Quamtum Critical Dynamics in Many Body Systems

Dr. Jianda Wu (University of California, San Diego)
Event Date and Time: 
Mon, 2016-09-19 12:00 - 13:00
Hennings 318

Thermal and quantum fluctuations, as two fundamental powers, dominate overall thermodynamics and dynamics of many body systems. At zero temperature the many body systems is uniquely driven by quantum fluctuations, and quantum phase transitions arise when ground state energy meets non-analyticity via tuning a non-thermal parameter. Physical properties around quantum critical points (QCPs) are of extensive current interests because the fierce competition between critical quantum and thermal fluctuations near the QCPs can strongly affect dynamics and thermodynamics, leading to unconventional quantum criticality, such as non-Fermi liquid behavior in heavy fermion systems, unconventional superconductivity, exotic spin dynamics in one-dimensional (1D) quantum magnetic systems. However, it remains challenge to analytically understand such real frequency dynamics in strongly-correlated quantum systems, even for the dynamics in the quantum systems of one spatial dimension. The difficulty is largely due to the far-beyond-reach infinite Hilbert space of excited states getting involved in the dynamics, which, however, also strongly indicates new physics lurking inside, as it is shown in the talk. In the talk, motivated by recent experimental progresses, we shall take the challenge via analytically exploring finite temperature local spin dynamics in quantum E8 model emerging near the QCP of 1D transverse-field Ising model, zero-temperature nonlocal transverse spin dynamics in the quantum critical regime of XXZ Heisenberg model, and finite temperature dynamics at the QCP of 3(space)+1(time) quantum ϕ 4 model. During the exciting excursion, sophisticated but powerful theoretical tools were introduced and a bunch of new physics beyond conventional pictures were discovered. Specifically, in quantum E8 model we found spin dynamics beyond conventional spin diffusion picture; in the XXZ Heisenberg model we discovered new dominant dynamic excitations completely beyond classic spinon picture; in the 3+1 quantum ϕ 4 model, we figured out dominant finite temperature dynamics at the QCP with an emerging “thermal” quasiparticle. At the end we shall also discuss the implication of our results for experiments in various relevant materials and suggest proper future experimental setups to test our theoretical findings.

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