Pomeranchuk cooling explained

Pomeranchuk cooling (named after Isaak Pomeranchuk) is the phenomenon in which liquid helium-3 will cool if it is compressed isentropically when it is below 0.3 K. This occurs because helium-3 has the unusual property that its solid state can have a higher entropy than its liquid state. The effect was first observed by Yuri Anufriev in 1965.^[1] This can be used to construct a cryogenic cooler.^[2]

In 2021 an analog effect has been observed on twisted bilayer graphene^{[3] [4] [5]} and in TMDs^[6]

Notes and References

1. Lee . David M. . The extraordinary phases of liquid $^$He . Reviews of Modern Physics . 1 July 1997 . 69 . 3 . 645–666 . 10.1103/RevModPhys.69.645 . free .
2. Web site: Pomeranchuk Cooling. Weisstein. Eric. Eric Weisstein's World of Science.
3. Web site: 2021-04-21. Electrons in twisted graphene 'freeze' when heated. 2021-11-21. Physics World. en-GB.
4. Rozen. Asaf. Park. Jeong Min. Zondiner. Uri. Cao. Yuan. Rodan-Legrain. Daniel. Taniguchi. Takashi. Watanabe. Kenji. Oreg. Yuval. Stern. Ady. Berg. Erez. Jarillo-Herrero. Pablo. April 2021. Entropic evidence for a Pomeranchuk effect in magic-angle graphene. Nature. en. 592. 7853. 214–219. 10.1038/s41586-021-03319-3. 33828314 . 2009.01836. 221516628 . 1476-4687.
5. Ablikim. M.. Achasov. M. N.. Adlarson. P.. Ahmed. S.. Albrecht. M.. Aliberti. R.. Amoroso. A.. An. Q.. Lavania. Anita. Bai. X. H.. Bai. Y.. November 2021. Oscillating features in the electromagnetic structure of the neutron. Nature Physics. en. 17. 11. 1200–1204. 10.1038/s41567-021-01345-6. 2103.12486 . 243888280 . 1745-2481.
6. Li . Tingxin . Jiang . Shengwei . Li . Lizhong . Zhang . Yang . Kang . Kaifei . Zhu . Jiacheng . Watanabe . Kenji . Taniguchi . Takashi . Chowdhury . Debanjan . Fu . Liang . Shan . Jie . Mak . Kin Fai . September 2021 . Continuous Mott transition in semiconductor moiré superlattices . Nature . en . 597 . 7876 . 350–354 . 10.1038/s41586-021-03853-0 . 34526709 . 2103.09779 . 232257656 . 1476-4687.