Pressure-tuned quantum criticality in the locally non-centrosymmetric superconductor CeRh$_2$As$_2$

TL;DR

This study investigates pressure-induced quantum criticality in CeRh$_2$As$_2$, revealing a quantum critical point where a phase transition vanishes and influences superconductivity, with non-Fermi-liquid behavior transitioning to Fermi-liquid as pressure increases.

Contribution

It demonstrates the suppression of the $T_{0}$ phase transition at a critical pressure, establishing a quantum critical point and linking quantum fluctuations to the superconducting pairing mechanism.

Findings

$T_{0}$ order vanishes at $P_{0}=0.5$ GPa, indicating a QCP.

Resistivity changes from linear to quadratic temperature dependence with pressure.

Superconducting $T_{c}$ exhibits a dome-shaped dependence around $P_{0}$.

Abstract

The unconventional superconductor CeRh$_2$As$_2$ (critical temperature $T_{\mathrm{c}}\approx0.4\,\mathrm{K}$) displays an exceptionally rare magnetic-field-induced transition between two distinct superconducting (SC) phases, proposed to be states of even and odd parity of the SC order parameter, which are enabled by a locally noncentrosymmetric structure. The superconductivity is preceded by a phase transition of unknown origin at $T_{0}\approx0.5\,\mathrm{K}$. Electronic low-temperature properties of CeRh$_2$As$_2$ show pronounced non-Fermi-liquid behavior, indicative of a proximity to a quantum critical point (QCP). The role of quantum fluctuations and normal state orders for the superconductivity in a system with staggered Rashba interaction is currently an open question, pertinent to explaining the occurrence of two-phase superconductivity. In this work, using measurements of resistivity and specific heat under hydrostatic pressure, we show that the $T_{0}$ order vanishes completely at a modest pressure of $P_{0}=0.5\,\mathrm{GPa}$, revealing a QCP. In line with the quantum criticality picture, the linear temperature dependence of the resistivity at $P_{0}$ evolves into a Fermi-liquid quadratic dependence as quantum critical fluctuations are suppressed by increasing pressure. Furthermore, the domelike behavior of $T_{\mathrm{c}}$ around $P_{0}$ implies that the fluctuations of the $T_{0}$ order are involved in the SC pairing mechanism.