Mechanism of strange metal state near a heavy fermion quantum critical point*

Unconventional metallic or strange metal (SM) behavior with non-Fermi liquid (NFL) properties, generic features of heavy fermion (HF) systems near quantum phase transitions, are yet to be understood microscopically. A paradigmatic example is the magnetic field-tuned quantum critical HF metal YbRh₂Si₂, revealing a possible SM state over a finite range of fields at low T when substituted with Ge. Above a critical field, the SM state gives way to a heavy Fermi liquid with Kondo correlation. The NFL behavior, suc as a linear-in-temperature (T) electrical resistivity and a logarithmic-in-T followed by a power-law singularity in the specific heat coefficient at low T, still lacks a definite understanding. We propose a quasi-2d fluctuating short-ranged resonating-valence-bond spin liquid competing with the Kondo correlation as the mechanism of the experimentally observed behavior. Applying a field-theoretical renormalization group analysis on an effective field theory beyond a large-N approach to an antiferromagnetic Kondo-Heisenberg model, we identify the critical point and explain well the SM behavior.