Thermoelectric power measurements of YBa2Cu3O7?? up to 950�C and their application to test the band structure near EF

Fisher, B.; Genossar, J.; Lelong, I.O.; Kessel, Aharon; Ashkenazi, J.

doi:10.1007/bf00617951

Cited by 51 publications

(19 citation statements)

References 18 publications

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“…This is similar to the case of a previous study in which Fisher et al. found that the transport coefficients of the YBa 2 Cu 3 O 7 − δ cuprate superconductor were corresponding to a narrow conduction band of about 0.1 eV . Furthermore, in the BPBO SCR, there also exists a high‐energy gap near the energy range of approximately 0.5 eV (relative to the Fermi level) and above.…”

Section: Resultssupporting

confidence: 90%

“…44 This is similar to the case of a previous study in which Fisher et al found that the transport coefficients of the YBa 2 Cu 3 O 7Àd cuprate superconductor were corresponding to a narrow conduction band of about 0.1 eV. [45][46][47][48] Furthermore, in the BPBO SCR, there also exists a highenergy gap near the energy range of approximately 0.5 eV (relative to the Fermi level) and above. Interestingly, when the Bi content in the SCR increases, the high-energy gap increases and reaches the maximum value of approximately 3 eV at x Bi =0.…”

Section: Energetics and Phase Stabilitysupporting

confidence: 85%

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Phase stability, electronic structures, and superconductivity properties of the BaPb_1−xBi_xO₃ and Ba_1−xK_xBiO₃ perovskites

et al. 2016

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Abstact With extensive first‐principles calculations, we investigate the phase stability, electronic structures, and superconductivity properties of the BaPb1−xBixO3 (BPBO) and Ba1−xKxBiO3 (BKBO) perovskites with the cubic (C), tetragonal (T), and orthorhombic (O) phases. Our calculations show that the tetragonal superconducting phases of both perovskites are metastable. However, the orthorhombic phase of the BPBO perovskite in the superconductivity region is only slightly more stable than the tetragonal phase. The small energy difference between the T and O phases and the discontinuous T‐to‐O phase transition account for the experimentally observed coexistence of the T and O phases. On the other hand, the BKBO perovskite involves a large energy difference between the T and O phases, which induces a low equilibrium temperature of the discontinuous T‐to‐O phase transition, in agreement with the experimental observation that the tetragonal BKBO is maintained down to low temperatures. Moreover, the electronic structures of both BPBO and BKBO superconductors show a flat band near the Fermi level, which is favorable for superconductivity. Furthermore, we find that the longer the total length of the flat band segment is, the higher the critical temperature of the BPBO or BKBO perovskite is. This key finding could be generalized straightforwardly to other unconventional superconductors and can be used to design and find optimal composition with maximum Tc for new unconventional superconductors.

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Section: Resultssupporting

confidence: 90%

Section: Energetics and Phase Stabilitysupporting

confidence: 85%

Phase stability, electronic structures, and superconductivity properties of the BaPb_1−xBi_xO₃ and Ba_1−xK_xBiO₃ perovskites

et al. 2016

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“…In order to separate the effect of doping on the density of states and the carriers density we introduceρ The results for S [ Fig. 1(a)] reproduce very well the systematic TEP behavior, which is characteristic of the doping level [13][14][15] (determined here mainly through n p ). The position of the maximum in S depends on the choice of ω p .…”

mentioning

confidence: 75%

“…The ω dependencies (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) derived in the auxiliary space remain valid in the physical space, both for the coherent bands, and for the incoherent background, detected, e.g., in ARPES results. The present results for Γ q (13) are reflected in the observed non-Fermi-liquid bandwidths, having a ∝ ω and a constant term.…”

mentioning

confidence: 92%

Stripe fluctuations, carriers, spectroscopies, transport, and BCS–BEC crossover in the high-Tc cuprates

