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Localization and Interaction in Ultra-High-Quality Two-Dimensional Electron Systems.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Localization and Interaction in Ultra-High-Quality Two-Dimensional Electron Systems./
Author:	Thekke Madathil, Pranav.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2024,
Description:	112 p.
Notes:	Source: Dissertations Abstracts International, Volume: 85-12, Section: B.
Contained By:	Dissertations Abstracts International85-12B.
Subject:	Electrical engineering. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=31295765
ISBN:	9798382809922

Localization and Interaction in Ultra-High-Quality Two-Dimensional Electron Systems.
Thekke Madathil, Pranav.

Localization and Interaction in Ultra-High-Quality Two-Dimensional Electron Systems. - Ann Arbor : ProQuest Dissertations & Theses, 2024 - 112 p.

Source: Dissertations Abstracts International, Volume: 85-12, Section: B.

Thesis (Ph.D.)--Princeton University, 2024.

Interaction and localization are two fundamental pillars in understanding the physics of solid-state systems. In quantum Hall systems, through the application of a strong magnetic field, the kinetic energy of the electrons can be quenched sufficiently so that the dominant energy scale is the Coulomb repulsion between electrons. The strong electron-electron correlations lead to exotic physics such as a many-body liquid phase, called the fractional quantum Hall state (FQHS) and many-body solid phase, namely the Wigner crystal (WC). However, the inherent disorder in the material deters the development of such novel states and leads to deviations from ideal behavior. Recent improvements in molecular beam epitaxy have enabled the growth of extremely pure, ultra-high-quality GaAs crystals.This PhD thesis deals with the interplay of interaction and disorder in GaAs two-dimensional electron systems, particularly in the limit of very low disorder. Following a general introduction in Chapter 1, in Chapter 2, we discuss localization and interaction in the context of a strongly-correlated liquid phase, namely the FQHS. In twodimensional, quantum Hall systems, extensive studies of disorder-induced localization have led to the emergence of a scaling picture with a single extended state, characterized by a power-law divergence of the localization length in the zero-temperature limit. We report scaling measurements in the FQHS regime where interaction plays a dominant role. Our study is partly motivated by recent calculations, based on the composite fermion theory, that suggest identical critical exponents (κ) in both integer QHS (IQHS) and FQHS cases to the extent that the interaction between composite fermions is negligible. We find that κ varies for transitions between different FQHSs observed on the flanks of Landau level filling factor ν = 1/2, and has a value close to that reported for the IQHS transitions only for a limited number of transitions between high-order FQHSs with intermediate strength. We discuss possible origins of the non-universal κ observed in our experiments, namely, interactions and disorder.Next, we present the physics of localization and interaction in the WC phase, a strongly correlated solid. Chapter 3 discusses the role of interactions in the context of extremely-low-disorder WC phase. The nature of the disorderless, exotic, many-body, quantum WC phase is yet to be fully understood and experimentally revealed since one of WC's most fundamental parameters, namely the energy gap that determines its low-temperature conductivity has been plagued by the disorder in the system. In our ultra-high-quality samples, the WC domains are extremely large containing ≃ 1000 electrons. The measured gaps are a factor of three larger than previously reported for lower quality samples, and agree remarkably well with values predicted for the lowest-energy, intrinsic, hyper-correlated bubble defects in a WC made of flux-electron composite fermions, rather than bare electrons. The agreement is particularly noteworthy, given that the calculations are done for disorder-free composite fermion WCs, and there are no adjustable parameters. The results reflect the exceptionally high quality of the samples, and suggest that composite fermion WCs are indeed more stable compared to their electron counterparts.Finally in Chapter 4, we discuss the relevance of disorder in the physics of ultrahigh-quality WC. This manifests in non-linear current-voltage (I-V) and noise characteristics of the WC, with current thresholds delineating three distinct phases of the WC: a pinned phase (P1) with very low noise, a second phase (P2) in which dV/dI fluctuates between positive and negative values and is accompanied by very high noise, and a third phase (P3) where dV/dI is nearly constant and small, and noise is about an order of magnitude lower than in P2. In the depinned (P2 and P3) phases, the noise spectrum also reveals well-defined peaks at frequencies that vary linearly with the applied current, suggestive of washboard frequencies. We discuss the data in light of a recent theory that proposes different dynamic phases for a driven WC.

