Observation of the fractional quantum Hall effect in an oxide

Abstract

The quantum Hall effect arises from the cyclotron motion of charge carriers in two-dimensional systems. However, the ground states related to the integer and fractional quantum Hall effect, respectively, are of entirely different origin. The former can be explained within a single-particle picture; the latter arises from electron correlation effects governed by Coulomb interaction. The prerequisite for the observation of these effects is extremely smooth interfaces of the thin film layers to which the charge carriers are confined. So far, experimental observations of such quantum transport phenomena have been limited to a few material systems based on silicon, III-V compounds and graphene. In ionic materials, the correlation between electrons is expected to be more pronounced than in the conventional heterostructures, owing to a large effective mass of charge carriers. Here we report the observation of the fractional quantum Hall effect in MgZnO/ZnO heterostructures grown by molecular-beam epitaxy, in which the electron mobility exceeds 180,000 cm(2) V(-1) s(-1). Fractional states such as ν = 4/3, 5/3 and 8/3 clearly emerge, and the appearance of the ν = 2/5 state is indicated. The present study represents a technological advance in oxide electronics that provides opportunities to explore strongly correlated phenomena in quantum transport of dilute carriers.

Conductivity in transparent oxide semiconductors

“…Crucially, they demonstrated that such a device could exhibit high mobility, stimulating much work on this system [24,25]. A second milestone on the road towards oxide electronics can be seen as the observation of the integer [26] and, more recently, fractional [27] quantum Hall effects in ZnO/MgZnO heterostructures by Tsukazaki et al (Fig. 1(d-f)).…”

High Electron Mobility Thin‐Film Transistors Based on Solution‐Processed Semiconducting Metal Oxide Heterojunctions and Quasi‐Superlattices

“…A summary of the field‐effect electron mobility values reported in recent years for different metal oxide heterointerface systems grown by different methods (e.g., sputtering, molecular beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD), and atomic layer deposition (ALD) techniques) is given in Table S1 (Supporting Information). Despite these very promising early results and the tremendous potential of the 2DEG transistor technology, however, its widespread adoption in practical electronic applications is currently hampered by the rather complex23 and high temperature (600–900 °C, see Table S1, Supporting Information) manufacturing processes often required in order to ensure the formation of the all‐important high‐quality heterointerface 19, 24, 25. Because of the latter requirement it is not a trivial question whether high‐quality oxide heterointerfaces can be realized using simpler, cost‐efficient, and high‐throughput fabrication methods that are compatible with existing semiconductor fabrication processes (e.g., solution‐based) and even perhaps temperature‐sensitive substrate materials such as plastic.…”

Fractional quantum Hall effect in a dilute magnetic semiconductor

“…When the direction of the magnetic field B is tilted, the orbital LL splitting is given by the field component B ⊥ normal to the two-dimensional electron system (2DES) while the total field strength B determines the Zeeman splitting E Z . Early experiments on GaAs revealed that the ν = 4/3, 5/3, and 8/5 states behaved differently upon tilting the sample [4,5]: While the ν = 4/3 and 8/5 states were undergoing a transition from a spinunpolarized state to a polarized one, the ν = 5/3 state was always fully spin polarized.Although the FQHE has been reported in quite a number of different materials [6][7][8][9][10][11][12], the FQHE has never been observed in a diluted magnetic semiconductor in which atoms with magnetic moment (e.g., Mn 2+ ) are placed in a 2DES. Then, the localized spins in the magnetic impurities' d orbitals interact with the correlated electron system via the quantum mechanical s-d exchange interaction, causing giant Zeeman splitting [13] which is tunable in magnitude, sign, and field dependence [14].…”

“…Although the FQHE has been reported in quite a number of different materials [6][7][8][9][10][11][12], the FQHE has never been observed in a diluted magnetic semiconductor in which atoms with magnetic moment (e.g., Mn 2+ ) are placed in a 2DES. Then, the localized spins in the magnetic impurities' d orbitals interact with the correlated electron system via the quantum mechanical s-d exchange interaction, causing giant Zeeman splitting [13] which is tunable in magnitude, sign, and field dependence [14].…”