arXiv subjects

Hassan Chamati

Publications and source records attributed to Hassan Chamati.

8 recordsLinked to original sources

arXiv2025

Kondo $s$-$d$ exchange in the CuO$_2$ plane as the long sought interaction determining $T_c$ in cuprates

The well-known Pavarini et al. [Phys. Rev. Lett. 87, 047003 (2001)] correlation between the critical temperature $T_{c,\,\mathrm{max}}$ and the shape of the Fermi contour of the optimally hole-doped cuprates is explained within the framework of the BCS theory with Kondo exchange interaction incorporated as a pairing mechanism. The strong influence of the relative position of the Cu4$s$ level with respect to the Cu3$d_{x^2-y^2}$ level on the critical temperature $T_c$ reveals the importance of the $s$-$d$ hybridization of the conduction band. This hybridization is proportional to the $s$-$d$ exchange scattering amplitude between the conduction electrons -- the mechanism of $d$-wave pairing in the CuO$_2$ plane. In other words the Kondo interaction considered as a pairing mechanism in the CuO$_2$ plane gives a natural explanation of the correlation between the critical temperature and the shape of the Fermi contour. This result suggests that the long-sought pairing mechanism in high-$T_c$ superconducting cuprates has possibly been found and that the Kondo exchange interaction as a property of strongly correlated quantum matter deserves further attention in the physics of layered cuprates. To test the developed theoretical scheme, we explored in detail the recent results of the scanned Josephson modulation microscopy experiment of the modulation of the order parameter due to apex distance super-modulation. Our analysis shows a satisfactory agreement between our theory and the named experiment.

cond-mat.supr-con↗

arXiv2022

Hot spots along the Fermi contour of high-$T_c$ cuprates analyzed by $s$-$d$ exchange interaction

We perform a thorough theoretical study of the electron properties of a generic CuO$_2$ plane in the framework of Shubin-Kondo-Zener $s$-$d$ exchange interaction that simultaneously describes the correlation between $T_c$ and the Cu4$s$ energy. To this end, we apply the Pokrovsky theory [J. Exp. Theor. Phys. 13, 447-450 (1961)] for anisotropic gap BCS superconductors. It takes into account the thermodynamic fluctuations of the electric field in the dielectric direction perpendicular to the conducting layers. We microscopically derive a multiplicatively separable kernel able to describe the scattering rate in the momentum space, as well as the superconducting gap anisotropy within the BCS theory. These findings may be traced back to the fact that both the Fermi liquid and the BCS reductions lead to one and the same reduced Hamiltonian involving a separable interaction, such that a strong electron scattering corresponds to a strong superconducting gap and vice versa. Moreover, the superconducting gap and the scattering rate vanish simultaneously along the diagonals of the Brillouin zone. We would like to stress that our theoretical study reproduces the phenomenological analysis of other authors aiming at describing Angle Resolved Photoemission Spectroscopy measurements. Within standard approximations one and the same $s$-$d$ exchange Hamiltonian describes gap anisotropy of the superconducting phase and the anisotropy of scattering rate of charge carriers in the normal phase.

cond-mat.supr-con↗

arXiv2022

Possible zero sound in layered perovskites with ferromagnetic $s$-$d$ exchange interaction

We analyze the conditions for observation of zero sound in layered perovskites with transition metal ion on chalcogenide oxidizer. We conclude that propagation of zero sound is possible only for anti-ferromagnetic sign of the $s$-$d$ interaction. If the $s$-$d$ exchange integral $J_{sd}$ has antiferromagnetic sign, as it is perhaps in the case for layered cuprates, zero sound is a thermally activated dissipation mode,which generates only "hot spots" in the Angle Resolved Photoemission Spectroscopy (ARPES) data along the Fermi contour. We predict that zero sound will be observable for transition metal perovskites with 4$s$ and 3$d$ levels close to the $p$-level of the chalcogenide. The simultaneous lack of superconductivity, the appearance of hot spots in ARPES data, and the proximity of the three named levels, represents the significant hint for the choice of material to be investigated.

cond-mat.supr-con↗

arXiv2018

Application of two-sublattice bilinearly coupled Heisenberg model to the description of certain ferrimagnetic materials

