Condensed Matter Seminar

Abstract: Controlling phases of matter with light is a central goal in condensed matter physics. I will present new theories of light–matter interaction that show how light shapes and drives instabilities in quantum materials across electronic, structural, and collective-mode sectors. First, I show that resonant optical absorption can drive layer sliding in van der Waals flakes (e.g. in CrI3, MoTe2, MoSe2) via nonlinear light–matter coupling.

Abstract: Semiconductor moiré lattices provide a flexible platform to study flat, topological bands that host a variety of closely competing many-body ground states. In this talk, I will present single-electron transistor microscopy of WSe2 bilayers at low twist angles, which reveals rich interplay between magnetism, correlations, and topology. At zero magnetic field, we observe a series of quantum anomalous Hall states and demonstrate topological phase transitions as a function of twist angle and electric field.

Abstract: Crystals with layered structures have recently attracted tremendous research interest. In these materials, individual layers are held together by relatively weak van der Waals interactions and can be exfoliated into atomically thin sheets. A variety of metastable stacking configurations can emerge in such systems, which can be further exploited to tune their physical properties through twistronics and slidetronics.

(Pizza will be served.)

Abstract: Nontrivial topological defects such as knotted solitons called hopfions have been observed in a variety of materials including chiral magnets, nematic liquid crystals and even in ferroelectrics as well as studied in other physical contexts such as Bose-Einstein condensates.  These topological entities can be modeled using the relevant physical variable, e.g., magnetization, polarization or the director field.  Specifically, we find exact static soliton solutions for the unit spin vector field of an inhomogeneous, anisotropic three-dimensional (3D) Heisenberg ferro

Abstract: Photocathodes—materials that convert photons into electrons through the photoelectric effect (explained by Einstein)—are important for many modern technologies that rely on light detection or electron-beam generation. However, existing photocathode materials have become increasingly difficult to meet the performance requirements of related cutting-edge technology upgrades. Most of these materials, and the theory (Spicer’s three-step model) to understand their photoemission properties, were discovered and established more than 60 years ago.

Abstract: Time-reversed pairs of topological bands with opposite Chern numbers are commonly found in moiré superlattices based on transition metal dichalcogenides. Recent experimental breakthroughs have demonstrated that these topological bands provide a rich platform for realizing fractional quantum matter at zero external magnetic fields.

Abstract: Lithium-ion battery is featured by structural and chemical complexities across a broad range of length scales and, ultimately, it is the hierarchy of the battery structure that determines its functionality. Investigating battery function, degradation, and failure mechanisms requires a comprehensive exploration encompassing structural, chemical, mechanical, and dynamic perspectives.

Abstract: The Hall effect [1] is widely used to probe the electronic structure of materials and has found applications in various electronic devices. Research on the Hall effect has expanded to include related phenomena such as the anomalous Hall effect, the spin Hall effect, and the quantum Hall effect. More recently, these studies have been extended to the nonlinear regime [2].

Abstract: The antiferromagnetic ground state of the two-dimensional Hubbard model on a square lattice at half-filling was shown to become ferromagnetic with the addition of a single hole for infinite e-e repulsion (Nagaoka, 1966). However, Nagaoka ferromagnetism has not been seen in naturally occurring solid-state materials. The advent of synthetic platforms - atoms in optical lattices, and quantum dots/dopant clusters in semiconductors has led us to study Hubbard-like models on large finite lattices using DMRG techniques.