Two-dimensional graphene semiconductors enhance high-temperature exotic state

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Two-dimensional graphene semiconductors enhance high-temperature exotic state. The phenomenon of Bose–Einstein condensation is typically limited to extremely low temperatures. The effect has now been spotted at much higher temperatures for particles called excitons in atomically thin semiconductors. Cornell University researchers Zefang Wang, Jie Shan, and Kin Fai Mak; Daniel A. Rhodes and James C. Hone of Columbia University; and Kenji Watanabe and Takashi Taniguchi of Japan’s National Institute for Materials Science collaborated on this research.

At sufficiently low temperatures, large assemblies of particles that are classified as bosons condense into a single quantum state. This remarkable phenomenon, known as Bose–Einstein condensation (BEC), can allow the particles to become a superfluid, whereby they flow without friction. Superfluidity has been seen in gaseous helium-4 and in ultracold atoms, but only at extremely low temperatures (a few kelvin). In the past few decades, there have been many attempts to achieve high-temperature BEC in semiconductors using electrically neutral composite particles called excitons, which are bound states of a negatively charged electron and a positively charged hole (electron vacancy). Writing in Nature, Wang et al. report compelling experimental evidence that charge-separated excitons in a pair of atomically thin semiconductors can exhibit BEC at temperatures as high as 100 K.

When an electron is excited from the ‘valence’ energy states of a semiconductor material to higher-energy conducting states, it leaves behind a hole. The electrostatic attraction between electrons and holes can bind them into excitons. Separately, electrons and holes are particles that are classified as fermions, which cannot form Bose–Einstein condensates. But because a bound state of two fermions is a boson, excitons can condense. Read full article here.

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