Quantum fluctuations in percolating superconductors: an evolution with effective dimensionality

Abstract

We investigate percolating films of superconducting nanoparticles and observe an evolution from superconducting to metallic to insulating states as the surface coverage of the nanoparticles is decreased. We demonstrate that this evolution is correlated with a reduction in the effective/dominant dimensionality of the system, from 2D to 1D to 0D, and that the physics in each regime is dominated by vortices, phase slips and tunnelling respectively. Finally we construct phase diagrams that map the various observed states as a function of surface coverage (or, equivalently, normal state resistance), temperature and measurement current.

Percolating transport in superconducting nanoparticle films

“…Finally, we do in fact observe BKT behaviour in high coverage (small R N ) samples at lower currents -see for example the data in Fig. 8(a) at voltages less than $10 À4 V. The BKT transition in these samples is, however, complex 22 and here we simply note that vortex unbinding is observed for I < I c , whilst percolative behaviour in the form of Eq. (1) is associated with the regime I > I c .…”

“…Percolation theory provides significant insight into the behavior of disordered superconducting systems such as granular films [1][2][3][4][5][6][7][8][9][10] and artificial Josephson-Junction (JJ) arrays, [11][12][13] and is especially relevant to the critical behavior of superconducting systems. [14][15][16][17][18][19][20][21][22] More specifically, in twodimensional (2D) superconducting systems, percolation underpins our understanding of the superconductor-insulator transitions in both granular [7][8][9][10] and thin film [19][20][21][23][24][25][26] systems, the effects of inter-particle connectivity on system conductivity, 6,7,27,28 and the nature of the superconducting-normal state transition. 13,18,[29][30][31][32] This understanding impacts on important technological issues; for example, an understanding of percolative transport between grains has been used to engineer an increase in the current-carrying capacity in high temperature superconductors (HTSCs).…”

“…2] is observed for the low R N samples and is discussed elsewhere. 22 The paper is organized as follows: Section II summarizes the aspects of percolation theory (and previous experimental studies) that are relevant to the present work and Sec. III describes the preparation of samples and measurement techniques; Section IV describes the experimental results, focusing first on the measured V(I) curves, and then the determination of I c which finally shows that the data are well represented by Eq.…”

Substrate mediated nitridation of niobium into superconducting Nb2N thin films for phase slip study

“…Hence, the dissipation related to current-induced unbound vortex-antivorex movement can also be disregarded. In reduced dimension, phase fluctuation is one of the dominant mechanisms behind the resistive tailing & residual resistance 44 and above T BKT , the phase fluctuation leads to vortex proliferation which eventually brings the system to the normal state 45 . In quasi 0D granular superconductors, depending on the dimension of the nano-grains, phase fluctuations can lead to total suppression of superconductivity and may lead to even an insulating state 46,47 .…”

Phase Slips and Metastability in Granular Boron-doped Nanocrystalline Diamond Microbridges

“…Despite the fact that these films are clearly three-dimensional, as evidenced by the fitting to the EEI theory, the residual resistance below T c has features reminiscent of the Langer-Ambegaokar-McCumber-Halperin (LAMH) [14,15] behaviors commonly seen in one-dimensional superconductors. The appearance of 1D phenomena in higher dimensional systems has recently been reported in systems such as percolating films of Pb nanoparticles [35], and Pb x (SiO 2 ) 1−x nanocrystalline films [36]. The various theories of thermally activated phase slips all predict a resistance below T c of the activated tunneling form…”