Crystallographic and superconducting properties of the fully gapped noncentrosymmetric 5d-electron superconductors CaMSi3

Abstract

We report crystallographic, specific heat, transport, and magnetic properties of the recently discovered noncentrosymmetric 5d -electron superconductors CaIrSi3 (Tc = 3.6 K) and CaPtSi3 (Tc = 2.3 K). The specific heat suggests that these superconductors are fully gapped. The upper critical fields are less than 1 T, consistent with limitation by conventional orbital depairing. High, non-Pauli-limited µ0Hc2 values, often taken as a key signature of novel noncentrosymmetric physics, are not observed in these materials because the high carrier masses required to suppress orbital depairing and reveal the violated Pauli limit are not present.

The effect of spin orbit interaction for superconductivity in the noncentrosymmetric superconductor CaIrSi3

“…The calculated equilibrium lattice parameters (a and c), the volume of primitive unit cell (V ), internal parameters (z Ir , z Si1 and z Si2 ), bulk modulus (B) and its pressure derivative (B ′ ) with and without SOI are presented in Tab. 1, together with previous theoretical [23,24] and experimental [18,21] results for comparison. As can be seen from this table, the effect of SOI on the structural properties of CaIrSi 3 is very small.…”

“…In particular, Smidman and co-workers [16] report magnetic susceptibility, specific-heat, and muon spin rotation/relaxation (µSR) measurements on LaPtSi 3 and LaPdSi 3 and conclude that LaPtSi 3 is a type-II superconductor with T c = 1.52 K, whereas LaPdSi 3 is a type-I superconductor with T c = 2.65 K. Furthermore, the synthesis of nine new noncentrosymmetric ternary silicide superconductors, including CaIrSi 3 (T c = 3.6 K), by arc melting has been reported [17]. Following this experimental work [17], Eguchi and co-workers [18,19] have shown that CaIrSi 3 is nonmagnetic, fully gapped superconductor based on studies with polycrystalline samples. Thus, in contrast to the cerium-based NCS, no magnetic order exists to possibly weaken or interfere with the superconducting state.…”

Probing the superconducting ground state of the noncentrosymmetric superconductorsCaTSi3(T= Ir, Pt) using muon-spin relaxation and rotation

“…After subtracting σ nm from σ to give σ sc as described above, λ can be calculated at each temperature, with a correction for the strong field dependence of the depolarization rates made using the B c2 (T ) data from Ref. [35] and Eq. 4.…”

“…CaIrSi 3 and CaPtSi 3 are NCS with superconducting transition temperatures of 3.6 and 2.3 K respectively and therefore do not require pressure to induce the superconducting state unlike their Ce analogues 35,36 . Specific heat data are in general agreement with these superconductors being fully gapped, however, CaIrSi 3 appears to show a deviation from a pure s-wave gap, which has been suggested as evidence for a multiband or anisotropic gap 35 . In the presence of Ir and Pt it is expected that spin-orbit coupling will be significant, strengthening the possibility that the mechanisms for superconductivity might not be entirely conventional in these materials.…”

Theoretical investigation of superconductivity in SrAuSi3 and SrAu2Si2

“…The majority of Ce materials are antiferromagnetic and become superconducting only under pressure. However, in materials such as BaPtSi 3 [17], LaRhSi 3 [18], CaPtSi 3 [19,20], CaIrSi 3 [19,20], LaPtSi 3 [21], and LaPdSi 3 [21], which also adopt the body-centered tetragonal BaNiSn 3 -type structure but do not show strong electronic correlations, superconductivity with the BCS characteristics has been discovered at ambient pressure.…”