Chemical and structural stability of superconducting In5Bi3 driven by spin-orbit coupling

Relativistic effects play a prominent role in many electronic material properties such as the Rashba and Dresselhaus spin splitting in inversion asymmetric crystals, or the bulk band gap in topological insulators. By contrast, macroscopic material properties are typically not connected to relativistic phenomena. As an exception to this rule, we show that the macroscopic chemical and structural properties of superconducting In5Bi3 are driven by relativistic physics. In the non-relativistic limit In5Bi3 decomposes into elemental indium and bismuth, but the inclusion of relativistic spin-orbit coupling chemically stabilizes the In5Bi3 stoichiometry. Similarly, the structural stability of tetragonal In5Bi3 is driven by the spin-orbit interaction, which eliminates a phonon instability present in the non-relativistic limit. Low-temperature resistivity and heat capacity measurements show that In5Bi3 is a strong coupling superconductor, with a superconducting critical temperature of 4.2 K and a superconducting critical field of 0.3 T. The unconventional interplay between relativity with chemistry and structure, together with the presence of superconductivity, make In5Bi3 a versatile material that provides, for example, a simple model for the study of strong coupling superconductivity in quasiperiodic crystals.