39 research outputs found
Dressed tunneling approximation for electronic transport through molecular transistors
A theoretical approach for the non-equilibrium transport properties of
nanoscale systems coupled to metallic electrodes with strong electron-phonon
interactions is presented. It consists in a resummation of the dominant Feynman
diagrams from the perturbative expansion in the coupling to the leads. We show
that this scheme eliminates the main pathologies found in previous simple
analytical approaches for the polaronic regime. The results for the spectral
and transport properties are compared with those from several other approaches
for a wide range of parameters. The method can be formulated in a simple way to
obtain the full counting statistics. Results for the shot and thermal noise are
presented.Comment: 11 pages, 11 figures. Accepted for publication in Physical Review
Topological superconductivity in semiconductor-superconductor-magnetic insulator heterostructures
Hybrid superconductor-semiconductor heterostructures are promising platforms
for realizing topological superconductors and exploring Majorana bound states
physics. Motivated by recent experimental progress, we theoretically study how
magnetic insulators offer an alternative to the use of external magnetic fields
for reaching the topological regime. We consider different setups, where: (1)
the magnetic insulator induces an exchange field in the superconductor, which
leads to a splitting in the semiconductor by proximity effect, and (2) the
magnetic insulator acts as a spin-filter tunnel barrier between the
superconductor and the semiconductor. We show that the spin splitting in the
superconductor alone cannot induce a topological transition in the
semiconductor. To overcome this limitation, we propose to use a spin-filter
barrier that enhances the magnetic exchange and provides a mechanism for a
topological phase transition. Moreover, the spin-dependent tunneling introduces
a strong dependence on the band alignment, which can be crucial in
quantum-confined systems. This mechanism opens up a route towards networks of
topological wires with fewer constraints on device geometry compared to
previous devices that require external magnetic fields.Comment: 9+5 pages, 6 figure
Spin-polarized bound states in semiconductor-superconductor-ferromagnetic insulator islands
We report Coulomb blockade transport studies of InAs nanowires grown with
epitaxial superconducting Al and ferromagnetic insulator EuS on overlapping
facets. By comparing experimental results to a theoretical model, we associate
cotunneling features in even-odd bias spectra with spin-polarized Andreev
levels, indicating that spin splitting exceeding the induced superconducting
gap at zero applied magnetic field. Energies of the polarized subgap states can
be tuned on either side of zero by electrostatic gates
Full counting statistics of information content
We review connections between the cumulant generating function of full
counting statistics of particle number and the R\'enyi entanglement entropy. We
calculate these quantities based on the fermionic and bosonic path-integral
defined on multiple Keldysh contours. We relate the R\'enyi entropy with the
information generating function, from which the probability distribution
function of self-information is obtained in the nonequilibrium steady state. By
exploiting the distribution, we analyze the information content carried by a
single bosonic particle through a narrow-band quantum communication channel.
The ratio of the self-information content to the number of bosons fluctuates.
For a small boson occupation number, the average and the fluctuation of the
ratio are enhanced.Comment: 16 pages, 5 figure
Supercurrent transport through 1-periodic full-shell Coulomb islands
We experimentally investigate supercurrent through Coulomb islands, where
island and leads are fabricated from semiconducting nanowires with fully
surrounding superconducting shells. Applying flux along the wire yields a
series of destructive Little-Parks lobes with reentrant supercurrent. We find
Coulomb blockade with 2 peak spacing in the zeroth lobe and 1 average
spacing, with regions of significant even-odd modulation, in the first lobe.
Evolution of Coulomb-peak amplitude through the first lobe is consistent with a
theoretical model of supercurrent carried predominantly by zero-energy states
in the leads and the island.Comment: 11 pages, 5+5 figure
Why Are Outcomes Different for Registry Patients Enrolled Prospectively and Retrospectively? Insights from the Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF).
