Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Conference Object Citation - WoS: 1Citation - Scopus: 1Self-Heating Effect in Intrinsic Tunneling Spectroscopy of Hgbr2 Intercalated Bi2.1sr1.4ca1.5cu 2o8+? Single Crystals(IEEE, 2007) Kurter, Cihan; Özyüzer, Lütfi; Zasadzinski, John F.; Hinks, David G.; Gray, Kenneth E.We report tunneling results in intrinsic Josephson junction (IJJ) stacks fabricated in the form of square micromesas on HgBr2 intercalated Bi2.1Sr1.4Ca1.5Cu2O 8+δ (Bi2212) single crystals using photolithography and Ar ion milling techniques. Self-heating is the most common problem encountered in interlayer tunneling and it is likely to reduce the reliability of IJJ data. Although intercalation reduces heating a hundredfold, it still needs to be minimized substantially in order to approach the authentic superconducting energy gap observed by tunneling using more conventional junctions. We report tunneling characteristics of two mesas with the same height but different sizes (5 × 5 μm2 and 10 × 10 μm2) to show that heating effects are strongly related to IJJ stack size. For the smaller mesa, we observed an energy gap close to that seen in single SIN (S: superconductor, I: insulator, N: normal metal) and SIS break junctions as well as the dip and hump structures at high bias. The subgap data of 5 × 5 μm2 mesa were successfully fit with a momentum averaged d-wave model using convenient parameters. Thus our data is consistent with the predominant pairing symmetry suggested by point contact tunneling, break junction, scanning tunneling microscopy/spectroscopy and angle resolved photoemission measurements in Bi2Sr2CaCu2O8+δ.Conference Object Citation - WoS: 2Citation - Scopus: 2Spin Polarized Current Injection Through Hgbr2 Intercalated Bi2212 Intrinsic Josephson Junctions(Institute of Electrical and Electronics Engineers Inc., 2007) Özyüzer, Lütfi; Kurter, Cihan; Özdemir, Mustafa; Zasadzinski, John F.; Gray, Kenneth E.; Hinks, David G.To investigate the effect of polarized current on tunneling characteristics of intrinsic Josephson junctions (IJJs), spin-polarized and spin-degenerate current have been injected through the c-axis of HgBr2 intercalated Bi2.1Sr1.5Ca1.4Cu2O 8+δ (Bi2212) single crystals on which 10 × 10 μm 2 mesas have been fabricated. These two spin conditions are achieved by depositing either Au (15 nm)/Co (80 nm)/Au (156 nm) multilayers or single Au film on HgBr2 intercalated Bi2212 with Tc = 74 K followed by photolithography and Ar ion beam etching. The I-V characteristics have been measured with and without a magnetic field parallel to c-axis at 4.2 K. A fine, soft Au wire is used to make a gentle mechanical contact on the top of a particular mesa in the array. Tunneling conductance characteristics were obtained and the magnetic field dependence of sumgap voltage peaks was investigated. These peaks do not change in position with increasing magnetic field for both contact configurations. In addition, the temperature dependence of tunneling characteristics of the IJJs are obtained and existence of pseudogap feature is observed above Tc for HgBr2 intercalated Bi2212.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.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 stackConference Object Citation - WoS: 6Citation - Scopus: 6Fabrication of Array of Mesas on Superconducting Bi2sr 2cacu2o8+? Single Crystals(National Institute of Optoelectronics, 2005) Kurter, Cihan; Özyüzer, LütfiThe superconducting properties of multi-layered high temperature superconductors (HTS) result mainly from the CuO2 planes, while the other structural components behave simply as charge reservoirs. Using these perfect-layered structures of HTS, arrays of mesas have been fabricated on the surfaces of Bi2Sr2CaCu2O8+δ (Bi2212) single crystals using hotolithography and argon ion beam etching techniques. These arrays have current-voltage (I-V) characteristics that consist of some branches corresponding to different intrinsic Josephson junctions in the mesas, The surface topography and heights of the mesas were examined with atomic force microscopy. Due to the small mesa area, conventional wire bonding techniques are not applicable. A novel method, point contact tunneling apparatus with a sharp Au tip, was used to obtain the I-V characteristics of the fabricated intrinsic Josephson junctions, below the critical temperature of Bi2212. Since the ultimate goal was to obtain an ordered group of mesas with small lateral dimensions, to eliminate heating effects during I-V measurements, we showed that submicron-sized mesas could be characterized by the new technique.Conference Object Citation - WoS: 4Citation - Scopus: 5Comparison of Intrinsic Josephson and Sis Tunneling Spectroscopy of Bi 2sr2cacu2o8+?(IEEE, 2005) Özyüzer, Lütfi; Kurter, Cihan; Zasadzinski, John F.; Gray, Kenneth E.; Hinks, David G.; Miyakawa, NobuakiTunneling spectroscopy measurements are reported on optimally-doped and overdoped Bi2Sr2Ca2Cu2O 8+δ single crystals. A novel point contact method is used to obtain superconductor-insulator-normal metal (SIN) and SIS break junctions as well as intrinsic Josephson junctions (IJJ) from nanoscale crystals. Three junction types are obtained on the same crystal to compare the quasiparticle peaks and higher bias dip/hump structures which have also been found in other surface probes such as scanning tunneling spectroscopy and angle-resolved photoemission spectroscopy. However, our IJJ quasiparticle spectra consistently reveal very sharp conductance peaks and no higher bias dip structures. The IJJ conductance peak voltage divided by the number of junctions in the stack consistently leads to a significant underestimate of Δ when compared to the single junction values. The comparison of the three methods suggests that the markedly different characteristics of IJJ are a consequence of nonequilibrium effects and are not intrinsic quasiparticle features.