Elementary Excitations in Liquid Helium
Elementary Excitations in Liquid Helium
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液氦中的基本激发
DOI：
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发表时间：
1962
期刊：
影响因子：
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通讯作者：
P. Nozières
中科院分区：
文献类型：
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作者：
A. Miller;D. Pines;P. Nozières
分析了近年来对液体He II基元激发光谱的一些实验和理论研究。在非弹性中子散射实验中测量的密度涨落谱由两个不同的部分组成：从凝聚零动量态直接激发单个准粒子，以及由两个、三个或更多个准粒子相互作用产生的更复杂构型的激发。借助于一般求和规则的证明：(1)在长波极限下，单个准粒子激发耗尽了f和规则，所得到的激发谱与Feynman提出并由Henshaw和Wood实验发现的声子谱相同：(2)密度涨落谱的这种渐近行为可用于归一化Henshaw和Wood的实验结果；由此，我们得到了一个稍有改变的液体结构-因子曲线，关于入射慢中子凝聚态的准粒子激发效率的详细信息，以及作为粒子相互作用结果的零动量态耗尽的估计；(3)Feynman和Cohen引入的回流对应于考虑到Feynman激发和涉及几个基本激发的更高组态之间的耦合。
An analysis of some recent experimental and theoretical investigations of the elementary excitation spectrum of liquid He II is carried out. The spectrum of density fluctuations, which is measured in an inelastic neutron scattering experiment, is shown to consist of two distinct parts: direct excitation of single quasi-particles from the condensed zero-momentum state; and excitation of more complex configurations arising from the interaction of two, three, or more quasi-particles. With the aid of general sum-rule arguments it is demonstrated that: (1) in the long-wavelength limit, a single quasi-particle excitation exhausts the $f$-sum rule; the resulting excitation spectrum is identical to the phonon spectrum proposed by Feynman and found experimentally by Henshaw and Woods; (2) this asymptotic behavior of the density fluctuation spectrum may be used to normalize the experimental results of Henshaw and Woods; one thereby obtains a somewhat altered liquid structure-factor curve, detailed information on the efficiency of quasi-particle excitation from the condensed state of an incident slow neutron, and an estimate of the depletion of the zero-momentum state as a consequence of particle interaction; (3) the backflow introduced by Feynman and Cohen corresponds to taking into account the coupling between a Feynman excitation and higher configurations involving several elementary excitations.