Two-dimensional superconductivity and magnetotransport from topological surface states in AuSn4 semimetal

Abstract

Topological materials such as Dirac or Weyl semimetals are new states of matter characterized by symmetry-protected surface states responsible for exotic low-temperature magnetotransport properties. Here, transport measurements on AuSn 4 single crystals, a topological nodal-line semimetal candidate, reveal the presence of two-dimensional superconductivity with a transition temperature T c~2 .40 K. The two-dimensional nature of superconductivity is verified by a Berezinsky-Kosterlitz-Thouless transition, Bose-metal phase, and vortex dynamics interpreted in terms of thermally-assisted flux motion in two dimensions. The normal-state magnetoconductivity at low temperatures is found to be well described by the weak-antilocalization transport formula, which has been commonly observed in topological materials, strongly supporting the scenario that normal-state magnetotransport in AuSn 4 is dominated by the surface electrons of topological Dirac-cone states. The entire results are summarized in a phase diagram in the temperature-magnetic field plane, which displays different regimes of transport. The combination of twodimensional superconductivity and surface-driven magnetotransport suggests the topological nature of superconductivity in AuSn 4 .

Superconductivity and band structure of layered AuSn$_4$

“…The superconducting transition (inset of Fig. 1(b)) provides T c = 2.35 K in agreement with previous reports [15,16].…”

“…In Fig. 1(b) we show the temperature dependence of the resistivity up to 300 K, from which we obtain a residual resistivity ratio of 122, twice the value found in a recent work [16]. We estimate a residual resistivity of ρ 0 ∼ 0.62 µΩ cm, which confirms the excellent quality of the samples.…”

“…1(b) and Ref. [16]) is of a few hundred Oe. This gives an intervortex distance well above 100 nm at the upper critical field, which is larger than the largest flat surfaces we could find.…”

“…A recent examination of the bulk and transport properties of single crystals of AuSn 4 provides a clear specific heat jump at the superconducting transition. The proposed magnetic field temperature phase diagram provides indications for weak antilocalization and two-dimensional superconductivity [16].…”

“…PtSn 4 and PdSn 4 are not superconducting, but AuSn 4 is superconducting with a critical temperature of T c = 2.35 K [15]. In spite of the different electron count (Pt and Pd are on group 10, whereas Au is on group 11 of the periodic table), it is of interest to ask whether AuSn 4 can show anomalous properties in the band structure and superconductivity at the same time [16,17]. A recent examination of the bulk and transport properties of single crystals of AuSn 4 provides a clear specific heat jump at the superconducting transition.…”