L.D. Shustov

Influence of the doping level on the charge distribution among the inequivalent CuO2 layers in Tl2Ba2Ca2Cu3O10−δ : a NMR study

Abstract 63 Cu and 17 O NMR measurements in the normal and superconducting states of Tl2Ba2Ca2Cu3O10−δ with different δ are reported. In the overdoped Tl2223 sample with Tc=117 K (Tcopt=123 K) and δ1 17 K are revealed for inequivalent CuO2 layers. For the inner CuO2 layer with the square oxygen coordination of Cu the decrease of 17 K with temperature is more gradual. In going towards the underdoped Tl2223 with Tc=104 K and δ2>δopt the changes of 63,17 K with temperature are found to be the same for both types of copper layers. The quadrupole coupling constants for copper and oxygen from different CuO2 layers were obtained. From the variations with doping of the valence contribution to the electric field gradient at copper sites, we estimate both the hole numbers at Cu and oxygen sites and the real concentration of mobile hole carriers nh in each of inequivalent CuO2 layers. In the overdoped Tl2223 sample the charge density in the inner layer differs from the one in the outer plane (with five-fold oxygen coordination for Cu). Our results show that the inhomogeneity of the charge distribution disappears in the underdoped regime. The results are compared with calculations of the charge distribution among the CuO2 planes in multilayered cuprates reported by Haines and Tallon [E.M. Haines, J.L. Tallon, Phys. Rev. B 45 (1992) 3127].

Interlayer CuO2 antiferromagnetic spin correlations in Tl-based superconducting Tl2Ba2CanCun+1O6+2n and Tl0.5Pb0.5Sr2Ca0.8Y0.2Cu2O7 oxides: 63Cu and 205Tl NMR and spin-lattice relaxation data

Abstract We analyzed 205 Tl and 63 Cu spin-lattice relaxation rate data T −1 1 for thallium-based Tl 0.5 Pb 0.5 Sr 2 Ca 0.80 Y 0.2 Cu 2 O 7 ( T ons c = 107 K) and Tl 2 Ba 2 Ca n Cu n +1 O 6+1 n ( T ons c = 104 K) ( n = 1), T ons c = 125 K ( n = 2)) cuprates which contain one or two TlO layers, respectively. The difference in temperature dependences T −1 1 ( 63 Cu) and T −1 1 ( 205 Tl) for the one TlO layer compound gives us evidence for the presence of interlayer antiferromagnetic spin correlations between the nearest copper atoms placed in the neighbouring CuO 2 layers.

Flux creep and flux flow for thallium ceramics in a pulsed magnetic field

Abstract The resistive properties of Tl-ceramics with T c | ϱ =0=114 K were investigated in a pulsed magnetic field ( B ) up to 30 T and in the temperature range of 4.2 K T T ⪅80K) temperatures the dynamic magnetoresistance arising in the sample is analogous to that observed earlier in LaSrCuO [1] and YBaCuO [2] ceramics. This magnetoresistance is defined by the magnetic field variation rate B = d B/ d t and leads to the appearance of a ϱ minimum at the maximum of the magnetic field pulse, i.e. at B =0 . In the region of high temperatures (80 K ⪅ T T c ) or magnetic fields (at T⪆60 K ) the sample resistance rises monotonically with B increase, and dynamic resistance is not observed. In this temperature range the existence of a scaling relation B ∗ ∝ (1−T ∗ /T c ) 3 2 is shown (here B ∗ and T ∗ meet the condition k=ϱ(B ∗ , T ∗ )/ ϱ n (T ∗ )= const ) for the ceramics resistance ϱ ( B , T ), which can be represented as ϱ/ϱ n =(B/B 0 ) 1 2 (1−T/T c ) −3 4 . An estimate for the upper critical field B c2 (0)≅ B o =1030±40 T is obtained.

Spin susceptibility and doping dependence in Tl0.5Pb0.5Sr2Ca1−xYxCu2O7−δ a round the metal-insulator transition 63,65Cu, 207Pb and 205Tl NMR and spin-lattice relaxation

Abstract NMR line shifts of 63Cu, 207Pb and 205Tl were measured in the cuprates Tl0.5Pb0.5Sr2Ca1−xCu2O7 (x = 0.0–1.0) in order to investigate the evolution of the spin susceptibility χS around the metal-insulator transition, which occurs when the yttrium content increases up to x ≌ 0.6. The Knight shift was evaluated for 63Cu, 207Pb and 205Tl and the corresponding change of the static spin susceptibility χS (q = 0) was determined from the NMR data in the superconducting state. In the superconducting phase, where Tc has a maximum at x = 0.2, the value of χS (q = 0) increases gradually with hole doping. The 63Cu zero-field NMR and the NMR spectra of 207Pb and 205Tl for Tl0.5Pb0.5Sr2YCu2O7 reported here present the first NMR observation of antiferromagnetic ordering in these thallium-based cuprates.

XPS studies of Cu3+ ions in Ba(CuO2)2nH2O

X-ray photoelectron studies (XPS) were carried out for Cu3+ ions in Ba(CuO2)2nH2O. No intense satellites were observed in the spectra of Cu2p- electrons. The Cu2p32-level chemical shift was 1.4 and 2.4 eV when moving from Ba(CuO2)2nH2O (Cu3+) to CuO (Cu2+) and Cu2O (Cu1+), respectively.

Features of the spin fluctuations and superconductivity of Tl2Ba2CaCu2O8−δ according to 63Cu and 17O NMR data

Data on the NMR line shifts, the spin-lattice relaxation rate of 63Cu and 17O nuclei, and the spin-spin relaxation rate of 63Cu are obtained for Tl2Ba2CaCu2O8−δ (Tc=112 K) in the normal and superconducting states. The hyperfine constants at the copper and oxygen atoms in a CuO2 plane are estimated from an analysis of the temperature dependence of the Knight shift. The temperature-dependent behavior of the long-and short-wavelength parts of the dynamic spin susceptibility is discussed by modeling an antiferromagnetic Fermi liquid. The possible relation between the characteristics of the spin-fluctuation spectrum and the superconducting transition temperature is analyzed for the oxide investigated.

X-Ray photoelectron study of TlBaCaCuO ceramics

Abstract In this work X-ray photoelectron studies have been carried out for core level electron states of thallium, barium, calcium and copper in cuprates Tl2Ba2Ca1Cu2O8+Δ, Tl2Ba2Ca2Cu3O10+Δ′, their metals and oxides. It has been found that on going from the oxides to the cuprates Ba4d 5 2 , Ca2p 3 2 electron core levels move to lower binding energies towards those in the metals and the binding energies of Tl3+4f and Cu2+2p electrons are close to the corresponding values in the oxides. It is assumed that the fine spectral structure in the energy range 10–40 eV is connected with interaction of Tl5d, Ca3p, Ba5p, 5s and O2s shells of neighbour atoms with formation of inner valence molecular orbitals affecting the electron states of outer valence molecular orbitals.

Spin-lattice relaxation, NQR 63Cu and NMR 205Tl, 17O IN Tl2Ba2CanCun+1O6+n, (n=0,1,2)

We report the results on spin-lattice relaxation, NQR 63Cu, NMR 205Tl, 17O measurements in normal and superconducting states for high-T thallium-based compound Tl2Ba2CuO6+δ (Tonsc=89K), Tl2Ba2Ca1Cu2O8+δ (Tonsc=105K), Tl2Ba2CaCu3O10+δ (Tonsc=121K).