Condensed Matter Theory Seminar - Igor Blinov - “Partial exciton condensation in a graphene trilayer”

Event time: 
Thursday, May 2, 2024 - 1:00pm to 2:00pm
Sloane Physics Laboratory SPL, Room 51 See map
217 Prospect Street
New Haven, CT 06511
Igor Blinov - University of Texas at Austin
Event description: 

In a system with an annular Fermi surface an instability towards creation of a density wave at a vector corresponding to the thickness of the annulus exists. Recently, a number of phase transitions in ABC-trilayer was observed as a function of hole doping [1]. Before formation of the first correlated phase, quantum oscillations [1] have an unusual form that can be explained by the fact that the Fermi surface within each flavor (valley and spin) have an annulus. Soon after the opening of the second Fermi surface, a phase transition, accompanied by the increase in resistance, occurs. The state was called a partially isospin polarized state (PIP). The evidence points towards the breaking of the gauge freedom for each valley (intervalley coherent order, IVC). At low temperatures, on the boundary between the PIP and the paramagnetic phase, a superconducting phase occurs [2].

Response analysis in the electron-hole channel between two valleys for a simple two-valley model with a Mexican-hat type of dispersion showed that the instability is the strongest for the formation of a state at nonzero transferred momentum q. We call the intervalley coherent phase at a finite q partial exciton condensation. Critical temperature of this state can be within the experimentally relevant range. Resistance of this phase at low temperatures, unlike the one of IVC, can be much larger (by a factor of 2) than the resistance of the paramagnetic phase. The correction to the conductance has a badly diverging part that goes as the second power of scattering time. The phase has long-period (tenth of nm) oscillations of density.

[1] Zhou, H., Xie, T., Ghazaryan, A., Holder, T., Ehrets, J. R., Spanton, E. M., … & Young, A. F. (2021). Half-and quarter-metals in rhombohedral trilayer graphene. Nature, 598(7881), 429-433.
[2] Zhou, H., Xie, T., Taniguchi, T., Watanabe, K., & Young, A. F. (2021). Superconductivity in rhombohedral trilayer graphene. Nature, 598(7881), 434-438.