Title: Zero Sound in Strange Metallic Holography Show Chinese title

Title: 奇异金属全息理论中的零声速

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: 一种建模某些材料的奇异金属相的方法是通过全息描述，即在具有动力学指数 z 的 Lifshitz 时空中的探针 D-膜。背景几何与强相互作用量子临界理论对偶，而探针 D-膜与有限密度的电荷载体对偶，这些电荷载体可以表现出奇异金属的特征性质。 我们用全息方法计算了无质量电荷载流子在这种系统的电荷密度和电流推迟格林函数在低频和低动量下的形式。结果表明，当 z < 2 时存在准粒子激发，我们将其类比朗道费米液体称为零声波。色散关系的实部线性依赖于动量 k，而虚部则随 k^2/z 变化。当 z ≥ 2 时，零声波不再是定义明确的准粒子。 我们还计算了任意时空维度下的频率相关电导率。以该电导率为电荷电流谱函数的度量，我们发现只有当谱函数由零频率处的一个单一 δ 函数组成时，零声波才会出现。