The speed of light is a fundamental constant of nature. At the same time, condensed matter systems with emergent relativistic behavior may display multiple speeds of light. An experimentally relevant recent example is twisted trilayer graphene, where two types of Dirac fermions (slow and fast) co-exist. In our work, we study their interplay due to many-body interactions: At quantum criticality, we find that Lorentz symmetry and thus a single speed of light is restored.
[L Classen, JH Pixley, EJ König, 2D Materials 9 (3), 031001 (2022)] |
Fig: Wavefunctions are localized in momentum space in the semimetallic phase and delocalize at the magic angle.
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The discovery of correlated insulating and accompanying superconducting states at magic angles of twisted graphene heterostructures proves the potential of controlled quantum design of strongly correlated states of matter.
In our recent preprints [1,2] we demonstrate that the magic angle phenomenon appears in a wide class of semimetals in a (quasi-) periodic potential, of which twisted graphene heterostructures are only one out of many representatives. Furthermore, we uncover a previously unnoticed connection to the physics of Anderson localization without randomness and argue that this is the ultimate root of flat bands. Our proposal may be readily implemented in present day cold atomic labs. In a separate research direction [3] on network models in twisted bilayer graphene at small twist angles we demonstrate that modern quantum sensing techniques (noise magnetometry) can be used to detect fractionalized states of matter in twisted graphene devices. We furthermore present a careful study of ``stripe superconductivity'', comparing cuprate and twisted bilayer graphene superconductors. [1] YX Fu*, EJ König*, YZ Chou, JH Wilson, JH Pixley, npj Quantum Materials 5 (1), 1-8 (2020)
[2] YZ Chou, Y Fu, JH Wilson, EJ König, JH Pixley Physical Review B 101 (23), 235121 (2020) [Editor's suggestion] [3] EJ König, P Coleman, AM Tsvelik, Physical Review B 102 (10), 104514 (2020) |