论文标题
在存在Dirac Fermions存在下Néel量子临界点的稳定性
Stability of the Néel quantum critical point in the presence of Dirac fermions
论文作者
论文摘要
我们研究了由非线性$σ$模型（NL $σ$ m）描述的二维量子抗铁磁铁的Néel量子临界点的稳定性，在存在的近核耦合到$ n_f $ n_f $的味道的情况下。长波长阶参数波动会受到电子孔孔波动的降水。使用动量壳RG，我们证明了Landau阻尼在Néel量子临界点上微弱无关，尽管事实上相应的自我能源校正在IR限制中以二次梯度项为主导。在有序阶段，Landau阻尼在RG下增加，表明自旋波激发。尽管Kondo耦合非常相关，但足够强大的Landau抑制作用使Néel量子临界点准稳定为$ n_f \ ge 4 $，并且以$ n_f <4 $ $ n_f <4 $稳定。在后一种情况下，我们确定了一个新的多临界点，该点描述了NéelCritical和Kondo失控政权之间的过渡。在这个固定点上的对称性破裂导致dirac fermion频谱中的间隙打开。 Fermionic准粒子残基从无序阶段接近多临界点，从而导致非富特液体行为。
We investigate the stability of the Néel quantum critical point of two-dimensional quantum antiferromagnets, described by a non-linear $σ$ model (NL$σ$M), in the presence of a Kondo coupling to $N_f$ flavours of two-component Dirac fermion fields. The long-wavelength order parameter fluctuations are subject to Landau damping by electronic particle-hole fluctuations. Using momentum-shell 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 quasi-stable for $N_f\ge 4$ and thermodynamically stable for $N_f<4$. In the latter case, we identify a new multi-critical point which describes the transition between the Néel critical and Kondo run-away regimes. The symmetry breaking at this fixed point results in the opening of a gap in the Dirac fermion spectrum. Approaching the multi-critical point from the disordered phase, the fermionic quasiparticle residue vanishes, giving rise to non-Fermi-liquid behavior.
