A length-dependent analysis of quantized conductance in split-gate constrictions fabricated on InAs/AlSb quantum-well heterostructures is presented. Conductance steps with spacing within a few percent of 2e 2 /h are observed in constrictions with channel lengths of 0.2 m. With increasing constriction length nearly ideal quantized conductance can still be observed, even in constrictions as long as 2.0 m. The values of the quantized step heights are found to vary more from device to device with increasing length. Our lengthdependent data differ considerably from previous reports on GaAs/Al x Ga 1Ϫx As split-gate devices where the quantized conductance was severely degraded for constriction lengths տ 0.6 m. Temperature-dependent measurements indicate that the 2.0-m-long devices have one-dimensional ͑1D͒ subband spacings close to 10 meV. The improved length performance of our devices is believed to be due primarily to the increased 1D subband spacings relative to the magnitude of potential fluctuations in the channel region. Our explanation is shown to be in agreement with recent theoretical analyses relating various scattering mechanisms to the breakdown of quantized conductance. ͓S0163-1829͑96͒03719-8͔
The surface of a thin-film disk can be patterned using standard lithographic techniques to form discrete tracks as narrow as 0.5 μm. These studies have been extended to patterns formed when an etched track is broken into discrete segments by etching away some portions of a discrete track. Abrupt changes in the magnetization can be obtained by dc erasing the medium, giving readback signals with ∼50% of the amplitude of conventional transitions when the gap of the readback head is aligned with the edge of the media pattern. The implications of these results for servo and read-only applications are discussed.
The magnetic moment of the positive muon has been redetermined in terms of proton moments using a precession technique. The sensitivity achieved yields an error of 13 parts per million. The muons are stopped in various targets in a homogeneous magnetic field. The anisotropic distribution of the decay electrons relative to the muon spin direction permits the measurement of the spin precession frequency. The proton spin resonance is measured in the same field, yielding / M // P = 3.18338±0.00004. This result may be combined with that of other experiments, the muon g factor, and the ratio of electron cyclotron frequency to proton resonance, f e /f P , to obtain a more precise evaluation of the muon mass in terms of electron masses, m^/rrie equals 206.765±0.005.
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