Title: Zero Sound in Strange Metallic Holography Show Chinese title

Title: 奇异金属全息中的零声波

Abstract: One way to model the strange metal phase of certain materials is via a holographic description in terms of probe D-branes in a Lifshitz spacetime, characterised by a dynamical exponent z. The background geometry is dual to a strongly-interacting quantum critical theory while the probe D-branes are dual to a finite density of charge carriers that can exhibit the characteristic properties of strange metals. We compute holographically the low-frequency and low-momentum form of the charge density and current retarded Green's functions in these systems for massless charge carriers. The results reveal a quasi-particle excitation when z<2, which in analogy with Landau Fermi liquids we call zero sound. The real part of the dispersion relation depends on momentum k linearly, while the imaginary part goes as k^2/z. When z is greater than or equal to 2 the zero sound is not a well-defined quasi-particle. We also compute the frequency-dependent conductivity in arbitrary spacetime dimensions. Using that as a measure of the charge current spectral function, we find that the zero sound appears only when the spectral function consists of a single delta function at zero frequency. Show Chinese abstract

Abstract: 通过在Lifshitz时空中的探测D膜的全息描述来建模某些材料的奇异金属相是一种方法，该时空由一个动力学指数z表征。背景几何对应于一种强相互作用的量子临界理论，而探测D膜对应于可以表现出奇异金属特征性质的电荷载流子有限密度。我们以无质量电荷载流子为例，全息计算了这些系统中电荷密度和电流的滞后格林函数的低频和低动量形式。结果揭示了当z<2时存在准粒子激发，我们将其类比于朗道费米液体，称为零声。色散关系的实部与动量k成线性关系，而虚部则与k^2/z成比例。当z大于或等于2时，零声不是一个定义良好的准粒子。我们还计算了任意时空维度中的频率依赖电导率。利用其作为电荷电流谱函数的度量，我们发现只有当谱函数在零频率处由单个狄拉克δ函数组成时，零声才会出现。