Jäck, BertholdBertholdJäckEltschka, MatthiasMatthiasEltschkaAssig, MaximilianMaximilianAssigHardock, AndreasAndreasHardockEtzkorn, MarkusMarkusEtzkornAst, Christian R.Christian R.AstKern, KlausKlausKern2021-09-102021-09-102015-01-05Applied Physics Letters 106 (1): 013109 (2015-01-05)http://hdl.handle.net/11420/10307Using the AC Josephson effect in the superconductor-vacuum-superconductor tunnel junction of a scanning tunneling microscope (STM), we demonstrate the generation of GHz radiation. With the macroscopic STM tip acting as a λ/4-monopole antenna, we first show that the atomic scale Josephson junction in the STM is sensitive to its frequency-dependent environmental impedance in the GHz regime. Further, enhancing Cooper pair tunneling via excitations of the tip eigenmodes, we are able to generate high-frequency radiation. We find that for vanadium junctions, the enhanced photon emission can be tuned from about 25GHz to 200GHz and that large photon flux in excess of 1020cm-2 s-1 is reached in the tunnel junction. These findings demonstrate that the atomic scale Josephson junction in an STM can be employed as a full spectroscopic tool for GHz frequencies on the atomic scale.en1077-311820151American Institut of PhysicsPhysikJournal Article10.1063/1.4905322Other