LMU/MPQ-physicists succeed in measuring geometric properties
of energy bands in light crystals.
Geometrical phases occur in many places in nature. One of
the simplest examples is the Foucault pendulum: a tall pendulum free to swing
in any vertical plane. Due to the earth rotation, the actual plane of swing
rotates relative to the earth. One observes that every day the plane of
rotation changes by a small “geometric” angle, associated to the spherical
shape of the earth. In quantum mechanics a similar effect was discovered in
1984 by the British physicist Sir Michael Berry, who identified a geometrical
phase in quantum-mechanical problems that is today known as the “Berry’s
phase”. Such quantum-mechanical phases can have a profound effect on material
properties and are responsible for a variety of phenomena. Some examples are
the dielectric polarization or the quantum Hall effect, with the latter one
being used nowadays to define the standard of resistance. For the first time,
scientists in the group of Professor Immanuel Bloch
(Ludwig-Maximilians-University, Munich and Max-Planck-Institute of Quantum
Optics, Garching) in close collaboration with theoretical physicists from
Harvard University in the group of Professor Eugene Demler have succeeded in
measuring such a phase in a one dimensional solid-state like system. This phase
is known as the “Zak-phase” named after the Israeli physicist Joshua Zak