An experimental and theoretical study achieving direct microscopic visualization of the intervalley coherent (IVC) phase — a correlated state formed by coherent superposition of wave functions from opposite ±K valleys of few-layer graphene, spontaneously breaking valley U(1) symmetry. MBE-grown monolayer PtSe2 on highly oriented pyrolytic graphite forms a higher-order moire superlattice; spectroscopic-imaging STM reveals a sqrt(3)x(sqrt3) (R3) modulation superimposed on the moire lattice, correlated with a ~140 meV gap at the Fermi level and anti-phase real-space conductance at the two gap edges. The pattern vanishes on bilayer-graphene/SiC, where higher electron doping suppresses correlations. Self-consistent Hartree-Fock calculations with first-principles input show the PtSe2 interface dipole field gates the underlying bilayer graphene into the IVC phase, whose atomic-scale R3 density modulation is magnified onto the moire period by the interfacial higher-order moire pattern.
Intervalley coherent (IVC) phase in graphene systems arises from the coherent superposition of wave functions of opposite valleys, whose direct microscopic visualization provides pivotal insight into…