De Nardis Jacopo, Gopalakrishnan Sarang, Vasseur Romain, Ware Brayden
Laboratoire de Physique Théorique et Modélisation, CNRS UMR 8089, CY Cergy Paris Université, 95302 Cergy-Pontoise Cedex, France.
Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16820, USA.
Phys Rev Lett. 2021 Jul 30;127(5):057201. doi: 10.1103/PhysRevLett.127.057201.
Superdiffusive finite-temperature transport has been recently observed in a variety of integrable systems with non-Abelian global symmetries. Superdiffusion is caused by giant Goldstone-like quasiparticles stabilized by integrability. Here, we argue that these giant quasiparticles remain long-lived and give divergent contributions to the low-frequency conductivity σ(ω), even in systems that are not perfectly integrable. We find, perturbatively, that σ(ω)∼ω^{-1/3} for translation-invariant static perturbations that conserve energy and σ(ω)∼|logω| for noisy perturbations. The (presumable) crossover to regular diffusion appears to lie beyond low-order perturbation theory. By contrast, integrability-breaking perturbations that break the non-Abelian symmetry yield conventional diffusion. Numerical evidence supports the distinction between these two classes of perturbations.
最近在各种具有非阿贝尔全局对称性的可积系统中观察到了超扩散有限温度输运。超扩散是由可积性稳定的类戈德斯通巨准粒子引起的。在这里，我们认为，即使在并非完全可积的系统中，这些巨准粒子仍然寿命很长，并对低频电导率σ(ω) 做出发散贡献。我们通过微扰发现，对于守恒能量的平移不变静态微扰，σ(ω)∼ω^(-1/3)，而对于噪声微扰，σ(ω)∼|logω|。（可能的）向常规扩散的转变似乎超出了低阶微扰理论。相比之下，破坏非阿贝尔对称性的可积性破坏微扰会产生常规扩散。数值证据支持了这两类微扰之间的区别。
