Photoinduced absorption from localized intra-gap states

A model is developed for photoinduced absorption from localized states observed in femtosecond pump-probe experiments in high-Tc superconductors and other materials. The dynamics of localized carriers are described in terms of phenomenological approach similar to that originaly proposed by Rothwarf and Taylor. Expanding the relaxation rate in powers of the order parameter we have shown that density of localized carriers is sensitive to Tc. From the analysis of the experimental data on YBa2Cu3O(7-x) and K0.3MoO3 we conclude that significant intra-gap density of localized states exists in these materials. Temperature dependence of the density of photoexcited localized carriers in underdoped YBa2Cu3O(7-x) and in K0.3MoO3 is consistent with the observation of the pseudogap above Tc.Comment: 4 pages, 2 figures, acepted for publication in Physica C, invited poster presented at M2S, Feb. 20 - 25, 2000, Houston, US

Low-temperature proximity effect in clean metals with repulsive electron-electron interaction

Theories of proximity effect in layered superconductor–normal-metal SN structures usually deal with a hypothetic normal metal with no direct repulsive interaction between electrons and with finite temperatures often close to the superconductor critical temperature. We present an asymptotic solution of the Gor’kov equations in the opposite low-temperature limit for a clean normal metal with a repulsive interaction between electrons. The order parameter in the metal exhibits a power-law decay, x /x, as a function of the distance from the SN boundary, x, with a proximity length strongly depending on the repulsive interaction

Erratum: Magnetic quantum oscillations in doped antiferromagnetic insulators [Phys. Rev. B 77, 132403 (2008)]

Erratum: Magnetic quantum oscillations in doped antiferromagnetic insulators [Phys. Rev. B 77, 132403 (2008)

Strings in charge-transfer Mott insulators: effects of lattice vibrations and the Coulomb interaction

Applying the canonical transformation with the 1/\lambda perturbation expansion in the nonadiabatic and intermediate regime and the discrete generalisation of Pekar's continuous nonlinear equation in the extreme adiabatic regime we show that there are no strings in narrow-band ionic insulators due to the Frohlich electron-phonon interaction alone. The multi-polaron system is a homogeneous state in a wide range of physically interesting parameters, no matter how strong correlations are. At the same time the Frohlich interaction allows the antiferromagnetic interactions and/or a short-range electron-phonon interactions to form short strings in doped antiferromagnetic insulators if the static dielectric constant is large enough

Quasiparticle relaxation dynamics in cuprates and lifetimes of low-energy states: Femtosecond data from underdoped to overdoped YBCO and mercury compounds

We show that low-energy spectral features in the cuprates can be separated into different components by the measurement of the recombination dynamics of different low-energy excitations in real-time using femtosecond laser spectroscopy. Quasiparticle (QP) recombination across the gap and intra-gap localized state relaxation processes exhibit qualitatively different time- and temperature-dependences. The relaxation measurements also show the existence of two distinct coexisting energy gaps near optimum doping and in the overdoped region, one more or less temperature independent (which exists above and below Tc) and one which closes at Tc in a mean-field like fashion. Thus systematic studies of QP recombination as a function of doping and temperature suggest that the ground state of the cuprates is a mixed Boson-Fermion system with localised states present over the entire region of the phase diagram.Comment: 4 pages, acepted for publication in Physica C, invited paper given at M2S, Feb. 20 - 25, 2000, Houston, US

Shubnikov–de Haas effect in multiband quasi-two-dimensional metals

We analyze the behavior of the longitudinal conductivity zz in a field perpendicular to the highly conducting plane of a quasi-two-dimensional multiband metal in the case of a closed system where chemical potential oscillations may be observed compared with the case of an open system for various forms of scattering. In all but one case, we find that there are mixing frequencies present. However, they exhibit different qualitative behaviors, as befits their different origins, and in the case of interband scattering in an open system, may in fact be absent in the de Haas–van Alphen oscillations of that system

Theory of the charged Bose gas: Bose-Einstein condensation in an ultrahigh magnetic field

The Bogoliubov-de Gennes equations and the Ginzburg-Landau-Abrikosov-Gor'kov-type theory are formulated for the charged Bose gas (CBG). The theory of the Bose-Einstein condensation of the CBG in a magnetic field is extended to ultralow temperatures and ultrahigh magnetic fields. A low-temperature dependence of the upper critical field Hc2(T) is obtained both for the particle-impurity and particle-particle scattering. The normal-state collective plasmon mode in ultrahigh magnetic fields is studied

Universal upper critical field of unconventional superconductors

The resistive upper critical field, Hc2(T) of cuprates, superconducting spin-ladders, and organic (TMTSF)2X systems is shown to follow a universal nonlinear temperature dependence in a wide range near Tc, while its low-temperature behaviour depends on the chemical formula and sample quality. Hc2(T) is ascribed to the Bose-Einstein condensation field of preformed pairs. The universality originates from the scaling arguments. Exceeding the Pauli paramagnetic limit is explained. Controversy in the determination of Hc2(T) from the kinetic and thermodynamic measurements is resolved in the framework of the charged Bose-gas model with impurity scattering

Coherent 'ab' and 'c' transport theory of high-Tc cuprates

We propose a microscopic theory of the `$c$'-axis and in-plane transport of copper oxides based on the bipolaron theory and the Boltzmann kinetics. The fundamental relationship between the anisotropy and the spin susceptibility is derived, $\rho_{c}(T,x)/\rho_{ab}(T,x)\sim x/\sqrt{T}\chi_{s}(T,x)$. The temperature $(T)$ and doping $(x)$ dependence of the in-plane, $\rho_{ab}$ and out-of-plane, $\rho_{c}$ resistivity and the spin susceptibility, $\chi_{s}$ are found in a remarkable agreement with the experimental data in underdoped, optimally and overdoped $La_{2-x}Sr_{x}CuO_{4}$ for the entire temperature regime from $T_{c}$ up to $800K$. The normal state gap is explained and its doping and temperature dependence is clarified

Contrasting effects of magnetic field on thermodynamic and resistive transitions in high- Tc cuprates

For a number of high-Tc cuprates it has been observed that the resistive transition reveals an upper critical field with increasingly negative gradient on cooling. However, the λ point of the specific heat scarcely shifts with applied magnetic field. Either phenomenon is highly unusual in itself, but also appears to be irreconcilable with one another under the BCS framework. This Letter offers an explanation of the observed phenomena on the basis of the bipolaron theory