ISBN: 9798382809922Subjects--Topical Terms:

649834
Electrical engineering.
Subjects--Index Terms:

Wigner crystal

Localization and Interaction in Ultra-High-Quality Two-Dimensional Electron Systems.
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500 $a Source: Dissertations Abstracts International, Volume: 85-12, Section: B.
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520 $a Interaction and localization are two fundamental pillars in understanding the physics of solid-state systems. In quantum Hall systems, through the application of a strong magnetic field, the kinetic energy of the electrons can be quenched sufficiently so that the dominant energy scale is the Coulomb repulsion between electrons. The strong electron-electron correlations lead to exotic physics such as a many-body liquid phase, called the fractional quantum Hall state (FQHS) and many-body solid phase, namely the Wigner crystal (WC). However, the inherent disorder in the material deters the development of such novel states and leads to deviations from ideal behavior. Recent improvements in molecular beam epitaxy have enabled the growth of extremely pure, ultra-high-quality GaAs crystals.This PhD thesis deals with the interplay of interaction and disorder in GaAs two-dimensional electron systems, particularly in the limit of very low disorder. Following a general introduction in Chapter 1, in Chapter 2, we discuss localization and interaction in the context of a strongly-correlated liquid phase, namely the FQHS. In twodimensional, quantum Hall systems, extensive studies of disorder-induced localization have led to the emergence of a scaling picture with a single extended state, characterized by a power-law divergence of the localization length in the zero-temperature limit. We report scaling measurements in the FQHS regime where interaction plays a dominant role. Our study is partly motivated by recent calculations, based on the composite fermion theory, that suggest identical critical exponents (κ) in both integer QHS (IQHS) and FQHS cases to the extent that the interaction between composite fermions is negligible. We find that κ varies for transitions between different FQHSs observed on the flanks of Landau level filling factor ν = 1/2, and has a value close to that reported for the IQHS transitions only for a limited number of transitions between high-order FQHSs with intermediate strength. We discuss possible origins of the non-universal κ observed in our experiments, namely, interactions and disorder.Next, we present the physics of localization and interaction in the WC phase, a strongly correlated solid. Chapter 3 discusses the role of interactions in the context of extremely-low-disorder WC phase. The nature of the disorderless, exotic, many-body, quantum WC phase is yet to be fully understood and experimentally revealed since one of WC's most fundamental parameters, namely the energy gap that determines its low-temperature conductivity has been plagued by the disorder in the system. In our ultra-high-quality samples, the WC domains are extremely large containing ≃ 1000 electrons. The measured gaps are a factor of three larger than previously reported for lower quality samples, and agree remarkably well with values predicted for the lowest-energy, intrinsic, hyper-correlated bubble defects in a WC made of flux-electron composite fermions, rather than bare electrons. The agreement is particularly noteworthy, given that the calculations are done for disorder-free composite fermion WCs, and there are no adjustable parameters. The results reflect the exceptionally high quality of the samples, and suggest that composite fermion WCs are indeed more stable compared to their electron counterparts.Finally in Chapter 4, we discuss the relevance of disorder in the physics of ultrahigh-quality WC. This manifests in non-linear current-voltage (I-V) and noise characteristics of the WC, with current thresholds delineating three distinct phases of the WC: a pinned phase (P1) with very low noise, a second phase (P2) in which dV/dI fluctuates between positive and negative values and is accompanied by very high noise, and a third phase (P3) where dV/dI is nearly constant and small, and noise is about an order of magnitude lower than in P2. In the depinned (P2 and P3) phases, the noise spectrum also reveals well-defined peaks at frequencies that vary linearly with the applied current, suggestive of washboard frequencies. We discuss the data in light of a recent theory that proposes different dynamic phases for a driven WC.
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653 $a Kinetic energy
653 $a Molecular beam
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653 $a Coulomb repulsion
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