Doping dependence of superconducting parameters in HgBa2CuO4+δ single crystals

Hofer, J.; Karpiński, J.; Willemin, M.; Meijer, G. I.; Kopnin, E.M.; Molinski, R.; Schwer, H.; Rossel, C.; Keller, H.

doi:10.1016/s0921-4534(97)01855-8

Cited by 74 publications

(73 citation statements)

References 38 publications

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“…Similar behavior in the other overdoped cuprates have been found by subsequent µSR measurements in YBCO with (Y,Ca) substitution [75] and in CaLaBaCuO [31], and torque measurements of Hg1201 [76]. Other signatures of this anomaly include the un-gapped response in optical conductivity [77] in optimal to overdoped YBCO, and the recombination time of photo-induced anti-nodal quasiparticles which becomes independent of laser excitation power in the overdoped region of Bi2212 [78].…”

Section: Phase Separation In the Overdoped Regionsupporting

confidence: 77%

Condensation, excitation, pairing, and superfluid density in high-T_c superconductors: the magnetic resonance mode as a roton analogue and a possible spin-mediated pairing

Uemura¹

2004

J. Phys.: Condens. Matter

100

123

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To find out a primary determing factor of Tc and a pairing mechanism in high-Tc cuprates, we combine the muon spin relaxation results on ns/m * (superconducting carrier density / effective mass), accumulated over the last 15 years, with the results from neutron and Raman scattering, STM, specific heat, Nernst effect and ARPES measurements. We identify the neutron magnetic resonance mode as an analogue of roton minimum in the superfluid 4 He, and argue that ns/m * and the resonance mode energy ωres play a primary role in determining Tc in the underdoped region. We propose a picture that roton-like excitations in the cuprates appear as a coupled mode, which has the resonance mode for spin and charge responses at different momentum transfers but the same energy transfers, as detected respectively, by the neutron S=1 mode and the Raman S=0 A1g mode. We shall call this as the "hybrid spin/charge roton". After discussing the role of dimensionality in condensation, we propose a generic phase diagram of the cuprates with spatial phase separation in the overdoped region as a special case of the BE-BCS crossover conjecture where the superconducting coupling is lost rapidly in the overdoped region. Using a microscopic model of charge motion resonating with antiferomagnetic spin fluctuations, we propose a possibility that the hybrid spin/charge roton and higher-energy spin fluctuations mediate the superconducting pairing. In this model, the resonance modes can be viewed as a meson-analogue and the "dome" shape of the phase diagram can be understood as a natural consequence of departure from the competing Mott insulator ground state via carrier doping.

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Section: Phase Separation In the Overdoped Regionsupporting

confidence: 77%

Condensation, excitation, pairing, and superfluid density in high-T_c superconductors: the magnetic resonance mode as a roton analogue and a possible spin-mediated pairing

Uemura¹

2004

J. Phys.: Condens. Matter

100

123

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“…As shown in Fig.1 for La 2−x Sr x CuO 4 the effective mass anisotropy, measured in terms of γ = M c /M ab increases drastically by approaching the underdoped limit. This property, also observed in HgBa 2 CuO 4+δ [20] and YBa 2 Cu 3 O 7−x [22], appears to be generic and reveals the crossover from three (3D) to two dimensional (2D) behavior.In our considerations the starting point is the critical endpoint of the phase transition line T c (x), where at T = 0 and x = x u , driven by variation of the dopant concentration x, the QSI transition occurs. Close to this critical endpoint the bulk superconductors correspond to a stack of independent superconducting slabs of thickness d s .…”

mentioning

confidence: 62%

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confidence: 62%

Isotope Effects in Underdoped Cuprate Superconductors: A Quantum Critical Phenomenon

Schneider

Keller

2001

Phys. Rev. Lett.

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We show that the unusual doping dependence of the isotope effects on transition temperature and zero temperature in -plane penetration depth naturally follows from the doping driven 3D-2D crossover, the 2D quantum superconductor to insulator transition (QSI) in the underdoped limit and the change of the relative doping concentration upon isotope substitution. Close to the QSI transition both, the isotope coefficient of transition temperature and penetration depth approach the coefficient of the relative dopant concentration, and its divergence sets the scale. These predictions are fully consistent with the experimental data and imply that close to the underdoped limit the unusual isotope effect on transition temperature and penetration depth uncovers critical phenomena associated with the quantum superconductor to insulator transition in two dimensions. PACS numbers: 74.20. Mn, 74.25Dw, The observation of an unusual isotope effect in underdoped cuprate superconductors on transition temperature [1][2][3] and zero temperature penetration depth [4][5][6][7] poses a challenge to the understanding of high temperature superconductivity. In this letter we show that this behavior naturally follows from the doping driven 3D-2D crossover, the 2D superconductor to insulator (QSI) transition in the underdoped limit and the change of the relative doping concentration upon isotope substitution. Thus, the unusual isotope effect on superconducting properties of underdoped cuprates is derived to be a quantum critical phenomenon driven by variation of the dopant concentration.Consider [23], only the underdoped and optimally doped regimes appear to be accessible. As shown in Fig.1 for La 2−x Sr x CuO 4 the effective mass anisotropy, measured in terms of γ = M c /M ab increases drastically by approaching the underdoped limit. This property, also observed in HgBa 2 CuO 4+δ [20] and YBa 2 Cu 3 O 7−x [22], appears to be generic and reveals the crossover from three (3D) to two dimensional (2D) behavior.In our considerations the starting point is the critical endpoint of the phase transition line T c (x), where at T = 0 and x = x u , driven by variation of the dopant concentration x, the QSI transition occurs. Close to this critical endpoint the bulk superconductors correspond to a stack of independent superconducting slabs of thickness d s . Moreover, close to such a critical point, low energy properties depend only on the spatial dimensionality of the system, the number of components of the order parameter and the range of the interaction. The theory of quantum critical phenomena predicts that the transition temperature and zero temperature in -plane penetration depth scale as [24,17,18] z is the dynamic critical exponent, ν the exponent of the diverging length, a and b nonuniversal critical amplitudes, andmeasures the distance from the quantum critical point at x u , where in cuprate superconductors the QSI transition occurs. For a complex scalar order parameter and in D=2 the critical amplitudes a and b and the slab thickness d s ...

