arXiv subjects

G. I. Japaridze

Publications and source records attributed to G. I. Japaridze.

41 records · Page 3Linked to original sources

arXiv2000

η-superconductivity in the Hubbard chain with pair hopping

The ground state phase diagram of the 1D Hubbard chain with pair-hopping interaction is studied. The analysis of the model is performed using the continuum-limit field theory approach and exact diagonalization studies. At half-filling the phase diagram is shown to consist of two superconducting states with Cooper pair center-of-mass momentum Q=0 (BCS-η_0 phase) and Q=π(η_π-phase) and four insulating phases corresponding to the Mott antiferromagnet, the Peierls dimerized phase, the charge-density-wave (CDW) insulator as well as an unconventional insulating phase characterized by the coexistence of a CDW and a bond-located staggered magnetization. Away from half-filling the phase diagram consists of the superconducting BCS-η_0 and η_πphases and the metallic Luttinger-liquid phase. The BCS-η_0 phase exhibits smooth crossover from a weak-coupling BCS type to a strong coupling local-pair regime. The η_πphase shows properties of the doublon (zero size Cooper pair) superconductor with Cooper pair center-of-mass momentum Q=π. The transition into the η_π- paired state corresponds to an abrupt change in the groundstate structure. After the transition the conduction band is completely destroyed and a new η_π-pair band corresponding to the strongly correlated doublon motion is created.

cond-mat.str-el↗

arXiv1999

Triplet superconductivity in a one-dimensional ferromagnetic t-J model

In this paper we study the ground state phase diagram of a one-dimensional $t-U-J$ model, at half-filling. In the large-bandwidth limit and for ferromagnetic exchange with easy-plane anisotropy, a phase with gapless charge and massive spin excitations, characterized by the coexistence of triplet superconducting ($TS$) and spin density wave ($SDW^{z}$) instabilities is realized in the ground state. With reduction of the bandwidth, a transition into an insulating phase showing properties of the spin-1/2 XY model takes place. In the case of weakly anisotropic antiferromagnetic exchange the system shows a long range dimerized (Peierls) ordering in the ground state. The complete weak-coupling phase diagram of the model, including effects of the on-site Hubbard interaction, is obtained.

cond-mat.str-el↗

arXiv1998

Phase Diagram of the Extended Hubbard Model with Correlated Hopping Interaction

A one-dimensional model of interacting electrons with on-site $U$, nearest-neighbor $V$, and correlated-hopping interaction $T^{\ast}$ is studied at half-filling using the continuum-limit field theory approach. The ground state phase diagram is obtained for a wide range of coupling constants. In addition to the insulating spin- and charge-density wave phases for large $U$ and $V$, respectively, we identify bond-located ordered phases corresponding to an enhanced Peierls instability in the system for $T^\ast>0$, $|U-2V|<8T^\ast/π$ and to a staggered magnetization located on bonds between sites for $T^\ast<0$, $|U-2V|<8|T^\ast|/π$. The general ground state phase diagram including insulating, metallic, and superconducting phases is discussed.

cond-mat.str-el↗

arXiv1998

Elementary Excitations in Dimerized and Frustrated Heisenberg Chains

We present a detailed numerical analysis of the low energy excitation spectrum of a frustrated and dimerized spin $S=1/2$ Heisenberg chain. In particular, we show that in the commensurate spin--Peierls phase the ratio of the singlet and triplet excitation gap is a universal function which depends on the frustration parameter only. We identify the conditions for which a second elementary triplet branch in the excitation spectrum splits from the continuum. We compare our results with predictions from the continuum limit field theory . We discuss the relevance of our data in connection with recent experiments on $CuGeO_{3}$, $NaV_2O_5$, and $(VO)_2P_2O_7$.

cond-mat.str-el↗

arXiv1996

$η$-superconductivity in the one-dimensionnal pair hopping model

Using exact Lanczos diagonalizations we have shown that the pair-hopping model for {\it negative} $W$ exhibits a phase transition into $η$-{\it superconducting state}. The transition occurs at {\it any band filling} and the critical value $W_{c}$ varies between $W_{c} \simeq -1.75t$ at half-filling to $W_{c} \simeq -2t$ for two particles on the lattice.

cond-mat↗