Quantum phase transition in the heavy-fermion compound YbIr$_2$Si$_2$

TL;DR

This study explores the pressure-induced quantum phase transition in YbIr$_2$Si$_2$, revealing a first-order transition, Fermi-liquid behavior, and weak valence changes, contributing to understanding of heavy-fermion compounds under pressure.

Contribution

It provides the first detailed pressure-temperature phase diagram of YbIr$_2$Si$_2$, highlighting a ferromagnetic transition and valence fluctuations, expanding knowledge beyond the well-studied YbRh$_2$Si$_2$.

Findings

First-order ferromagnetic transition at ~8 GPa.

Fermi-liquid behavior consistent with NFFL model.

Weak valence transition indicated by KW ratio and resistivity changes.

Abstract

We investigate the pressure-temperature phase diagram of YbIr$_2$Si$_2$ by measuring the electrical resistivity $\rho(T)$. In contrast to the widely investigated YbRh$_2$Si$_2$, YbIr$_2$Si$_2$ is a paramagnetic metal below $p_c\simeq 8$ GPa. Interestingly, a first-order, presumably ferromagnetic, transition develops at $p_c$. Similar magnetic properties were also observed in YbRh$_2$Si$_2$ and YbCu$_2$Si$_2$ at sufficiently high pressures, suggesting a uniform picture for these Yb compounds. The ground state of YbIr$_2$Si$_2$ under pressure can be described by Landau Fermi-liquid (LFL) theory, in agreement with the nearly ferromagnetic Fermi-liquid (NFFL) model. Moreover, evidence of a weak valence transition, characterized by a jump of the Kadowaki-Woods (KW) ratio as well as an enhancement of the residual resistivity $\rho_0$ and of the quasiparticle-quasiparticle scattering cross section, is observed around 6 GPa.