Background: Retrospective and prospective observational studies are designed to reflect real-world evidence on clinical practice, but can yield conflicting results. The GARFIELD-AF Registry includes both methods of enrolment and allows analysis of differences in patient characteristics and outcomes that may result. Methods and Results: Patients with atrial fibrillation (AF) and â„1 risk factor for stroke at diagnosis of AF were recruited either retrospectively (nâ=â5069) or prospectively (nâ=â5501) from 19 countries and then followed prospectively. The retrospectively enrolled cohort comprised patients with established AF (for a least 6, and up to 24 months before enrolment), who were identified retrospectively (and baseline and partial follow-up data were collected from the emedical records) and then followed prospectively between 0-18 months (such that the total time of follow-up was 24 months; data collection Dec-2009 and Oct-2010). In the prospectively enrolled cohort, patients with newly diagnosed AF (â€6 weeks after diagnosis) were recruited between Mar-2010 and Oct-2011 and were followed for 24 months after enrolment. Differences between the cohorts were observed in clinical characteristics, including type of AF, stroke prevention strategies, and event rates. More patients in the retrospectively identified cohort received vitamin K antagonists (62.1% vs. 53.2%) and fewer received non-vitamin K oral anticoagulants (1.8% vs . 4.2%). All-cause mortality rates per 100 person-years during the prospective follow-up (starting the first study visit up to 1 year) were significantly lower in the retrospective than prospectively identified cohort (3.04 [95% CI 2.51 to 3.67] vs . 4.05 [95% CI 3.53 to 4.63]; pâ=â0.016). Conclusions: Interpretations of data from registries that aim to evaluate the characteristics and outcomes of patients with AF must take account of differences in registry design and the impact of recall bias and survivorship bias that is incurred with retrospective enrolment. Clinical Trial Registration: - URL: http://www.clinicaltrials.gov . Unique identifier for GARFIELD-AF (NCT01090362)
Risk profiles and one-year outcomes of patients with newly diagnosed atrial fibrillation in India: Insights from the GARFIELD-AF Registry.
BACKGROUND: The Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF) is an ongoing prospective noninterventional registry, which is providing important information on the baseline characteristics, treatment patterns, and 1-year outcomes in patients with newly diagnosed non-valvular atrial fibrillation (NVAF). This report describes data from Indian patients recruited in this registry. METHODS AND RESULTS: A total of 52,014 patients with newly diagnosed AF were enrolled globally; of these, 1388 patients were recruited from 26 sites within India (2012-2016). In India, the mean age was 65.8 years at diagnosis of NVAF. Hypertension was the most prevalent risk factor for AF, present in 68.5% of patients from India and in 76.3% of patients globally (P < 0.001). Diabetes and coronary artery disease (CAD) were prevalent in 36.2% and 28.1% of patients as compared with global prevalence of 22.2% and 21.6%, respectively (P < 0.001 for both). Antiplatelet therapy was the most common antithrombotic treatment in India. With increasing stroke risk, however, patients were more likely to receive oral anticoagulant therapy [mainly vitamin K antagonist (VKA)], but average international normalized ratio (INR) was lower among Indian patients [median INR value 1.6 (interquartile range {IQR}: 1.3-2.3) versus 2.3 (IQR 1.8-2.8) (P < 0.001)]. Compared with other countries, patients from India had markedly higher rates of all-cause mortality [7.68 per 100 person-years (95% confidence interval 6.32-9.35) vs 4.34 (4.16-4.53), P < 0.0001], while rates of stroke/systemic embolism and major bleeding were lower after 1 year of follow-up. CONCLUSION: Compared to previously published registries from India, the GARFIELD-AF registry describes clinical profiles and outcomes in Indian patients with AF of a different etiology. The registry data show that compared to the rest of the world, Indian AF patients are younger in age and have more diabetes and CAD. Patients with a higher stroke risk are more likely to receive anticoagulation therapy with VKA but are underdosed compared with the global average in the GARFIELD-AF. CLINICAL TRIAL REGISTRATION-URL: http://www.clinicaltrials.gov. Unique identifier: NCT01090362
Transient dynamics of a magnetic impurity coupled to superconducting electrodes : Exact numerics versus perturbation theory
Impurities coupled to superconductors offer a controlled platform to understand the interplay between superconductivity, many-body interactions, and nonequilibrium physics. In the equilibrium situation, local interactions at the impurity induce a transition from the spin-singlet to the spin-doublet ground state, resulting in a supercurrent sign reversal (0-Ï transition). In this work, we apply the exact time-dependent density matrix renormalization group method to simulate the transient dynamics of such superconducting systems. We also use a perturbative approximation to analyze their properties at longer times. These two methods agree for a wide range of parameters. In a phase-biased situation, the system gets trapped in a metastable state characterized by a lower supercurrent compared to the equilibrium case. We show that local Coulomb interactions do not provide an effective relaxation mechanism for the initially trapped quasiparticles. In contrast, other relaxation mechanisms, such as coupling to a third normal lead, make the impurity spin relax for parameter values corresponding to the equilibrium 0 phase. For parameters corresponding to the equilibrium Ï phase the impurity converges to a spin-polarized stationary state. Similar qualitative behavior is found for a voltage-biased junction, which provides an effective relaxation mechanism for the trapped quasiparticles in the junction