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Fluctuation-response relation as a probe of long-range correlations in nonequilibrium quantum and classical fluids
1Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742, USA; Department of Physics and Institute for Fundamental Science, University of Oregon, Eugene, Oregon 97403, USA; and Materials Science Institute, University of Oregon, Eugene, Oregon 97403, USA.
Physical Review. E
|May 17, 2024
Summary
Researchers found a modified fluctuation-response relation for nonequilibrium steady states. This allows studying long-range correlations in quantum fluids using response experiments, even in the collisionless regime.
Area of Science:
- Non-equilibrium statistical mechanics
- Condensed matter physics
- Quantum fluids
Background:
- Studying systems out of thermodynamic equilibrium is challenging due to the lack of a simple fluctuation-dissipation theorem.
- Nonequilibrium steady states exhibit unique correlation behaviors not seen in equilibrium systems.
Purpose of the Study:
- To establish a modified fluctuation-response relation for nonequilibrium steady states.
- To investigate long-range correlations in fermionic quantum fluids under a temperature gradient.
- To probe these correlations through response experiments.
Main Methods:
- Analysis of commutator correlation functions and their relation to bilinear response functions.
- Comparison of classical and quantum fluid behavior in hydrodynamic and collisionless regimes.
- Investigation of velocity fluctuations and their impact on correlations.
Main Results:
- A modified fluctuation-response relation is established for systems in a nonequilibrium steady state with a constant temperature gradient.
- This relation connects commutator correlation functions to bilinear response, applicable to both quantum and classical systems.
- Long-range correlations, similar to classical fluids, are found in fermionic quantum fluids, persisting into the collisionless regime with modified singularity behavior.
Conclusions:
- The modified fluctuation-response relation provides a new tool for studying nonequilibrium systems, particularly quantum fluids.
- Response experiments can probe long-range correlations where direct fluctuation observation is difficult.
- The transition from hydrodynamic to collisionless regimes alters velocity fluctuations and correlation singularities.
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