Absence of an Isotope Effect in the Pseudogap in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>YBa</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>Cu</mml:mi></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>O</mml:mi></mml:mrow><mml:mrow><mml:mn>8</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>as Determined b

Williams, G. V. M.; Tallon, J. L.; Quilty, J. W.; Trodahl, H. J.; Flower, N.E.

doi:10.1103/physrevlett.80.377

Cited by 91 publications

(66 citation statements)

References 26 publications

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“…We have shown previously [13,17] that the isotope effect in T c across the entire phase diagram is consistent with an underlying exponent (in the absence of scattering and pseudogap) of α(T c0 ) ≈ 0.06. The red line in Fig.…”

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confidence: 77%

“…Surprisingly, an isotope effect was also found in the superfluid density [14] (and attempts were made to resolve this into a dominant isotope effect just in m * [15,16]). We will show that both of these unusual effects can be understood in terms of a normal-state pseudogap which competes with SC [17]. We also predict and confirm an isotope effect in ρ s induced by impurity scattering.…”

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confidence: 80%

“…First, we recall that there is no isotope effect in the pseudogap. We have examined the 89 Y Knight shift in YBa 2 Cu 4 O 8 using magic angle spinning with extremely narrow linewidths (≈100 Hz) and found no isotope effect within the bounds α(E g ) ≤ 0.01 [17]. Though not essential, we proceed under the assumption that an isotope effect is confined to the pairing gap, ∆ 0 , and absent from the pseudogap, E g .…”

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Isotope Effect in the Superfluid Density of High-Temperature Superconducting Cuprates: Stripes, Pseudogap, and Impurities

et al. 2005

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Underdoped cuprates exhibit a normal-state pseudogap, and their spins and doped carriers tend to spatially separate into 1-or 2-D stripes. Some view these as central to superconductivity, others as peripheral and merely competing. Using La2−xSrxCu1−yZnyO4 we show that an oxygen isotope effect in Tc and in the superfluid density can be used to distinguish between the roles of stripes and pseudogap and also to detect the presence of impurity scattering. We conclude that stripes and pseudogap are distinct, and both compete and coexist with superconductivity.PACS numbers: 71.10. Hf, 74.25.Dw, 74.62.Dh, 74.72.Dn High-T c superconductors (HTS) remain a puzzle. Various correlated states have been identified in HTS including antiferromagnetism, the pseudogap[1], nanoscale spin-charge stripes [2] and, of course, superconductivity (SC). (Here we generalise"stripes" to include possible 2D checkerboard structures [3]). The pseudogap is a nodal energy gap of uncertain origin that appears in the normal-state (NS) density of states (DOS). Its effects can be observed in many physical properties [1,4]. Several opposing views are still current. One is that stripes play a central role [5], forming the pseudogap correlation [6] and/or mediating the SC pairing. Another is that the NS pseudogap arises from incoherent superconducting fluctuations which set in well above T c [7]. Another is that these states are independently competing [8]. Here stripes and pseudogap play a secondary role and SC is mediated by some other pairing boson. An unambiguous test of these opposing views is urgently needed. We show here that isotope effects provide such a test.The isotope exponent α(E) in a given property E is defined as α(E) = − (∆E/E)/(∆M/M ), where M is the isotopic mass and E may be T c , the SC gap parameter, ∆ 0 , the pseudogap energy scale, E g , or the superfluid density ρ s = λ −2 ab = µ 0 e 2 (n s /m * ab ). (λ ab is the in-plane London penetration depth, n s is the carrier density and m * ab is the effective electronic mass for in-plane transport). An isotope effect on T c was first discovered in 1950 by Allen et al. for Sn [9]. They found α(T c ) ≈ 0.5 ± 0.05 which provided the central clue for the role of phonons in pairing and led 7 years later to the BCS theory of SC [10].The situation with HTS is more complex. The oxygen isotope effect on T c was found[11] to be small, with α(T c ) ≈ 0.06. However, with decreasing doping the effect rises and eventually diverges as T c → 0[12, 13]. Surprisingly, an isotope effect was also found in the superfluid density [14] (and attempts were made to resolve this into a dominant isotope effect just in m * [15,16]). We will show that both of these unusual effects can be understood in terms of a normal-state pseudogap which competes with SC [17]. We also predict and confirm an isotope effect in ρ s induced by impurity scattering. The isotope effects in T c and ρ s are mapped as a function of doping in La 2−x Sr x Cu 1−y Zn y O 4 and we observe a canonical pseudogap behavior as well as a huge an...

