Interest in the superconducting proximity effect has been reinvigorated recently by novel optoelectronic applications as well as by the possible emergence of the elusive majorana fermion at the interface between topological insulators and superconductors. Here we produce high-temperature superconductivity in Bi 2 se 3 and Bi 2 Te 3 via proximity to Bi 2 sr 2 CaCu 2 o 8 + δ , to access higher temperature and energy scales for this phenomenon. This was achieved by a new mechanical bonding technique that we developed, enabling the fabrication of highquality junctions between materials, unobtainable by conventional approaches. We observe proximity-induced superconductivity in Bi 2 se 3 and Bi 2 Te 3 persisting up to at least 80 K-a temperature an order of magnitude higher than any previous observations. moreover, the induced superconducting gap in our devices reaches values of 10 mV, significantly enhancing the relevant energy scales. our results open new directions for fundamental studies in condensed matter physics and enable a wide range of applications in spintronics and quantum computing.

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Coupling the surface state of a topological insulator to an s-wave superconductor is predicted to produce the long-sought Majorana quasiparticle excitations. However, superconductivity has not been measured in surface states when the bulk charge carriers are fully depleted, that is, in the true topological regime relevant for investigating Majorana modes. Here we report measurements of d.c. Josephson effects in topological insulator-superconductor junctions as the chemical potential is moved through the true topological regime characterized by the presence of only surface currents. We compare our results with three-dimensional quantum transport simulations, and determine the effects of bulk/surface mixing, disorder and magnetic field; in particular, we show that the supercurrent is largely carried by surface states, due to the inherent topology of the bands, and that it is robust against disorder. Our results thus clarify key open issues regarding the nature of supercurrents in topological insulators.

We report a nuclear magnetic resonance (NMR) study of Bi2Se3 single crystals grown by three different methods. All the crystals show 9 well-resolved peaks in their 209 Bi NMR spectra of the nuclear quadrupolar splitting, albeit with an intensity anomaly. Spectra at different crystal orientations confirm that all the peaks are purely from the nuclear quadrupolar effect, with no other hidden peaks. We identify the short nuclear transverse relaxation time (T2) effect as the main cause of the intensity anomaly. We also show that the 209 Bi signal originates exclusively from bulk, while the contribution from the topological surface states is too weak to be detected by NMR. However, the bulk electronic structure in these single crystals is not the same, as identified by the NMR frequency shift and nuclear spin-lattice relaxation rate (1/T1). The difference is caused by the different structural defect levels. We find that the frequency shift and 1/T1 are smaller in samples with fewer defects and a lower carrier concentration. Also, the low temperature power law of the temperature-dependent 1/T1 (∝ T α ) changes from the Korringa behavior α = 1 in a highly degenerate semiconductor (where the electrons obey Fermi statistics) to α < 1 in a less degenerate semiconductor (where the electrons obey Boltzmann statistics).2

We report the demonstration of hybrid high-T c -superconductor-semiconductor tunnel junctions, enabling new interdisciplinary directions in condensed matter research. The devices are fabricated by our newly developed mechanical-bonding technique, resulting in high-T c -superconductor-semiconductor tunnel diodes. Tunneling-spectra characterization of the hybrid junctions of Bi 2 Sr 2 CaCu 2 O 8þ combined with bulk GaAs, or a GaAs/AlGaAs quantum well, exhibits excess voltage and nonlinearity, similarly to spectra obtained in scanning-tunneling microscopy, and is in good agreement with theoretical predictions for a Superconductors enable the implementation of fast ultrasensitive detectors [1,2] and large-scale quantumcomputation technology [3,4]. These materials pose major scientific and technological challenges, however. A potential alternative avenue may be provided by hybrid semiconductor-superconductor devices, which have been attracting growing attention lately as they combine the controllability of semiconductor structures with the macroscopic quantum states of superconductors [5,6]. The interaction of light with semiconductor-superconductor structures has recently emerged as a new interdisciplinary field of superconducting optoelectronics, with demonstrations of light emission from hybrid light-emitting diodes [7,8] enhanced by the superconducting state [9,10], and various proposals for novel lasers [11] and quantum light sources [12,13]. These hybrid devices have also proven useful in nonlinear electronics [14,15] and infrared detection [16], taking advantage of the relatively small size of the superconducting gap in the tunneling spectrum [17]. All previously studied semiconductor-superconductor devices were based on conventional low-criticaltemperature (low-T c ) superconductors, requiring cooling to extremely low temperatures. Moreover, the small superconducting gaps of these materials limit the energy scales over which they can be employed. A high operating temperature and large d-wave gaps can be obtained by incorporating unconventional high-T c superconductors [18,19] that exhibit a variety of novel phenomena and provide a more practical alternative for device implementation. Furthermore, by combining high-T c materials with semiconductors, one could take advantage of mature semiconductor technology to probe the unconventional nature of high-T c superconductors [20] in hybrid tunneling junctions.Tunneling spectroscopy is among the most widely used techniques for the study of novel materials and new phenomena in condensed matter physics [21]. Various effects have been observed with tunneling spectroscopy such as weak localization [22], superconducting-gap dependence on a magnetic field [23], bound states and broken symmetries in high-T c superconductors [24], as well as studies of the pseudogap, preformation of Cooper pairs [25], and electron-hole asymmetry [26]. These experiments usually require sophisticated and expensive scanning-tunneling spectroscopy equipment. A simple method of constructing high