Yusuke Kozuka1,Shinji Isogami1,Keisuke Masuda1,Yoshio Miura1,Saikat Das1,Jun Fujioka2,Tadakatsu Ohkubo1,Shinya Kasai1
National Institute for Materials Science1,University of Tsukuba2
Yusuke Kozuka1,Shinji Isogami1,Keisuke Masuda1,Yoshio Miura1,Saikat Das1,Jun Fujioka2,Tadakatsu Ohkubo1,Shinya Kasai1
National Institute for Materials Science1,University of Tsukuba2
Spin-charge conversion is one of the core concepts in the current spintronics research. With an aid of the spin-orbit interaction, the charge current is efficiently converted to the transverse spin current through the spin Hall effect. In the presence of a warped Fermi surface with nontrivial spin texture, the higher-order spin Hall effect additionally emerges in noncentrosymmetric materials and is detected by the second-harmonic planar Hall effect. Conversely, the nonlinear planar Hall effect has been utilized to detect nontrivial spin textures in the momentum space without relying on spin- and angle-resolved photoemission spectroscopy.<br/>Here, we present the observation of the nonlinear planar Hall effect in Dirac semimetal SrIrO<sub>3</sub> thin films [1]. This observation is unexpected because SrIrO<sub>3</sub> has a centrosymmetric GdFeO<sub>3</sub>-type crystal structure and thus nontrivial spin texture in the momentum space is unlikely in bulk. Experimentally, a large second-order planar Hall coefficient is observed at room temperature compared with other noncentrosymmetric materials such as Bi<sub>2</sub>Te<sub>3</sub> or WTe<sub>2</sub>. The nonlinear planar Hall signal depends on the substrate used to grow SrIrO<sub>3</sub> thin films. When orthorhombic GdScO<sub>3</sub> substrate, isostructural with SrIrO<sub>3</sub>, is used, large in-plane anisotropy of the nonlinear planar Hall signal is observed depending on the current direction. These results suggest that the observed nonlinear planar Hall effect is driven by the inversion symmetry breaking at the surface and interface of the SrIrO<sub>3</sub> films together with symmetry constraint from the substrate.<br/>First-principles calculations for the slab model show that the antisymmetric spin-orbit interaction at the interface of Dirac semimetallic bands can generate warped Fermi surfaces with nonuniform spin texture. Our study suggests that nonlinear spin-charge conversion can be induced in many materials with strong spin-orbit interaction at the interface by breaking the local inversion symmetry to give rise to spin splitting in otherwise spin degenerate systems.<br/>[1] Y. Kozuka <i>et al.</i>, Phys. Rev. Lett. <b>126</b>, 236801 (2021).