Ilya Esterlis

Abstract: When the Coulomb repulsion between electrons dominates over their kinetic energy, electrons in two-dimensional systems are predicted to spontaneously break continuous-translation symmetry and form a quantum crystal1. Efforts to observe2–12 this elusive state of matter, termed a Wigner crystal, in two-dimensional extended systems have primarily focused on conductivity measurements on electrons confined to a single Landau level at high magnetic fields. Here we use optical spectroscopy to demonstrate that electrons in a monolayer semiconductor with density lower than 3 × 1011 per centimetre squared form a Wigner crystal. The combination of a high electron effective mass and reduced dielectric screening enables us to observe electronic charge order even in the absence of a moire potential or an external magnetic field. The interactions between a resonantly injected exciton and electrons arranged in a periodic lattice modify the exciton bandstructure so that an umklapp resonance arises in the optical reflection spectrum, heralding the presence of charge order13. Our findings demonstrate that charge-tunable transition metal dichalcogenide monolayers14 enable the investigation of previously uncharted territory for many-body physics where interaction energy dominates over kinetic energy. The signature of a Wigner crystal—the analogue of a solid phase for electrons—is observed via the optical reflection spectrum in a monolayer transition metal dichalcogenide.

TL;DR: In this paper, the superconducting and charge density wave susceptibilities of the two-dimensional Holstein model are computed using determinant quantum Monte Carlo, and compared with results computed using the Migdal-Eliashberg (ME) approach.

TL;DR: In this paper, a new model of strongly interacting electrons and phonons is proposed, in close analogy with the well-known Sachdev-Ye-Kitaev model, and the authors explore how superconductivity can emerge from quantum critical and highly incoherent non-Fermi-liquid normal states.

TL;DR: The observation of bilayer Wigner crystals without magnetic fields or moiré potentials in an atomically thin transition metal dichalcogenide heterostructure, which consists of two MoSe2 monolayers separated by hexagonal boron nitride, demonstrates that anatomically thin heterost structure is a highly tunable platform for realizing many-body electronic states and probing their liquid-solid and magnetic quantum phase transitions.

TL;DR: In this paper, the authors analyze the Eliashberg theory of phonon-mediated superconductivity in 2D systems in light of recent extensive Monte Carlo studies of the Holstein model.