Browsing by Author "Schakel, AMJ"

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Ground state of electron gases at negative compressibility
(2001-12-15)
Schakel, AMJ
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電子物理學系
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Department of Electrophysics
Two- and three-dimensional electron gases with a uniform neutralizing background are Studied at negative compressibility. Parametrized expressions for the dielectric function are used to access this strong-coupling regime, where the screened Coulomb potential becomes overall attractive for like charges. Closely examining these expressions reveals that the ground state with a periodic modulation of the charge density, albeit exponentially damped, replaces the homogeneous one at positive compressibility. The wave vector characterizing the new ground state depends on the density and is complex. having a positive imaginary part, as does the homogeneous ground state, and real part, as does the genuine charge density wave.
Superconductor-insulator quantum phase transitions
(2000-12-01)
Schakel, AMJ
;
電子物理學系
;
Department of Electrophysics
In these lectures, superconductivity in impure thin films close to the absolute zero of temperature is discussed. The behavior as function of the applied magnetic field and the amount of impurities suggests the presence of a superconductor-insulator transition at zero temperature. The theory of superconductivity in the limit where all the electrons become tightly bound in pairs is used to explain the main characteristics of the transition. In that limit, where the theory becomes equivalent to a phase-only theory, electron pairs exist on either side of the transition. The presentation is pedagogical in nature and includes exercises as a learning aid for those new to the field.