Electron Tunneling Study of Coulomb Correlations across the Metal-Isulator Transition in Si:B

We have performed a Monte Carlo study of a classical three dimensional Coulomb system in which we systematically increase the positional disorder. We start from a completely ordered system and gradually transition to a Coulomb glass. The phase transition as a function of temperature is second order for all values of disorder. We use finite size scaling to determine the transition temperature TC and the critical exponent ν. We find that TC decreases and that ν increases with increasing disorder. We also observe changes in the specific heat, the single particle density of states, and the staggered occupation as a function of disorder and temperature.

Section: Introductionmentioning

confidence: 94%

Effect of increasing disorder on the critical behavior of a Coulomb system

Overlin

Wong

2004

“…Closer to the MIT, the precise form of P(ε) may be affected by quantum fluctuations, as argued in Ref. 35 , and it may need to be self-consistently calculated, in order to accurately capture the interplay of Anderson localization and the effects of the Coulomb interactions. Such a calculation may be possible within the framework of a DMFT-like formulation, by combining TMT with the EDMFT approach to Coulomb correlations 36 , but this rather complicated analysis is left as a challenge for future work.…”

Section: Model and Numerical Solution Of Tmt Equationsmentioning

confidence: 99%

Quantum criticality at the Anderson transition: A typical medium theory perspective

Mahmoudian¹,

Tang²,

Dobrosavljević³

2015

We present a complete analytical and numerical solution of the Typical Medium Theory (TMT) for the Anderson metal-insulator transition. This approach self-consistently calculates the typical amplitude of the electronic wave-functions, thus representing the conceptually simplest order-parameter theory for the Anderson transition. We identify all possible universality classes for the critical behavior, which can be found within such a meanfield approach. This provides insights into how interaction-induced renormalizations of the disorder potential may produce qualitative modifications of the critical behavior. We also formulate a simplified description of the leading critical behavior, thus obtaining an effective Landau theory for Anderson localization.

“…As the MIT is approached from the insulating side, the Coulomb energy U in our samples increases as a result of a decrease in the mean separation of the electrons. As the MIT is approached from the metallic side, U also increases because the screening becomes less efficient [5,10,11]. Therefore, we expect U to have a maximum in the transition region.…”

mentioning

confidence: 98%

Mesoscopic behavior near a two-dimensional metal-insulator transition

Popović

Washburn

1997

We study conductance fluctuations in a two-dimensional electron gas as a function of chemical potential (or gate voltage) from the strongly insulating to the metallic regime. Power spectra of the fluctuations decay with two distinct exponents (1/v l and 1/v h ). For conductivity σ ∼ 0.1 e 2 /h, we find a third exponent (1/vi) in the shortest samples, and non-monotonic dependence of vi and v l on σ. We study the dependence of vi, v l , v h , and the variances of corresponding fluctuations on σ, sample size, and temperature. The anomalies near σ ≃ 0.1 e 2 /h indicate that the dielectric response and screening length are critically behaved, i. e. that Coulomb correlations dominate the physics.PACS Nos. 73.23.Ps, 73.40.Gk, 73.40.Qv, 71.30.+h The metal-insulator transition (MIT) is one of the fundamental problems in condensed matter science. Recent theoretical work [1] strongly suggests the crucial role played by electron-electron interactions in the transition regime. However, since the development of the scaling theory of localization [2], it has been asserted that all states are localized in 2D, in agreement with early experiments [3] on relatively low-mobility samples. A recent experiment [4] on a two-dimensional electron gas (2DEG) in Si metal-oxide-semiconductor field-effect transistors (MOSFETs) provides evidence for the existence of a true MIT. The samples used in that experiment [4] had a much higher mobility and, as a result, the Coulomb interactions played a greater role relative to disorder. Thus it has been speculated [4] that this MIT is driven by interaction effects. Using mesoscopic measurements, we provide direct evidence for the crucial role of Coulomb interactions at the MIT in a 2DEG.We investigate the statistics of conductance fluctuations in a 2DEG as it undergoes a transition from strongly insulating to metallic behavior. In the insulating regime, electrons move in a strong, random potential by tunneling through localized states. In our relatively small samples and at low temperatures, the total number of states that contribute to conduction can be small, e. g. of the order of 50-100. By sweeping the gate voltage V g , the chemical potential µ is shifted relative to the energy of localized states. As a result, the number and nature of localized states that dominate the transport change, and the conductance G changes up to several orders of magnitude. In addition, it is well established that, deep in the insulating regime, the density of states D(E) increases exponentially with increasing V g [5].Our measurements were carried out on n-channel MOSFETs fabricated on the (100) surface of Si doped at ≈ 3 × 10 14 acceptors/cm 3 with 500Å gate oxide thickness and (unintentional) oxide charge < 10 10 cm −2 . The peak mobilities of our samples were of the order of 2 m 2 /Vs -comparable to those exhibiting a true MIT [4].In contrast to those samples, ours are much smaller: rectangular with source-to-drain lengths L = 1 − 8 µm, and widths W = 11.5 − 162 µm. They were short enough to exhibit conductance...