Tuning low-energy scales in YbRh$_2$Si$_2$ by non-isoelectronic substitution and pressure

TL;DR

This study explores how non-isoelectronic substitution and pressure affect the low-energy scales and quantum critical behavior of YbRh₂Si₂, revealing that Fe substitution suppresses certain crossover features and challenges previous interpretations of Kondo breakdown.

Contribution

It provides new insights into the effects of chemical and hydrostatic pressure on the quantum critical properties of YbRh₂Si₂, especially regarding the suppression of the T* crossover by Fe substitution.

Findings

Fe substitution suppresses the T* crossover

Pressure and substitution effects disentangled

Fe substitution eliminates ferromagnetic fluctuations

Abstract

The heavy-fermion metal YbRh$_2$Si$_2$ realizes a field-induced quantum critical point with multiple vanishing energy scales $T_{\rm N}(B)$ and $T^\ast(B)$. We investigate their change with partial non-isoelectronic substitutions, chemical and hydrostatic pressure. Low-temperature electrical resistivity, specific heat and magnetic susceptibility of Yb(Rh$_{1-x}$T$_x$)$_2$Si$_2$ with T=Fe or Ni for $x\leq 0.1$, magnetic fields $B\leq 0.3$~T (applied perpendicular to the c-axis) and hydrostatic pressure $p\leq 1.5$~GPa are reported. The data allow to disentangle the combined influences of hydrostatic and chemical pressure, as well as non-isoelectronic substitution. In contrast to Ni- and Co-substitution, which enhance magnetic order, Fe-substitution acts oppositely. For $x=0.1$ it also completely suppresses the $T^\ast$ crossover and eliminates ferromagnetic fluctuations. The pressure, magnetic field and temperature dependences of $T^\ast$ are incompatible with its interpretation as Kondo breakdown signature.