We calculate the zero-temperature differential conductance dI/dV of a voltage-biased one-dimensional junction between a nontopological and a topological superconductor for arbitrary junction transparency using the scattering matrix formalism. We consider two representative models for the topological superconductors: (i) spinful p-wave and (ii) s-wave with spin-orbit coupling and spin splitting. We verify that in the tunneling limit (small junction transparencies) where only single Andreev reflections contribute to the current, the conductance for voltages below the nontopological superconductor gap Delta(s) is zero and there are two symmetric conductance peaks appearing at eV = +/-Delta(s). with the quantized value (4-pi)2e(2)/h due to resonant Andreev reflection from the Majorana zero mode. However, when the junction transparency is not small, there is a finite conductance for e vertical bar V vertical bar \< Delta(s) arising from multiple Andreev reflections. The conductance at eV = +/-Delta(s). in this case is no longer quantized. In general, the conductance is particle-hole asymmetric except for sufficiently small transparencies. We further show that, for certain values of parameters, the tunneling conductance from a zero-energy conventional Andreev bound state can be made to mimic the conductance from a true Majorana mode.

}, issn = {2469-9950}, doi = {10.1102/PhysRevB.95.020501}, author = {Setiawan, F. and Cole, William S. and Sau, Jay D. and S. Das Sarma} } @article { ISI:000413372300001, title = {Ising quantum criticality in Majorana nanowires}, journal = {PHYSICAL REVIEW B}, volume = {96}, number = {13}, year = {2017}, month = {OCT 20}, issn = {2469-9950}, doi = {10.1103/PhysRevB.96.134517}, author = {Cole, William S. and Sau, Jay D. and S. Das Sarma} } @article { ISI:000413442100006, title = {Strong-coupling phases of the spin-orbit-coupled spin-1 Bose-Hubbard chain: Odd-integer Mott lobes and helical magnetic phases}, journal = {PHYSICAL REVIEW A}, volume = {96}, number = {4}, year = {2017}, month = {OCT 23}, issn = {2469-9926}, doi = {10.1103/PhysRevA.96.043622}, author = {Pixley, J. H. and Cole, William S. and Ian B Spielman and Rizzi, Matteo and S. Das Sarma} } @article {ISI:000401997600008, title = {Transport in superconductor-normal metal-superconductor tunneling structures: Spinful p-wave and spin-orbit-coupled topological wires}, journal = {PHYSICAL REVIEW B}, volume = {95}, number = {17}, year = {2017}, month = {MAY 22}, pages = {174515}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We theoretically study transport properties of voltage-biased one-dimensional superconductor-normal metal-superconductor tunnel junctions with arbitrary junction transparency where the superconductors can have trivial or nontrivial topology. Motivated by recent experimental efforts on Majorana properties of superconductor-semiconductor hybrid systems, we consider two explicit models for topological superconductors: (i) spinful p-wave, and (ii) spin-split spin-orbit-coupled s-wave. We provide a comprehensive analysis of the zero-temperature dc current I and differential conductance dI/dV of voltage-biased junctions with or without Majorana zero modes (MZMs). The presence of an MZM necessarily gives rise to two tunneling conductance peaks at voltages eV = +/-Delta(lead), i.e., the voltage at which the superconducting gap edge of the lead aligns with the MZM. We find that the MZM conductance peak probed by a superconducting lead without a BCS singularity has a nonuniversal value, which decreases with decreasing junction transparency. This is in contrast to the MZM tunneling conductance measured by a superconducting lead with a BCS singularity, where the conductance peak in the tunneling limit takes the quantized value GM = (4 - pi)2e(2)/h independent of the junction transparency. We also discuss the {\textquoteleft}{\textquoteleft}subharmonic gap structure{{\textquoteright}{\textquoteright}}, a consequence of multiple Andreev reflections, in the presence and absence of MZMs. Finally, we show that for finite-energy Andreev bound states (ABSs), the conductance peaks shift away from the gap bias voltage eV = +/-Delta(lead) to a larger value set by the ABSs energy. Our work should have important implications for the extensive current experimental efforts toward creating topological superconductivity and MZMs in semiconductor nanowires proximity coupled to ordinary s-wave superconductors.}, \%\%Address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA

}, issn = {2469-9950}, doi = {10.1103/PhysRevB.95.174515}, author = {Setiawan, F. and Cole, William S. and Sau, Jay D. and S. Das Sarma} } @article { ISI:000383235000012, title = {Induced spectral gap and pairing correlations from superconducting proximity effect}, journal = {PHYSICAL REVIEW B}, volume = {94}, number = {12}, year = {2016}, month = {SEP 6}, issn = {2469-9950}, doi = {10.1103/PhysRevB.94.125304}, author = {Chiu, Ching-Kai and Cole, William S. and S. Das Sarma} } @article {ISI:000390349100003, title = {Proximity effect and Majorana bound states in clean semiconductor nanowires coupled to disordered superconductors}, journal = {PHYSICAL REVIEW B}, volume = {94}, number = {14}, year = {2016}, month = {OCT 27}, pages = {140505}, abstract = {We model a semiconductor wire with strong spin-orbit coupling which is proximity-coupled to a superconductor with chemical potential disorder. When tunneling at the semiconductor-superconductor interface is very weak, disorder in the superconductor does not affect the induced superconductivity nor, therefore, the effective topological superconductivity that emerges above a critical magnetic field. Here we demonstrate, nonperturbatively, how this result breaks down with stronger proximity coupling by obtaining the low-energy (i.e., subgap) excitation spectrum through direct numerical diagonalization of an appropriate Bogoliubov-de Gennes Hamiltonian. We find that the combination of strong proximity coupling and superconductor disorder suppresses the (nontopological) induced gap at zero magnetic field by disordering the induced pair potential. In the topological superconducting phase at large magnetic field, strong proximity coupling also reduces the localization length of Majorana bound states, such that the induced disorder eliminates the topological gap while bulk zero modes proliferate, even for short wires.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.94.140505}, author = {Cole, William S. and Sau, Jay D. and S. Das Sarma} } @article { ISI:000364471100001, title = {Effects of large induced superconducting gap on semiconductor Majorana nanowires}, journal = {PHYSICAL REVIEW B}, volume = {92}, number = {17}, year = {2015}, month = {NOV 12}, issn = {1098-0121}, doi = {10.1103/PhysRevB.92.174511}, author = {Cole, William S. and S. Das Sarma and Stanescu, Tudor D.} } @article {2732, title = {Striped ferronematic ground states in a spin-orbit-coupled $S=1$ Bose gas}, journal = {Phys. Rev. A}, volume = {91}, year = {2015}, month = {Feb}, pages = {023608}, doi = {10.1103/PhysRevA.91.023608}, url = {http://link.aps.org/doi/10.1103/PhysRevA.91.023608}, author = {Natu, Stefan S. and Li, Xiaopeng and Cole, William S.} }