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1.
Shinsaku Kambe Hiroshi Yasuoka Akihiko Hayashi Yutaka Ueda 《Hyperfine Interactions》1993,79(1-4):891-896
The temperature dependence and the anisotropy of the Knight shift and the spin-lattice relaxation time (T
1) at the Cu and the O sites of the full over-doped Tl2Ba2CuO
y
(T
c=0 K: Tl2201L) were measured. The Knight shift values at the Cu and the o sites in the CuO2 plane are larger in Tl2201L compared to those in Tl2Ba2CuO
y
(T
c=85 K: Tl2201M). This indicates the increase of the spin part of the Knight shift due to the over-doping. Based on the comparison between theT
1 in Tl2201L and Tl2201M, the enhancement of the antiferromagnetic correlation still remains in the whole over-doped region. 相似文献
2.
C. F. J. Flipse G. van der Laan B. T. Thole S. Myhra 《Zeitschrift für Physik B Condensed Matter》1993,90(1):89-91
Polarization dependent X-ray absorption measurements on single crystal Bi2Sr2CuO6 (T
c
=9 K) and Bi2Sr2CaCu2O8 (T
c
=80 K) with one and two CuO2 layers, respectively, show no energy shift of the Cu 2p main peak, and no relation between the amount of 3d(m=0, ±1) character and the critical temperatureT
c
. At grazing incidence a structure in Bi2Sr2CaCu2O8 is found at 937 eV, which can be ascribed to a composite state of Cu 3d(z
2), Cu 4s ando–2p(z). 相似文献
3.
We have measured the temperature (T) dependence of the transverse relaxation rate (T
G
–1
) of the Cu(1) nuclear spin in YBa2Cu3O6.98 (T
c=92 K) and YBa2Cu4O8 (T
c=82 K). From the scaling ratio ofT
G
–2
(Cu1) toT
G
–2
(Cu2), we have estimated the strength of a covalent bonding between the CuO2 plane and the CuO chain to be B0.38×A
zz. The experimentalT
G
–1
(Cu1) in YBa2Cu4O8 was of the same order of magnitude as the estimated one fromT
G
–1
(Cu2). These results appear to indicate that the electrons in the CuO2 plane fairly spread out of the plane in both compounds. 相似文献
4.
The appearance of superconductivity and relaxation of the transition temperature to its equilibrium value T
c≈30 K over the course of five days have been observed in a tetragonal sample of NdBa2Cu3O6.67 under 1 GPa pressure. The time dependence T
c(t) correlates with a decrease of the room-temperature electrical resistance R(t). The superconducting phase disappears 1.3 h after the pressure is removed. This behavior is explained by a redistribution
of charge as a result of pressure-induced oxygen reordering in the CuOx planes. A large effect of oxygen ordering on the transition temperature under pressure has been observed near the metal-insulator
transition (the largest of all those measured in the 1-2-3 system), along with a nonlinear temperature dependence of T
c.
Fiz. Tverd. Tela (St. Petersburg) 39, 1328–1334 (August 1997) 相似文献
5.
Y. V. Piskunov K. N. Mikhalev Yu. I. Zhdanov A. P. Gerashenko S. V. Verkhovskii K. A. Okulova E. Yu. Medvedev A. Yu. Yakubovskii L. D. Shustov P. V. Bellot A. Trokiner 《Physica C: Superconductivity and its Applications》1998,300(3-4)
and
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<δopt different temperature dependencies of the Knight shift
are revealed for inequivalent CuO2 layers. For the inner CuO2 layer with the square oxygen coordination of Cu the decrease of
with temperature is more gradual. In going towards the underdoped Tl2223 with Tc=104 K and δ2>δopt the changes of
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]. 相似文献
6.
EPR investigations using Cu2+ ion as a probe have been performed on supersaturated sucrose solution with percent concentration c = 66 as a function of temperature T, and at room temperature as a function of c. The motionally averaged spectrum of [Cu(H2O)6]2+ was used to monitor the changes in intermolecular interactions that occur as a function of [c, T]. A drastic increase in the line width, symptomatic of increase in the rotational correlation time of [Cu(H2O)6]2+, is observed between 293 and 288 K. The motionally averaged spectrum disappears below 281 K. The motionally averaged spectrum is also absent in the room temperature spectra of the solution with c= 85. Even in the [c, T] range where [Cu(H2O)6]2 is found to be nearly static, these molecules appear to have an orientational fluctuation manifesting in the m 1 dependence of the line width of the parallel component. 相似文献
7.
M. Takigawa 《Applied magnetic resonance》1992,3(3-4):495-508
Results of63Cu and17O NMR experiments in YBa2Cu3O7 and YBa2Cu3O6.63 are reviewed. The normal state data revealed two important aspects of the magnetic properties of these materials, namely, the temperature dependent antiferromagnetic Cu spin correlations and the spin gap behavior, the latter being observed in the reduced oxygen material. These features appear to be the general properties of many high-T c cuprates. Anomalous temperature dependence of the anisotropy of the Cu relaxation rate was found in the superconducting state of YBa2Cu3O7, which can be explained by a d-wave pairing model. 相似文献
8.
