TITLE: Valley-controlled many-body exciton interactions in monolayer WSe2 phototransistors 

AUTHOR: Daniel Vaquero Monte - University of Groningen 

INVITED BY: Jorge Quereda Bernabeu

WHEN: June, 26 - 3PM

WHERE: Salón de Actos, ICMM

ABSTRACT: Many-body exciton interactions shape the optoelectronic response of atomically thin transition-metal dichalcogenides (TMDs), where strong Coulomb interactions produce tightly bound electron–hole pairs (excitons) [1]. To date, modulation of exciton–exciton interactions has primarily relied on electrical gating or van der Waals engineering, while, optical control of these interactions remains largely unexplored. Monolayer TMDs host two inequivalent valleys at the K and K&#8242\; points, with excitonic transitions selectively addressable by using circularly polarized light, allowing for the control of excitonic valley populations. Here, we demonstrate all-optical control of many-body exciton interactions in monolayer WSe2 via valley-selective excitation using helicity-resolved pulsed-laser photocurrent spectroscopy [2]. Circular excitation selectively populates excitons in a single valley, whereas linear excitation populates both valleys, inducing a valley-dependent nonlinear

photoresponse. We observe a helicity-dependent exciton renormalization, alongside a 2-fold enhancement of sublinear photocurrent scaling under circular excitation, reflecting a single-valley population of interacting excitons. A microscopic model incorporating intervalley-exchange [3] and exciton–exciton annihilation mediated by dark and bright exciton populations [4] reproduces the nonlinear valley-selective response. These results establish the valley degree of freedom as an all-optical control parameter for tuning many-body excitonic effects and exploring correlated exciton states and valleytronic applications in two-dimensional semiconductors [5].

[1]               G. Wang et al. Review of Modern Physics, 90 (2018), 021001

[2]             D.Vaquero et al., Communications Physics, 194 (2020), 3 

[3]         M. Selig et al. Physical Review Research, 2 (2020), 023322

[4]       D. Erkensten et al, Physical Review B, 104 (2021), L241406

[5]             D. Vaquero et al., Nano Letters, 26 (2026), 6641&#8722\;6648