Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Conference Object Investigation of In-Gap Field Enhancement at Terahertz Frequencies for a Metasurface Enhanced Sensor(Institute of Electrical and Electronics Engineers, 2021) Tugay, Halime; Altan, Hakan; Demirhan, Yasemin; Özyüzer, Lütfi; Sabah, CumaliThe arrangements of subwavelength inclusions in a metasurface can serve as an effective absorber for the terahertz region. When such an absorber is combined with a unique material, the absorption can induce effects that can lead to a change in the materials electrical properties. Vanadium dioxide shows a passive and reversible change from monoclinic insulator phase to metallic tetragonal rutile structure by using external stimuli such as temperature (340K), photo excitation, electric field, mechanical strain or magnetic field [1,2]. Upon absorption of the THz radiation, the high electric fields that are generated inside the gaps of the metasurface can serve as trigger points, as was shown previously using kV strength THz E-fields.Conference Object Spin Polarized Tunneling in Large Area Mesas of Superconducting Bi 2sr2cacu2o8+δ for the Generation of the Thz Waves(Institute of Electrical and Electronics Engineers Inc., 2009) Türkoğlu, Fulya; Şimşek, Yılmaz; Köseoğlu, Hasan; Demirhan, Yasemin; Meriç Polster, Zeynep; Özyüzer, LütfiRectangular intrinsic Josephson junction mesa structures of superconducting Bi2Sr2CaCu2O8+delta (Bi2212) can be used as a source of continuous, coherent and polarized terahertz (THz) radiation. THz emitting mesas are below a certain underdoped level of Bi2212. They have small Josephson critical current in contrast to optimally doped and overdoped Bi2212. We deposited Au/Co/Au multilayer top of mesa and obtained small critical current from mesas fabricated by as-grown Bi2212 single crystals due to injection of spin polarized current. The spin injection eliminates adjustment of doping level for successful THz emission.Conference Object Reactive Ion Beam Etching of Superconducting Bi2212 by Ta/Pr and Pr'/ta/pr Masks for the Generation of Thz Waves(Institute of Electrical and Electronics Engineers Inc., 2009) Köseoğlu, Hasan; Türkoğlu, Fulya; Demirhan, Yasemin; Meriç Polster, Zeynep; Özyüzer, LütfiGeneration of powerful THz radiation from intrinsic Josephson Junctions (Ills) of Bi(2)Sr(2)CaCu(2)O(8+delta) (Bi2212) may require mesas with large lateral dimension. However, there are difficulties in fabrication of perfect rectangular mesas. Mesa lateral angles should be close to 90 degrees to obtain IJJs with same planar dimensions for synchronization of IJJs. Since thick photoresist (PR) layer shades the lateral dimension of mesa during ion beam etching, we patterned Ta/PR and PR'/Ta/PR masks on Bi2212 and used selective ion etching to overcome this problem. The reactive ion beam etchings have done with ion beam of Ar, N(2) and O(2) and we have obtained mesas about 1 mu m with lateral angle of approximately 50 to 75 degrees which is better than the mesas fabricated with single layer mask.Conference Object Terahertz Transmission Through Patterened Vanadium Oxide Thin Films on Dielectric Substrates(SCITEPRESS, 2017) Akkaya, M.; Demirhan, Yasemin; Yüce, Hürriyet; Aygün, Gülnur; Özyüzer, Lütfi; Sabah, Cumali; Altan, HakanPatterned and unpatterned films of vanadium oxide grown on dielectric substrates such as fused silica and sapphire were grown and analysed by varying the temperature using terahertz time domain spectroscopy. After investigating the critical transition temperature near 340K, a well-known cross-shaped pattern was studied to observe any resonances upon transmission. Due to the poor conductivity of the films the frequency selective nature of the structure was not observed, however an etalon effect could be seen in the sapphire substrate as opposed to the fused silica substrate above the critical temperature. Dependence of the refractive index difference between substrates upon transmission of the THz pulse is likely in explaining this observed difference.Conference Object Citation - Scopus: 1Cleo®/Europe - Eqec 2015, an Indium Tin Oxide Metamaterial Filter for the Terahertz Regime: Design, Fabrication and Characterization(Optical Society of America (OSA), 2015) Takan, Taylan; Nebioğlu, Mehmet Ali; Kurt, Metin; Demirhan, Yasemin; Özyüzer, Lütfi; Sabah, Cumali; Altan, Hakan[No abstract available]Article Citation - WoS: 2Citation - Scopus: 3Reply To "comment on 'counterintuitive Consequence of Heating in Strongly-Driven Intrinsic Junctions of Bi2sr2cacu 2o8+? Mesas'"(American Physical Society, 2011) Kurter, Cihan; Özyüzer, Lütfi; Proslier, Thomas; Zasadzinski, John F.; Hinks, David G.; Gray, Kenneth E.The main criticism raised in the preceding Comment concerns our suggestion that sharp conduction peaks in Bi 2Sr 2CaCu 2O 8+δ mesas, along with absent dip-hump features, may, in general, be a result of self-heating. The author points to the variety of experimental configurations, matrix-element effects, and doping