Abstract
Strong Rashba effects at semiconductor surfaces and interfaces have attracted great attention for basic scientific exploration and practical applications. Here, we show through first-principles investigation that applying biaxial stress can cause tunable and giant Rashba effects in ultrathin KTaO3 (KTO) (001) films with the most stable surfaces. When increasing the in-plane compressive strain to −5%, the Rashba spin splitting energy reaches ER = 140 meV, corresponding to the Rashba coupling constant αR = 1.3 eV Å. We investigate its strain-dependent crystal structures, energy bands, and related properties, and thereby elucidate the mechanism for the giant Rashba effects. Further calculations show that the giant Rashba spin splitting can remain or be enhanced when capping layer and/or Si substrate are added, and a SrTiO3 capping can make the Rashba spin splitting energy reach the record 190 meV. Furthermore, it is elucidated that strong circular photogalvanic effect can be achieved for spin-polarized photocurrents in the KTO thin films or related heterostructures, which is promising for future spintronic and optoelectronic applications.
Highlights
IntroductionSpin injection by applying electric eld[16,17] and produce spinpolarized photocurrents through polarized light.[18,19,20,21,22,23]
The Rashba spin–orbit interaction[1,2,3] due to the broken inversion symmetry and the atomic spin–orbit coupling (SOC) can bring about the momentum-dependent spin splitting of the electron states
Through rst-principles calculations and theoretical analyses, we investigate the in-plane strain dependencies of the structural features, intrinsic electrostatic potentials, band edges, carrier concentrations, carrier effective masses, and Rashba parameters of the ultrathin KTO (001) lms. We show that their Rashba spin splitting can be controlled by applying biaxial stress, and giant Rashba spin splitting can be obtained by applying compressive biaxial stress, being able to reach 140 meV
Summary
Spin injection by applying electric eld[16,17] and produce spinpolarized photocurrents through polarized light.[18,19,20,21,22,23]. Through rst-principles calculations and theoretical analyses, we investigate the in-plane strain dependencies of the structural features, intrinsic electrostatic potentials, band edges, carrier concentrations, carrier effective masses, and Rashba parameters of the ultrathin KTO (001) lms. We show that their Rashba spin splitting can be controlled by applying biaxial stress, and giant Rashba spin splitting can be obtained by applying compressive biaxial stress, being able to reach 140 meV. Such giant Rashba effects in the ultrathin KTO lms can be used to generate spin-polarized photocurrents through circular photogalvanic effect.[18,19,20,21,22,23] More detailed results will be presented in the following
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