“Nonequilibrium Heat Transport in Elemental Metals Probed by an Ultrathin Magnetic Thermometer”

Dr. Hyejin Jang
Department of Materials Science and Engineering,
Seoul National University

Dec. 3 (Fri.), 04:00 PM
https://kaist.zoom.us/j/85193398774
회의 ID: 851 9339 8774
암호: 867451

Abstract:
The interaction between electrons and phonons is responsible for a variety of physical properties of solids, such as electrical conductivity, superconductivity, polaron conduction, and piezoelectricity. In particular, in metals, electrons and phonons exchange energy at picosecond timescales when they are not in thermal equilibrium. This energy transfer serves as an important driver for the ultrafast switching of magnetic memory. However, the experimental investigation of nonequilibrium dynamics in metals remains challenging and limits our fundamental understanding and applications for fast and energy-efficient devices. In this work, I demonstrate that a magnetic thermometer, which is a sub-nm-thick cobalt layer, can effectively examine the nonequilibrium dynamics in adjacent metals. The magnetization of Co informs the magnon temperature specific to the position of the ultrathin Co layer, and can be conveniently detected via the magneto-optic Kerr effect. I first characterize the carrier interaction parameters of Co and then investigate the nonequilibrium dynamics in Pt by using Co embedded in thicker Pt layers. I report that for transition metals, such as Pt and Ru, the electron-phonon nonequilibrium length scales are comparable to the optical absorption depths, and much shorter than the nonequilibrium length scales in noble metals, e.g., Au and Cu. Thus, the distribution of most of the injected energy in transition metals occurs via diffusion of thermalized electrons and phonons, in contrast to noble metals, in which electron diffusion governs overall heat transport.