Oxygen Isotope Effect Research Articles

Anomalously enhanced oxygen isotope effect in La1.85Sr0.15CuO4 doped with Fe

The effect of oxygen isotope substitution on superconducting transition temperature Tc has been studied in La1.85Sr0.15Cu1−yFeyO4 (0 < y < 0.01). The substitution for Cu by Fe suppresses TC and dramatically increases the oxygen isotope exponent αO, where TC ∝ MO−αo, Mo is an oxygen isotope mass. The data are analyzed in terms of the Abrikosov-Gor'kov (AG) theory of superconductors with paramagnetic impurities. Both TC and αO show stronger dependence on the Fe concentration than predicted by this theory, while our experimental data on TC(y) and αO(y) for LSCO doped with Ni and Zn are in a good agreement with the AG theory.

Theoretical study of isotope effect in La-doped Y-123

The recent oxygen isotope effect measurement made in the system YBa2-x La x Cu3O7 (0≤x≤0.5) is analyzed using the “two-carrier” model which describes a superconducting system as a mass anisotropic system consisting of charge carriers with two different masses as a result of lattice defects or oxygen deficiency. The extent to which Ba, Cu, and O atoms participate in the phonon-mediated Cooper pairing interaction is elucidated. The relationship between the theoretically deduced mass anisotropic factor andT c agrees closely with the experimental results of Uemuraet al. [28]. Furthermore, the superconducting energy gap toT c ratio is found to be close to 3.5. Excellent agreement is also achieved between the theoretically calculated oxygen isotopic constant and the experimental results of Bornemann and Morris [12].

On the composition‐dependent isotope effect of HTSC in the two‐band model

AbstractThe oxygen isotope effect in high‐TC superconductors has been investigated on the basis of a two‐band model where superconducting phase transition is induced by interband (mainly Coulombic) interaction. The isotope shift of TC appears due to the dependence of averaged interband electronphonon coupling constant on oxygen mass. This coupling has a repulsive nature and gives a relatively small contribution to the total interaction inducing superconductivity. The calculated isotope effect exponent depending on the carrier concentration has been compared with the experimental one as a function of x for La2‐xSrxCuO4.

Mass-anisotropy and oxygen-deficiency effects on the Tc of the YBa2Cu3O7- delta system using the excitonic-enhancement model.

In a previous work [K. W. Wong, P. C. W. Fung, H. Y. Yeung, and W. Y. Kwok, Phys. Rev. B 45, 13 017 (1992)] we carried out a detailed numerical analysis of the oxygen isotope effect on the La-doped Y-Ba-Cu-O system using the excitonic-enhancement model (EEM). Following up such work, we present here another numerical analysis of the effects of oxygen deficiency on the superconductivity of the ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ ceramic based on experimental data and the EEM. We derive also an explicit expression for the ground-state energy of a charged exciton in terms of the mass anisotropic factor \ensuremath{\alpha} and obtain explicit expressions for the renormalized chemical potential \ensuremath{\mu}\ifmmode\bar\else\textasciimacron\fi{} and energy gap functions ${\mathrm{\ensuremath{\Delta}}}_{\mathrm{BCS}}$, ${\mathrm{\ensuremath{\Delta}}}_{\mathrm{ex}}$, etc., for the ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ system. We have found that there is an inherent similarity and difference in the processes of doping and attaining oxygen deficiency. A numerical relation for \ensuremath{\alpha} versus \ensuremath{\delta} is obtained and its justification awaits further experiments.

Analysis of the isotope effect of high-Tc ceramic YBa2-xLaxCu3O7 using the excitonic-enhancement model.

The excitonic-enhancement model (EEM) is based on the simultaneous excitonic and ``generalized'' Cooper-pair condensation of a charge-unbalanced system that is described by a two-band model consisting of a valence and a conduction band separated by a band gap G. A detailed numerical analysis of the consequences of the EEM with respect to shift of ${\mathit{T}}_{\mathit{c}}$ due to the oxygen isotope effect on the La-doped Y-Ba-Cu-O system is carried out. The results are found to be in excellent agreement with the recent experimental data of Bornemann and Morris, covering a ${\mathit{T}}_{\mathit{c}}$ range of 38.3--92.3 K.

