We show that a broad class of quantum critical points can be stable against locally correlated disorder even if they are unstable against uncorrelated disorder. Although this result seemingly contradicts the Harris criterion, it follows naturally from the absence of a random-mass term in the associated order-parameter field theory. We illustrate the general concept with explicit calculations for quantum spin-chain models. Instead of the infinite-randomness physics induced by uncorrelated disorder, we find that weak locally correlated disorder is irrelevant. For larger disorder, we find a line of critical points with unusual properties such as an increase of the entanglement entropy with the disorder strength. We also propose experimental realizations in the context of quantum magnetism and cold-atom physics.
Numerical Study of Stability of Clean Critical Points across Aperiodic, Topological, and Uncorrelated Disorder
School of Physics and Astronomy, Beijing Normal University（北京师范大学物理与天文学院）；Key Laboratory of Multiscale Spin Physics (Beijing Normal University), Ministry of Education（教育部多尺度自旋物理重点实验室（北京师范大学））；School of Physics, Beijing Institute of Technology（北京理工大学物理学院）
Nonanalytic Magnetization Dependence of the Magnon Effective Mass in Itinerant Quantum Ferromagnets
计算了干净和无序巡游量子铁磁体中的自旋波色散关系。研究发现，类似于弱局域化物理的效应使自旋波的频率成为磁化强度m的非解析函数。对于低频Ω、小波矢k和小m，色散关系为Ω~ m^{1-α} k^2，其中对于无序系统，α=（4-d）/2（2<d<4）;对于干净系统，α=（3-d）（1<d<3）。在d=4（无序）和d=3（干净）的情况下，Ω~ m ln（1/m）k^2。实验来测试这些预测提出。
