Neufeld Ofer, Tancogne-Dejean Nicolas, De Giovannini Umberto, Hübener Hannes, Rubio Angel
Max Planck Institute for the Structure and Dynamics of Matter and Center for Free-Electron Laser Science, Hamburg 22761, Germany.
IKERBASQUE, Basque Foundation for Science, E-48011 Bilbao, Spain.
Phys Rev Lett. 2021 Sep 17;127(12):126601. doi: 10.1103/PhysRevLett.127.126601.
We predict the generation of bulk photocurrents in materials driven by bichromatic fields that are circularly polarized and corotating. The nonlinear photocurrents have a fully controllable directionality and amplitude without requiring carrier-envelope-phase stabilization or few-cycle pulses, and can be generated with photon energies much smaller than the band gap (reducing heating in the photoconversion process). We demonstrate with ab initio calculations that the photocurrent generation mechanism is universal and arises in gaped materials (Si, diamond, MgO, hBN), in semimetals (graphene), and in two- and three-dimensional systems. Photocurrents are shown to rely on sub-laser-cycle asymmetries in the nonlinear response that build-up coherently from cycle to cycle as the conduction band is populated. Importantly, the photocurrents are always transverse to the major axis of the co-circular lasers regardless of the material's structure and orientation (analogously to a Hall current), which we find originates from a generalized time-reversal symmetry in the driven system. At high laser powers (∼10^{13} W/cm^{2}) this symmetry can be spontaneously broken by vast electronic excitations, which is accompanied by an onset of carrier-envelope-phase sensitivity and ultrafast many-body effects. Our results are directly applicable for efficient light-driven control of electronics, and for enhancing sub-band-gap bulk photogalvanic effects.
我们预测，在由圆偏振且同向旋转的双色场驱动的材料中会产生体光电流。这种非线性光电流具有完全可控的方向性和幅度，无需载波包络相位稳定或少周期脉冲，并且可以在光子能量远小于带隙的情况下产生（减少光转换过程中的发热）。我们通过从头算计算证明，光电流产生机制具有普遍性，存在于带隙材料（硅、金刚石、氧化镁、六方氮化硼）、半金属（石墨烯）以及二维和三维系统中。结果表明，光电流依赖于非线性响应中的亚激光周期不对称性，随着导带被填充，这种不对称性会逐周期相干积累。重要的是，无论材料的结构和取向如何，光电流总是垂直于共圆激光的主轴（类似于霍尔电流），我们发现这源于驱动系统中的广义时间反演对称性。在高激光功率（约10^{13} W/cm^{2}）下，这种对称性会因大量电子激发而自发破缺，同时伴随着载波包络相位敏感性的出现和超快多体效应。我们的结果可直接应用于电子学的高效光驱动控制以及增强亚带隙体光伏效应。
