MITの物理学者が、超流体中の熱の「ドロッ」という音を初めて捉えた(MIT physicists capture the first sounds of heat ”sloshing” in a superfluid)

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2024-02-08 マサチューセッツ工科大学(MIT)

A wavey array of pink spheres floats like on water. A wavey orange arrow points to the right, and a wavey purple arrow points to the left.

For the first time, MIT physicists have captured direct images of “second sound,” the movement of heat sloshing back and forth within a superfluid. The results will expand scientists’ understanding of heat flow in superconductors and neutron stars. Credits:Image: Jose-Luis Olivares, MIT

MITの物理学者たちは、通常は珍しい状態の物質において、熱が波として振る舞い、物質の粒子が異なる動きをする中で、熱が波のように動く様子を初めて直接観測しました。この「第2音」と呼ばれる現象は、超流動状態のリチウム6原子で観測され、通常の熱伝導とは異なる波動として示されました。これにより、熱の動きを正確に理解し、高温超伝導体や中性子星などの強く相互作用する物質における熱の挙動を予測する上での重要な知見が得られると期待されています。

<関連情報>

強く相互作用するフェルミ気体における超流動転移のサーモグラフィ Thermography of the superfluid transition in a strongly interacting Fermi gas

ZHENJIE YAN , PARTH B. PATEL , BISWAROOP MUKHERJEE , CHRIS J. VALE , […], AND MARTIN W. ZWIERLEIN
Science  Published:8 Feb 2024
DOI:https://doi.org/10.1126/science.adg3430

Editor’s summary

In superfluids, heat propagates like a wave in a phenomenon dubbed “second sound. ” However, observing this propagation directly is tricky. Yan et al. used a quantum gas of strongly interacting fermionic lithium atoms held in a box potential to visualize second sound. The researchers used radiofrequency spectroscopy to map out local changes to the temperature. Above the superfluid transition, heat propagated diffusively, but below the transition, wave-like propagation characteristic of second sound was observed. —Jelena Stajic

Abstract

Heat transport can serve as a fingerprint identifying different states of matter. In a normal liquid, a hotspot diffuses, whereas in a superfluid, heat propagates as a wave called “second sound.” Direct imaging of heat transport is challenging, and one usually resorts to detecting secondary effects. In this study, we establish thermography of a strongly interacting atomic Fermi gas, whose radio-frequency spectrum provides spatially resolved thermometry with subnanokelvin resolution. The superfluid phase transition was directly observed as the sudden change from thermal diffusion to second-sound propagation and is accompanied by a peak in the second-sound diffusivity. This method yields the full heat and density response of the strongly interacting Fermi gas and therefore all defining properties of Landau’s two-fluid hydrodynamics.

1700応用理学一般
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