Graduate student Dharma Basaula, Department of Physics, University of Connecticut

Graduate student Bochao Xu, DEpartment of Physics, University of Connecticut

Scanning SQUID Investigation of Time-reversal Symmetry Breaking in Exotic Quantum Materials

Spontaneous breaking of time-reversal symmetry in condensed matter systems arises from correlated electronic arrangements leading to various quantum phenomena, such as ferromagnetism, unconventional superconductivity, and topological states of matter. However, these underlying electronic orders are often difficult to detect experimentally if the magnetism associated with the time reversal symmetry breaking is weak. In such cases, the subtle magnetization and complex domain structure call for investigation by experimental techniques with both high magnetic sensitivity and high spatial resolution. In this dissertation talk, I will discuss my exploration of time-reversal symmetry breaking in two systems: a magnetic Weyl semimetal and a Kagome material detected using scanning superconducting quantum interference device (SQUID) microscopy. Both materials exhibit intriguing magnetic structures which were not detectable by the bulk measurements. We show that the Weyl semimetal hosts a tunable heterogeneous domain structure that is likely linked to its unconventional electronic properties. Additionally, our local probe reveals a ferromagnetic-like state in the Kagome material system, contributing evidence to the highly controversial problem within the community regarding the existence of time-reversal symmetry breaking and its underlying mechanism in this material. These results highlight the significance of quantum sensing in advancing the frontier of new correlated materials, and showcase these materials as an ideal playground for studying the magnetism-electrons interplay.

Graduate student Hanzhen Ma, Department of Physics, University of Connecticut

 

Cooperative radiation has been a long-standing open question in many-body physics. The dipole-dipole interaction between the atoms gives rise to the all-to-all coupling, and can lead to novel collective phenomena. In this talk, I will introduce an integrated method for studying cooperative radiation in many-body systems. This method allows us to study extended systems with arbitrarily large number of particles, and can be formulated by an effective, nonlinear, two-atom master equation that describes the dynamics using a closed form. We apply this method to various systems to demonstrate the appearance of superradiance, subradiance, collective Lamb shift, spin-squeezing and so on. We investigate how the properties of radiation depend on system parameters such as the optical depth and geometry of the system.  

Graduate Student Jonathan Smucker, Department of Physics, University of Connecticut Charge Transfer Collisions Involving Nano-Particles or Large Molecules Charge transfer has been a popular field of study since the advent of quantum mechanics due to its applications to astrophysics, plasma physics, atmospheric science, chemistry, and fundamental physics. Various experimental and theoretical studies have been developed for charge transfer in atom-ion collisions and the process is generally considered well-understood in these systems. However, the models developed for atom-ion collisions are not sufficient to explain charge transfer processes in systems with large molecules, such as fullerenes. The added degrees of freedom in these more complex systems bring many theoretical complications but also many opportunities to explore new types of charge transfer. In this dissertation talk, I will present several models that we have developed to explain different charge transfer processes involving fullerenes. These models are the first to accurately predict many existing experimentally measured charge transfer cross-sections.