Topological insulators are characterized by an insulating bulk with a finite band gap and conducting edge or surface states, where charge carriers are protected against backscattering. These states give rise to the quantum spin Hall effect without an external magnetic field, where electrons with opposite spins have opposite momentum at a given edge. The surface energy spectrum of a threedimensional topological insulator is made up by an odd number of Dirac cones with the spin locked to the momentum. The long-sought yet elusive Majorana fermion is predicted to arise from a combination of a superconductor and a topological insulator. An essential step in the hunt for this emergent particle is the unequivocal observation of supercurrent in a topological phase. Here, we present the first measurement of a Josephson supercurrent through a topological insulator. Direct evidence for Josephson supercurrents in superconductor (Nb) - topological insulator (Bi2Te3) - superconductor e-beam fabricated junctions is provided by the observation of clear Shapiro steps under microwave irradiation, and a Fraunhofer-type dependence of the critical current on magnetic field. The dependence of the critical current on temperature and length shows that the junctions are in the ballistic limit. Shubnikov-de Haas oscillations in magnetic fields up to 30 T reveal a topologically non-trivial two-dimensional surface state. We argue that the ballistic Josephson current is hosted by this surface state despite the fact that the normal state transport is dominated by diffusive bulk conductivity. The lateral Nb-Bi2Te3-Nb junctions hence provide prospects for the realization of devices supporting Majorana fermions

Oxide heterostructures often exhibit unusual physical properties that are absent in the constituent bulk materials. Here, we report an atomically sharp transition to a ferromagnetic phase when polar antiferromagnetic LaMnO3 (001) films are grown on SrTiO3 substrates. For a thickness of six unit cells or more, the LaMnO3 film abruptly becomes ferromagnetic over its entire area, which is visualized by scanning superconducting quantum interference device microscopy. The transition is explained in terms of electronic reconstruction originating from the polar nature of the LaMnO3 (001) films. Our results demonstrate that functionalities can be engineered in oxide films that are only a few atomic layers thick.

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)

Combining topology and superconductivity provides a powerful tool for investigating fundamental physics as well as a route to fault-tolerant quantum computing. There is mounting evidence that the Fe-Based superconductor FeTe 0.55 Se 0.45 (FTS) may also be topologically non-trivial. Should the superconducting order be s ± , then FTS could be a higher order topological superconductor with Helical Hinge Zero Modes (HHZM).To test the presence of these modes we've fabricated normal-metal/superconductor junctions on different surfaces via 2D atomic crystal heterostructures. As expected, junctions in contact with the hinge reveal a sharp zero-bias anomaly that is absent when tunneling purely into the c-axis. Additionally, the shape and suppression with temperature are consistent with highly coherent modes along the hinge and are incongruous with other origins of zero bias anomalies. Furthermore, additional measurements with soft-point contacts in bulk samples with various Fe interstitial contents demonstrate the intrinsic nature of the observed mode. Thus we provide evidence that FTS is indeed a higher order topological superconductor.ASSOCIATED CONTENT: Supporting information available. Supporting information includes details regarding: exfoliation and fabrication of devices, experimental measurement setup, additional crystal measurements, and additional controls and checks performed on the devices.

