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Fundamental dissipation due to bound fermions in the zero-temperature limit
S Autti1, S L Ahlstrom2, R P Haley2
1Department of Physics, Lancaster University, Lancaster, LA1 4YB, UK. s.autti@lancaster.ac.uk.
Nature Communications
|September 22, 2020
Summary
In superfluid 3He, moving objects cause damping via Andreev-bound states, not bulk pair breaking. These bound states exhibit complex dynamics, with one timescale much longer than expected.
Area of Science:
- Condensed matter physics
- Superfluidity
- Quantum phenomena
Background:
- Fermionic condensates possess a ground state protected by an isotropic gap.
- Gap suppression in regions like surfaces and vortex cores creates Andreev-bound states.
- These states were thought to compromise the condensate's protection.
Purpose of the Study:
- To investigate the role of Andreev-bound states in superfluid 3He.
- To understand the origin of damping when objects move in superfluid 3He at critical velocities.
- To characterize the dynamics and interactions of these bound states.
Main Methods:
- Theoretical analysis of superfluid 3He dynamics.
- Investigation of Andreev-bound state behavior around a moving macroscopic object.
- Identification of timescales governing bound state dynamics.
Main Results:
- Damping of a moving object in superfluid 3He primarily arises from Andreev-bound states, not bulk pair breaking.
- Two distinct timescales govern the dynamics of these bound states.
- One observed timescale for bound state dynamics is significantly longer than predicted.
- Andreev-bound states do not interact with bulk excitations in the superfluid.
Conclusions:
- Andreev-bound states play a crucial, non-trivial role in the dissipation mechanisms of superfluid 3He.
- The dynamics of bound states are more complex than previously understood, with implications for superfluid behavior.
- The findings challenge existing models of protection and dissipation in fermionic condensates.
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