An array of superconducting islands placed on a normal metal film offers a tunable realization of nanopatterned superconductivity. This system enables investigation of the nature of competing vortex states and phase transitions between them. A square array creates the eggcrate potential in which magnetic field-induced vortices are frozen into a vortex insulator. We observed a vortex insulator-vortex metal transition driven by the applied electric current and determined critical exponents that coincided with those for thermodynamic liquid-gas transition. Our findings offer a comprehensive description of dynamic critical behavior and establish a deep connection between equilibrium and nonequilibrium phase transitions.

Abstractmagnified imageThe surface of a three‐dimensional (3D) topological insulator is conducting and the topologically nontrivial nature of the surface states is observed in experiments. It is the aim of this paper to review and analyze experimental observations with respect to the magnetotransport in Bi‐based 3D topological insulators, as well as the superconducting transport properties of hybrid structures consisting of superconductors and these topological insulators. The helical spin‐momentum coupling of the surface state electrons becomes visible in quantum corrections to the conductivity and magnetoresistance oscil‐lations. An analysis will be provided of the reported magnetoresistance, also in the presence of bulk conductivity shunts. Special attention is given to the large and linear magnetoresistance. Superconductivity can be induced in topological superconductors by means of the proximity effect. The induced supercurrents, Josephson effects and current–phase relations will be reviewed. These materials hold great potential in the field of spintronics and the route towards Majorana devices. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A scanning SQUID microscope was used to image vortex trapping as a function of the magnetic induction during cooling in thin-film YBa2Cu3O 7−δ (YBCO) strips for strip widths W from 2 to 50 µm. We found that vortices were excluded from the strips when the induction Ba was below a critical induction Bc. We present a simple model for the vortex exclusion process which takes into account the vortex -antivortex pair production energy as well as the vortex Meissner and self-energies. This model predicts that the real density n of trapped vortices is given by n = (Ba − BK )/Φ0 with BK = 1.65Φ0/W 2 and Φ0 = h/2e the superconducting flux quantum. This prediction is in good agreement with our experiments on YBCO, as well as with previous experiments on thin-film strips of niobium. We also report on the positions of the trapped vortices. We found that at low densities the vortices were trapped in a single row near the centers of the strips, with the relative intervortex spacing distribution width decreasing as the vortex density increased, a sign of longitudinal ordering. The critical induction for two rows forming in the 35 µm wide strip was (2.89 + 1.91 − 0.93)Bc, consistent with a numerical prediction.

We demonstrate topological insulator (Bi 2 Te 3 ) dc SQUIDs, based on superconducting Nb leads coupled to nano-fabricated Nb-Bi 2 Te 3 -Nb Josephson junctions. The high reproducibility and controllability of the fabrication process allows the creation of dc SQUIDs with parameters that are in agreement with design values. Clear critical current modulation of both the junctions and the SQUID with applied magnetic fields have been observed. We show that the SQUIDs have a periodicity in the voltage-flux characteristic of Φ 0 , of relevance to the ongoing pursuit of realizing interferometers for the detection of Majorana fermions in superconductor-topological insulator structures.

Abstract. A Josephson supercurrent has been induced into the three-dimensional topological insulator Bi 1.5 Sb 0.5 Te 1.7 Se 1.3 .We show that the transport in Bi 1.5 Sb 0.5 Te 1.7 Se 1.3 exfoliated flakes is dominated by surface states and that the bulk conductivity can be neglected at the temperatures where we study the proximity induced superconductivity. We prepared Josephson junctions with widths in the order of 40 nm and lengths in the order of 50 to 80 nm on several Bi 1.5 Sb 0.5 Te 1.7 Se 1.3 flakes and measured down to 30 mK. The Fraunhofer patterns unequivocally reveal that the supercurrent is a Josephson supercurrent. The measured critical currents are reproducibly observed on different devices and upon multiple cooldowns, and the critical current dependence on temperature as well as magnetic field can be well explained by diffusive transport models and geometric effects. ‡ Current address: