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International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz)

A Tunable 350–780 GHz CW solid state oscillator of intrinsic Josephson junctions in a high-Tc superconductor

Huabing Wang, M. Y. Li, Jie Yuan, Nickolay V. Kinev, J. Li, Boris Gross, Stefan Guénon, Akira Ishii, Toshihisa Hatano, D. Koelle, R. Kleiner, V. P. Koshelets, Peiheng Wu

Published Sep 1, 2012• 0 citations
Publisher

Abstract

We report on THz emission measurements and low temperature scanning laser imaging of Bi2Sr2CaCu2O8intrinsic Josephson junction stacks. Coherent emission is observed at large dc input power, where a hot spot and a standing wave, formed in the “cold” part of the stack, coexist. By changing bias current and bath temperature the emission frequency can be varied over a wide range of 350–780 GHz; the variation matches the well-known Josephson-frequency relation. The linewidth of radiation, recently measured with an integrated superconductor-insulator-superconductor (SIS) receiver, is as narrow as 6 MHz, much smaller than expected from a purely cavity-induced synchronization. Thus, an additional mechanism seems to play a role. Some scenarios, related to the presence of the hot spot, are discussed.

DOI
10.1109/irmmw-thz.2012.6380171

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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

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High frequency behaviour of coupled and uncoupled Josephson junctions based on high temperature superconductors

Jens Scherbel

Josephson junctions made from high temperature superconductors (HTS) are active high frequency devices which can be used as oscillators or frequency mixers in the submillimeter-wave region. The frequencies of these electromagnetic waves range from 300 GHz up to 3 THz. Up to now, this wave band is a relatively unexploited region of the electromagnetic spectrum because it is very difficult to produce and detect submillimeter-waves. However, submillimeter-wave technologies are becoming important in many practical scientific applications such as radio astronomy, atmospheric research, plasma diagnostics and THz-imaging, recently. In this work, the behaviour HTS Josephson junctions have been investigated experimentally and theoretically with the aim to THz-applications. In the first part the behaviour of intrinsic Josephson junction stacks are measured, and the possibility of phase locking is discussed by the theoretical analysis of two different shunt technologies depending on the parameter spread of the junction and the shunt parameters. It could be shown that stacks made from sputtered BSCCO layers does not act as intrinsic Josephson junction arrays because of their many micro shorts resulting from the layer growth. However, the stacks made from sputtered TBCCO show clear intrinsic Josephson junction behaviour. But their quasiparticle branches in the current-voltage characteristic deviate from the behaviour predicted by the common used RCSJ model. These branches can be discussed within a tunneling model using d-wave superconductor density of states. A temperature dependent current distribution and a zero bias anomaly was found. Furthermore, the coherent behaviour is studied for intrinsic arrays with additional side-wall shunts. The existence of thresholds of phase locking at especial junction and shunt parameters are demonstrated and discussed in regard to THz-oscillator applications. It was found that the Josephson junctions in a stack can be phase locked even if they have a parameter spread in the critical current up to 15% using a resonant shunt. In the second part of this work the mixing properties of HTS bicrystal Josephson junctions as wave guide mixers for 115 and 345 GHz have been investigated. (orig.)

•Jan 1, 2001•0 citations
We report on THz emission measurements and low temperature scanning laser imaging of Bi2Sr2CaCu2O8intrinsic Josephson junction stacks. Coherent emission is observed at large dc input power, where a hot spot and a standing wave, formed in the “cold” part of the stack, coexist. By changing bias current and bath temperature the emission frequency can be varied over a wide range of 350–780 GHz; the variation matches the well-known Josephson-frequency relation. The linewidth of radiation, recently measured with an integrated superconductor-insulator-superconductor (SIS) receiver, is as narrow as 6 MHz, much smaller than expected from a purely cavity-induced synchronization. Thus, an additional mechanism seems to play a role. Some scenarios, related to the presence of the hot spot, are discussed.
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.
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.
Using a double-sided fabrication method, we fabricated Bi2Sr2CaCu2O8(BSCCO) intrinsic Josephson junctions (IJJs) with a gold-BSCCO-gold structure. Coherent emission is observed at large dc input power, where a hot spot and “cold” part of the stack, coexist. The power, directly detected with a bolometer, is as high as 25 μW, implying the integrated power should be already in the order of sub-mW. We have successfully pumped a Nb-based Josephson junction and a grain boundary Josephson junction. Also with a wide tunable frequency range, BSCCO THz emitters will find themselves many practical applications, e.g., local oscillators of SIS, HEB, and Josephson mixers.
From the photoluminescence of SiC microcrystals uniformly covering a rectangular mesa of the high transition temperature Tc{T}_{c}Tc​ 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 III 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 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 $T(\mathbit{r})$ standing waves were observed.
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
Josephson junctions made from high temperature superconductors (HTS) are active high frequency devices which can be used as oscillators or frequency mixers in the submillimeter-wave region. The frequencies of these electromagnetic waves range from 300 GHz up to 3 THz. Up to now, this wave band is a relatively unexploited region of the electromagnetic spectrum because it is very difficult to produce and detect submillimeter-waves. However, submillimeter-wave technologies are becoming important in many practical scientific applications such as radio astronomy, atmospheric research, plasma diagnostics and THz-imaging, recently. In this work, the behaviour HTS Josephson junctions have been investigated experimentally and theoretically with the aim to THz-applications. In the first part the behaviour of intrinsic Josephson junction stacks are measured, and the possibility of phase locking is discussed by the theoretical analysis of two different shunt technologies depending on the parameter spread of the junction and the shunt parameters. It could be shown that stacks made from sputtered BSCCO layers does not act as intrinsic Josephson junction arrays because of their many micro shorts resulting from the layer growth. However, the stacks made from sputtered TBCCO show clear intrinsic Josephson junction behaviour. But their quasiparticle branches in the current-voltage characteristic deviate from the behaviour predicted by the common used RCSJ model. These branches can be discussed within a tunneling model using d-wave superconductor density of states. A temperature dependent current distribution and a zero bias anomaly was found. Furthermore, the coherent behaviour is studied for intrinsic arrays with additional side-wall shunts. The existence of thresholds of phase locking at especial junction and shunt parameters are demonstrated and discussed in regard to THz-oscillator applications. It was found that the Josephson junctions in a stack can be phase locked even if they have a parameter spread in the critical current up to 15% using a resonant shunt. In the second part of this work the mixing properties of HTS bicrystal Josephson junctions as wave guide mixers for 115 and 345 GHz have been investigated. (orig.)