Most of superconductors in a magnetic field are penetrated by a lattice of quantized flux vortices. In the presence of a transport current causing the vortices to cross sample edges, emission of electromagnetic waves is expected due to the continuity of tangential components of the fields at the surface. Yet, such a radiation has not been observed so far due to low radiated power levels and lacking coherence in the vortex motion. Here, we clearly evidence the emission of electromagnetic waves from vortices crossing the layers of a superconductor/insulator Mo/Si superlattice. The emission spectra consist of narrow harmonically related peaks which can be finely tuned in the GHz range by the dc bias current and, coarsely, by the in-plane magnetic field value. Our findings show that superconductor/insulator superlattices can act as dc-tunable microwave generators bridging the frequency gap between conventional radiofrequency oscillators and (sub-)terahertz generators relying upon the Josephson effect.

中文翻译：

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Mo / Si超晶格中超导涡流的微波发射。

磁场中的大多数超导体都被量化的磁通涡流的晶格穿透。在存在导致涡旋穿过样品边缘的传输电流的情况下，由于表面处的场的切向分量的连续性，预计会发出电磁波。然而，由于辐射功率水平低且涡旋运动缺乏相干性，至今尚未观察到这种辐射。在这里，我们清楚地证明了穿过超导体/绝缘体Mo / Si超晶格层的涡流发出的电磁波。发射光谱由窄的谐波相关峰组成，这些峰可以在dc范围内通过直流偏置电流进行微调，而在粗糙范围内可以通过面内磁场值进行微调。