Quantitative Evaluation of "Diracness" from the Quantum Oscillations in PbTe

The Dirac electron systems, which are characterized by their highly mobile carriers governed by the relativistic Dirac equation, have been one of the biggest topics in condensed matter physics. Still, it has not been clear how to identify them experimentally. Recent theoretical study proposed a quantitative prescription to experimentally evaluate "Diracness" of materials, which focuses on the ratio of Zeeman energy to cyclotron energy (ZC ratio). In this context, we focus on lead telluride (PbTe) to investigate physical properties tuning Diracness by external parameters. We investigated quantum oscillations in various physical quantities (resistivity, magnetization, sound velocity, and ultrasonic attenuation) in high magnetic fields, and determined ZC ratio of PbTe as 0.52. Further, we investigated the pressure dependence of the quantum oscillations, and obtained an indication that PbTe approaches the Dirac system by applying pressure.