N. Katase T. Shibauchi T. Tamegai I. Tsukada K. Uchinokura 《Czechoslovak Journal of Physics》1996,46(Z2):1119-1120
We report the surface impedance (Z
s
) measurements in high quality single crystals of Bi2Sr2CaCu2O8+y
. At relatively low oxygen content, the change of the penetration depth, Δλ(T) ≡λ(T)-λ(0), of the pure single crystals exhibits linear temperature dependence both parallel to the CuO2 planes and in thec direction. In contrast to this behavior, by further oxygenation or 0.6% Zn substitution, theT-linear dependence is disrupted andT
2 dependence of Δλ is observed. We also found that 0.9% Ni-substitution induces no pairbreaking effect. The present results
suggest that the low-lying excitation spectrum of quasiparticles depends on the carrier concentration and is easily changed
by a small amount of Zn substitution. 相似文献
9.
Emission Mössbauer spectroscopy on 67Cu (67Zn) and 67Ga (67Zn) isotopes was used to show that for the superconductors Nd1.85Ce0.15CuO4, La1.85 Sr0.15CuO4, and Tl2Ba2 CaCuO8 in the temperature range T > T c the temperature dependence of the center of gravity S of the Mössbauer spectrum is determined by the second-order Doppler shift, while in the range T < T c the Bose condensation of Cooper pairs influences the value of S (here T c is the superconducting transition temperature). The spatial nonuniformity produced in the electron density by a Bose condensate of Cooper pairs was observed for La1.85 Sr0.15CuO4. 相似文献
10.
A comprehensive review of structure work on high-T
c
oxides as reported during the years 1987 and 1988 is given. Thirteen structures are refined from X-ray single-crystal and/or neutron powder diffraction data:I. (Ba1–x
,K
x
)BiO3 (T
c
=30 K),II. (La2–x
, Sr
x
)CuO4 (T
c
=40 K),III. (Nd, Ce, Sr)2CuO4 (T
c
=28 K),IV. (Nd2–x
, Ce
x
)CuO4 (T
c
=24 K),V. YBa2Cu3O7 (T
c
=90 K),VI. YBa2Cu4O8 (T
c
=80 K),VII. Y2Ba4Cu7O14 (T
c
=40 K),VIII. Pb2Sr2NdCu3O8 (T
c
=70 K),IX. TlBa2CaCu2O7 (T
c
=103 K),X. TlBa2Ca2Cu3O9 (T
c
=120 K),XI. Tl2Ba2CuO6 (T
c
=90 K),XII. Tl2Ba2CaCu2O8 (T
c
=112 K),XIII. Tl2Ba2Ca2Cu3O10 (T
c
=125 K). Except forI (perovskite type),II (K2NiF4 type) andIV (Nd2CuO4 type) they represent new structure types. Structure data, bond distances, structure drawings and calculated X-ray powder diffraction patterns are given for each compound. Structural features and correlations with superconductivity are discussed. The review contains 301 citations. 相似文献
11.
12.
V. Železny D. B. Tanner K. Kamarás L. P. Kozeeva A. A. Pavlyuk 《Zeitschrift für Physik B Condensed Matter》1995,96(3):313-318
The optical spectrum of reduced-T
c GdBa2Cu3O7– has been measured for polarizations parallel and perpendicular to theab plane. The sample was an oxygen-deficient single crystal with a large face containing thec axis. The polarized reflectance from this face was measured from 20–300 K in the spectral region from 30–3000 cm–1, with 300 K data to 30000 cm–1. Kramers-Kronig analysis was used to determine the spectral dependence of theab and thec components of the dielectric tensor. The optical properties are strongly anisotropic. Theab-plane response resembles that of other reduced-T
c materials whereas thec axis, in contrast, shows only the presence of several phonons. There is a complete absence of charge carrier response alongc aboveand belowT
c. This observation allows us to set an upper limit to the free-carrier spectral weight for transport perpendicular to the CuO2 planes.Permanent address: Institute of Physics, CSAV, Prague, Czechoslovakia 相似文献
13.
K. Kumagai Y. Nakamichi Y. Nakamura I. Watanabe H. Nakajima T. Fujita 《Hyperfine Interactions》1989,50(1-4):583-591
Nuclear quadrupole resonances (NQR) of139La in La2−xMxCuO4 (M=Ba, Sr) and63Cu in YBa2CU3O7 have been investigated with substitution of Cu by magnetic impurities. For La-system, the strong enhancement of the nuclear
relaxation rate, 1/T
1 atT
c
*≈10 K (suggesting the occurrence of magnetic instability with hole-doping), is suppressed by 3D-antiferromagnetism induced
by magnetic impurities. In the superconducting region, fluctuations of Cu moments at low temperatures remain extremely fast
as at high temperatures. For Y-system, Fe-ions are substituted for both Cu(1) and Cu(2) sites, But Co-ions are preferentially
substituted to Cu1 sites. The peaks in the relaxation rate of Cu indicate the appearance of magnetic ordering without destroying
superconductivity for the 0.5%-Fe doped sample. 相似文献
14.
