Experimental Studies of the Isotope Effect in High Temperature Superconductors

Franck, J. P.

doi:10.1142/9789814440981_0004

Cited by 93 publications

(75 citation statements)

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“…By changing the oxygen content, Zech et al (8) observed that ␣ remains rather small at T c Ӎ 61 K and then increases for a further decrease of T c down to Ϸ53 K in YBa 2 Cu 3 O 7Ϫ␦ (0.47 Ͼ ␦ Ͼ 0.01). The gradual increase of ␣ with the dramatic reduction of T c was reported in YBa 2 (Cu 1Ϫx Zn x ) 3 O 7Ϫ␦ (7). As is clearly seen in Fig.…”

Section: [3]supporting

confidence: 66%

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Unified picture of the oxygen isotope effect in cuprate superconductors

Chen

Struzhkin

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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High-temperature superconductivity in cuprates was discovered almost exactly 20 years ago, but a satisfactory theoretical explanation for this phenomenon is still lacking. The isotope effect has played an important role in establishing electron-phonon interaction as the dominant interaction in conventional superconductors. Here we present a unified picture of the oxygen isotope effect in cuprate superconductors based on a phonon-mediated d-wave pairing model within the Bardeen-Cooper-Schrieffer theory. We show that this model accounts for the magnitude of the isotope exponent as functions of the doping level as well as the variation between different cuprate superconductors. The isotope effect on the superconducting transition is also found to resemble the effect of pressure on the transition. These results indicate that the role of phonons should not be overlooked for explaining the superconductivity in cuprates.electron-phonon interaction ͉ high-temperature superconductivity ͉ pressure effect U nderstanding the high-temperature superconductivity in cuprate superconductors is at the heart of current research in solid-state physics. The isotope effect is an important experimental probe in revealing the underlying pairing mechanism of superconductivity. Early measurements (1) of the isotope effect on the superconducting transition temperature, T c , provided key experimental evidence for phonon-mediated pairing and supported strongly the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity in conventional materials. When hightemperature superconductivity was discovered in copper oxides, the oxygen isotope exponents, defined by ␣ ' ϪdlnT c /dlnM, with M being the isotopic mass, were promptly measured. The initial finding of the small value of ␣ in La 1.85 Sr 0.15 CuO 4 (2, 3) and near zero value in YBa 2 Cu 3 O 7Ϫ␦ (␦ ϳ 0) (4-6) was taken to be convincing evidence against electron-phonon interaction as the dominant mechanism in these materials. However, later experiments have revealed a much richer and more complex situation (7). There is a striking variation of ␣ with doping level in a given cuprate material (8-11). Meanwhile, ␣ also varies among various compounds of different cuprate families (7,12). Interestingly, ␣ is a remarkably monotonic function of the number of CuO 2 layers in a way opposite to T c in optimally doped compounds (12). Such elaborate isotope effects strongly suggest that one should include phonons in the theory of high-T c superconductivity. Studies of neutron scattering (13), angleresolved photoemission spectroscopy (14, 15), and scanning transmission electron microscopy (16) provide further evidence for phonons being an important player in the basic physics of high-T c superconductivity.Compared with isotope substitution, pressure has been realized not only to be another effective way to change T c for a superconductor (17) but also to yield information on the interaction causing the superconductivity. So far, the record high T c of 164 K was achieved under high pressure in HgBa 2 C...

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Section: [3]supporting

confidence: 66%

“…There is a striking variation of ␣ with doping level in a given cuprate material (8-11). Meanwhile, ␣ also varies among various compounds of different cuprate families (7,12). Interestingly, ␣ is a remarkably monotonic function of the number of CuO 2 layers in a way opposite to T c in optimally doped compounds (12).…”

mentioning

confidence: 99%

Unified picture of the oxygen isotope effect in cuprate superconductors

Chen

Struzhkin

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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“…A comprehensive review was given by Franck [17]. The role of the anharmonicity of the apical oxygen on the isotope effect was discussed in detail by Müller [18].…”

Section: Isotope Effect On the Superconducting Transition Temperamentioning

confidence: 99%

“…The small OIS observed in the optimally doped cuprates suggest that phonons might not be important in bringing about high temperature superconductivity. However, the doping dependence of the OIS has been extensively studied in different cuprate systems [17,[20][21][22][23][24][25][26][27]. For a particular family of doped cuprates the OIS increases with decreasing T c , and can be even larger than the BCS value.…”

Section: Isotope Effect On the Superconducting Transition Temperamentioning

confidence: 99%

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Unconventional isotope effects in the high-temperature cuprate superconductors

Zhao

Keller

Conder

2001

J. Phys.: Condens. Matter

139

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We review various isotope effects in the high-Tc cuprate superconductors to assess the role of the electron-phonon interaction in the basic physics of these materials. Of particular interest are the unconventional isotope effects on the supercarrier mass, on the charge-stripe formation temperature, on the pseudogap formation temperature, on the EPR linewidth, on the spin-glass freezing temperature, and on the antiferromagnetic ordering temperature. The observed unconventional isotope effects strongly suggest that lattice vibrations play an important role in the microscopic pairing mechanism of high-temperature superconductivity.

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Theory of the Isotope Effect in High-Tc Cuprates

Zeyher¹,

Greco

1999

phys. stat. sol. (b)

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Experimental Studies of the Isotope Effect in High Temperature Superconductors

Cited by 93 publications

References 0 publications

Unified picture of the oxygen isotope effect in cuprate superconductors

Unified picture of the oxygen isotope effect in cuprate superconductors

Unconventional isotope effects in the high-temperature cuprate superconductors

Theory of the Isotope Effect in High-Tc Cuprates

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