Abstract-Superconducting emitters of THz radiation

                                                           The layered crystal structure of Bi₂Sr₂CaCu₂O_8+δ consists
                                                            of superconducting CuO₂ bilayers and intervening insulating
                                                            Bi–Sr–O layers, forming a stack of IJJs. The shaded background
                                                            represents the magnitude of the superconducting order

Ulrich Welp,¹ Kazuo Kadowaki², Reinhold Kleiner³
http://www.nature.com/nphoton/journal/v7/n9/full/nphoton.2013.216.html

Layered superconductors such as the copper-oxide high-temperature superconductor Bi₂Sr₂CaCu₂O_8+δ are emerging as compact sources of coherent continuous-wave electromagnetic radiation in the subterahertz and terahertz frequency ranges. The basis of their operation is the Josephson effect, which intrinsically occurs between the superconducting layers. The Josephson effect naturally converts a direct-current voltage into a high-frequency electric current. Therefore, a unique property of the devices reviewed here is the wide tunability of their frequency by varying the bias voltage. Recently, emission powers of free-space radiation of several hundreds of microwatts and emission linewidths as low as 6 MHz at 600 GHz have been achieved. These devices are promising for new applications in imaging, medical diagnostics, spectroscopy and security

Abstract-Linewidth dependence of coherent terahertz emission from Bi2Sr2CaCu2O8 intrinsic Josephson junction stacks in the hot-spot regime

http://prb.aps.org/abstract/PRB/v86/i6/e060505
Mengyue Li^1,2, Jie Yuan^2,3,*, Nickolay Kinev⁴, Jun Li^2,5, Boris Gross⁶, Stefan Guénon⁶, Akira Ishii², Kazuto Hirata², Takeshi Hatano², Dieter Koelle⁶, Reinhold Kleiner⁶, Valery P. Koshelets⁴, Huabing Wang^1,2,†, and Peiheng Wu^1 
1Research Institute of Superconductor Electronics, Nanjing University, Nanjing 210093, China
²National Institute for Materials Science, Tsukuba 3050047, Japan
³Department of Applied Physics, Wuhan University of Science and Technology, Wuhan 430081, China
⁴Kotel'nikov Institute of Radio Engineering and Electronics, Moscow 125009, Russia
⁵Hokkaido University, Hokkaido 0600810, Japan
⁶Physikalisches Institut and Center for Collective Quantum Phenomena in LISA⁺, Universität Tübingen, D-72076 Tübingen, Germany

 Received 3 April 2012; revised 20 July 2012; published 8 August 2012

We report on measurements of the linewidth Δf of terahertz radiation emitted from intrinsic Josephson junction stacks, using a Nb/AlN/NbN integrated receiver for detection. Previous resolution-limited measurements indicated that Δf may be below 1 GHz—much smaller than expected from a purely cavity-induced synchronization. While at low bias we found Δf to be not smaller than ∼500 MHz, at high bias, where a hot spot coexists with regions which are still superconducting, Δfturned out to be as narrow as 23 MHz. We attribute this to the hot spot acting as a synchronizing element. Δf decreases with increasing bath temperature, a behavior reminiscent of motional narrowing in NMR or electron spin resonance (ESR), but hard to explain in standard electrodynamic models of Josephson junctions.

©2012 American Physical Society

URL:

http://link.aps.org/doi/10.1103/PhysRevB.86.060505

DOI:

10.1103/PhysRevB.86.060505

PACS:

74.50.+r, 74.72.-h, 85.25.Cp

^*phy.wust@gmail.com

^†hbwang1000@gmail.com