Title: Symmetry and Correlation Aspects of Quantum Dynamics
Speaker: Congjun Wu (UCSD)
Abstract: Symmetry and correlation are two fundamental aspects of condensed matter studies, and they also play important roles in quantum dynamics. In analogy to crystal and the Bloch theorem which set up the symmetry foundation of condensed matter physics, we propose the concept of “dynamic crystal”, which applies for a large class of systems including laser-driven solid crystals, dynamic photonic crystals and optical lattices, and generalize the Bloch theorem for the dynamic crystal. It includes both the static crystal and the Floquet system as special cases, and also ex-tends to systems with intertwined space-time symmetries but neither spatial nor temporal perio-dicities. A new mathematic group structure, “space-time group”, which augments space group with dynamic non-symmorophic symmetries of “time-screw-rotation” and “time-glide-reflection”, are constructed to classify dynamic crystals. We also studied the real frequency re-sponses at high energies in strongly correlated systems, which is a hardcore problem of con-densed matter physics. Our new progress is to employ integrable methods to theoretically inves-tigate the Bethe string states, which are exotic many-body spin excitations, in quantum spin dy-namics. Their dominant role in quantum spin dynamics is identified when spin chains are close to the field-tuned criticality. These states have been observed for the first time in the electron-spin-resonance spectroscopy measurement on SrCo2V2O8, and we identified their appearance as a se-ries of characteristic spectra lines.
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