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

TL;DR

This paper critiques a recent study on YbRh₂Si₂, emphasizing the need for specific measurements to validate the Kondo destruction model and clarifying misinterpretations of existing data regarding quantum criticality.

Contribution

It clarifies the requirements for Fermi surface measurements and corrects misinterpretations of crossover data, reaffirming the validity of Kondo destruction in YbRh₂Si₂.

Findings

Schubert et al.'s data are insufficient to challenge Kondo destruction.

Friedemann et al.'s crossover width is linearly dependent on temperature.

Misinterpretations of data and neglect of error bars undermine Schubert et al.'s claims.

Abstract

In Ref. 1, Schubert et al. [Phys. Rev. Research 1, 032004 (2019)] reported measurements of the isothermal magnetoresistance of Fe- and Ni-substituted YbRh$_2$Si$_2$, based on which they raised questions about the Kondo destruction description for the magnetic field-induced quantum critical point (QCP) of pristine YbRh$_2$Si$_2$. Here we make three points. Firstly, as shown by studies on pristine YbRh$_2$Si$_2$ in Paschen et al. and Friedemann et al., isothermal crossed-field and single-field Hall effect measurements are necessary to ascertain the evolution of the Fermi surface across this QCP. Because Schubert et al. did not carry out such measurements, their results on Fe- and Ni-substituted YbRh$_2$Si$_2$ cannot be used to assess the validity of the Kondo destruction picture neither for substituted nor for pristine YbRh$_2$Si$_2$. Secondly, when referring to the data of Friedemann et al. on the isothermal crossover of YbRh$_2$Si$_2$, they did not recognize the implications of the crossover width, quantified by the full width at half maximum (FWHM), being linear in temperature, with zero offset, over about $1.5$ decades in temperature, from 30 mK to 1 K. Finally, in claiming deviations of Hall crossover FWHM data of Friedemann et al. from the above linear-in-$T$ dependence they neglected the error bars of these measurements and discarded some of the data points. The claims of Schubert et al. are thus not supported by data, neither previously published nor new (Ref. 1). As such they cannot invalidate the evidence that has been reported for Kondo destruction quantum criticality in YbRh$_2$Si$_2$.