125 research outputs found
Scaling of von Neumann entropy at the Anderson transition
Extensive body of work has shown that for the model of a non-interacting
electron in a random potential there is a quantum critical point for dimensions
greater than two---a metal-insulator transition. This model also plays an
important role in the plateau-to-plateu transition in the integer quantum Hall
effect, which is also correctly captured by a scaling theory. Yet, in neither
of these cases the ground state energy shows any non-analyticity as a function
of a suitable tuning parameter, typically considered to be a hallmark of a
quantum phase transition, similar to the non-analyticity of the free energy in
a classical phase transition. Here we show that von Neumann entropy
(entanglement entropy) is non-analytic at these phase transitions and can track
the fundamental changes in the internal correlations of the ground state wave
function. In particular, it summarizes the spatially wildly fluctuating
intensities of the wave function close to the criticality of the Anderson
transition. It is likely that all quantum phase transitions can be similarly
described.Comment: 15 pages, 3 figures, submitted as a chapter in the book "50 years of
Anderson localization
High temperature superconductivity: from complexity to simplicity
I discuss the recent quantum oscillation experiments in the underdoped high
temperature superconductors.Comment: An edited shorter version is published in Scienc
Do electrons change their c-axis kinetic energy upon entering the superconducting state?
The interlayer tunneling mechanism of the cuprate high temperature
superconductors involves a conversion of the confinement kinetic energy of the
electrons perpendicular to the CuO-planes (-axis) in the normal state to the
pair binding energy in the superconducting state. This mechanism is discussed
and the arguments are presented from the point of view of general principles.
It is shown that recent measurements of the -axis properties support the
idea that the electrons substantially lower their -axis kinetic energy upon
entering the superconducting state, a change that is nearly impossible in any
conventional mechanism. The proper use of a -axis conductivity sum rule is
shown to resolve puzzles involving the penetration depth and the optical
measurements.Comment: A few typos are corrected and the footnote 11 expande
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