Anomalous Phase-Coherence Scaling in a Quantum-Critical Dirac Semimetal

Abstract

We have investigated the weak antilocalization (WAL) in the pressurized Dirac semimetal $\alpha$-(BEDT-TTF)${}_2$I${}_3$ across a correlation-driven quantum phase transition to a charge-ordered insulating state and evaluated the phase coherence length $L_{\varphi }$ and its temperature scaling under various pressures from the low-temperature magnetoconductivity. In the high-pressure regime, the system exhibits the conventional two-dimensional dephasing behavior ($L_{\varphi }\propto T^{-p}$ with $p\approx 1/2$), characteristic of electron-electron scattering in diffusive conductors. As the pressure approaches the critical pressure ($P_c\sim 1.2$ GPa), the temperature exponent is suppressed to $p\sim 0.3$, while $L_{\varphi }$ remains large ($700\text{-}800$ nm at 0.5 K). This anomalous scaling suggests nontrivial inelastic scattering associated with Dirac electrons near the quantum critical point. The persistence of WAL across the transition supports a gapless or nearly gapless quantum phase transition.

12 pages, 4 figures

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