Kavli Affiliate: Jing Wang
| First 5 Authors: Linghao Huang, Jing Wang, , ,
| Summary:
We develop a theory of the nonlinear optical responses in superconducting
systems in the presence of a dc supercurrent. The optical transitions between
particle-hole pair bands across the superconducting gap are allowed in clean
superconductors as the inversion-symmetry-breaking by supercurrent. Vertex
correction is included in optical conductivity to maintain the $U(1)$ gauge
symmetry in the mean-field formalism, which contains the contributions from
collective modes. We show two pronounced current dependent peaks in the
second-order nonlinear optical conductivity $sigma^{(2)}(omega)$ at the gap
edge $2hbaromega=2Delta$ and $hbaromega=2Delta$, which diverge in the
clean limit. We demonstrate this in the models of single-band superconductor
with $s$-wave and $d$-wave pairings, and Dirac fermion systems with $s$-wave
pairing. Our theory predicts the current induced peak in
$text{Im}[sigma^{(2)}(omega)]$ is proportional to square of the supercurrent
density in the $s$-wave single-band model, with the same order of magnitude as
the recent experimental observation of second-harmonic generation in NbN by
Nakamura et al. [Phys. Rev. Lett. 125, 097004 (2020)]. The supercurrent induced
nonlinear optical spectroscopy provides a valuable toolbox to explore novel
superconductors.
| Search Query: ArXiv Query: search_query=au:”Jing Wang”&id_list=&start=0&max_results=3