Unconventional and conventional quantum criticalities in CeRh$_{0.58}$Ir$_{0.42}$In$_5$

TL;DR

This study reveals two distinct quantum critical points in CeRh$_{0.58}$Ir$_{0.42}$In$_5$, demonstrating both unconventional and conventional critical behaviors driven by a single tuning parameter, with implications for understanding quantum phase transitions.

Contribution

It provides experimental evidence of two different quantum criticalities within a single heavy-fermion compound, supporting theoretical models of multiple critical points.

Findings

Discontinuous thermopower sign change at $p_{c1}$ indicating an unconventional QCP.

Abrupt Fermi-surface reconstruction at $p_{c1}$.

Smooth Fermi surface evolution at $p_{c2}$ indicating a conventional QCP.

Abstract

An appropriate description of the state of matter that appears as a second order phase transition is tuned toward zero temperature, {\it viz.} quantum-critical point (QCP), poses fundamental and still not fully answered questions. Experiments are needed both to test basic conclusions and to guide further refinement of theoretical models. Here, charge and entropy transport properties as well as AC specific heat of the heavy-fermion compound CeRh$_{0.58}$Ir$_{0.42}$In$_5$, measured as a function of pressure, reveal two qualitatively different QCPs in a {\it single} material driven by a {\it single} non-symmetry-breaking tuning parameter. A discontinuous sign-change jump in thermopower suggests an unconventional QCP at $p_{c1}$ accompanied by an abrupt Fermi-surface reconstruction that is followed by a conventional spin-density-wave critical point at $p_{c2}$ across which the Fermi surface evolves smoothly to a heavy Fermi-liquid state. These experiments are consistent with some theoretical predictions, including the sequence of critical points and the temperature dependence of the thermopower in their vicinity.