Condensed Matter Theory

Abstract:

We establish twisted SnSe₂ as a tunable platform for simulating dimension-dependent correlated physics, distinct from conventional K-valley moiré systems. By constructing interacting Wannier models, we show that the stacking configuration dictates the effective lattice geometry. In AAstacked bilayers, a momentum-space nonsymmorphic symmetry constrains the single-particle hopping within each valley to be effectively one-dimensional, while still allowing fully two-dimensional interactions, thereby giving rise to an effective quasi-one-dimensional system. This dimensional reduction stabilizes exotic phases including dimerized states with finite residual entropy, valence bond solids, and quantum paramagnetism. Conversely, AB-stacking maps to a frustrated Kagome lattice; here, strong interactions drive the emergence of a classical spin liquid. The high tunability of this moiré system, which allows control over both the filling and interaction strength (via twist angle), renders twisted SnSe₂ a versatile platform for realizing a wide range of exotic correlated quantum phases.

Abstract:

Many strongly correlated states, such as those arising in the fractional quantum Hall effect and spin liquids, are described by wavefunctions obtained by dividing particles into multiple clusters, constructing a readily evaluable wavefunction in each cluster, and (anti)symmetrizing across these clusters. We introduce a method to compute quantities such as energies and correlators, using Monte Carlo simulations for these states. Our framework overcomes the factorial scaling of explicit (anti)symmetrization, allowing for studies of systems beyond the reach of exact diagonalization.

Abstract:

We investigate channel-confined, nematic liquid crystals using the Beris–Edwards model of nematohydrodynamics. Using strong homeotropic anchoring at the walls, we find multistability, i.e. multiple coexisting states where the uniform nematic state coexists with states having spatially varying scalar nematic order and director fields. When a pressure gradient is applied, flows develop, and the inherent multistability of the system organises a variety of complex dynamics. For low pressure gradients, steady flows are established, and the director fields that emerge from the multistable states at equilibrium correspond to Bowser and Dowser configurations similar to those reported in experiments. An increasing pressure gradient destabilises steady Bowser and Dowser flow states sequentially, leading to unsteady periodic and chaotic regimes featuring cyclical topological transitions, pulsating flows, advecting defects and spatiotemporal chaos. These findings demonstrate that modest variations in the scalar nematic order, as captured by the Beris–Edwards model, can qualitatively modify equilibrium structures and give rise to complex non-equilibrium behaviour in confined nematics – contrasting with the Ericksen–Leslie model, which assumes a constant scalar order parameter. Our key model predictions – multistability, periodically oscillating states and advecting defect-mediated turbulence – can be experimentally investigated in pressure-driven channel flows of nematic fluids.