclean single crystals of UTe$_2$ have become available, and thus measurements on these crystals are crucial to elucidate the intrinsic superconducting properties. Here, we report the thermodynamic critical field $H_{\rm c}$, the lower critical field $H_{\rm c1}$, and the upper critical field $H_{\rm c2}$ at low fields of these high-quality single crystals. From the comparison of the anisotropies in $H_{\rm c1}$ and $H_{\rm c2}$, we find that the experimental $H_{\rm c1}$ values with the magnetic field along $b$- and $c$-axes are anomalously enhanced, showing unusual low-temperature upturns. We propose an effect of the strong Ising-like ferromagnetic fluctuations on the vortex line energy as the origin of the anisotropic enhancement of $H_{\rm c1}$.
Ferromagnetic spin valves offer the key building blocks to integrate giant- and tunneling-magnetoresistance effects into spintronics devices. Starting from a generalized Blonder-Tinkham-Klapwijk approach, we theoretically investigate the impact of interfacial Rashba and Dresselhaus spin-orbit couplings on the tunneling conductance, and thereby the magnetoresistance characteristics, of ferromagnet/superconductor/ferromagnet spin-valve junctions embedding thin superconducting spacers between the either parallel or antiparallel magnetized ferromagnets. We focus on the unique interplay between usu…
Anisotropic Neutron Spin Resonance in Superconducting BaFe$_{1.9}$Ni$_{0.1}$As$_2$
本文用极化非弹性中子散射证明了超导BaFe $_{1.9}$ Ni $_{0.1}$ As $_2$（$T_c=20$ K）中低于$T_c$的中子自旋共振是纯磁性的。我们的分析进一步揭示了7~meV附近的共振峰只出现在平面响应。这挑战了普遍的看法，即在pnictides的自旋共振是一个各向同性的三重激发态的单线态库珀对，因为我们的研究结果意味着，只有$S_{001}=\pm1$组件的三重态参与。
Fundamental symmetry breaking and relativistic spin-orbit coupling give rise to fascinating phenomena in quantum materials. Of particular interest are the interfaces between ferromagnets and common s-wave superconductors, where the emergent spin-orbit fields support elusive spin-triplet superconductivity, crucial for superconducting spintronics and topologically-protected Majorana bound states. Here, we report the observation of large magnetoresistances at the interface between a quasi-two-dimensional van der Waals ferromagnet Fe0.29TaS2 and a conventional s-wave superconductor NbN, which prov…
We study the electronic transport properties of a superconductor (S) with a mixed s+p-wave pairing attached to a ferromagnetic metal (F) and a normal electrode (N) in an SFN configuration. Using the quasiclassical Green's function method, we compute the differential conductance $σ$ of the junction and demonstrate its dependence on the direction of the exchange field relative to the direction of the d-vector of the pair potential. If the p-wave triplet dominates the pairing, the zero bias conductance depends on the relative direction between the triplet d-vector and the exchange field. In contr…
We present a theoretical investigation of anisotropic superconducting spin transport at a magnetic interface between a p-wave superconductor and a ferromagnetic insulator. Our formulation describes the ferromagnetic resonance modulations due to spin current generation depending on spin-triplet Cooper pair, including the frequency shift and enhanced Gilbert damping, in a unified manner. We find that the Cooper pair symmetry is detectable from the qualitative behavior of the ferromagnetic resonance modulation. Our theory paves the way toward anisotropic superconducting spintronics.
