arXiv subjects

A. W. Sandvik

Publications and source records attributed to A. W. Sandvik.

41 records · Page 3Linked to original sources

arXiv1995

Spin dynamics of SrCu$_2$O$_3$ and the Heisenberg ladder

The $S=1/2$ Heisenberg antiferromagnet in the ladder geometry is studied as a model for the spin degrees of freedom of SrCu$_2$O$_3$. The susceptibility and the spin echo decay rate are calculated using a quantum Monte Carlo technique, and the spin-lattice relaxation rate is obtained by maximum entropy analytic continuation of imaginary time correlation functions. All calculated quantities are in reasonable agreement with experimental results for SrCu$_2$O$_3$ if the exchange coupling $J \approx 850$K, i.e. significantly smaller than in high-T$_c$ cuprates.

cond-mat↗

arXiv1995

Effects of intrabilayer coupling on the magnetic properties of YBa$_2$Cu$_3$O$_6$

A two-layer Heisenberg antiferromagnet is studied as a model of the bilayer cuprate YBa$_2$Cu$_3$O$_6$. Quantum Monte Carlo results are presented for the temperature dependence of the spin correlation length, the static structure factor, the magnetic susceptibility, and the $^{63}$Cu NMR spin-echo decay rate $1/T_{2G}$. As expected, when the ratio $J_2/J_1$ of the intrabilayer and in-plane coupling strengths is small, increasing $J_2$ pushes the system deeper inside the renormalized classical regime. Even for $J_2/J_1$ as small as $0.1$ the correlations are considerably enhanced at temperatures as high as $T/J_1 \approx 0.4-0.5$. This has a significant effect on $1/T_{2G}$, and it is suggested that measurements of this quantity at high temperatures can reveal the strength of the intrabilayer coupling in YBa$_2$Cu$_3$O$_6$.

cond-mat↗

arXiv1994

Spin Dynamics of La_2CuO_4 and the Two-Dimensional Heisenberg Model

The spin-lattice relaxation rate $1/T_1$ and the spin echo decay rate $1/T_{2G}$ for the 2D Heisenberg model are calculated using quantum Monte Carlo and maximum entropy analytic continuation. The results are compared to recent experiments on La$_2$CuO$_4$, as well as predictions based on the non-linear $σ$-model.

supr-con↗

arXiv1994

Interplane relaxation and the bilayer coupling in Y$_2$Ba$_4$Cu$_7$O$_{15}$

The origin of the spin gap in the underdoped cuprate superconductors is still mysterious. Experimental evidence from neutron scattering and NMR experiments indicates that the spin gap might be present only in the bilayer compounds. A naive calculation for a two plane Heisenberg model locates the order-disorder transition only for very large exchange coupling between the bilayers. We propose a interplane relaxation experiment which might quantitatively estimate the strength of the bilayer coupling. We make detailed predictions for the size and the temperature dependence of the interplane relaxation rate.

cond-mat↗

arXiv1994

Order-Disorder Transition in a Two-Layer Quantum Antiferromagnet

We have studied the antiferromagnetic order -- disorder transition occurring at $T=0$ in a 2-layer quantum Heisenberg antiferromagnet as the inter-plane coupling is increased. Quantum Monte Carlo results for the staggered structure factor in combination with finite-size scaling theory give the critical ratio $J_c = 2.51 \pm 0.02$ between the inter-plane and in-plane coupling constants. The critical behavior is consistent with the 3D classical Heisenberg universality class. Results for the uniform magnetic susceptibility and the correlation length at finite temperature are compared with recent predictions for the 2+1-dimensional nonlinear $σ$-model. The susceptibility is found to exhibit quantum critical behavior at temperatures significantly higher than the correlation length.

cond-mat↗