Subband Structure of a Two-Dimensional Electron Gas Formed at the Polar Surface of the Strong Spin-Orbit Perovskite ${\mathrm{KTaO}}_{3}$

Subband Structure of a Two-Dimensional Electron Gas Formed at the Polar Surface of the Strong Spin-Orbit Perovskite ${KTaO}_{3}$

P. D. C. King, R. H. He, T. Eknapakul, P. Buaphet, S.-K. Mo, Y. Kaneko, S. Harashima, Y. Hikita, M. S. Bahramy, C. Bell, Z. Hussain, Y. Tokura, Z.-X. Shen, H. Y. Hwang, F. Baumberger, and W. Meevasana

Phys. Rev. Lett. 108, 117602 – Published 14 March 2012

Abstract

We demonstrate the formation of a two-dimensional electron gas (2DEG) at the (100) surface of the $5 d$ transition-metal oxide ${KTaO}_{3}$ . From angle-resolved photoemission, we find that quantum confinement lifts the orbital degeneracy of the bulk band structure and leads to a 2DEG composed of ladders of subband states of both light and heavy carriers. Despite the strong spin-orbit coupling, our measurements provide a direct upper bound for the potential Rashba spin splitting of only $Δ k_{∥} \sim 0.02 Å^{- 1}$ at the Fermi level. The polar nature of the ${KTaO}_{3} (100)$ surface appears to help mediate the formation of the 2DEG as compared to nonpolar ${SrTiO}_{3} (100)$ .

Received 31 August 2011

DOI:https://doi.org/10.1103/PhysRevLett.108.117602

Authors & Affiliations

P. D. C. King¹, R. H. He², T. Eknapakul³, P. Buaphet³, S.-K. Mo², Y. Kaneko⁴, S. Harashima⁵, Y. Hikita^6,7, M. S. Bahramy⁸, C. Bell^6,7, Z. Hussain², Y. Tokura^4,5,8, Z.-X. Shen^6,7, H. Y. Hwang^6,7,8, F. Baumberger^1,*, and W. Meevasana^3,9,†

¹SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews, Fife KY16 9SS, United Kingdom
²Advanced Light Source, Lawrence Berkeley National Lab, Berkeley, California 94720, USA
³School of Physics, Suranaree University of Technology and Synchrotron Light Research Institute, Nakhon Ratchasima, 30000, Thailand
⁴Multiferroics Project, ERATO, JST, Tokyo 113-8656, Japan
⁵Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
⁶Departments of Physics and Applied Physics, Stanford University, California 94305, USA
⁷Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, California 94025, USA
⁸Correlated Electron Research Group (CERG), RIKEN-ASI, Wako 351-0918, Japan
⁹Thailand Center of Excellence in Physics, CHE, Bangkok, 10400, Thailand