Ashkenazi

2002

Journal of Physics and Chemistry of Solids

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Abstract-The quasiparticles of the high-Tc cuprates are found to consist of: polaronlike "stripons" carrying charge, and associated primarily with large-U orbitals in stripe-like inhomogeneities; "quasi-electrons" carrying charge and spin, and associated with hybridized small-U and large-U orbitals; and "svivons" carrying spin and lattice distortion. It is shown that this electronic structure leads to the systematic behavior of spectroscopic and transport properties of the cuprates. High-Tc pairing results from transitions between pair states of stripons and quasi-electrons through the exchange of svivons. The cuprates fall in the regime of crossover between BCS and preformed-pairs Bose-Einstein condensation behaviors.First-principles calculations in the cuprates support an approach based on the existence of both "large-U " and "small-U " orbitals in the vicinity of the Fermi level (E F ). Let us denote the fermion creation operator of a small-U electron in band ν, spin σ (which can be assigned a number ±1), and wave vector k by c † νσ (k). The large-U orbitals in the CuO 2 planes are approached through the "slavefermion" method [1]. A large-U electron in site i and spin σ is then created by d † iσ = e † i s i,−σ , if it is in the "upper-Hubbard-band", and by dif it is in a Zhang-Rice-type "lower-Hubbard-band". Here e i and h i are ("excession" and "holon") fermion operators, and s iσ are ("spinon") boson operators. These auxiliary particles have to satisfy the constraint:Within the "auxiliary space" a chemicalpotential-like Lagrange multiplier is introduced to impose the constraint on the average. Physical observables are calculated as combinations of Green's functions of the auxiliary space. Since the time evolution of Green's functions is determined by the Hamiltonian which obeys the constraint rigorously, it is not expected to be violated as long as the approximations used for these Green's functions are justifiable.The spinon states are diagonalized by applying the Bogoliubov transformation [2]:The Bose operators ζ † σ (k) create spinon states of "bare" energies ǫ ζ (k) which have a V-shape zero minimum at k = k 0 . Bose condensation results in antiferromagnetic (AF) order at wave vector

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“…This result is consistent with the typical behavior of the TEP in the cuprates, and has been [15] parametrized as: S = AT + BT α /(T + Θ) α . It was found [16,17] that S p = 0 (namely the stripon band is half full) for slightly overdoped cuprates.…”

Section: Transport Propertiesmentioning

confidence: 99%

Stripes, carriers, and high-T[sub c] in the cuprates

Ashkenazi¹

1999

AIP Conference Proceedings

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Abstract. Considering both "large-U " and "small-U " orbitals it is found that the high-T c cuprates are characterized by a striped structure, and three types of carriers: polaron-like "stripons" carrying charge, "quasielectrons" carrying charge and spin, and "svivons" carrying spin and lattice distortion. It is shown that this electronic structure leads to the anomalous physical properties of the cuprates, and specifically the systematic behavior of the resistivity, Hall constant, and thermoelectric power. High-T c pairing results from transitions between pair states of quasielectrons and stripons through the exchange of svivons. A pseudogap phase occurs when pairing takes place above the temperature where stripons become coherent, and this temperature determines the Uemura limit. INTRODUCTIONThe existence of static stripes in the CuO 2 planes has been observed in some superconducting cuprates [1,2], and there is growing evidence on the existence of dynamic stripes in others [3]. Many experimental observations have been pointing to the presence of both itinerant and almost localized (or polaron-like) carriers in these materials.Though one-band theoretical models have been quite popular, and easier to treat, first-principles calculations [4] indicate that such models are probably oversimplified. Here an approach is proposed to the cuprates, taking into account the existence of both "large-U" and "small-U" orbitals in the vicinity of the Fermi level (E F ). AUXILIARY PARTICLESThe large-U orbitals are treated using the "slave-fermion" method [5]. An electron of these orbitals at site i and of spin σ is then created by d † iσ = e † i s i,−σ , if it is in the "upper-Hubbard-band", and by d ′ † iσ = σs † iσ h i , if it is in a Zhang-Rice-type

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Thermoelectric power measurements of YBa2Cu3O7?? up to 950�C and their application to test the band structure near EF

Cited by 51 publications

References 18 publications

Phase stability, electronic structures, and superconductivity properties of the BaPb_1−xBi_xO₃ and Ba_1−xK_xBiO₃ perovskites

Phase stability, electronic structures, and superconductivity properties of the BaPb_1−xBi_xO₃ and Ba_1−xK_xBiO₃ perovskites

Stripe fluctuations, carriers, spectroscopies, transport, and BCS–BEC crossover in the high-Tc cuprates

Stripes, carriers, and high-T[sub c] in the cuprates

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Thermoelectric power measurements of YBa2Cu3O7?? up to 950�C and their application to test the band structure near EF

Cited by 51 publications

References 18 publications

Phase stability, electronic structures, and superconductivity properties of the BaPb1−xBixO3 and Ba1−xKxBiO3 perovskites

Phase stability, electronic structures, and superconductivity properties of the BaPb1−xBixO3 and Ba1−xKxBiO3 perovskites

Stripe fluctuations, carriers, spectroscopies, transport, and BCS–BEC crossover in the high-Tc cuprates

Stripes, carriers, and high-T[sub c] in the cuprates

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Product

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Phase stability, electronic structures, and superconductivity properties of the BaPb_1−xBi_xO₃ and Ba_1−xK_xBiO₃ perovskites

Phase stability, electronic structures, and superconductivity properties of the BaPb_1−xBi_xO₃ and Ba_1−xK_xBiO₃ perovskites