Clear Reduction in Spin Susceptibility and Superconducting Spin Rotation for $H \parallel a$ in the Early-Stage Sample of Spin-Triplet Superconductor UTe$_2$
Even-parity interorbital spin-triplet pairing emerges as an intriguing candidate in multiorbital superconductors with significant Hund's and spin-orbit coupling. Within such a state, the pairing is dominated by the intraband pseudospin-singlet component via the spin-orbit coupling, distinguishing it from a pure spin triplet and motivating the name, shadowed triplet. With atomic spin-orbit coupling, it was shown that this pairing exhibits an anisotropic $s$-wave character, while higher angular momentum pairing symmetries such as $d$- or $g$-wave have been proposed based on phenomenological anal…
Recent experiments in quantum critical heavy fermion metals have pushed to the fore the question about whether antiferromagnetic fluctuations can promote both spin-singlet and spin-triplet superconductivity. Here we address the issue through non-perturbative calculations in antiferromagnetically correlated Kondo systems. We identify Kondo-destruction quantum critical points in both the SU(2) symmetric and Ising-anisotropic cluster Bose-Fermi Anderson models. The spin-singlet pairing correlations are significantly enhanced near the quantum critical point in the SU(2) case; however, with adequat…
Materials with transition metals in triangular lattices are of great interest for their potential combination of strong correlation, exotic magnetism and electronic topology. Kagome nets are of particular importance since the discovery of geometrically frustrated magnetism and topological band structures in crystals like Herbertsmithite and Fe3Sn2, respectively. KV3Sb5 was discovered to be a layered topological metal with a Kagome net of vanadium. Here, we fabricated Josephson Junctions (JJ) of K1-xV3Sb5 and induced superconductivity over long junction lengths. Through magnetoresistance and cu…
To investigate spin susceptibility in a superconducting (SC) state, we measured the $^{125}$Te-nuclear magnetic resonance (NMR) Knight shifts at magnetic fields ($H$) up to 6.5 T along the $b$ and $c$ axes of single-crystal UTe$_2$, a promising candidate for a spin-triplet superconductor. In the SC state, the Knight shifts along the $b$ and $c$ axes ($K_b$ and $K_c$, respectively) decreased slightly and the decrease in $K_b$ was almost constant up to 6.5 T. The reduction in $K_c$ decreased with increasing $H$, and $K_c$ was unchanged through the SC transition temperature at 5.5 T, excluding th…
Shortly after the discovery of superconductivity in Sr$_2$RuO$_4$, spin-triplet pairing was proposed and further corroborated by a constant Knight shift ($K$) across the transition temperature (T$_c$). However, a recent experiment observed a drop in $K$ at T$_c$ which becomes larger under uniaxial strain, ruling out several spin-triplet scenarios. Here we show that inter-orbital spin-triplet pairing features a d-vector that rotates when uniaxial strain is applied, leading to a larger drop in the spin polarization perpendicular to the strain direction, distinct from spin-singlet pairing. We pro…
Anisotropic fully-gapped superconductivity in quasi-one-dimensional Li$_{0.9}$Mo$_6$O$_{17}$
H. H. Wills Physics Laboratory, University of Bristol（布里斯托大学 H.H. 威尔斯物理实验室）；Department of Chemistry and Chemical Biology, Rutgers University（罗格斯大学化学与化学生物学系）；School of Mathematics and Physics, Queen’s University Belfast（贝尔法斯特女王大学数学与物理学院）；Institute of Fundamental Technological Research, Polish Academy of Sciences（波兰科学院基础技术研究所学）；High Field Magnet Laboratory (HFML-FELIX) and Institute for Molecules and Materials, Radboud University（拉得堡大学分子与材料研究所及高场磁实验室（HFML-FELIX））
Electronic Origin of Ferromagnetic Excitations in the Candidate Spin-Triplet Superconductor CeSb2
Shanghai Research Center for Quantum Sciences（上海量子科学研究中心）；Fudan University（复旦大学）；Chinese Academy of Sciences（中国科学院）；University of Science and Technology of China（中国科学技术大学）
Electron-Hole Scattering Dichotomy and Anisotropic Warping in Quasi-Two-Dimensional Fermi Surfaces of UTe2
Advanced Science Research Center, Japan Atomic Energy Agency（日本原子力机构先进科学研究中心）；Faculty of Engineering, Niigata University（新潟大学工学部）；Institute of Solid State and Materials Physics, Dresden University of Technology（德累斯顿工业大学固体与材料物理研究所）；Helmholtz-Zentrum Dresden-Rossendorf（亥姆霍兹德累斯顿-罗斯多夫中心）；Institute for Solid State Physics (ISSP), University of Tokyo（东京大学固体物理学研究所）；Institute for Materials Research, Tohoku University（东北大学物质材料研究所学）；Max Planck Institute for Chemical Physics of Solids（马克斯·普朗克固体化学物理学研究所）；Department of Physics, Graduate School of Science, Kyoto University（京都大学理学研究科物理学系）
We report the magnetic susceptibility and the magnetization under pressures up to 1.7GPa above the critical pressure, Pc ~ 1.5GPa, for H // a, b, c-axes in the novel spin triplet superconductor UTe2. The anisotropic magnetic susceptibility at low pressure with the easy magnetization a-axis changes to the quasi-isotropic behavior at high pressure, revealing a rapid suppression of the susceptibility for a-axis, and a gradual increase of the susceptibility for the b-axis. At 1.7GPa above Pc, magnetic anomalies are detected at T_MO ~ 3K and T_WMO ~ 10K. The former anomaly corresponds to long-range…
