Editing Exciton (section)

==Interaction==
Excitons are the main mechanism for [[light emission]] in semiconductors at low [[temperature]] (when the characteristic thermal energy ''[[Boltzmann constant|k]]T'' is less than the exciton [[binding energy]]), replacing the free electron-hole recombination at higher temperatures.

The existence of exciton states may be inferred from the absorption of light associated with their excitation. Typically, excitons are observed just below the [[band gap]].

When excitons interact with photons a so-called [[polariton]] (or more specifically [[exciton-polariton]]) is formed. These excitons are sometimes referred to as ''dressed excitons''.

Provided the interaction is attractive, an exciton can bind with other excitons to form a [[biexciton]], analogous to a dihydrogen [[molecule]]. If a large density of excitons is created in a material, they can interact with one another to form an [[Carrier generation and recombination|electron-hole]] liquid, a state observed in k-space indirect semiconductors.

{{anchor|excitonium}}<!-- Used by redirect -->Additionally, excitons are integer-spin particles obeying [[Bosons|Bose]] statistics in the low-density limit. In some systems, where the interactions are repulsive, a [[Bose–Einstein condensate|Bose–Einstein condensed state]], called excitonium, is predicted to be the ground state. Some evidence of excitonium has existed since the 1970s but has often been difficult to discern from a Peierls phase.<ref>{{cite news|title=New form of matter 'excitonium' discovered|url=https://timesofindia.indiatimes.com/home/science/new-form-of-matter-excitonium-discovered/articleshow/61994947.cms|access-date=10 December 2017|work=The Times of India}}</ref> Exciton condensates have allegedly been seen in a double quantum well systems.<ref>{{Cite journal |last1=Eisenstein |first1=J. P. |date=January 10, 2014 |title=Exciton Condensation in Bilayer Quantum Hall Systems |journal=Annual Review of Condensed Matter Physics |volume=5 |pages=159–181 |arxiv=1306.0584 |bibcode=2014ARCMP...5..159E |doi=10.1146/annurev-conmatphys-031113-133832 |s2cid=15776603}}</ref> In 2017 Kogar et al. found "compelling evidence" for observed excitons condensing in the three-dimensional semimetal 1''T''-[[Titanium diselenide|TiSe<sub>2</sub>]].<ref>.{{cite journal |last1=Kogar |first1=Anshul |last2=Rak |first2=Melinda S |last3=Vig |first3=Sean |last4=Husain |first4=Ali A |last5=Flicker |first5=Felix |last6=Joe |first6=Young Il |last7=Venema |first7=Luc |last8=MacDougall |first8=Greg J. |last9=Chiang |first9=Tai C. |last10=Fradkin |first10=Eduardo |last11=Van Wezel |first11=Jasper |last12=Abbamonte |first12=Peter |year=2017 |title=Signatures of exciton condensation in a transition metal dichalcogenide |journal=Science |volume=358 |issue=6368 |pages=1314–1317 |arxiv=1611.04217 |bibcode=2017Sci...358.1314K |doi=10.1126/science.aam6432 |pmid=29217574 |s2cid=206656719}}</ref>