arXiv subjects

Sumathi Rao

Publications and source records attributed to Sumathi Rao.

79 records · Page 5Linked to original sources

arXiv1995

Field Theories of Frustrated Heisenberg Antiferromagnets

We study the Heisenberg antiferromagnetic chain with both dimerization and frustration. The classical ground state has three phases: a Neel phase, a spiral phase and a colinear phase. In each phase, we discuss a non-linear sigma model field theory governing the low energy excitations. We study the theory in the spiral phase in detail using the renormalization group. The field theory, based on an $SO(3)$ matrix-valued field, becomes $SO(3) \times SO(3)$ and Lorentz invariant at long distances where the elementary excitation is analytically known to be a massive spin-$1/2$ doublet. The field theory supports $Z_2 ~$ solitons which lead to a double degeneracy in the spectrum for half-integer spins (when there is no dimerization).

cond-mat↗

arXiv1995

MIRROR SYMMETRY IN THE FEW ANYON SPECTRA IN A HARMONIC OSCILLATOR POTENTIAL

We find that the energy spectra of four and five anyons in a harmonic potential exhibit some mirror symmetric (reflection symmetric about the semionic statistics point $θ=π/2$) features analogous to the mirror symmetry in the two and three anyon spectra. However, since the $\ell=0$ sector remains non-mirror symmetric, the fourth and fifth virial coeffients do not reflect this symmetry.

hep-th↗

arXiv1995

QUANTUM HALL EFFECT OF HARD-CORE BOSONS

Motivated by a mean-field approach, which has been employed for anyon superfluidity and the fractional quantum Hall effect, the quantum Hall effect (QHE) of hard-core bosons is investigated. It is shown that QHE is possible {\em only} in the thermodynamic limit. The filling factors where QHE may be expected are obtained with the help of two adiabatic schemes.

cond-mat↗

arXiv1993

A Bosonic Mean-Field Theory for Frustrated Heisenberg Antiferromagnets in Two Dimensions

We use a recently developed bosonic mean-field theory (MFT) to study the ordered ground states of frustrated Heisenberg antiferromagnets (FHAFM) in two dimensions. We emphasize the role of condensates in satisfying the MF variational equations and their relation to spin correlation functions at low temperatures. Our results are similar to those obtained using Schwinger boson MFT. However, we emphasize here that our MFT has three bosons at each site and that it is not necessary to rotate the quantization axes on appropriate sub-lattices to align all the spins ferromagnetically. This MFT is also closely related to a new spin-wave theory which enables us to obtain the spin-wave spectrum easily (without any rotation of axes) for an entire class of three-dimensionally ordered states. For the FHAFM on a triangular lattice, we use this theory to compute the spin-wave spectrum for all values of $~J_2 ~/J_1 ~$ and demonstrate the phenomenon of order from disorder. (1 figure not included. Hard copy available on request.)

cond-mat↗

arXiv1993

Bosonic Mean Field Theory of the Spiral Phases of Heisenberg Antiferromagnets on a Chain

We develop a novel bosonic mean field theory to describe the spiral phases of a Heisenberg antiferromagnet on a one-dimensional chain, in terms of three bosons at each site. The ground state is disordered and for large values of the spin $S$, two different and exponentially small energy gaps are found. The spin-spin correlation function is computed and is shown to decay exponentially at large distances. Our mean field theory is also shown to be exact in a large-$N$ generalization.

cond-mat↗

arXiv1992

Non-linear Field Theory of a Frustrated Heisenberg Spin Chain

We derive a continuum field theory for the Majumdar-Ghosh model in the large-$S$ limit, where the field takes values in the manifold of the $SO(3)$ group. No topological term is induced in the action and the cases for integer spin and half-integer spin appear to be indistinguishable. A one-loop $β-$function calculation indicates that the theory flows towards a strong coupling (disordered) phase at long distances. This is verified in the large-$N$ limit, where all excitations are shown to be massive. (Three figures not included)

hep-th↗

arXiv1992

Chirality Ordering of Chiral Spin Liquids

We study the effect of introducing a weak antiferromagnetic interplanar exchange coupling in the two dimensional frustrated Heisenberg model. We show that a ferromagnetic(FM) ordering of chirality - {\it i.e.}, same chirality on adjacent planes - is energetically favoured, thus leading to bulk violation of the discrete symmetries parity($P$) and time reversal($T$).

cond-mat↗