Role of Dirac nodal lines and strain on the high spin Hall conductivity of epitaxial IrO2 thin films

Abstract

Since the discovery of a 'giant' spin Hall effect (SHE) in certain heavy metal elements there has been an intense effort to identify and develop new and technologically viable, heavy-metal-based thin film materials that could generate spin currents with even greater efficiency to exert spin-orbit torques (SOT) on adjacent ferromagnetic nanostructures. In parallel, there have been wide ranging fundamental studies of the spin currents that can arise from robust, intrinsic spin-orbit interaction (SOI) effects in more exotic systems including topological insulators, transition metal dichalcogenides with broken crystalline symmetry, Weyl and Dirac semimetals where gapless electronic excitations are protected by topology and symmetry. Here we experimentally study strong SOT from the topological semimetal IrO2 in (001) and (110) normal films, which exhibit distinctly different SHE strengths. Angle resolved photoemission spectroscopy studies have shown IrO2 exhibits Dirac nodal lines (DNL) in the band structure, which could enable a very high spin Hall conductivity (SHC). The (001) films exhibit exceptionally high damping like torque efficiency ranging from 0.45 at 293 K to 0.65 at 30 K which sets the lower bound of SHC that is ten times higher and of opposite sign than the theoretical prediction. We observe a substantial reduction of SHC in anisotropically strained (110) films, which suggests that the DNLs that are present in the (001) films and contribute to SHC, are disrupted and gapped due to the large anisotropic strain in (110) films, which in turn significantly lowers SHC. Very large value of SHC at room temperature of this Dirac semimetal could be very promising for the practical application.

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Cited by in corpus (13)

• Observation of spin splitting torque in a collinear antiferromagnet RuO2
• Tilted spin current generated by the collinear antiferromagnet RuO2
• Maximizing Spin-Orbit Torque Generated by the Spin Hall Effect of Pt
• Detection of long-range orbital-Hall torques
• Efficient Spin-Orbit Torque Generation in Semiconducting WTe2 with Hopping Transport
• Substrate-induced spin-torque-like signal in spin-torque ferromagnetic resonance measurement
• Giant spin torque efficiency in naturally oxidized polycrystalline TaAs thin films
• Spin-orbit torque generation in bilayers composed of CoFeB and epitaxial SrIrO${}_3$ grown on an orthorhombic DyScO${}_3$ substrate
• Stacking-order effect on spin-orbit torque, spin-Hall magnetoresistance, and magnetic anisotropy in Ni${}_{81}$Fe${}_{19}$-IrO${}_2$ bilayers
• Spin current generation from an epitaxial tungsten dioxide WO${}_2$
• Coexistence of unconventional spin Hall effect and antisymmetric planar Hall effect in IrO${}_2$
• Effect of crystallinity on spin-orbit torque in 5$\text{d}$ iridium oxide IrO${}_2$
• Effect of interface quality on spin Hall magnetoresistance in Pt/MgFe${}_2$O${}_4$ bilayers