Coherent emission from the intrinsic Josephson junctions in thermally-managed, high-symmetry Bi2Sr2CaCu2O8+δ devices

Abstract

The emission of coherent radiation from the intrinsic Josephson junctions in the high transition temperature Tc superconductor Bi2Sr2CaCu2O8+δ (Bi2212) arises from two sources: (1) the uniform part of the ac Josephson current satisfying the Josephson relation f = fJ = 2ev/h, where e is the electronic charge, v is the applied voltage per junction, and h is Planck's constant, and (2) when f = fc (n,m) matches that of the (n,m) the electromagnetic geometrical cavity mode of the thin device, the emission power can be greatly enhanced [1]. For conventional devices such as mesas carved from the top of a Bi2212 single crystal [2,4], the Bi2212 substrate not only absorbs much of the emission nearly parallel to the substrate [1], but its poor thermal conductivity leads to Joule heating,f < 1THz, and the inevitable formation of hot spots, inside of which the local temperature T(r) > Tc [5]. However, “thermally-managedstand-alone” devices constructed by removing the mesa from its Bi2212 substrate, covering its top and bottom surfaces with Au and sandwiching it between sapphire plates [3,6], narrow-linewidth emission at the world-record 2.4 THz from a superconductor was observed [7], placing a lower limit of ∆min ≥ 9.8meV on the bulk Bi2212 gap function, and filling the “THz gap” with a tunable, continuous-wave emitter. Moreover, the emission spectra from that high-symmetry disk [7] and unpublished high-symmetry square devices strongly suggest that only cavity modes obtained from wave functions that are one-dimensional representations of the appropriate point group can lead to electromagnetic cavity mode enhancements [3,7-9]. A theoretical explanation of this previously unknown restriction is presented. [1] R.A.Klemm and K.Kadowaki, J. Phys.: Condens. Matter 22, 375701 (2010). [2] M. Tsujimoto et al., Phys. Rev. Lett. 105, 037005 (2010). [3] M. Tsujimoto et al., Phys. Rev. Lett. 108, 107006 (2012). [4] K. Delfanazari et al., Opt. Express 21, 2171 (2013). [5] H. Minami et al., Phys. Rev. B 89, 054503 (2014). [6] T. Kashiwagi et al., Phys. Rev. Applied 4, 054018 (2015). [7] T. Kashiwagi et al., Appl. Phys. Lett.107, 082601 (2015). [8] D. P. Cerkoney et al., J. Phys.: Condens. Matter 29, 015601 (2017). [9] R. A. Klemm, A. E. Davis, and Q. X. Wang, IEEE J. Sel. Top. Quant. Electron.(2017, inpress) DOI 10.1109/JSTQE.2017.2649459