Kondo destruction in heavy fermion quantum criticality and the photoemission spectrum of YbRh2Si2

• Quantum critical points (QCPs) in heavy fermion (HF) metals come in different types.
• Various HF metals show evidence for a Kondo destruction (KD) QCP.
• Thermodynamic and transport quantities show jumps of finite size at KD QCPs.
• With increasing temperature these jumps evolve into crossovers of grow- ing width.
• Detection of the Fermi surface jump requires measurements beyond the crossover region.

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 YbRh2Si2. 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*BT*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≳0.5K, YbRh2Si2 at zero magnetic field belongs to the quantum-critical fluctuation regime, where the single-particle spectral function has significant 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 experiments recently reported for YbRh2Si2 at T>1K are consistent with this expectation, and therefore support the association of the T*BT*B line with the physics of Kondo destruction.