{Reference Type}: Journal Article
{Title}: Terahertz Spin-Conductance Spectroscopy: Probing Coherent and Incoherent Ultrafast Spin Tunneling.
{Author}: Rouzegar R;Wahada MA;Chekhov AL;Hoppe W;Bierhance G;Jechumtál J;Nádvorník L;Wolf M;Seifert TS;Parkin SSP;Woltersdorf G;Brouwer PW;Kampfrath T;
{Journal}: Nano Lett
{Volume}: 24
{Issue}: 26
{Year}: 2024 Jul 3
{Factor}: 12.262
{DOI}: 10.1021/acs.nanolett.4c00498
{Abstract}: Thin-film stacks F|H consisting of a ferromagnetic-metal layer F and a heavy-metal layer H are spintronic model systems. Here, we present a method to measure the ultrabroadband spin conductance across a layer X between F and H at terahertz frequencies, which are the natural frequencies of spin-transport dynamics. We apply our approach to MgO tunneling barriers with thickness d = 0-6 Å. In the time domain, the spin conductance Gs has two components. An instantaneous feature arises from processes like coherent spin tunneling. Remarkably, a longer-lived component is a hallmark of incoherent resonant spin tunneling mediated by MgO defect states, because its relaxation time grows monotonically with d to as much as 270 fs at d = 6.0 Å. Our results are in full agreement with an analytical model. They indicate that terahertz spin-conductance spectroscopy will yield new and relevant insights into ultrafast spin transport in a wide range of spintronic nanostructures.