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DOE OSTI · 2945936

Unconventional Superconductivity Mediated by Exciton Density Wave Fluctuations

Abstract

Synthetic platforms afford an unparalleled degree of controllability in realizing strongly correlated phases of matter. In this Letter, we study the possibility of electrically tunable exciton-mediated superconductivity arising in charge-imbalanced bilayer semiconductors. Focusing on the case of a bilayer semiconductor heterostructure, we identify the gating conditions required to achieve exciton density wave order within a self-consistent Hartree-Fock approximation. We analyze the role of the coupling of excitonic fluctuations to the fermionic charge carriers to find that the Goldstone mode of the density wave order can mediate attractive interactions leading to superconductivity. Furthermore, when the system is close to the density wave ordering, the interactions mediated by low-energy exciton modes can support an interlayer pair-density wave superconductor of anisotropic character. We discuss experimental signatures associated with these phenomena.

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BibTeXRIS

Kumar, Ajesh [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)] (ORCID:0000000262801845), Patri, Adarsh S. [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Univ. of British Columbia, Vancouver, BC (Canada)] (ORCID:0000000278457823), Senthil, T. [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)]. 2025-12-22. Unconventional Superconductivity Mediated by Exciton Density Wave Fluctuations. https://doi.org/10.1103/7f6c-jh1k

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Long-range Coulomb forces give rise to correlated insulating states when charge particles populate a moiré superlattice at certain fractional filling factors. Such behavior is characterized by a broken translation symmetry wherein particles spontaneously form a Wigner crystal. Here, focusing on the experimental findings of Xu et al. [Nature (London) 587, 214 (2020)], we present a theory that captures the correlated insulating state of a fractionally filled moiré superlattice through the energy shift and change in oscillator strength of the exciton absorption resonance. The theory shows that the experimental findings can only be supported if the electrons reside in a charge-ordered state (i.e., electrons are not randomly distributed among the sites of the moiré superlattice). Furthermore, we explain why the energy shifts of exciton resonances are qualitatively different in cases where the superlattice is nearly empty compared with a superlattice whose sites are doubly occupied.

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