Charge Transfer Excitations, Pair Density Waves, and Superconductivity in Moiré Materials

Kevin Slagle; Liang Fu

doi:10.1103/PhysRevB.102.235423

paper

Charge Transfer Excitations, Pair Density Waves, and Superconductivity in Moiré Materials

arXiv:2003.13690 · doi:10.1103/PhysRevB.102.235423

Abstract

Transition metal dichalcogenide (TMD) bilayers are a new class of tunable moiré systems attracting interest as quantum simulators of strongly-interacting electrons in two dimensions. In particular, recent theory predicts that the correlated insulator observed in WSe $_{2}$ /WS $_{2}$ at half filling is a charge-transfer insulator similar to cuprates and, upon further hole doping, exhibits a transfer of charge from anion-like to cation-like orbitals at different locations in the moiré unit cell. In this work, we demonstrate that in this doped charge-transfer insulator, tightly-bound charge-2e excitations can form to lower the total electrostatic repulsion. This composite excitation, which we dub a trimer, consists of a pair of holes bound to a charge-transfer exciton. When the bandwidth of doped holes is small, trimers crystallize into insulating pair density waves at a sequence of commensurate doping levels. When the bandwidth becomes comparable to the pair binding energy, itinerant holes and charge-2e trimers interact resonantly, leading to unconventional superconductivity similar to superfluidity in an ultracold Fermi gas near Feshbach resonance. Our theory is broadly applicable to strongly-interacting charge-transfer insulators, such as WSe $_{2}$ /WS $_{2}$ or TMD homobilayers under an applied electric field.

arXiv comment5+7 pages, 3+6 figures

Charge Transfer Excitations, Pair Density Waves, and Superconductivity in Moiré Materials

Abstract

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