Superconducting phase diagram and nontrivial band topology of structurally modulated Sn1−xSbx

Abstract

We report the discovery of superconductivity in binary alloy Sn1−xSbx with x in the range of 0.43 to 0.6, which possesses a modulated rhombohedral structure due to the incommensurate ordering of Sn and Sb layers along the c axis. The specific heat measurements indicate a weakly coupled, fully gapped superconducting state in this homogeneity range with a maximum bulk Tc of 1.58 K at x=0.46, though the electronic specific heat and Hall coefficients remain nearly x independent. The nonmonotonic dependence of the bulk Tc is discussed in relation to the effects of Sb-layer intercalation between the [Sn4Sb3] seven-layer lamellae that are the essential building blocks for superconductivity. On the other hand, a zero-resistivity transition is found to take place well above the bulk superconducting transition, and the corresponding Tc increases monotonically with x from 2.06 K to 3.29 K. This contrast, together with the uniform elements distribution revealed by energy dispersive x-ray mapping, implies that the resistive transition is due to the strain effect at the grain boundary rather than the compositional inhomogeneity. The first-principles calculations on the representative composition Sn4Sb3 (x=0.43) indicate that it is topologically nontrivial similar to Sb, but with different Z2 invariants (0;111). Our results not only identify a second superconducting region in the Sn-Sb phase diagram, but also provide a viable platform to study the interplay between structural modulation, nontrivial band topology, and superconductivity.

Source-reported materials — not catalogue approval

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