arXiv subjects

Yiyang Lai

Publications and source records attributed to Yiyang Lai.

3 recordsLinked to original sources

arXiv2026

Lattice Relaxation in Moiré Heterobilayers

We develop an analytical theory for lattice relaxation in twisted moiré heterobilayers, accounting for lattice mismatch, twist, external biaxial heterostrain, and different elastic constants. Starting from continuum elasticity, we derive the self-consistent equations for the in-plane displacement fields and obtain simple perturbative expressions for the layer-resolved in-plane displacement fields induced by lattice relaxation. We apply our theory to graphene on hBN and representative 2H transition metal dichalcogenide heterobilayers, including MoTe$_2$/WSe$_2$ and WSe$_2$/WS$_2$. Our analytical results agree very well with full numerical solutions over experimentally relevant parameters. We further show that heterobilayers can exhibit a buckling instability near alignment, driven by compressive in-plane strain due to moiré relaxation. Our results provide a simple theoretical framework for incorporating lattice relaxation in realistic moiré heterostructures.

cond-mat.mes-hall↗

arXiv2025

Itinerant Magnetism in Twisted Bilayer WSe$_2$ and MoTe$_2$

Using a self-consistent Hartree-Fock theory, we show that the recently observed ferromagnetism in twisted bilayer WSe$_2$ [Nat. Commun. 16, 1959 (2025)] can be understood as a Stoner-like instability of interaction-renormalized moiré bands. We quantitatively reproduce the observed Lifshitz transition as function of hole filling and applied electric field that marks the boundary between layer-hybridized and layer-polarized regimes. The former supports a ferromagnetic valley-polarized ground state below half-filling, developing a topological charge gap at half-filling for smaller twist angles. At larger twist angles, the system hosts a gapped triangular Néel antiferromagnet. On the other hand, the layer-polarized regime supports a stripe antiferromagnet below half-filling and a wing-shaped multiferroic ground state above half-filling. We map the evolution of these states as a function of filling factor, electric field, twist angle, and interaction strength. Our results demonstrate that long-range exchange in a symmetry-unbroken parent state with strongly renormalized moiré bands provides a broadly applicable framework to understand itinerant magnetism in moiré TMDs.

cond-mat.str-el↗

arXiv2025

Bichromatic Moiré Superlattices for Tunable Quadrupolar Trions and Correlated States

Moiré superlattices in transition metal dichalcogenide heterostructures provide a platform to engineer many-body interactions. Here, we realize a bichromatic moiré superlattice in an asymmetric WSe$_2$/WS$_2$/WSe$_2$ heterotrilayer by combining R- and H-stacked bilayers with mismatched moiré wavelengths. This structure hosts fermionic quadrupolar moiré trions -- interlayer excitons bound to an opposite-layer hole -- with vanishing dipole moments. These trions arise from hybridized moiré potentials enabling multiple excitonic orbitals with tunable interlayer coupling, allowing control of excitonic and electronic ground states. We show that an out-of-plane electric field could effectively reshape moiré excitons and interlayer-intralayer electron correlations, driving a transition from interlayer to intralayer Mott states with enhanced Coulomb repulsion. The asymmetric stacking further enriches excitonic selection rules, broadening opportunities for spin-photon engineering. Our results demonstrate bichromatic moiré superlattices as a reconfigurable platform for emergent quantum states, where quadrupolar moiré trion emission may enable coherent and entangled quantum light manipulation.

cond-mat.mes-hall↗