Nonlocal Kondo effect and quantum critical phase in heavy-fermion metals
Jiangfan Wang, Yi‐feng Yang
Abstract
Heavy-fermion metals typically exhibit an unconventional quantum critical point or quantum critical phase at zero temperature due to the competition of the Kondo effect and magnetism. Previous theories were often based on certain local types of assumptions, and a fully consistent explanation of experiments has not been achieved. Here we develop an efficient algorithm for the Schwinger boson approach to explore the effect of spatial correlations on the Kondo lattice, and we introduce the concept of a nonlocal Kondo effect in the quantum critical region with deconfined spinons. We predict a global phase diagram containing a non-Fermi liquid quantum critical phase with a hidden holon Fermi surface and a partially enlarged electron Fermi surface for strong quantum fluctuations but a single quantum critical point for weak quantum fluctuations. This explains the unusual metallic spin liquid recently reported in the frustrated Kondo lattice CePdAl and resolves the Fermi volume puzzle in $\mathrm{Yb}{\mathrm{Rh}}_{2}{\mathrm{Si}}_{2}$. Our theory highlights the importance of nonlocal physics and provides a unified understanding of heavy-fermion quantum criticality.