arXiv subjects

Haranath Ghosh

Publications and source records attributed to Haranath Ghosh.

42 records · Page 3Linked to original sources

arXiv1998

Coexistence of Band Jahn Teller Distortion and superconductivity in correlated systems

The co-existence of band Jahn-Teller (BJT) effect with superconductivity (SC) is studied for correlated systems, with orbitally degenerate bands using a simple model. The Hubbard model for a doubly degenerate orbital with the on-site intraorbital Coulomb repulsion treated in the slave boson formalism and the interorbital Coulomb repulsion treated in the Hartree-Fock mean field approximation, describes the correlated system. The model further incorporates the BJT interaction and a pairing term to account for the lattice distortion and superconductivity respectively. It is found that structural distortion tends to suppress superconductivity and when SC sets in at low temperatures, the growth of the lattice distortion is arrested. The phase diagram comprising of the SC and structural transition temperatures $T_c$ and $T_s$ versus the dopant concentration $δ$ reveals that the highest obtainable $T_c$ for an optimum doping is limited by structural transition. The dependence of the occupation probabilities of the different bands as well as the density of states (DOS) in the distorted-superconducting phase, on electron correlation has been discussed.

cond-mat↗

arXiv1998

Effect of electron corelation on superconducting pairing symmetry

The role of electron correlation on different pairing symmetries are discussed in details where the electron correlation has been treated within the slave boson formalism. It is shown that for a pure $s$ or pure $d$ wave pairing symmetry, the electronic correlation suppresses the $s$ wave gap magnitude (as well as the $T_c$) at a faster rate than that for the $d$ wave gap. On the otherhand, a complex order parameter of the form ($s+id$) shows anomalous temperature dependence. For example, if the temperature ($T_{c}^d$) at which the $d$ wave component of the complex order parameter vanishes happens to be larger than that for the $s$ wave component ($T_{c}^s$) then the growth of the $d$ wave component is arrested with the onset of the $s$ wave component of the order parameter. In this mixed phase however, we find that the suppression in different components of the gap as well as the corresponding $T_c$ due to coulomb correlation are very sensitive to the relative pairing strengths of $s$ and $d$ channels as well as the underlying lattice. Interestingly enough, in such a scenario (for a case of $T_{c}^s > T_{c}^d$) the gap magnitude of the $d$ wave component increases with electron correlation but not $T_{c}^d$ for certain values of electron correlation. However, this never happens in case of the $s$ wave component. We also calculate the temperature dependence of the superconducting gap along both the high symmetry directions ($Γ$ - M and $Γ$ - X) in a mixed $s+id$ symmetry pairing state and the thermal variation of the gap anisotropy ($\frac{Δ_{Γ- M}}{Δ_{Γ- X}}$) with electron correlation. The results are discussed with reference to experimental observations.

cond-mat↗

arXiv1996

Mutual influence of structural distortion and superconductivity in systems with degenerate bands

The interplay between the band Jahn-Teller distortion and the superconductivity is studied for the system whose Fermi level lies in two-fold degenerate band. Assuming that the lattice distortion is coupled to the orbital electron density and the superconductivity arises due to BCS pairing mechanism between the electrons, the phase diagram is obtained for different doping with respect to half-filled band situation. The coexistence phase of superconductivity and distortion occurs within limited range of doping and the distortion lowers the superconducting transition temperature $T_c$. In presence of strong electron-lattice interaction the lattice strain is found to be maximum at half-filling and superconductivity does not appear for low doping. The maximum value of $T_c$ obtainable for an optimum doping is limited by the structural transition temperature $T_s$. The growth of distortion is arrested with the onset of superconductivity and the distortion is found to disappear at lower temperature for some hole density. Such arresting of the growth of distortion at $T_c$ produces discontinuous jump in thermal expansion coefficient. The variation of strain with temperature as well as with doping, thermal expansion coefficient, the $T_c$ vs $δ$ behaviour are in qualitative agreement with recent experimental observations on interplay of distortion and superconductivity in cuprates.

cond-mat.supr-con↗

arXiv1996

Raman scattering in high temperature superconductors : An integrated view

The common features in the Raman data of high temperature superconductors: (the cuprates, bismathates, alkali doped fullerides and some organic superconductors), are analyzed. It was shown that qualitative understanding of the data can be achieved in terms of non-Fermi liquid models for their normal state, with appropiate bag mechanisms for the superconducting state.

cond-mat↗

arXiv1996

Raman continuum in high-$T_c$ superconductors

Experimentally, Raman continuum for $A_g$ and $B_g$ geometry exhibits peaks far apart from each other (about 80 to 150 $\rm cm^{-1}$) in frequency. The former is insensitive to doping over a small range where $T_c$ does not vary much whereas the latter shifts towards higher frequencies. We calculate the electronic Raman scattering intensities using the `modified spin bag model'. We show that the calculated results have natural explanation to the observed anamolous peak separation and peculiar doping dependence.

cond-mat↗

arXiv1995

Enhancement of superconducting correlation due to interlayer tunneling.

Interlayer single particle tunneling between the $Cu-O$ layers suppress the in-plane short range magnetic order (which is modeled as spin density wave (SDW) insulator). Doping over the SDW state kills perfect nesting of the Fermi surface (FS) in certain directions and hence SDW gap reduces to zero in those directions of the FS. Coupling between the planes through interlayer tunneling ($t_{\perp}$) further suppresses the in-plane magnetic SDW-gap and hence becomes anisotropic. Superconductivity arises in the gapless regions of the FS under the `modified spin bag' mechanism. We show that the highest $T_c$ can only be obtained for non-zero $t_{\perp}$ based on this mechanism.

cond-mat↗