Observation of the fractional quantum Hall effect in an oxide

Journal name:
Nature Materials
Volume:
9,
Pages:
889–893
Year published:
DOI:
doi:10.1038/nmat2874
Received
Accepted
Published online

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 origin1, 2, 3, 4, 5. 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, IIIV compounds and graphene1, 2, 3, 4, 5, 6, 7, 8, 9. 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 cm2 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.

At a glance

Figures

  1. Transport properties of MgZnO/ZnO field-effect heterostructures.
    Figure 1: Transport properties of MgZnO/ZnO field-effect heterostructures.

    a, Schematic cross-sections of the samples. The 2DEG is located near the MgZnO/ZnO interface in a Zn-polar ZnO substrate (sample A) or in a ZnO homoepitaxial layer (500 nm thick) (sample B). b, An optical microscope image of Hall-bar devices and measurement configurations. c, The electron density (n) dependence of electron mobility (μ) for samples A (left) and B (right) at temperatures of 0.06 K, 2 K and 10 K, indicated by red, blue and black symbols, respectively. Insets: Linear gate voltage dependence of n for each sample.

  2. Comparison of electron–electron interaction and scattering time in some material systems.
    Figure 2: Comparison of electron–electron interaction and scattering time in some material systems.

    Transport scattering time (τtr=μm*/e, where e is the elementary charge and m* is the effective mass of electrons; 0.29 m0 for bulk ZnO (ref. 28)) plotted as a function of the strength of electron–electron interaction
    ( , where aB* is the effective Bohr radius) for sample A (red open squares), B (red filled squares) and GaAs electron systems (0.067m0) reported in refs 15,16,17, Si/SiGe (0.22 m0; ref. 6), AlAs (0.46 m0; ref. 7) and GaN (0.2 m0; ref. 18).

  3. FQHE at 0.06 K.
    Figure 3: FQHE at 0.06 K.

    a, Magnetoresistance ρxx (red curve) and ρxy (black curve) at 0.06 K for sample B with n=4.1×1011 cm−2 (top) and 3.7×1011 cm−2 (bottom). Destructive behaviour of zero-resistance states is denoted by the red arrow in the bottom panel. Landau filling factors ν are indicated with integer and fractional numbers. b, ρxx (blue curve) and ρxy(black curve) for sample A with n=3.9×1011 cm−2 (top) and n=1.2×1011 cm−2 (bottom). dρxy/dB (green curve) is also shown in the bottom panel.

  4. Determination of the activation energy for ν=4/3, 5/3 and 8/3 states.
    Figure 4: Determination of the activation energy for ν=4/3, 5/3 and 8/3 states.

    a, Temperature dependence of ρxx (coloured curves) and ρxy at 0.06 K (black curve) for sample B with n=4.1×1011 cm−2 as a function of the magnetic field. b, The Arrhenius plots of the resistance minima for each fractional state to determine the activation energy. The error bars correspond to the background noise of the minimum resistance in the ρxx measurements. The values are evaluated by the black fitting lines. c, The activation energies as a function of scattering rate for representative material systems. The previously reported data are extracted from refs 20,21,22,23. The dashed line is a guide to the eye for the experimental upper bound in GaAs.

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Affiliations

  1. Quantum-Phase Electronics Center and Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan

    • A. Tsukazaki
  2. PRESTO, Japan Science and Technology Agency (JST), Tokyo 102-0075, Japan

    • A. Tsukazaki
  3. Interdisciplinary Devices R&D Center, ROHM Co. Ltd., Kyoto 615-8585, Japan

    • S. Akasaka &
    • K. Nakahara
  4. Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, Sendai 980-8577, Japan

    • Y. Ohno &
    • H. Ohno
  5. WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan

    • D. Maryenko &
    • M. Kawasaki
  6. Department of Applied Chemistry, Tokyo Institute of Technology, Tokyo 152-8552, Japan

    • A. Ohtomo
  7. Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan

    • M. Kawasaki
  8. CREST, Japan Science and Technology Agency (JST), Tokyo 102-0075, Japan

    • M. Kawasaki

Contributions

A.T., A.O. and M.K. designed this research; A.T. carried out the experiments; A.T. and D.M. analysed the data; S.A. and K.N. fabricated the sample; Y.O. and H.O. contributed to the experimental set-up; and all authors co-wrote the manuscript.

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The authors declare no competing financial interests.

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