We study phenomenologically on the basis of two bilinearly coupled Heisen- berg models the phase diagram of some ferrimagnetic substances. Calculations are performed with the help of Landau energy obtained through applying the Hubbard-Stratonovich transformation to the initial microscopic Heisenberg Hamiltonian. The phase transitions within the model are of second order with the emergence of a compensation point at lower temperatures for some values of parameters of the system. The main phase is a two-sublattice collinear ferrimagnet but also a metastable non-collinear phase is present within the exchange approximation presented here. The numerical results give a detailed description of temperature dependence of magnetization on the strength of in- tersublattice interaction and the difference between the effective exchanges of two ferromagnetically ordered sublattices.

cond-mat.other↗

arXiv2016

Nematic order in a simple-cubic lattice-spin model with full-ranged dipolar interactions

In a previous paper [Phys. Rev. E 90, 022506 (2014)], we had studied thermodynamic and structural properties of a three-dimensional simple-cubic lattice model with dipolar-like interaction, truncated at nearest-neighbor separation, for which the existence of an ordering transition at finite temperature had been proven mathematically; here we extend our investigation addressing the full-ranged counterpart of the model, for which the critical behavior had been investigated theoretically and experimentally. In addition the existence of an ordering transition at finite temperature had been proven mathematically as well. Both models exhibited the same continuously degenerate ground-state configuration, possessing full orientational order with respect to a suitably defined staggered magnetization (polarization), but no nematic second-rank order; in both cases, thermal fluctuations remove the degeneracy, so that nematic order does set in at low but finite temperature via a mechanism of order by disorder. On the other hand, there were recognizable quantitative differences between the two models as for ground-state energy and critical exponent estimates; the latter were found to agree with early Renormalization Group calculations and with experimental results.

cond-mat.stat-mech↗

arXiv2015

Classical lattice spin models involving singular interactions isotropic in spin space

We address here a few classical lattice--spin models, involving $n-$component unit vectors ($n=2,3$), associated with a $D-$dimensional lattice $\mathbb{Z}^D,\,D=1,2$, and interacting via a pair potential restricted to nearest neighbours and being isotropic in spin space, i.e. defined by a function of the scalar product between the interacting spins. When the potential involves a continuous function of the scalar product, the Mermin--Wagner theorem and its generalizations exclude orientational order at all finite temperatures in the thermodynamic limit, and exclude phase transitions at finite temperatures when $D=1$; on the other hand, we have considered here some comparatively simple functions of the scalar product which are bounded from below, diverge to $+\infty$ for certain mutual orientations, and are continuous almost everywhere with integrable singularities. Exact solutions are presented for $D=1$, showing absence of phase transitions and absence of orientational order at all finite temperatures in the thermodynamic limit; for $D=2$, and in the absence of more stringent mathematical results, extensive simulations carried out on some of them point to the absence of orientational order at all finite temperatures, and suggest the existence of a Berezinski\vı-Kosterlitz-Thouless transition.

cond-mat.stat-mech↗

arXiv1999

Finite size scaling investigations in the quantum $ϕ^4$-model with long-range interaction

In this paper, we study in details the critical behavior of the ${\cal O}(n)$ quantum $ϕ^4$ model with long-range interaction decaying with the distances r by a power law as $r^{-d-σ}$ in the large n-limit. The zero-temperature critical behavior is discussed. Its alteration by the finite temperature and/or finite sizes in the space is studied. The scaling behaviours are studied in different regimes depending upon whether the finite temperature or the finite sizes of the system is leading. A number of results for the correlation length, critical amplitudes and the finite size shift, for different dimensionalities between the lower $d_<=σ/2$ and the upper $d_>=3σ/2$ critical dimensions, are calculated.

cond-mat.stat-mech↗

arXiv1997

Theory of a spherical quantum rotors model: low--temperature regime and finite-size scaling

The quantum rotors model can be regarded as an effective model for the low-temperature behavior of the quantum Heisenberg antiferromagnets. Here, we consider a $d$-dimensional model in the spherical approximation confined to a general geometry of the form $L^{d-d'}\times\infty^{d'}\times L_τ^{z}$ ( $L$-linear space size and $L_τ$-temporal size) and subjected to periodic boundary conditions. Due to the remarkable opportunity it offers for rigorous study of finite-size effects at arbitrary dimensionality this model may play the same role in quantum critical phenomena as the popular Berlin-Kac spherical model in classical critical phenomena. Close to the zero-temperature quantum critical point, the ideas of finite-size scaling are utilized to the fullest extent for studying the critical behavior of the model. For different dimensions $1<d<3$ and $0\leq d'\leq d$ a detailed analysis, in terms of the special functions of classical mathematics, for the susceptibility and the equation of state is given. Particular attention is paid to the two-dimensional case.

cond-mat↗