1,566 research outputs found
Subgap states in dirty superconductors and their effect on dephasing in Josephson qubits
We present a theory of the subgap tails of the density of states in a
diffusive superconductor containing magnetic impurities. We show that the
subgap tails have two contributions: one arising from mesoscopic gap
fluctuations, previously discussed by Lamacraft and Simons, and the other
associated to the long-wave fluctuations of the concentration of magnetic
impurities. We study the latter both in small superconducting grains and in
bulk systems [], and establish the dimensionless parameter that
controls which of the two contributions dominates the subgap tails. We observe
that these contributions are related to each other by dimensional reduction. We
apply the theory to estimate the effects of a weak concentration of magnetic
impurities [] on the phase coherence of Josephson
qubits. We find that at these typical concentrations, magnetic impurities are
relevant for the dephasing in large qubits, designed around a
scale, where they limit the quality factor to be .Comment: 13 pages, 1 figur
Rashba split surface states in BiTeBr
Within density functional theory, we study bulk band structure and surface
states of BiTeBr. We consider both ordered and disordered phases which differ
in atomic order in the Te-Br sublattice. On the basis of relativistic ab-initio
calculations, we show that the ordered BiTeBr is energetically preferable as
compared with the disordered one. We demonstrate that both Te- and
Br-terminated surfaces of the ordered BiTeBr hold surface states with a giant
spin-orbit splitting. The Te-terminated surface-state spin splitting has the
Rashba-type behavior with the coupling parameter \alpha_R ~ 2 eV\AA.Comment: 8 pages, 7 figure
Local electronic structures on the superconducting interface
Motivated by the recent discovery of superconductivity on the heterointerface
, we theoretically investigate its local electronic
structures near an impurity considering the influence of Rashba-type spin-orbit
interaction (RSOI) originated in the lack of inversion symmetry. We find that
local density of states near an impurity exhibits the in-gap resonance peaks
due to the quasiparticle scattering on the Fermi surface with the reversal sign
of the pairing gap caused by the mixed singlet and RSOI-induced triplet
superconducting state. We also analyze the evolutions of density of states and
local density of states with the weight of triplet pairing component determined
by the strength of RSOI, which will be widely observed in thin films of
superconductors with surface or interface-induced RSOI, or various
noncentrosymmetric superconductors in terms of point contact tunneling and
scanning tunneling microscopy, and thus reveal an admixture of the spin singlet
and RSOI-induced triplet superconducting states.Comment: Phys. Rev. B 81, 144504 (2010)
Iron based superconductors: magnetism, superconductivity and electronic structure
Angle resolved photoemission spectroscopy (ARPES) reveals the features of the
electronic structure of quasi-two-dimensional crystals, which are crucial for
the formation of spin and charge ordering and determine the mechanisms of
electron-electron interaction, including the superconducting pairing. The newly
discovered iron based superconductors (FeSC) promise interesting physics that
stems, on one hand, from a coexistence of superconductivity and magnetism and,
on the other hand, from complex multi-band electronic structure. In this review
I want to give a simple introduction to the FeSC physics, and to advocate an
opinion that all the complexity of FeSC properties is encapsulated in their
electronic structure. For many compounds, this structure was determined in
numerous ARPES experiments and agrees reasonably well with the results of band
structure calculations. Nevertheless, the existing small differences may help
to understand the mechanisms of the magnetic ordering and superconducting
pairing in FeSC.Comment: Invited Revie
The photon absorption edge in superconductors and gapped 1D systems
Opening of a gap in the low-energy excitations spectrum affects the power-law
singularity in the photon absorption spectrum . In the normal state,
the singularity, , is
characterized by an interaction-dependent exponent . On the contrary,
in the supeconducting state the divergence, , is
interaction-independent, while threshold is shifted, ; the ``normal-metal'' form of resumes
at . If the core
hole is magnetic, it creates in-gap states; these states transform drastically
the absorption edge. In addition, processes of scattering off the magnetic core
hole involving spin-flip give rise to inelastic absorption with one or several
{\it real} excited pairs in the final state, yielding a structure of peaks in
