Superdiffusion in quantum models from momentum-space nodal structures

by Prof. Chen Fang (Institute of Physics, Chinese Academy of Science)

Tuesday 27 May 2025, 15:00 → 16:00 Asia/Shanghai

Tsung-Dao Lee Institute/N6F-N601 - Meeting Room (Tsung-Dao Lee Institute)

Time: 15:00 May 27 (Tuesday), 2025

Host: Prof.  Xin Liu

Venue: TDLI Meeting Room N601

Tencent meeting link: https://meeting.tencent.com/dm/UlME4V1Q0AXd  Meeting ID: 149626096 , no password

 

Abstract:

Transport behavior in a macroscopic system is qualitatively classified by the scaling exponent of the resistance with respect to the length: $R\propto{L}^\gamma$. $\gamma=1$ gives the Ohmic resistance and corresponds to the diffusive transport; $\gamma=0$ in the ballistic transport, only realizable in ultra-clean 1D systems or topological edge states. $0<\gamma<1$ corresponds to the "superdiffusive transport", where quantum numbers like charge or energy dissipate faster than the diffusive, but slower than the ballistic transport, and is considered anomalous. In this talk, I introduce the "nodal-structure mechanism" for superdiffusion that is realizable in three different scenarios where a Bloch band coexists with (i) quantum noise from Lindbladian operators, (ii) disorder from local impurity operators, and (iii) fermion interactions. In each scenario, the Lindbladian/disorder/interaction operator commutes with the Bloch band number operator $n_k$ at certain $k_0\in{BZ}$ called the "nodes". The Bloch states near the nodes have long quasiparticle lifetime, and are shown to lead to superdiffusion. Using this mechanism, we have found disordered systems in 1D and 2D that violate Anderson localization, and the first non-integrable model showing superdiffusion at high temperatures. We show that in realistic materials, these nodes may naturally emerge if the Fermi surface wavefunction has nonzero topological numbers (e.g., the Chern number), or if the elementary band representation (EBR) of the Bloch band mismatches that of the impurities.

 

References:

[1]Y.-P. Wang, CF and J. Ren, SciPost Phys. 17, 150 (2024)

[2]Y.-P. Wang, J. Ren, and CF, Phys. Rev. B 110, 144201(2024)

[3]S. Huang, Y.-P. Wang, J. Ren, and CF, to appear

 

Biography:

Chen Fang granduated from Purdue University in 2011 with the Ph.D. degree. He worked at Princeton University and Massachusetts Institute of Technology from 2012 to 2015 as a postdoctoral research associate, before joining the Institute of Physics, Chinese Acadmey of Sciences in 2015. Chen's earlier works include the topological classification of insulators, semimetals, and superconductors. In recent years, his interest moves to related areas such as the non-Hermitian band theory and quantum dynamics.