Bose--Einstein condensation: Where many become
one and,
therefore, there is plenty of room at the
bottom
Raman Research Institute,
E-mail: nkumar@rri.res.in
Abstract. Bose--Einstein condensation and superfluidity are well
known to occur in the dilute
gaseous as well as in the dense liquid
state of matter having a fixed
number of Bose particles. Very
recently, experimental evidence has
been obtained for the probable
realization of BEC and superfluidity in $^4$He in the solid state
too, as revealed through its
non-classical rotational moment of
inertia -- smaller than that for
the solid. Such a
solid that can also subtend a flow
as superfluid -- and hence a supersolid
-- is indeed a surprise of condensed matter physics. In this
conversation, an order-parameter
description for the supersolid state
will be given in which the superfluid flow is decoupled from the
crystalline density modulation
which remains at rest in the
laboratory frame, thus giving it a
non-classical inertia.
Keywords. Bose--Einstein condensation; Bose--Einstein statistics; indistinguishability; Bosonic
stimulation; condensate; quantized vortex; de Boer quantum parameter;
non-classical rotational inertia; supersolid.
PACS Nos 03.75.Fi; 34.50.-s; 67.90.-fz