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The material in our experiment is compound semiconductor, such as, GaAs and InGaAs, two dimensional electron gas (2DEG)  is confined inside the quantum well and random distributed in a plane

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V3final      band gap        band gap1.jpg

FIG.1 a) structure of InGaAs/InAlAs/InGaAs  b) band structure c) quantum well and one side Si+ doping layer

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The density of state of 2DEG is uniform to different energy which is different from one dimensional electron gas (1DEG)  and three dimensional electron gas(3DEG).  But when the sample in a perpendicular magnetic field, all the electrons in the plane start cyclotron motion which causes the density of state discrete.(FIG2.) and occupied energy level become not continue anymore and landau level appear.


Density of StatesLandau Levels

FIG2 first one is density of state without magnetic filed second one (a,b,c included) is with magetic filed.


Landau level isimage002,image004. So the energy space between each level is image006. In room temperature, the exciting energyimage008. Landau level cannot be observed. Only when in very low temperature,image010. landau level becomes well resolvable. So usually we run experiment in 0.3 K in a top loading He-3 refrigerate.  (FIG3 ). The magnetic field is from a superconducting magnet.






FIG3.top loading He-3 refrigerate


Integral quantum Hall Effect is usually found in hall trace magentotransport experiment. (FIG4). See integral quantum hall effect link



FIG4  Magnetotransport result , Rxy is hall trace, integral quantum hall effect clearly show. Rxx is magneto resistance.

  Spin effect sometimes also involved in magnetotransport. Rashba effect is one kind (FIG.5) In the asymmetric quantum well. , there is an electric field perpendicular to layers and it transforms into magnetic field  in the rest frame of an electron moving along the layer. And this magnetic field leads to spin splitting. So without external magnetic fields, we also see spin splitting effect and this is the Rashba effect.  

FIG.5 illustration of Rashba effect


For some semiconductor ,the carrier is holes. Two dimensional holes gas (2DHG) has it unique band structure. Unlike electrons, only single conduction band is available, holes have three subband in valence band: two heavy hole band , one light hole band. With the magnetic filed change ,its band structure change as well. So, the property of the 2DHG become more complicated.

Recently, we are looking in the current induced magento transport of hole carrers and find the similar peak to zener tunneling in electrons system [1]. More results will be present for this special topic.




[1]  Yang et al. Phys. Rev. Lett. 89, 076801 (2002)


Dr. Rui-Rui Du
Rice University Physics & Astronomy
Dell Butcher Hall Rm. 170
1900 Rice Blvd. Ent. 20
Houston, TX 77005

>Office Phone: 1-713-348-5780

>Lab Phone/Fax: 1-713-348-5719

Rice Physics & Astronomy
Page Last Updated 1-21-09 by Kristjan Stone