24 research outputs found
Finite-temperature conductance of strongly interacting quantum wire with a nuclear spin order
We study the temperature dependence of the electrical conductance of a clean
strongly interacting quantum wire in the presence of a helical nuclear spin
order. The nuclear spin helix opens a temperature-dependent partial gap in the
electron spectrum. Using a bosonization framework we describe the gapped
electron modes by sine-Gordon-like kinks. We predict an internal resistivity
caused by an Ohmic-like friction these kinks experience via interacting with
gapless excitations. As a result, the conductance rises from at
temperatures below the critical temperature when nuclear spins are fully
polarized to at higher temperatures when the order is destroyed,
featuring a relatively wide plateau in the intermediate regime. The theoretical
results are compared with the experimental data for GaAs quantum wires obtained
recently by Scheller et al. [Phys. Rev. Lett. 112, 066801 (2014)].Comment: 18 pages, 10 figure
Lifetime of Majorana qubits in Rashba nanowires with non-uniform chemical potential
We study the lifetime of topological qubits based on Majorana bound states
hosted in a one-dimensional Rashba nanowire (NW) with proximity-induced
superconductivity and non-uniform chemical potential needed for manipulation
and read-out. If nearby gates tune the chemical potential locally so that part
of the NW is in the trivial phase, Andreev bound states (ABSs) can emerge which
are localized at the interface between topological and trivial phases with
energies significantly less than the gap. The emergence of such subgap states
strongly decreases the Majorana qubit lifetime at finite temperatures due to
local perturbations that can excite the system into these ABSs. Using Keldysh
formalism, we study such excitations caused by fluctuating charges in
capacitively coupled gates and calculate the corresponding Majorana lifetimes
due to thermal noise, which are shown to be much shorter than those in NWs with
uniform chemical potential.Comment: 9 pages, 8 figure
Degeneracy lifting of Majorana bound states due to electron-phonon interactions
We study theoretically how electron-phonon interaction affects the energies
and level broadening (inverse lifetime) of Majorana bound states (MBSs) in a
clean topological nanowire at low temperatures. At zero temperature, the energy
splitting between the right and left MBSs remains exponentially small with
increasing nanowire length . At finite temperatures, however, the absorption
of thermal phonons leads to the broadening of energy levels of the MBSs that
does not decay with system length, and the coherent absorption/emission of
phonons at opposite ends of the nanowire results in MBSs energy splitting that
decays only as an inverse power-law in . Both effects remain exponential in
temperature. In the case of quantized transverse motion of phonons, the
presence of Van Hove singularities in the phonon density of states causes
additional resonant enhancement of both the energy splitting and the level
broadening of the MBSs. This is the most favorable case to observe the
phonon-induced energy splitting of MBSs as it becomes much larger than the
broadening even if the topological nanowire is much longer than the coherence
length. We also calculate the charge and spin associated with the energy
splitting of the MBSs induced by phonons. We consider both a spinless
low-energy continuum model, which we evaluate analytically, as well as a
spinful lattice model for a Rashba nanowire, which we evaluate numerically
Photoelectrochemical properties of full composition InxGa1-xN/Si photoanodes
Recently InxGa1-xN (x=0-1) thin films and nanostructures have attracted considerable interest in the field of solar assisted water splitting. As a standalone photoelectrode it is very appealing due to its direct, tunable bandgap covering nearly the entire solar spectrum (Fig. 1a), high absorption coefficient and mobility, along with near-perfect band-edge potentials. Moreover,
because of the special bands alignment it can be grown on p-Si photocathode and exhibit vertical conductivity without complex tunnel junction. These facts open a possibility to achieve high efficiency, relatively cheap InGaN/Si-based two-photon tandem devices for water splitting
XRD analysis of InGaN uniform layers grown on Si (111) without any buffer layers and on Sapphire
The International Workshop on Nitride Semiconductors (IWN) is a biennial academic conference in the field of group III nitride research. The IWN and the International Conference on Nitride Semiconductors (ICNS) are held in alternating years and cover similar subject areas
Field effect enhancement in buffered quantum nanowire networks
III-V semiconductor nanowires have shown great potential in various quantum
transport experiments. However, realizing a scalable high-quality
nanowire-based platform that could lead to quantum information applications has
been challenging. Here, we study the potential of selective area growth by
molecular beam epitaxy of InAs nanowire networks grown on GaAs-based buffer
layers. The buffered geometry allows for substantial elastic strain relaxation
and a strong enhancement of field effect mobility. We show that the networks
possess strong spin-orbit interaction and long phase coherence lengths with a
temperature dependence indicating ballistic transport. With these findings, and
the compatibility of the growth method with hybrid epitaxy, we conclude that
the material platform fulfills the requirements for a wide range of quantum
experiments and applications
Electrocatalytic oxidation enhancement at the surface of InGaN films and nanostructures grown directly on Si(111)
Pronounced electrocatalytic oxidation enhancement at the surface of InGaN layers and nanostructures directly grown on Si by plasma-assisted molecular beam epitaxy is demonstrated. The oxidation enhancement, probed with the ferro/ferricyanide redox couple increases with In content and proximity of nanostructure surfaces and sidewalls to the c-plane. This is attributed to the corresponding increase of the density of intrinsic positively charged surface donors promoting electron transfer. Strongest enhancement is for c-plane InGaN layers functionalized with InN quantum dots (QDs). These results explain the excellent performance of our InN/InGaN QD biosensors and water splitting electrodes for further boosting efficiency
Ballistic InSb Nanowires and Networks via Metal-Sown Selective Area Growth
Selective area growth is a promising technique to realize semiconductor-superconductor hybrid nanowire networks, potentially hosting topologically protected Majorana-based qubits. In some cases, however, such as the molecular beam epitaxy of InSb on InP or GaAs substrates, nucleation and selective growth conditions do not necessarily overlap. To overcome this challenge, we propose a metal-sown selective area growth (MS SAG) technique, which allows decoupling selective deposition and nucleation growth conditions by temporarily isolating these stages. It consists of three steps: (i) selective deposition of In droplets only inside the mask openings at relatively high temperatures favoring selectivity, (ii) nucleation of InSb under Sb flux from In droplets, which act as a reservoir of group III adatoms, done at relatively low temperatures, favoring nucleation of InSb, and (iii) homoepitaxy of InSb on top of the formed nucleation layer under a simultaneous supply of In and Sb fluxes at conditions favoring selectivity and high crystal quality. We demonstrate that complex InSb nanowire networks of high crystal and electrical quality can be achieved this way. We extract mobility values of 10※000-25※000 cm V s consistently from field-effect and Hall mobility measurements across single nanowire segments as well as wires with junctions. Moreover, we demonstrate ballistic transport in a 440 nm long channel in a single nanowire under a magnetic field below 1 T. We also extract a phase-coherent length of ∼8 μm at 50 mK in mesoscopic rings
Stranski-Krastanov InN/InGaN quantum dots grown directly on Si(111)
The authors discuss and demonstrate the growth of InN surface quantum dots on a high-In-content In0.73Ga0.27N layer, directly on a Si(111) substrate by plasma-assisted molecular beam epitaxy. Atomic force microscopy and transmission electron microscopy reveal uniformly distributed quantum dots with diameters of 10–40 nm, heights of 2–4 nm, and a relatively low density of ∼7 × 109 cm−2. A thin InN wetting layer below the quantum dots proves the Stranski-Krastanov growth mode. Near-field scanning optical microscopy shows distinct and spatially well localized near-infrared emission from single surface quantum dots. This holds promise for future telecommunication and sensing devices