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Spontaneous frequency shift and phase retardation of coupled Josephson oscillations in cuprate superconductors

Riki Kobayashi, Ken Hayama, Suwako Fujita, Manabu Tsujimoto, Itsuhiro Kakeya

Published Sep 18, 2021• 0 citations
OpenAlex

Abstract

We examine coupling interactions used to synchronize macroscopic Josephson oscillations induced in intrinsic Josephson junction (IJJ) mesa stacks made of Bi2212 single crystals. Synchronized emissions of terahertz electromagnetic (EM) waves are detected under common voltage and current bias operations of two connected mesas with close individual emission frequencies, while uncoupled and bimodal emissions are frequently observed in two mesas with different individual emission frequencies. Detailed observations of the polarization of the EM wave emitted when two mesas are biased in parallel or series allow us to reveal the coupling matrix components, which include ratios of synchronized IJJs in the mesas and phase retardation between the macroscopic Josephson oscillations. This finding stimulates systematic survey on polarization of EM wave emitted from synchronized multiple mesa devices in order to realize powerful emissions from superconductors.

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We examine coupling interactions used to synchronize macroscopic Josephson oscillations induced in intrinsic Josephson junction (IJJ) mesa stacks made of Bi2212 single crystals. Synchronized emissions of terahertz electromagnetic (EM) waves are detected under common voltage and current bias operations of two connected mesas with close individual emission frequencies, while uncoupled and bimodal emissions are frequently observed in two mesas with different individual emission frequencies. Detailed observations of the polarization of the EM wave emitted when two mesas are biased in parallel or series allow us to reveal the coupling matrix components, which include ratios of synchronized IJJs in the mesas and phase retardation between the macroscopic Josephson oscillations. This finding stimulates systematic survey on polarization of EM wave emitted from synchronized multiple mesa devices in order to realize powerful emissions from superconductors.
We examine coupling interactions used to synchronize macroscopic Josephson oscillations induced in intrinsic Josephson junction (IJJ) mesa stacks made of a Bi2212 single crystal. Synchronized radiations of terahertz electromagnetic (EM) waves are detected under common voltage and current bias operations of two connected mesas with close individual radiation frequencies, while uncoupled and bimodal radiations are frequently observed in two mesas with different individual radiation frequencies. Detailed observations of the polarizations of the EM waves emitted when two mesas are biased in parallel or series allow us to reveal the coupling matrix components, which include ratios of synchronized IJJs in the mesas and phase delay between the macroscopic Josephson oscillations. A frequency evolution of the phase delay implies that the coupling between the Josephson oscillations is mediated by the small amplitude Josephson plasmon inside the superconducting substrate. This finding stimulates systematic survey on polarization of EM wave emitted from synchronized multiple mesa devices in order to realize powerful terahertz emissions from superconductors.
We discuss coupling interactions to synchronize macroscopic Josephson oscillations induced in intrinsic Josephson junction (IJJ) mesa stacks made of Bi2212 single crystals. Synchronized emissions are found under common voltage and current bias operations of connected two mesas with close individual emission frequencies while uncoupled and bimodal emissions are often found in two mesas with different individual emission frequencies. The detailed observations on polarization of the emitted electromagnetic wave when two mesas are biased in parallel or series allow us to reveal the coupling matrix components which includes ratios of synchronized IJJs in the mesas and phase retardation between the macroscopic Josephson oscillations.
We examine coupling interactions used to synchronize macroscopic Josephson oscillations induced in intrinsic Josephson-junction (IJJ) mesa stacks made of a Bi2212\mathrm{Bi}2212Bi2212 single crystal. Synchronized radiations of terahertz electromagnetic (EM) waves are detected under common voltage and current bias operations of two connected mesas with close individual radiation frequencies, while uncoupled and bimodal radiations are frequently observed in two mesas with different individual radiation frequencies. Detailed observations of the polarizations of the EM waves emitted when two mesas are biased in parallel or series allow us to reveal the coupling matrix components, which include ratios of synchronized IJJs in the mesas and phase delay between the macroscopic Josephson oscillations. A frequency evolution of the phase delay implies that the coupling between the Josephson oscillations is mediated by the small amplitude Josephson plasmon inside the superconducting substrate. This finding stimulates systematic survey on polarization of EM wave emitted from synchronized multiple mesa devices in order to realize powerful terahertz emissions from superconductors.
Studies on intrinsic Josephson junctions (IJJs) of cuprate superconductors are reviewed. A system consisting of a few IJJs provides phenomena to test the Josephson phase dynamics and its interaction between adjacent IJJs within a nanometer scale, which is unique to cuprate superconductors. Quasiparticle density of states, which provides direct information on the Cooper-pair formation, is also revealed in the system. In contrast, Josephson plasma emission, which is an electromagnetic wave radiation in the sub-terahertz frequency range from an IJJ stack, arises from the synchronous phase dynamics of hundreds of IJJs coupled globally. This review summarizes a wide range of physical phenomena in IJJ systems having capacitive and inductive couplings with different nanometer and micrometer length scales, respectively.
We investigate the response of a stack of intrinsic Josephson junctions (IJJs) to terahertz (THz) electromagnetic (EM) irradiation. A significant amplification of the EM wave can be achieved by the IJJs stack when the incident frequency equals to one of the cavity frequencies. The irradiation excites $\ensuremath{\pi}$-phase kinks in the junctions, which stimulate the cavity resonance when the bias voltage is tuned. A large amount of dc energy is then pumped into the Josephson plasma oscillation and the incident wave gets amplified. From the profound current step in IVIVIV characteristics induced at the cavity resonance, the system can also be used for detection of the THz wave.