Kondo Destruction in Heavy Fermion Quantum Criticality and the Photoemission Spectrum of YbRh$_2$Si$_2$

TL;DR

This paper analyzes quantum criticality in heavy fermion metals, especially YbRh₂Si₂, showing how Kondo destruction influences the Fermi surface and supports recent ARPES findings at finite temperatures.

Contribution

It provides a theoretical analysis linking the crossover behavior in YbRh₂Si₂ to Kondo destruction and quantum critical fluctuations, supporting recent experimental ARPES results.

Findings

YbRh₂Si₂ enters a quantum-critical fluctuation regime at T > 0.5 K.

Spectral weight is present at both small and large Fermi surfaces in this regime.

ARPES experiments at T > 1 K are consistent with Kondo destruction physics.

Abstract

Heavy fermion metals provide a prototype setting to study quantum criticality. Experimentally, quantum critical points have been identified and studied in a growing list of heavy fermion compounds. Theoretically, Kondo destruction has provided a means to characterize a class of unconventional quantum critical points that goes beyond the Landau framework of order-parameter fluctuations. Among the prominent evidence for such local quantum criticality have been measurements in YbRh$_2$Si$_2$. A rapid crossover is observed at finite temperatures in the isothermal field dependence of the Hall coefficient and other transport and thermodynamic quantities, which specifies a $T^*(B)$ line in the temperature ($T$)-magnetic field ($B$) phase diagram. Here, we discuss what happens when temperature is raised, by analyzing the ratio of the crossover width to the crossover position. With this ratio approaching unity at $T \gtrsim 0.5$ K, YbRh$_2$Si$_2$ at zero magnetic field belongs to the quantum-critical fluctuation regime, where the single-particle spectral function has significant spectral weight at both the small and large Fermi surfaces. This implies that, in this temperature range, any measurements sensitive to the Fermi surface will also see a significant spectral weight at the large Fermi surface. The angle-resolved photoemission spectroscopy (ARPES) experiments recently reported for YbRh$_2$Si$_2$ at $T>1$ K are consistent with this expectation, and therefore support the association of the $T^*(B)$ line with the physics of Kondo destruction.