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Physics Colloquium, Spring 2019
Thursdays 4:00 p.m., Room 104 Physics
Refreshments served at 3:40 p.m.
Title: Spintronics in Quantum Materials
Abstract: Recent advancements in spintronic techniques originally developed for spin-based devices now enable us to study fundamental spin physics of various quantum materials with unprecedented spin-current control and measurement, opening a new area of theoretical and experimental investigation of quantum systems. In the first half of the talk, we will discuss the development history of spintronics with a concrete example of the evolution of the domain-wall technology in spintronics. In the second part, we will introduce an emerging research area of spin transport in quantum materials which is fueled by the aforementioned advanced spintronic techniques. As examples, we will discuss our researches on quantum phase slips in spin transport through quantum spin chains , which shows how spintronic techniques can be used for probing elusive quantum materials, and long-range spin transport mediated by a vortex liquid in superconductors , which shows that quantum materials can provide novel platforms for efficient spin-transport devices.
 S. K. Kim and Y. Tserkovnyak, “Topological Effects on Quantum Phase Slips in Superfluid Spin Transport,” Phys. Rev. Lett. 116, 127201 (2016)
 S. K. Kim, R. Myers, and Y. Tserkovnyak, "Nonlocal Spin Transport Mediated by a Vortex Liquid in Superconductors," Phys. Rev. Lett. 121, 187203 (2018)
Why Isn’t God Ambidextrous?: Chirality in Nature and the Role it Plays in Physics, Chemistry, and Biology
Title: Approaching the Attosecond keV X-ray Frontier
Abstract: It was demonstrated experimentally in 2001 that the cutoff of high harmonic spectrum could be extended by increasing the center wavelength of driving lasers. In recent years, mJ level, few-cycle, carrier-envelope phase stabilized lasers at 1.6 to 2.1 mm have been developed for generating attosecond X-rays pulses in the water window (282-533 eV). When a 3 mJ, 12 fs laser at 1.7 mm laser was used to implement polarization gating, isolated soft X-rays reaching the carbon K-edge (282 eV) were generated in our laboratory. Isolated X-ray pulses with 53-as duration were characterized by attosecond streaking measurements. Such ultrabroadband light sources are now being used in time-resolved X-ray absorption near edge structure measurements for studying charge dynamics in atoms, molecules and solids. The rapid progress in the development of mid-infrared (MIR) and long wavelength infrared (LWIR), few-cycle, carrier-envelope phase stable lasers with mJ pulse energy at a kilohertz repetition rate opens the door for the generation of the isolated keV attosecond X-ray pulses.
Title: A tale of two states: the complex relationship between superconductivity and magnetism in quantum materials
Abstract: Much of our current technology was enabled by our understanding of semiconductors, whose electrons behave collectively in a similar way as how an individual electron does. In contrast, a hallmark of quantum materials is the emergence of unusual collective electronic behaviors that give rise to fascinating phenomena with unique potential for novel applications. A posterchild is the phenomenon of high-temperature superconductivity, by which materials carry electric currents without dissipation at relatively high temperatures. An important clue to elucidate this highly debated state of matter comes from the observation that it tends to appear in close proximity to the very different phenomenon of magnetism. These two states seem to live a love-hate relationship, displaying a mixture of competition and cooperation. In this talk, I will discuss new and exciting progress on this problem enabled by recent Quantum Monte Carlo simulations of an effective low-energy model.