11,858 research outputs found

    Spin-orbit coupling induced by a mass gradient

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    The existence of a spin-orbit coupling (SOC) induced by the gradient of the effective mass in low-dimensional heterostructures is revealed. In structurally asymmetric quasi-two-dimensional semiconductor heterostructures the presence of a mass gradient across the interfaces results in a SOC which competes with the SOC created by the electric field in the valence band. However, in graded quantum wells subjected to an external electric field, the mass-gradient induced SOC can be finite even when the electric field in the valence band vanishes.Comment: 4 pages, 2 figures, 1 tabl

    Nonradiative Recombination of Excitons in Carbon Nanotubes Mediated by Free Charge Carriers

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    Free electrons or holes can mediate the nonradiative recombination of excitons in carbon nanotubes. Kinematic constraints arising from the quasi one-dimensional nature of excitons and charge carriers lead to a thermal activation barrier for the process. However, a model calculation suggests that the rate for recombination mediated by a free electron is the same order of magnitude as that of two-exciton recombination. Small amounts of doping may contribute to the short exciton lifetimes and low quantum yields observed in carbon nanotubes.Comment: 18 pages, 4 figures. Submitted to Physical Review

    Probing the largest scale structure in the universe with polarization map of galaxy clusters

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    We introduce a new formalism to describe the polarization signal of galaxy clusters on the whole sky. We show that a sparsely sampled, half-sky map of the cluster polarization signal at z1z\sim 1 would allow to better characterize the very large scale density fluctuations. While the horizon length is smaller in the past, two other competing effects significantly remove the contribution of the small scale fluctuations from the quadrupole polarization pattern at z1z\sim 1. For the standard Lambda-CDM universe with vanishing tensor mode, the quadrupole moment of the temperature anisotropy probed by WMAP is expected to have a ~32% contribution from fluctuations on scales below 6.3h^{-1}Gpc. This percentage would be reduced to ~2% level for the quadrupole moment of polarization pattern at z1z\sim 1. A cluster polarization map at z1z \sim 1 would shed light on the potentially anomalous features of the largest scale structure in the observable universe.Comment: 5 pages, 2 figures, revised version, to appear in PR

    Quantum corrected Langevin dynamics for adsorbates on metal surfaces interacting with hot electrons

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    We investigate the importance of including quantized initial conditions in Langevin dynamics for adsorbates interacting with a thermal reservoir of electrons. For quadratic potentials the time evolution is exactly described by a classical Langevin equation and it is shown how to rigorously obtain quantum mechanical probabilities from the classical phase space distributions resulting from the dynamics. At short time scales, classical and quasiclassical initial conditions lead to wrong results and only correctly quantized initial conditions give a close agreement with an inherently quantum mechanical master equation approach. With CO on Cu(100) as an example, we demonstrate the effect for a system with ab initio frictional tensor and potential energy surfaces and show that quantizing the initial conditions can have a large impact on both the desorption probability and the distribution of molecular vibrational states

    Dispersion and wavefunction symmetry in cold atoms experiencing artificial gauge fields

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    We analyze the single particle quantum mechanics of an atom whose dispersion is modified by spin orbit coupling to Raman lasers. We calculate how the novel dispersion leads to unusual single particle physics. We focus on the symmetry of the ground state wavefunction in different potentials.Comment: 5 pages, 7 figure

    Couplings in coupled channels versus wave functions in the case of resonances: application to the two Λ(1405)\Lambda(1405) states

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    In this paper we develop a formalism to evaluate wave functions in momentum and coordinate space for the resonant states dynamically generated in a unitary coupled channel approach. The on shell approach for the scattering matrix, commonly used, is also obtained in Quantum Mechanics with a separable potential, which allows one to write wave functions in a trivial way. We develop useful relationships among the couplings of the dynamically generated resonances to the different channels and the wave functions at the origin. The formalism provides an intuitive picture of the resonances in the coupled channel approach, as bound states of one bound channel, which decays into open ones. It also provides an insight and practical rules for evaluating couplings of the resonances to external sources and how to deal with final state interaction in production processes. As an application of the formalism we evaluate the wave functions of the two Λ(1405)\Lambda(1405) states in the πΣ\pi \Sigma, KˉN\bar{K} N and other coupled channels.Comment: 23 pages, 3 figures. v2: Added a section to calculate form factor

    Role of gauge invariance in B -> V gamma radiative weak decays

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    The role of gauge invariance in calculating B -> V gamma radiative weak decays is clarified. It is shown that the gauge invariance severely restricts the contributions mediated by the usual weak non-leptonic Hamiltonian dominated by u and c quaks with one photon attachment. Such contributions are found to be almost negligible.Comment: 5 pages, Revtex, no figure

    Zitterbewegung is not an observable

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    It has recently been claimed that Zitterbewegung has been observed. However, we argue that it is not an observable and that the authors' observations must be reinterpreted
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