中心对称有机超导体中电子加速驱动的对称性破缺
Symmetry breaking driven by petahertz electron acceleration in a centrosymmetric organic superconductor
摘要：
强光场作用于固体期间的电荷加速作为高次谐波产生和光电子发射的基本过程引起了人们的广泛关注[1-7]。为了操纵电荷的这种阿秒动力学，载流子包络相位（CEP：光场的载流子振荡与其包络函数之间的相对相位）控制已被用于绝缘体、纳米金属和石墨烯[8-10]。在超导材料中，由于准粒子的强相干性质，期望对电荷运动进行集体控制。在这里，在层状有机超导体中，通过使用单周期6飞秒近红外脉冲观察到二次谐波产生（SHG），这与通常认为的中心对称系统中禁止偶次谐波相反。二次谐波在超导温度附近表现出CEP敏感性和增强效应。结果及其量子多体分析表明，极化电流是由电荷的非耗散加速度引起的，并被超导涨落放大。这将导致超导体和强关联系统的拍赫兹函数。
英文摘要：
Charge acceleration during an intense light field application to solids attracts much attention as elementary processes in high-harmonic generation and photoelectron emission [1-7]. For manipulating such attosecond dynamics of charge, carrier-envelope-phase (CEP:relative phase between carrier oscillation of light field and its envelope function) control has been employed in insulators, nanometal and graphene [8-10]. In superconducting materials, collective control of charge motion is expected because of its strongly coherent nature of quasi-particles. Here, in a layered organic superconductor, second harmonic generation (SHG) is observed by using a single-cycle 6 femtosecond near infrared pulse, which is in contrast to the common belief that even harmonics are forbidden in the centrosymmetric system. The SHG shows a CEP sensitive nature and an enhancement near the superconducting temperature. The result and its quantum many-body analysis indicate that a polarized current is induced by non-dissipative acceleration of charge, which is amplified by superconducting fluctuations. This will lead to petahertz functions of superconductors and of strongly correlated systems.
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