Experimental Research Of Quantum Phases And Quantum Phase Transitions In Quantum Hall System

Starting from the quantum transport experiments of two-dimensional electron gas (2DEG) in GaAs/AlGaAs semiconductor quantum well system under condition of low temperature and high magnetic field,by varying the parameters such as the magnetic field,tilted angle,electron density,temperature and radio frequency,the longitudinal and Hall resistance of the Hall bar samples were measured and we studied the quantum phases and quantum phase transitions which exist in quantum Hall system.To study the phases and phase transitions in quantum Hall system,not only helps us understand the nature of the interaction beneath the phenomena,but also gives us the techniques to control them.Considering that some of these states can be utilized as the candidate for the quantum information process,I think our works will give us clues to realize the quantum computer based on two-dimensional electron gas system in future.The main content and characteristics of this dissertation are listed as follows:1.Described the classical and quantum transport phenomena of 2DEG in magnetic field.Based on incompressible quantum states and disorder,we gave an explanation to quantum Hall effect.2.Introduced the scaling theory for plateau transition in quantum Hall system.In GaAs/AlGaAs quantum well with single subband 2DEG system,we studied the quantum Hall effect and the plateau transition.3.Studied the topological phase diagram of GaAs/AlGaAs quantum well with twosubband 2DEG system.Found a phase transition of pseudo-spin quantum Hall ferromagnetic state which is induced by in-plane magnetic field.4.Studied the phase transition between localized and extended state in the region of Landau level mixing in two-subband quantum Hall system.5.Described the principle of Resistively Detected Nuclear Magnetic Resonance (RD-NMR),and studied the NMR signal and nuclear spin relaxation time T₁ in the filling factorν=4 where the pseudo-spin quantum Hall ferromagnetic states are well developed.6.Provided the summary of the works during the PhD research,and gave a perspective about the future research works.And the recent progress in the quantum information process based on quantum Hall system were introduced.The main innovations of this dissertation are summarized as follows:1.Gave an experimental support for theoretical proposed scaling functions,and proved that different scaling functions applied in different range of the critical region.2.Firstly found a phase transition at filling factorν=4,which is induced by inplane magnetic field and during the phase transition the pseudo-spin quantum Hall ferromagnetic state with SU(2) symmetry changes into an unknown state with SU(4) symmetry.3.Studied the scaling behavior in the region of Landau levels crossing in twosubband system.And gave a conclusion that the mixing of Landau levels doesn't change the scaling behavior of system for a given disorder profile.4.Used the RD-NMR to detect the pseudo-spin quantum Hall ferromagnetic state, and found that only easy-axis pseudospin quantum Hall state is sensitive to the RD-NMR measurement and there is signature of low energy spin excitation.And at the same time the distribution of NMR signal is asymmetry.