Department of Physics and Astronomy, University of Ghent, Krijgslaan 281, 9000 Gent, Belgium.
Institut de Physique Théorique Philippe Meyer, École Normale Supérieure, PSL University, Sorbonne Universités, CNRS, 75005 Paris, France.
Phys Rev Lett. 2019 Nov 1;123(18):186601. doi: 10.1103/PhysRevLett.123.186601.
The problem of characterizing low-temperature spin dynamics in antiferromagnetic spin chains has so far remained elusive. Here we reinvestigate it by focusing on isotropic antiferromagnetic chains whose low-energy effective field theory is governed by the quantum nonlinear sigma model. Employing an exact nonperturbative theoretical approach, we analyze the low-temperature behavior in the vicinity of nonmagnetized states and obtain exact expressions for the spin diffusion constant and the NMR relaxation rate, which we compare with previous theoretical results in the literature. Surprisingly, in SU(2)-invariant spin chains in the vicinity of half filling we find a crossover from the semiclassical regime to a strongly interacting quantum regime characterized by zero spin Drude weight and diverging spin conductivity, indicating superdiffusive spin dynamics. The dynamical exponent of spin fluctuations is argued to belong to the Kardar-Parisi-Zhang universality class. Furthermore, by employing numerical time-dependent density matrix renormalization group simulations, we find robust evidence that the anomalous spin transport persists also at high temperatures, irrespective of the spectral gap and integrability of the model.
目前，描述反铁磁自旋链低温自旋动力学的问题仍然难以捉摸。在这里，我们通过关注各向同性反铁磁链来重新研究这个问题，这些链的低能有效场理论由量子非线性西格玛模型控制。我们采用精确的非微扰理论方法，分析了非磁化态附近的低温行为，并获得了自旋扩散常数和 NMR 弛豫率的精确表达式，我们将其与文献中的先前理论结果进行了比较。令人惊讶的是，在半满时 SU(2)不变的自旋链附近，我们发现从半经典区域到以零自旋 Drude 权重和发散的自旋电导率为特征的强相互作用量子区域的交叉，表明自旋动力学具有超扩散性。自旋涨落的动力指数被认为属于 Kardar-Parisi-Zhang 普适类。此外，通过使用数值时变密度矩阵重整化群模拟，我们发现了强有力的证据，表明异常的自旋输运即使在高温下也能持续存在，而与模型的谱隙和可积性无关。
