Joint ICTP/SISSA CM Seminar @SISSA Via Bonomea 265 - Friday 30 November 11:30 - G.BASKARAN

[CM Section]

Joint ICTP/SISSA Informal Condensed Matter Seminar

Friday 30 November 11:30 a.m.
SISSA, Via Bonomea 265

G. BASKARAN (Perimeter Institute for Theoretical Physics,
Waterloo Ontario, Canada and The Institute of Mathematical
Sciences, Chennai, India)

Title: AA to AB via Twist in Bilayer Graphene: Moire' is Different

Abstract:
Single layer graphene hides manybody physics, Bilayer graphene,
with AA and AB registry, exposes some of them. Twist springs more
surprises. A theory [1] for superconductivity seen after tiny commensurate
twists in bilayer graphene is discused. We invoke resonating valence
bond (RVB) pairing contained in the dense p-pi electron fluid in graphene.
RVB pairing fails to produce superconductivity in neutral graphene, as
electron density of states vanish at the Fermi level. In a twisted bilayer,
interlayer tunneling adds equal number of electrons and holes in regions
of dominant AA registry. Self doped carriers use RVB pairing and develop
charge -2e and +2e Cooper pair correlations, in spite of Coulomb repulsion.
Resulting periodic superlattice of Cooper pair puddles form a Josephson
lattice. Coulomb blockade makes it a Bosonic Mott insulator. Gate voltage
dopes the Bose Mott insulator and interesting consequences follow.

[1] G. Baskaran, arXiv:1804.00627