Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 2Citation - Scopus: 2The Icrn Value in Intrinsic Josephson Tunnel Junctions in Bi2sr2cacu2o8+? (bi2212) Mesas(Springer Verlag, 2011) Kurter, Cihan; Özyüzer, Lütfi; Hinks, David G.; Gray, Kenneth E.; Zasadzinski, John F.The c-axis current-voltage I(V) characteristics have been obtained on a set of mesas of varying height sculpted on Bi2Sr2CaCu2O8+δ (Bi2212) crystals intercalated with HgB2. The intercalation, along with the small number of junctions in the mesa, N = 6–30, minimizes the degree of self-heating, leading to a consistent Josephson critical current, IC, among junctions in the mesa. The Bi2212 crystals with a bulk TC =74 K are overdoped and display negligible pseudogap effects allowing an accurate measure of the normal state resistance, RN. These properties make themesas nearlyideal for the determinationof the Josephson ICRN product.Wefind ICRN valuesconsistently ∼30% of the quasiparticle gap parameter, /e, which was measured independently using a mechanical contact, break junction technique. The latter was necessitated by higher bias heating effects in the mesas which prevented direct measurements of the superconducting gap. These values are among the highest reported and may represent the maximum intrinsic value for ICRN. The results indicate that the c-axis transport is a mixture of coherent and incoherent tunneling.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.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.Conference Object Citation - WoS: 4Citation - Scopus: 4Probing the Phase Diagram of Bi2sr2cacu 2o8+? With Tunneling Spectroscopy(Institute of Electrical and Electronics Engineers Inc., 2003) Özyüzer, Lütfi; Zasadzinski, John F.; Gray, Kenneth E.; Hinks, David G.; Miyakawa, NobuakiTunneling measurements are performed on Ca-rich single crystals of Bi 2Sr2CaCu2O8+δ (Bi2212), with various oxygen doping levels, using a novel point contact method. At 4.2 K, SIN and SIS tunnel junctions are obtained with well-defined quasiparticle peaks, robust dip and hump features and in some cases Josephson currents. The doping dependence of tunneling conductances of Ca-rich Bi2212 are analyzed and compared to stoichiometric Bi2212. A similar profile of energy gap vs. doping concentration is found although the Ca-rich samples have a slighly smaller optimum Tc and therefore smaller gap values for any doping level. The evolution of tunneling conductance peak height to background ratios with hole concentration are compared. For a given doping level, the Ca-rich spectra showed more broadened features compared to the stoichiometric counterparts, most likely due to increased disorder from the excess Ca. Comparison of the dip and hump features has provided some potential insights into their origins.Article Citation - WoS: 4Citation - Scopus: 4Simultaneous Quasiparticle and Josephson Tunneling in Bscco-2212 Break Junctions(Institute of Electrical and Electronics Engineers Inc., 1999) Özyüzer, Lütfi; Miyakawa, Nobuaki; Zasadzinski, John F.; Yusof, Zikri M.; Romano, Pierom; Kendziora, Christopher A.; Hinks, David G.; Gray, Kenneth E.Tunneling measurements are reported for superconductor-insulator-superconductor (SIS) break junctions on underdoped, optimally-doped, and overdoped single crystals of tSrsCaCiOs-).,! (Bi2212). The junction I -V characteristics exhibit welldefined quasiparticle current jumps at eV = 2A as well as hysteretic Josephson currents. The quasiparticle branch has been analyzed in the framework of dxa_y2 (d-wave) superconductivity and indicates that there is preferential tunneling along the lobe directions of the d-wave gap. For overdoped Bi-2212 with TC-62 K, the Josephson current is measured as a function of junction resistance, Rn, which varied by two orders of magnitude (1 kO to 100 kO). IcRn product is proportional to the 0.47 power of /c and displays a maximum of 7.0 mV. When the hole doping is decreased from overdoped (Tc=62 K) to the underdoped regime (Tc=70 K), the average IcRn product increases as does the quasiparticle gap. The maximum IcRn is ~ 40% of the A/e at each doping level, with a value as high as 25 mV in underdoped Bi-2212.