Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 13Citation - Scopus: 13Fourcross Shaped Metamaterial Filters Fabricated From High Temperature Superconducting Ybco and Au Thin Films for Terahertz Waves(IOP Publishing Ltd., 2017) Demirhan, Yasemin; Alaboz, Hakan; Nebioğlu, Mehmet Ali; Mulla, B.; Akkaya, M.; Altan, Hakan; Sabah, Cumali; Özyüzer, LütfiIn this study, we present a new, unique fourcross shaped metamaterial terahertz (THz) filter fabricated from both gold thin films and YBa2Cu3O7-δ high Tc superconducting thin films. A commercial electromagnetic simulation software, CST Microwave Studio, is used to design and optimize the metamaterial filter structures. The proposed fourcross shaped rectangular filter structure consists of periodic metallic rings where strip lines are located at the sides of the ring. Fourcross metamaterial filters are fabricated by using e-beam lithography and ion beam exhing techniques. Terahertz time-domain spectroscopy measurements validated the design predictions for both the center frequencies and bandwidths of the resonances due to the fourcross structures. The resonance switching of the transmission spectra was investigated by lowering the temperature below the critical transition temperature. This resonance switching effect is not observed in filters made up of metals. This novel fourcross rectangular resonator with a temperature-dependent resonance behavior holds great potential for active, tunable and low loss THz devices for imaging, sensing, and detection applications.Article Citation - WoS: 31Citation - Scopus: 30Absence of Pseudogap in Heavily Overdoped Bi2sr2cacu2o8+? From Tunneling Spectroscopy of Break Junctions(Institute of Physics Publishing, 2002) Özyüzer, Lütfi; Zasadzinski, John F.; Gray, Kenneth E.; Kendziora, Christopher A.; Miyakawa, NobuakiWe report tunneling spectroscopy of superconductor-insulator-superconductor break junctions on heavily overdoped Bi2Sr2CaCu2O8+δ with Tc = 56 K. At T ≪ Tc, the junction conductances display well-defined quasiparticle peaks at ±2Δ and in some cases a Josephson current at zero bias. Gap values as small as Δ = 10.5 meV have been observed leading to 2Δ/kTc near the BCS limit for dx2-y2 pairing. Temperature dependence of the gap magnitude, Δ(T), follows the BCS relation and both the quasiparticle gap and Josephson current vanish for T > Tc. Above Tc, the tunneling conductance shows a flat background without any indication of a pseudogap near the Fermi level.Conference Object Citation - WoS: 7Citation - Scopus: 7Aspects of the Tunneling Dip Feature in Bi2sr2cacu2o8+? and Its Relation To the Resonance Spin Excitation(Elsevier Ltd., 2002) Zasadzinski, John F.; Özyüzer, Lütfi; Miyakawa, Nobuaki; Gray, Kenneth E.; Hinks, David G.; Kendziora, Christopher A.Break-junction tunneling data are reported in Bi2Sr2CaCu2O8+δ over a wide range of hole concentration from underdoped to overdoped. The strong conductance peaks in the superconducting state reveal a single gap consistent with d-wave symmetry. In addition, sharp dips are observed at a voltage, Ω/□, measured with respect to the gap edge. These features are shown to be reproduced in other junction types from the literature including atomically resolved STM and □-axis mesas, establishing their intrinsic character. Trends are observed with doping and temperature which link the dip to the resonance spin excitation and indicate that the quasiparticles are strongly coupled to this mode.Article Citation - WoS: 53Quasiparticle and Josephson Tunneling of Overdoped Bi2sr2cacu2o8+? Single Crystals(American Physical Society, 2000) Özyüzer, Lütfi; Zasadzinski, John F.; Kendziora, Christopher A.; Gray, Kenneth E.The point contact tunneling technique is used to examine quasiparticle and Josephson currents in overdoped Bi2Sr2CaCu2O8+δ (Bi-2212) single crystals with bulk Tc values ranging from 82 K down to 62 K. Superconductor-insulator-normal-metal (SIN) tunnel junctions are formed between Bi-2212 crystals and a Au tip, which display well-resolved quasiparticle gap features including sharp conductance peaks. Reproducible superconductor-insulator-superconductor (SIS) tunnel junctions are also obtained between two pieces of the Bi-2212 crystals, resulting in simultaneous quasiparticle and Josephson currents. The dynamic conductances of both SIN and SIS junctions are qualitatively similar to those found on optimally doped Bi-2212, but with reduced gap values, e.g., Δ = 15-20 meV for Tc = 62 K. Fits to the conductance data in the gap region are obtained using a model with dx2-y2 symmetry, and it is shown that this provides a better fit than s-wave symmetry. Both SIN and SIS tunneling conductances also display dip and hump features at high bias voltages similar to those found on optimal and underdoped crystals, indicating that these are intrinsic properties of the quasiparticles. The SIS data indicate that these features appear to be part of a larger spectrum that extends out to 300-400 mV. The Josephson current has been measured for 13 SIS junctions on the 62 K crystals with resistances varying over two decades. It is found that the maximum value depends on junction resistance in a manner consistent with Ambegaokar-Baratoff theory, but with a reduced IcRn product.Article Citation - WoS: 1Citation - Scopus: 1Modification of Al-Oxide Tunnel Barriers With Organic Self-Assembled Monolayers(American Institute of Physics, 1999) Okur, Salih; Zasadzinski, John F.Al-oxide tunneling barriers were modified by exposure to a vapor of n-octadecyltrimethoxysilane which forms self-assembled monolayers. The dynamic conductance dI/dV of the modified Al-oxide barrier between Al and Pb electrodes was measured at 4.2 K. Quasilinear conductance backgrounds are observed up to 200 mV with a strength that increases with increasing exposure time from 10 to 60 min. A saturation effect is observed around 200 mV. Beyond 200 mV the dynamic conductance shows a parabolic behavior indicative of elastic tunneling from an asymmetric barrier. The linear background is attributed to inelastic tunneling from a continuum of excitations