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SUMMARY:Kekule Spirals in Twisted Graphene - Steve Simon\, Oxford
DTSTART:20250227T140000Z
DTEND:20250227T153000Z
UID:TALK224797@talks.cam.ac.uk
CONTACT:Gaurav
DESCRIPTION:One of the major challenges in the study of magic angle twiste
 d bilayer graphene  (MATBG) has been the understanding the insulating stat
 es that arise as a result of inter-electron interaction.   A combination o
 f recent theoretical [1\,2\,3\,4] and experimental [5\,6] work has now est
 ablished the presence of a new type of order which we call "Incommensurate
  Kekule Spiral" (IKS) order.   This order spontaneously breaks both the va
 lley-charge conservation and moiré translation symmetries\, but preserves
  a modified translation symmetry which simultaneously shifts the spatial c
 oordinates and rotates the U(1) angle which characterizes the spontaneous 
 inter-valley coherence.  This type of order appears ubiquitous in the pres
 ence of miniscule amounts of strain at temperatures above the superconduct
 ing transitions.    In this talk I will give an introduction to the physic
 s of MATBG emphasizing the strong coupling approximations.  I will then tu
 rn to the Hartree-Fock calculations we used to predict the IKS order and I
  will explain the physics that drives the system towards this ground state
 .   I will also briefly discuss the experiments that have observed this ph
 ase\, the competing phases that are observed in ultra-small strain samples
 \, as well as the closely related physics of magic angle trilayer graphene
 .\n\n[1]  Yves H. Kwan\, Glenn Wagner\, Tomohiro Soejima\, Michael P. Zale
 tel\, Steven H. Simon\, Siddharth A. Parameswaran\, Nick Bultinck\,  Phys.
  Rev. X 11\, 041063 (2021)\n[2]  Glenn Wagner\, Yves H. Kwan\, Nick Bultin
 ck\, Steven H. Simon\, S. A. Parameswaran\, Phys. Rev. Lett. 128\, 156401 
 (2022)\n[3]  Yves H. Kwan\, Glenn Wagner\, Nick Bultinck\, Steven H. Simon
 \, Erez Berg\, S. A. Parameswaran\,   Phys. Rev. B 110\, 085160 (2024).\n[
 4] Tianle Wang\, Daniel E. Parker\, Tomohiro Soejima\, Johannes Hauschild\
 , Sajant Anand\, Nick Bultinck\, and Michael P. Zaletel\, Phys. Rev. B 108
 \, 235128 (2023).\n[5]  Kevin P. Nuckolls et al\,  Nature 620\, 525-532 (2
 023).\n[6]  Hyunjin Kim\, et al\, Nature 623\, 942-948 (2023).
LOCATION:TCM Seminar Room
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