Probable observation in tunneling of two distinct gaps and {Tc}`s in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} (original) (raw)
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Microscopic modeling of tunneling spectra in Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+\delta}$ (Bi-2223)
arXiv (Cornell University), 2013
We study a series of spectra measured in the superconducting state of optimally-doped Bi-2223 by scanning-tunneling spectroscopy. Each spectrum, as well as the average of spectra presenting the same gap, is fit using a microscopic model that takes into account the band structure, the BCS gap, and the interaction of electrons with the spin-resonance mode. After describing our measurements and the main characteristics of the strong-coupling model, we report the whole set of parameters determined from the fits, and we discuss trends as a function of the gap magnitude. We also simulate angle-resolved photoemission spectra using the parameters resulting from our fits, and compare with recent experimental data.
Superconducting energy gap of single-crystal Bi2Sr2Ca1Cu2O8+δ by electron tunneling
Physica C: Superconductivity, 1990
We report measurements of the superconducting energy gap in a Bi,Sr&a,Cu 2 0 8+6 single crystal using point contact electron tunneling. We show data related to the energy gap spectra in these new ceramics. The energy gap was determined to be around 27-32 meV. The results give values for the ratio 24 (7'=4.6 K)/k,T, (80 K) of between 7.8 and 9.3. The data also reveal a reproducible structure at energies of 67 and 120 meV.
Superconducting gap in the presence of bilayer splitting in underdoped (Pb,Bi)(2)Sr2CaCu2O8+delta
2002
The clearly resolved bilayer splitting in ARPES spectra of the underdoped Pb-Bi2212 compound rises the question of how the bonding and antibonding sheets of the Fermi surface are gapped in the superconducting state. Here we compare the superconducting gaps for both split components and show that within the experimental uncertainties they are identical. By tuning the relative intensity of the bonding and antibonding bands using different excitation conditions we determine the precise k-dependence of the leading edge gap. Significant deviations from the simple cos(kx)-cos(ky) gap function for the studied doping level are detected. PACS numbers: 74.25.Jb, 74.72.Hs, 71.18.+y One of the crucial steps in the evolution of our understanding of superconductors has been the discovery of the energy gap between the ground state and the quasiparticle excitations of the system. Photoemission is one of those experimental techiques which provided direct evidence for the existence of such a gap in the high-temperature superconducting cuprates 1,2,3 . Subsequent ARPES investigations 4,5,6 clearly demonstrated the anisotropic character of the gap which now is considered as a hallmark of the high temperature superconductors. Detailed studies of the symmetry properties of the gap suggested a purely d -wave character 7 in case of the optimally 8 and overdoped 9 samples, as well as noticeable deviations from the simplest d-wave scenario upon underdoping 9 .
Physica C: Superconductivity, 2001
From intrinsic tunneling spectroscopy, superconducting-and pseudo-gaps could be separated within a wide range of temperatures. We have found that the two gaps have dierent temperature (T) and magnetic ®eld (H) dependencies. The superconducting gap closes both as T 3 T c and H 3 H c2 , while the pseudo-gap does not change neither with T, or H. This would speak in favor of two coexisting phenomena and against the precursor superconductivity scenario of the pseudo-gap.
Pseudogap Precursor of the Superconducting Gap in Under- and Overdoped Bi_{2}Sr_{2}CaCu_{2}O_{8+δ}
Physical Review Letters, 1998
We present tunneling spectroscopy of Bi 2 Sr 2 CaCu 2 O 81d single crystals as a function of oxygen doping and temperature. The doping dependence amounts essentially to an energy scaling of the tunneling spectra, with a quasiparticle gap that is reduced with increasing oxygen concentration. This superconducting gap is temperature independent up to the superconducting transition where the superconducting spectra merge continuously into another gaplike feature at the Fermi level. This pseudogap is found to be present both in underdoped and overdoped samples, and it scales with the superconducting gap. [S0031-9007(97)04902-8]
Tunneling spectroscopy of various underdoped Bi2Sr2CaCu2O8+δ
Physica C: Superconductivity, 2001
Tunneling spectra of vacuum annealed and Y-substituted underdoped Bi2212 single crystals have been measured using break junctions. The observed gap value is indeed larger than that of the as-grown (slightly overdoped) Bi2212 with T c 87 K, but the peak structure disappears at the lower T c % 40±70 K depending on the growth condition. This thermal behavior is in contrast to the as-grown sample showing the gap-closing temperature as high as %250 K. Further, the gap value of the vacuum-annealed Bi2212 is larger than that of the Y-substituted Bi2212 for the same T c , suggesting the existence of another control parameter than T c . Ó
2008
The tunnel conductance G͑V͒ for break junctions made of single-crystal as-grown Bi 2 Sr 2 CaCu 2 O 8+␦ samples with T c Ϸ 86-89 K were measured and clear-cut dip-hump structures ͑DHSs͒ were found in the range 80-120 mV of the bias voltage V. A theory of tunneling in symmetrical junctions between inhomogeneous charge-density-wave ͑CDW͒ superconductors, considered in the framework of the s-pairing model, has been developed. CDWs have been shown to be responsible for the appearance of the DHS in the tunnel currentvoltage characteristics and properly describe the experimental results.
2008
Tunnel conductance G V ( ) for break-junctions made of as-grown single-crystal Bi2Sr2CaCu2O8+ samples with Tc 86 89 K was measured and clear-cut dip-hump structures (DHSs) were found in the range 80 120 mV of the bias voltage V . The theory of tunneling in symmetric junctions between inhomogeneous charge-density-wave (CDW) superconductors, considered in the framework of the s-pairing model, has been developed. CDWs have been shown to be responsible for the appearance of the DHS in the tunnel current-voltage characteristics and properly describes experimental results.
Break junction tunnelling on Bi2Sr2CaCu2O8+?-single crystals
Zeitschrift f�r Physik B Condensed Matter, 1992
Break junction tunnelling experiments on Bi2Sr2Ca-Cu20 s +o-single crystals were performed at different temperatures. Carefully adjusted samples exhibited conductance curves showing only one large peak at positive and negative bias voltages. From these measurements a gap value A=(21.2_2.8)meV, i.e. 2A/kBTc=(5.5+_0.8), was inferred. The behaviour of the conductance curves is similar to that of conventional superconductors but with a much larger broadening of the tunnelling characteristic. Therefore, several models which could explain this smearing are compared with the experimental data. However, it is found that none of them is capable of fitting the conductance curves convincingly. In some cases tunnel characteristics similar to those predicted by a charging effect model or a multigap model were obtained.