Intermediate bosonic metallic state in the superconductor-insulator transition

Abstract

Whether a metallic ground state exists in a two-dimensional system beyond Anderson localization remains an unresolved question. We studied how quantum phase coherence evolves across superconductor–metal–insulator transitions through magnetoconductance quantum oscillations in nanopatterned high-temperature superconducting films. We tuned the degree of phase coherence by varying the etching time of our films. Between the superconducting and insulating regimes, we detected a robust intervening anomalous metallic state characterized by saturating resistance and oscillation amplitude at low temperatures. Our measurements suggest that the anomalous metallic state is bosonic and that the saturation of phase coherence plays a prominent role in its formation.

Superfluid Properties of Superconductors with Disorder at the Nanoscale: A Random Impedance Model

“…Quite interestingly, the experimental measurements carried out on these compounds have revealed unexpected physical characteristics. Among the open and more controversial issues, there is the emergence of a low-temperature metallic state, called quantum metal: by decreasing the temperature, the resistivity undergoes a superconductivity-driven drop, but it does not vanish and reaches a plateau saturating at a finite value down to the lowest accessible temperatures [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Even when no low-temperature saturation of the resistance is observed, the resistance curves R(T) show a peculiar behavior as a function of the temperature T. Under certain conditions, as it can be an applied magnetic field (for graphene) or an ionic-liquid gating (for TMD), the superconducting transition appears to be very broad, i.e., much broader than one would expected by taking into account only standard superconductive fluctuations [17,18].…”

Free at last: Bose metal uncaged

“…The authors [6] observe three phases with a critical value for the resistance roughly twice the quantum of resistance, R q [5]. The metallic phase persists down to 50mK.…”

“…The experiment [6] utilized a series of high-temperature superconducting YBCO films, which were tuned through the superconductor-insulator transition by reactive-ion-etching (RIE). This technique transfers a patterned array of hexagonally plated holes to YBCO.…”

Film-thickness-driven superconductor to insulator transition in cuprate superconductors

“…variation of film thickness, can be an alternative pathway to derive the SIT in superconducting layers [9][10][11][12][13] . Despite many identifications of SIT [1][2][3][4][5][6][7][8][9][10][11][12][13] , the exact origin has not yet been fully understood. In addition to the film thickness what one intends to control, many other intrinsic and/or extrinsic factors can be involved in significant modifications of electronic conduction [9][10][11][12][13] .…”

“…Despite many identifications of SIT [1][2][3][4][5][6][7][8][9][10][11][12][13] , the exact origin has not yet been fully understood. In addition to the film thickness what one intends to control, many other intrinsic and/or extrinsic factors can be involved in significant modifications of electronic conduction [9][10][11][12][13] . In particular, unconventional cuprate superconductors are vulnerable to disorder due to the presence of nodes in the superconducting gap [14][15][16] .…”