Radiation from a Josephson STAR-emitter

We calculate the angular dependence of the radiation-zone output power and electric polarization of stimulated terahertz amplified radiation (STAR) emitted from a $dc$ voltage applied across cylindrical and rectangular stacks of intrinsic Josephson junctions. During coherent emission, a spatially uniform $ac$ Josephson current density in the stack acts as a surface electric current density antenna source, leading to an harmonic radiation frequency spectrum, as in experiment, but absent in all cavity modesl of cylindrical mesas. Spatial fluctuations of the $ac$ Josephson current cause its fundamental mode to lock onto the lowest finite energy cylindrical cavity mode, causing it to resonate, leading to a non-uniform magnetic surface current density radiation source, and a non-trivial combined fundamental frequency output power with linear polarization We also present a model of the superconducting substrate, and present results for rectangular mesas.Comment: 18 pages, 26 figures, submitted to PR

Josephson Plasma Mode in Fields Parallel to Layers of Bi_2Sr_2CaCu_2O_{8+\delta}

Josephson plasma resonance measurements under magnetic fields parallel to the CuO_2 layers as functions of magnetic field, temperature, and microwave frequency have been performed in Bi_2Sr_2CaCu_2O_{8+\delta} single crystals with doping range being from optimal to under-doped side. The feature of the resonance is quite unique and cannot be explained by the conventional understandings of the Josephson plasma for H \parallel c, that requires a new theory including coupling effect between Josephson vortex lattice and Josephson plasma.Comment: 2 pages, 2 figure

Effect of thermal inhomogeneity for THz radiation from intrinsic Josephson junction stacks of Bi2_2Sr2_2CaCu2_2O8+δ_{8+\delta}

Terahertz radiation from the mesa structures of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ is detected in samples with thin electrodes $< 100$ nm. In samples with thick electrodes $\simeq$ 400 nm, neither radiations nor voltage jumps in current-voltage characteristics are detected. This suggests that the thin electrode helps excite the Josephson plasma oscillation as a result of the poor heat flow through the electrode. The shielding effect by the electrode is not essential. We consider that the local temperature rise is the origin of the synchronization of the phase kink for terahertz radiation.Comment: 4 pages, 3 figure

Broadly Tunable CW Terahertz Sources Using Intrinsic Josephson Junction Stacks in High‐Temperature Superconductors

Electromagnetic waves in the 0.3–3.0 THz frequency range are considered to have great potential in research and industry; thus, compact, solid‐state and continuous‐wave (CW) terahertz sources have been developed throughout the vast field of science and technology. Since the first demonstration of terahertz emission from intrinsic Josephson junctions (IJJs) in the high‐temperature (high‐Tc ) superconductor Bi2Sr2CaCu2O8+δ , terahertz generation utilizing stacks of IJJs has become a major topic of research, both experimentally and theoretically. In this chapter, we describe recent progress on the development of high‐Tc superconducting terahertz sources. We demonstrate that these superconducting terahertz sources emit continuous terahertz radiation and generate power in the microwatt range at broadly tunable frequencies in the range of 0.5–2.4 THz. The solid‐state source is extremely small in size and its output power is sufficiently stable during operation. In addition, we also established a transmission imaging system using high‐Tc sources to promote effective use in various applications

Precise magnetization measurements of single crystalline Bi2Sr2CaCu2O8+δ

Precise dc-magnetization measurements, using a superconducting quantum interference device magnetometer (SQUID), have been performed on single crystalline Bi2Sr2CaCu2O8+δ in magnetic fields both parallel to the c axis (H∥c) and tilted away from the c axis towards the ab plane to investigate the vortex state at various temperatures between 40 K and Tc=83.0 K. The magnetization curves at a fixed temperature as a function of magnetic field (H∥c) show a clear jump at HM, which corresponds to the flux-line-lattice-melting transition (FLLMT) as observed previously. In the vicinity of Tc=83.0 K, it is shown that the HM(T) line changes its character near T*=79.5 K, below which it can be described well by the FLLMT and above which the change of magnetization, ΔM, and the corresponding change of the entropy, ΔS, at HM, falls sharply as Tc is approached. A simultaneous decoupling of the Josephson coupling and the melting of the flux-line lattice may be an appropriate picture below T*, whereas above T* an additional degree of freedom makes a contribution to the FLLMT due, perhaps, to vortex-antivortex creation and annihilation processes. In a tilted magnetic field, it is found that the angular dependence of HM, as well as ΔM and ΔS, obeys a scaling law up to θ<~80°. The deduced anisotropy parameter γs≃9 is found to be much lower than the value of γl≃150–200 found in the liquid state. We interpret such a discrepancy as due to the difference of the dimensionality of the vortex pancake state above and below HM. Furthermore, from the scaling behavior of ΔS in tilted fields, it is inferred that the FLLMT is predominantly ruled by the number of pancake vortices, n, in the superconducting CuO2 layers and that Josephson vortices do not play an important role for the FLLMT

