Study of the spin Nernst effect: absolute moments and dynamics

我们建议研究和量化在具有有限自旋-轨道相互作用的材料中由热流(自旋能斯特效应)产生的自旋积累。这些实验将使用两种互补的方法，一种是超敏感的，另一种是超快速的。在一组实验中，微型鱿鱼技术将被用来直接测量由金属棒边缘的自旋能斯特效应引起的绝对磁矩。棒受到由阻性或光学加热引起的温度梯度。利用这项超灵敏技术(低至几百个电子自旋)，我们计划直接量化近地天体的大小。此外，设计合适的SQUID几何结构将允许我们直接获得自旋扩散长度。在与理论的密切合作中，这项技术将被应用于各种金属(铜，金)，包括掺杂杂质，以便在分离本征和外在贡献的同时最大化自旋能斯特效应。在一系列补充实验中，将使用超快泵浦-探测技术产生非常大的温度梯度，以研究自旋能斯特效应的动力学。太赫兹蝴蝶结天线结构将由100个飞秒单周太赫兹瞬变激励，峰值幅度为1 mV/cm。通过适当的设计，天线中的太赫兹电流可以限制在亚微米大小的耗散分流中，从而实现超快的阻性加热。通过这种方式，我们希望达到超过1K/nm的温度梯度。这些大的温度梯度将反过来驱动具有自旋-轨道相互作用的金属结构中的热流，在那里由于自旋能斯特效应而产生自旋流。同时，时间分辨磁光响应将被用来研究相应的自旋极化(空间分辨率为200 nm)的动力学。由于加热脉冲被施加在亚皮秒的时间尺度上，这些实验允许实时研究由自旋能斯特效应产生的自旋积累的时间演化和衰变。

We propose to investigate and quantify the spin accumulation that is generated by heat currents (spin Nernst effect) in a material with finite spin-orbit interaction. The experiments will use two complementary approaches, one ultra-sensitive and one ultra-fast. In one set of experiments micro SQUID technology will be used to directly measure the absolute magnetic moments that are induced by the spin Nernst effect on the edges of a metallic bar. The bar is subjected to a thermal gradient which is either induced by resistive or by optical heating. With this ultra-sensitive technique (down to a few hundred electron spins) we plan to directly quantify the magnitude of the SNE. In addition, suitable design of the SQUID geometry will allow us to directly access the spin diffusion length. In close collaboration with theory this technique will be applied to various metals (Cu, Au) including doping by impurities in order to maximize the spin Nernst effect while separating intrinsic and extrinsic contributions.In a complementary set of experiments very large thermal gradients will be generated using an ultrafast pump-probe technique in order to study the dynamics of the spin Nernst effect. THz bow-tie antenna structures will be excited by 100 femtosecond single cycle THz-transients with a peak amplitude of 1 MV/cm. By proper design the THz-current in the antenna can be confined to a sub-micron sized dissipative shunt allowing for ultra-fast resistive heating. In this way we expect to reach thermal gradients in excess of 1 K/nm. These large temperature gradients will in turn drive heat currents in metallic structures with spin-orbit interaction where due to spin Nernst effect spin currents are generated. Simultaneously the time resolved magneto optic response will be used to study the dynamics of the corresponding spin polarization (with a spatial resolution of 200 nm). Since the heating pulses are applied on a sub-picosecond time scale these experiments allow a real time study of the time evolution and the decay of the spin accumulation generated by the spin Nernst effect.