15.
Cu-site substitution effects onT
c in La2CuO4-derived superconductors: A proposal of rationalization
M. Acquarone 《Il Nuovo Cimento D》1990,12(11):1553-1574
Summary An interpretation of the Cu-site substitution effects on the critical temperature of La2CuO4-derived superconductors is presented. We argue that the available data on the dependence ofT
c on the amount of Cu-site substitutions indicate that the integrity of the Cu spin lattice is not fundamental to the superconductivity.
A consistent way of systematizing the published data is proposed, by focusing on the interplay of valence fluctuations and
accompanying lattice deformations. 相似文献
16.
Yasushi Idemoto Mitsuru Matsuzawa Ken Takeuchi Chun-K Loong 《Solid State Communications》2004,131(8):513-517
The effects of oxygen doping on the hole-carrying CuO2-layers in Tl2(Ba1−xSrx)2Ca2Cu3Oy were studied by combined chemical and valence analysis, Tc measurements and neutron diffraction. The highest Tc is characterized by an optimal excess oxygen content, Δy, dichotomizing the under- and over-doped regions for each Sr concentration. While the average Tl valence is close to 3.0 and independent of Δy, the average Cu valence shows a linear dependence with Δy. An increase of the flatness of the CuO2 plane, characterized by the O(2)-Cu(2)-O(2) bond angle of ∼176°, was observed at the optimal Δy. 相似文献
17.
A. W. Sleight J. Gopalakrishnan C. C. Torardi M. A. Subramanian 《Phase Transitions》2013,86(4):149-159
A brief survey of compositions and structures of high-temperature copper oxide superconductors containing thallium, bismuth and lead is presented. All these compounds possess CuO2 sheets but not Cu[sbnd]O chains. Another structural feature common to all these compounds is that the part of the structure between nonconsecutive CuO2 sheets is ill-defined. Possible correlations of Tc with the structure and bonding of these compounds are pointed out. 相似文献
18.
M. V. Eremin S. G. Solov’yanov S. V. Varlamov 《Journal of Experimental and Theoretical Physics》1997,85(5):963-970
We solve the problem of the effect of strong electron correlations on the homogeneous spin susceptibility of current carriers
in CuO2 planes. We show that the dependence of the spin susceptibility χ(T) of high-T
c superconductors of the La2−x
SrxCuO4 type on temperature and the doping index x can be explained fairly well by the two-band model suggested earlier (the singlet-correlated oxygen band plus the lower Hubbard
band of copper). The model has features in common with the phenomenological t-J model but cannot be reduced to the latter completely. In contrast to the t-J model, the density of states of the oxygen holes has a peak near the bottom of the band. It is the presence of this peak
together with the non-Fermi-liquid properties that explain the unusual behavior of the spin susceptibility of La2−x
SrxCuO4.
Zh. éksp. Teor. Fiz. 112, 1763–1777 (November 1997) 相似文献
19.
P. Steiner J. Albers V. Kinsinger I. Sander B. Siegwart S. Hüfner C. Politis 《Zeitschrift für Physik B Condensed Matter》1987,66(3):275-278
Photoemission spectra of the La2–x
Sr
x
CuO4 system which recently has been demonstrated of being capable to produce high temperature (T
c
>35 K) superconducting compounds are reported. The photoemission spectra of the basic system (La2CuO4) and of samples which contain up to 20% Sr are not significantly different. The density of states at the Fermi energy is small (smaller than that of metallic Cu) and the samples show a possible small shift of the Cu 2p lines towards the trivalent position with increasing tendency to superconductivity. From the Sr 3d spectra a considerable amount of oxygen defects coordinated to the Sr ions is estimated. 相似文献
20.
P. Allenspach S. -W. Choeng A. Dommann P. Fischer Z. Fisk A. Furrer H. R. Ott B. Rupp 《Zeitschrift für Physik B Condensed Matter》1989,77(2):185-191
Bulk-magnetisation measurements and neutron-scattering experiments were performed both on a polycrystalline sample and on a single-crystal of Pr2CuO4 in the temperature range from 1.5 to 300 K. Pr2CuO4 crystallizes with theT (Nd2CuO4)-type structure. We observed antiferromagnetic ordering of the Cu moments belowT
N
=(190±2) K in a single crystal and belowT
N
=(250±10)K in powder material. The magnetic unit cell dimensions area
m
=2a
o
,c
m
=c
o
;the Cu moments are oriented in the basal plane with a magnetic saturation moment of Cu=(0.45±0.12)
B
. Pr3+ does not order magnetically above 1.5K due to its crystal-field induced singlet ground state as verified by inelastic neutron scattering. 相似文献