Raman studies of two-dimensional quantum materials under pressure | Colóquio IFUSP

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: 

Possui graduação em Engenharia Química e mestrado em Física, ambos pela Universidade Federal de Minas Gerais (UFMG) e doutorado em Física pelo Massachusetts Institute of Technology (MIT). Durante mestrado e doutorado, investigou materiais bidimensionais (2D) e heteroestruturas de moiré sob altas pressões via diferentes técnicas de espectroscopia óptica, com foco em espectroscopia Raman. Realizou pós-doutorado na Harvard University, como um Harvard Quantum Initiative Postdoctoral Fellow, trabalhando com espectroscopia ótica de equilíbrio e ultrarrápida (THz pump-visible probe) de materiais quânticos, tais quais supercondutores de alta temperatura e multiferróicos. Atualmente é Professor Doutor no Departamento de Física Aplicada no Instituto de Física da USP. Sua área de atuação é Física da Matéria Condensada experimental com ênfase em espectroscopia óptica de materiais quânticos 2D, incluindo materiais atomicamente finos, heteroestruturas de moiré e materiais "bulk" nos quais a física importante está nas camadas 2D.  Tem ampla experiência em espectroscopia Raman, fotoluminescência, reflexão/absorção, dicroísmo linear e técnicas de pump-probe como refletividade e rotação Kerr óptica transiente, e física de altas pressões.

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