Dirac材料中宇宙学粒子产生的类比
Analog of cosmological particle production in Dirac materials
AI总结：
本文研究了具有对称性破缺质量隙的Dirac材料中的低能费米子激发，通过引入动态费米速度或含时质量隙，展示了宇宙学费米子对产生的类比，并证明此类材料可作为膨胀宇宙学的类比模型。
摘要：
二维范德华材料近期在实验上被确立为一个高度可调的凝聚态平台，促进了能带结构和相互作用的可控操纵。在其中几种材料中，费米能级附近的低能区存在Dirac锥。因此，这些材料中在Dirac锥附近出现的费米子激发，在费米面附近具有无质量相对论性Dirac费米子的线性色散关系。在此，我们研究此类Dirac材料在由对称性破缺产生的质量隙存在时的低能费米子激发。通过为Dirac准粒子引入动态费米速度和/或含时质量隙，我们展示了在期望占据数或两点关联函数等可观测量方面，宇宙学费米子对产生的类比的涌现。我们发现，准粒子产生的充要条件是仅质量隙与费米速度之间的比值为含时的。由此，我们确立了高度可调的Dirac材料可作为宇宙学时空几何的类比模型，特别是Friedmann-Lemaître-Robertson-Walker膨胀宇宙学。我们简要讨论了实验实现的可能性。
英文摘要：
Two-dimensional van der Waals materials have recently been established experimentally as a highly-tunable condensed matter platform, facilitating the controlled manipulation of band structures and interactions. In several of these materials, Dirac cones are present in the low-energy regime near the Fermi level. Thus, fermionic excitations emerging in these materials close to the Dirac cones have a linear dispersion relation near the Fermi surface as massless relativistic Dirac fermions. Here, we study low-energy fermionic excitations of such Dirac materials in the presence of a mass gap that may be generated by symmetry breaking. Introducing a dynamical Fermi velocity and/or time-dependent mass gap for the Dirac quasiparticles, we exhibit the emergence of an analog of cosmological fermion pair production in terms of observables such as the expected occupation number or two-point correlation functions. We find that it is necessary and sufficient for quasiparticle production that only the ratio between the mass gap and the Fermi velocity is time-dependent. In this way, we establish that highly-tunable Dirac materials can serve as analog models for cosmological spacetime geometries, in particular, for Friedmann-Lemaître-Robertson-Walker expanding cosmologies. We briefly discuss possibilities for experimental realization
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