A most fundamental goal in spintronics is to electrically tune highly efficient spin injectors and detectors, preferably compatible with nanoscale electronics and superconducting elements. These functionalities can be obtained using semiconductor quantum dots, spin-polarized by a ferromagnetic split-gate, which we demonstrate in a double quantum dot spin valve with two weakly coupled quantum dots in series, with individual split gates magnetized in parallel or anti-parallel. In tunneling magnetoresistance experiments we find a strongly reduced spin valve conductance for the two anti-parallel configurations, with a single dot polarization of ~27%. This value can be significantly improved by a small external magnetic field and optimized gate voltages, which results in a continuously electrically tunable quantum dot spin polarization of ±80%. Such versatile quantum dot spin filters are compatible with superconducting electronic elements and suitable for single spin projection and correlation experiments, as well as initialization and read-out of spin qubits.

自旋电子学的最基本目标是对高效自旋注射器和检测器进行电调谐，最好与纳米级电子器件和超导元件兼容。这些功能可以使用通过铁磁分裂栅自旋极化的半导体量子点获得，我们在双量子点自旋阀中演示了该序列，其中两个弱耦合量子点串联，各个分裂栅以平行或反平行方式磁化。在隧道磁阻实验中，我们发现两种反平行配置的自旋阀电导大大降低，单点极化约为27％。较小的外部磁场和优化的栅极电压可以显着提高该值，从而可实现±80％的连续电可调量子点自旋极化。