Abstract
In fermionic superfluids that are charge neutral, Nambu-Goldstone (NG) modes also known as Anderson-Bogoliubov modes emerge as a result of spontaneous symmetry breaking. Here, we discuss DC transport properties of such NG modes through a quantum point contact. We show that contrary to a naive view that enhancement of the phase stiffness may suppress transport of the NG modes, there must be an anomalous contribution that survives at low temperature. This contribution originates from the conversion process between the condensate and NG mode. We find that within the BCS regime the anomalous contribution is enhanced with increasing channel transmittance and attractive interaction, and leads to a temperature-dependent Lorenz number and absence of the bunching effect in current noise.
Highlights
In mesoscopic transport phenomena through small constrictions, quantum-mechanical effects are known to be directly reflected in transport coefficients
We demonstrate that the naive view mentioned above is partially correct in that the exchange process of the NG modes between reservoirs is suppressed at low temperature
> μ, T, we conclude that the current contributions related to the NG modes are absent in charged superconductors
Summary
In mesoscopic transport phenomena through small constrictions, quantum-mechanical effects are known to be directly reflected in transport coefficients. The prototype example is a superconducting point contact where reservoirs consist of superconductors [4,5] In this case, it is known that the direct current does not obey Ohm’s law [4,5]. A two-terminal transport setup with a quantum point contact has been realized in experiments of ultracold Fermi gases [8], which observed the conductance quantization [9] and nonlinear current-bias characteristics [10]. It must be noted, that the presence or absence of charge may cause a difference in transport between elec-.
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