at multiples of above the threshold frequency. The above
conclusions apply to a broad class of systems, e.g., Mott insulators, where a
gap opens at the Fermi level due to the interactions.Comment: 6 pages, 5 figures; published versio
The redox transformations and nucleophilic replacements as possible metabolic reactions of the drug “Triazaverin”. The chemical modeling of the metabolic processes
As a model of metabolic transformations of antiviral drug “Triazaverin” and its analogues‑2-alkylthio‑6-nitro‑1,2,4-triazolo[5,1-c][1,2,4]triazine‑7-ones 1a-d examined the oxidation of alkylthio groups to the corresponding sulfoxides 2a-d and sulfones 3a-d, as well as the process of nucleophilic substitution sulfonyloxy group of cysteine and cysteamine with the formation of compounds 5 and 6
Many-body effects on the Rashba-type spin splitting in bulk bismuth tellurohalides
We report on many-body corrections to one-electron energy spectra of bulk
bismuth tellurohalides---materials that exhibit a giant Rashba-type spin
splitting of the band-gap edge states. We show that the corrections obtained in
the one-shot approximation noticeably modify the spin-orbit-induced spin
splitting evaluated within density functional theory. We demonstrate that
taking into account many-body effects is crucial to interpret the available
experimental data.Comment: 6 pages, 1 figur
Pressure effects on crystal and electronic structure of bismuth tellurohalides
We study the possibility of pressure-induced transitions from a normal
semiconductor to a topological insulator (TI) in bismuth tellurohalides using
density functional theory and tight-binding method. In BiTeI this transition is
realized through the formation of an intermediate phase, a Weyl semimetal, that
leads to modification of surface state dispersions. In the topologically
trivial phase, the surface states exhibit a Bychkov-Rashba type dispersion. The
Weyl semimetal phase exists in a narrow pressure interval of 0.2 GPa. After the
Weyl semimetal--TI transition occurs, the surface electronic structure is
characterized by gapless states with linear dispersion. The peculiarities of
the surface states modification under pressure depend on the band-bending
effect. We have also calculated the frequencies of Raman active modes for BiTeI
in the proposed high-pressure crystal phases in order to compare them with
available experimental data. Unlike BiTeI, in BiTeBr and BiTeCl the topological
phase transition does not occur. In BiTeBr, the crystal structure changes with
pressure but the phase remains a trivial one. However, the transition appears
to be possible if the low-pressure crystal structure is retained. In BiTeCl
under pressure, the topological phase does not appear up to 18 GPa due to a
relatively large band gap width in this compound
Optical signature of sub-gap absorption in the superconducting state of Ba(Fe,Co)2As2
The optical conductivity of Ba(FeCo)As shows a
clear signature of the superconducting gap, but a simple -wave description
fails in accounting for the low frequency response. This task is achieved by
introducing an extra Drude peak in the superconducting state representing
sub-gap absorption, other than thermally broken pairs. This extra peak and the
coexisting -wave response respect the total sum rule indicating a common
origin for the carriers. We discuss the possible origins for this absorption as
(i) quasiparticles due to pair-breaking from interband impurity scattering in a
two band gap symmetry model, which includes (ii) the possible
existence of impurity levels within an isotropic gap model; or (iii) an
indication that one of the bands is highly anisotropic.Comment: 5 pages, 4 figure
Nonequilibrium transport via spin-induced sub-gap states in superconductor/quantum dot/normal metal cotunnel junctions
We study low-temperature transport through a Coulomb blockaded quantum dot
(QD) contacted by a normal (N), and a superconducting (S) electrode. Within an
effective cotunneling model the conduction electron self energy is calculated
to leading order in the cotunneling amplitudes and subsequently resummed to
obtain the nonequilibrium T-matrix, from which we obtain the nonlinear
cotunneling conductance. For even occupied dots the system can be conceived as
an effective S/N-cotunnel junction with subgap transport mediated by Andreev
reflections. The net spin of an odd occupied dot, however, leads to the
formation of sub-gap resonances inside the superconducting gap which gives rise
to a characteristic peak-dip structure in the differential conductance, as
observed in recent experiments.Comment: 13 pages, 13 figures (new version contains reformulations and
corrections of typos etc
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