Filters

2020 - 20224

More filters

2021 - 20224
Reset filters

Settings

Author: Sharma, S. × WGL Institute: MBI ×

Search Results

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Ab initio theory of plasmonic superconductivity within the Eliashberg and density-functional formalisms
    (Woodbury, NY : Inst., 2020) Davydov, A.; Sanna, A.; Pellegrini, C.; Dewhurst, J.K.; Sharma, S.; Gross, E.K.U.
    We extend the two leading methods for the ab initio computational description of phonon-mediated superconductors, namely Eliashberg theory and density-functional theory for superconductors (SCDFT), to include plasmonic effects. Furthermore, we introduce a hybrid formalism in which the Eliashberg approximation for the electron-phonon coupling is combined with the SCDFT treatment of the dynamically screened Coulomb interaction. The methods have been tested on a set of well-known conventional superconductors by studying how the plasmon contribution affects the phononic mechanism in determining the critical temperature (TC). Our simulations show that plasmonic SCDFT leads to a good agreement between predicted and measured TC's, whereas Eliashberg theory considerably overestimates the plasmon-mediated pairing and, therefore, TC. The hybrid approach, on the other hand, gives results close to SCDFT and overall in excellent agreement with experiments.
  • Thumbnail Image
    Item
    Valley control by linearly polarized laser pulses: example of WSe2
    (Washington, DC : OSA, 2022) Sharma, S.; Elliott, P.; Shallcross, S.
    Electrons at the band edges of materials are endowed with a valley index, a quantum number locating the band edge within the Brillouin zone. An important question is then how this index may be controlled by laser pulses, with current understanding that it couples exclusively via circularly polarized light. Employing both tight-binding and state-of-the-art time dependent density function theory, we show that on femtosecond time scales valley coupling is a much more general effect. We find that two time separated linearly polarized pulses allow almost complete control over valley excitation, with the pulse time difference and polarization vectors emerging as key parameters for valley control. Our findings highlight the possibility of controlling coherent electronic excitation by successive femtosecond laser pulses, and offer a route towards valleytronics in two-dimensional materials.
  • Thumbnail Image
    Item
    Ultrafast Optically Induced Ferromagnetic State in an Elemental Antiferromagnet
    (College Park, Md. : APS, 2021) Golias, E.; Kumberg, I.; Gelen, I.; Thakur, S.; Gördes, J.; Hosseinifar, R.; Guillet, Q.; Dewhurst, J.K.; Sharma, S.; Schüßler-Langeheine, C.; Pontius, N.; Kuch, W.
    We present evidence for an ultrafast optically induced ferromagnetic alignment of antiferromagnetic Mn in Co/Mn multilayers. We observe the transient ferromagnetic signal at the arrival of the pump pulse at the Mn L3 resonance using x-ray magnetic circular dichroism in reflectivity. The timescale of the effect is comparable to the duration of the excitation and occurs before the magnetization in Co is quenched. Theoretical calculations point to the imbalanced population of Mn unoccupied states caused by the Co interface for the emergence of this transient ferromagnetic state.
  • Thumbnail Image
    Item
    Ultrafast optically induced spin transfer in ferromagnetic alloys
    (Washington, DC [u.a.] : Assoc., 2020) Hofherr, M.; Häuser, S.; Dewhurst, J.K.; Tengdin, P.; Sakshath, S.; Nembach, H.T.; Weber, S.T.; Shaw, J.M.; Silva, T.J.; Kapteyn, H.C.; Cinchetti, M.; Rethfeld, B.; Murnane, M.M.; Steil, D.; Stadtmüller, B.; Sharma, S.; Aeschlimann, M.; Mathias, S.
    The vision of using light to manipulate electronic and spin excitations in materials on their fundamental time and length scales requires new approaches in experiment and theory to observe and understand these excitations. The ultimate speed limit for all-optical manipulation requires control schemes for which the electronic or magnetic subsystems of the materials are coherently manipulated on the time scale of the laser excitation pulse. In our work, we provide experimental evidence of such a direct, ultrafast, and coherent spin transfer between two magnetic subsystems of an alloy of Fe and Ni. Our experimental findings are fully supported by time-dependent density functional theory simulations and, hence, suggest the possibility of coherently controlling spin dynamics on subfemtosecond time scales, i.e., the birth of the research area of attomagnetism.