Edge-Dependent Superconductivity in Twisted Bismuth Bilayers

Twisted bilayers offer a compelling and, at times, confounding platform for the engineering of new twistronic materials. Whereas standard studies almost exclusively focus on the explicit enigma that is presented by twist-angles, perhaps better epitomized by the related phenomena that have been observed in twisted bilayer graphene, functional devices necessarily face a fundamental concern: boundary heterogeneity in their structures. In this study, we address this concern by strictly investigating the electronic properties of twisted bismuth bilayers at the flake's edges and the vibrational properties of the flake. Twisted flakes exhibit continuous variations of these properties, away from the bulk, as we herein report using ab initio density functional theory, by systematically mapping the drastic evolution of band topology, electronic density of states, and possible superconductivity. Our work reveals a dramatic, non-fortuitous consequence of the structural disorder at the edges of the flakes: an enhanced electronic density of states at the Fermi level. This enhancement reaches a maximum of 10 times that of perfect-crystalline bismuth. Given that the superconducting critical temperature, Tc, is exponentially dependent on the electronic density of states at the Fermi level, this substantial structural variation immediately suggests a powerful mechanism for vastly increasing Tc. We also identify the twist-angle as a new critical parameter in designing novel engineering devices with topologically enhanced properties. Our results provide a necessary theoretical framework for interpreting new data for the upcoming generation of twistronic heterogeneous materials, and pave the way to search for atomic disordered metastable structures that could lead to enhanced superconducting transition temperatures.