Awards & achievements
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Aug 2007Scholarship: PhD Scholarship
Other
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LanguagesEnglish, German, French, Italian
Questions and Answers (20) View all
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Answer added in Neuroscience2504 Neuroscience vs. Philosophy : Is free will an illusion?@Ammon: When I said Einstein was "wrong", I referred to the fact that Einstein refused to believe in the "chances" involved in quantum mechanics. Whet... [more]
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Answer added in Neuroscience2504 Neuroscience vs. Philosophy : Is free will an illusion?Ok. Herewith I will for now quit this discussion about will willingly, will see how my will evolves regarding future insights into how we function. Th... [more]
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Answer added in Neuroscience2504 Neuroscience vs. Philosophy : Is free will an illusion?Graeme: I am totally confused by your elaborations. Maybe I have a totally different definition of what "free will" is. For me, the question is not wh... [more]
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Answer added in Consciousness1001 What is consciousness? What is its nature and origin?I agree. As a side remark, slowness should be the virtue of the 21st century, deceleration instead of acceleration. Our bodies and minds are not const... [more]
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Answer added in Consciousness1001 What is consciousness? What is its nature and origin?Thanks, Graeme, for clarifying this. I understand stereochemistry, but it is still electro-magnetic. The electroweak and strong forces do not really p... [more]
Publications (16) View all
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Article: Doping Evolution of Oxygen K-edge X-ray Absorption Spectra in Cuprate Superconductors
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ABSTRACT: We study oxygen K-edge x-ray absorption spectroscopy (XAS) and investigate the validity of the Zhang-Rice singlet (ZRS) picture in overdoped cuprate superconductors. Using large-scale exact diagonalization of the three-orbital Hubbard model, we observe the effect of strong correlations manifesting in a dynamical spectral weight transfer from the upper Hubbard band to the ZRS band. The quantitative agreement between theory and experiment highlights an additional spectral weight reshuffling due to core-hole interaction. Our results confirm the important correlated nature of the cuprates and elucidate the changing orbital character of the low-energy quasi-particles, but also demonstrate the continued relevance of the ZRS even in the overdoped region.11/2012; -
Article: Understanding quantum decoherence using time-resolved spectroscopy
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ABSTRACT: In condensed matter physics, nonequilibrium pump-probe time domain spectroscopies have become an important tool to disentangle degrees of freedom whose coupling leads to broad structures in the frequency domain. Here, using the time-resolved solution of a model photoexcited electron-phonon system we show that the relaxational dynamics are governed by the equilibrium self-energy so that the phonon frequency sets a window for "slow" versus "fast" recovery. The overall temporal structure of this relaxation spectroscopy allows for a reliable and quantitative extraction of the electron-phonon coupling strength without requiring an effective temperature model.12/2012; -
Article: Mapping of the unoccupied states and relevant bosonic modes via the time dependent momentum distribution
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ABSTRACT: The unoccupied states of complex materials are difficult to measure, yet play a key role in determining their emergent properties. We propose a novel technique that can measure the unoccupied states, time-resolved Compton scattering, which measures the time-dependent momentum distribution (TDMD). Using a non-equilibrium Keldysh formalism, we study the TDMD for electrons coupled to a lattice in a pump-probe setup. We find a direct relation between temporal oscillations in the TDMD and the underlying unoccupied states, suggesting that both can be measured by time-resolved Compton scattering.10/2012; -
Article: Correlation tuned cross-over between thermal and nonthermal states following ultrafast transient pumping
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ABSTRACT: We examine electron-electron mediated relaxation following excitation of a correlated system by an ultrafast electric field pump pulse. The results reveal a dichotomy in the temporal evolution as one tunes through a Mott metal-to-insulator transition: in the metallic regime relaxation can be characterized by evolution toward a steady-state electronic distribution well described by Fermi-Dirac statistics with an increased effective temperature; however, in the insulating regime this quasithermal paradigm breaks down with relaxation toward a nonthermal state with a more complicated electronic distribution that does not vary monotonically as a function of energy. We characterize the behavior by studying changes in the energy, photoemission response, and electronic distribution as functions of time. Qualitatively these results should be observable on short enough time scales that the electrons behave like an isolated system not in contact with additional degrees of freedom which can act as a thermal bath. Importantly, proper modeling used to analyze experimental findings should account for this behavior, especially when using strong driving fields or studying materials whose physics may manifest the effects of strong correlations.07/2012; -
Article: Spin transport in Heisenberg antiferromagnets
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ABSTRACT: We analyze spin transport in insulating antiferromagnets described by the XXZ Heisenberg model in two and three dimensions. Spin currents can be generated by a magnetic-field gradient or, in systems with spin-orbit coupling, perpendicular to a time-dependent electric field. The Kubo formula for the longitudinal spin conductivity is derived analogously to the Kubo formula for the optical conductivity of electronic systems. The spin conductivity is calculated within interacting spin-wave theory. In the Ising regime, the XXZ magnet is a spin insulator. For the isotropic Heisenberg model, the dimensionality of the system plays a crucial role: In d=3 the regular part of the spin conductivity vanishes linearly in the zero frequency limit, whereas in d=2 it approaches a finite zero frequency value.01/2007;
