Observation of the quantum Hall effect in δ-doped SrTiO3.

Y Matsubara,Y Tokura,D Maryenko,K S Takahashi,Y Kozuka,A Tsukazaki,J Falson,M S Bahramy,M Kawasaki

doi:10.1038/ncomms11631

Abstract

The quantum Hall effect is a macroscopic quantum phenomenon in a two-dimensional electron system. The two-dimensional electron system in SrTiO3 has sparked a great deal of interest, mainly because of the strong electron correlation effects expected from the 3d orbitals. Here we report the observation of the quantum Hall effect in a dilute La-doped SrTiO3-two-dimensional electron system, fabricated by metal organic molecular-beam epitaxy. The quantized Hall plateaus are found to be solely stemming from the low Landau levels with even integer-filling factors, ν=4 and 6 without any contribution from odd ν's. For ν=4, the corresponding plateau disappears on decreasing the carrier density. Such peculiar behaviours are proposed to be due to the crossing between the Landau levels originating from the two subbands composed of d orbitals with different effective masses. Our findings pave a way to explore unprecedented quantum phenomena in d-electron systems.

Highlights

The quantum Hall effect is a macroscopic quantum phenomenon in a two-dimensional electron system
While the fact that the ratio of slope change is close to two may be interpreted as the spin degeneracy lifting at high field, this change turns out to be due to the peculiar subband structure of the present STO 2DES
Taking the spin degeneracy into account, the total carrier density extracted from these two Shubnikov-de Haas (SdH) frequencies (6.4 and 12.9 T) is found to be 9.0 Â 1011 cm À 2 (3.0 Â 1011 cm À 2 for 6.4 T and 6.0 Â 1011 cm À 2 for 12.9 T); slightly lower than the carrier density estimated from the Hall effect, 1.0 Â 1012 cm À 2

Summary

Introduction

The quantum Hall effect is a macroscopic quantum phenomenon in a two-dimensional electron system. We employ molecular-beam epitaxy (MBE) at a very high temperature (1,200 °C) with metal organic (MO) precursors (MOMBE)[21] to grow STO heterostructures confining the 2DES and reach electron mobility exceeding 20,000 cm[2] V À 1 s À 1 at charge-carrier densities below 1 Â 1012 cm À 2. With such a high mobility-low carrier density heterostructure, we can successfully reach the quantum Hall regime in STO. To elucidate the origin for those, we performed first principles calculations and found that these features can be modelled if the spin susceptibility is small compared with the Landau level broadening and the crossover of hybridized two d orbitals made of dyz and dzx are taken into account

Methods

Results

Conclusion