Factors affecting the optimal design of high-Tc superconductors — the pseudogap and critical doping

Tallon, J. L.; Williams, G. V. M.; Loram, J. W.

doi:10.1016/s0921-4534(00)00195-7

Cited by 56 publications

(68 citation statements)

References 36 publications

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“…Therefore, to achieve maximum J c for a given family of cuprates, one must try to increase the superfluid density as much as possible to strengthen the depairing contribution to the critical current. A similar proposal was made by Tallon et al [20] in an earlier study based on collective flux pinning model. To summarize, we have studied the temperature dependent zero-field critical current density of high-quality c-axis oriented Y123 thin films in this paper.…”

Section: Discussionsupporting

confidence: 69%

Temperature Dependence of the Zero-Field In-Plane Critical Current Density of YBa2Cu3O7-d High-Tc Superconductors

Sarkar¹,

Naqib

2012

J. Sci. Res.

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The nature of the temperature dependence of the zero-field critical current density, J c0 (T), in the CuO 2 planes has been investigated for c-axis oriented YBa 2 Cu 3 O 7-δ (Y123) thin films over a range of hole content, p. The hole concentration was varied by changing the oxygen deficiency, δ, in the CuO 1-δ chains by annealing the films under different oxygen partial pressures and temperatures. The J c0 (T) values were extracted from the magnetic hysteresis (M-H) loops obtained at different temperatures. From the analysis of the J c0 (T) data for different sample compositions, we have extracted valuable information regarding the nature of the underlying magnetic flux pinning mechanisms in Y123 superconductors. We have found that the oxygen defects play only a secondary role in pinning of the vortices, the superfluid density, on the other hand plays a significant role. The exponent, n, governing the J c0 (T) behavior for a given sample composition showed a systematic behavior as hole contents are changed.

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Section: Discussionsupporting

confidence: 69%

Temperature Dependence of the Zero-Field In-Plane Critical Current Density of YBa2Cu3O7-d High-Tc Superconductors

Sarkar¹,

Naqib

2012

J. Sci. Res.

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“…There are few informative reviews and papers devoted to this problem( see for example [1][2][3][4]). One of the most reasonable point of view is that a pseudogap in the density of states shows up due to an instability in two-dimensional copper-oxygen planes.…”

Section: Introductionmentioning

confidence: 99%

Dynamical charge susceptibility in layered cuprates: Beyond the conventional random-phase-approximation scheme

2001

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The analytical expression for dynamical charge susceptibility in layered cuprates has been derived in the frame of singlet-correlated band model beyond random-phase-approximation (RPA) scheme. Our calculations performed near optimal doping regime show that there is a peak in real part of the charge susceptibility χ(q, ω) at Q = (π, π) at strong enough inter-site Coulomb repulsion. Together with the strong maximum in the Im χ(Q, ω) at 15 meV it confirms the formation of low-energetic plasmons or charge fluctuations. This provides a jsutification that these excitations are important and together with a spin flcutuations can contribute to the Cooper pairing in layered cuprates. Analysing the charge susceptibilitiy with respect to an instability we obtain a new plasmon branch, ωq, along the Brillouin Zone. In particular, we have found that it goes to zero near QCDW ≈ (2π/3, 2π/3).

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“…2(b) correspond to the PG. The SC in Bi2212 is weak in the heavily underdoped region [15,16]. This may explain why it is possible to observe separately the PG in the heavily underdoped Bi2212 by taking into account that tunneling spectroscopy probes the local DOS.…”

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confidence: 99%

Evidence for a quasi-1D topological-excitation liquid in Bi ₂ Sr ₂ CaCu ₂ O _{8 +
x} from tunneling spectroscopy

Mourachkine

2001

Europhys. Lett.

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Tunneling measurements have been carried out on heavily underdoped and slightly overdoped Bi2Sr2CaCu2O8+x (Bi2212) single crystals by using a break-junction technique. We find that inplane tunneling spectra below Tc are the combination of incoherent part from the pseudogap and coherent quasiparticle peaks. There is a correlation between the magnitude of the pseudogap and the magnitude of the superconducting gap in Bi2212. We find that the quasiparticle conductance peaks are caused by condensed solitonlike excitations. [7]). In fig. 1(b), one can see that the I(V ) curve at high positive (low negative) bias passes not below (above) the straight dash line [8] but far above (below) the line. This fact cannot be explained by the d-wave symmetry of the order parameter. To our knowledge, this question has never been raised in the literature before. This finding is the main motivation of the present work.To the best of our knowledge, the soliton SC was for the first time considered in ref. [9] in order to explain the SC in organic quasi-one-dimensional (quasi-1D) conductors. Later, Davydov [10,11] applied the model of soliton SC to cuprates. The theory is based on the concept of bisolitons, or electron (or hole) pairs coupled in a singlet state due to local deformation of the lattice.Tunneling spectroscopy is an unique probe of SC state in that it can, in principle, reveal the quasiparticle (QP) excitation density of states (DOS) directly with high energy resolution. In this paper, we present tunneling measurements performed on heavily underdoped and slightly overdoped Bi2212 single crystals by using a break-junction technique. We find that in -plane tunneling spectra below T c are the combination of incoherent part from the PG and coherent QP peaks. There is a correlation between the magnitude of the PG and the magnitude of the SG in Bi2212. We find that the QP conductance peaks are caused by condensed topological solitons. Thus, we present an evidence for a quasi-1D topological-excitation liquid in Bi2212.The overdoped Bi2212 single crystals were grown using a self-flux method as described elsewhere [12]. The underdoped samples were obtained from the overdoped single crystals by annealing them in vacuum. The T c value was determined by the four-contact method. The transition width is less than 1 K in the overdoped crystals, and a few degrees in the underdoped Bi2212.Experimental details of our break-junction setup can be found elsewhere [13]. In short, many break-junctions were prepared by gluing a sample with epoxy on a flexible insulating substrate, and then were broken in the abplane by bending the substrate with a differential screw at low temperature in a He ambient. The electrical con-1

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Factors affecting the optimal design of high-Tc superconductors — the pseudogap and critical doping

Cited by 56 publications

References 36 publications

Temperature Dependence of the Zero-Field In-Plane Critical Current Density of YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-d</sub> High-<i>T</i><sub>c</sub> Superconductors

Temperature Dependence of the Zero-Field In-Plane Critical Current Density of YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-d</sub> High-<i>T</i><sub>c</sub> Superconductors

Dynamical charge susceptibility in layered cuprates: Beyond the conventional random-phase-approximation scheme

Evidence for a quasi-1D topological-excitation liquid in Bi ₂ Sr ₂ CaCu ₂ O _{8 +
x} from tunneling spectroscopy

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Factors affecting the optimal design of high-Tc superconductors — the pseudogap and critical doping

Cited by 56 publications

References 36 publications

Temperature Dependence of the Zero-Field In-Plane Critical Current Density of YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-d</sub> High-<i>T</i><sub>c</sub> Superconductors

Temperature Dependence of the Zero-Field In-Plane Critical Current Density of YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-d</sub> High-<i>T</i><sub>c</sub> Superconductors

Dynamical charge susceptibility in layered cuprates: Beyond the conventional random-phase-approximation scheme

Evidence for a quasi-1D topological-excitation liquid in Bi 2 Sr 2 CaCu 2 O 8 + x from tunneling spectroscopy

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Evidence for a quasi-1D topological-excitation liquid in Bi ₂ Sr ₂ CaCu ₂ O _{8 +
x} from tunneling spectroscopy