M. Smidman

Superconductivity and spin-orbit coupling in non-centrosymmetric materials: A review

In non-centrosymmetric superconductors, where the crystal structure lacks a centre of inversion, parity is no longer a good quantum number and an electronic antisymmetric spin-orbit coupling (ASOC) is allowed to exist by symmetry. If this ASOC is sufficiently large, it has profound consequences on the superconducting state. For example, it generally leads to a superconducting pairing state which is a mixture of spin-singlet and spin-triplet components. The possibility of such novel pairing states, as well as the potential for observing a variety of unusual behaviors, led to intensive theoretical and experimental investigations. Here we review the experimental and theoretical results for superconducting systems lacking inversion symmetry. Firstly we give a conceptual overview of the key theoretical results. We then review the experimental properties of both strongly and weakly correlated bulk materials, as well as two dimensional systems. Here the focus is on evaluating the effects of ASOC on the superconducting properties and the extent to which there is evidence for singlet-triplet mixing. This is followed by a more detailed overview of theoretical aspects of non-centrosymmetric superconductivity. This includes the effects of the ASOC on the pairing symmetry and the superconducting magnetic response, magneto-electric effects, superconducting finite momentum pairing states, and the potential for non-centrosymmetric superconductors to display topological superconductivity.

Neutron scattering and muon spin relaxation measurements of the noncentrosymmetric antiferromagnet CeCoGe3

The magnetic states of the noncentrosymmetric pressure-induced superconductor CeCoGe3 have been studied with magnetic susceptibility, muon spin relaxation (?SR), single-crystal neutron diffraction, and inelastic neutron scattering (INS). CeCoGe3 exhibits three magnetic phase transitions at TN1=21,TN2=12, and TN3=8K. The presence of long-range magnetic order below TN1 is revealed by the observation of oscillations of the asymmetry in the ?SR spectra between 13 and 20 K and a sharp increase in the muon depolarization rate. Single-crystal neutron-diffraction measurements reveal magnetic Bragg peaks consistent with propagation vectors of k=(0,0,23) between TN1 and TN2,k=(0,0,58) between TN2 and TN3 and k=(0,0,12) below TN3. An increase in intensity of the (110) reflection between TN1 and TN3 also indicates a ferromagnetic component in these phases. These measurements are consistent with an equal moment two-up two-down magnetic structure below TN3 with a magnetic moment of 0.405(5)?B/Ce. Above TN2, the results are consistent with an equal moment two-up one-down structure with a moment of 0.360(6)?B/Ce. INS studies reveal two crystal-electric-field (CEF) excitations at ?19 and ?27meV. From an analysis with a CEF model, the wave functions of the J=52 multiplet are evaluated along with a prediction for the magnitude and direction of the ground-state magnetic moment. Our model correctly predicts that the moments order along the c axis, but the observed magnetic moment of 0.405(5)?B is reduced compared to the predicted moment of 1.0?B. This is ascribed to hybridization between the localized Ce3+ f electrons and the conduction band. This suggests that CeCoGe3 has a degree of hybridization between that of CeRhGe3 and the noncentrosymmetric superconductor CeRhSi3

Investigations of the superconducting states of noncentrosymmetric LaPdSi3 and LaPtSi3

The noncentrosymmetric superconductors LaPdSi3 and LaPtSi3 have been studied with magnetization, specific-heat, resistivity, and μSR measurements. These crystallize in the tetragonal BaNiSn3 structure and superconductivity is observed at Tc=2.65(5) K for LaPdSi3 and Tc=1.52(6) K for LaPtSi3. The results are consistent with both compounds being weakly coupled, fully gapped superconductors but μSR measurements reveal that LaPdSi3 is a bulk type-I superconductor while LaPtSi3 is a type-II material with a Ginzburg-Landau parameter of κ=2.49(4). This is further supported by specific-heat measurements, where the transition in an applied field is first order in LaPdSi3 but second order in LaPtSi3. The electronic specific heat in the superconducting state was analyzed using an isotropic s-wave model that gave Δ0/kBTc=1.757(4) for LaPdSi3 and 1.735(5) for LaPtSi3. The temperature dependence of the effective penetration depth [λeff(T)] of LaPtSi3 was extracted from μSR measurements and was fitted giving Δ0/kBTc=1.60(8) and λeff(0)=239(3) nm. A critical field of Bc(0) = 182.7 G was obtained for LaPdSi3 from μSR measurements, which is in good agreement with the calculated thermodynamic critical field.

Evidence for two distinct superconducting phases in EuBiS

We present a pressure study of the electrical resistivity, AC magnetic susceptibility and powder x-ray diffraction (XRD) of the newly discovered BiS

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F under pressure

-based superconductor EuBiS

Possible Weyl fermions in the magnetic Kondo system CeSb

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Two-Gap Superconductivity in LaNiGa2 with Nonunitary Triplet Pairing and Even Parity Gap Symmetry

F. At ambient pressure, EuBiS

Weak interband-coupling superconductivity in the filled skutterudite LaPt4Ge12

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Large magnetoresistance and Fermi surface topology of PrSb

F shows an anomaly in the resistivity at around