Non-Josephson Emission from Intrinsic Junctions in Bi_2Sr_2CaCu_2O_8: Cherenkov Radiation by Josephson Vortices
Abstract
We have investigated the collective motion of Josephson vortices in stacks of intrinsic Josephson junctions in Bi_2Sr_2CaCu_2O_8+x (BSCCO). The stacks were realized as mesa structures on top of BSCCO single crystals. Experiments were performed in external magnetic fields of up to 5 T, oriented parallel to the layers. Microwave emission was measured between 6 and 18 GHz. In magnetic fields larger than17 kOe we find, in addition to Josephson radiation, a strong broadband non-Josephson microwave emission signal which is not expected for conventional Josephson junctions. The signal appears at bias voltages that are two orders of magnitude larger than the voltage where Josephson emission occurs. We explain this signal by Cherenkov radiation occurring when the vortex velocity exceeds the lowest of N possible mode velocities for electromagnetic waves in an N junction stack.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 1998
- Bibcode:
- 1998APS..MAR.A3507K