Terahertz Spin-Conductance Spectroscopy: Probing Coherent and Incoherent Ultrafast Spin Tunneling

• Published in: Nano letters Vol. 24; no. 26; pp. 7852 - 7860
• Main Authors: Rouzegar, Reza, Wahada, Mohamed Amine, Chekhov, Alexander L., Hoppe, Wolfgang, Bierhance, Genaro, Jechumtál, Jiří, Nádvorník, Lukáš, Wolf, Martin, Seifert, Tom S., Parkin, Stuart S. P., Woltersdorf, Georg, Brouwer, Piet W., Kampfrath, Tobias
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 03-07-2024
• Subjects: Letter; Terahertz spintronics; spin conductance; terahertz spectroscopy; coherent tunneling; incoherent resonant tunneling; MgO tunnel junctions
• ISSN: 1530-6984; 1530-6992; 1530-6992
• DOI: 10.1021/acs.nanolett.4c00498

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 G s 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.