Quantum-critical phase from frustrated magnetism in a strongly correlated metal

Abstract

In Ref. 1, Schubert et al. [Phys. Rev. Research 1, 032004 (2019)] reported measurements of the isothermal magnetoresistance of Fe-and Ni-substituted YbRh2Si2, based on which they raised questions about the Kondo destruction description for the magnetic field-induced quantum critical point (QCP) of pristine YbRh2Si2. Here we make three points. Firstly, as shown by studies on pristine YbRh2Si2 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 YbRh2Si2 cannot be used to assess the validity of the Kondo destruction picture neither for substituted nor for pristine YbRh2Si2. Secondly, when referring to the data of Friedemann et al. on the isothermal crossover of YbRh2Si2, 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 YbRh2Si2.Quantum criticality is a topic of considerable interest for a variety of strongly correlated electron systems, with antiferromagnetic heavy fermion systems representing a prototype. From extensive experimental measurements across QCPs of several heavy fermion metals, a variety of properties are found 2-16 to be inconsistent with spin-density-wave quantum criticality [17][18][19] , which is based on Landau's framework of order-parameter fluctuations. Instead, they support Kondo destruction quantum criticality 20-22 , which goes beyond the Landau framework through a critical destruction of the static Kondo entanglement. In particular, across the magnetic field-induced QCP in YbRh 2 Si 2 , the linear-response Hall coefficient determined from a crossed-field Hall measurement 3,5 , along with single-field Hall effect 3,5 , magnetoresistance 3,5 , and thermodynamic properties 4 , provided evidence for an extra energy scale, T * , in the T -B plane. This energy scale goes to zero as the QCP is approached from the non-magnetic side. Isothermal magnetotransport and thermodynamic properties undergo a rapid crossover across the T * -line, which extrapolates to a jump in the T = 0 limit, across generations of YbRh 2 Si 2 samples. These properties are in contrast with the po-larization crossover scenario 1 .Recently, Schubert et al. 1 studied the magnetoresistance of Fe-and Ni-substituted YbRh 2 Si 2 . Primarily based on the isothermal behavior of the magnetoresistance in these dope...

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