290S/290K Quantum Materials Special. Seminar speaker Ewelina Hankiewicz (Würzburg University), Tuesday, January 17 at 2 pm in Physics South 402

Time/Venue Tuesday, January 17 at 2:00 pm Pacific Time in Physics South 402 and via Zoom:
https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09
Meeting ID: 995 2349 9113 Passcode: 600704
Host Joel Moore
Title Quantum anomalies in topological materials and spin chains
Abstract Recent theoretical and experimental advances allow for an observation of signatures of quantum anomalies in non-interacting condensed matter systems. Quantum anomalies violates one of the classical symmetries and bridge between condensed matter and high- energy physics.
The possibility of observation of signatures of the parity anomaly (failure of the existence of single Dirac fermion in two spatial dimensions characterized by broken parity symmetry) in Dirac-like materials [1,2] is especially interesting. Using effective field theories and analyzing band structures in external out-of-plane magnetic fields (orbital field), we show that topological properties of quantum anomalous Hall (QAH) insulators are related to the parity anomaly [2]. Moreover, we showed together with experimentalists a novel transition from -1 to 1 Hall plateau, caused by scattering processes between counter-propagating quantum Hall and QAH edge states related to the parity anomaly [3]. This model can be extended easily to any three-dimensional topological insulators (TIs) or magnetic 3D TIs with odd numbers of surface states propagating in transport. 

Further, we turn our attention to the conformal anomaly in one-dimensional spin systems. The conformal anomaly signals itself in a breaking of scale invariance by quantum effects, visible in multi-point functions of the energy-momentum tensor. We relate the variance of the on-site static magnetization that could be observed in neutron scattering experiments to the conformal anomaly in these systems. This paves a path to observe quantum anomalies in strongly interacting spin systems [4].

[1] F. D. M. Haldane, Phys. Rev. Lett. 61, 2015 (1988).[2] J. Böttcher, C. Tutschku, L. W. Molenkamp, and E. M. Hankiewicz Phys. Rev. Lett. 123, 226602 (2019); C. Tutschku, F. S. Nogueira, C. Northe, J. van den Brink, and E. M. Hankiewicz Phys. Rev. B102, 205407 (2020); C. Tutschku, J. Böttcher, R. Meyer, and E. M. Hankiewicz Phys. Rev. Research2, 033193 (2020).
[3] S. Shamim, P. Shekhar, W. Beugeling, J. Böttcher, A. Budewitz, J.-Benedikt Mayer, L. Lunczer, E. M. Hankiewicz, H. Buhmann, L. W. Molenkamp,Nat. Commun. 13, Article number: 2682 (2022).
[4] C. Northe, C. Zhang, S. Galeski and E.M. Hankiewicz, arXiv:2210.07972 (2022).