%0 Journal Article
%T Terahertz Spin-Conductance Spectroscopy: Probing Coherent and Incoherent Ultrafast Spin Tunneling.
%A Rouzegar R
%A Wahada MA
%A Chekhov AL
%A Hoppe W
%A Bierhance G
%A Jechumtál J
%A Nádvorník L
%A Wolf M
%A Seifert TS
%A Parkin SSP
%A Woltersdorf G
%A Brouwer PW
%A Kampfrath T
%J Nano Lett
%V 24
%N 26
%D 2024 Jul 3
%M 38904438
%F 12.262
%R 10.1021/acs.nanolett.4c00498
%X 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.