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Journal Articles

Magnetic excitations in overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$

Wakimoto, Shuichi; Yamada, Kazuyoshi*; Tranquada, J. M.*; Frost, C. D.*; Swainson, I.*; Birgeneau, R. J.*

Physica C, 460-462(1), p.166 - 169, 2007/09

 Times Cited Count:1 Percentile:7.1(Physics, Applied)

Spin excitations of overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$ ($$0.25 leq x leq 0.30$$) have been studied by neutron scattering utilizing triple-axis and time-of-flight spectrometers. Low-energy excitation spectra ($$omega leq 10$$ $$sim$$meV) for all of the superconducting samples show a maximum around $$omega = 6$$ meV with a maximum value of dynamic spin susceptibility $$chi''(omega)$$ that decreases linearly with ${it T$_{rm c}$}$ as doping increases. The magnetic scattering cross section finally disappears at $$x=0.30$$, coincident with the disappearance of bulk superconductivity. Time-of-flight measurements for $$x=0.25$$ and $$0.30$$ shows markedly suppressed magnetic scattering intensities at intermediate energies (20$$leq$$$$omega$$$$leq$$80$$sim$$meV) in contrast to those of the stripe-ordered La$$_{1.875}$$Ba$$_{0.125}$$CuO$$_{4}$$. These facts imply a cooperative correlation between the dynamic incommensurate state and the superconductivity.

Journal Articles

Magnetic properties of the overdoped superconductor La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$ with and without Zn impurities

Wakimoto, Shuichi; Birgeneau, R. J.*; Kagedan, A.*; Kim, H.-K.*; Swainson, I.*; Yamada, Kazuyoshi*; Zhang, H.*

Physical Review B, 72(6), p.064521_1 - 064521_9, 2005/08

 Times Cited Count:27 Percentile:71.83(Materials Science, Multidisciplinary)

The magnetic properties of the Zn-substituted overdoped high-$$T_c$$ superconductor La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$ (LSCO) have been studied by magnetization measurements and neutron scattering. Magnetization measurements reveal that for Zn-free samples with $$x geq 0.22$$ a Curie term is induced implying the existence of local paramagnetic moments. A comparison of the Curie behaviour between Zn-doped and Zn-free samples signifies a general competitive relationship between the superconductivity and the induced paramagnetic moment. Neutron scattering measurements show that Zn-substitution in overdoped LSCO anomalously enhances the inelastic magnetic scattering spectra around the $$(pi, pi)$$ position, peaking at $$omega sim 7$$meV. These facts are discussed on the basis of a "swiss-cheese" model of Zn-substituted systems as well as a microscopic phase separation scenario in the overdoped region indicated by muon-spin-relaxation measurements.

Oral presentation

Spin Excitations of overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$

Wakimoto, Shuichi; Birgeneau, R. J.*; Frost, C. D.*; Kagedan, A.*; Kim, H.*; Swainson, I.*; Tranquada, J. M.*; Yamada, Kazuyoshi*; Zhang, H.*

no journal, , 

Spin excitations of LSCO in the overdoped regime has been studied by neutron scattering. Incommensurate excitations around 6 meV which are clearly observed in the $$x=0.25$$ sample decrease with $$T_c$$ as doping increases, and finally, become unobservable at $$x=0.30$$ coincidentally with the disappearance of bulk superconductivity. High-energy measurements performed at the MAPS spectrometer show remarkably weakened magnetic excitations of the overdoped samples also in the high energy region. These observations are apparently consistent with a microscopic phase separation of the overdoped samples into the superconducting and Fermi liquid phases based on muSR results. In contrast, magnetization measurements of overdoped LSCO with and without Zn impurities have revealed that the superconductivity vanishes in the overdoped regime as a result of a competition between the superconductivity and paramagnetism which is induced even in the Zn-free overdoped LSCO.

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