Phonon density of states and oxygen-isotope effect in Ba1-xKxBiO3.

The phonon densities of states (DOS) of insulating ${\mathrm{BaBiO}}_{3}$ and superconducting ${\mathrm{Ba}}_{0.6}$${\mathrm{K}}_{0.4}$${\mathrm{BiO}}_{3}$ and the variation of the phonon spectrum of the superconducting compound upon oxygen-isotope ${(}^{16}$O, $^{18}\mathrm{O}$) substitution are determined by inelastic neutron scattering (INS) and molecular-dynamics (MD) simulations. The MD simulations are carried out with an effective interaction potential which includes steric effects, Coulomb interactions, and the charge-dipole interactions due to the electronic polarizability of ${\mathrm{O}}^{2\mathrm{\ensuremath{-}}}$. The MD results are in good agreement with the INS experiments and electron-tunneling measurements. Partial DOS of Ba, K, Bi, and O in ${\mathrm{BaBiO}}_{3}$ and ${\mathrm{Ba}}_{0.6}$${\mathrm{K}}_{0.4}$${\mathrm{BiO}}_{3}$ are also determined from MD simulations. In the superconducting material, the phonon spectrum softens and is comprised of broad bands around 15, 30, and 60 meV. The partial DOS reveal that phonons above 20 meV are due to oxygen vibrations, whereas phonons below 20 meV are due to Ba, K, and Bi. The reference oxygen-isotope-effect exponent, ${\mathrm{\ensuremath{\alpha}}}_{\mathrm{O}}$r=-\ensuremath{\partial} ln〈\ensuremath{\omega}〉/\ensuremath{\partial} ln${\mathit{M}}_{\mathrm{O}}$, of ${\mathrm{Ba}}_{0.6}$${\mathrm{K}}_{0.4}$${\mathrm{BiO}}_{3}$ is determined to be ${\mathrm{\ensuremath{\alpha}}}_{\mathrm{O}}$r=0.42\ifmmode\pm\else\textpm\fi{}0.05 from the mass (${\mathit{M}}_{\mathrm{O}}$) variation of the first moment of the phonon DOS, $_{\mathrm{O}}^{16}\mathrm{〉}$ and $_{\mathrm{O}}^{18}\mathrm{〉}$.This value is close to the oxygen-isotope-effect exponent, ${\mathrm{\ensuremath{\alpha}}}_{\mathrm{O}}$, determined from the variation of ${\mathit{T}}_{\mathit{c}}$ (0.41\ifmmode\pm\else\textpm\fi{}0.03 by Hinks et al. and 0.35\ifmmode\pm\else\textpm\fi{}0.05 by Kondoh et al.), indicating that ${\mathrm{Ba}}_{0.6}$${\mathrm{K}}_{0.4}$${\mathrm{BiO}}_{3}$ is a weak- to moderate-coupling BCS-like superconductor and that the high ${\mathit{T}}_{\mathit{c}}$ (\ensuremath{\sim}30 K) results from large electron-phonon matrix elements involving high-energy oxygen-related phonons.

Dependence of the oxygen isotope effect upon hole density in Bi 2Sr 2Ca 1−xY xCu 2O 8+δ and Y 1−xCa xBa 2Cu 4O 8

We have investigated the dependence of the oxygen isotope effect on the hole density in the high- T c cuprates Bi 2Sr 2CaCu 2O 8 and YBa 2Cu 4O 8. The hole density n was varied by partial replacement of Ca by Y (hole acceptor) in Bi 2Sr 2CaCu 2O 8, and by partial replacement of Y by Ca (hole donor) in YBa 2Cu 4O 8. In both cases the dopant was introduced into the eightfold coordinated site between the two CuO 2 sheets. The hole concentration could be varied to reach maximum T c and upon further doping T c decreased. The oxygen isotope effect α 0 was found to be strongly correlated to n and T c . When n is optimized to give maximum T c ,α 0 is very small, close to zero and α 0 increases rapidly when n is either less than or greater than the optimum.

Oxygen isotope effect and structural phase transitions in La 2−xM xCuO 4

The 18O/ 16O isotope effect on Tc in La 2−xCa xCuO 4 has been determined and is compared with previous work on the Ba and Sr-doped materials. α o values greater than 0.5 are observed and unusual lattice dynamics at 1/8 hole per Cu are again indicated.

