The Experts below are selected from a list of 336 Experts worldwide ranked by ideXlab platform
T P Devereaux - One of the best experts on this subject based on the ideXlab platform.
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using rixs to uncover Elementary Charge and spin excitations
Physical Review X, 2016Co-Authors: Chunjing Jia, Krzysztof Wohlfeld, Yao Wang, Brian Moritz, T P DevereauxAbstract:X-ray photons can be used as unique probes to understand the properties of Elementary excitations. A theoretical study demonstrates that a complex x-ray scattering technique captures richer spectral information than simpler two-particle correlation functions in cuprate superconductors.
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using rixs to uncover Elementary Charge and spin excitations in correlated materials
arXiv: Strongly Correlated Electrons, 2015Co-Authors: Chunjing Jia, Krzysztof Wohlfeld, Yao Wang, Brian Moritz, T P DevereauxAbstract:Despite significant progress in resonant inelastic x-ray scattering (RIXS) experiments on cuprates at the Cu L-edge, a theoretical understanding of the cross-section remains incomplete in terms of Elementary excitations and the connection to both Charge and spin structure factors. Here we use state-of-the-art, unbiased numerical calculations to study the low energy excitations probed by RIXS in undoped and doped Hubbard model relevant to the cuprates. The results highlight the importance of scattering geometry, in particular both the incident and scattered x-ray photon polarization, and demonstrate that on a qualitative level the RIXS spectral shape in the cross-polarized channel approximates that of the spin dynamical structure factor. However, in the parallel-polarized channel the complexity of the RIXS process beyond a simple two-particle response complicates the analysis, and demonstrates that approximations and expansions which attempt to relate RIXS to less complex correlation functions can not reproduce the full diversity of RIXS spectral features.
W Poirier - One of the best experts on this subject based on the ideXlab platform.
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practical quantum realization of the ampere from the Elementary Charge
Physical Review X, 2016Co-Authors: J Brunpicard, S Djordjevic, D Leprat, F Schopfer, W PoirierAbstract:A precision quantum current source has been designed to calibrate currents in terms of the soon-to-be-redefined International System of Units.
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resistance metrology based on the quantum hall effect
European Physical Journal-special Topics, 2009Co-Authors: W Poirier, F SchopferAbstract:The Quantum Hall effect (QHE), a macroscopic effect of solid state physics, provides a universal representation of the unit of resistance which depends on the Elementary Charge e and the Planck constant h only. If implemented according to specific technical guidelines, the quantum resistance standard can be reproduced with a relative uncertainty below one part in 109. Calibrations of wire resistors in terms of the QHE can be carried out with similarly low uncertainties by using resistance bridges equipped with cryogenic current comparators, the performance of which relies on the magnetic flux sensitivity of superconducting quantum interference devices (SQUID). Using a special connection technique, the fundamental properties of the QHE allow the fabrication of arrays combining a large number of single Hall bars connected in series or in parallel and which demonstrate quantum accuracy. Similar to the case of voltage metrology with Josephson array voltage standards, an improvement of resistance metrology is expected from the availability of quantum Hall array resistance standards (QHARS). The QHE Wheatstone bridge, which is another application of the same connection technique, opens the way to new universality tests of the QHE with a relative uncertainty below one part in 1011. At frequencies in the kilohertz range, the recent progress in the application of coaxial bridges to the QHE allows metrologists to operate a quantum resistance standard with alternating current reaching an accuracy of some parts in 108. Finally, the discovery of the QHE in graphene opens new horizons for the resistance metrology.
Wolfgang Belzig - One of the best experts on this subject based on the ideXlab platform.
