Alexander Yu. Zyuzin | Searcharxiv

arXiv2020

Superconductivity in dilute system of sites with strong electron-electron attraction

We consider the effect of strong electron-electron attraction on superconductivity in the dilute system of the negative U-centers. They couple to the conducting electronic states and mediate attraction between electrons. We predict the formation of the local Cooper pairs provided attraction exceeds a certain threshold value. The global coherent superconducting state appears only due to the Andreev scattering between the centers at low temperatures. The dependence of the superconducting transition temperature and the second critical magnetic field on attraction strength is calculated.

cond-mat.supr-con↗

arXiv2019

Disorder-driven exceptional lines and Fermi ribbons in tilted nodal-line semimetals

We consider the impact of disorder on the spectrum of three-dimensional nodal-line semimetals. We show that the combination of disorder and a tilted spectrum naturally leads to a non-Hermitian self-energy contribution that can split a nodal line into a pair of exceptional lines. These exceptional lines form the boundary of an open and orientable bulk Fermi ribbon in reciprocal space on which the energy gap vanishes. We find that the orientation and shape of such a disorder-induced bulk Fermi ribbon is controlled by the tilt direction and the disorder properties, which can also be exploited to realize a twisted bulk Fermi ribbon with nontrivial winding number. Our results put forward a paradigm for the exploration of non-Hermitian topological phases of matter.

cond-mat.mes-hall↗