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Quantum states in low-dimensional spin systems are characterized by their characteristic spin dynamics. In this seminar, I will talk about our recent works on terahertz spectroscopy of quantum spin dynamics in low-dimensional quantum magnets, such as quantum spin dimer, quantum spin chain, and two-dimensional frustrated magnet. I will briefly introduce how spin excitations in a spin system could be probed and magnetic interactions be determined by terahertz spectroscopy [1]. The main focus of the seminar will be on dynamics of a spin-1/2 Heisenberg-Ising antiferromagnetic chain for longitudinal and transverse magnetic fields [2–5]. In addition to the well-known low-energy spin dynamics, I will show that high-energy excitations, such as confined spinons [2] and Bethe strings [3], are realized in the spin chain system for a longitudinal field. Moreover, in a transverse field, our study of spin dynamics allowed us to identify a quantum critical point of the transverse-field Ising-chain [4,5]. The experimental results are well very compared to theoretical calculations, as the spin chain model is exactly solvable [6,7]. In addition, spin dynamics in α-RuCl3, a candidate for realizing quantum spin liquid, will be discussed [8].
Dr. Zhe Wang studied physics in Nanjing Universtity, and obtained his master (2010) and doctor degrees (2015) at the University of Augsburg, Germany. Since 2017, he has been a director’s postdoctoral fellow in the Helmholtz-Center Dresden-Rossendorf, Germany. His research focuses on linear and nonlinear terahertz spectroscopy of condensed matter, particularly on quantum magnetism, unconventional superconductivity, and multiferroics.