Local SiC photoluminescence evidence of non-mutualistic hot spot formation and sub-THz coherent emission from a rectangular Bi2_2Sr2_2CaCu2_2O8+δ_{8+\delta} mesa

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$_{8+\delta}$, the local surface temperature $T({\bm r})$ was directly measured during simultaneous sub-THz emission from the $N\sim10^3$ intrinsic Josephson junctions (IJJs) in the mesa. At high bias currents $I$ and low bath temperatures $T_{\rm bath}\lesssim~35$ K, the center of a large elliptical hot spot with $T({\bm r})> T_c$ jumps dramatically with little current-voltage characteristic changes. The hot spot doesn't alter the ubiquitous primary and secondary emission conditions: the ac Josephson relation and the electromagnetic cavity resonance excitation, respectively. Since the intense sub-THz emission was observed for high $T_{\rm bath}\gtrsim~50$ K in the low $I$ bias regime where hot spots are absent, hot spots can not provide the primary mechanisms for increasing the output power, the tunability, or for promoting the synchronization of the $N$ IJJs for the sub-THz emission, but can at best coexist non-mutualistically with the emission. No $T({\bm r})$ standing waves were observed

Integrated, portable, tunable, and coherent terahertz sources and sensitive detectors based on layered superconductors

Current compact emitter and receiver technologies are generally inefficient and impractical at terahertz (THz) frequencies between 0.1 and 10 THz. Hence, a gap exists between mature microwave and developed optical technologies. On-chip, integrated broadly tunable and powerful quantum sources that coherently radiate THz waves between 0.1 and 11 THz (potentially extendable to 15 THz) and with potential output power of >1 mW can be achieved based on quantum tunneling of electron pairs across the stack of intrinsic Josephson junctions (IJJs) naturally present in a single crystal of the layered high-Tc superconducting Bi2Sr2CaCu2O8+δ (BSCCO). Such devices have been found to be especially promising solid-state THz sources capable of bridging the entire THz gap, as their wide-frequency tunability range is superior to that obtained from their semiconducting-based rivals, either single resonant-tunneling diodes (RTDs) or THz-quantum cascade lasers (QCLs). Due to the unique electrodynamics of BSCCO, they can also be operated as switching current detectors, paving the way for the realization of on-chip THz-integrated circuits for applications in ultrahigh-speed telecommunications, quantum information, on-chip spectroscopy, and nondestructive sensing, testing, and imaging. This article reviews the history and recent advances in THz sources and detectors based on IJJs with a focus on the application of IJJ THz devices in THz spectroscopy and various types of THz imaging systems such as reflection, transmission, and computed tomography. We show that compact IJJ THz devices with sub-centimeter-sized modules are easy to use in many applications, as they can be regarded as pocket quantum THz torches

Scanning SQUID microscopy of vortex clusters in multiband superconductors

In type-1.5 superconductors, vortices emerge in clusters, which grow in size with increasing magnetic field. These novel vortex clusters and their field dependence are directly visualized by scanning SQUID microscopy at very low vortex densities in MgB2 single crystals. Our observations are elucidated by simulations based on a two-gap Ginzburg-Landau theory in the type-1.5 regime.Comment: 4 pages, 5 figures, to be published in Physical Review

Crossover from crossing to tilted vortex phase in Bi2Sr2CaCu2O8+δ single crystals near ab-plane

International audienceIn extremely anisotropic layered superconductors of Bi2Sr2CaCu2O8+δ the stacks of vortex pancakes (PV) and the Josephson vortex (JV) interpenetrate, and due to PV-JV mutual pinning energy, weakly interact and form various tilted and crossing lattice structures including vortex chains, stripes, mixed chain + lattice phases, etc. In order to study these phenomena, it is decisive to have excellent quality of samples and the ideal experimental techniques. The vortex phases in high-quality Bi2Sr2CaCu2O8+δ single crystals were studied by in-plane resistivity measurement and local ac magnetic permeability. The sharp crossover was shown by both techniques, deep in the vortex solid state separating the Abrikosov dominant 'strong pinning' phase from the Josephson dominant 'weak pinning' phase. Those two vortex states were recognized as the mixed chain + lattice vortex phase and chains (tilted) vortex phase, respectively