Abstract
In a superconductor that lacks inversion symmetry, the spatial part of the Cooper pair wave function has a reduced symmetry, allowing for the mixing of spin-singlet and spin-triplet Cooper pairing channels and thus providing a pathway to a non-trivial superconducting state. Materials with a non-centrosymmetric crystal structure and with strong spin–orbit coupling are a platform to realize these possibilities. Here, we report the synthesis and characterisation of high quality crystals of Sn4As3, with non-centrosymmetric unit cell (R3m). We have characterised the normal and superconducting states using a range of methods. Angle-resolved photoemission spectroscopy shows a multiband Fermi surface and the presence of two surface states, confirmed by density-functional theory calculations. Specific heat measurements reveal a superconducting critical temperature of Tc ∼ 1.14 K and an upper critical magnetic field of μ0Hc ≳ 7 mT, which are both confirmed by ultra-low temperature scanning tunneling microscopy and spectroscopy. Scanning tunneling spectroscopy shows a fully formed superconducting gap, consistent with conventional s-wave superconductivity.
Highlights
Identification of a spin-triplet superconductor would provide us with a potential solid state platform for topological quantum computations, a variant that is robust against decoherence—one of the main impediments to realization of larger scale quantum calculations
A possible triplet component is expected to manifest in a number of observables: the upper critical magnetic field will be much higher than for a singlet superconductor and the SC gap will exhibit a more complex structure than the hard gap predicted by the Bardeen–Cooper–Schrieffer (BCS) theory for a singlet SC
We report a detailed study of the properties of single crystal samples of Sn4As3, through thermodynamic and spectroscopic characterisation of both normal and SC states using angle-resolved photoemission spectroscopy (ARPES) and ultra-low temperature scanning tunneling microscopy and spectroscopy (STM/STS)
Summary
Identification of a spin-triplet superconductor would provide us with a potential solid state platform for topological quantum computations, a variant that is robust against decoherence—one of the main impediments to realization of larger scale quantum calculations. One would expect topologically protected bound states near defects and boundaries that could be detected in local measurements. Evidence for this mixing has been found in the non-centrosymmetric heavy fermion superconductor CePt3Si, where the strong SOC gives rise to an SC gap with line nodes [2]. If spin-singlet pairing interactions are dominant, the SC in the non-centrosymmetric material will follow the predictions by the BCS theory, as has been found in the case of BiPd [4], and it is independent of the SOC strength. In BiPd the breaking of inversion symmetry together with strong SOC leads to Dirac-cone surface states [5] with an intricate spin texture [6]
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