4,305 research outputs found

    Inter-site Coulomb interaction and Heisenberg exchange

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    Based on exact diagonalization results for small clusters we discuss the effect of inter-site Coulomb repulsion in Mott-Hubbard or charge transfer insulators. Whereas the exchange constant J for direct exchange is substantially enhanced by inter-site Coulomb interaction, that for superexchange is suppressed. The enhancement of J in the single-band models holds up to the critical value for the charge density wave (CDW) instability, thus opening the way for large values of J. Single-band Hubbard models with sufficiently strong inter-site repulsion to be near a CDW instability thus may provide `physical' realizations of t-J like models with the `unphysical' parameter ratio J/t=1.Comment: Revtex file, 4 PRB pages, with 5 embedded ps-files. To appear in PRB, rapid communications. Hardcopies of figures or the entire manuscript may also be obtained by e-mail request to: [email protected]

    Conformal Fixed Points of Unidentified Gauge Theories

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    In this article we discuss gauge/strings correspondence based on the non-critical strings. With this goal we present several remarkable sigma models with the AdS target spaces. The models have kappa symmetry and are completely integrable. The radius of the AdS space is fixed and thus they describe isolated fixed points of gauge theories in various dimensionsComment: 14 page

    Direct observation of the glue pairing the halo of the nucleus 11Li

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    With the help of a unified description of the nuclear structure and of the direct reaction mechanism we show that a recent 1H(11Li,9Li)3H experiment provides, for the first time in nuclear physics, direct evidence of phonon mediated pairing.Comment: 9 pages, 4 figures. Major change

    Charged excitons in doped extended Hubbard model systems

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    We show that the charge transfer excitons in a Hubbard model system including nearest neighbor Coulomb interactions effectively attain some charge in doped systems and become visible in photoelectron and inverse photoelectron spectroscopies. This shows that the description of a doped system by an extended Hubbard model differs substantially from that of a simple Hubbard model. Longer range Coulomb interactions cause satellites in the one electron removal and addition spectra and the appearance of spectral weight if the gap of doped systems at energies corresponding to the excitons of the undoped systems. The spectral weight of the satellites is proportional to the doping times the coordination number and therefore is strongly dependent on the dimension.Comment: 10 pages revtex, 5 figures ps figures adde

    Thermal detection of single e-h pairs in a biased silicon crystal detector

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    We demonstrate that individual electron-hole pairs are resolved in a 1 cm2^2 by 4 mm thick silicon crystal (0.93 g) operated at \sim35 mK. One side of the detector is patterned with two quasiparticle-trap-assisted electro-thermal-feedback transition edge sensor (QET) arrays held near ground potential. The other side contains a bias grid with 20\% coverage. Bias potentials up to ±\pm 160 V were used in the work reported here. A fiber optic provides 650~nm (1.9 eV) photons that each produce an electron-hole (eh+e^{-} h^{+}) pair in the crystal near the grid. The energy of the drifting charges is measured with a phonon sensor noise σ\sigma \sim0.09 eh+e^{-} h^{+} pair. The observed charge quantization is nearly identical for h+h^+'s or ee^-'s transported across the crystal.Comment: 4 journal pages, 5 figure

    Measurement Of Quasiparticle Transport In Aluminum Films Using Tungsten Transition-Edge Sensors

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    We report new experimental studies to understand the physics of phonon sensors which utilize quasiparticle diffusion in thin aluminum films into tungsten transition-edge-sensors (TESs) operated at 35 mK. We show that basic TES physics and a simple physical model of the overlap region between the W and Al films in our devices enables us to accurately reproduce the experimentally observed pulse shapes from x-rays absorbed in the Al films. We further estimate quasiparticle loss in Al films using a simple diffusion equation approach.Comment: 5 pages, 6 figures, PRA

    Strong-field approximation for Coulomb explosion of H_2^+ by short intense laser pulses

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    We present a simple quantum mechanical model to describe Coulomb explosion of H2+_2^+ by short, intense, infrared laser pulses. The model is based on the length gauge version of the molecular strong-field approximation and is valid for pulses shorter than 50 fs where the process of dissociation prior to ionization is negligible. The results are compared with recent experimental results for the proton energy spectrum [I. Ben-Itzhak et al., Phys. Rev. Lett. 95, 073002 (2005), B. D. Esry et al., Phys. Rev. Lett. 97, 013003 (2006)]. The predictions of the model reproduce the profile of the spectrum although the peak energy is slightly lower than the observations. For comparison, we also present results obtained by two different tunneling models for this process.Comment: 8 pages, 4 figure

    Superstring action in AdS_5 x S^5: kappa symmetry light cone gauge

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    As part of program to quantize superstrings in AdS_5 x S^5 background in light cone approach we find the explicit form of the corresponding Green-Schwarz action in fermionic light-cone kappa-symmetry gauge. The resulting action is quadratic and quartic in fermions. In the flat space limit it reduces to the standard light-cone Green-Schwarz action, and also has the correct superparticle limit. We discuss fixing the bosonic light-cone gauge and a reformulation of the action in terms of 2-d Dirac spinors.Comment: 32 pages, latex. v4: misprints corrected in Appendix A, to appear in Phys Rev

    Mixed-symmetry massless gauge fields in AdS(5)

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    Free AdS(5) mixed-symmetry massless bosonic and fermionic gauge fields of arbitrary spins are described by using su(2,2) spinor language. Manifestly covariant action functionals are constructed and field equations are derived.Comment: 13 pages; v2: title changed, typos corrected, minor changes, reference added; v3: minor changes, published versio
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