Edge-dependent superconductivity in twisted bismuth bilayers.

Abstract

Twisted bilayers offer a platform for engineering new twistronic materials. Whereas standard studies focus on the enigma of twist-angles, epitomized by twisted graphene bilayers, functional devices face a fundamental concern: boundary heterogeneity. In this study, we address this by investigating the electronic and vibrational properties of twisted bismuth bilayer flakes. Twisted flakes exhibit interesting variations of these properties, away from the bulk, as we report herein using ab initio density functional theory, systematically mapping the evolution of the electronic density of states, the vibrational densities and possible superconductivity. Our work reveals a non-fortuitous consequence of structural disorder at the edges: an enhanced electronic density of states at the Fermi level. This enhancement reaches a maximum of 10 times that of crystalline bismuth. Given that the superconducting critical temperature is exponentially dependent on the electronic density of states, this structural variation suggests a mechanism for increasing T _c. We identify the edge disorder as a parameter in designing devices with enhanced properties. Our results provide a theoretical framework for interpreting new twistronic data, paving the way to search for disordered metastable structures that could lead to enhanced superconducting transition temperatures.