Low temperature magnetoresistance in a narrow wire of GaAs/AlGaAs

Ishíbashi, K.; Noh, Sam Kyu; Aoyagi, Yoshinobu; Namba, Susumu; Mizuno, Misao; Ochiai, Y.; Kawabe, Mitsuo; Gamo, Kenji

doi:10.1016/0039-6028(90)90311-u

Cited by 16 publications

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“…However, the amplitude dependence is predicted to be universal in that if 1$ is known then the amplitude of the fluctuations can be predicted. This universality has been confirmed by several authors [3,4] at magnetic fields sufficiently small that (O C T<K\.Recently, there have been several experiments [5][6][7][8][9][10] in which the aperiodic UCF were investigated for o) c r > 1 in a high-mobility two-dimensional electron gas (2DEG) in which the electron mean free path t^VfT, where vp is the Fermi velocity, is larger than the sample width w. In such a system the ALS theory is not expected to be valid.In this Letter we describe the UCF behavior in an orthodox mesoscopic system, with I <&w ("dirty metal" regime) as required by the ALS theory, but with W C T > 1. We find that the typical period of the fluctuations increases by ~5 as the magnetic field increases from 0 to 12 T but the amplitude of the oscillations is approximately constant over the same range of magnetic field.…”

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Breakdown of universal scaling of conductance fluctuations in high magnetic fields

et al. 1992

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We have studied universal conductance fluctuations in the nonlocal magnetoresistance of /? + -GaAs wires. The Lee-Stone correlation field AB C increases by a factor of 5 as the magnetic field increases from 0 to 12 T but the amplitude of the fluctuations does not change. It is possible to explain the increase of AB C quantitatively in terms of a variation of the size of the phase coherence length. However, this should also give rise to a large change in the fluctuation amplitude, which is not observed. This implies that the universal scaling of the conductance fluctuations is not valid in high magnetic fields.PACS numbers: 72.15.Gd, 72.20.Ht, 72.20.My Universal conductance fluctuations (UCF) arise in mesoscopic systems as a direct consequence of the quantum interference of electron waves and have been widely investigated over the last decade. Most experiments have been confined to the low-magnetic-field limit, CO C T<£\, where co c is the cyclotron frequency and r the electron scattering time. In this regime, there is good agreement between experiment and the theory of Altshuler and Lee and Stone (ALS) [1,2]. The fluctuations have been termed "universal" because, at absolute zero, their amplitude is independent of the material of the conductor. At finite temperature, the amplitude of the fluctuations depends on the phase coherence length l 0 which varies with temperature and is material dependent. However, the amplitude dependence is predicted to be universal in that if 1$ is known then the amplitude of the fluctuations can be predicted. This universality has been confirmed by several authors [3,4] at magnetic fields sufficiently small that (O C T 1 in a high-mobility two-dimensional electron gas (2DEG) in which the electron mean free path t^VfT, where vp is the Fermi velocity, is larger than the sample width w. In such a system the ALS theory is not expected to be valid.In this Letter we describe the UCF behavior in an orthodox mesoscopic system, with I <&w ("dirty metal" regime) as required by the ALS theory, but with W C T > 1. We find that the typical period of the fluctuations increases by ~5 as the magnetic field increases from 0 to 12 T but the amplitude of the oscillations is approximately constant over the same range of magnetic field. We employ a nonlocal geometry to enhance the effect of lp on the UCF amplitude and to remove effects associated with the average resistance. We demonstrate that in this experimental regime the typical period and the amplitude of the fluctuations cannot be characterized universally in terms of a single parameter.A micrograph of a typical structure used in our experiments is shown in Fig. 1, with a schematic representation in the inset of Fig. 4. The wire was fabricated using electron-beam lithography and dry etching from an n*-GaAs epilayer (n ~ 1.1 x 10 24 m " 3 ) grown by molecularbeam epitaxy on a conventional, semi-insulating GaAs substrate. ...

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confidence: 55%

“…Recently, there have been several experiments [5][6][7][8][9][10] in which the aperiodic UCF were investigated for o) c r > 1 in a high-mobility two-dimensional electron gas (2DEG) in which the electron mean free path t^VfT, where vp is the Fermi velocity, is larger than the sample width w. In such a system the ALS theory is not expected to be valid.…”

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confidence: 99%