Metal-Insulator Quantum Phase Transitions
Metal or insulator - and why? To answer this simple
question has been the goal and the driving force for much of the
physical science as we know it today. Going back to Newton’s
not-so-successful exercises in Alchemy, the scientist had tried to
understand what controls the flow of electricity in metals and what
prevents it in insulators. To understand it and to control it -
achieving this could prove more useful and lucrative than converting
lead into gold.
In almost every instance, these advances are based on materials that
find themselves somewhere between metals
and insulators.
Material
properties
are
easy
to
tune
in
this
regime,
where
several
possible
ground
states
compete.
Here
most
physical
quantities
display
unusual
behavior, and prove difficult to interpret using conventional
ideas and approaches. In this regime, the electrons simply do not seem
to be able to decide: move fast and conduct electricity or get stuck by
impurities or inter-particle repulsion - leading to insulating behavior.
Strange properties of the "no-man's land" between metals and insulators can be understood as the Quantum Critical Regime of the metal-insulator transition. To come to grips with this unfamiliar regime, one has to develop conceptual understanding of the interplay of quantum fluctuations and strong electronic correlations on one hand, and the tendency to form strongly inhomogeneous states of matter and slow glassy dynamics on the other. This very difficult but fundamentally important task is the central goal of our theoretical work.
The
fractal
background
pattern
behind this Web page shows the distribution
of
currents
in
a
Coulomb
Glass - a Coulomb system in presence
of moderate to strong disorder. Using JAVA simulations, we apply an
external electric field and watch the electrons move. Here each
electron is assigned a different color, and a "tracer" protocol is
implemented, creating a colorful trace for each electron. In presence
of disorder we observe very large "white" regions - domains where
almost no current flows. Remarkably, the flow then assumes "filamentary"
form, where the current paths form "rivers". The
fractal shapes of these current flows reflect the critical
("marginally stable") nature of the Coulomb Glass.
This is a green
website.
We are committed
to conserve energy - we
only use
Baym-Kadanoff conserving approximations
This
research is
supported by
NSF grant DMR-1005751