TMDs as a platform for spin liquid physics: A strong coupling study of twisted bilayer WSe$_2$

Abstract

The advent of twisted moiré heterostructures as a playground for strongly correlated electron physics has led to a plethora of experimental and theoretical efforts seeking to unravel the nature of the emergent superconducting and insulating states. Amongst these layered compositions of two dimensional materials, transition metal dichalcogenides (TMDs) are by now appreciated as highly-tunable platforms to simulate reinforced electronic interactions in the presence of low-energy bands with almost negligible bandwidth. Here, we focus on the twisted homobilayer WSe 2 and the insulating phase at half-filling of the flat bands reported therein. More specifically, we explore the possibility of realizing quantum spin liquid (QSL) physics on the basis of a strong coupling description, including up to second nearest neighbor Heisenberg couplings J 1 and J 2 , as well as Dzyaloshinskii-Moriya (DM) interactions. Mapping out the global phase diagram as a function of an out-of-plane displacement field, we indeed find evidence for putative QSL states, albeit only close to SU(2) symmetric points. In the presence of finite DM couplings and XXZ anisotropy, long-range order is predominantly present, with a mix of both commensurate and incommensurate magnetic phases.

Tunable Stripe Order and Weak Superconductivity in the Moiré Hubbard Model

“…This observation would be consistent with recent proposals of a chiral spin liquid in the intermediate coupling regime at φ = 0 [15][16][17]. This putative chiral spin liquid regime is suppressed by a finite displacement field, which is consistent with the expectation that breaking the SU(2) symmetry disfavors the formation of spin singlet and hence makes the spinon condensation harder to realize [8]. At the particular values φ = π/6, π/2, 5π/6 close to U/t = 0 we observe several regimes where the first excitation has momentum q = M ≡ (π, π/ √ 3).…”

“…Exotic emergent phenomena including correlated insulating states [1,2], quantum critically and tunable metal-insulator transitions (MIT) [3,4] have been recently realized in the twisted WSe 2 system, a typical class of transition metal dichalcogenides. The low energy physics of twisted WSe 2 is well captured by the so-called moiré Hubbard model, a variant of the standard triangular lattice Hubbard model in which the electron hopping amplitude acquires a spin-dependent phase (pseudomagnetic field) [5][6][7][8][9][10]. The Hamiltonian H of the moiré Hubbard model is the sum of kinetic (H 0 ) and interaction (H I ) terms with H 0 = −t σ=↑,↓ r,j=1,2,3 e iσφ c † r+aj ,σ c r,σ + h.c. , (1) and H I = U r n r↑ n r↓ is the standard onsite repulsive Hubbard interaction.…”

Moiré engineering of spin–orbit coupling in twisted platinum diselenide

“…Beyond graphene, experiments have studied twisted sheets of transition metal dichalcogenides (TMDs), concentrating primarily on group-VI homo-or hetero-bilayers of MoS 2 /Se 2 or WeS 2 /Se 2 , with fascinating observations of strongly correlated behavior [59][60][61][62][63][64][65][66][67][68][69] and excitonic physics [70][71][72][73][74][75][76]. Further proposals for TMD materials include exotic SC states with topological features [36,60], possible spin-liquid phases [61] and engineering of multi-orbital systems in group-IV TMDs as a realization of the elusive Kagome lattice with strong and tunable spin-orbit coupling (SOC) which exhibits fractional quantum anomalous Hall and Chern insulating states [77].…”

Proximity-driven ferromagnetism and superconductivity in the triangular Rashba-Hubbard model

“…A related Moiré system, which has also been studied both theoretically and experimentally in recent years, are bilayers of group-VI semiconducting transition metal dichalcogenides (TMDs) such as WSe 2 [26,27], which realize an effective triangular lattice [10,18,[27][28][29][30]. These materials can host exotic quantum phases such as correlated insulating states, unconventional superconductors, fractional quantum Hall states, and quantum spin liquids [10,18,27,[30][31][32][33][34][35][36]. While graphene behaves like a Dirac semimetal with SU(2) spin rotational symmetry, TMDs are semiconductors with a large band gap and a large spin-orbit coupling (SOC) [10,26,37].…”