Guest seminar: New emergent phases at the interface of 2D materials

Dirac fermions to excitonic insulators—2D materials host a range of exotic states as a result of quantum confinement. Due to the very nature of 2D materials, these states appear at the surface, making them susceptible to external disturbances from their immediate surroundings. Deliberate manipulation of such interactions by tuning chemical potential, or pressure, can give rise to novel emergent states and lead to novel functional devices. We aim to study surfaces and interfaces of 2D materials by external perturbations such as electric field and pressure.

In the first part of the talk, I will demonstrate a large-area passivation layer for graphene, a single layer of Carbon, by mechanical transfer of ultrathin Ga₂O₃ synthesized on the surface of liquid Ga metal [1]. Electrical measurements of millimeter-scale passivated and bare CVD graphene on SiO₂ substrate indicate that the passivated graphene maintains its high field effect mobility, desirable for applications. Surprisingly, the temperature-dependent resistivity is reduced in our passivated graphene over a range of temperatures below 230 K, due to the interplay of screening of the remote optical phonon modes of SiO₂ by the high dielectric constant of Ga₂O₃, and the relatively high characteristic phonon frequencies of Ga₂O₃. Raman spectroscopy and electrical measurements indicate that Ga₂O₃ passivation also protects graphene from further processing such as plasma-enhanced atomic layer deposition of Al₂O₃.

It is well-known that when a 2D magnetic material is proximitized with a 2D non-magnetic material, a magnetic proximity effect is induced through the interface which can often lead to new quantum states. We are interested in understanding the physical mechanism responsible for this effect and how it can be strengthened by application of pressure. In the second part of the talk, I will first introduce how we customized the pressure cell to make it suitable for measuring van der Waals heterostructures in our cryostat. I will further discuss our investigations of the complex magnetism in a Kagome metal, Yb_0.5Co₃Ge₃, under pressure.

REFERENCES
[1] M. Gebert, S. Bhattacharyya et al., Nano Lett., 23, 363 (2023).

[2] Zhiyuan Cheng, Yaojia Wang, Heng Wu, Mazhar N. Ali, Julia Y. Chan, and Semonti Bhattacharyya, arXiv:2410.23872