THz induced giant spin and valley currents: Data storage

Journal Ref: Sci. Adv. 9, eadf3673 (2023). DOI:10.1126/sciadv.adf3673 Spin and valley indices represent the key quantum labels of quasi-particles in a wide class of two-dimensional materials and form the foundational elements of the fields of spintronics and valleytronics. Control over these degrees of freedom, therefore, remains the central challenge in these fields. Here, we show that femtosecond laser light combining optical frequency circularly polarized pulse and a terahertz (THz) frequency linearly polarized pulse, a so-called “hencomb” pulse, can generate precisely tailored and 90% pure spin currents for the dichalcogenide WSe2 and >75% pure valley currents for bilayer graphene with gaps greater than 120 millielectron volts (dephasing time, 20 femtoseconds). The frequency of the circular light component and the polarization vector of the THz light component are shown to represent the key control parameters of these pulses. Our results thus open a route toward light control over spin/valley current states at ultrafast times.期刊引用：Science Advances（Sci. Adv.）9卷，eadf3673（2023年）。 DOI：10.1126/sciadv.adf3673 自旋与谷指数是诸多二维材料中准粒子的关键量子标识，亦是自旋电子学（spintronics）与谷电子学（valleytronics）领域的核心基础要素。因此，对这些自由度的调控始终是该领域的核心挑战。本研究表明，结合光频圆偏振脉冲与太赫兹（THz）频干线偏振脉冲的飞秒激光——即所谓"hencomb"脉冲——可针对二硒化钨（WSe₂）生成精准调控且纯度达90%的自旋流，针对带隙大于120毫电子伏特（退相时间为20飞秒）的双层石墨烯生成纯度超过75%的谷流。研究表明，圆偏振光分量的频率与太赫兹光分量的偏振矢量，是此类脉冲的关键调控参数。本研究结果因此为在超快时间尺度下通过光调控自旋/谷电流态开辟了全新路径。