1,237 research outputs found
Effect of the type I to type II Weyl semimetal topological transition on superconductivity
The influence of recently discovered topological transition between type I
and type II Weyl semi-metals on superconductivity is considered. A set of
Gorkov equations for weak superconductivity in Weyl semi-metal under
topological phase transition is derived and solved. The critical temperature
and superconducting gap both have spike in the point the transition point as
function of the tilt parameter of the Dirac cone determined in turn by the
material parameters like pressure. The spectrum of superconducting excitations
is different in two phases: the sharp cone pinnacle is characteristic for a
type I, while two parallel almost flat bands, are formed in type II. Spectral
density is calculated on both sides of transition demonstrate different weight
of the bands. The superconductivity thus can be used as a clear indicator for
the topological transformation. Results are discussed in the light of recent
experiments.Comment: 13 pages, 5 figure
Chiral universality class of the normal-superconducting and the exciton condensation transition on the surface of topological insulator
New two dimensional systems like surface of topological insulator and
graphene offer a possibility to experimentally investigate situations
considered "exotic" just a decade ago. One of those is the quantum phase
transition of the "chiral" type in electronic systems with relativistic
spectrum. Phonon mediated ("conventional") pairing in the Dirac semimetal
appearing on the surface of topological insulator leads to transition into a
chiral superconducting state, while exciton condensation in these gapless
systems has been envisioned long time ago in the physics of the narrow band
semiconductors. Starting from the microscopic Dirac Hamiltonian with local
attraction or repulsion, the BCS type gaussian approximation is developed in
the framework of functional integrals. It is shown that due to an
"ultra-relativistic" dispersion relation there is a quantum critical point
governing the zero temperature transition to a superconducting or the exciton
condensed state. The quantum transitions that have critical exponents very
different from the conventional ones. They belong to the chiral universality
class. We discuss the application of these results to recent experiments in
which surface superconductivity was found in topological insulators and
estimate feasibility of the phonon pairing.Comment: 19pages, 4 figures. arXiv admin note: substantial text overlap with
arXiv:1405.594
Superconductivity in 2D electron gas induced by high energy optical phonon mode and large polarization of the STO substrate
Theory of superconductivity generated in one atomic layer thick two
dimensional electron gas by a single flat band of high energy longitudinal
optical phonons is considered. The polar dielectric (STO) exhibits
such an energetic phonon mode and the 2DEG is created both when one unit cell
layer is grown on its surface and on the interface
with another dielectric like (LAO). We obtain a quantitative
description of both systems solving the gap equation for without making
use of approximations like the Kirzhnits Ansatz for arbitrary chemical
potential , electron-phonon coupling and the phonon frequency
, and direct (RPA) electron-electron repulsion strength . The
high temperature superconductivity in 1UC/STO is possible due to a
combination of three factors: high LO phonon frequency, large electron-phonon
coupling and huge dielectric constant of the substrate
suppression the Coulomb repulsion. It is shown that very low density electron
gas in the interfaces is still capable of generating superconductivity of the
order of K in LAO/STO. Superconductivity persists even on the band edge
.Comment: 19 pages, 7 figure
Magnetic impurities make superconductivity in 3D Dirac semi-metal triplet
Conventional electron-phonon coupling induces either odd (triplet) or even
(singlet) pairing states in a time reversal and inversion invariant Dirac semi
- metal. In certain range of the chemical potential and parameters
characterizing the pairing attraction (effective electron-electron coupling
constant and the Debye energy ) the energy of the singlet
although always lower, prevails by a very slim margin over the triplet. This
means that interactions that are small but discriminate between the spin
singlet and the spin triplet determine the nature of the superconducting order
there. It shown that in materials close enough to the Dirac point () magnetic impurities stabilize the odd pairing superconducting
state.Comment: 5 pages, 4 figures.Supplemenatry materials, 5 pages, 2 figures. arXiv
admin note: substantial text overlap with arXiv:1407.077
Singular solutions of the L^2-supercritical biharmonic Nonlinear Schrodinger equation
We use asymptotic analysis and numerical simulations to study peak-type
singular solutions of the supercritical biharmonic NLS. These solutions have a
