Sharp Superconductor-Insulator Transition in Short Wires

Abstract

Recent experiments on short MoGe nanowires show a sharp superconducting-insulating transition at the universal resistance R Q h= 4e 2 , contrary to the expectation of a smooth temperature dependence of the resistance for such Josephson-like systems. We present a self-consistent renormalization-group treatment of interacting quantum phase slips in short superconducting wires, which reproduces this sharp universal transition. Our method should also apply to other systems in the sine-Gordon universality class, in the previously inaccessible intermediate-coupling regime. DOI: 10.1103/PhysRevLett.98.187001 PACS numbers: 74.78.Na, 73.21.Hb, 74.20.ÿz, 74.40.+k One of the most intriguing problems in low-dimensional superconductivity is the understanding of the mechanism that drives the superconductor-insulator transition (SIT). Experiments conducted on quasi-one-dimensional (1D) systems have shown that varying the resistivity and dimensions of thin metallic wires can suppress superconductivity [1,2], and in certain cases lead to an insulating-like behavior [3][4][5][6].Particularly interesting are recent experiments conducted on short MoGe nanowires [6] that explore the SIT tuned by the wire's normal state resistance with a critical resistance R c R Q . The universal critical resistance may suggest that at a temperature much lower than the meanfield transition temperature, T T c , the wire acts as a superconducting (SC) weak link resembling a Josephson junction (JJ) connecting two SC leads. Schmid [7] and Chakravarty [8] showed that a JJ undergoes a SIT as a function of the junction's shunt resistance, R s , with a critical resistance of R Q , and that the resistance across the junction obeys the power law R T / T 2 R Q =R s ÿ1 . The theory was later extended to JJ arrays and SC wires [9][10][11]. Within these theories, a similar power-law temperature dependence of the resistance at low temperature prevails.Contrary to this prediction, Bollinger et al. [6] observe that the resistance of quasi-1D MoGe nanowires exhibits a much stronger temperature dependence, even close to the SIT. In fact, the resistance could be fitted with a modified LAMH theory [12,13] of thermally activated phase slips down to very low temperatures. Nevertheless, for these narrow wires it appears that the LAMH theory is valid only in a narrow temperature window [14,15]. Moreover, the LAMH analysis does not explain the appearance of a critical resistance R c R Q .We propose an approach that captures both the critical resistance of R c R Q at the SIT and the sharp decay of the resistance as a function of temperature. As in previous works, we treat the SIT in nanowires as a transition governed by quantum phase-slip (QPS) proliferation. This picture alone, however, cannot account for the observed strong temperature dependence of the resistance. We note that in SC wires, collective excitations involving phase and amplitude fluctuations have considerably different propagation velocities. Hence, there is an intermediate regime for which QPSs that occur...

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