Phase diagram of the strongly disordereds-wave superconductor NbN close to the metal-insulator transition

Abstract

We present a phase diagram as a function of disorder in three-dimensional NbN thin films, as the system enters the critical disorder for the destruction of the superconducting state.The superconducting state is investigated using a combination of magnetotransport and tunneling spectroscopy measurements. Our studies reveal 3 different disorder regimes. At low disorder (k F l~10-4), the system follows the mean field Bardeen-Cooper-Schrieffer behavior where the superconducting energy gap vanishes at the temperature where electrical resistance appears. For stronger disorder ( k F l<4 ) a "pseudogap" state emerges where a gap in the electronic spectrum persists up to temperatures much higher than T c , suggesting that Cooper pairs continue to exist in the system even after the zero resistance state is destroyed. Finally, at even stronger disorder (k F l<1) the global superconducting ground state is completely destroyed, though superconducting correlations continue to survive as evidenced from a pronounced magnetoresistance peak at low temperatures. *

Amplitude, density, and current correlations of strongly disordered superconductors

“…14 Moreover, the observation of a pseudogap in strongly disordered SC films [8][9][10][11][12][13] bears some resemblance to similar experimental findings in high-temperature superconductors [15][16][17] that may suggest a common mechanism in some regions of the phase diagram.…”

“…NbN, InO x and TiN. [8][9][10][11][12][13] It is then crucial to assess how this inhomogeneous SC state affects the behavior of the amplitude, density and current correlations, in order to interpret the results of the various experimental probes.…”

Paraconductivity of pseudogapped superconductors

“…Strongly disordered superconductors near quantum phase transition into an insulator state attract great interest during last years [1][2][3][4][5][6][7][8][9][10][11][12][13] . On experimental side [5][6][7][8][9][10][11][12][13][14] , new methods which became available, like low-temperature scanning tunneling spectroscopy which makes it possible to study properties of superconducting state locally with a nanometer-scale resolution.…”

“…On experimental side [5][6][7][8][9][10][11][12][13][14] , new methods which became available, like low-temperature scanning tunneling spectroscopy which makes it possible to study properties of superconducting state locally with a nanometer-scale resolution. As a result 5,6 an existence of a strong density-of-states (DoS) suppression at temperatures much above the superconducting transition T c was demonstrated.…”

Collective modes and ultrasonic attenuation in a pseudogapped superconductor

“…Strongly disordered superconductors near quantum phase transition QPT) into an insulator state became again an object of great interest during last decade, both on experimental side [1][2][3][4][5][6][7][8][9] and among theorists [12][13][14][15] (references given above are certainly incomplete, due to a large number of papers in the field). On experimental side, revival of the interest to this subject comes about due to new methods which became available.…”