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Elementary Charge transfer processes in mesoscopic conductors
Bulletin of the American Physical Society, 2009Co-Authors: Mihajlo Vanevic, Yuli V. Nazarov, Wolfgang BelzigAbstract:We determine Charge-transfer statistics in a quantum conductor driven by a time-dependent voltage and identify the Elementary transport processes. At zero temperature unidirectional and bidirectional single-Charge transfers occur. The unidirectional processes involve electrons injected from the source terminal due to excess dc bias voltage. The bidirectional processes involve electron-hole pairs created by time-dependent voltage bias. This interpretation is further supported by the Charge-transfer statistics in a multiterminal beam-splitter geometry in which injected electrons and holes can be partitioned into different outgoing terminals. The probabilities of Elementary processes can be probed by noise measurements: the unidirectional processes set the dc noise level, while bidirectional ones give rise to the excess noise. For ac voltage drive, the noise oscillates with increasing the driving amplitude. The decomposition of the noise into the contributions of Elementary processes reveals the origin of these oscillations: the number of electron-hole pairs generated per cycle increases with increasing the amplitude. The decomposition of the noise into Elementary processes is studied for different time-dependent voltages. The method we use is also suitable for systematic calculation of higher-order current correlators at finite temperature. We obtain current noise power and the third cumulant in the presence of time-dependent voltage drive. The Charge-transfer statistics at finite temperature can be interpreted in terms of multiple-Charge transfers with probabilities which depend on energy and temperature.
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Elementary Charge transfer processes in a superconductor ferromagnet entangler
EPL, 2008Co-Authors: Jan Petter Morten, Daniel Huertashernando, Wolfgang Belzig, Arne BrataasAbstract:We study the production of spatially separated entangled electrons in ferromagnetic leads from Cooper pairs in a superconducting lead. We give a complete description of the Elementary Charge transfer processes, i) transfer of Cooper pairs out of the superconductor by Andreev reflection and ii) distribution of the entangled quasiparticles among the ferromagnetic leads, in terms of their statistics. The probabilities that entangled electrons flow into spatially separated leads are completely determined by experimentally measurable tunnel conductances and polarizations. Finally, we investigate how currents, noise and cross-correlations are affected by transport of entangled electrons.
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Elementary Charge transfer processes in a superconductor ferromagnet entangler
arXiv: Superconductivity, 2006Co-Authors: Jan Petter Morten, Daniel Huertashernando, Wolfgang Belzig, Arne BrataasAbstract:We study the production of spatially separated entangled electrons in ferromagnetic leads from Cooper pairs in a superconducting lead. We give a complete description of the Elementary Charge transfer processes, i) transfer of Cooper pairs out of the superconductor by Andreev reflection and ii) distribution of the entangled quasiparticles among the ferromagnetic leads, in terms of their statistics. The probabilities that entangled electrons flow into spatially separated leads are completely determined by experimentally measurable conductances and polarizations. Finally, we investigate how currents, noise and cross correlations are affected by transport of entangled electrons.
Yuli V. Nazarov - One of the best experts on this subject based on the ideXlab platform.
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Elementary Charge transfer processes in mesoscopic conductors
Bulletin of the American Physical Society, 2009Co-Authors: Mihajlo Vanevic, Yuli V. Nazarov, Wolfgang BelzigAbstract:We determine Charge-transfer statistics in a quantum conductor driven by a time-dependent voltage and identify the Elementary transport processes. At zero temperature unidirectional and bidirectional single-Charge transfers occur. The unidirectional processes involve electrons injected from the source terminal due to excess dc bias voltage. The bidirectional processes involve electron-hole pairs created by time-dependent voltage bias. This interpretation is further supported by the Charge-transfer statistics in a multiterminal beam-splitter geometry in which injected electrons and holes can be partitioned into different outgoing terminals. The probabilities of Elementary processes can be probed by noise measurements: the unidirectional processes set the dc noise level, while bidirectional ones give rise to the excess noise. For ac voltage drive, the noise oscillates with increasing the driving amplitude. The decomposition of the noise into the contributions of Elementary processes reveals the origin of these oscillations: the number of electron-hole pairs generated per cycle increases with increasing the amplitude. The decomposition of the noise into Elementary processes is studied for different time-dependent voltages. The method we use is also suitable for systematic calculation of higher-order current correlators at finite temperature. We obtain current noise power and the third cumulant in the presence of time-dependent voltage drive. The Charge-transfer statistics at finite temperature can be interpreted in terms of multiple-Charge transfers with probabilities which depend on energy and temperature.
