WEEKLY COLLOQUIUM
Thursday, September 12, 3:05 - 4:20 PM
Location: Biological Sciences Room 241
Spectroscopic investigation of the pseudo gap, inter-valley coherence and superconductivity in magic-angle twisted trilayer graphene
Hyunjin Kim
Caltech
The question of whether the superconductivity in magic-angle twisted graphene systems originates from the phonon-mediated pairing or more exotic mechanisms motivates experimental studies on this system. Scanning tunneling spectroscopy measurements, along with theoretical calculations, point that the repulsive Coulomb interaction sets the largest energy scale when the strain is moderately low. Here, we first show how Coulomb interaction shapes band dispersion in a twisted bilayer / trilayer system. Electrostatic interaction due to the charge imbalance within the moire unit cell deforms the band structure by several tens of millielectron volts. Next, we identify the symmetry-broken ground state around the half-filling of the flat band as incommensurate Kekule spiral (IKS) based on large area tunneling conductance maps showing spatially varying Kekule patterns. Magnetic field and temperature range we observe IKS corresponds to a region where correlated insulators or pseudogap appears in the spectrum. Finally, we observe a two-gap spectrum at base temperature in a certain doping range. The outer gap follows the behavior of previously identified pseudogap, while the inner gap shows pronounced suppression with field, consistent with the superconductivity measured in transport. We hope this promotes a better understanding of the nature of pseudogap and superconductivity in this system.
Acknowledgment: This work has been primarily supported by the Office of Naval Research (grant no. N142112635) and National Science Foundation (grant no. DMR-2005129). Nanofabrication efforts have been in part supported by the Department of Energy DOE-QIS program (DE-SC0019166) and the Sloan Foundation. H.K. acknowledge support from the Kwanjeong fellowship.
Fall 2024 Department of Physics and Astronomy Colloquium Schedule
(This schedule will be updated throughout the semester.)
- Thursday, August 22: Welcome Back Pizza Party
- Thursday, August 29: No Colloquium
- Thursday, September 5: Dr. Derek Davis, Caltech, “Decoding LIGO Detector Data for High-Precision Gravitational-Wave Astronomy”
- Thursday, September 12: Hyunjin Kim, Caltech, “Spectroscopic investigation of the pseudo gap, inter-valley coherence and superconductivity in magic-angle twisted trilayer graphene”
- Thursday, September 19: TBA
- Thursday, September 26: TBA
- Thursday, October 3: TBA
- Thursday, October 10: TBA
- Thursday, October 17: TBA
- Thursday, October 24: TBA
- Thursday, October 31: TBA
- Thursday, November 7: TBA
- Thursday, November 14: TBA
- Thursday, November 21: TBA
- Thursday, November 28: Thanksgiving Holiday, No Colloquium
- Thursday, December 5: TBA