Our serie of Scientific Seminars continues with the next talk:
Title: Heavy electrons and cascades, the fascinating normal state of magic angle twisted bilayer graphene
Author: Leni Bascones, ICMM-CSIC
Where: Sala de Seminarios, ICMM-CSIC
When: 12 November, 12h
Abstract: The discovery of superconducting and correlated insulating states in magic-angle twisted bilayer graphene (MATBG), two graphene layers rotated by an angle ⍬ ~1.1°, opened the door to the discovery of numerous novel electronic states that can be tuned in situ.
In some materials, electronic interactions can substantially modify their properties with respect to the predictions of conventional band theory, even turning a metal into an insulator. These effects are particularly pronounced in materials with narrow bands, due to the reduced kinetic energy of the electrons. When two graphene layers are rotated to the magic angle, their bands become nearly flat. MATBG presents a plethora of correlated states, far beyond those observed in the first experiments. These states display highly unconventional properties, even by the standards of strongly correlated materials. This is particularly evident in the so-called cascades, early detected in scanning tunnelling microscopy (STM) and compressibility measurements as a function of doping.
In this seminar, I will show that the cascades constitute the normal state from which the other correlated states emerge. I will explain how the interplay between electronic correlations and the topology of the flat bands in MATBG leads to a highly unusual reorganization of the electronic spectrum, even in the absence of electronic ordering. This reorganization is already present at charge neutrality and exhibits a series of asymmetric resets as a function of doping, whose signatures can be observed in the STM spectra, the compressibility and the conductivity among other experimental probes. Our predictions have recently been confirmed by experiments using the new Quantum Twisting Microscope (QTM).
