Generation and manipulation of spin current in topological semimetal heterostructures

Emerging topological and two-dimensional (2D) material systems synthesized by molecular beam epitaxy (MBE) have greatly expanded the materials toolkit used for fundamental studies of spin current and current-induced spin-orbit torques (SOTs). These MBE-grown heterostructures provide a potential pathway toward wafer-scale, energy-efficient, topological 2D spintronic devices for memory applications. In this talk, we discuss the generation and manipulation of spin current in MBE-grown topological semimetal/2D heterostructures. We first briefly discuss the measurement of charge-to-spin interconversion in 3D topological semimetals (TSs) of contemporary interest, including Dirac and Weyl semimetals [Phys. Rev. Appl. 16, 054031 (2021), ibid (in press)/arxiv: 2202.10656]. In their pristine state, the spin-Hall conductivity (SHC) of MBE-grown TS films quantitatively agrees with the intrinsic values predicted by first-principles calculations. We also observe that an oxidized interface enhances the SOT in these TSs. Next, we focus on the synthesis and characterization of a full van der Waals epitaxial heterostructure consisting of a Dirac semimetal, ZrTe₂, and a 2D ferromagnet, CrTe₂ [Nat. Comm. 13, 2972 (2022)]. We observe robust ferromagnetism with perpendicular magnetic anisotropy in quasi-2D CrTe₂ thin films down to one-unit-cell thickness. Anomalous Hall effect measurements in thicker CrTe₂ films suggest the existence of chiral magnetic structures. Finally, we demonstrate SOT-assisted magnetization switching in quasi-2D CrTe₂ via the current-induced SOT from ZrTe₂. Work done with W. Yanez, R. Xiao, M. Stanley, S. Ghosh, B. Zheng, Y.-S. Huang, T. Pillsbury, A. Richardella, T. Low, C.-X. Liu, V. H. Crespi, B.-H. Yan. K. A. Mkhoyan, and N. Samarth.