6,212 research outputs found
Observation of cooper pair splitting and andreev bound states in carbon nanotubes
Get PDFIn this thesis, we investigate Cooper pair splitting in double quantum dot devices made from carbon nanotubes. We present transport measurements in which the controlled splitting of Cooper pairs dominates the current through such a device, reaching unprecedented splitting efficiencies of up to 90%.
In another experiment we use Cooper pair splitting (and a related non-local transport processes) as a tool to investigate Andreev bound states. Andreev bound states are a key concept in mesoscopic superconductivity. They can form due to the penetration of Cooper pairs into a quantum dot, leading to a new type of energy level that differs drastically from conventional particle-in-a-box states
N. S. Gumilyov in the light of the “new Hesychasm” by D. Andreev
Get PDFThe problem of N. S. Gumilyov’s philosophical and artistic reception in the work of D. Andreev is considered. Works devoted to the Russian writer N. S. Gumilev are investigated in connection with this. The relevance of the research is due to the need to state and highlight the problems of the Hesychast traditions in the work of Andreev, since the very life and work of the author of the “Rose of the World” became a continuation of the Russian Hesychastic spiritual, cultural and artistic tradition in the twentieth century. The definitions of the concepts “new Hesychasm by D. Andreev”, “Metaisihazm” are given. The novelty of the research is seen in the fact that for the first time in literary criticism the problem of the “new Hesychasm” of D. Andreev is raised. The Hesychast interpretation of the image and fate of Gumilyov is revealed. A classification of Hesychast practices of spiritual achievement is proposed, which Andreev refers to in order to characterize his older brother of the quill. The results of a comparative analysis of key lexemes in the works of Gumilev and Andreev are presented. The presence of these lexical markers is considered as evidence of a poetic dialogue, a convergence of poets through the decades. The significance of this dialogue in the construction of the metahistorical and life-giving poetic world of D. Andreev is revealed. The question regarding the interpretation of the image of N. S. Gumilev as a symbol of the “ennobled man” in the “Rose of the World” by D. Andreev is raised
Tunable Crossed Andreev Reflection and Elastic Cotunneling in Hybrid Nanowires
No full textA short superconducting segment can couple attached quantum dots via elastic cotunneling (ECT) and crossed Andreev reflection (CAR). Such coupled quantum dots can host Majorana bound states provided that the ratio between CAR and ECT can be controlled. Metallic superconductors have so far been shown to mediate such tunneling phenomena, albeit with limited tunability. Here, we show that Andreev bound states formed in semiconductor-superconductor heterostructures can mediate CAR and ECT over mesoscopic length scales. Andreev bound states possess both an electron and a hole component, giving rise to an intricate interference phenomenon that allows us to tune the ratio between CAR and ECT deterministically. We further show that the combination of intrinsic spin-orbit coupling in InSb nanowires and an applied magnetic field provides another efficient knob to tune the ratio between ECT and CAR and optimize the amount of coupling between neighboring quantum dots.QRD/Kouwenhoven LabQRD/Wimmer GroupQRD/Goswami LabBUS/Quantum DelftQN/Wimmer GroupQN/Kouwenhoven LabQubit Research Divisio
Transient electromagnetic fields generated in experiments at the PHELIX laser facility
No full textLarge-amplitude electromagnetic radiofrequency fields are created by the charge-separation induced in interactions of high-intensity, short-pulse lasers with solid targets and have intensity that decreases with the distance from the target. Alternatively, it was experimentally proved very recently that charged particles emitted by petawatt laser-target interactions can be deposited on a capacitor-collector structure, far away from the target, and lead to the rapid (nanosecond-scale) generation of large quasi-static electric fields , over wide regions. We demonstrate here the generation of both these fields in experiments at the PHELIX laser facility, with approximately energy and approximately intensity, for picoseconds laser pulses, interacting with pre-ionized polymer foams of near critical density. Quasi-static fields, up to tens of kV/m, were here observed at distances larger than from the target, with results much higher than the radiofrequency component. This is of primary importance for inertial-confinement fusion and laser-plasma acceleration and also for promising applications in different scenarios
Andreev bound states in superconductor/ferromagnet point contact Andreev reflection spectra
Get PDFAs charge carriers traverse a single superconductor ferromagnet interface, they experience an additional spin-dependent phase angle that results in spin mixing and the formation of a bound state called the Andreev bound state. Here we explore whether point contact Andreev reflection can be used to detect the Andreev bound state and, within the limits of our experiment, we extract the resulting spin mixing angle. By examining spectra taken from
