MSE Seminar: Mit Naik

Event interval: Single day event
Campus room: SIG 134
Accessibility Contact: Matthew Yankowitz, myank@uw.edu
Event Types: Lectures/Seminars

Title: Emergence of Moiré Excitons and Taco-Shaped Flat Bands in Twisted Transition Metal Dichalcogenides.

Abstract: Moiré patterns of 2D van der Waals materials have proven to be an ideal platform to host unusual correlated electronic phases, emerging magnetism, and novel exciton physics. In this talk, I will present state-of-the-art first-principles calculations revealing how structural reconstruction, flat electronic bands, and moiré localization collectively shape excitonic states in twisted transition metal dichalcogenide (TMD) heterostructures. These calculations uncover distinct excitonic states with different spatial and optical characteristics and provide microscopic design principles for tailoring excitonic properties in moiré materials. Our predictions have been validated through close collaborations with experiments including reflection contrast spectroscopy, electron energy-loss spectroscopy, and scanning tunneling spectroscopy.
Moiré physics in large twist angles have received relatively less attention since the K valley states are largely decoupled between layers at such angles and the superlattice exhibits minimal structural reconstruction. I will discuss our surprising discovery of a new kind of valley system in bilayer transition metal dichalcogenides twisted to a large magic angle, where interlayer hybridization between like-spin Λ valleys generates extended, spin-polarized flat bands with quasi-one-dimensional dispersion. These “taco"-shaped valleys form six anisotropic channels that interconnect across the moiré Brillouin zone, exhibiting alternating spin polarization under sixfold rotation, reminiscent of altermagnetic textures. The flat band shows a power-law divergent density of states due to its quasi-one-dimensional character, enhancing the potential for correlated phases. A direct consequence of this flat band observed recently is the emergence of phonon-assisted intervalley absorption peaks in reflection contrast spectra measurements.

Bio: Mit Naik is an assistant professor in the physics department at the University of Texas at Austin working in the field of computational condensed matter physics and material science. His research particularly targets electronic and optical excitations in nanostructured quantum materials studied using first-principles electronic-structure calculations. He obtained his Ph.D. in physics at the Indian Institute of Science, Bangalore, and held a postdoctoral position at the University of California, Berkeley.