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Ultrafast dynamics in the high-symmetry and in the charge density wave phase of 2H-NbSe<sub>2</sub>

ORAL

Abstract

We investigate carrier and collective mode dynamics in 2H-NbSe2 using time-resolved optical pump-probe spectroscopy and compare the results with first-principle calculations. Broadband ultrafast reflectivity studies of 2H-NbSe2 in a wide temperature interval covering the normal, charge density wave (CDW) and superconducting phase were performed. Spectral features observed in the transient reflectivity experiment were associated with specific optical transitions obtained from band structure calculations. Displacive excitation of coherent phonons show CDW-associated coherent oscillations of the soft phonon mode across the whole spectral range. Temperature evolution of this coherent phonon mode in the low-excitation linear regime shows softening of the mode down to the TCDW with subsequent hardening below TCDW. From first principle calculations of electron-phonon coupling we associate the few picosecond electron-phonon relaxation time τ2 with a specific group of phonons with frequencies around 20 meV. On the other hand, the anomalously long relaxation time of τ3~100 ps is associated with anharmonicity-driven phonon-phonon scattering. All time dependent relaxation processes result from anomalies near the second order CDW phase transition.

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Presenters

  • Goran Karapetrov

    Physics and Materials Science and Engineering, Drexel University, Physics, Drexel University, Department of Physics, Drexel University

Authors

  • Goran Karapetrov

    Physics and Materials Science and Engineering, Drexel University, Physics, Drexel University, Department of Physics, Drexel University

  • A. A. Anikin

    Physics, Drexel University

  • Richard D Schaller

    Northwestern University, Center for Nanoscale Materials, Argonne National Laboratory

  • Gary P Wiederrecht

    Center for Nanoscale Materials, Argonne National Laboratory

  • Elena R Margine

    Department of Physics, Applied Physics and Astronomy, Binghamton University-SUNY, Department of Physics, Applied Physics, and Astronomy, Binghamton University-SUNY, Department of Physics, Applied Physics and Astronomy, Binghamton University-SUNY – Binghamton, NY13902, USA, Department of Physics, Binghamton University-SUNY

  • Igor Mazin

    Physics & Astronomy, George Mason University, Department of Physics and Astronomy, George Mason University, George Mason University, Physics and Astronomy, George Mason University, Physics, George Mason University, Department of Physics and Astronomy,, George Mason University, Department of Physics and Astronomy and Quantum Science and Engineering Center, George Mason University – Fairfax, VA, USA