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Isotope Effect in the Superfluid Density of High-Temperature Superconducting Cuprates: Stripes, Pseudogap, and Impurities

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“…According to many researchers, HTSC can be explained by a purely electronic model, such as that described by the t − J or the Hubbard Hamiltonians, for which charge and/or spin interactions are paramount. This view is essentially based on the absence of isotope effects seen in some experiments [7] and the apparent d-symmetry of the superconducting wavefunction. However, accumulating experimental evidence exists for electronlattice effects in high temperature superconductors [8,10,11], and theories based on electron-phonon interactions have also been proposed [2,3,4,5].…”

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confidence: 99%

Dynamical two electron states in a Hubbard-Davydov model

et al. 2004

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We study a model in which a Hubbard Hamiltonian is coupled to the dispersive phonons in a classical nonlinear lattice. Our calculations are restricted to the case where we have only two quasi-particles of opposite spins, and we investigate the dynamics when the second quasi-particle is added to a state corresponding to a minimal energy single quasi-particle state. Depending on the parameter values, we find a number of interesting regimes. In many of these, discrete breathers (DBs) play a prominent role with a localized lattice mode coupled to the quasiparticles. Simulations with a purely harmonic lattice show much weaker localization effects. Our results support the possibility that DBs are important in HTSC.

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“…Currently there are two main different proposals to explain the existence of the pseudogap: In the first one, the pseudogap is regarded as a normal state precursor of the superconducting gap due to local dynamic pairing correlations in a state without long range phase coherence, and T c is much smaller than T * because of strong phase fluctuations 14,15 . In the second proposal, the pseudogap is a normal state gap, which is necessarily independent of the superconducting gap and which competes with the superconductivity, existing even below T c for compounds around the optimum doping, ending in a quantum critical point [16][17][18] at zero temperature.…”

Section: Introductionmentioning

confidence: 99%

Theory for high-Tcsuperconductors considering inhomogeneous charge distribution

2003

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We propose a general theory for the critical and pseudogap temperatures Tc and T * dependence on the doping concentration for high-Tc oxides, taking into account the charge inhomogeneities in the CuO2 planes. Several recent experiments have revealed that the charge density ρ in a given compound (mostly underdoped) is intrinsic inhomogeneous with large spatial variations which leads to a local charge density ρ(r). These differences in the local charge concentration yield insulator and metallic regions, either in an intrinsic granular or in a stripe morphology. In the metallic region, the inhomogeneous charge density produces also spatial or local distributions which form Cooper pairs at a local superconducting critical temperatures Tc(r) and zero temperature gap ∆0(r). For a given compound, the measured onset of vanishing gap temperature is identified as the pseudogap temperature, that is, T * , which is the maximum of all Tc(r). Below T * , due to the distribution of Tc(r)'s, there are some superconducting regions surrounded by insulator or metallic medium. The transition to a coherent superconducting state corresponds to the percolation threshold among the superconducting regions with different Tc(r)'s. The charge inhomogeneities have been studied by recent STM/S experiments which provided a model for our phenomenological distribution. To make definite calculations and compare with the experimental results, we derive phase diagrams for the BSCO, LSCO and YBCO families, with a mean field theory for superconductivity using an extended Hubbard Hamiltonian. We show also that this novel approach provides new insights on several experimental features of high-Tc oxides.

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Absence of an Isotope Effect in the Pseudogap inYBa2Cu4O8as Determined b

Cited by 91 publications

References 26 publications

Isotope Effect in the Superfluid Density of High-Temperature Superconducting Cuprates: Stripes, Pseudogap, and Impurities

Isotope Effect in the Superfluid Density of High-Temperature Superconducting Cuprates: Stripes, Pseudogap, and Impurities

Dynamical two electron states in a Hubbard-Davydov model

Theory for high-Tcsuperconductors considering inhomogeneous charge distribution

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