近日，德国马克斯·普朗克固体研究所的Hidenori Takagi&Yosuke Matsumoto及其研究团队取得一项新进展。经过不懈努力，他们对准二维反铁磁体YbCl3中磁振子的量子临界玻色气体进行研究。相关研究成果已于2024年5月9日在国际知名学术期刊《自然—物理学》上发表。
该研究团队证明了一个量子临界二维玻色气体在跃迁场中的形成，随着场的逐渐降低，在微弱的层间耦合作用下，经历了一个边缘稳定的玻色-爱因斯坦凝聚（BEC）过程。这一观察确立了YbCl3，这种原先被视为基塔耶夫量子自旋液体材料的物质，在二维极限下实现了量子临界BEC。
据悉，玻色子-爱因斯坦凝聚(BEC)是一种宏观数量的玻色子占据最低能态，并在低温下获得相干性的量子现象。在三维反铁磁体中，磁场诱导跃迁已被成功地描述为磁振子BEC。对于一个严格的二维(2D)系统，已知由于存在有限密度的零能量态而不能发生BEC。然而，在由堆叠磁层构成的实际准二维磁体中，尽管存在小而有限的层间耦合稳定了边缘BEC，但二维物理效应仍然预计占据主导地位。这种二维极限下的BEC行为虽然已在某些材料中得到报道，但通常需要在难以达到的极高磁场中才能实现。蜂窝S=1/2海森堡反铁磁体YbCl3在相对较低的面内磁场下表现出向完全极化状态的跃迁。
附：英文原文
Title: A quantum critical Bose gas of magnons in the quasi-two-dimensional antiferromagnet YbCl3 under magnetic fields
Author: Matsumoto, Yosuke, Schnierer, Simon, Bruin, Jan A. N., Nuss, Jrgen, Reiss, Pascal, Jackeli, George, Kitagawa, Kentaro, Takagi, Hidenori
Issue&Volume: 2024-05-09
Abstract: Bose–Einstein condensation (BEC) is a quantum phenomenon in which a macroscopic number of bosons occupy the lowest energy state and acquire coherence at low temperatures. In three-dimensional antiferromagnets, a magnetic-field-induced transition has been successfully described as a magnon BEC. For a strictly two-dimensional (2D) system, it is known that BEC cannot take place due to the presence of a finite density of states at zero energy. However, in a realistic quasi-2D magnet consisting of stacked magnetic layers, a small but finite interlayer coupling stabilizes marginal BEC but such that 2D physics is still expected to dominate. This 2D-limit BEC behaviour has been reported in a few materials but only at very high magnetic fields that are difficult to access. The honeycomb S=1/2 Heisenberg antiferromagnet YbCl3 exhibits a transition to a fully polarized state at a relatively low in-plane magnetic field. Here, we demonstrate the formation of a quantum critical 2D Bose gas at the transition field, which, with lowering the field, experiences a BEC marginally stabilized by an extremely small interlayer coupling. Our observations establish YbCl3, previously a Kitaev quantum spin liquid material, as a realization of a quantum critical BEC in the 2D limit.
DOI: 10.1038/s41567-024-02498-w
Source: https://www.nature.com/articles/s41567-024-02498-w