Strain-tuning of transport gaps and semiconductor-to-conductor phase transition in twinned graphene

We show, through the use of the Landauer-Buttiker (LB) formalism and a tight-binding (TB) model, that the transport gap of twinned graphene can be tuned through the application of a uniaxial strain in the direction normal to the twin band. Remarkably, we find that the transport gap E-gap bears a square-root dependence on the control parameter epsilon(x) - epsilon(c), where epsilon(x) is the applied uniaxial strain and epsilon(c) similar to 19% is a critical strain. We interpret this dependence as evidence of criticality underlying a continuous phase transition, with epsilon(x) - epsilon(c) playing the role of control parameter and the transport gap E-gap playing the role of order parameter. For is an element of(x) < is an element of(c), the transport gap is non-zero and the material is semiconductor, whereas for epsilon(x) > epsilon(c) the transport gap closes to zero and the material becomes conductor, which evinces a semiconductor-to-conductor phase transition. The computed critical exponent of 1/2 places the transition in the meanfield universality class, which enables far-reaching analogies with other systems in the same class. (C) 2022 The Author(s). Published by Elsevier Ltd on behalf of Acta Materialia Inc.