Dichotomy in short superconducting nanowires: Thermal phase slippage vs. Coulomb blockade

Abstract

PACS. 74.78.Na -Mesoscopic and nanoscale systems. PACS. 73.23.Hk -Coulomb blockade; single-electron tunneling.Abstract. -Quasi-one-dimensional superconductors or nanowires exhibit a transition into a nonsuperconducting regime, as their diameter shrinks. We present measurements on ultrashort nanowires (∼40-190 nm long) in the vicinity of this quantum transition. Properties of all wires in the superconducting phase, even those close to the transition, can be explained in terms of thermally activated phase slips. The behavior of nanowires in the nonsuperconducting phase agrees with the theories of the Coulomb blockade of coherent transport through mesoscopic normal metal conductors. Thus it is concluded that the quantum transition occurs between two phases: a "true superconducting phase" and an "insulating phase". No intermediate, "metallic" phase was found.Under certain conditions, usually associated with a critical resistance per square [1,2], critical total resistance [3][4][5][6], or a characteristic diameter [7,8], a wire made of a superconducting metal looses its superconductivity and acquires two signatures of insulating behavior: i) The resistance increasing with cooling and ii) a zero-bias resistance peak [3,4]. There are many models that capture certain features of the SIT in 1D wires. Some rely on the "fermionic" mechanism, in which disorder combined with electron-electron repulsion suppresses the critical temperature, T c , to zero [9]. In other, "bosonic", models the order parameter remains nonzero in the "insulating" phase while the coherence is destroyed by proliferating quantum phase slips (QPS) [10][11][12][13][14][15]. Existing theoretical models frequently predict a quantum superconductor-insulator transition (SIT) in thin wires [11,13,16,17], driven, in many cases, by the interaction of the fluctuating phase with the Caldeira-Leggett environment [18]. Conditions that make QPS experimentally observable and the relation of the QPS to the SIT are still being actively researched [1][2][3][4][5][6][7][8][19][20][21][22].Here we present a quantitative analysis of the transport properties of ultrashort nanowires in each of the two phases -the insulating phase and the superconducting phase. We show that the insulating phase is characterized by the normal-electron transport and governed by the Coulomb blockade physics [23,24]. The wires in the superconducting phase exhibit good agreement with the Langer-Ambegaokar-McCumber-Halperin (LAMH) theory of thermally activated phase slips (TAPS) [25][26][27], without any QPS contribution. The TAPS physics is dominant, even in the vicinity of the SIT. Thus we conclude that the observed transition c EDP Sciences

Zero-bias anomaly in homogeneously disordered MoGe nanowires undergoing a superconductor-insulator transition

“…It can be found from the formula The zero bias anomaly in short a-Mo 78 Ge 22 nanowires was carefully studied in Ref. [26]. The nanowires were fabricated by deposition of material on top of suspended carbon nanotubes; the length was varied over a range of 40-150 nm.…”

“…In particular, even in the absence of morphological or structural defects, coherent scattering can occur at the nanowire -rectangular electrode connection because of the discontinuity in the number of quantum channels. This was one of the arguments to suggest coherent-scatterer Coulomb blockade as the origin of the ZBA in very short (50-150 nm) MoGe nanowires 26 . To verify this possibility, we fabricated and tested several wires with electrodes gradually narrowing to nanowire width.…”

“…To reveal the origin of the ZBA in nanowires, we carried out low-temperature transport measurements on MoGe nanowires spanning the length from 150 nm to 11 µm. In contrast to previous studies 26,27,28,29,30 , we used the advantage of our fabrication method, high-resolution electron-beam lithography, and fabricated and studied several nanowire-based structures with varying size and geometries of electrodes and with a side gate. We have not found any change in the ZBA parameters in these more complex nanowire-based devices; this allowed us to consider and reject several physical processes thought to be responsible for ZBA.…”

Sharp Superconductor-Insulator Transition in Short Wires

“…For the wires in Ref. [6], the applicability of LAMH is marginal as T 0:9T c , and estimates for T G range between 0:85T c and 0:94T c (see Table I). This is in contrast to the well established fit of the LAMH theory to tin whisker crystals [15], where the theory is applicable for 1 10 ÿ5 < < 0:1, and the range of fitting was 1:1 10 ÿ4 < < 3:5 10 ÿ4 .…”

“…This is in contrast to the well established fit of the LAMH theory to tin whisker crystals [15], where the theory is applicable for 1 10 ÿ5 < < 0:1, and the range of fitting was 1:1 10 ÿ4 < < 3:5 10 ÿ4 . Comparison between the theory (solid line) and the experimental data [6]. Details of the wires, and fitting parameters, are summarized in Table I.…”