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Tuesday Anomalous Thermopower in a Low-Density Two-Dimensional Electron System: Metallic Dependence, Giant Magnitude and Oscillatory density-dependence Vijay Narayan 1 , M. Pepper 2 , J. Griffiths 1 , H. Beere 1 , F. Sfigakis 1 , G. Jones 1 , D. Ritchie 1 and A. Ghosh 3 1 Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom 2 Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, United Kingdom 3 Department of Physics, Indian Institute of Science, Bangalore 560012, India We present thermopower S and electrical resistivity ρ 2DES measurements in a low-density (~ 10 14 m -2 ) two-dimensional electron system (2DES). We are interested in the regime where ρ 2DES >> h/e 2 and consequently the 2DES is expected to be strongly localised. Remarkably, however, we observe several aspects to the 2DES behaviour that are not consistent with insulating behaviour. First, the temperature-dependence of S is manifestly metallic, S growing linearly as a function of temperature up to ≈ 0.7 K. Second, the magnitude of S exceeds the Mott value valid for non-interacting metallic 2DESs at similar carrier densities by over two orders of magnitude. And third, we observe a seeming decoupling between ρ 2DES and S in their density-dependence whereby strong oscillations and even sign changes are observed in the latter which are completely absent in the former. We explore the role of the many-body Coulomb potential in these observations and the scope offered by this system towards sub-Kelvin Peltier refrigeration. [1] Vijay Narayan, M. Pepper, J. Griffiths, H. Beere, F. Sfigakis, G. Jones, D. Ritchie and A. Ghosh, Unconventional metallicity and giant thermopower in a strongly interacting twodimensional electron system, Phys. Rev. B 86, 125406 (2012) [2] Vijay Narayan, M. Pepper, J. Griffiths, H. Beere, F. Sfigakis, G. Jones, D. Ritchie and A. Ghosh, Evidence of Novel Quasiparticles in a Strongly Interacting Two-Dimensional Electron System: Giant Thermopower and Metallic Behaviour, J. Low Temp. Phys (accepted), DOI 10.1007/s10909-012-0718-0 __________________________________________________________________________ Delay-time and thermopower distributions at the spectrum edges of a chaotic scatterer A. Abbout (1,2) , G. Fleury (1) , J.-L. Pichard (1) and K. Muttalib (3) (1) Service de Physique de l'Etat Condensé CNRS URA 2464, CEA Saclay, 91191 Gif-sur- Yvette, France (2) Laboratoire CRISMAT, CNRS UMR 6508, 6 boulevard Maréchal Juin, F-14050, Caen, France (3) Department of Physics, University of Florida, Gainesville, FL 32611-8440, USA We study chaotic scattering outside the wide band limit, as the Fermi energy E F approaches the band edges E B of a one-dimensional lattice embedding a scattering region of M sites [1]. The Hamiltonian H M of this region is taken from the Cauchy orthogonal ensemble. The scattering is chaotic at E F if the average level density per site of H M at E F describes a semicircle as E F varies inside the conduction band. The edges of this semi-circle coincide with the band edges E B . We show that the delay-time and thermopower distributions differ near the edges from the universal expressions valid in the bulk [2]. To obtain the asymptotic universal forms of these edge distributions, one must keep constant the energy distance E F – E B measured in unit of the same energy scale (proportional to M -1/3 ) which is used for rescaling
Tuesday the energy level spacings at the spectrum edges of large Gaussian matrices. In particular the delay-time and the thermopower have the same universal edge distributions for arbitrary M as those for an M=2 scatterer, which we obtain analytically. [1] A. Abbout, G. Fleury, J.-L. Pichard and K. Muttalib, in preparation [2] P. W. Brouwer, K. M. Frahm and C. W. J. Beenakker, Quantum Mechanical Time-Delay Matrix in Chaotic Scattering, Phys. Rev. Lett. 78, 4737 (1997) __________________________________________________________________________ Harvesting fluctuations at electrical hot spots Rafael Sánchez Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), Madrid, Spain In electrical circuits hot spots occur naturally at places where energy is dissipated. Here we propose a controlled experiment which can demonstrate the appearance of directed current as a consequence of a hot spot. We investigate transport generated in Coulomb coupled electrical conductors from excess electric or thermal fluctuations at the coupling capacitance. If one of the conductors supports a bias voltage, out of equilibrium charge fluctuations remove detailed balance in the unbiased system manifested in a drag current. Non linear fluctuation relations can nevertheless be obtained [1]. Coulomb coupled conductors permit separate directions of the heat and current flux [2]. In our model, one of the conductors is connected via only one lead to a hot reservoir. The other conductor is connected to two leads. Such a geometry can be used for detection of non linear heat fluctuations [3]. We investigate the minimal conditions needed to generate directed current flow for a system of two quantum dot conductors in which both energy and charge states are quantized. In quantum dots energy to current conversion can be optimal with one electron transferred for every heat quantum given up by the hot reservoir. We show that at the point of maximum power extraction the efficiency approaches one half of the Carnot efficiency. However, the generated power is small. Larger currents can be generated in a chaotic mesoscopic cavity coupled to two leads. Non linearities due to energy dependent contact transmission to leads are responsible for the rectification of thermal fluctuations in a coupled hot cavity, leading to an electrical current [4]. The maximum power produced by the system will be discussed. [1] R. Sánchez, R. López, D. Sánchez, and M. Büttiker, Mesoscopic Coulomb drag, broken detailed balance and fluctuation relations, Phys. Rev. Lett. 104 076801 (2010) [2] R. Sánchez, and M. Büttiker, Optimal energy quanta to current conversion, Phys. Rev. B 83 085428 (2011) [3] R. Sánchez, and M. Büttiker, Detection of single electron heat transfer statistics, arXiv:1207:2587 [4] B. Sothmann, R. Sánchez, A.N. Jordan, and M. Büttiker, Rectification of termal fluctuations in a chaotic cavity heat engine, Phys. Rev. B 85 205301 (2012)
Page 1 and 2: 2012 22 Octobre 27 Octobre WORKSHOP
Page 3 and 4: Afternoon Morning Timetable Monday
Page 5 and 6: 15h50 - 16h20 Coffee Break 16h20 -
Page 7 and 8: Monday Abstracts Monday, October 22
Page 9 and 10: Monday Single-Electron Tunneling an
Page 11: Tuesday Tuesday, October 23 Random-
Page 15 and 16: Tuesday Electron refrigeration by n
Page 17 and 18: Wednesday [4] K. Saito, G. Benenti,
Page 19 and 20: Thursday [3] B. A. Bernevig, T. L.
Page 21 and 22: Thursday Electronic standing waves
Page 23 and 24: Friday Nanoscale inhomogeneities in
Page 25 and 26: Friday Electron focusing in graphem
Page 27 and 28: Friday molecules. We explain the or
Page 29 and 30: Posters Posters Ab-initio study of
Page 31 and 32: Posters Nonclassical photon-pair pr

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