TY - JOUR
T1 - Theory of correlated insulating behaviour and spin-triplet superconductivity in twisted double bilayer graphene
AU - Lee, Jong Yeon
AU - Khalaf, Eslam
AU - Liu, Shang
AU - Liu, Xiaomeng
AU - Hao, Zeyu
AU - Kim, Philip
AU - Vishwanath, Ashvin
N1 - We thank Shiang Fang, Yahui Zhang, Yizhuang You, Erez Berg, and Bertrand Halperin for helpful discussion. In particular, we thank Mikito Koshino for clarification on his earlier works on BLG parameters. A.V., J.Y., and E.K. were supported by a Simons Investigator Fellowship. P.K., X.L., and Z.H. acknowledge partial support from the Gordon and Betty Moore Foundation’s EPiQS Initiative through Grant GBMF4543 and the DoD Vannevar Bush Faculty Fellowship N00014-18-1-2877.
PY - 2019/12/1
Y1 - 2019/12/1
N2 - Two graphene monolayers twisted by a small magic angle exhibit nearly flat bands, leading to correlated electronic states. Here we study a related but different system with reduced symmetry - twisted double bilayer graphene (TDBG), consisting of two Bernal stacked bilayer graphenes, twisted with respect to one another. Unlike the monolayer case, we show that isolated flat bands only appear on application of a vertical displacement field. We construct a phase diagram as a function of twist angle and displacement field, incorporating interactions via a Hartree-Fock approximation. At half-filling, ferromagnetic insulators are stabilized with valley Chern number Cv= ± 2. Upon doping, ferromagnetic fluctuations are argued to lead to spin-triplet superconductivity from pairing between opposite valleys. We highlight a novel orbital effect arising from in-plane fields plays an important role in interpreting experiments. Combined with recent experimental findings, our results establish TDBG as a tunable platform to realize rare phases in conventional solids.
AB - Two graphene monolayers twisted by a small magic angle exhibit nearly flat bands, leading to correlated electronic states. Here we study a related but different system with reduced symmetry - twisted double bilayer graphene (TDBG), consisting of two Bernal stacked bilayer graphenes, twisted with respect to one another. Unlike the monolayer case, we show that isolated flat bands only appear on application of a vertical displacement field. We construct a phase diagram as a function of twist angle and displacement field, incorporating interactions via a Hartree-Fock approximation. At half-filling, ferromagnetic insulators are stabilized with valley Chern number Cv= ± 2. Upon doping, ferromagnetic fluctuations are argued to lead to spin-triplet superconductivity from pairing between opposite valleys. We highlight a novel orbital effect arising from in-plane fields plays an important role in interpreting experiments. Combined with recent experimental findings, our results establish TDBG as a tunable platform to realize rare phases in conventional solids.
UR - http://www.scopus.com/inward/record.url?scp=85075574133&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85075574133&partnerID=8YFLogxK
U2 - 10.1038/s41467-019-12981-1
DO - 10.1038/s41467-019-12981-1
M3 - Article
C2 - 31767862
AN - SCOPUS:85075574133
SN - 2041-1723
VL - 10
JO - Nature communications
JF - Nature communications
IS - 1
M1 - 5333
ER -