[qmeso-seminar] семинар 22 ноября

[Quantum Mesoscopics Dept.]

СЕМИНАР СЕКТОРА КВАНТОВОЙ МЕЗОСКОПИКИ

пятница 22 ноября, 15:00, ИТФ



Igor Blinov

Intervalley partial exciton condensation in a graphene trilayer



Recently, a number of phase transitions in ABC-trilayer was observed as a function of hole doping [1]. The first phase
transition occurs after opening of the second, electron-like Fermi surface within each flavor. The symmetry-broken state
was called a partially isospin polarized state (PIP). The evidence points towards 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]. PIP state has an unusually high resistance, by a factor of 1.5 exceeding that
of the paramagnetic phase.

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. Its value close to the difference between 2 Fermi momentums, inner- and outer-Fermi surfaces. We call such phase an
intervalley partial exciton condensate.

On the mean-field level, critical temperature of this state is within the experimentally relevant range. Resistance of
this phase at low temperatures unlike that of IVC, can be much larger (by a factor of 2) than the resistance of the
paramagnetic phase at least within the NCA approximation.

Interestingly, correction to the conductance due to the formation of the order has a badly diverging part that goes as
the second power of scattering time. The phase has large-period (hundreds of the lattice constant) 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.



[Трансляция: https://zoom.us/j/96948399564?pwd=RXlKbW96Qm1tZEV6SHB0Q2JYeTdrdz09]

подробнее: http://qmeso.itp.ac.ru/seminars.php?abstract=true