2021/04/27
Keio University
A research group led by Tomoyuki Tani, then a doctoral student in the School of Fundamental Science and Technology, Graduate School of Science and Technology, Keio University, along with Professor Keiya Shirahama and Assistant Professor Yusuke Nago from the Department of Physics, Faculty of Science and Technology at the same university, has revealed that liquid helium confined in a nanoporous medium (a glass material with sponge-like pores of nanometer size) undergoes a superfluid phase transition known as the 4D XY model. This means that a substance has actually been found that exhibits a four-dimensional phase transition, despite being spatially three-dimensional.
Phase transition phenomena are classified into categories called "universality classes," and normal liquid helium belongs to the 3D XY universality class. It was also known that thin films of helium exhibit a 2D XY BKT superfluid phase transition. While it was known from past research by this group that helium in a nanoporous medium exhibits a 4D XY quantum phase transition at absolute zero, this study has revealed for the first time that the superfluid phase transition occurring at normal temperatures is also four-dimensional. The 4D phase transition is theoretically the simplest type of phase transition, and its discovery is expected to contribute significantly to the understanding of phase transition phenomena.
The results of this research were published in March 2021 in the "Journal of the Physical Society of Japan," the English-language journal of the Physical Society of Japan. The paper was selected as an Editors’ Choice and was also featured on the English website JPS Hot Topics.
Please see below for the full press release.