Probing collective magnetic excitations in twisted bilayer graphene via electron spin resonance spectroscopy

ORAL

Abstract

In magic-angle twisted bilayer graphene (MATBG), correlated insulating (CI) states emerge at an integer number of electrons per moiré unit cell. These states are suspected to emerge from successive filling of the fourfold degenerate spin and valley states of the nearly-flat miniband [1][2]. However, the order in which the spin/valley flavor states are populated remains unknown, as does the nature of how electrons in these states couple to one another and to external magnetic fields. The nature of these states could be clarified by probing their excitations. We implement this by measuring near-DC transport through an encapsulated TBG device, noting the change in resistivity as a function of an externally applied static magnetic field in the presence of oscillating microwave magnetic fields. We couple in microwave magnetic fields from a nearby microfabricated superconducting coplanar waveguide. Similar measurements have been performed on several CVD graphene samples [3][4][5][6] as well as on MATBG with spin-orbit coupling induced by a proximal TMDC layer [7], but no such signal has been reported in canonical hBN encapsulated MATBG with clear CI states.

[1] Zondiner, U., et al. Nature 582, 203–208 (2020).

[2] Park, J.M., et al. Nature 592, 43–48 (2021).

[3] Sichau, J., et al. Phys. Rev. Lett. 122, 046403 (2019).

[4] Mani, R. G., et al. Nature Communications 3, 996 (2012)

[5] Singh, U. R., et al. Physical Review B 102.24 (2020): 245134.

[6] Sharma, Chithra H., et al. AIP Advances 12.3 (2022): 035111.

[7] Morissette, Erin, et al. Nat. Phys. 19, 1156–1162 (2023).

* This work is primarily supported by the Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under contract DE-AC02-76SF00515. For early stages of the project, R.K. was supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE1656518. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

–

Presenters

  • Rupini Kamat

    Stanford Institute for Materials and Energy Sciences, Stanford University Physics Department, Stanford University

Authors

  • Rupini Kamat

    Stanford Institute for Materials and Energy Sciences, Stanford University Physics Department, Stanford University

  • Sandesh S Kalantre

    Stanford Institute for Materials and Energy Sciences, Stanford University Physics Department, Stanford University

  • Aaron L Sharpe

    Sandia National Laboratories, Materials Physics Department, Sandia National Laboratories

  • Kenji Watanabe

    National Institute for Materials Science, NIMS, Research Center for Electronic and Optical Materials, National Institute for Materials Science, Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan, National Institute for Material Science

  • Takashi Taniguchi

    Kyoto Univ, National Institute for Materials Science, Research Center for Materials Nanoarchitectonics, Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, National Institute for Materials Sciences, NIMS, International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan, National Institute for Material Science, International Center for Materials Nanoarchitectonics, NIMS, Japan, International Center for Materials Nanoarchitectonics, Tsukuba, National Institue for Materials Science, Kyoto University, National Institute of Materials Science, International Center for Materials Nanoarchitectonics and National Institute for Materials Science

  • Marc Kastner

    Stanford University, Stanford Institute for Materials and Energy Sciences, Stanford University Physics Department, Massachusetts Institute of Technology Physics Department, Stanford Univ

  • David Goldhaber-Gordon

    Stanford University, Stanford Institute for Materials and Energy Sciences, Stanford University Physics Department, Department of Physics, Stanford University, Stanford, California, Stanford Institute for Materials & Energy Sciences, Stanford University