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junctions, together with a compilation of literature data on highly spin polarized systems, we suggest that the existence of the Andreev bound state would resolve a number of long standing controversies in the literature of Andreev reflection, as well as defining a route to quantify the strength of spin mixing at superconductor-ferromagnet interfaces. Intriguingly, we find that for high transparency junctions, the spin mixing angle appears to take a relatively narrow range of values across all the samples studied. The ferromagnets we have chosen to study share a common property in terms of their spin arrangement, and our observations may point to the importance of this property in determining the spin mixing angle under these circumstances
Spin-filtered measurements of Andreev bound states in semiconductor-superconductor nanowire devices
No full textSemiconductor nanowires coupled to superconductors can host Andreev bound states with distinct spin and parity, including a spin-zero state with an even number of electrons and a spin-1/2 state with odd-parity. Considering the difference in spin of the even and odd states, spin-filtered measurements can reveal the underlying ground state. To directly measure the spin of single-electron excitations, we probe an Andreev bound state using a spin-polarized quantum dot that acts as a bipolar spin filter, in combination with a non-polarized tunnel junction in a three-terminal circuit. We observe a spin-polarized excitation spectrum of the Andreev bound state, which can be fully spin-polarized, despite strong spin-orbit interaction in the InSb nanowires. Decoupling the hybrid from the normal lead causes a current blockade, by trapping the Andreev bound state in an excited state. Spin-polarized spectroscopy of hybrid nanowire devices, as demonstrated here, is proposed as an experimental tool to support the observation of topological superconductivity.QRD/Kouwenhoven LabQRD/Wimmer GroupBUS/Quantum DelftQN/Kouwenhoven La
Quantum perfect crossed Andreev reflection in top-gated quantum anomalous Hall insulator-superconductor junctions
No full textWe investigate the quantum tunneling and Andreev reflection in a top-gated quantum anomalous Hall insulator proximity coupled with a superconductor junction. A quantized perfect crossed Andreev reflection with its coefficient being integer 1 is obtained and all other scattering processes (the normal reflection, normal tunneling, and local Andreev reflection) are completely suppressed when the topological superconductor phase with Chern number N = 1 is realized. This perfect crossed Andreev reflection originates from the tunneling of the chiral Majorana edge states, and the phase of tunneling amplitude only being 0 and pi plays a decisive role. Furthermore, because of the chiral characteristic of the Majorana edge states, the perfect crossed Andreev reflection is robust against the disorder and can work in a wide range of system parameters.NBRP of China [2015CB921102]; NSF-China [11004046, 11474084, 11574007, 11274364]SCI(E)ARTICLE249
Phase Sensitive Shot Noise in an Andreev Interferometer
No full textWe investigate nonequilibrium noise in a diffusive Andreev interferometer, in which currents emerging from two normal metal/superconductor (N-S) interfaces can interfere. We observe a modulation of the shot noise when the phase difference between the two N-S interfaces is varied by a magnetic flux. This is the signature of phase-sensitive fluctuations in the normal metal. The effective charge inferred from the shot noise measurement is close to qeff = 2e but shows phase-dependent deviations from 2e at finite energy, which we interpret as being due to pair correlations. Experimental data are in good agreement with predictions based on an extended Keldysh Green s function approach.publishe
Competition of multiband superconducting and magnetic order in ErNi 2 B 2 C observed by Andreev reflection
Get PDFPoint contacts (PC) Andreev reflection dV/dI spectra for the antiferromagnetic ( 6 K) superconductor ( 11 K) ErNi2B2C have been measured for the two main crystallographic directions. The observed retention of the Andreev reflection minima in dV/dI up to Tc directly points to an unusual superconducting order parameter (OP) vanishing at Tc. The temperature dependence of the OP was obtained from dV/dI using the recent theory of Andreev reflection including the pair-breaking effect. For the first time the existence of two superconducting OPs in ErNi2B2C is shown. A distinct decrease of both OPs as temperature is lowered below TN is observed
The optimal sequence compression
Get PDFThis paper presents the optimal compression for sequences with
undefined values.
Let we have undefined and defined positions in the
boolean sequence of length . The sequence code length
can't be less then in general case, otherwise at least two
sequences will have the same code.
We present the coding algorithm which generates codes of almost
length, i.e. almost equal to the lower bound.
The paper presents the decoding circuit too. The circuit has low
complexity which depends from the inverse density of defined values
.
The decoding circuit includes RAM and random logic. It performs
sequential decoding. The total RAM size is proportional to the
the number of random logic cells is proportional to
So the decoding circuit will be small enough even for the very low
density sequences. The decoder complexity doesn't depend of the
sequence length at all
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