The pyrochlore compounds Ho 2 Ti 2 O 7 and Dy 2 Ti 2 O 7 show an exotic form of magnetism called the spin ice state, resulting from the interplay between geometrical frustration and ferromagnetic coupling. A fascinating feature of this state is the appearance of magnetic monopoles as emergent excitations above the degenerate ground state. Over the past years, strong effort has been devoted to the investigation of these monopoles and other properties of the spin ice state in bulk crystals. A tantalising prospect is to incorporate spin ice materials into devices for spintronics and devices that can manipulate the magnetic monopoles. This would require the availability of spin ice thin films. Here, we report the fabrication of Ho 2 Ti 2 O 7 thin films using pulsed laser deposition. These films not only show a high crystalline quality, but also exhibit the hallmarks of a spin ice: a pronounced magnetic anisotropy and an intermediate plateau in the magnetisation along the [111] crystal direction.The magnetic Ho 3+ ions in Ho 2 Ti 2 O 7 form a lattice of corner-sharing tetrahedra in the pyrochlore structure and interact via ferromagnetic coupling 1-7 . Their magnetic moments are Ising-like due to the crystal field anisotropy and are aligned along the set of ‹111› axes. The resulting degenerate ground state of each tetrahedron has two holmium spins pointing inwards and two holmium spins pointing outwards. This is the so-called "ice rule", from the analogy with the H-O bond lengths in solid water. A local breaking of the ice rule, due to the flipping of one holmium spin shared between two neighbouring tetrahedra, results in a 3-in-1-out and a 1-in-3-out configuration. This effectively creates a positive and a negative magnetic charge in the adjacent tetrahedra 8 , which can be regarded as a monopole-antimonopole pair 9-10 . Such pairs can dissociate and the individual monopoles can move away from each other by flipping a chain of spins along their route. This process takes place without further violating the ice rule, so that the energy cost for the monopoles to be brought to infinity stays finite, being linked to the energy required for the first excitation. Signatures of emergent magnetic monopoles in bulk spin ice crystals have been observed by several groups [11][12][13][14][15] . The magnetic counterparts of two fundamental effects in electronics have also been demonstrated: a basic capacitor effect for magnetic charges 16 and the introduction of magnetic defects hindering the monopole flow, similar to residual defectinduced resistance for electrons 17 . Further effort has been dedicated to tune the monopole chemical potential in a range where mutual interaction plays a role, to mimic electronic correlations in a purely magnetic Coulomb gas 18 . In conjunction with all the mentioned experiments, the term "magnetricity" is coined to describe the flow of magnetic charges as the equivalent of electricity.However, until now all experiments on spin ice materials have been performed on bulk crystals. The possibility of ma...

The exploration of new materials, novel quantum phases, and devices requires ways to prepare cleaner samples with smaller feature sizes. Initially, this meant the use of a cleanroom that limits the amount and size of dust particles. However, many materials are highly sensitive to oxygen and water in the air. Furthermore, the ever-increasing demand for a quantum workforce, trained and able to use the equipment for creating and characterizing materials, calls for a dramatic reduction in the cost to create and operate such facilities. To this end, we present our cleanroom-in-a-glovebox, a system that allows for the fabrication and characterization of devices in an inert argon atmosphere. We demonstrate the ability to perform a wide range of characterization as well as fabrication steps, without the need for a dedicated room, all in an argon environment. Finally, we discuss the custom-built antechamber attached to the back of the glovebox. This antechamber allows the glovebox to interface with ultra-high vacuum equipment such as molecular-beam epitaxy and scanning tunneling microscopy.

We study Andreev reflection and Josephson currents in topological bilayer exciton condensates (TECs). These systems can create 100% spin-entangled nonlocal currents with high amplitudes due to perfect nonlocal Andreev reflection. This Andreev reflection process can be gate tuned from a regime of purely retro reflection to purely specular reflection. We have studied the bound states in TEC-topological-insulator-TEC Josephson junctions and find a gapless dispersion for perpendicular incidence. The presence of a sharp transition in the supercurrent-phase relationship when the system is in equilibrium is a signature of fractional charge, which can be further revealed in ac measurements faster than relaxation processes via Landau-Zener processes.

Scanning nano-focused X-ray diffraction and high-angle annular dark-field scanning transmission electron microscopy are used to investigate the crystal structure of ramp-edge junctions between superconducting electron-doped Nd1.85Ce0.15CuO4 and superconducting hole-doped La1.85Sr0.15CuO4 thin films, the latter being the top layer. On the ramp, a new growth mode of La1.85Sr0.15CuO4 with a 3.3° tilt of the c-axis is found. We explain the tilt by developing a strain accommodation model that relies on facet matching, dictated by the ramp angle, indicating that a coherent domain boundary is formed at the interface. The possible implications of this growth mode for the creation of artificial domains in morphotropic materials are discussed.