Roton
Encyclopedia
A roton is an elementary excitation, or quasiparticle
, in superfluid
Helium
-4. The dispersion relation
of elementary excitations in this superfluid shows a linear
increase from the origin, but exhibits first a maximum and then a minimum in energy
as the momentum
increases. Excitations with momenta in the linear region are called phonon
s; those with momenta close to the minimum are called rotons. Excitations with momenta near the maximum are sometimes called maxons.
Quasiparticle
In physics, quasiparticles are emergent phenomena that occur when a microscopically complicated system such as a solid behaves as if it contained different weakly interacting particles in free space...
, in superfluid
Superfluid
Superfluidity is a state of matter in which the matter behaves like a fluid without viscosity and with extremely high thermal conductivity. The substance, which appears to be a normal liquid, will flow without friction past any surface, which allows it to continue to circulate over obstructions and...
Helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
-4. The dispersion relation
Dispersion relation
In physics and electrical engineering, dispersion most often refers to frequency-dependent effects in wave propagation. Note, however, that there are several other uses of the word "dispersion" in the physical sciences....
of elementary excitations in this superfluid shows a linear
Linear
In mathematics, a linear map or function f is a function which satisfies the following two properties:* Additivity : f = f + f...
increase from the origin, but exhibits first a maximum and then a minimum in energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
as the momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
increases. Excitations with momenta in the linear region are called phonon
Phonon
In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, such as solids and some liquids...
s; those with momenta close to the minimum are called rotons. Excitations with momenta near the maximum are sometimes called maxons.