Electron clouds can freeze into an "Orbital Glass" at low temperatures.
In the modern picture of quantum mechanics, electrons take the form
of "clouds" within the atoms and molecules in which they inhabit. The
clouds, which have various shapes such as spheres or dumbbells, represent
the general boundaries within which one may find an electron at any
one measurement in time. Typically, processes involving electron clouds
(more formally known as "orbitals") are blazingly fast. In the order
of a femtosecond (10^-15 s), for example, an electron orbital can make
transitions between degenerate states (those containing the same amount
of energy), transforming from a vertical dumbbell to a horizontal one
with respect to some axis.
Now, scientists have found evidence that
these and other orbital processes can slow down dramatically--to as
long as 0.1 seconds, a slowing by 14 orders of magnitude--for electrons
in low-temperature FeCr2S4, a spinel (class of mineral) with a relatively
simple crystalline structure. The researchers, who hail from the Center
for Electronic Correlations and Magnetism at the University of Augsburg
in Germany (Peter Lunkenheimer, Peter.Lunkenheimer@Physik.Uni-Augsburg.de)
and the Academy of Sciences of Moldova (a former Soviet republic), consider
these frozen electron orbitals in spinels to constitute a new class
of material which they have dubbed an orbital glass. By measuring the
response of the material to alternating-current electric fields in the
audio- to radio-frequency range, they found that processes involving
non-spherical orbitals dramatically slow down at low temperatures to
form a glass-like state, in a manner very similar to the arrest of molecular
motion that occurs when glass blowers perform their craft.
just the orbitals that slow down; the neighboring atomic nuclei that
surround the electrons also distort more slowly in response to the glacially
changing orbitals. In contrast to conventional glasses, a complete "freeze"
of the electron clouds does not occur at the lowest temperatures. Completely
frozen orbitals are prevented by quantum-mechanical tunneling: the clouds
keep themselves moving by making transitions between different low-energy
cloud configurations even without the energy they normally require.
al., Physical Review Letters, 21 January 2005