Bose–Einstein condensation can occur in quasiparticles, particles that are constructive descriptions of commonage excitations in materials. Some have integer spins and can be expected to obey Bose–Einstein statistics like traditional particles. Conditions for condensation of various quasiparticles take been predicted and observed. The topic continues to exist an active field of study.
BECs course when low temperatures cause nearly all particles to occupy the lowest quantum state. Condensation of quasiparticles occurs in ultracold gases and materials. The lower masses of cloth quasiparticles relative to atoms atomic number 82 to higher BEC temperatures. An ideal Bose gas has a phase transitions when inter-particle spacing approaches the thermal De-Broglie wavelength:
. The critical concentration is then
, leading to a disquisitional temperature:
. The particles obey the Bose–Einstein distribution and all occupy the ground state:
The Bose gas can exist considered in a harmonic trap,
, with the ground state occupancy fraction equally a function of temperature:
This can be accomplished past cooling and magnetic or optical command of the arrangement. Spectroscopy tin observe shifts in peaks indicating thermodynamic phases with condensation. Quasiparticle BEC can be superfluids. Signs of such states include spatial and temporal coherence and polarization changes. Observation for excitons in solids was seen in 2005 and for magnons in materials and polaritons in microcavities in 2006. Graphene is another important solid state organization for studies of condensed matter including quasi particles; It’southward a 2nd electron gas, similar to other thin films.
Excitons are electron-pigsty pairs. Similar to helium-4 superfluidity[iii]
a condensate was proposed past Böer et al. in 1961.
Experimental miracle were predicted leading to various pulsed laser searches that failed to produce evidence. Signs were first seen by Fuzukawa et al. in 1990, but definite detection was published afterward in the 2000s. Condensed excitons are a superfluid and will not interact with phonons. While the normal exciton absorption is broadened by phonons, in the superfluid assimilation degenerates to a line.
Excitons results from photons heady electrons creating holes, which are then attracted and tin form bound states. The 1s paraexciton and orthoexciton are possible. The 1s triplet spin land, 12.1meV below the degenerate orthoexciton states(lifetime ~ns), is decoupled and has a long lifetime to an optical decay. Dilute gas densities (n~ten14cm−3) are possible, but paraexcition generation scales poorly, and then significant heating occurs in creating high densities(ten17cm−three) preventing BECs. Assuming a thermodynamic phase occurs when separation reaches the de Broglie wavelength(
is the exciton density, effective mass(of electron mass order)
are the Planck and Boltzmann constants. Density depends on the optical generation
and lifetime as:
. Tuned lasers create excitons which efficiently self-annihilate at a rate:
, preventing a high density paraexciton BEC.[vii]
A potential well limits diffusion, damps exciton decay, and lowers the critical number, yielding an improved critical temperature versus the
scaling of free particles:
In an ultrapure CutwoO crystal:
= 10s. For an doable T = 0.01K, a manageable optical pumping rate of 105/southward should produce a condensate.[eight]
More detailed calculations by J. Keldysh[nine]
and later past D. Snoke et al.
started a large number of experimental searches into the 1990s that failed to notice signs.
Pulse methods led to overheating, preventing condensate states. Helium cooling allows mili-kelvin setups and continuous wave optics improves on pulsed searches. Relaxation explosion of a condensate at lattice temperature 354 mK was seen by Yoshioka et al. in 2011.
Recent experiments by Stolz et al. using a potential trap have given more prove at ultralow temperature 37 mK.
In a parabolic trap with exciton temperature 200 mK and lifetime broadened to 650ns, the dependence of brilliance on light amplification by stimulated emission of radiation intensity has a kink which indicates condensation. The theory of a Bose gas is extended to a mean field interacting gas by a Bogoliubov arroyo to predict the exciton spectrum; The kink is considered a sign of transition to BEC. Signs were seen for a dense gas BEC in a GaAs breakthrough well.
Magnons, electron spin waves, can be controlled by a magnetic field. Densities from the limit of a dilute gas to a strongly interacting Bose liquid are possible. Magnetic ordering is the analog of superfluidity. The condensate appears every bit the emission of monochromatic microwaves, which are tunable with the applied magnetic field.
In 1999 condensation was demonstrated in antiferromagnetic TlCuCl3,
at temperatures as big every bit fourteen Thousand. The loftier transition temperature (relative to atomic gases) is due to the modest mass (nigh an electron) and greater density. In 2006, condensation in a ferromagnetic Yttrium-iron-garnet sparse motion-picture show was seen even at room temperature
with optical pumping. Condensation was reported in gadolinium in 2011.[nineteen]
Magnon BECs have been considered equally qubits for breakthrough computing.
Polaritons, caused by light coupling to excitons, occur in optical cavities and condensation of exciton-polaritons in an optical microcavity was outset published in Nature in 2006.
Semiconductor cavity polariton gases transition to ground country occupation at 19K.
Bogoliubov excitations were seen polariton BECs in 2008.
The signatures of BEC were observed at room temperature for the first time in 2013, in a large exciton free energy semiconductor device
and in a polymer microcavity.
Rotons, an elementary excitation in superfluid
4He introduced by Landau,
were discussed by Feynman
Rotons condense at low temperature. Experiments have been proposed and the expected spectrum has been studied,
but roton condensates have not been detected. Phonons were first observed in a condensate in 2004 past ultrashort pulses in a bismuth crystal at 7K.
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