Oxygen isotope effect in LaSrCuO system with T c modified by Ni and Zn doping

The effect of the oxygen isotope substitution on the superconducting transition temperature T c has been studied in La 1.85Sr 0.15Cu 1−xNi xO 4 (x=0; 0.005; 0.01; 0.015; 0.02; 0.025; 0.03), La 1.85Sr 0.15Cu 1−xZn x O 4 (x = 0.0; 0.1) and La 2−xCa xCuO 4 (x = 0.1; 0.08) oxides. The isotope shift exponent α increases with the T c fall down. The results are in a good agreement with the BSC based theory of magnetic pair breaking.

The oxygen isotope effect in Pr, Ca, and Zn substituted YBa 2Cu 3O 7−δ and EuBa 2Cu 3O 7−δ

The oxygen isotope effect α was studied for Pr and Ca substituted YBCO, and for Zn substituted EuBCO and YBCO, α increases to values near 0.5 for the highest Pr concentrations, and lowest transition temperatures. In the Zn substituted system α remains small to the lowest transition temperatures. It is shown that the isotope exponent is a function of mobile hole concentration, it decreases with increasing hole concentration and remains low for over-doping.

Van Hove singularity and isotope effect in high-Tc copper oxides.

Recently it was proposed that a very small oxygen-isotope effect in the high-${\mathit{T}}_{\mathit{c}}$ Cu oxides can be understood in terms of a logarithmic singularity in the density of states, N(E), near the Fermi energy, along with a conventional BCS phonon-mediated pairing. In this paper we show that a relatively realistic N(E), derived from a tight-binding model on two-dimensional lattices, contains a logarithmic term plus a constant term. The calculated result indicates that the additional constant term in N(E) makes the minimum for the isotope-mass exponent \ensuremath{\alpha} well exceed the corresponding experimental value (\ensuremath{\alpha}\ensuremath{\simeq}0--0.2). The interplanar hopping is shown to smear out the sharp peak of N(E) so that \ensuremath{\alpha} shifts further towards the standard BCS value of 1/2. So it appears to us that an explanation of the isotope effect as a function of doping in terms of a Van Hove singularity is not tenable.

Observation of an oxygen isotope effect in superconducting (Y1-xPrx)Ba2Cu3O7- delta.

The oxygen isotope effect was studied in the system (${\mathrm{Y}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Pr}}_{\mathit{x}}$)${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ for x=0.2, 0.3, 0.4, and 0.5. It is found that the oxygen isotope exponent \ensuremath{\alpha} increases with increasing x and therefore decreasing transition temperature ${\mathit{T}}_{\mathit{c}}$. For the highest Pr concentrations \ensuremath{\alpha} tends toward \ensuremath{\alpha}=0.5. The value of the isotope exponent depends on the concentration of mobile holes. The lower this concentration is, the larger becomes the isotope exponent.

Oxygen isotope effect in superconducting Ba1-xKxBiO3 from phonon density of states.

The variation of the phonon spectrum of ${\mathrm{Ba}}_{0.6}$${\mathrm{K}}_{0.4}$${\mathrm{BiO}}_{3}$ upon oxygen isotope substitution is determined by inelastic neutron scattering (INS). By combining the INS results with molecular-dynamics computer simulation, a value of 0.42\ifmmode\pm\else\textpm\fi{}0.05 is obtained for the reference isotope-effect exponent. This is close to the isotope-effect exponent determined from the variation of ${\mathit{T}}_{\mathit{c}}$ upon oxygen substitution, indicating that ${\mathrm{Ba}}_{0.6}$${\mathrm{K}}_{0.4}$${\mathrm{BiO}}_{3}$ is a weak-coupling superconductor with large matrix elements coupling the electrons to high-energy phonons involving oxygen vibrations.

Oxygen isotope effect in superconducting (Y 1−xPr x) Ba 2Cu 3O 7−δ

Oxygen isotope effect studies were performed on the (Y 1−xPr x) Ba 2Cu 3O 7−δ system for 0⩽x⩽0.5. With increasing x, and falling transition temperature, we find a large isotope effect, the coefficient α 0 is approaching 0.5. The results show the importance of the electron-phonon interaction for the superconductivity of these compounds.

