Proximity effects at the interface of a superconductor and a topological insulator in NbN - Bi_2Se_3 thin film bilayers

In a search for a simple proximity system of a topological insulator and a superconductor for studying the role of surface versus bulk effects by gating, we report here on a first step toward this goal, namely the choice of such a system and its characterization. We chose to work with thin film bilayers of grainy 5 nm thick NbN films as the superconductor, overlayed with 20 nm thick topological layer of $\rm Bi_2Se_3$ and compare the transport results to those obtained on a 5 nm thick reference NbN film on the same wafer. Bilayers with ex-situ and in-situ prepared $\rm NbN-Bi_2Se_3$ interfaces were studied and two kinds of proximity effects were found. At high temperatures just below the superconducting transition, all bilayers showed a conventional proximity effect where the topological $\rm Bi_2Se_3$ suppresses the onset or mid-transition $T_c$ of the superconducting NbN films by about 1 K. At low temperatures, a cross-over of the resistance versus temperature curves of the bilayer and reference NbN film occurs, where the bilayers show enhancement of $T_c(R=0)$, $I_c$ (the supercurrent) and the Andreev conductance, as compared to the bare NbN films. This indicates that superconductivity is induced in the $\rm Bi_2Se_3$ layer at the interface region in between the NbN grains. Thus an inverse proximity effect in the topological material is demonstrated.Comment: 8 pages, 11 figure

M{\o}ller Energy-Momentum Complex of a Static Axially Symmetric Vacuum Space-Time

The energy and momentum densities associated with the Weyl metric are calculated using M{\o}ller's energy-momentum complex. These results are compared with the results obtained by using the energy-momentum complexes of Einstein, Landau and Lifshitz, Papapetrou and Bergmann. We show that the aforementioned different prescriptions and that of M{\o}ller do not give the same energy density, while give the same momentum density.Comment: LATEX, 9 pages, no figures, an improved version, references added, corrections [Admin note: substantial overlap with gr-qc/0403097, gr-qc/0404108 , gr-qc/0303009 , hep-th/0311050

In defense of science—What would John do?

Recent onslaughts on the importance of pure research to our collective well-being are trending. In this essay, I discuss the issues involved and offer a rebuttal. The thoughts are inspired by my mentor, academic sibling, and idol John Leask Lumley

Single-Particle Spectrum of Pure Neutron Matter

We have calculated the self-consistent auxiliary potential effects on the binding energy of neutron matter using the Brueckner Hartree Fock approach by adopting the Argonne V18 and CD-Bonn potentials. The binding energy with the four different choices for the self-consistent auxiliary potential is discussed. Also, the binding energy of neutron matter has been computed within the framework of the self-consistent Green s function approach. We also compare the binding energies obtained in this study with those obtained by various microscopic approaches.Comment: 5 pages,4 figures in Journal of the Physical Society of Japan Volume 84, Issue 3 (March 15, 2015) Journal of the Physical Society of Japan Volume 84, Issue 2 (February 15, 2015). arXiv admin note: text overlap with arXiv:1310.1547 by other author