Abstract: Applications of thermoelectric materials span from powering space missions through waste heat recovery, up to cooling medical products in remote environments. Furthermore, this field is a remarkable platform for exploring functionality of ideas appearing within condensed-matter physics. The thermoelectric community has recently been focused on exotic phenomena, which can lead to extreme reduction of phonon propagation. While the number of notable experimental observations in a few past years has been significant, the connection between crystal structure and transport properties is frequently still under-discussed. In the first part of this seminar, I will address one of the difficulties in this area, namely I will discuss the significance of rattling in the context of phonon transport. The original approach in the literature was correlating the rattling behavior with low reported values of lattice thermal conductivity. Further research undermined this concept, as it turned out that rattling in the conventional clathrates is localized in narrow frequency range, hence its overall effect on bulk properties must be limited. We show, that some of the unconventional (pnictide-based) clathrates can be built from a variety of cavities in its crystal structure, spanning to sizes much bigger than observed ever before. As shown by phonon dispersion, such crystal structure leads to dense ladder of flat, ultra-low lying optical modes that significantly contribute to scattering of acoustic phonons; i.e. we have shown that rattling can have a vital influence on some materials. Proper understanding of the thermal transport in structurally complex materials will be crucial for developing the next generation of thermoelectrics and other functional materials. In the second part of the talk, I will show that zinc-antimonides can also be fascinating from electronic and magnetic perspective. The 2019 discovery in Toberer lab has revealed Kagome compounds AV₃Sb₅ (A = K, Cs, Rb), that intertwine complex quantum phenomena: topological band structures, charge density waves, and superconductivity. The curious properties seem to emerge from Kagome net of vanadium atoms. We recently obtained a new grant focused on exploration of broad chemical space for novel materials with frustrated vanadium nets and emergent electronic effects. I will describe our research plan therein, combining experiments with state-of-the-art calculations, and discuss our first findings.

Bio: Kamil Ciesielski is a Research Associate at Physics Department, Colorado School of Mines. He obtained his B.S. and M.E. from Gdansk University of Technology in Poland and PhD from Institute of Low Temperature and Structure Research, Polish Academy of Sciences. His work focuses primarily on thermoelectricity and crystallographic disorder. Chemical systems he studied span from half-Heusler phases, binary chalcogenides, clathrates and other Zintl phases, as well as various intermetallics. In 2021 he received Graduate Student Award from International Thermoelectric Society. Currently, he is working on the application of his expertise in thermal transport  to novel functional materials, including solid-state electrolytes.

Abstract: The 2023 Nobel Prize in Chemistry was awarded for the discovery and synthesis of quantum dots, often referred to as “artificial atoms”, due to their discrete electronic energy levels resembling those of natural atoms. Since their discovery, quantum dots have been widely utilized in bioimaging, energy harvesting, illumination, displays, machine vision, and communications. Recently, significant progress has been made in creating single artificial atoms with excellent quantum coherence properties, enabling the development of quantum devices based on these artificial atoms. In this talk, I will discuss several ongoing experiments in my group that showcase the unique advantages of solid-state artificial atoms in studying quantum optics and advancing quantum technologies. A key feature of solid-state artificial atoms is their compatibility with various devices (e.g., photonic, acoustic, electronic) defined on their host material. This compatibility allows us to experimentally investigate the resonance fluorescence of a strongly driven atom in novel regimes, where the atom is simultaneously influenced by both longitudinal (σz-driven) and transverse (σx-driven) fields. Remarkably, our observations reveal distinct features in the resonance fluorescence spectrum as we modulate the Rabi frequency of the σx drive across the frequency of the σz drive field, including the cancellation of the central spontaneous spectral line and the anti-crossing of different sidebands. The experimental results align well with our theoretical calculations and can be effectively explained using a dynamically-dressed-state framework. Additionally, I will discuss another ongoing experiment that leverages strong light-matter interactions in a quantum nanophotonic device to develop a deterministic source of photonic graph states. These photonic graph states are crucial resources in optical quantum computing and all-photonic quantum repeaters. I will discuss our experimental progresses, as well as our theory proposal for generating loss-tolerant photonic graph states using only a single quantum dot. Moving forward, solid-state artificial atoms also offer tremendous opportunities for studying quantum many-body physics. I will discuss some of these opportunities at the end of my talk, including the study of photon-mediated many-body interactions defined by a structured photonic bath, and electron-spin mediated interactions among a bath of nuclear spins.

Bio: Shuo Sun is an Assistant Professor of Physics and an Associate Fellow of JILA at the University of Colorado Boulder. Before joining the University of Colorado Boulder in Fall 2020, he worked at Stanford University as a postdoctoral fellow and later as a research scientist in the Ginzton Lab. Sun received his B.S. in Zhejiang University (2011), and his M.S. (2015) and Ph.D. (2016) from the University of Maryland College Park. Sun is a recipient of the Sloan Research Fellowship and the Ralph E. Powe Junior Faculty Enhancement Awards.