The tunability of the chemical potential for a wide range encompassing the Dirac point is important for many future devices based on topological insulators. Here we report a method to fabricate highly efficient top gates on epitaxially grown (Bi_{1-x
}Sb_x)2Te3 topological insulator thin films without degrading the film quality. By combining an in situ deposited Al2O3 capping layer and a SiN_x dielectric layer deposited at low temperature, we were able to protect the films from degradation during the fabrication processes. We demonstrate that by using this top gate, the carriers in the top surface can be efficiently tuned from n- to p-type. We also show that magnetotransport properties give evidence for decoupled transport through top and bottom surfaces for the entire range of gate voltage, which is only possible in truly bulk-insulating samples.
The existence of topological superconductors preserving time-reversal symmetry was recently predicted, and they are expected to provide a solid-state realization of itinerant massless Majorana fermions and a route to topological quantum computation.
Their first concrete example, CuxBi2Se3, was discovered last year, but the search for new materials has so far been hindered by the lack of guiding principle. Here, we report point-contact spectroscopy experiments showing that the low-carrier-density superconductor Sn_{1-x}In_{x}Te is accompanied with surface Andreev bound states which, with the help of theoretical analysis, give evidence for odd-parity pairing and topological superconductivity. The present and previous finding of topological superconductivity in Sn_{1-x}In_{x}Te and CuxBi2Se3 demonstrates that odd-parity pairing favored by strong spin-orbit coupling is a common underlying mechanism for materializing topological superconductivity.
Recently, it was proposed that phonons are specularly reflected below about 0.5 K in ordinary single-crystal samples of high-T_c cuprates, and that the low-temperature thermal conductivity should be analyzed by fitting the data up to 0.5 K using an a
rbitrary power law. Such an analysis yields a result different from that obtained from the conventional analysis, in which the fitting is usually restricted to a region below 0.15 K. Here we show that the proposed new analysis is most likely flawed, because the specular phonon reflection means that the phonon mean free path ell gets LONGER than the mean sample width, while the estimated ell is actually much SHORTER than the mean sample width above 0.15 K.
