Discovery of an excited pair state in superfluid 3 He
Discovery of an excited pair state in superfluid 3 He
复制标题
超流体 3 He 中激发对态的发现
DOI：
10.1038/nphys969
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发表时间：
2008
期刊：
影响因子：
19.6
通讯作者：
W. Halperin
中科院分区：
文献类型：
--
作者：
J. Davis;J. Pollanen;H. Choi;J. Sauls;W. Halperin
集体模式是凝聚相的指纹。超流体3He和非常规超导体中这些模式的光谱可以提供凝聚态对称性的关键信息，以及基态和激发能的微观配对机制。在这里，我们使用对横向声速变化非常敏感的声腔内干涉测量法来揭示超流体3He (3He-B) B相中的新集体模式。我们将模式确定为库珀对的激发态，它是弱束缚态，激发能在破缺边的1%以内。根据3He-B中横向声与集体模式耦合的选择规则，结合在集体模式频率附近的声学双折射观测，我们推断出新的模式很可能是一个总角动量J=4的自旋三重态（S=1）、f波对激子（轨道动量L=3）。存在一个J=4的激子对表明在液体3He中存在一个吸引的、亚优势的f波对相互作用。超流体He是一种量子凝聚体，其中He原子以一种非常规的方式配对。然而，尽管对超流体3He的集体模式进行了广泛的研究，但迄今为止仍未发现一种模式。
Collective modes are the fingerprint of a condensed phase. The spectroscopy of these modes in superfluid 3He and unconventional superconductors can provide key information on the symmetry of the condensate as well as the microscopic pairing mechanism responsible for the ground state and excitation energies. Here, we use interferometry within an acoustic cavity—which is very sensitive to changes in the velocity of transverse sound—to reveal a new collective mode in the B phase of superfluid 3He (3He-B). We identify the mode as an excited bound state of Cooper pairs, which is weakly bound with an excitation energy within 1% of the pair-breaking edge. On the basis of the selection rules for coupling of transverse sound to a collective mode in 3He-B, combined with the observation of acoustic birefringence near the collective mode frequency, we infer that the new mode is most likely a spin-triplet (S=1), f-wave pair exciton (orbital momentum L=3) with total angular momentum, J=4. The existence of a pair exciton with J=4 suggests an attractive, subdominant, f-wave pairing interaction in liquid 3He. Superfluid 3He is a quantum condensate in which the He atoms are paired in an unconventional way. Yet despite extensive research on the collective modes of superfluid 3He, one mode has remained undiscovered, until now.