Suppression of the superconductivity in ultrathin amorphous Mo78Ge22 films observed by STM

Abstract

In contact with a superconductor a normal metal modifies its properties due to Andreev reflection. In the current work the local density of states (LDOS) of superconductor-normal metal Mo 78 Ge 22 -Au bilayers are studied by means of STM applied from the Au side. Three bilayers have been prepared on silicate glass substrate consisting of 100, 10 and 5 nm MoGe thin films covered always by 5 nm Au layer. The tunneling spectra were measured at temperatures from 0.5 to 7 K. The two-dimensional cross-correlation between topography and normalized zero-bias conductance indicates a proximity effect between 100 and 10 nm MoGe thin films and Au layer where a superconducting gap slightly smaller than that of bulk MoGe is observed. The effect of the thinnest 5 nm MoGe layer on Au leads to much smaller gap moreover the LDOS reveals almost completely suppressed coherence peaks. This is attributed to a strong pair-breaking effect of spin-flip processes at the interface between MoGe films and the substrate.

Melting of the Vortex Lattice through Intermediate Hexatic Fluid in an a−MoGe Thin Film

“…In contrast, the ratio ∆(0)/(k B T ∆ ) hovers between 2 and 2.5, as expected for a strongcoupling type-II superconductor. The emergence of a pseudogap between T c and T ∆ , coupled with the anomalously large value of ∆(0)/(k B T c ) signals a departure from the BCS ( or Fermionic ) scenario 113,129,131 for a-MoGe films with a thickness below 5 nm.…”

“…These discoveries have led to the unexpected breakdown of the frequently mentioned Fermionic and Bosonic dichotomy and necessitate a new microscopic description of superconductivity under conditions of strong disorder. It appears to be a common feature in many superconductors such as TiN, NbN and MoGe that the same system can follow the Fermionic route at moderate disorder and crossover to a Bosonic scenario at a stronger disorder 127,[129][130][131] . It is therefore interesting to investigate whether a system can follow the Fermionic route all the way to the disorder level where the superconducting ground state is completely destroyed.…”

Exploring the impact of core expansion on the vortex distribution in superconducting–normal-metal hybrid nanostructures

“…As a result, a nanostructured superconducting-normal-metal bilayer is created. The STS measurements directly show the presence of a minigap in the Au layer [27,28], which allows us to directly observe the vortex distributions in the mesoscopic squares as a function of the applied magnetic field [8]. To understand the observed vortex distributions in both nanostructures,…”

Superconductivity suppression in disordered films: Interplay of two-dimensional diffusion and three-dimensional ballistics

“…It is usually assumed that T c is a material property and does not depend on the sample size. However there is a strong experimental evidence of the systematic decrease of the critical temperature in disordered superconducting films with decreasing its thickness, d (V [1], NbN [2][3][4][5][6][7][8][9], TiN [10], MoGe [11,12], MoSi [13,14], MoC [15], WRe [16], InO [17] etc. [18]).…”