Unusual Electric and Optical Tuning of KTaO₃-Based Two-Dimensional Electron Gases with 5d Orbitals

Abstract

Controlling electronic processes in low-dimension electron systems is centrally important for both fundamental and applied researches. While most of the previous works focused on SrTiO 3 -based two-dimensional electron gases (2DEGs), here we report on a comprehensive investigation in this regard for amorphous-LaAlO 3 / KTaO 3 2DEGs with the Fermi energy ranging from ∼13 meV to ∼488 meV. The most important observation is the dramatic variation of the Rashba spin−orbit coupling (SOC) as Fermi energy sweeps through 313 meV: The SOC effective field first jumps and then drops, leading to a cusp of ∼2.6 T. Above 313 meV, an additional species of mobile electrons emerges, with a 50-fold enhanced Hall mobility. A relationship between spin relaxation distance and the degree of band filling has been established in a wide range. It indicates that the maximal spin precession length is ∼70.1 nm and the maximal Rashba spin splitting energy is ∼30 meV. Both values are much larger than the previously reported ones. As evidenced by density functional theory calculation, these unusual phenomena are closely related to the distinct band structure of the 2DEGs composed of 5d electrons. The present work further deepens our understanding of perovskite conducting interfaces, particularly those composed of 5d transition-metal oxides.

Stimulating Oxide Heterostructures: A Review on Controlling SrTiO3‐Based Heterointerfaces with External Stimuli

“…This advantage shows promising application for the optical nonvolatile devices. Zhang et al have expanded the application of optical gating to other oxide heterointerfaces such as KTaO 3 ‐based 2DEGs . In their KTaO 3 ‐based samples, the Fermi energy was tuned from 13 to 488 meV via optical gating leading to a control of the electronic structure and the Lifshitz transition, which echoes previous theoretical predictions and experimental findings in STO‐based 2DEGs …”

“…Light illumination can generate electron–hole pairs, which not only can contribute to the conductivity but also affect the diffusion of oxygen vacancies and thereby significantly modify the transport properties . For example, tunable persistent photoconductivity (PPC) has been reported in STO‐based heterointerfaces and combining light illumination with a gate bias, an enhancement of the resistance gatability has been demonstrated . In this section, we review the optical tunability and the underlying physical mechanisms.…”

Probing surfaces and interfaces in complex oxide films via in situ X-ray photoelectron spectroscopy

“…In the case of KTaO 3 , surface 2DEGs have been reported in ultrahigh vacuum conditions from oxygen vacancies [33,34]. Since these reports, a variety of means have been developed to produce interfacial 2DEGs in KTaO 3 , primarily through the introduction of polar/non-polar interfaces [35,36,37]. These interfaces have exhibited such interesting properties as optically tunable Rashba effect and greater Hall mobility than analogous LaAlO 3 /SrTiO 3 interfaces.…”

Strain-enhanced giant Rashba spin splitting in ultrathin KTaO3 films for spin-polarized photocurrents

“…24 For another 2DEG at an amorphous-LAO/ KTO interface, an experimental analysis of the weak antilocalization effect resulted in a Rashba coupling constant 0.1 eVÅ and a 50-fold enhanced Hall mobility of charge carriers. 26 Surprisingly, hysteretic magnetoresistance up to 25 K and anomalous Hall effect up to 70 K were observed at an EuO/ KTO interface. 27 It was shown that LaVO 3 /KTO heterostructure with strong spin-orbits interactions can be used to produce planar Hall effect, anisotropic magnetoresistance, and 2DEG.…”