Temperature-driven massless Kane fermions in HgCdTe crystals: verification of universal velocity and rest-mass description

TL;DR

This study uses magneto-spectroscopy to verify that Kane fermions in HgCdTe exhibit universal velocity and a sign-changing rest-mass across a topological phase transition, confirming their pseudo-relativistic behavior.

Contribution

It provides experimental evidence that the velocity of Kane fermions remains constant while their rest-mass changes sign at the phase transition, validating a universal relativistic description.

Findings

Rest-mass of Kane fermions changes sign at critical temperature.

Velocity of Kane fermions remains constant across the transition.

Universal relation Eg = 2mc^2 with constant c is confirmed.

Abstract

It has recently been shown that the electronic states in bulk gapless HgCdTe offer another realization of pseudo-relativistic three-dimensional particles in a condensed matter system. These single valley relativistic states, referred to as massless Kane fermions, cannot be described by any other well-known relativistic massless particles. Furthermore, the HgCdTe band structure can be continuously tailored by modifying either the cadmium content or temperature. At the critical concentration or temperature, the bandgap, Eg, collapses as the system undergoes a semimetal-to-semiconductor topological phase transition between the inverted and normal alignments. Here, using far-infrared magneto-spectroscopy we explore the continuous evolution of band structure of bulk HgCdTe as temperature is tuned across the topological phase transition. We demonstrate that the rest-mass of the Dirac-like Kane fermions, m changes sign at the critical temperature, while their velocity, c remains constant. The relation Eg = 2mc2 with the universal value of c = (1.07 +- 0.05)10x6 m/s remains valid in a broad range of temperatures and Cd concentrations, indicating a striking universality of the pseudo-relativistic description of the Dirac-like Kane fermions in HgCdTe.