Tunable Noninteger Flux Quantum of Vortices in Superconducting Strips

Abstract

Flux quantization has been widely regarded as the hallmark of the macroscopic quantum state of superconductivity. However, practical design of superconductor devices exploiting finite size confinement effects may induce exotic phenomena, including nonquantized vortices. In our research, the magnetic flux of vortices has been studied in a series of superconducting strips as a function of the strip width and the penetration depth. In both circumstances, the observation using scanning Hall probe microscope (SHPM) displays a controlled evolution from singly quantized vortices to nonquantized ones. It is also found that the magnetic flux is immune to the flowing supercurrent. The simulations based on Ginzburg−Landau theory agree well with experimental results. The observed behavior of the vortex flux may open new perspectives for fundamental research and applications based on vortex matter, such as vortex-memory devices and magnetic field traps for ultracold atoms.

Vortex matter and critical magnetic fields in mesoscopic superconducting strips

“…When performing FC as we shown in figure 3, the coherence length as in equation ( 1) corresponds exactly to the value at T f . In the inset of figure 4, we show the temperature dependence of the coherence length derived in [19] from the upper critical field H c2 (T) = Φ 0 /2πµ 0 ξ 2 , which were measured by using the scanning susceptibility microscope [30,31]. The results can be well described by the two-fluid model [32] ξ = 0.24 µm corresponds to T f = 0.9724T c , slightly smaller than the freezing temperature for the above mentioned superconductors.…”

“…The superconducting Pb strips were fabricated using the standard e-beam lithography technique followed by the e-beam evaporation as have been reported in [19]. All the strips have a length of 200 µm, the thickness of 90 nm, and various widths (W = 1, 2, 3, 4, 6, 10, 12 µm).…”