Magnetization of a two-dimensional electron gas with a second filled subband

We have measured the magnetization of a dual-subband two-dimensional electron gas, confined in a GaAs/AlGaAs heterojunction. In contrast to two-dimensional electron gases with a single subband, we observe non-1/B-periodic, triangularly shaped oscillations of the magnetization with an amplitude significantly less than $1 \mu_{\mathrm{B}}^*$ per electron. All three effects are explained by a field dependent self-consistent model, demonstrating the shape of the magnetization is dominated by oscillations in the confining potential. Additionally, at 1 K, we observe small oscillations at magnetic fields where Landau-levels of the two different subbands cross.Comment: 4 pages, 4 figure

Torque Magnetometry Studies of Two-Dimensional Electron Systems

Contains fulltext : 19470_torqmasto.pdf (publisher's version ) (Open Access)This thesis describes a study of the magnetization two-dimensional electron gases (2DEGs). To detect the typically small magnetization, a sensitive magnetometer with optical angular detection was developed. The magnetometer uses a quadrant detector to measure the rotation of the sample. By mounting a current-coil and using a feedback system, the magnetization is directly determined quantitatively. An additional advantage is the active damping of mechanical vibrations. The magnetometer has a sensitivity of 1 pJ/T in a Bitter-magnet and 0.2 pJ/T at 15 T in a superconducting magnet. First a single 2DEG is investigated. The measured magnetization can be well described by a simple model: a sharp, 1/B-periodic sawtooth with an amplitude of 1 Bohr magneton per electron. Contrary to this model, the magnetization steps have a finite width attributed to a background density of states. The density of electrons in the 2DEG can be increased far enough to occupy a second electronic subband. In contrast to the single 2DEG, the magnetization of such a 2DEG in a heterojunction shows non-1/B-periodic, triangularly shaped oscillations with a significantly smaller amplitude. A field-dependent self-consistent model quantitatively explains all three effects. At 1 K additional minima become visible at magnetic fields where Landau levels of the two subbands cross. Finally, the magnetization of bilayer 2DEGs in a double quantum well is determined. This system has an extra energy gap, determined by the inter-well barrier. Although it is purely electronic in nature, a magnetization step is clearly visible when a transition across this gap takes place. This observation is quantitatively explained by thermodynamics. Surprisingly, the apparent size of the magnetization oscillations at Landau-level transitions is significantly less than 1 Bohr magneton per electron. This reduction suggests the magnetization has an in-plane component.RU Radboud Universiteit Nijmegen, 06 juli 2004Promotor : Maan, J.C. Co-promotor : Christianen, P.C.M.102 p

A multipurpose torsional magnetometer with optical detection

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Magnetization of a double-layer and of a double subband two-dimensional electron gas

Item does not contain fulltextSemimag 15, 05 augustus 200

Magnetization of multi-component two-dimensional quantum-Hall systems

Contains fulltext : 60496.pdf (publisher's version ) (Closed access)We present a torque-magnetometry study of bilayer two-dimensional electron gases with different inter-layer barrier widths. At filling factors where a symmetric-anti-symmetric transition takes place we clearly observe steps in magnetization, even though this transition is purely electronic in nature and no direct change of spin or orbital angular momentum is involved. Additionally, in both samples, the apparent size of the magnetization steps associated to the Landau-level transitions is reduced by approximately a factor of two compared to the value typical for a single two-dimensional electron system. (C) 2003 Elsevier B.V. All rights reserved