Colóquios Agendados

Resumo: Two-dimensional (2D) materials and Moiré superlattices formed by certain stacking configurations of 2D crystals, represent a new frontier for quantum matter research due to the emergent properties associated to their reduced dimensionality and tunability. To glean insight into the physics of these atomically thin van der Waals materials, their properties have been extensively studied by tuning of external parameters such as temperature, electrostatic doping, electric and magnetic fields. However, there is an external tuning parameter that has not been used systematically in studies of these systems – pressure. The relative scarcity of high-pressure (HP) studies involving atomically thin materials is due to experimental challenges, e.g., loading of micron-sized samples into the also micron-sized pressure chamber. In this talk, I will describe how I addressed some of these challenges and I will discuss different HP studies involving those systems using diamond anvil cells. In the first study [1], I will detail the pressure-tuning of minibands in MoS₂/WSe₂ heterostructures revealed by moiré phonons: Raman-inactive phonons from the individual layers that are activated by the moiré potential. Moiré phonons manifest as satellite Raman peaks appearing exclusively in the heterostructure region, increasing in intensity under applied pressure. Our theoretical analysis reveals that their Raman scattering rate is directly connected to the moiré potential strength. By comparing the experimental and calculated pressure-induced enhancement, we obtain numerical estimates for the moiré potential amplitude and its pressure dependence. This work establishes moiré phonons as a sensitive probe of the moiré potential and of the electronic structure of moiré systems. In the second study [2], I will report on the electronic-band tuning and multivalley scattering at high pressures in monolayer MoS₂ and WSe₂ revealed by double-resonance Raman. This work establishes the double-resonance 2LA and LA Raman bands as sensitive probes of strain-induced modifications to the electronic structure of monolayer TMDs. In the third study [3], we investigated the mechanism stabilizing the helimagnetic/multiferroic (HM/MF) order in the type-II multiferroic NiI₂ under pressure via Raman spectroscopy, optical linear dichroism (LD) and x-ray diffraction [3]. We demonstrated a three-fold enhancement of the HM/MF order in the bulk and few-layer NiI₂ and revealed the importance of interlayer exchange and magneto-structural coupling in stabilizing this phase.

References

[1] L. G. Pimenta Martins*; D. A. Ruiz-Tijerina* et al. Pressure-tuning of minibands in MoS₂/WSe₂ heterostructures revealed by moiré phonons. Nature Nanotechnology. 18, 1147–1153 (2023).

[2] L. G. Pimenta Martins et al. Electronic band tuning and multivalley Raman scattering in monolayer TMDs at high pressures. ACS Nano 16.5 (2022): 8064-8075.

[3] C. A. Occhialini *; L. G. Pimenta Martins* et al.  Signatures of pressure-enhanced helimagnetic order in van der Waals multiferroic NiI₂. arXiv preprint arXiv:2306.11720 (2023).

Sobre o palestrante: 
Pesquisador no Laboratório Nacional de Luz Síncrotron (LNLS) desde 2012, atua como responsável da linha de luz IMBUIA no acelerador Sirius. Está principalmente envolvido nos campos de Nano-espectroscopia de Infravermelho Síncrotron, interferometria óptica de campo próximo, design de linhas de luz de infravermelho síncrotron e análise de materiais por espectroscopia de infravermelho. Tem interesse em estudos relacionados à propriedades vibracionais de materiais na nanoescala. Antes de atuar na área de infravermelho e óptica de campo próximo, trabalhou na área de difração de raios-X síncrotron, assunto de seu doutoramento junto a Universidade de São Paulo (USP) e Universidade de Guelph (UoG-Canadá) e posteriormente assunto de seu Post-Doc no LNLS em projeto colaborativo com a Hewllet Packard (HP-Labs/EUA). Ainda como Post-Doc, atuou brevemente como pesquisador visitante no Surface Science Lab no ESRF-França. É revisor de importantes revistas científicas, líder do peer-review committee das linhas de IR-THz e membro do Scientific Advisor committee do Canadian Light Source. Também faz parte de comitês revisores de projetos do Advanced Light Source (Berkeley/USA), Brookhaven National Lab (NY/USA), Diamond Lightsource (Oxford/UK). Antes da vida acadêmica/científica, atuou como Designer em multinacional do setor de combustíveis.

 

• Auditório Abrahão de Moraes no IFUSP;
• Transmissão pública: acompanhe pelo YouTube do IFUSP.