Separation of energy scales in undoped YbRh$_2$Si$_2$ under hydrostatic pressure

TL;DR

This study investigates the phase diagram of YbRh$_2$Si$_2$ under pressure, revealing that the energy scale related to Kondo breakdown remains unchanged while the antiferromagnetic critical field increases, crossing the energy scale at higher pressure.

Contribution

It demonstrates that the energy scale $T^ullet(H)$ remains unaffected by pressure, while the antiferromagnetic critical field increases, showing the robustness of the Kondo breakdown scale against pressure.

Findings

The energy scale $T^ullet(H)$ is pressure-independent.

The antiferromagnetic critical field increases with pressure.

The crossing of $T_N(H)$ and $T^ullet(H)$ occurs at higher pressure.

Abstract

The temperature ($T$)-magnetic field ($H$) phase diagram of YbRh$_2$Si$_2$ in the vicinity of its quantum critical point is investigated by low-$T$ magnetization measurements. Our analysis reveals that the energy scale $T^\star(H)$, previously related to the Kondo breakdown and terminating at 0.06 T for $T\to 0$, remains unchanged under pressure, whereas the antiferromagnetic critical field increases from 0.06 T ($p=0$) to 0.29 T ($p=1.28$ GPa), resulting in a crossing of $T_N(H)$ and $T^\star(H)$. Our results are very similar to those on Yb(Rh$_{1-x}$Co$_x$)$_2$Si$_2$, proving that the Co-induced disorder can not be the reason for the detachment of both scales under chemical pressure.