Quantum Transport Studies On GaAs/AlGaAs Two-dimensional Electron Systems

Due to lower spatial dimensions and high mobility,two-dimensional electrons exhibit rich and interesting physical phenomena at high magnetic field and low temperature.The studies of these quantum transport properties,including ballistic transport near zero magnetic field,magneto-electrical energy band transport at low magnetic field,and quantum Hall states at high magnetic field(including integer and fractional quantum Hall edge states),played a key role in revealing the unique physical nature and exploring potential device applications of two-dimensional electronic materials.In the past three decades,quantum transport based on two-dimensional electron systems(2DEG)has been one of the important topics in condensed matter physics.Two-dimensional electronic system(2DES)based on GaAs/AlGaAs heterostructure is the purest solid state electronic material achieved in laboratories,and provides an important platform for studying basic physics in the condensed matter physics and exploring quantum devices.In this thesis,the low temperature transport properties of quantum devices,which are fabricated on GaAs/AlGaAs two-dimensional electronic materials grown by our high vacuum molecular beam epitaxy(MBE)machine,are further studied:Firstly,in chapter two,we report the nonlinear characteristics on high mobility GaAs/AlGaAs two-dimensional electronic samples when electrons transport in the ballistic regime.More experimental and theoretical works have studied that,when the width of Hall bar w is smaller than electron mean free length le and the boundary is rough,resistance maximum,quenching and ”last plateau”,negative value near zero magnetic field can occur in the longitudinal resistance Rxx,Hall resistance RH,bend resistance RB,respectively.Our experiments mainly focused on what kinds of changes related to these resistance anomalies may happen in differential measurement under large dc bias.The results show that the maxima of longitudinal differential resistance Rxxmove with increasing dc bias,or resistance maxima and minima evolve into each other.Similarly,the differential bend resistance RBalso exhibits conversion between resistance maxima and minima when increasing dc bias.But these phenomena do not occur under direct dc measurement.We preliminarily consider that these phenomena can be attributed to the nonlinear response of resistance to dc bias.Secondly,in chapter three,we investigated the Zener tunneling oscillations of ultra-high mobility GaAs/AlGaAs two-dimensional electron gas(2DEG)systems with dc bias across sound barrier.In an intermediate temperature range(1.0K ? 5.0 K),the phase of Zener tunneling oscillations inverses when Hall drift velocity vdcreaches in the vicinity of sound velocity vphwhich is attributed to the permission of phonon scattering in the supersonic regime(vdc> vph),but prohibition in the subsonic regime(vdc< vph).However,the oscillations remain regular periodicity at both lower and higher temperature no matter in subsonic(vdc> vph)or supersonic regime(vdc< vph).Distinctly,our observation qualitatively agrees with a theoretic predication,and a quantitative explanation need to be further studied.Finally,in chapter four,by fabricating Fabry-Perot quantum Hall interferometer(FPQHI)on GaAs/AlGaAs two-dimensional electron gas(2DEG)systems,we have studied magnetoresistance oscillations arising from interfering of quantum Hall edge states.In experiments,we have observed periodic resistance oscillations in Fabry-Perot quantum Hall interferometers at integer filling factors of the constrictions,fc= 1,2,3,4,5,and 6.Rather than Aharonov-Bohm interference,these oscillations are attributed to Coulomb interactions between interfering edge states and localized states in the central island of a interferometer.Similar resistance oscillations were also observed when the area A of the center regime and the backscattering probability of interfering edge states are varied,by changing the sidegate voltages and the configuration of the quantum point contacts(QPCs)respectively.These works,performed in the integer quantum Hall regime on samples with relative low mobilities,paved the way for our future study on the observation of CD and AB oscillations in the fractional quantum Hall regime of samples with higher mobility.