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“…These terms are mainly responsible for the breakdown of the Wiedemann-Franz law in the bipolaronic system. It has been shown that the bipolaron model fits nicely the temperature dependencies of the in-plane [32] and out-of-plane [33] resistivities and the Hall ratio in the cuprates. Here we show that it also fits the Hall Lorenz number measured by Zhang et al [30].…”

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confidence: 86%

Lorenz Number in HighTcSuperconductors: Evidence for Bipolarons

2003

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Strong electron-phonon interaction in the cuprates has gathered support over the last decade in a number of experiments. While phonons remain almost unrenormalised, electrons are transformed into itinerent bipolarons and thermally excited polarons when the electron-phonon interaction is strong. We calculate the Lorenz number of the system to show that the Wiedemann-Franz law breaks down because of the interference of polaron and bipolaron contributions in the heat flow. The model fits numerically the experimental Hall Lorenz number, which provides a direct evidence for bipolarons in the cuprates.The discovery of high-temperature superconductors [1,2] has broken constraints on the maximum T c predicted by the conventional theory of low-temperature superconducting metals and alloys. Understanding the pairing mechanism of carriers and the nature of the normal state in the cuprates and other novel superconductors has been a challenging problem of the Condensed Matter Physics. A number of theoretical models have been proposed, which rely on different non-phononic mechanisms of pairing (see, for example [3,4]). On the other hand, over the last decade, increasing evidence for the electron-phonon interaction has been provided by isotope effect measurements [5], infrared [6,7,8] and thermal conductivity [9], neutron scattering [10], and more recently by ARPES [11,12].To account for the high values of T c in the cuprates, one has to consider electron-phonon (e-ph) interactions, which are larger than those used in the intermediate coupling theory of superconductivity [13]. Regardless of the adiabatic ratio, the Migdal-Eliashberg theory of superconductivity and the Fermi-liquid have been shown to breakdown at the e-ph coupling constant λ ≈ 1 [14]. The many-electron system collapses into the small (bi)polaron regime at λ 1 with well separated vibration and chargecarrier degrees of freedom. Although it might have been thought that these carriers would have a mass too large to be mobile, the inclusion of the on-site Coulomb repulsion and the poor screening of the long-range e-ph interaction do lead to mobile intersite bipolarons [15,16]. Above T c the Bose gas of these bipolarons is non-degenerate and below T c their phase coherence sets in and superfluidity of the doubly-charged 2e bosons can occur. In this picture, the thermally excited single polarons co-exist with the Bose gas.There is much evidence for the crossover regime at T * and normal state charge and spin gaps in the cuprates [17]. These energy gaps could be understood as being half of the binding energy ∆ and the singlet-triplet gap of preformed bipolarons, respectively [18]. Many other experimental observations were explained using the bipolaron model [19]. These include the Hall ratio, the Hall angle, ab and c-axis resistivities, magnetic susceptibility, and angle-resolved photoemission. The bipolaron model provides parameter-free fits of critical temperatures, upper critical fields, explains a remarkable increase of the quasiparticle lifetime below T c [21], an...

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Doping dependence of superconducting parameters in HgBa2CuO4+δ single crystals

Cited by 74 publications

References 38 publications

Condensation, excitation, pairing, and superfluid density in high-T_c superconductors: the magnetic resonance mode as a roton analogue and a possible spin-mediated pairing

Condensation, excitation, pairing, and superfluid density in high-T_c superconductors: the magnetic resonance mode as a roton analogue and a possible spin-mediated pairing

Isotope Effects in Underdoped Cuprate Superconductors: A Quantum Critical Phenomenon

Lorenz Number in HighTcSuperconductors: Evidence for Bipolarons

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Doping dependence of superconducting parameters in HgBa2CuO4+δ single crystals

Cited by 74 publications

References 38 publications

Condensation, excitation, pairing, and superfluid density in high-Tc superconductors: the magnetic resonance mode as a roton analogue and a possible spin-mediated pairing

Condensation, excitation, pairing, and superfluid density in high-Tc superconductors: the magnetic resonance mode as a roton analogue and a possible spin-mediated pairing

Isotope Effects in Underdoped Cuprate Superconductors: A Quantum Critical Phenomenon

Lorenz Number in HighTcSuperconductors: Evidence for Bipolarons

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Condensation, excitation, pairing, and superfluid density in high-T_c superconductors: the magnetic resonance mode as a roton analogue and a possible spin-mediated pairing

Condensation, excitation, pairing, and superfluid density in high-T_c superconductors: the magnetic resonance mode as a roton analogue and a possible spin-mediated pairing