dependencies that might allow a diversity of conductance spectra. We argue that numerous mesa studies (with fixed matrix elements) firmly establish the systematic development of sharp conductance peaks with increased self-heating, and thus, the issue of nonuniversality of tunneling characteristics is not relevant. The author mentions a number of studies that show that the mesa is superconducting near the conductance peak voltage. This is not in dispute and indicates a misinterpretation of our analysis that is clarified here. To address further comments on the technical details of our heating model, we reiterate that our conclusions are independent of our model but rather are based solely on experimental data that are not in dispute.Conference Object Fabrication of Double Mesa Structures by E-Beam Lithography From High Temperature Superconducting Bi2sr2cacu2o 8+? (bi2212) for Powerful Terahertz Emission(Institute of Electrical and Electronics Engineers Inc., 2011) Demirhan, Yasemin; Türkoğlu, Fulya; Köseoğlu, Hasan; Minematsu, M.; Araki, H.; Miyakawa, Nobuaki; Özyüzer, LütfiWe work on a frequency tunable solid state device to meet the needs of continuous, coherent, powerful terahertz emission sources that fill practically important terahertz gap. High temperature superconducting (HTS) coherently oscillating Josephson junctions in Bi2Sr2CaCu 2O8+δ (Bi2212) crystal make this approach very promising. Since doping dependence of Bi2212 is an important parameter, Bi2212 crystals are annealed in vacuum or purified argon gas flow at 425°C. For further processing we pattern both single and double rectangular mesa structures by using electron beam lithography on the cleaved surface of the crystal. Resistance-temperature (R-T), and current-voltage behavior (I-V) measurements achieved. © 2011 IEEE.Conference Object Terahertz Wave Emission From Layered Superconductors: Interferometer Measurements(Institute of Electrical and Electronics Engineers Inc., 2011) Özyüzer, Lütfi; Türkoğlu, Fulya; Demirhan, Yasemin; Köseoğlu, Hasan; Preu, S.; Ploss, D.; Malzer, S.; Şimşek, Yılmaz; Wang, Huabing; Müller, P.Rectangular Bi2Sr2CaCu2O 8+δ (Bi2212) mesa structures were fabricated on as-grown Bi2212 single crystal superconductors using standard photolithography and Ar ion beam etching techniques. We have performed c-axis resistance versus temperature (R-T), current-voltage (I-V) characteristics and bolometer measurements. Furthermore, in contrast to previous studies, the emission frequency was determined using interferometer set up instead of FTIR. The interference patterns were detected outside the cryostat after traveling long way through ambient space. The emission frequency calculated by Fourier transform of interference data is consistent with Josephson frequency-voltage relation. © 2011 IEEE.Article Citation - WoS: 13Citation - Scopus: 12Modeling Study of the Dip-Hump Feature in Bi2 Sr2 Cacu2 O8+? Tunneling Spectroscopy(American Physical Society, 2006) Romano, Pierom; Özyüzer, Lütfi; Yusof, Zikri; Kurter, Cihan; Zasadzinski, John F.The tunneling spectra of high-temperature superconductors on Bi2 Sr2 CaCu2 O8+δ (Bi-2212) reproducibly show a high-bias structure in the form of a dip-hump at voltages higher than the gap voltage. Of central concern is whether this feature originates from the normal state background or is intrinsic to the superconducting mechanism. We address this issue by generating a set of model conductance curves-a "normal state" conductance that takes into account effects such as the band structure and a possible pseudogap, and a pure superconducting state conductance. When combined, the result shows that the dip-hump feature present in the experimental conductance curves cannot be naively attributed to a normal state effect. In particular, strong dip features found in superconductor-insulator-superconductor data on optimally doped Bi-2212, including negative dI dV, cannot be a consequence of an extrinsic pseudogap. However, such features can easily arise from state-conserving deviations in the superconducting density of states, e.g., from strong-coupling effects.Conference Object Citation - WoS: 3Citation - Scopus: 3Spin Polarized and Degenerate Tunneling Spectra in Intrinsic Josephson Junctions of Bi2212(John Wiley and Sons Inc., 2007) Özdemir, Mustafa; Özyüzer, Lütfi; Kurter, CihanTunneling characteristics of HgBr2 intercalated superconducting Bi2212 single crystals have been obtained by using 10×10 μm2 intrinsic Josephson junction stacks, so called mesa structures. The spin degenerate current is driven along the c-axis with Au layer using point contact tunneling assembly at 4,2 K. The spin polarized current is also driven along the c-axis of crystals with Au/Co/Au multilayer. In order to understand the role of ferromagnetic layer (Co), quasiparticle branches are examined with and without magnetic field. The magnetic field evolution of switching currents are obtained for gaining further insight about the spin injection through the stack