Nature of the quantum critical point as disclosed by extraordinary behavior of magnetotransport and the Lorentz number in the heavy-fermion metal YbRh2Si2

TL;DR

This paper investigates the quantum critical point in heavy-fermion metal YbRh2Si2, revealing non-Fermi-liquid behavior, resistivity jumps, and violations of the Wiedemann-Franz law, supporting a fermion-condensation phase transition model.

Contribution

It provides experimental evidence linking the QCP to a fermion-condensation phase transition and predicts observable jumps in resistivity and Hall resistivity at the QCP.

Findings

Resistivity and Hall resistivity exhibit jumps at the QCP.

Violation of the Wiedemann-Franz law observed near the QCP.

Multiple energy scales relate to quasiparticle effective mass scaling.

Abstract

Physicists are engaged in vigorous debate on the nature of the quantum critical points (QCP) governing the low-temperature properties of heavy-fermion (HF) metals. Recent experimental observations of the much-studied compound YbRh2Si2 in the regime of vanishing temperature incisively probe the nature of its magnetic-field-tuned QCP. The jumps revealed both in the residual resistivity rho_0 and the Hall resistivity R_H, along with violation of the Wiedemann-Franz law, provide vital clues to the origin of such non-Fermi-liquid behavior. The empirical facts point unambiguously to association of the observed QCP with a fermion-condensation phase transition. Based on this insight, the resistivities rho_0 and R_H are predicted to show jumps at the crossing of the QCP produced by application of a magnetic field, with attendant violation of the Wiedemann-Franz law. It is further demonstrated that experimentally identifiable multiple energy scales are related to the scaling behavior of the effective mass of the quasiparticles responsible for the low-temperature properties of such HF metals.