arXiv subjects

V. N. Muthukumar

Publications and source records attributed to V. N. Muthukumar.

25 records · Page 2Linked to original sources

arXiv1996

The J_1-J_2 model revisited : Phenomenology of CuGeO_3

We present a mean field solution of the antiferromagnetic Heisenberg chain with nearest (J_1) and next to nearest neighbor (J_2) interactions. This solution provides a way to estimate the effects of frustration. We calculate the temperature-dependent spin-wave velocity, v_s(T) and discuss the possibility to determine the magnitude of frustration J_2/J_1 present in quasi 1D compounds from measurements of v_s(T). We compute the thermodynamic susceptibility at finite temperatures and compare it with the observed susceptibility of the spin-Peierls compound CuGeO_3. We also use the method to study the two-magnon Raman continuum observed in CuGeO_3 above the spin-Peierls transition.

cond-mat.str-el↗

arXiv1996

Frustration induced Raman scattering in CuGeO_3

We present experimental data for the Raman intensity in the spin-Peierls compound CuGeO_3 and theoretical calculations from a one-dimensional frustrated spin model. The theory is based on (a) exact diagonalization and (b) a recently developed solitonic mean field theory. We find good agreement between the 1D-theory in the homogeneous phase and evidence for a novel dimerization of the Raman operator in the spin-Peierls state. Finally we present evidence for a coupling between the interchain exchange, the spin-Peierls order parameter and the magnetic excitations along the chains.

cond-mat↗

arXiv1996

Theory of Non-Reciprocal Optical Effects in Antiferromagnets: The Case Cr_2O_3

A microscopic model of non-reciprocal optical effects in antiferromagnets is developed by considering the case of Cr_2O_3 where such effects have been observed. These effects are due to a direct coupling between light and the antiferromagnetic order parameter. This coupling is mediated by the spin-orbit interaction and involves an interplay between the breaking of inversion symmetry due to the antiferromagnetic order parameter and the trigonal field contribution to the ligand field at the magnetic ion. We evaluate the matrix elements relevant for the non-reciprocal second harmonic generation and gyrotropic birefringence.

cond-mat↗

arXiv1995

A Microscopic Model of Non-Reciprocal Optical Effects in Cr_2 O_3

This manuscript deals with the question "How does light couple to an antiferromagnetic order parameter"? For that we develop a microscopic model that explains the non-reciprocal optical effects in centrosymmetric Cr_2 O_3. It is shown that light can couple {\em directly} to the antiferromagnetic order parameter. This coupling is mediated by the spin-orbit interaction and involves an interplay between the breaking of inversion symmetry due to the antiferromagnetic order parameter and the trigonal field contribution to the ligand field at the Cr^{3+} ion.

cond-mat↗

arXiv1994

Temperature Dependent Gap Anisotropy from Interlayer Tunneling

A recent experiment by Ma and collaborators shows that the gap anisotropy in ${\rm Bi}_2 {\rm Sr}_2 {\rm Ca}_1 {\rm Cu}_2 {\rm O}_{8+x}$ is strongly temperature dependent. In particular, the superconducting gap along the $Γ- M$ direction shows a weaker temperature dependence than the gap along the $Γ- X$ direction which decreases rapidly with temperature. We explain this novel feature as a natural consequence of the interlayer tunneling mechanism of superconductivity.

cond-mat↗

arXiv1994

A Toy Model of Interlayer Pair Hopping

We extend the correlated electron model of Baskaran [Mod. Phys. Lett. {\bf B5}, 643(1991)] to the case of coupled layers. We show that the nature of the non-Fermi liquid ground state leads to the absence of electron-like quasiparticles at the Fermi surface, thereby suppressing coherent transport of electrons between the coupled layers (``confinement''). On the other hand, motion of singlet pairs between the layers is not blocked. We also discuss how pair tunneling can be used to construct a superconducting ground state.

cond-mat↗

arXiv1992

Numerical Study of the Wheatley-Hsu-Anderson Interlayer Tunneling mechanism of High $T_c$ Superconductivity

We present results obtained (by exact diagonalization) for the problem of two t-J planes with an interlayer coupling $t_\perp$. Our results for small hole concentrations show that in-plane superconducting correlations are enhanced by $t_\perp$. When the constraint on double occupancy in the t-J model is relaxed, the enhancement disappears. These results illustrate the inter--layer tunneling mechanism for superconductivity.

cond-mat↗