Instability of incoherent photons

Ar. Abanov, Andrey V. Chubukov, Alexander M. Finkel’stein

We study the superconductivity in 2D fermionic systems near antiferromagnetic instability, assuming that the pairing is mediated by spin fluctuations. This pairing involves fully incoherent fermions and diffusive spin excitations. We show that the competition between fermionic incoherence and strong pairing interaction yields the pairing instability temperature T ins which increases and saturates as the magnetic correlation length ξ → ∞ . We argue that in this quantum-critical regime the pairing problem is qualitatively different from the BCS one.

A. Ll. Hughes, G. E. M. Jauncey

H. Aswath Babu, Harshawardhan Wanare

We obtain optical instabilities in all-optical bistable systems arising from competing cooperative pathways at low input light levels. In particular, for three-level atomic systems in the $\ensuremath{\Lambda}$ and V configuration interacting with two independent cavity modes, we identify the necessary conditions related to the incoherent pathways required to obtain instabilities. The instabilities arise when atomic states involved in the bistable transition are leaky and have substantial population, where the incoherent processes directly hinder the cooperative preparation of the atomic ensemble.

Guerman A. Pasmanik

A. K. Das

Debanjan Chowdhury, Erez Berg

We construct a family of translationally invariant lattice models with a large number (N) of orbitals at every site coupled together via single-electron tunneling. By tuning the relative strength of the electronic bandwidth and on-site interactions, which have a modified Sachdev-Ye-Kitaev form, we demonstrate a number of unusual features at strong coupling and in the large-N limit. We find examples of (i) an intrinsic non-BCS superconducting instability arising out of an incoherent non-Fermi-liquid metal, and (ii) an instability of an incipient heavy Fermi-liquid metal to superconductivity with transition temperatures comparable to its renormalized bandwidth. At strong coupling, these solvable models display pairing instabilities that are not driven by any special “nesting” properties associated with an underlying Fermi surface.