Quasiparticle spin resonance and coherence in superconducting aluminium

Abstract

Conventional superconductors were long thought to be spin inert; however, there is now increasing interest in both (the manipulation of) the internal spin structure of the ground-state condensate, as well as recently observed long-lived, spin-polarized excitations (quasiparticles). We demonstrate spin resonance in the quasiparticle population of a mesoscopic superconductor (aluminium) using novel on-chip microwave detection techniques. The spin decoherence time obtained (∼100 ps), and its dependence on the sample thickness are consistent with Elliott–Yafet spin–orbit scattering as the main decoherence mechanism. The striking divergence between the spin coherence time and the previously measured spin imbalance relaxation time (∼10 ns) suggests that the latter is limited instead by inelastic processes. This work stakes out new ground for the nascent field of spin-based electronics with superconductors or superconducting spintronics.

Fingerprints of Majorana fermions in current-correlation measurements from a superconducting tunnel microscope

“…Indeed, the spin decoherence time in superconductors is generally quite small (i.e., ∼100 ps for aluminum [51]) which means that the measurement has to be shorter than this time. A quick calculation gives ∼200 μm for the spin decoherence length with a Fermi velocity of ∼2 × 10 6 m/s leading to a reasonable system size allowing us to detect our effect.…”

Stimulated quasiparticles in spin-split superconductors

“…The effects are experimentally accessible with state-of-the art methods. A number of recent experiments in similar systems exist [5,8,9], including also microwave excitation in the GHz frequency range [9]. In addition to using ferromagnetic probes for detecting the photospin signal, the effect can also be seen indirectly by observing the discontinuous transitions in the superconducting order parameter.…”

“…Spin accumulation in a superconductor can be generated by injecting current from a spin-polarized electrode, for example, a ferromagnet. A second approach for spin injection studied in a number of recent experiments [4][5][6][7][8][9] is to use a magnetic field or proximity to ferromagnetic insulators to Zeeman split the density of states of the superconductor [10,11] (cf. Fig.…”

“…Based on the above discussion, a photo-spin-electric effect should be present also in spin-split superconductorsthe absorbed radiation generates spin imbalance, which relaxes slowly via inelastic scattering. This is interesting to consider, e.g., in the context of measurements that use microwave signals to probe spin resonances of the quasiparticles [9].…”

Thermal, electric and spin transport in superconductor/ferromagnetic-insulator structures

“…An applied RF field excites quasiparticle spin resonance in a thin Al film (S), which is indirectly probed by observing modification of the I(V ) curve of probe N1. Figure adapted from Ref [198]. (Creative Commons Attribution 4.0 International License).…”