quartic-root blowup rate, and collapse with a quasi self-similar universal
profile, which is a zero-Hamiltonian solution of a fourth-order nonlinear
eigenvalue problem
Correction To: Better Beware: Comparing Metacognition for Phishing and Legitimate Emails (Metacognition and Learning, (2019), 14, 3, (343-362), 10.1007/S11409-019-09197-5)
The article Better beware: comparing metacognition for phishing and legitimate emails , written by Casey Inez Canfield, Baruch Fischhoff and Alex Davis, was originally published electronically on the publisher\u27s internet portal (currently SpringerLink) on 20 July 2019 without open access
Dynamic Equilibrium between Coupled and Uncoupled Modes of a Neuronal Glutamate Transporter
In the brain, the neurotransmitter glutamate is removed from the synaptic cleft by (Na+ + K+)-coupled transporters by an electrogenic process. Moreover, these transporters mediate a sodium- and glutamate-dependent uncoupled chloride conductance. In contrast to the wild type, the uptake of radiolabeled substrate by the I421C mutant is inhibited by the membrane-impermeant [2-(trimethylammonium)ethyl]methanethiosulfonate and also by other sulfhydryl reagents. In the wild-type and the unmodified mutant, substrate-induced currents are inwardly rectifying and reflect the sum of the coupled electrogenic flux and the anion conductance. Remarkably, the I421C mutant modified by sulfhydryl reagents exhibits currents that are non-rectifying and reverse at the equilibrium potential for chloride. Strikingly, almost 10-fold higher concentrations ofd-aspartate are required to activate the currents in the modified mutant as compared with untreated I421C. Under conditions in which only the coupled currents are observed, the modified mutant does not exhibit any currents. However, when the uncoupled current is dominant, sulfhydryl reagents cause \u3e4-fold stimulation of this current. Thus, the modification of the cysteine introduced at position 421 impacts the coupled but not the uncoupled fluxes. Although both fluxes are activated by substrate, they behave as independent processes that are in dynamic equilibrium
Tyrosine 140 of the γ-Aminobutyric Acid Transporter GAT-1 Plays a Critical Role in Neurotransmitter Recognition
The γ-aminobutyric acid (GABA) transporter GAT-1 is located in nerve terminals and catalyzes the electrogenic reuptake of the neurotransmitter with two sodium ions and one chloride. We now identify a single tyrosine residue that is critical for GABA recognition and transport. It is completely conserved throughout the superfamily, and even substitution to the other aromatic amino acids, phenylalanine (Y140F) and tryptophan (Y140W), results in completely inactive transporters. Electrophysiological characterization reveals that both mutant transporters exhibit the sodium-dependent transient currents associated with sodium binding as well as the chloride-dependent lithium leak currents characteristic of GAT-1. On the other hand, in both mutants GABA is neither able to induce a steady-state transport current nor to block their transient currents. The nontransportable analog SKF 100330A potently inhibits the sodium-dependent transient in the wild type GAT-1 but not in the Y140W transporter. It partly blocks the transient of Y140F. Thus, although sodium and chloride binding are unimpaired in the tyrosine mutants, they have a specific defect in the binding of GABA. The total conservation of the residue throughout the family suggests that tyrosine 140 may be involved in the liganding of the amino group, the moiety common to all of the neurotransmitters
Better Beware: Comparing Metacognition for Phishing and Legitimate Emails
Every electronic message poses some threat of being a phishing attack. If recipients underestimate that threat, they expose themselves, and those connected to them, to identity theft, ransom, malware, or worse. If recipients overestimate that threat, then they incur needless costs, perhaps reducing their willingness and ability to respond over time. In two experiments, we examined the appropriateness of individuals\u27 confidence in their judgments of whether email messages were legitimate or phishing, using calibration and resolution as metacognition metrics. Both experiments found that participants had reasonable calibration but poor resolution, reflecting a weak correlation between their confidence and knowledge. These patterns differed for legitimate and phishing emails, with participants being better calibrated for legitimate emails, except when expressing complete confidence in their judgments, but consistently overconfident for phishing emails. The second experiment compared performance on the laboratory task with individuals\u27 actual vulnerability, and found that participants with better resolution were less likely to have malicious files on their home computers. That comparison raised general questions about the design of anti-phishing training and of providing feedback essential to self-regulated learning
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