Abstract
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.
Highlights
Most of superconductors in a magnetic field are penetrated by a lattice of quantized flux vortices
Many Josephson junction-related effects have been observed in these systems, including terahertz emission[5,6], Shapiro steps in the I–V curve induced by external microwave radiation[7,8], Fiske resonances[9], and oscillations of the critical current on the in-plane dc magnetic field
The spectrum of the em radiation from the Abrikosov vortex lattice crossing a sample edge has been predicted to peak at the harmonics of the washboard frequency f0 = v/d, where v is the vortex velocity and d is the distance between the vortex rows in the direction of motion[28]
Summary
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 Such a radiation has not been observed so far due to low radiated power levels and lacking coherence in the vortex motion. The spectrum of the em radiation from the Abrikosov vortex lattice crossing a sample edge has been predicted to peak at the harmonics of the washboard frequency f0 = v/d, where v is the vortex velocity and d is the distance between the vortex rows in the direction of motion[28] Such a radiation has not been observed so far, as its detection poses a severe experimental challenge. Our findings show that superconductor/insulator multilayers can act as dc-tunable microwave generators bridging the frequency gap between conventional radio frequency (rf) oscillators and (sub-) terahertz generators relying upon the Josephson effect
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