Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 20Citation - Scopus: 20Area Dependence and Influence of Crystal Inhomogeneity on Superconducting Properties of Bi2212 Mesa Structures(Elsevier Ltd., 2015) Demirhan, Yasemin; Sağlam, Hilal; Türkoğlu, Fulya; Alaboz, Hakan; Özyüzer, Lütfi; Miyakawa, Nobuaki; Kadowaki, K.The rapid increase in applications of terahertz waves requires new techniques to obtain continuous wave terahertz sources. Mesa structures fabricated from high-Tc superconductor Bi2Sr2CaCu2O8+δ (Bi2212) single crystal have been observed as an intense, coherent, continuous electromagnetic wave source in the terahertz (THz) frequency region. However, in order to produce coherent radiation with high applicable power, we need large mesa structures that enter a collective electromagnetic state in which their oscillations are largely synchronized in phase. On the other hand, large mesa structures cause a heating problem. In this study, we report on the critical current density dependence of mesa area and the crystal inhomogeneity to understand heating problems in large area mesas for terahertz radiation. Since the doping dependence of Bi2212 is an important parameter, the as-grown Bi2212 crystals were heat-treated at various temperatures under vacuum conditions. We have fabricated triple mesa structures from Bi2212 single crystal using e-beam lithography and argon ion beam etching techniques with same area and with different area on the same chip. We investigated and compared characteristics of triple mesas which are on the same chip and next to each other. In this way, we searched the crystal inhomogeneity in triple mesa structures and studied the critical current density dependence of mesa area to obtain high emission power for the THz radiation. Our experimental results clearly show that the Josephson critical current density is decreasing when the area of mesa is increasing. © 2015 Elsevier Ltd. All rights reserved.Article Citation - WoS: 12Citation - Scopus: 13Emission of the Thz Waves From Large Area Mesas of Superconducting Bi 2sr2cacu2o8+? by the Injection of Spin Polarized Current(Elsevier Ltd., 2013) Türkoğlu, Fulya; Özyüzer, Lütfi; Köseoğlu, Hasan; Demirhan, Yasemin; Preu, S.; Malzer, S.; Şimşek, Yılmaz; Wang, Huabing; Muller, P.Rectangular Au/Co/Au/Bi2Sr2CaCu2O 8+δ (Bi2212) mesa structures with large areas and high thicknesses were fabricated on as-grown Bi2212 single crystals in order to obtain small critical current from as-grown mesas by the injection of spin polarized current and so eliminate the adjustment of doping level for successful THz emission. We have performed c-axis resistance versus temperature (R-T), current-voltage (I-V) characteristics and bolometer measurements. It is the first time that THz emission has been observed from as-grown mesas due to injection of spin polarized current. © 2013 Elsevier Ltd. All rights reserved.Article Citation - WoS: 1Effect of Magnetic Field on Quasiparticle Branches of Intrinsic Josephson Junctions With Ferromagnetic Layer(Elsevier Ltd., 2007) Özyüzer, Lütfi; Özdemir, Mustafa; Kurter, Cihan; Hinks, David G.; Gray, Kenneth E.The interlayer tunneling spectroscopy has been performed on micron-sized mesa arrays of HgBr2 intercalated superconducting Bi2212 single crystals. A ferromagnetic multilayer (Au/Co/Au) is deposited on top of the mesas. The spin-polarized current is driven along the c-axis of the mesas through a ferromagnetic Co layer and the hysteretic quasiparticle branches are observed at 4.2 K. Magnetic field evolution of hysteretic quasiparticle branches is obtained to examine the effect of injected spin-polarized current on intrinsic Josephson junction characteristics. It is observed that there is a gradual distribution in quasiparticle branches with the application of magnetic field and increasing field reduces the switching current progressively.Article Investigation of the Tunneling Spectra in Hgbr2-Intercalated Bi-2212 Single Crystals Below and Above Tc(Elsevier Ltd., 2007) Kurter, Cihan; Mazur, Daniel; Özyüzer, Lütfi; Hinks, David G.; Gray, Kenneth E.Interlayer tunneling spectroscopy measurements were performed on mesa arrays of Bi-2212 single crystals, intercalated with HgBr2. Tunneling conductances were obtained over a wide temperature range to examine the spectral features, especially the behavior of the quasiparticle peaks corresponding to superconducting energy gaps (SGs). Experimental spectra showed that gap-like features are still present even for the temperatures far above the transition temperature, Tc. This evidence is consistent with the idea that the SG evolves into a pseudogap above Tc for HgBr2-intercalated Bi-2212 single crystals.