Bulletin of the American Physical Society
Mid-Atlantic Section Meeting 2021
Volume 66, Number 18
Friday–Sunday, December 3–5, 2021; Rutgers University, New Brunswick, New Jersey
Session E01: Quantum Matter 4: Bilayers |
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Chair: Vladimir Dobrosavljevic, Florida State University Room: 201A |
Saturday, December 4, 2021 2:00PM - 2:36PM |
E01.00001: \textbf{\textit{Moire-Wigner-Mott freezing in transition-metal dichalcogenide heterobilayers}} Invited Speaker: Vladimir Dobrosavljevic \textit{The Moire pattern induced by lattice mismatch in transition-metal dichalcogenide heterobilayers causes the formation of flat bands, where interactions dominate the kinetic energy. At fractional fillings of the flat valence band, the long-range Coulomb interaction then induces generalized Wigner crystals or frozen electron glasses. On top of these charge ordering patterns, electrons on occupied site experience strong Mott correlations. Here, we use a combination of first-principle modelling with strong-coupling many-body theory to study the interplay of Moire Wigner and Mott physics. At certain commensurate fillings ~(e.g. n}$=$\textit{1/3) we find periodic Wigner-Mott states and a crossover to heavy Fermi liquids in their vicinity. At other fillings we also identify metastable inhomogeneous (glassy) charge ordering with a characteristic weak bad metal behavior.} [Preview Abstract] |
Saturday, December 4, 2021 2:36PM - 3:12PM |
E01.00002: Landau level spectroscopy in small-angle twisted double bilayer graphene. Invited Speaker: Yulia Maximenko A new field of moir\'{e} materials established itself soon after superconductivity and strongly correlated electronic states were observed in magic-angle twisted bilayer graphene (MATBG). A small mismatch in rotational alignment or lattice parameters generates a periodic moir\'{e} pattern in stacked van der Waals monolayers. In certain such systems, the moir\'{e} potential gives rise to emerging flat electronic bands which can host a variety of quantum phases due to enhance electron-electron interaction. Multilayer twisted systems, such as small-angle twisted double bilayer graphene (TDBG), offer further opportunities to engineer flat or narrow bands and reveal new phenomena. The physics in twisted Bernal-stacked graphene bilayers is broadly tunable by electric field, which can drive the system into a correlated phase in a continuous range of twist angles. Here, we use a multi-mode instrument combining force microscopy, tunneling microscopy, and electrostatic gating to study TDBG at 10 mK under magnetic field up to 15 T. We present high-resolution Landau level spectroscopy and provide the analysis of magnetic-field-induced behavior in TDBG. Spatially resolved local density of states measurements allow us to see the spatial interplay between the Landau levels and high-symmetry moir\'{e} sites. We use an analytical model to further interpret the complexity of this tunable system. [Preview Abstract] |
Saturday, December 4, 2021 3:12PM - 3:24PM |
E01.00003: Fractional metals and superconductivity in graphene heterostructure Bitan Roy, Andras Szabo Graphene-based layered materials accommodate nodal quasiparticles that (a) feature continuous SU(2) chiral symmetries stemming from the valley or isospin and real spin degrees of freedom, for example, each of which leads to two-fold band degeneracy and (b) can develop (spontaneously or externally) Dirac masses leading to uniform and isotropic spectral gap. Irrespective of the band curvature of such chiral quasiparticle dispersion, I will show that it is always conceivable to construct a right number of mutually commuting masses that systematically lift the band degeneracy. I then show how such generic picture can be germane to recently observed half and quarter metal in Bernal bilayer and rhobmohedral trilayer graphene in the presence of external electric displacement field. Finally, I will also discuss the possible superconducting states originating from such fractional metal. [Preview Abstract] |
Saturday, December 4, 2021 3:24PM - 4:00PM |
E01.00004: Correlated states in twisted bilayer WSe$_{2}$ Invited Speaker: En-Min Shih Artificial moir\'{e} superlattices have emerged as a new platform for realizing and manipulating correlated electron phenomena. Because the Coulomb interaction energy is comparable to the bandwidth in the narrow electron bands formed by the superlattices, electron interactions may induce new quantum phases. In twisted graphene-based systems, such flat bands lead to correlated insulator, superconducting, and topological states. Unlike graphene, which has extremely mobile Dirac electrons, semiconductor TMDs have a large effective mass that greatly enhances interaction effects and therefore display correlated states in a broad range of twist angles. In this talk, I will discuss how we utilized transport measurements to investigate quantum phases in the twist bilayer WSe$_{2}$. I will demonstrate that correlated states can be observed in this system with twist angles ranging from 4 to 5.1 degree. A correlated insulator that is tunable by both the twist angle and the displacement field emerges at half-band filling of the moir\'{e} subband. We further characterize the displacement field driven metal-insulator transitions and the metallic phase in twisted WSe$_{2}$. The metal-insulator transition is shown to be continuous as a function of density and displacement field. At low temperatures, the resistivity at the metal-insulator border exhibits strange metal behavior, with dissipation comparable to the Planckian limit. The existence of strong quantum fluctuations in the insulating phase is shown by an examination of the residual resistivity. These findings establish twisted WSe$_{2}$ as a unique platform for investigating correlated states and metal-insulator quantum phase transitions on a triangular lattice. [Preview Abstract] |
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