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Chmaissem, O.; Eckstein, Y.; Kuper, C.G.

doi:10.1103/physrevb.63.174510

Cited by 36 publications

(29 citation statements)

References 24 publications

(22 reference statements)

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“…For La 1.90 Sr 0.10 CuO 4+y , λ ab (0) = 291 nm (see [37]), γ = 43 (see [55]) and x = 0.1. These parameters lead to T c = 31.8 K, in quantitative agreement with the measured value of 29 K. For the optimally doped YBa 2 Cu 3 O 6.95 with T c = 93 K, λ ab (0) = 1600 Å ( [40]), x = 0.264 (see [39]) and γ = 8 (see [56]), T c is calculated to be 162 K, which is higher than the measured value of 93 K, pointing to the BEC-BCS crossover [32].…”

Section: Acknowledgmentssupporting

confidence: 85%

Isotope effects in high-T_ccuprate superconductors as support for the bipolaron theory of superconductivity

Alexandrov

Zhao

2012

New J. Phys.

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We provide a unified parameter-free explanation of the observed oxygen-isotope effects on the critical temperature, the magnetic-field penetration depth and on the normal-state pseudogap for underdoped cuprate superconductors within the framework of the multi-(bi)polaron theory with strong Coulomb and Fröhlich interactions. We also quantitatively explain the measured critical temperature and the magnitude of the magnetic-field penetration depth. This paper thus represents an important support for the bipolaron theory of high-temperature superconductivity, compatible with many other independent observations. On the long journey towards a microscopic understanding of superconductivity, the observation of an isotope effect on the critical temperature, T c , in 1950 [1,2] provided an important clue to the microscopic mechanism of superconductivity. The presence of an isotope effect thus implies that superconductivity is not of purely electronic origin. In the same year, Fröhlich [3] pointed out that the electron-phonon interaction gave rise to an attractive interaction between electrons, which might be responsible for superconductivity. Fröhlich's theory played a decisive role in establishing the correct mechanism. Finally, in 1957, Bardeen, Cooper and Schrieffer (BCS) [4] developed the BCS theory that was the first successful microscopic theory of superconductivity. The BCS theory implies an isotope-mass dependence of T c , with an isotope-effect exponent α = −d ln T c /d ln M = 1/2, in excellent agreement with the reported isotope exponents in simple metallic superconductors such as Hg, Sn and Pb.The doping-dependent oxygen-isotope effect (OIE) on the critical temperature T c , α O = −d ln T c /d ln M O (where M O is the oxygen-isotope mass) [5] and the substantial OIE on the in-plane supercarrier mass m * * ab , α O m * = dm * * ab /d ln M O [6-11], provide direct evidence for a significant electron-phonon interaction (EPI) also in high-temperature cuprate superconductors. High-resolution angle-resolved photoemission spectroscopy (ARPES) [12] provides further evidence for strong EPI with c-axis-polarized optical phonons [13]. These results, along with optical [14], neutron scattering [15,16] and tunneling data [17][18][19], unambiguously show that lattice vibrations play a significant but unconventional role in high-temperature superconductivity. The interpretation of the optical spectra of high-T c materials as the polaron absorption [20,21] strengthens the view [22] that the Fröhlich EPI is important in those structures. Operating together with a shorter-range deformation potential and molecular-type (e.g. Jahn-Teller [23]) EPIs, the Fröhlich EPI can readily overcome the Coulomb repulsion at a short distance of about the lattice constant for electrons to form real-space inter-site bipolarons [24].Despite all these remarkable and well-performed experiments that lead to the consistent conclusion about the important role of EPI in high-temperature superconductors, there is no consensus on the microscopic origin of ...

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Section: Acknowledgmentssupporting

confidence: 85%

Isotope effects in high-T_ccuprate superconductors as support for the bipolaron theory of superconductivity

Alexandrov

Zhao

2012

New J. Phys.

