The appearance of almost flat bands at so-called “magic angles,” first predicted in early theoretical works 68, 69, 70, 71, puts a variety of exotic correlated phases within experimental reach, including correlated insulators 27, 28, 29, 30, 31, 32, 37, 40, 41, 42, 43, 44, 45, 46, orbital ferromagnetism 27, 38, 39, 72, and magnetic field induced Chern insulators 33, 34, 35, 36, 73.Īmong the findings that have sparked the most interest in the field of twistronics is the discovery of robust and reproducible superconductivity in MATBG 1, 27, 30, with preliminary evidence for possible superconductivity also present in twisted double-bilayer graphene 49, 50, 51, ABC trilayer graphene aligned to hexagonal boron nitride 74, and twisted transition metal dichalcogenides 58. These systems are fascinating because of the precise control of electronic properties and correlations that can be achieved by tuning twist angle 1, 2, doping level 1, 2, 27, temperature 28, 29, pressure 30, 66, and external screening 31, 32, 33, 67.
In the quickly developing field of twistronics 4, tremendous theoretical 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26 and experimental 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46 efforts have been undertaken to unravel the nature of strong correlations 47, 48 and to access new moiré engineered structures with twisted double-bilayer graphene 49, 50, 51, 52, twisted trilayer graphene 53, 54, 55, 56, 57, transition metal dichalcogenide homobilayers and heterobilayers 58, 59, 60, 61, 62 as well as other materials 63, 64, 65 at the frontier of condensed matter research 3.
Since the discovery of superconductivity and correlated insulating states in magic-angle twisted bilayer graphene (MATBG) 1, 2, twisted van der Waals materials have become indispensable for the design of novel quantum materials at will 3. We show that the nematic unconventional superconductivity leads to pronounced signatures in the local density of states detectable by scanning tunneling spectroscopy measurements. Applying a perpendicular electric field enhances superconductivity on the electron-doped side which we relate to changes in the spin-fluctuation spectrum. We show that in a phase diagram as a function of doping ( ν) and temperature, nematic superconducting regions are surrounded by ferromagnetic states and that a superconducting dome with T c ≈ 2 K appears between the integer fillings ν = −2 and ν = −3. In this work, we discuss the role of spin-fluctuations arising from atomic-scale correlations in MATTG for the superconducting state. Superconductivity occurs in a range of doping levels that is bounded by van Hove singularities, which stimulates the debate of the origin and nature of superconductivity in this material. Magic-angle twisted trilayer graphene (MATTG) recently emerged as a highly tunable platform for studying correlated phases of matter, such as correlated insulators and superconductivity.
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