Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 31Citation - Scopus: 30Absence of Pseudogap in Heavily Overdoped Bi2sr2cacu2o8+? From Tunneling Spectroscopy of Break Junctions(Institute of Physics Publishing, 2002) Özyüzer, Lütfi; Zasadzinski, John F.; Gray, Kenneth E.; Kendziora, Christopher A.; Miyakawa, NobuakiWe report tunneling spectroscopy of superconductor-insulator-superconductor break junctions on heavily overdoped Bi2Sr2CaCu2O8+δ with Tc = 56 K. At T ≪ Tc, the junction conductances display well-defined quasiparticle peaks at ±2Δ and in some cases a Josephson current at zero bias. Gap values as small as Δ = 10.5 meV have been observed leading to 2Δ/kTc near the BCS limit for dx2-y2 pairing. Temperature dependence of the gap magnitude, Δ(T), follows the BCS relation and both the quasiparticle gap and Josephson current vanish for T > Tc. Above Tc, the tunneling conductance shows a flat background without any indication of a pseudogap near the Fermi level.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.