Searcharxiv⌕ Search

arXiv subjects

Sudip Chakravarty

Publications and source records attributed to Sudip Chakravarty.

97 records · Page 6Linked to original sources
arXiv1997

The NMR relaxation rate of O in undoped Sr_2CuO_2Cl_2: Probing two-dimensional magnons at short distances

We calculate the nuclear relaxation rate of oxygen in the undoped quasi two-dimensional quantum Heisenberg antiferromagnet Sr_2CuO_2Cl_2 above the Neel temperature. The calculation is performed at two-loop order with the help of the Dyson-Maleev formulation of the spin-wave expansion, taking all scattering processes involving two and three magnons into account. At low temperatures T we find 1 / T_1 = c_1 T^3 + c_2 T^4 + O (T^5), and give explicit expressions for the coefficients c_1 (two-magnon scattering) and c_2 (three magnon scattering). We compare our result with a recent experiment by Thurber et al. and show that this experiment directly probes the existence of short-wavelength magnons in a two-dimensional antiferromagnet.

cond-mat.str-el↗
arXiv1997

Scaling theory of two-dimensional metal-insulator transitions

We discuss the recently discovered two-dimensional metal-insulator transition in zero magnetic field in the light of the scaling theory of localization. We demonstrate that the observed symmetry relating conductivity and resistivity follows directly from the quantum critical behavior associated with such a transition. In addition, we show that very general scaling considerations imply that any disordered two dimensional metal is a perfect metal, but most likely not a Fermi liquid.

cond-mat.dis-nn↗
arXiv1997

Low Temperature Correlation Lengths of Bilayer Heisenberg AntiFerromagnets and Neutron Scattering

The low temperature correlation length and the static structure factor are computed for bilayer antiferromagnets such as YBa_2Cu_3O_6. It is shown that energy integrated two-axis scan in neutron scattering experiments can be meaningfully interpreted to extract correlation length in such bilayer antiferromagnets despite intensity modulation in the momentum perpendicular to the layers. Thus, precise measurements of the spin-spin correlation length can be performed in the future, and the theoretical predictions can be tested. It is also shown how the same correlation length can be measured in nuclear magnetic resonance experiments.

cond-mat.str-el↗
arXiv1997

Interchain Coupling Effects and Solitons in CuGeO_3

The effects of interchain coupling on solitons and soliton lattice structures in CuGeO3 are explored. It is shown that interchain coupling substantially increases the soliton width and changes the soliton lattice structures in the incommensurate phase. It is proposed that the experimentally observed large soliton width in CuGeO3 is mainly due to interchain coupling effects.

cond-mat.str-el↗
arXiv1997

Correlation Lengths in Quantum Spin Ladders

Analytic expressions for the correlation length temperature dependences are given for antiferromagnetic spin-1/2 Heisenberg ladders using a finite-size non-linear sigma-model approach. These calculations rely on identifying three successive crossover regimes as a function of temperature. In each of these regimes, precise and controlled approximations are formulated. The analytical results are found to be in excellent agreement with Monte Carlo simulations for the Heisenberg Hamiltonian.

cond-mat.str-el↗
arXiv1996

Dimensional Crossover in Quantum Antiferromagnets

The dimensional crossover in a spin-$S$ nearest neighbor Heisenberg antiferromagnet is discussed as it is tuned from a two-dimensional square lattice, of lattice spacing $a$, towards a spin chain by varying the width $L_y$ of a semi-infinite strip $L_x\times L_y$. For integer spins and arbitrary $L_y$, and for half integer spins with $L_y/a$ an arbitrary even integer, explicit analytical expressions for the zero temperature correlation length and the spin gap are given. For half integer spins and $L_y/a$ an odd inetger, it is shown that the $c=1$ behavior of the $SU(2)_1$ WZW fixed point is squeezed out as the width $L_y\to \infty$; here $c$ is the conformal charge. The results specialized to $S=1/2$ are relevant to spin-ladder systems.

cond-mat↗