Scanning tunneling microscopy/spectroscopy on multi-layered cuprate superconductor Ba2Ca5Cu6O12 (O1−x Fx)2

Abstract

Scanning tunneling microscopy/spectroscopy (STM/STS) measurements on multi-layered cuprate superconductor Ba 2 Ca 5 Cu 6 O 12 (O 1-x F x) 2 are carried out. STM topographies show randomly distributed bright spot structures with a typical spot size of ~ 0.8 nm. These bright spots are occupied about 28% per one unit cell of c-plane, which is comparable to the regular amount of apical oxygen of 20% obtained from element analysis. Tunneling spectra simultaneously show both the small and the large gap structures. These gap sizes at 4.9 K are about ∆ ~ 15 meV and ~ 90 meV, respectively. The small gap structure disappears at the temperature close to T C , while the large gap persists up to ~200 K. Therefore, these features correspond to the superconducting gap and pseudogap, respectively. These facts give evidence for some ordered state with large energy scale even in the superconducting state. For the superconducting gap, the ratio of 2∆ S /K B T C = 4.9 is obtained with T C = 70 K, which is determined from temperature dependence of the tunneling spectra.

Scanning tunneling spectroscopy and break junction spectroscopy on iron-oxypnictide superconductor NdFeAs(O0.9F0.1)

“…A similar topography with randomly distributed granular structures was reported by Pan et al [8]. We note that random spot structures were also observed in apical fluorine cuprate superconductors [10]. It is quite interesting that such similar spot structures were observed, despite the two different kinds of superconducting system, cuprate and iron-pnictide.…”

“…T c $ 48 K was inferred from the temperature, T, dependence of electrical resistance and magnetic susceptibility. The STM equipment used in this experiment is commercially supplied system (Omicron LT-STM) with some modifications [9,10]. Polycrystalline samples were cracked at T = 77 K under the ultra-high vacuum atmosphere of $10 À8 Pa.…”

Scanning-tunneling microscopy/spectroscopy and break-junction tunneling spectroscopy of FeSe1–xTex

“…The STM apparatus used in this experiment was an Omicron LT-UHV-STM system, which has been modified to further reduce external disturbance of the sample [16,17]. The sample was cleaved along the layer in situ at T = 77 K in an ultra-high vacuum (UHV) sample preparation chamber of ~10 -8 Pa to avoid any contamination or migration of atoms on the crystal surface.…”

Competition of Superconductivity and Charge Density Waves in Cuprates: Recent Evidence and Interpretation

“…In this section, we are going to show that two very important features are common to all high-T c families. Specifically, these are the intrinsic inhomogeneity of nonstoichiometric superconducting ceramic and single crystalline samples [334][335][336][337][338][339][340][341][342][343] and the persistence of CDWs [340,344,345] and other phenomena, which we also consider as CDW manifestations (dip-hump structures, DHS [339,[346][347][348], and pseudogaps below and above T c [349][350][351][352][353][354][355][356][357][358] in tunneling spectra and angle-resolved photoemission spectra, ARPES). [12,334,[359][360][361][362][363][364][365][366][367][368][369][370].…”