Search NASA⌕ Search

Engineering topics

Allocca, Andrew A.

Publications and source records attributed to Allocca, Andrew A..

7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Manifestations of spin-orbit coupling in a cuprate superconductor

We report exciting new work on Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212) shows the presence of nontrivial spin-orbit coupling effects as seen in spin-resolved angle-resolved photoemission spectroscopy data. Motivated by these observations we consider how the picture of spin-orbit coupling through local inversion symmetry breaking might be observed in cuprate superconductors. Furthermore, we examine two spin-orbit driven effects, the spin-Hall effect and the Edelstein effect, focusing on the details of their realizations within both the normal and superconducting states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Cavity Quantum Eliashberg Enhancement of Superconductivity

Driving a conventional superconductor with an appropriately tuned classical electromagnetic field can lead to an enhancement of superconductivity via a redistribution of the quasiparticles into a more favorable nonequilibrium distribution—a phenomenon known as the Eliashberg effect. Here, we theoretically consider coupling a two-dimensional superconducting film to the quantized electromagnetic modes of a microwave resonator cavity. As in the classical Eliashberg case, we use a kinetic equation to study the effect of the fluctuating, dynamical electromagnetic field on the Bogoliubov quasiparticles. We find that when the photon and quasiparticle systems are out of thermal equilibrium, a redistribution of quasiparticles into a more favorable nonequilibrium steady state occurs, thereby enhancing superconductivity in the sample. Here, we predict that by tailoring the cavity environment (e.g., the photon occupation and spectral functions), enhancement can be observed in a variety of parameter regimes, offering a large degree of tunability.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Cavity superconductor-polaritons

Following the recent success of realizing exciton-polariton condensates in cavities, we examine the hybridization of cavity photons with the closest analog of excitons within a superconductor, states called Bardasis-Schrieffer modes. Although these modes do not typically couple linearly to light, one can engineer a coupling with an externally imposed supercurrent, leading to the formation of hybridized Bardasis-Schrieffer-polariton states, which we obtain both as poles of the bosonic Green's function and through the derivation of an effective Hamiltonian picture for the model. Here, these new excitations have nontrivial overlap with both the original photon states and d-wave superconducting fluctuations. We conjecture that a phase-coherent density of these objects could produce a finite d-wave component of the superconducting order parameter—an s ± id superconducting state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