Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
Browse
6 results
Search Results
Article Citation - WoS: 150Citation - Scopus: 7Correlation of Tunneling Spectra in Bi2sr2cacu2o8+? With the Resonance Spin Excitation(American Physical Society, 2001) Zasadzinski, John F.; Özyüzer, Lütfi; Miyakawa, Nobuaki; Gray, Kenneth E.; Hinks, David G.; Kendziora, Christopher A.New break-junction tunneling data are reported in Bi2Sr2CaCu2O8+δ over a wide range of hole concentration from underdoped (Tc=74k) to optimal doped (Tc=95k) to overdoped (Tc=48k). The conductances exhibit sharp dips at a voltage, Ω/e, measured with respect to the superconducting gap. Clear trends are found such that the dip strength is maximum at optimal doping and that Ω scales as 4.9kTc over the entire doping range. These features link the dip to the resonance spin excitation and suggest quasiparticle interactions with this mode are important for superconductivity.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.Article Citation - WoS: 42Citation - Scopus: 43Counterintuitive Consequence of Heating in Strongly-Driven Intrinsic Junctions of Bi2 Sr2 Cacu2 O 8+? Mesas(American Physical Society, 2010) Kurter, Cihan; Özyüzer, Lütfi; Proslier, T.; Zasadzinski, John F.; Hinks, David G.; Gray, Kenneth E.Anomalously high and sharp peaks in the conductance of intrinsic Josephson junctions in Bi2 Sr2 CaCu2 O 8+δ (Bi2212) mesas have been commonly interpreted as superconducting energy gaps but here we show they are a result of strong self-heating. This conclusion follows directly from a comparison to the equilibrium gap measured by tunneling in single break junctions on equivalent crystals. As the number of junctions in the mesa, N, and thus heating increase, the peak voltages decrease and the peak width abruptly sharpens for N≥12. Clearly these widely variable features vs N cannot all represent the equilibrium properties. Our data imply that the sharp peaks represent a transition to the normal state. That it occurs at the same dissipated power for N=12-30 strongly implicates heating as the cause. Although peak sharpening due to heating is counterintuitive, as tunneling spectra usually broaden at higher temperatures, a lateral temperature gradient, leading to coexistence of normal hot spots and superconductive regions, qualitatively explains the behavior. However, a more uniform temperature profile cannot be ruled out. As the peak's width and voltage in our shortest mesa (N=6) are more consistent with the break junction data, we propose a figure of merit for Bi2212 mesas, the relative conductance peak width, such that small values signal a crossover into the strong self-heating regime. © 2010 The American Physical Society.Article Citation - WoS: 54Citation - Scopus: 55Persistence of Strong Electron Coupling To a Narrow Boson Spectrum in Overdoped Bi2sr2cacu2o8+î Tunneling Data(American Physical Society, 2006) Zasadzinski, John F.; Özyüzer, Lütfi; Coffey, L.; Gray, Kenneth E.; Hinks, David G.; Kendziora, Christopher A.A d-wave, Eliashberg analysis of break-junction and STM tunneling spectra on Bi2Sr2CaCu2O8+Î (Bi2212) reveals that the spectral dip feature is directly linked to strong electronic coupling to a narrow boson spectrum, evidenced by a large peak in I'2F(I). The tunneling dip feature remains robust in the overdoped regime of Bi2212 with bulk Tc values of 56Â Ka62Â K. This is contrary to recent optical conductivity measurements of the self-energy that suggest the narrow boson spectrum disappears in overdoped Bi2212 and therefore cannot be essential for the pairing mechanism. The discrepancy is resolved by considering the way each technique probes the electron self-energy, in particular, the unique sensitivity of tunneling to the off-diagonal or pairing part of the self-energy.Article Citation - WoS: 19Citation - Scopus: 25Large Energy Gaps in Ca C6 From Tunneling Spectroscopy: Possible Evidence of Strong-Coupling Superconductivity(American Physical Society, 2007) Kurter, Cihan; Özyüzer, Lütfi; Mazur, Daniel; Zasadzinski, John F.; Rosenmann, Daniel; Claus, Helmut; Hinks, David G.; Gray, Kenneth E.Tunneling in Ca C6 crystals reproducibly reveals superconducting gaps Δ of 2.3±0.2 meV that are ∼40% larger than reported earlier. In an isotropic s -wave scenario, that puts Ca C6 into the class of very strongly coupled superconductors, since 2Δ k Tc ∼4.6, implying that soft Ca phonons are primarily involved in the superconductivity. This conclusion explains the relatively large Ca isotope effect found recently for Ca C6, but it could also signal a strong anisotropy in the electron-phonon interaction.Article Citation - WoS: 200Citation - Scopus: 212Predominantly Superconducting Origin of Large Energy Gaps in Underdoped Bi2sr2cacu2o8+? From Tunneling Spectroscopy(American Physical Society, 1999) Miyakawa, Nobuaki; Zasadzinski, John F.; Özyüzer, Lütfi; Guptasarma, Prasenjit; Hinks, David G.; Kendziora, Christopher A.; Gray, Kenneth E.New tunneling data are reported in Bi2Sr2CaCu2O8+δ which show quasiparticle excitation gaps, Δ, reaching values as high as 60 meV for underdoped crystals with Tc = 70 K. These energy gaps are nearly 3 times larger than those of overdoped crystals with similar Tc. Despite the large differences in gap magnitude, the tunneling spectra display qualitatively similar characteristics over the entire doping range. Detailed examination of the spectra, including the Josephson IcRn product measured in break junctions, indicates that these energy gaps are predominantly of superconducting origin.