1,721,009 research outputs found
Impact of electrostatic fields in layered crystalline BCS superconductors
Full text linkMotivated by recent experiments reporting the suppression of the critical current in superconducting Dayem bridges by the application of strong electrostatic fields, in this paper we study the impact on the superconducting gap of charge redistribution in response to an applied electric field in thin crystalline metals. By numerically solving the BCS gap equation and the Poisson equation in a fully self-consistent way, we find that the gap becomes sensitive to the applied electric field when the size of the gap becomes an order of magnitude larger than the average level spacing of the spectrum in the normal state. In this case, the gap shows sudden rises and falls that are compatible with surface modifications of the local density of states. The effect is washed out by increasing the pairing strength toward the weak-to-moderate coupling limit or by introduction of a weak smearing in the density of states that effectively mimics a thicker sample and a weakly disordered system
Proposal for a Datta-Das transistor in the quantum Hall regime
No full textWe propose a resonant spin-field-effect transistor for chiral spin-resolved edge states in the integer quantum Hall effect with Rashba spin-orbit interaction. It employs a periodic array of voltage-controlled top gates that locally modulate the Rashba spin-orbit interaction. Strong resonant spin-field effect is achieved when the array periodicity matches the inverse of the wave-vector difference of the two chiral states involved. Well-known techniques of separately contacting the edge states make it possible to selectively populate and read out the edge states, allowing full spin readout. The resonant nature of the spin-field effect and the adiabatic character of the edge states guarantee a high degree of robustness with respect to disorder. Our device represents the quantum Hall version of the all-electrical Datta-Das spin-field effect transistor
Drude weight, cyclotron resonance, and the Dicke model of graphene cavity QED
Full text linkThe Dicke model of cavity quantum electrodynamics is approximately realized in condensed matter when the cyclotron transition of a two-dimensional electron gas is nearly resonant with a cavity photon mode. We point out that in the strong coupling limit the Dicke model of cavity cyclotron resonance must be supplemented by a term that is quadratic in the cavity photon field and suppresses the model's transition to a super-radiant state. We develop the theory of graphene cavity cyclotron resonance and show that the quadratic term, which is absent in graphene's low-energy Dirac model Hamiltonian, is in this case dynamically generated by virtual inter-band transitions.The unique optoelectronic properties of graphene make this two-dimensional material an ideal platform
for fundamental studies of cavity quantum electrodynamics in the strong-coupling regime. The celebrated
Dicke model of cavity quantum electrodynamics can be approximately realized in this material when the
cyclotron transition of its 2D massless Dirac fermion carriers is nearly resonant with a cavity photon
mode. We develop the theory of strong matter-photon coupling in this circumstance, emphasizing the
essential role of a dynamically generated matter energy term that is quadratic in the photon field and
absent in graphene’s low-energy Dirac model
Time-bin entanglement of quasiparticles in semiconductor devices
No full text10.1103/PhysRevB.84.195307Physical Review B - Condensed Matter and Materials Physics8419-PRBM
Coherent Detection of Electron Dephasing
Full text linkWe show that an Aharonov-Bohm ring with asymmetric electron injection can act as a coherent detector of electron dephasing. The presence of a dephasing source in one of the two arms of a moderately-tohighly asymmetric ring changes the response of the system from total reflection to complete transmission while preserving the coherence of the electrons propagating from the ring, even for strong dephasing. We interpret this phenomenon as an implementation of an interaction-free measurement
Bipolar thermoelectric superconducting single-electron transistor
Full text linkThermoelectric effects in normal metals and superconductors are usually very small due to the presence of electron -hole symmetry. Here, we show that superconducting junctions brought out of equilibrium manifest a sizable bipolar thermoelectric effect that stems from a strong violation of the detailed balance determined by the crucial role of the interactions at the mean -field level. To fully control the effect, we consider a thermally biased SIS'IS junction where the capacitance of the central S' region is small enough to establish a Coulomb blockade regime. By exploiting charging effects we are able to tune the Seebeck voltage, the thermocurrent, and thereby the power output of this structure, via an external gate voltage. We then analyze the main figures of merit of bipolar thermoelectricity and we prospect for possible applications
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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