Navegando por Autor "Venezuela, Pedro Paulo de Mello"
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Item Angle-tunable intersubband photoabsorption and enhanced photobleaching in twisted bilayer graphene.(2021) Pogna, Eva A. A.; Miao, Xianchong; Dreifus, Driele Von; Souza, Thonimar Vieira de Alencar; Moutinho, Marcus Vinicius de Oliveira; Venezuela, Pedro Paulo de Mello; Manzoni, Cristian; Ji, Minbiao; Cerullo, Giulio; Paula, Ana Maria deVan der Waals heterostructures obtained by artificially stacking two-dimensional crystals represent the frontier of material engineering, demonstrating properties superior to those of the starting materials. Fine control of the interlayer twist angle has opened new possibilities for tailoring the optoelectronic properties of these heterostructures. Twisted bilayer graphene with a strong interlayer coupling is a prototype of twisted heterostructure inheriting the intriguing electronic properties of graphene. Understanding the effects of the twist angle on its out-of-equilibrium optical properties is crucial for devising optoelectronic applications. With this aim, we here combine excitation-resolved hot photoluminescence with femtosecond transient absorption microscopy. The hot charge carrier distribution induced by photo-excitation results in peaked absorption bleaching and photo-induced absorption bands, both with pronounced twist angle dependence. Theoretical simulations of the electronic band structure and of the joint density of states enable to assign these bands to the blocking of interband transitions at the van Hove singularities and to photo-activated intersubband transitions. The tens of picoseconds relaxation dynamics of the observed bands is attributed to the angle-dependence of electron and phonon heat capacities of twisted bilayer graphene.Item Electronic band tuning and multivalley raman scattering in monolayer transition metal dichalcogenides at high pressures.(2022) Martins, Luiz Gustavo Pimenta; Carvalho, Bruno Ricardo de; Occhialini, Connor A.; Neme, Natália Paz; Park, Ji-Hoon; Song, Qian; Venezuela, Pedro Paulo de Mello; Mazzoni, Mário Sérgio de Carvalho; Kong, Jing; Comin, RiccardoTransition metal dichalcogenides (TMDs) possess spin-valley locking and spin-split K/K′ valleys, which have led to many fascinating physical phenomena. However, the electronic structure of TMDs also exhibits other conduction band minima with similar properties, the Q/Q′ valleys. The intervalley K−Q scattering enables interesting physical phenomena, including multivalley superconductivity, but those effects are typically hindered in monolayer TMDs due to the large K−Q energy difference (ΔEKQ). To unlock elusive multivalley phenomena in monolayer TMDs, it is desirable to reduce ΔEKQ, while being able to sensitively probe the valley shifts and the multivalley scattering processes. Here, we use high pressure to tune the electronic properties of monolayer MoS2 and WSe2 and probe K−Q crossing and multivalley scattering via double-resonance Raman (DRR) scattering. In both systems, we observed a pressure-induced enhancement of the double-resonance LA and 2LA Raman bands, which can be attributed to a band gap opening and ΔEKQ decrease. First-principles calculations and photoluminescence measurements corroborate this scenario. In our analysis, we also addressed the multivalley nature of the DRR bands for WSe2. Our work establishes the DRR 2LA and LA bands as sensitive probes of strain-induced modifications to the electronic structure of TMDs. Conversely, their intensity could potentially be used to monitor the presence of compressive or tensile strain in TMDs. Furthermore, the ability to probe K−K′ and K−Q scattering as a function of strain shall advance our understanding of different multivalley phenomena in TMDs such as superconductivity, valley coherence, and valley transport.