A theoretical preprint predicts distinctive light-driven currents from fluctuating Cooper pairs in a two-dimensional superconductor above its transition temperature. Its calculations suggest that polarization, frequency and the treatment of the pairs’ dynamics could help distinguish thermodynamic nonreciprocity from kinetic nonreciprocity.
A calculation of two kinds of response
The authors modeled a fluctuating pair field with relaxational dynamics using extended time-dependent Ginzburg–Landau equations. The model includes thermodynamic and kinetic Lifshitz invariants, along with noise tied to the fluctuation-dissipation theorem, and derives generalized Aslamazov–Larkin and Maki–Thompson current formulas.
The calculations were checked through a three-layer protocol: symbolic derivation, high-precision quadrature and expansion-free numerical evaluation of the master formulas.
That setup produces an important negative result. FDT locking leaves the model’s equilibrium distribution Gibbsian and unchanged by kinetic invariants, while the odd-in-field linear conductivity vanishes in both current channels. The distinctions reported in the study therefore appear in nonlinear optical and transport responses rather than in that linear term.
Two different fingerprints
In the paper’s C3v case, the thermodynamic Aslamazov–Larkin response has fixed polarization weights of 2:1 after radial integration. The leading kinetic drift instead carries weights of 4:−1. The contrast gives the calculation a possible fingerprint for identifying which form of nonreciprocity is contributing.
The thermodynamic Aslamazov–Larkin response also grows sharply near the transition. At fixed dimensionless frequency, it scales with the square of the Ginzburg–Landau relaxation time, equivalent to an inverse-square dependence on the distance from the transition. This is a model scaling law, not a measured current.
The Maki–Thompson calculation shows a different hierarchy. When pair breaking is weak, its thermodynamic nonlinear response is logarithmically enhanced relative to Aslamazov–Larkin. Trigonal warping alone produces no Maki–Thompson nonlinearity; a vector perturbation such as strain or an in-plane Rashba vector is required. Kinetic invariants are subleading in this channel, and kinetic warping vanishes by angular selection.
The circular-light test
The most distinctive proposed optical marker is a circular photogalvanic response—a dc current that is odd under reversal of light helicity. With reciprocal, momentum-structureless noise, the Aslamazov–Larkin channel is blind to polarization and its circular response is zero for any pair spectrum. In the kinetic Aslamazov–Larkin calculation, the circular master function begins as ν/192 at small dimensionless frequency, peaks near ν=2.2 and has an inverse-cubic tail.
The thermodynamic Maki–Thompson circular response has a different geometry: it is a second-order fluctuation photovoltaic Hall current, running transverse to strain in the strained TMD geometry and along the in-plane magnetic field in the Rashba geometry. The kinetic Maki–Thompson response has another frequency fingerprint: no low-frequency 1/ν quadrature anomaly, an even split between dc photogalvanic and in-phase second-harmonic components, and a sign reversal in the in-phase second harmonic on the stated frequency scale.
A prediction awaiting a test
The paper presents the polarization, frequency and dephasing patterns—especially a circular photogalvanic signal in an Aslamazov–Larkin-dominated regime—as possible ways to separate thermodynamic from kinetic nonreciprocity. The document is arXiv:2608.20166v1, dated 20 Aug 2026, and remains a preprint based on a theoretical model above the superconducting transition. Whether these currents appear in a real material remains to be established.
Paper data and sources
Original title: Photogalvanic transport of nonreciprocal Cooper-pair fluctuations
Authors: Joaquim Telles de Miranda, Alex Levchenko
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-08-20
DOI: Not available
Original paper · Full text