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“…All compounds are tetragonal, and there is no oxygen chain ordering as in YBCO [4]. The hole concentration in the CuO 2 planes does not depend on x [7,8]. The difference in the unit cell parameters a and c/3 between the two extreme families (x = 0.1 and 0.4) is 1% [4].…”

mentioning

confidence: 99%

Experimental investigation of the origin of the crossover temperature in cuprate superconductors via dc magnetic susceptibility

Lubashevsky

Keren

2008

Phys. Rev. B

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We investigate the cross-over temperature T * as a function of doping in (CaxLa1−x)(Ba1.75−xLa0.25+x)Cu3Oy, where the maximum Tc (T max c ) varies continuously by 30% between families (x) with minimal structural changes. T * is determined by DC-susceptibility measurements. We find that T * scales with the maximum Néel temperature T max N of each family. This result strongly supports a magnetic origin of T * , and indicates that three dimensional interactions play a role in its magnitude.PACS numbers: 74.25. Dw,74.25.Ha, Free electrons do not have high temperature crossovers such as a pseudogap (PG), spin gap (SG), or development of antiferromagnetic (AFM) correlations. In the cuprates all of these exist, yet the interactions that lead to them are not completely clear. Nevertheless, the crossovers occur at a temperature T * which is much higher than T c , and closer to the three dimensional (3D) ordering temperature of the parent compound in the AFM state. Therefore, it is speculated that T * emerges from AFM fluctuations, and that the cross-overs are intimately linked, namely, the interaction responsible for one might be responsible for all [1,2,3]. Therefore, it is crucial to test the possibility of correlations between T ⋆ of a particular system and its magnetic properties, such as the Néel temperature T N of the parent compound, or its constituents, the in-and out-of-plane Heisenberg coupling constant J and J ⊥ , respectively. This is the motivation of the work presented here. We provide experimental evidence that strongly supports a magnetic origin for T * . Moreover, we show that T * stems from 3D interactions, similar to the Néel order, involving both J and J ⊥ .We investigate the origin of the T ⋆ by studying its variations as a function of the compound's magnetic properties, where small chemical changes are an implicit parameter. The variations in the magnetic properties are achieved by using four different families of the (Ca x La 1−x )(Ba 1.75−x La 0.25+x )Cu 3 O y (CLBLCO) system, having the YBa 2 Cu 3 O y (YBCO) structure, with x = 0.1 . . . 0.4. The phase diagram of the CLBLCO families is shown in Fig. 1(a). T c was measured by resistivity [4], and the spin glass temperature T g [5] and T N [6] by muon spin relaxation. Despite the rich phase diagram, the different CLBLCO families have negligible structural differences. All compounds are tetragonal, and there is no oxygen chain ordering as in YBCO [4]. The hole concentration in the CuO 2 planes does not depend on x [7,8]. The difference in the unit cell parameters a and c/3 between the two extreme families (x = 0.1 and 0.4) is 1% [4]. Thus, variations in T max c due to variations in ionic radii are not relevant [9]. The level of disorder, as detected by Cu and Ca nuclear magnetic resonance, is also identical for the different families [8,10]. In fact, the only strong variation between families noticed at present is the in-plane oxygen buckling angle [11]. This property can modify the intraplane near-and next-nearneighbors hopping, or interplane hoppi...

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“…The nominal valence of Fe is also calculated by the charge balance from the chemical composition, as listed in Tables 2 and 3. In the cuprate superconductors, the T c value is closely related to the valence of Cu [15]. The results of…”

Section: Resultsmentioning

confidence: 87%

Enhanced superconductivity of SmFeAsO co-doped by Scandium and Fluorine to increase chemical inner pressure

Chen¹,

Zheng²,

Fang³

et al. 2012

Journal of Solid State Chemistry

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Structure and a bond-valence-sum study of the 1-2-3 superconductors(CaxLa1−x

Cited by 36 publications

References 24 publications

Isotope effects in high-T_ccuprate superconductors as support for the bipolaron theory of superconductivity

Isotope effects in high-T_ccuprate superconductors as support for the bipolaron theory of superconductivity

Experimental investigation of the origin of the crossover temperature in cuprate superconductors via dc magnetic susceptibility

Enhanced superconductivity of SmFeAsO co-doped by Scandium and Fluorine to increase chemical inner pressure

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Structure and a bond-valence-sum study of the 1-2-3 superconductors(CaxLa1−x

Cited by 36 publications

References 24 publications

Isotope effects in high-Tccuprate superconductors as support for the bipolaron theory of superconductivity

Isotope effects in high-Tccuprate superconductors as support for the bipolaron theory of superconductivity

Experimental investigation of the origin of the crossover temperature in cuprate superconductors via dc magnetic susceptibility

Enhanced superconductivity of SmFeAsO co-doped by Scandium and Fluorine to increase chemical inner pressure

Contact Info

Product

Resources

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Isotope effects in high-T_ccuprate superconductors as support for the bipolaron theory of superconductivity

Isotope effects in high-T_ccuprate superconductors as support for the bipolaron theory of superconductivity