2007 Fiscal Year Final Research Report Summary
Study of high Landau levels by spatial modulation technique
| Project/Area Number |
18540312
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Condensed matter physics I
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| Research Institution | The University of Tokyo |
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Principal Investigator |
ENDO Akira The University of Tokyo, Institute for Solid State Physics,, Research associate (20260515)
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| Project Period (FY) |
2006 – 2007
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| Keywords | two-dimensional electron gas / Landau quantization / quantum Hall effect / charge density wave / Fibonacci lateral superlattice / mesoscopic system / semiconductor physics / low-temperature physics |
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| Research Abstract |
Unidirectional periodic, unidirectional quasiperiodic (Fibonacci) and two-dimensional triangular lateral superlattices (LSLs) are prepared for detailed investigation of their behavior under magnetic fields.
Complicated commensurability oscillation and the geometric resonance of the open orbits are observed for Fibonacci LSLs. By detailed Fourier analyses, the profile of the modulated potential is found to be well-described by the superposition of periodic modulations with their periods scaled consecutively by the golden ratio. Strong enhancement in the zero-field resistivity, followed by sharp negative magnetoresistance is observed for Fibonacci LSL with short unit lengths close to the Fermi wave length. They can be explained by enhanced back-scattering rate by the diffraction from the Fibonacci lattice, and magnetic breakdown effect, respectively.
In periodic LSLs, the modulation of the amplitude and the phase of the Shubnikov-de Haas oscillations is studied. The modulations are shown t
… More
o be quantitatively explicable by taking the magnetic-field dependence of the collisional and diffusion contributions to the conductivity into account. Detailed analyses of the line shape of the Shubnikov-de Haas oscillation reveal that the Fermi energy oscillates with the magnetic field and that the disorder broadening of the Landau levels is well approximated by Gaussians.
Integral and Fractional quantum Hall effects under periodic modulation are also investigated. The periodic modulation lifts the degeneracy of the Landau levels, resulting in the Landau bands with the width oscillating with the magnetic field. The activation energies for odd-integer quantum Hall effects are found to decrease responding to the width acquired by the Landau bands. Odd numerator fractional quantum Hall effects are observed to vanish by the introduction of the modulation, while those with even numerator are found to survive or even to be enhanced. The disappearance of the fractional quantum Hall state may be signaling the phase transition into novel stripe state in the lowest Landau level. Less
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