Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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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: 22Citation - Scopus: 23Implications of Tunneling Studies on High-Tc Cuprates: Superconducting Gap and Pseudogap(Elsevier Ltd., 2001) Miyakawa, Nobuaki; Zasadzinski, John F.; Oonuki, S.; Asano, M.; Henmi, D.; Kaneko, Tsutomu; Özyüzer, Lütfi; Gray, Kenneth E.Tunneling spectra have been measured on high-Tc cuprates including single crystals Bi2Sr2-xLaxCuO6+δ (Bi2201) and Bi2Sr2CaCu2O8+δ (Bi2212) using superconductor-insulator-normal metal point contact or superconductor-insulator-superconductor break junction methods. The doping dependence of the energy gap parameter is similar in both Bi2212 and Bi2201, increasing monotonically to very large values in the underdoped regime even as Tc decreases. This doping dependence of superconducting gap is similar to that of pseudogap temperature, T*, indicating this is consistent with the scenario whereby the low-energy pseudogap is due to some type of precursor of superconductivity. The high-energy feature observed as the hump structure may be another kind of pseudogap whose energy scale is much larger than superconducting gap, and it may be magnetic in origin.Article Citation - WoS: 14Citation - Scopus: 14High Energy Secondary Peak Structure in Tunneling Spectra (hump) as Possible Magnetic Pseudogap(Elsevier Ltd., 2000) Zasadzinski, John F.; Özyüzer, Lütfi; Miyakawa, Nobuaki; Hinks, David G.; Gray, Kenneth E.It is demonstrated that tunneling spectra in various high Tc cuprates display generic features. The principal conductance peaks in superconductor-insulator-normal metal (SIN) junctions indicate the superconducting gap in the density of states (DOS), Higher energy features include a dip and hump structure with a strength that is asymmetric in bias voltage. The dip and hump features follow the doping trends of the superconducting gap, Δ, with a rough scaling as ∼2Δ and ∼3Δ respectively. Tunneling spectra in underdoped Bi2Sr2CaCu2O8+δ display a more pronounced hump feature suggestive of a second gap in the DOS. It is observed that the hump feature in the tunneling density of states is consistent with other experimental observations of the so-called high energy pseudogap which may have magnetic originsArticle Citation - WoS: 3Citation - Scopus: 3Tunneling Spectroscopy of Heavily Underdoped Crystals of Bi2sr2cacu2o8-?(Elsevier Ltd., 2000) Özyüzer, Lütfi; Zasadzinski, John F.; Miyakawa, Nobuaki; Kendziora, Christopher A.; Sha, J.; Hinks, David G.; Gray, Kenneth E.Crystals of Bi2Sr2CaCu2O8+δ with optimal Tc=95 K have been underdoped using two different methods and the superconducting gaps have been obtained by tunneling. In some cases, three different tunneling geometries have been utilized: point contact, STM and break junctions. The first doping method involves control of the oxygen content by annealing in various partial pressures of oxygen. These crystals exhibit a narrow spread of gap values over a wide doping range from overdoped (Tc=56 K) to underdoped with Tc=70 K. However, for underdoped crystals with Tc midpoints in the range 25 K - 63 K, there is a dramatic increase in the spread of gap values which may signal the development of static phase separation of either chemical or electronic origin. To avoid possible chemical phase separation, we have explored another doping procedure which incorporates Dy substitution on the Ca site. These crystals exhibit a relatively narrow superconducting transition width and some preliminary tunneling spectra will be presented.