23 research outputs found
Breakdown of sound in superfluid helium
Like elementary particles carry energy and momentum in the Universe,
quasiparticles are the elementary carriers of energy and momentum quanta in
condensed matter. And, like elementary particles, under certain conditions
quasiparticles can be unstable and decay, emitting pairs of less energetic
ones. Pitaevskii proposed that such processes exist in superfluid helium, a
quantum fluid where the very concept of quasiparticles was borne, and which
provided the first spectacular triumph of that concept. Pitaevskii's decays
have important consequences, including possible breakdown of a quasiparticle.
Here, we present neutron scattering experiments, which provide evidence that
such decays explain the collapsing lifetime (strong damping) of higher-energy
phonon-roton sound-wave quasiparticles in superfluid helium. This damping
develops when helium is pressurized towards crystallization or warmed towards
approaching the superfluid transition. Our results resolve a number of puzzles
posed by previous experiments and reveal the ubiquity of quasiparticle decays
and their importance for understanding quantum matter.Comment: 5 pages, 4 figures main text; 11 supplementary pages with 8
supplementary figure
A glimpse of a Luttinger liquid
The concept of a Luttinger liquid has recently been established as a
fundamental paradigm vital to our understanding of the properties of
one-dimensional quantum systems, leading to a number of theoretical
breakthroughs. Now theoretical predictions have been put to test by the
comprehensive experimental study.Comment: Unedited version of N&V article in Nature materials 4, 273 (2005