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Amplitude Mode in Quantum Magnets via Dimensional Crossover
Chengkang Zhou1, Zheng Yan1,2, Han-Qing Wu3
1Department of Physics and HKU-UCAS Joint Institute of Theoretical and Computational Physics, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China.
Physical Review Letters
|June 21, 2021
Summary
Researchers observed the Higgs mode in quantum magnets by studying quasi-one-dimensional spin chains. This amplitude mode, crucial for understanding phase transitions, was detected using advanced simulation techniques.
Area of Science:
- Condensed Matter Physics
- Quantum Magnetism
Background:
- The amplitude (Higgs) mode is associated with longitudinal fluctuations during continuous spontaneous symmetry breaking phase transitions.
- Observing the amplitude mode in quantum magnets is challenging due to its rapid decay into low-energy Goldstone excitations.
Purpose of the Study:
- To investigate the amplitude mode in a quasi-one-dimensional geometry, overcoming observational challenges.
- To analyze the behavior and characteristics of the amplitude mode in weakly coupled spin chains.
Main Methods:
- Quantum Monte Carlo simulations
- Stochastic analytic continuation
- Chain-mean field approach
- Mapping to the field-theoretic sine-Gordon model
Main Results:
- The amplitude mode was observed in the longitudinal spin susceptibility under a weak symmetry-breaking staggered field.
- The singlet bond mode, a common measure in higher dimensions, appeared at a lower frequency than the amplitude mode.
- These excitations correspond to the second and first breathers of the sine-Gordon theory, respectively.
- Amplitude and bond order fluctuations carry significant spectral weight in the quasi-1D limit, unlike in higher dimensions.
Conclusions:
- The quasi-1D geometry provides a viable pathway to study the elusive amplitude mode in quantum magnets.
- The findings offer new insights into the nature of excitations and phase transitions in low-dimensional quantum systems.
- The study successfully links experimental observations to theoretical models like the sine-Gordon theory.
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