Hu, Huanzhi; Lin, Jennifer; Uryszek, Mikolaj D; Krüger, Frank; (2023) Stability of the Néel quantum critical point in the presence of Dirac fermions. Physical Review B , 107 (8) , Article 085113. 10.1103/physrevb.107.085113.

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Abstract

We investigate the stability of the Néel quantum critical point of two-dimensional quantum antiferromagnets, described by a nonlinear σ model, in the presence of a Kondo coupling to Nf flavors of two-component Dirac fermion fields. The long-wavelength order parameter fluctuations are subject to Landau damping by electronic particle-hole fluctuations. Using the momentum-shell renormalization group (RG), we demonstrate that the Landau damping is weakly irrelevant at the Néel quantum critical point, despite the fact that the corresponding self-energy correction dominates over the quadratic gradient terms in the IR limit. In the ordered phase, the Landau damping increases under the RG, indicative of damped spin-wave excitations. Although the Kondo coupling is weakly relevant, sufficiently strong Landau damping renders the Néel quantum critical point quasistable for Nf 4 and thermodynamically stable for Nf < 4. In the latter case, we identify a multicritical point which describes the transition between the Néel critical and Kondo runaway regimes. The symmetry breaking at this fixed point results in the opening of a gap in the Dirac fermion spectrum. Approaching the multicritical point from the disordered phase, the fermionic quasiparticle residue vanishes, giving rise to non-Fermi-liquid behavior.

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