[seminar] SEMINAR na IF-u u SRIJEDU, 13. 04. 2011.

[Berislav Horvatic]

      Institut za fiziku, Bijenička cesta 46,

      predavaonica u zgradi Mladen Paić

      srijeda, 13. travnja 2011, u 15:00 sati

       
     
      Aspects of Nonequilibrium Physics: Ultrafast Population transfer and Quantum Hall effect

       
     
      Dr. Christoph Uiberacker
     
       

      Montanuniversität Leoben, Institut für Physik,

      Franz-Josef-Straße 18, 8700 Leoben, Austria

       

      E-mail: christoph.uiberacker at unileoben.ac.at

       
     
      N-level models are very useful in physics and chemistry, especially for discussing population transfer in strong, short laser pulses (e.g. isomerization reactions [1]). In most control strategies [2] the resulting field is complicated and hard to interpret. We therefore study numerically as well as analytically population transfer using the time-dependent Schrödinger equation with external fields that depend on a few concrete parameters. In this way we found a semi-classical resonance conditions on the amplitude of the field in the limit of highly multi-photon processes [3]. As an application we study isomerization of HCN to HNC in a pump-dump setup as well as the relevance of the dipole resonance to isomerization and in model systems with 2-4 levels.

      Using Floquet theory we recently were able to rigorously prove and generalize the criterion on population inversion in two-level systems by Holthaus [4] to arbitrary pulses.

      The Nonequilibrium Network Model (NNM) [5,6] describes the electrochemical potential in 2d electron systems by using the Landauer-Büttiker approach. The chemical potential distribution is obtained, for linear local response, from an inhomogeneous system of linear equations, respecting the potential boundary condition from injected currents. We show that the construction of the network guarantees current conservation even in the nonlinear transport regime.

      Due to the lack of simulation tools for realistic geometries of complicated quantum Hall samples there are experiments that are not fully understood yet. Already some years ago R. G. Mani recorded a shift of the Hall resistance transitions using partial gating of a sample consisting of an anti-Hall bar within a Hall bar. Using the NNM we find qualitative agreement. By fitting to the experimental Hall resistance we reproduce the carrier concentration, the bare gating voltage and the curvature of saddles points. Using a simple statistical argument by Gerhardts [7] we can estimate the height and correlation length of the charge fluctuations in the 2d electron gas.

      [1]      C.Uiberacker and W.Jakubetz, "Molecular isomerization induced by ultrashort infrared pulses. I. Few-cycle to sub-one-cycle gaussian pulses and the role of the carrier-envelope phase", J.Chem.Phys. 120,11532 (2004), ibid., "Molecular isomerization induced by ultrashort infrared pulses. II. Pump-dump isomerization using pairs of time-delayed half-cycle pulses", J.Chem.Phys. 120, 11540 (2004)

      [2]      H. Rabitz, R. de Vivie-Riedle, M. Motzkus, K. Kompa, "Whither the Future of Controlling Quantum Phenomena?", Science 288, 824 (2000)

      [3]      C.Uiberacker and W.Jakubetz, "Strong-field dipole resonance: Limiting analytical cases", Phys. Rev. A 80, 063406 (2009)

      [4]      M. Holthaus, "Pulse-Shape-Controlled Tunneling in a Laser Field", Phys. Rev. Lett. 69, 1596 (1992)

      [5]      J. Oswald and M. Oswald, "Circuit type simulations of magneto-transport in the quantum Hall effect regime", J. Phys.: Condens. Matter 18, R101 (2006)

      [6]      C. Uiberacker, C. Stecher, and J. Oswald, "Systematic study of nonideal contacts in integer quantum Hall systems", Phys. Rev. B 80, 235331 (2009).

      [7]      U. Wulf, V. Gudmundsson, and R. R. Gerhardts, "Screening properties of the two-dimensional electron gas in the quantum Hall regime", Phys. Rev. B 38, 4218 (1988)

       

      http://personal.unileoben.ac.at/oswald/nipi/nipihome.htm

       
     
      Voditelji seminara IF-a:  Berislav Horvatić  &  Ivica Živković
     

 
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