Oxygen Isotope Effect and Structural Phase Transitions in La 2 CuO 4 -Based Superconductors

The oxygen isotope effect on the superconducting transition temperature (alpha(o)) varies as a function of x in La2-xSrxCuO(4) and La2-xBaxCuO(4), with the maximum alpha(o) values (alpha(o) >/= 0.5) found for x near 0.12. This unusual x dependence implies that the isotope effect is influenced by proximity to the Abma --> P4(2)/ncm structural phase transition in these systems. Synchrotron x-ray difaction measurements reveal little change in lattice parameters or orthorhombicity due to isotope exchange in strontium-doped materials where alpha(o) > 0.5, eliminating static structural distortion as a cause of the large isotope effects. The anomalous behavior of alpha(o) in both strontium- and barium-doped materials, in combination with the previously discovered Abma --> P4(2)/ncm structural phase-transition in La(1.88)B(0.12)CuO(4), suggests that an electronic contribution to the lattice instability is present and maximizes at approximately 1/8 hole per copper atom. These observations indicate a dose connection between hole doping of the Cu-O sheets, tilting instabilities of the CuO(6) octahedra, and superconductivity in La(2)CuO(4)-based superconductors.

The oxygen isotope effect in superconducting YBa 2Cu 3O 7− δ

We report on measurements of the effect of 18O- 16O substitution on the superconducting properties of Y 1Ba 2Cu 3O 7−δ. Substitutions were made by gas-exchange alone, and by gas exchange in conjunction with substituted BaCO 3 and CuO. From Raman scattering we find that gas-exchange alone leads to lower substitution levels, particularly in the bridging oxygen O(4) position. Gas-exchanged samples give an isotope effect of 0.3 to 0.4 K. Use of substituted materials leads to samples with an isotope effect of up to 0.9 K in the resistance transition and 1.7 K in in the magnetically determinded transition.

Anomalous isotope effect and Van Hove singularity in superconducting Cu oxides.

High-${\mathit{T}}_{\mathit{c}}$ Cu oxides such as ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ and the Bi-Sr-Ca-Cu-O systems are characterized by a near-zero oxygen-isotope effect. Recent results by Crawford et al. show, however, that the isotope effect in the ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$ system depends strongly on the doping level (x) and can significantly exceed the BCS limit. Within the framework of the BCS phonon-mediated pairing, a logarithmic (2D) Van Hove singularity in the density of states can provide a basis for understanding these anomalous isotope effects and possibly the origin of high-temperature superconductivity.

On the oxygen isotope effect and apex anharmonicity in high-T c cuprates

Emphasis is put on aprecise knowledge of the oxygen isotope shift exponent αO is the so far synthesized high-T c superconductors in order to elucidate the basic mechanism. The known data, see α a in Table 6, indicate the presence of a presumably anharmonic coupling of pyramidal apex oxygen motion along thec-axis in these highly in-plane correlated superconductors. α a is computed from αO=rα a , based on the conjecture that the ratior of apex to total oxygen-ion content per unit cell is relevant. The related experimental and theoretical literature is reviewed.

Superconducting and ferroelectric transitions in reduced perovskite-like oxides

Abstract The role of oxygen network leading to quite different transitions such as Z.B. type phase transition and high-Tc superconducting transition in similar perovskite-like (ABO3 -based) oxides is discussed. Furthermore, in the case of superconducting transition, a simple theory is proposed so as to explain high transition temperature Tc and unusual properties on oxygen isotope effect and pressure dependence of Tc.

Solvent dependence of oxygen isotope effects on the decarboxylation of 4-pyridylacetic acid

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSolvent dependence of oxygen isotope effects on the decarboxylation of 4-pyridylacetic acidGeorge W. Headley and Marion H. O'LearyCite this: J. Am. Chem. Soc. 1990, 112, 5, 1894–1896Publication Date (Print):February 1, 1990Publication History Published online1 May 2002Published inissue 1 February 1990https://doi.org/10.1021/ja00161a038RIGHTS & PERMISSIONSArticle Views397Altmetric-Citations19LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (464 KB) Get e-Alerts Get e-Alerts