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supercurrent reversal in quantum dots
Nature, 2006Co-Authors: Yuli V. Nazarov, Erik P. A. M. Bakkers, Silvia Franceschi, Leo P. KouwenhovenAbstract:This paper reports a study of supercurrents through a quantum dot created in a semiconductor nanowire by local electrostatic gating. Owing to strong Coulomb interaction, electrons only tunnel one-by-one through the discrete energy levels of the quantum dot. This, nevertheless, can yield a supercurrent when subsequent tunnel events are coherent. When two superconductors are electrically connected by a weak link—such as a tunnel barrier—a zero-resistance supercurrent can flow1,2. This supercurrent is carried by Cooper pairs of electrons with a combined Charge of twice the Elementary Charge, e. The 2e Charge quantum is clearly visible in the height of voltage steps in Josephson junctions under microwave irradiation, and in the magnetic flux periodicity of h/2e (where h is Planck's constant) in superconducting quantum interference devices2. Here we study supercurrents through a quantum dot created in a semiconductor nanowire by local electrostatic gating. Owing to strong Coulomb interaction, electrons only tunnel one-by-one through the discrete energy levels of the quantum dot. This nevertheless can yield a supercurrent when subsequent tunnel events are coherent3,4,5,6,7. These quantum coherent tunnelling processes can result in either a positive or a negative supercurrent, that is, in a normal or a π-junction8,9,10, respectively. We demonstrate that the supercurrent reverses sign by adding a single electron spin to the quantum dot. When excited states of the quantum dot are involved in transport, the supercurrent sign also depends on the character of the orbital wavefunctions.
J S Reparaz - One of the best experts on this subject based on the ideXlab platform.
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comparative study of the pressure dependence of optical phonon transverse effective Charges and linewidths in wurtzite inn
Physical Review B, 2018Co-Authors: J S Reparaz, Markus R Wagner, Pereira K Da Silva, A H Romero, J Serrano, Gordon Callsen, Soojeong Choi, James S SpeckAbstract:We investigate the hydrostatic pressure dependence of the zone center optical phonons of $c$-plane and $a$-plane wurtzite InN epilayers grown on GaN substrates. The longitudinal to transverse mode splitting for the ${A}_{1}$ and ${E}_{1}$ modes was found to increase with increasing pressure, whereas the associated transverse effective Charge decreases for both modes as ${e}_{T}^{*}({A}_{1})=2.93--9.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}P$ and ${e}_{T}^{*}({E}_{1})=2.80--10.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}P$ (in units of Elementary Charge and $P$ in GPa). These observations are well in line with results for other II--VI, III--V, and group-IV semiconductor compounds as far as the relation between the magnitude and sign of the pressure derivative of ${e}_{T}^{*}$ and the bond ionicity is concerned. As the latter increases so does $|\ensuremath{\partial}{e}_{T}^{*}/\ensuremath{\partial}P|$ with a sign change from positive to negative for bond ionicities around ${f}_{i}=0.46$ for compounds with anions belonging to the first row of the Periodic Table. A comparison of the results for InN and other nine tetrahedrally bonded compounds indicate that the pressure behavior of the transverse effective Charge is mainly determined by the strength of the Pauli repulsion between cation valence electrons and those of the anion core. We also perform ab initio calculations in order to address the origin of the observed increase in linewidth of the ${E}_{2}^{\text{high}}$ mode which is found to arise from a pressure-induced increase in the rate of two-phonon decay processes. This broadening is associated with tuning into resonance of a steep edge in the two-phonon density of states around 460 ${\mathrm{cm}}^{\ensuremath{-}1}$ with the frequency of the ${E}_{2}^{\text{high}}$ mode.
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reduction of the transverse effective Charge of optical phonons in zno under pressure
Applied Physics Letters, 2010Co-Authors: J S Reparaz, Luis Antonio Muniz, Markus R Wagner, A R Goni, M I Alonso, A Hoffmann, B K MeyerAbstract:From Raman scattering on a-plane wurtzite ZnO crystals we obtained a decreasing splitting between longitudinal and transversal optical phonons with A1 and E1 symmetry as a function of hydrostatic pressure up to 5.5 GPa. Consequently, the transverse effective Charge (eT∗) exhibits a strong reduction with increasing pressure, yielding 2.17–14.6×10−3 P/GPa and 2.04–13.7×10−3 P/GPa (in units of the Elementary Charge) for the A1 and E1 phonons, respectively. We find a clear systematic in the linear pressure coefficient of eT∗ with bond polarity for the series of wide-band gap semiconductors SiC, AlN, GaN, and ZnO.