arXiv subjects

J. Zhu

Publications and source records attributed to J. Zhu.

94 records · Page 6Linked to original sources

arXiv2003

Spin Susceptibility of an Ultra-Low Density Two Dimensional Electron System

We determine the spin susceptibility in a two dimensional electron system in GaAs/AlGaAs over a wide range of low densities from 2$\times10^{9}$cm$^{-2}$ to 4$\times10^{10}$cm$^{-2}$. Our data can be fitted to an equation that describes the density dependence as well as the polarization dependence of the spin susceptibility. It can account for the anomalous g-factors reported recently in GaAs electron and hole systems. The paramagnetic spin susceptibility increases with decreasing density as expected from theoretical calculations.

cond-mat.mes-hall↗

arXiv2002

Density Induced Interchange of Anisotropy Axes at Half-Filled High Landau Levels

We observe density induced 90$^{\circ}$ rotations of the anisotropy axes in transport measurements at half-filled high Landau levels in the two dimensional electron system, where stripe states are proposed ($ν$=9/2, 11/2, etc). Using a field effect transistor, we find the transition density to be $2.9\times10^{11}$cm$^{-2}$ at $ν$=9/2. Hysteresis is observed in the vicinity of the transition. We construct a phase boundary in the filling factor-magnetic field plane in the regime $4.4<ν<4.6$. An in-plane magnetic field applied along either anisotropy axis always stabilizes the low density orientation of the stripes.

cond-mat.mes-hall↗

arXiv1999

Hysteresis and Spikes in the Quantum Hall Effect

We observe sharp peaks and strong hysteresis in the electronic transport of a two-dimensional electron gas (2DEG) in the region of the integral quantum Hall effect. The peaks decay on time scales ranging from several minutes to more than an hour. Momentary grounding of some of the contacts can vastly modify the strength of the peaks. All these features disappear under application of a negative bias voltage to the backside of the specimen. We conclude, that a conduction channel parallel to the high mobility 2DEG is the origin for the peaks and their hysteretic behavior.

cond-mat.mes-hall↗

arXiv1997

The t system: a new system for estimating the total magnitudes of galaxies

We present a new, but simple, procedure for estimating the total magnitudes of galaxies. This procedure involves the out-focusing of digital galaxy images numerically, the fitting of the resulting surface-brightness profiles with a single generalised profile model and the extrapolation of the fitted profiles to infinite radial distances. This new system, which we denote `t', differs fundamentally from the `T' system (of the `Reference Catalog of Bright Galaxies' series) in that: (1) it enables a galaxy's luminosity profile to be extrapolated without the need for any prior morphological classification, and (2) it is applicable to images of widely different spatial resolutions (including unresolved ones) because it takes into account systematic effects due to differential image resolution. It also differs fundamentally from the Kron system in that: (1) it can be derived directly from surface photometry without the need to go back to the plate scans or CCD frames (unless the surface photometry is of high resolution and/or the galaxies being measured are very bright), and (2) it can cope with merged images (provided they are separable by image-segmentation software). Through worked examples, we demonstrate the stability of `t'-system total magnitudes with respect to morphological type, the seeing conditions at the time of observation, degree of smoothing and limiting isophote. We also compare and contrast the new system with both the `T' system and the Kron system, and investigate the advantages and limitations of each of the three systems.

astro-ph↗