Latest Research Papers In Condensed Matter Physics | (Cond-Mat.Mes-Hall) 2019-05-13

arxivsanity (63)in #condensedmatter • 5 years ago

Latest Papers in Condensed Matter Physics

Mesoscale And Nanoscale Physics

Spin-Orbit Protection of Induced Superconductivity in Majorana Nanowires (1807.01940v2)

Jouri D. S. Bommer, Hao Zhang, Önder Gül, Bas Nijholt, Michael Wimmer, Filipp N. Rybakov, Julien Garaud, Donjan Rodic, Egor Babaev, Matthias Troyer, Diana Car, Sébastien R. Plissard, Erik P. A. M. Bakkers, Kenji Watanabe, Takashi Taniguchi, Leo P. Kouwenhoven

2018-07-05

Spin-orbit interaction (SOI) plays a key role in creating Majorana zero modes in semiconductor nanowires proximity coupled to a superconductor. We track the evolution of the induced superconducting gap in InSb nanowires coupled to a NbTiN superconductor in a large range of magnetic field strengths and orientations. Based on realistic simulations of our devices, we reveal SOI with a strength of 0.15-0.35 eV. Our approach identifies the direction of the spin-orbit field, which is strongly affected by the superconductor geometry and electrostatic gates.

Exact solution of a time-reversal-invariant topological superconducting wire (1905.04255v1)

Armando A. Aligia, Alberto Camjayi

2019-05-10

We consider a model proposed before for a time-reversal-invariant topological superconductor (TRITOPS) which contains a hopping term , a chemical potential , an extended -wave pairing and spin-orbit coupling . We show that for , , the model can be solved exactly defining new fermion operators involving nearest-neighbor sites. The many-body ground state is four-fold degenerate due to the existence of two zero-energy modes localized exactly at the first and the last site of the chain. These four states show entanglement in the sense that creating or annihilating a zero-energy mode at the first site is proportional to a similar operation at the last site. By continuity, this property should persist for general parameters. Using these results we correct some statements related with the so called "time-reversal anomaly". Addition of a small hopping term for a chain with an even number of sites breaks the degeneracy and the ground state becomes unique with an even number of particles. We also consider a small magnetic field applied to one end of the chain. We compare the many-body excitation energies and spin projection along the spin-orbit direction for both ends of the chains with numerical results %for a small chain obtaining good agreement.

Marginal Fermi liquid in twisted bilayer graphene (1903.01376v2)

J. González, T. Stauber

2019-03-04

Linear resistivity at low temperatures is a prominent feature of high-Tc superconductors which has been also found recently in twisted bilayer graphene. We show that due to an extended van Hove singularity, the -linear resistivity can be obtained from a microscopic model of twisted bilayer graphene around the van Hove singularities in the two highest valence bands. The linear behavior is shown to be related to the linear energy dependence of the electron quasiparticle decay rate, which implies the low-energy logarithmic attenuation of the quasiparticle weight. These are distinctive features of a marginal Fermi liquid, which we also see reflected in the respective low-temperature logarithmic corrections of the heat capacity and the thermal conductivity, leading to the consequent violation of the Wiedemann-Franz law.

Formation of Graphene atop a Si adlayer on the C-face of SiC (1905.04234v1)

Jun Li, Qingxiao Wang, Guowei He, Michael Widom, Lydia Nemec, Volker Blum, Moon Kim, Patrick Rinke, Randall M. Feenstra

2019-05-10

The structure of the SiC(000-1) surface, the C-face of the {0001} SiC surfaces, is studied as a function of temperature and of pressure in a gaseous environment of disilane (Si2H6). Various surface reconstructions are observed, both with and without the presence of an overlying graphene layer (which spontaneously forms at sufficiently high temperatures). Based on cross-sectional scanning transmission electron microscopy measurements, the interface structure that forms in the presence of the graphene is found to contain 1.4 - 1.7 monolayers (ML) of Si, a somewhat counter-intuitive result since, when the graphene forms, the system is actually under C-rich conditions. Using ab initio thermodynamics, it is demonstrated that there exists a class of Si-rich surfaces containing about 1.3 ML of Si that are stable on the surface (even under C-rich conditions) at temperatures above about 400 K. The structures that thus form consist of Si adatoms atop a Si adlayer on the C-face of SiC, with or without the presence of overlying graphene.

Atomic-scale imaging of a 27-nuclear-spin cluster using a single-spin quantum sensor (1905.02095v2)

M. H. Abobeih, J. Randall, C. E. Bradley, H. P. Bartling, M. A. Bakker, M. J. Degen, M. Markham, D. J. Twitchen, T. H. Taminiau

2019-05-06

Nuclear magnetic resonance (NMR) is a powerful method for determining the structure of molecules and proteins. While conventional NMR requires averaging over large ensembles, recent progress with single-spin quantum sensors has created the prospect of magnetic imaging of individual molecules. As an initial step towards this goal, isolated nuclear spins and spin pairs have been mapped. However, large clusters of interacting spins - such as found in molecules - result in highly complex spectra. Imaging these complex systems is an outstanding challenge due to the required high spectral resolution and efficient spatial reconstruction with sub-angstrom precision. Here we develop such atomic-scale imaging using a single nitrogen-vacancy (NV) centre as a quantum sensor, and demonstrate it on a model system of coupled C nuclear spins in a diamond. We present a new multidimensional spectroscopy method that isolates individual nuclear-nuclear spin interactions with high spectral resolution (mHz) and high accuracy ( mHz). We show that these interactions encode the composition and inter-connectivity of the cluster, and develop methods to extract the 3D structure of the cluster with sub-angstrom resolution. Our results demonstrate a key capability towards magnetic imaging of individual molecules and other complex spin systems.