5,243 research outputs found
Observability of surface Andreev bound states in a topological insulator in proximity to an s-wave superconductor
To guide experimental work on the search for Majorana zero-energy modes, we
calculate the superconducting pairing symmetry of a three-dimensional
topological insulator in combination with an s-wave superconductor. In analogy
to the case of nanowires with strong spin-orbit coupling we show how the
pairing symmetry changes across different topological regimes. We demonstrate
that a dominant p-wave pairing relation is not sufficient to realize a Majorana
zero-energy mode useful for quantum computation. Our main result of this paper
is the relation between odd-frequency pairing and Majorana zero energy modes by
using Green functions techniques in three-dimensional topological insulators in
the so-called Majorana regime. We discuss thereafter how the pairing relations
in the different regimes can be observed in the shape of the tunneling
conductance of an s-wave proximized three-dimensional topological insulator. We
will discuss the necessity to incorporate a ferromagnetic insulator to localize
the zero-energy bound state to the interface as a Majorana mode.Comment: Accepted for publication in Journal of Physics: Condensed Matte
Conductance anisotropy and linear magnetoresistance in La2-xSrxCuO4 thin films
We have performed a detailed study of conductance anisotropy and
magnetoresistance (MR) of La2-xSrxCuO4 (LSCO) thin films (0.10 < x < 0.25).
These two observables are promising for the detection of stripes. Subtle
features of the conductance anisotropy are revealed by measuring the transverse
resistance Rxy in zero magnetic field. It is demonstrated that the sign of Rxy
depends on the orientation of the LSCO Hall bar with respect to the terrace
structure of the substrate. Unit-cell-high substrate step edges must therefore
be a dominant nucleation source for antiphase boundaries during film growth. We
show that the measurement of Rxy is sensitive enough to detect the
cubic-tetragonal phase transition of the SrTiO3(100) (STO) substrate at 105 K.
The MR of LSCO thin films shows for 0.10 < x < 0.25 a non-monotonic temperature
dependence, resulting from the onset of a linear term in the MR above 90 K. We
show that the linear MR scales with the absolute Hall resistivity, with the
constant of proportionality independent of temperature. Such scaling suggests
that the linear MR originates from current distortions induced by structural or
electronic inhomogeneities. The possible role of stripes for both the MR and
the conductance anisotropy is discussed throughout the paper
Proximity effect in normal metal-multiband superconductor hybrid structures
A theory of the proximity effect in normal metal¿multiband superconductor hybrid structures is formulated within the quasiclassical Green's function formalism. The quasiclassical boundary conditions for multiband hybrid structures are derived in the dirty limit. It is shown that the existence of multiple superconducting bands manifests itself as the occurrence of additional peaks in the density of states in the structure. The interplay between the proximity effect and the interband coupling influences the magnitudes of the gaps in a superconductor in a nontrivial way and can even give rise to an enhancement of multiband superconductivity by the proximity to a superconductor with a lower transition temperature. The developed theory is applied to the calculation of supercurrent in multiband superconductor¿normal metal¿superconductor Josephson junctions with low-transparent interfaces, and the results are compared with the predictions for multiband tunnel junctions
Platelet deposition studies on copolyether urethanes modified with poly(ethylene oxide)
Pellethane ® 2363 80A films and tubings were chemically modified and the effect of these modifications on platelet deposition was studied. Grafting of high molecular weight poly(ethylene oxide) and graft polymerization of methoxy poly(ethylene glycol) 400 methacrylate resulted in surfaces with a good water wettability. The increased hydrophilicity of these modified surfaces could be demonstrated by contact angle measurements. The platelet deposition was investigated with tubings in a capillary flow system, using different types of perfusates. Platelet deposition from a buffer-containing perfusate on surfaces modified with either high molecular weight poly(ethylene oxide) or methoxy poly(ethylene glycol) 400 methacrylate was almost absent and less than on Pellethane 2363 80A. Using a citrated plasmacontaining perfusate the amount of deposited platelets on Pellethane 2363 80A modified with high molecular weight poly(ethylene oxide) was low and about the same as on unmodified surfaces. However, a marked reduced platelet deposition compared to unmodified Pellethane 2363 80A was found when the platelets were activated by Ca2+ ionophore. The improved blood compatibility of the modified Pellethane 2363 80A tubings obviously indicates the favourable effect of the presence of grafted PEO on the surface
Thermodynamics of an incommensurate quantum crystal
We present a simple theory of the thermodynamics of an incommensurate quantum
solid. The ground state of the solid is assumed to be an incommensurate
crystal, with quantum zero-point vacancies and interstitials and thus a
non-integer number of atoms per unit cell. We show that the low temperature
variation of the net vacancy concentration should be as , and that the
first correction to the specific heat due to this varies as ; these are
quite consistent with experiments on solid He. We also make some
observations about the recent experimental reports of ``supersolidity'' in
solid He that motivate a renewed interest in quantum crystals.Comment: revised, new title, somewhat expande
Nonlocal Andreev reflection, fractional charge and current-phase relation in topological bilayer exciton condensate junctions
We study Andreev reflection and Josephson currents in topological bilayer
exciton condensates (TEC). These systems can create 100% spin entangled
nonlocal currents with high amplitudes due to perfect nonlocal Andreev
reflection. This Andreev reflection process can be gate tuned from a regime of
purely retro reflection to purely specular reflection. We have studied the
bound states in TEC-TI-TEC Josephson junctions and find a gapless dispersion
for perpendicular incidence. The presence of a sharp transition in the
supercurrent-phase relationship when the system is in equilibrium is a
signature of fractional charge, which can be further revealed in ac
measurements faster than relaxation processes via Landau-Zener processes.Comment: Submitted to Physical Review
Preferential adsorption of high density lipoprotein (HDL) in blood plasma/polymer interaction
A few studies on the adsorption of plasma proteins to polymeric surfaces show that major plasma proteins: albumin (Alb), fibrinogen (Fb) and immunoglobulin (IgG) are adsorbed in much smaller quantities from plasma than from protein solutions (1,2). Present results show that this difference in adsorption is due to the preferential adsorption of high density lipoprotein from plasma onto the material surfaces studied (PVC and PS)
Nonlocal Cooper pair Splitting in a pSn Junction
Perfect Cooper pair splitting is proposed, based on crossed Andreev
reflection (CAR) in a p-type semiconductor - superconductor - n-type
semiconductor (pSn) junction. The ideal splitting is caused by the energy
filtering that is enforced by the bandstructure of the electrodes. The pSn
junction is modeled by the Bogoliubov-de Gennes equations and an extension of
the Blonder-Tinkham-Klapwijk theory beyond the Andreev approximation. Despite a
large momentum mismatch, the CAR current is predicted to be large. The proposed
straightforward experimental design and the 100% degree of pureness of the
nonlocal current open the way to pSn structures as high quality sources of
entanglement
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