Local SiC photoluminescence evidence of hot spot formation and sub-THz coherent emission from a rectangularBi2Sr2CaCu2O8

Abstract

From the photoluminescence of SiC microcrystals uniformly covering a rectangular mesa of the high transition temperature T c superconductor Bi 2 Sr 2 CaCu 2 O 8+δ , the local surface temperature T (r) was directly measured during simultaneous sub-THz emission from the N ∼ 10 3 intrinsic Josephson junctions (IJJs) in the mesa. At high bias currents I and low bath temperatures T bath 35 K, the center of a large elliptical hot spot with T (r) > T c jumps dramatically with little current-voltage characteristic changes. The hot spot does not alter the ubiquitous primary and secondary emission conditions: the ac-Josephson relation and the electromagnetic cavity resonance excitation, respectively. Since the most intense sub-THz emission was observed for high T bath 50 K in the low I bias regime where hot spots are absent, hot spots cannot provide the primary mechanisms for increasing the output power, the tunability, or promoting the synchronization of the N IJJs for the sub-THz emission, but can at best coexist nonmutualistically with the emission. No T (r) standing waves were observed.

Generation of electromagnetic waves from 0.3 to 1.6 terahertz with a high-Tc superconducting Bi2Sr2CaCu2O8+δ intrinsic Josephson junction emitter

“…52 An important issue for high P generation from the IJJ-THz emitter is how to minimize the Joule heating effects due to the dc bias current I. From the low temperature scanning laser microscopy technique, 5-7 the direct temperature distribution T(r) measurements of mesas by using photoluminescence techniques, [24][25][26][27] and the numerical simulations, 43,44 the Joule heating was often found to cause severely inhomogeneous T(r) in the mesa, including hot spots with T(r) > T c , greatly reducing P. Such heating effects reduce the hysteresis area of the currentvoltage (I-V) characteristics (IVCs), and lead to a discontinuous drop in V in the lower I bias region of the outer IVC branch.…”

Three-Dimensional Simulations of the Electrothermal and Terahertz Emission Properties ofBi2Sr2CaCu2Rudau1, Wieland2, Langer3 et al. 2016Phys. Rev. Applied300270View full textAdd to dashboardCite

“…For the best stacks, an emission power P e in the range of tens of µW has been achieved 17,19,20,32,33 , and arrays of mesas showed emission with P e up to 0.61 mW 19 . The physics of the huge IJJ stacks is affected by Joule heating 1, 3,5,6,8,13,18,22,26,30,49,52,54,55,63 . For sufficiently low bias currents, the temperature rises only slightly to values above the bath temperature T bath and the voltage V across the stack increases with increasing bias current I.…”

“…For sufficiently low bias currents, the temperature rises only slightly to values above the bath temperature T bath and the voltage V across the stack increases with increasing bias current I. With increasing I and input power the currentvoltage characteristics (IVCs) start to back-bend and, at some bias current in the back-bending region, a hot spot forms in the stack 3,6,8,13,18,[21][22][23]25,26,34,68 , creating a region heated to temperatures above the critical temperature T c . Similar effects also occur in other systems 69,70 .…”

“…For example, it has been found that the linewidth of radiation is much narrower in the high-bias regime than at low bias 12,60 . Other properties such as the emission frequency seem to be basically independent of the hot spot position, leading to some debate as to whether the hot spot is helpful for radiation or just coexists with the radiating regions 20,22,23 . In fact, recent results showed that there is a strong interaction 28 .…”

Applications using high-Tc superconducting terahertz emitters

“…The unique (sub-) THz source based on a single-crystalline mesa structure of the high transition-temperature T c superconductor Bi 2 Sr 2 CaCu 2 O 8+ δ (Bi2212) was first reported in 200716, and its subsequent development has proceeded rapidly171819202122232425262728293031323334353637383940414243444546. Output radiation powers of a few tens of μ W have been consistently achieved from single conventional mesas3743,44, and of about 600  μ W was reported from a synchronized conventional three-mesa array45, and the radiation frequency could be varied almost continuously between 0.3 and 2.4 THz from a stand-alone mesa sandwich device46.…”