Capturing the coupled dynamics of the charge, spin and lattice degrees of freedom through the ferromagnetic phase transition using time-resolved spectroscopies

ORAL

Abstract

The coupled interactions of the charge, spin and lattice give rise to intriguing phenomena in quantum materials. Because electrons respond faster than the lattice, ultrafast techniques can uncover which coupled interactions are dominant in a particular material. Here we investigate the ferromagnetic-to-paramagnetic phase transition in nickel using both time-resolved photoemission spectroscopy and magneto-optical Kerr spectroscopy and make several surprising findings. First, the spin system can absorb the laser energy within 20 fs after laser excitation. This is evidenced by a divergence in the transient heat capacity of the spin system as the electron temperature approaches the Curie temperature. Second, we observe a longer and universal timescale of 180 fs in the collapse of the exchange splitting or demagnetization. Moreover, there is a strong fluence dependence of both the phase transition itself and the recovery, which can proceed via two distinct pathways, with timescales of 540 fs and 70 ps, that are attributed to ultrafast spin-spin relaxation and slower timescale phonon coupling, respectively. Our results uncover the clear time sequence of the multiple dynamics and suggest that critical behavior dominates the ultrafast phase transition in nickel.

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Presenters

  • Xun Shi

    Department of Physics and JILA, University of Colorado and NIST, Institute of Physics, Chinese Academy of Sciences, University of Colorado Boulder, Univ of Colorado - Boulder, Univ of Colorado-Boulder

Authors

  • Xun Shi

    Department of Physics and JILA, University of Colorado and NIST, Institute of Physics, Chinese Academy of Sciences, University of Colorado Boulder, Univ of Colorado - Boulder, Univ of Colorado-Boulder

  • Phoebe Tengdin

    University of Colorado Boulder / JILA, Department of Physics and JILA, University of Colorado and NIST, Univ of Colorado - Boulder, Univ of Colorado-Boulder

  • Wenjing You

    JILA, Department of Physics, University of Colorado Boulder and National Institute of Standards and Technology, Department of Physics and JILA, University of Colorado and NIST, Univ of Colorado - Boulder, Univ of Colorado-Boulder

  • Cong Chen

    JILA, Department of Physics, University of Colorado Boulder and National Institute of Standards and Technology, Department of Physics and JILA, University of Colorado and NIST, Univ of Colorado - Boulder, Univ of Colorado-Boulder

  • Dmitriy Zusin

    University of Colorado Boulder / JILA, JILA, Department of Physics, University of Colorado Boulder and National Institute of Standards and Technology, Department of Physics and JILA, University of Colorado and NIST, Univ of Colorado - Boulder, Univ of Colorado-Boulder

  • Yingchao Zhang

    Department of Physics and JILA, University of Colorado and NIST, Univ of Colorado - Boulder, Univ of Colorado-Boulder

  • Christian Gentry

    University of Colorado Boulder / JILA, Department of Physics and JILA, University of Colorado and NIST, Univ of Colorado - Boulder, Univ of Colorado-Boulder

  • Adam Blonsky

    University of Colorado Boulder / JILA, Department of Physics and JILA, University of Colorado and NIST, Univ of Colorado - Boulder, Univ of Colorado-Boulder

  • Mark Keller

    National Institute of Standards and Technology, National Institute of Standards and Technology (NIST), NIST, NIST-Boulder

  • Peter Oppeneer

    Department of Physics and Astronomy, Uppsala University, Uppsala University

  • Henry Kapteyn

    Physics, Univ of Colorado - Boulder, Physics, University of Colorado Boulder, University of Colorado Boulder / JILA, JILA, Department of Physics, University of Colorado Boulder and National Institute of Standards and Technology, Department of Physics and JILA, University of Colorado and NIST, Univ of Colorado - Boulder, Univ of Colorado-Boulder

  • Zhensheng Tao

    JILA, Department of Physics, University of Colorado Boulder and National Institute of Standards and Technology, Department of Physics and JILA, University of Colorado and NIST, Univ of Colorado - Boulder, Univ of Colorado-Boulder

  • Margaret Murnane

    Physics, Univ of Colorado - Boulder, Physics, University of Colorado Boulder, University of Colorado Boulder / JILA, JILA, Department of Physics, University of Colorado Boulder and National Institute of Standards and Technology, Department of Physics and JILA, University of Colorado and NIST, Univ of Colorado - Boulder, Univ of Colorado-Boulder