Scientific Council of the Landau Institute, Friday, October 20, 2017, Landau Institute, 11:30 am L. Ioffe. M. Feigel'man Mikrovolnovye svoistva sverkhprovodnikov vblizi perekhoda v izolyator Predlozhena osnova teorii kollektivnykh mod v sil'no neuporyadochennykh sverkhprovodnikakh, nakhodyashchikhsya vblizi kvantovogo perekhoda v dielektricheskoe sostoyanie. Pokazano, chto s priblizheniem parametrov sverkhprovodnika k kvantovoi kriticheskoi tochke, v spektre vozbuzhdenii s neizbezhnost'yu voznikaet nenulevaya plotnost' nizkolezhashchikh (s energiyami sushchestvenno nizhe sverkhprovodyashchei shcheli) sostoyanii. Pri eshche bol'shem besporyadke eti podshchelevye sostoyaniya okazyvayutsya delokalizovannymi, chto dolzhno privodit' k zametnoi dissipatsii v mikrovolnovom otklike. 
Laboratory building, room 122
Moscow Institute of Physics and Technology
Dolgoprudny, Russia
contact email address: nanotheory@phystech.edu (head M.V.Feigel'man, deputy head I.V.Zagorodnev)
Research topics


Scientific Council of the Landau Institute, Friday, October 6, 2017, Landau Institute, 11:30 am Igor Poboiko and Mikhail Feigel'man Paraconductivity of pseudogapped superconductors We calculate AslamazovLarkin paraconductity for a model of strongly disordered superconductors (dimensions d=2,3) with a large pseudogap whose magnitude strongly exceeds transition temperature T_{c}. We show that, within Gaussian approximation over Cooperpair fluctuations, paraconductivity is just twice larger that the classical AL result at the same ε = (TT_{c})/T_{c}. Upon decreasing ε, Gaussian approximation is violated due to local fluctuations of pairing fields that become relevant at ε < ε_{1} « 1. Characteristic scale ε_{1} is much larger than the width ε_{2} of the thermodynamical critical region, that is determined via the Ginzburg criterion, ε_{2} ≈ ε_{1}^{d}. We argue that in the intermediate region ε_{2} < ε < ε_{1} paraconductivity follows the same AL power law, albeit with another (yet unknown) numerical prefactor. At further decrease of the temperature, all kinds of fluctuational corrections become strong at ε < ε_{2}; in particular, conductivity occurs to be strongly inhomogenuous in real space. 