Strong suppression of the resistivity near the superconducting transition in narrow microbridges in external magnetic fields

Abstract

We have investigated a series of superconducting bridges based on homogeneous amorphous WSi andMoSi films, with bridge widths w ranging from 2 to 1000 and film thicknesses ~ 4 − 6 nm and 100 nm. Upon decreasing the bridge widths below the respective Pearl lengths, we observe in all cases distinct changes in the characteristics of the resistive transitions to superconductivity. For each of the films, the resistivity curves R(B,T) separate at a well-defined and field-dependent temperature * ( ) with decreasing the temperature, resulting in a dramatic suppression of the resistivity and a sharpening of the transitions with decreasing bridge width w. The associated excess conductivity in all the bridges scales as 1⁄ , which may suggest the presence of a highly conducting region that is dominating the electric transport in narrow bridges. We argue that this effect can only be observed in materials with sufficiently weak vortex pinning.It is generally accepted that the superconductivity in superconducting bridges can be suppressed by gradually reducing their dimensions. While sufficiently thick and wide bridges reflect the properties of the bulk material, wide strips with a reduced thickness ≲ (where is the Ginzburg-Landau coherence length) can be viewed as quasi two-dimensional [1]. Their properties are then strongly influenced by the thickness d, with a certain reduction of the transition temperature to a zero-resistance state [2][3][4][5]. Upon further narrowing a bridge down towards to the one-dimensional (1D) limit < , the critical temperature decreases exponentially with the inverse of the cross section of the bridges[6], leading to a transition to insulating state in the 1D limit [6][7][8][9][10].Placing a type-II superconducting strip into an external magnetic field, magnetic-field-induced vortices can exist as long as > 4.4 [11]. In very thin films, vortices can interact in a different way than in their bulk peers, namely via their stray fields in the surrounding space. The characteristic length scale for this interaction is given by the Pearl length = 2 2 ⁄ , which can be substantially larger than the London penetration depth [12]. In wide bridges, where the bridge width w is larger than all length scales that are relevant for superconductivity, the vortex-vortex interactions are long-range logarithmic as a function of distance r for r < , and they determine the superconducting properties in clean enough samples. It has been suggested that in narrow bridges w < , the vortex-vortex interaction becomes short-range exponential for vortex-vortex separations r > w/π [13], thereby excluding aBerezinskii-Kosterlitz-Thouless (BKT) transition [14,15]. While in this low-field limit, surface barriers also play an important role [16], they are negligible in the high-field limit B ~ Bc2. In this letter we study the transition to superconductivity for amorphous superconducting films in this high-field limit, as a function of the bridge width w for w < and w > .We have fabricated micro-bridges based on four amorphous WSi and...

Different Single-Photon Response of Wide and Narrow Superconducting MoxSi1−x Strips

“…Both samples are characterized by a magnetic field penetration depth λ(0) of 708 nm and a Pearl length Λ(0) of 303 µm, as calculated from their resistivity and T c values. These estimates are in line with the values deduced from a recent experiments 13,14 and ensure that w Λ(0) for both detectors. Here, w is the strip width.…”

Size dependent nature of the magnetic-field driven superconductor-to-insulator quantum-phase transitions

“…This may prohibit the formation of a long-range ordered vortex lattice. As we recently demonstrated in similar superconducting microbridges 37 , an extra pinning effect for bridge widths smaller than Q(0) prohibits the vortices from moving, leading to a strong suppression of the resistivity even near the normal-to-superconductor transition at the critical temperature + # (4) (see also Supplementary Fig. 7).…”

“…Preparation and characterization of the WSi bridges. We fabricated a series of superconducting microbridges on a single 10 × 10 mm " amorphous WSi thin film with thickness d = 4 nm 36,37 , spanning the range of bridge widths w over almost three decades from 2 µm to 1000 µm. The amorphous nature of our films is illustrated in Fig.…”

“…The stray field in a 2D system is mainly mediated by the effective penetration depth Q = 2R 3 " ? ⁄ , with R 3 the London penetration depth, which is Q(0) ≈ 350 µm in our case 36,37 . For an infinitely large 2D superconducting thin film in a strong magnetic field, vortices localize due to the long-range logarithmic repulsive interactions S &'4 ∝ ln(Q/W), where W is the distance between two vortices.…”

Resistive transition of hydrogen-rich superconductors

“…phonons). However, for materials where the observed T c does not solely depend on the electron-phonon interaction (in particular, in cuprates [51,53,54], pnictides [75][76][77] and nickelates [78,79]), but instead on the thermodynamic fluctuations [58,[80][81][82][83], the presence of pseudogap [84,85], structural disorder [86][87][88][89], system dimensionality [90][91][92][93][94] or other mechanisms [95][96][97][98] for charge carrier wave function distortions, our equations (11) and (12) might not be a good fitting tool (however, it does not necessarily mean that in some cases these equations will still be a good fitting tool). Based on all the above, alternative R(T, B) models may be developed for other types of materials.…”