Abstract: Excitons are composite Bosons formed by pairing electrons and holes in a crystal.The idea that excitons might Bose condense dates to the 1960’s but has often been surrounded by controversy. My talk will focus on the important lessons learned
about exciton condensates from work on two-dimensional electron systems in the
quantum Hall regime, starting around twenty years ago, and on new opportunities
[1] to create exciton condensates and engineer their properties thanks to advances
in stacking individual layers of van der Walls materials. I will also discuss the recent
observation of dipolar condensates [2] in double bilayer graphene in the absence of
a magnetic field, highlighting the unusual connection [3] between electron-hole
pairing channels and Dirac point Berry phases in the isolated bilayers.
[1] Ma L, Nguyen PX, Wang Z, Zeng Y, Watanabe K, Taniguchi T, MacDonald AH, Mak
KF, Shan J. Strongly correlated excitonic insulator in atomic double layers. Nature.
2021 Oct 28;598(7882):585-9.
[2] “Strongly enhanced tunneling at total charge neutrality in double bilayer-
graphene-WSe 2 heterostructures”, G. William Burg et al., Phys. Rev. Lett. 120, 177702
(2018).
[3] “Spatially-indirect Exciton Condensate Phases in Double Bilayer Graphene”,
Jung-Jung Su and A.H. MacDonald, Phys. Rev. B 95, 045416 (2017).