Giant spin-splitting and gap renormalization driven by trions in single-layer WS2/h-BN heterostructures

In two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs), new electronic phenomena such as tunable bandgaps(1-3) and strongly bound excitons and trions emerge from strong many-body effects(4-6), beyond the spin and valley degrees of freedom induced by spin-orbit coupling and by lattice symmetry(7). Combining single-layer TMDs with other 2D materials in van der Waals heterostructures offers an intriguing means of controlling the electronic properties through these many-body effects, by means of engineered interlayer interactions(8-10). Here, we use micro-focused angle-resolved photoemission spectroscopy (microARPES) and in situ surface doping to manipulate the electronic structure of single-layer WS2 on hexagonal boron nitride (WS2/h-BN). Upon electron doping, we observe an unexpected giant renormalization of the spin-orbit splitting of the single-layer WS2 valence band, from 430 meV to 660 meV, together with a bandgap reduction of at least 325 meV, attributed to the formation of trionic quasiparticles. These findings suggest that the electronic, spintronic and excitonic properties are widely tunable in 2D TMD/h-BN heterostructures, as these are intimately linked to the quasiparticle dynamics of the materials(11-13).