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We show for high-symmetry disk, square, or equilateral triangular thin microstrip antennas of any composition respectively obeying C∞v, C4v, and C3v point group symmetries, that the transverse magnetic electromagnetic cavity mode wave functions are restricted in form to those that are one-dimensional representations of those point groups. Plots of the common nodal points of the ten lowest-energy non-radiating two-dimensional representations of each of these three symmetries are presented. For comparison with symmetry-broken disk intrinsic Josephson junction microstrip antennas constructed from the highly anisotropic layered superconductor Bi2 Sr2 CaCu2 O8+δ (BSCCO), we present plots of the ten lowest frequency orthonormal wave functions and of their emission power angular distributions. These results are compared with previous results for square and equilateral triangular thin microstrip antennas.

We examined the effect of the bias current position on the radiation of intense and coherent terahertz electromagnetic waves from the intrinsic Josephson junctions (IJJs) in regular pentagonal mesas of single crystalline high-Tc superconducting Bi2Sr2CaCu2O8+δ. The emission from Sample 1, a mesa with a current bias feed on its middle, is strong and sharply peaked at 0.47 THz, whereas that from Sample 2, a mesa with its feed along an edge, shows a comparably strong, sharp peak at 0.43 THz. The common backbending in the current-voltage characteristics due to Joule heating was seen for Sample 1 but almost not for Sample 2. The experimental results are in good agreement with numerical simulations and calculations, both for the cavity resonances and the angular emission patterns. The resonance peaks obtained from these pentagonal mesas are both stronger and narrower than those found previously from differently shaped mesas fabricated by focused ion beam milling. The overall devices are small enough to be cooled to their operational temperatures by Stirling refrigerators, so that properly designed devices could be held in one hand as for laser pointers. Therefore, our IJJ-based emitter devices are promising candidates to fill the THz gap with compact, continuous-wave quantum solid-state sources.

Impact Statement: We report on the first demonstration of a low loss and tunable metamaterial based on high-temperature superconducting BSCCO. BSCCO with large superconducting energy gap is the building block of a compact, powerful, continuous and coherent THz source which has been found promising to close the THz gap. Our proposed metamaterial can be integrated with BSSCO THz emitters to improve their functionalities., We introduce a class of low-loss subwavelength resonators and report the first demonstration of a high-temperature ( Tc) superconducting Bi 2Sr2 CaCu2O 8+δ (BSCCO) terahertz (THz) metamaterial. The numerical simulations and analytical calculations are performed to study the electromagnetic response of the subwavelength BSCCO split-ring resonators (SRRs) to the incident photons with energies below the superconducting gap energy. A transition of resonance strength is observed as a dip in resonance frequency for temperatures below BSCCO Tc. To interpret the transmission spectra, resonance switching, and frequency tuning of SRRs, we calculate the temperature dependent complex permittivity and surface impedance of a 200 nm thick unpatterned slightly underdoped BSCCO thin film. We compare the resonance tunability of SRRs made of the extremely disorder superconductor (BSCCO) with metamaterials made of a weakly disorder superconductor YBa2Cu3O7 (YBCO) and show that the resonance quality and frequency tuning are comparable for these two metamaterials. Our results may be useful for THz emitters and detectors developments, for instance, by integration of SRRs with BSCCO THz emitters and microstrip antennas, the device functionalities such as polarization, emission pattern directivity, and output power could be controlled and improved.

We have investigated the magneto-resistance (MR) from the two main AFe2As2 compounds (with A = Sr and Ba) and a low energy Ca ion implanted SrFe2As2 crystal up to 8 T. We show that MR from BaFe2As2 and SrFe2As2 single crystals are similar and a quantum linear MR model favoured by some authors is probably not appropriate especially since the MR is not linear. The SrFe2As2 sample with a near surface Ca concentration of 0.8 at.% has a larger MR at low temperatures that is probably due to current transport in the near surface region and in an inhomogeneous normal and superconducting state.

We introduce a class of low-loss subwavelength resonators and report the first demonstration of a high-temperature (Tc) superconducting Bi2Sr2CaCu2O8+d (BSCCO) terahertz (THz) metamaterial. The numerical simulations and analytical calculations are performed to study the electromagnetic response of the subwavelength BSCCO split-ring resonators (SRRs) to the incident photons with energies below the superconducting gap energy. A transition of resonance strength is observed as a dip in resonance frequency for temperatures below BSCCO Tc. To interpret the transmission spectra, resonance switching and frequency tuning of SRRs, we calculate the temperature dependent complex permittivity and surface impedance of a 200 nm thick unpatterned slightly-underdoped BSCCO thin film. We compare the resonance tunability of SRRs made of the extremely disorder superconductor (BSCCO) with metamaterials made of a weakly disorder superconductor (YBCO) and show that the resonance quality and frequency tuning are comparable for these two metamaterials. Our results may be useful for THz emitters and detectors developments, for instance, by integration of SRRs with BSCCO THz emitters and microstrip antennas, the device functionalities such as polarization, emission pattern directivity, and output power could be controlled and improved.

In the BiSrCaCuO (BSCCO) superconductors there has been considerable success in overcoming weak link problems, and at high temperatures intra-grain flux motion is thought to be the dominant dissipation mechanism. Polycrystalline BSCCO tapes have critical current densities (J(c)) at high temperatures that are large compared with those in BSCCO single crystals. In order to further improve J(c) in the tapes, it is essential to identify the additional flux pinning mechanisms in them. The microstructural and electrical homogeneity of Bi2Sr2CaCu2O8+d ribbon (Bi-2212/Ag) provides a good basis for comparison with of Bi-2212 single crystals, in order to investigate and highlight the pinning in polycrystalline ribbons. We report a detailed study on the effect of irradiation on J(c) in both Bi-2212 single crystals and Bi-2212/Ag ribbons using magnetisation measurements. Information regarding the intra-granular flux pinning of the grains within the ribbon has been obtained.

In superconductor-topological insulator-superconductor hybrid junctions, the barrier edge states are expected to be protected against backscattering, to generate unconventional proximity effects, and, possibly, to signal the presence of Majorana fermions. The standards of proximity modes for these types of structures have to be settled for a neat identification of possible new entities. Through a systematic and complete set of measurements of the Josephson properties we find evidence of ballistic transport in coplanar Al-Bi2Se3-Al junctions that we attribute to a coherent transport through the topological edge state. The shunting effect of the bulk only influences the normal transport. This behavior, which can be considered to some extent universal, is fairly independent of the specific features of superconducting electrodes. A comparative study of Shubnikov–de Haas oscillations and scanning tunneling spectroscopy gave an experimental signature compatible with a two-dimensional electron transport channel with a Dirac dispersion relation. A reduction of the size of the Bi2Se3 flakes to the nanoscale is an unavoidable step to drive Josephson junctions in the proper regime to detect possible distinctive features of Majorana fermions.