Hall effect and resistivity in underdoped cuprates

The behaviour of the Hall ratio $R_{H}(T)$ as a function of temperature is one of the most intriguing normal state properties of cuprate superconductors. One feature of all the data is a maximum of $R_{H}(T)$ in the normal state that broadens and shifts to temperatures well above $T_c$ with decreasing doping. We show that a model of preformed pairs-bipolarons provides a selfconsistent quantitative description of $R_{H}(T)$ together with in-plane resistivity and uniform magnetic susceptibility for a wide range of doping.Comment: 4 pages, 2 figures, the model and fits were refine

Reply to "Comment on 'Origin of combination frequencies in quantum magnetic oscillations of two-dimensional multiband metals' " by A.S. Alexandrov and A.M. Bratkovsky [cond-mat/0207173]

In their comment on the paper (Phys. Rev. B 65, 153403 (2002); cond-mat/0110154), Alexandrov and Bratkovsky (cond-mat/0207173) argue that they correctly took into account the chemical potential oscillations in their analytical theory of combination frequencies in multiband low-dimensional metals by expanding the free energy in powers of the chemical potential oscillations. In this reply, we show that this claim contradicts their original paper (Phys. Rev. B 63, 033105 (2001)). We demonstrate that the condition given for the expansion is mathematically incorrect. The correct condition allows to understand the limits of validity of the analytical theory.Comment: 4 page

Semi-classical theory of magnetic quantum oscillations in a two-dimensional multiband canonical Fermi liquid

The semi-classical Lifshitz-Kosevich (LK) description of quantum oscillations is extended to a multiband two-dimensional Fermi liquid with a constant number of electrons. The amplitudes of novel oscillations with combination frequencies, recently predicted and observed experimentally, are analytically derived and compared with the single-band amplitudes. The combination amplitudes decay with temperature exponentially faster than the standard harmonics, and this provides a valuable tool for their experimental identification.Comment: 3 pages, REVTeX 3.0, one eps-figure included in the tex

New Fundamental dHvA Frequency in Canonical Low-Dimensional Fermi Liquids

We show that a new fundamental period $P_{f}$ of dHvA oscillations, which appears along with other ``forbidden'' combination frequencies in a multi-band canonical Fermi-liquid, is very robust with respect to a finite smearing of Landau levels and a background of non-quantized states. We analyse the possibility of measuring small Fermi surface pockets with the use of the ``forbidden'' frequencies.Comment: 10 pages, RevTeX 3.0, with 2 PS Figure

Low temperature thermodynamics of charged bosons in a random potential and the specific heat of La_{2-x}Sr_{x}CuO_{4} below Tc

We propose a simple analytical form of the partition function for charged bosons localised in a random potential and derive the consequent thermodynamics below the superfluid transition temperature. In the low temperature limit, the specific heat, C, depends on the localisation length exponent nu: C is linear for nu1 we find C proportional to T^{1/nu}. This unusual sub-linear temperature dependence of the specific heat has recently been observed in La_{2-x}Sr_{x}CuO_{4} below Tc.Comment: Revtex, 6 pages, 4 postscript figure

Bipolaron anisotropic flat bands, Hall mobility edge, and metal-semiconductor duality of overdoped high-Tc oxides

Hole bipolaron band structure with two flat anisotropic bands is derived for oxide superconductors. Strong anisotropy leads to one-dimensional localization in a random field which explains the metal-like value of the Hall effect and the semiconductorlike doping dependence of resistivity of overdoped oxides. Doping dependence of Tc and λH(0) as well as the low-temperature dependence of resistivity, of the Hall effect, Hc2(T) and robust features of angle-resolved photoemission spectroscopy of several high-Tc copper oxides are explained

Vortex in the charged Bose liquid

Equations describing a single vortex in the charged Bose liquid at zero temperature are derived. The zero-temperature coherence length, magnetic-field penetration depth, vortex structure and energy, and lower critical field are calculated. The vortex differs from that in type-II BCS superconductors or in neutral superfluids. Its core is charged, and there is an electric field inside the core

Unconventional pairing symmetry of layered superconductors caused by acoustic phonons

An inevitable anisotropy of sound velocity in crystals makes the phonon-mediated attraction of electrons nonlocal in space providing unconventional Cooper pairs with a nonzero orbital momentum. As a result of this anisotropy, quasi-two-dimensional charge carriers weakly coupled with acoustic phonons undergo a quantum phase transition from a conventional s-wave to an unconventional d-wave superconducting state with less carriers per unit cell. In the opposite strong-coupling regime, rotational symmetry breaking appears as a result of a reduced Coulomb repulsion between unconventional bipolarons dismissing thereby some constraints on unconventional pairing in the Bose-Einstein condensation limit. The conventional acoustic phonons, and not superexchange, are shown to be responsible for the d-wave symmetry of cuprate superconductors, where the on-site Coulomb repulsion is large

Bipolarons in the Extended Holstein Hubbard Model

We numerically and analytically calculate the properties of the bipolaron in an extended Hubbard Holstein model, which has a longer range electron-phonon coupling like the Fr\" ohlich model. In the strong coupling regime, the effective mass of the bipolaron in the extended model is much smaller than the Holstein bipolaron mass. In contrast to the Holstein bipolaron, the bipolaron in the extended model has a lower binding energy and remains bound with substantial binding energy even in the large-U limit. In comparison with the Holstein model where only a singlet bipolaron is bound, in the extended Holstein model a triplet bipolaron can also form a bound state. We discuss the possibility of phase separation in the case of finite electron doping.Comment: 5 pages, 3 figure

From Hurwitz numbers to Kontsevich-Witten tau-function: a connection by Virasoro operators

In this letter,we present our conjecture on the connection between the Kontsevich--Witten and the Hurwitz tau-functions. The conjectural formula connects these two tau-functions by means of the $GL(\infty)$ group element. An important feature of this group element is its simplicity: this is a group element of the Virasoro subalgebra of $gl(\infty)$. If proved, this conjecture would allow to derive the Virasoro constraints for the Hurwitz tau-function, which remain unknown in spite of existence of several matrix model representations, as well as to give an integrable operator description of the Kontsevich--Witten tau-function.Comment: 13 page