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arXiv:1307.3651 · Physical Review B

Local SiC photoluminescence evidence of hot spot formation and sub-THz coherent emission from a rectangular Bi 2 Sr 2 CaCu 2 O 8 + δ mesa

Hidetoshi Minami, Chiharu Watanabe, Kota Sato, Shunsuke Sekimoto, Takashi Yamamoto, Takanari Kashiwagi, Richard A. Klemm, Kazuo Kadowaki

Published Feb 7, 2014• 63 citations
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Abstract

From the photoluminescence of SiC microcrystals uniformly covering a rectangular mesa of the high transition temperature ${T}_{c}$ superconductor ${\text{Bi}}_{2}{\text{Sr}}_{2}{\text{CaCu}}_{2}{\text{O}}_{8+\ensuremath{\delta}}$, the local surface temperature $T(\mathbit{r})$ was directly measured during simultaneous sub-THz emission from the $N\ensuremath{\sim}{10}^{3}$ intrinsic Josephson junctions (IJJs) in the mesa. At high bias currents $I$ and low bath temperatures ${T}_{\mathrm{bath}}\ensuremath{\lesssim}35$ K, the center of a large elliptical hot spot with $T(\mathbit{r})>{T}_{c}$ 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 ${T}_{\mathrm{bath}}\ensuremath{\gtrsim}50$ 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 $T(\mathbit{r})$ standing waves were observed.

DOI
10.1103/physrevb.89.054503

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From the photoluminescence of SiC microcrystals uniformly covering a rectangular mesa of the high transition temperature Tc{T}_{c}Tc​ superconductor Bi2Sr2CaCu2O8+\ensuremathδ{\text{Bi}}_{2}{\text{Sr}}_{2}{\text{CaCu}}_{2}{\text{O}}_{8+\ensuremath{\delta}}Bi2​Sr2​CaCu2​O8+\ensuremathδ​, the local surface temperature T(\mathbitr)T(\mathbit{r})T(\mathbitr) was directly measured during simultaneous sub-THz emission from the N\ensuremath∼103N\ensuremath{\sim}{10}^{3}N\ensuremath∼103 intrinsic Josephson junctions (IJJs) in the mesa. At high bias currents III and low bath temperatures Tbath\ensuremath≲35{T}_{\mathrm{bath}}\ensuremath{\lesssim}35Tbath​\ensuremath≲35 K, the center of a large elliptical hot spot with T(\mathbitr)>TcT(\mathbit{r})>{T}_{c}T(\mathbitr)>Tc​ 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 Tbath\ensuremath≳50{T}_{\mathrm{bath}}\ensuremath{\gtrsim}50Tbath​\ensuremath≳50 K in the low III 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 NNN IJJs for the sub-THz emission, but can at best coexist nonmutualistically with the emission. No T(\mathbitr)T(\mathbit{r})T(\mathbitr) standing waves were observed.
Recently, it has been shown that large stacks of intrinsic Josephson junctions in Bi2Sr2CaCu2O8 emit synchronous THz radiation, the synchronization presumably triggered by a cavity resonance. To investigate this effect we use low temperature scanning laser microscopy to image electric field distributions. We verify the appearance of cavity modes at low bias and in the high input-power regime we find that standing-wave patterns are created through interactions with a hot spot, possibly pointing to a new mode of generating synchronized radiation in intrinsic Josephson junction stacks.
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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
Intense and coherent terahertz electromagnetic wave (THz-wave) emission from the intrinsic Josephson junctions (IJJs) in single crystalline high-Tc superconductor Bi2Sr2CaCu2O8+δ (Bi-2212) was reported in 2007 [L. Ozyuzer \\textit{et al}., Science \\textbf{318}, (2007) 1291.]. In the present work, we demonstrate the relationship between the bias condition and the resonance state by controlling both the applied voltage, V, and the number of resistive junctions, N. We directly observed that if N junctions are in resistive state, the resonance frequency, fJ, varies in accordance with the ac-Josephson relation; fJ = (2|e|/h)V/N, although frequency fJ has previously been thought to be uniquely determined by the geometrical condition due to the cavity resonance effect [M. Tsujimoto \\textit{et al}., Phys. Rev. Lett. \\textbf{105}, (2010) 037005.]. We also found that the emission intensity varies as a function of both fJ and N. *CREST-JST, WPI-MANA, Strategic Initiative A (University of Tsukuba)
We report on measurements of the linewidth $\ensuremath{\Delta}f$ of terahertz radiation emitted from intrinsic Josephson junction stacks, using a Nb/AlN/NbN integrated receiver for detection. Previous resolution-limited measurements indicated that $\ensuremath{\Delta}f$ may be below 1 GHz---much smaller than expected from a purely cavity-induced synchronization. While at low bias we found $\ensuremath{\Delta}f$ to be not smaller than $\ensuremath{\sim}$500 MHz, at high bias, where a hot spot coexists with regions which are still superconducting, $\ensuremath{\Delta}f$ turned out to be as narrow as 23 MHz. We attribute this to the hot spot acting as a synchronizing element. $\ensuremath{\Delta}f$ 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.
We report the novel nonequilibrium microwave emission from current-injected Bi 2 Sr 2 CaCu 2 O y (BSCCO)/I/Au intrinsic Josephson junctions and two-mesa array of intrinsic Josephson junctions. For the single intrinsic junctions, it appeared as three different modes of oscillations. Among them, two modes are Josephson plasma emissions which appeared at the quasiparticle branches and the gap-edges. The mutual phase interaction between two-mesa structures of BSCCO intrinsic Josephson junctions has been studied. The measured output power of the two-mesa structures of intrinsic Josephson junctions was almost four times larger than that of the single junction, indicating an exact phase-locking state between the two intrinsic Josephson junctions. The maximum detected power was about microwatt level at millimetre-wave range.