Random-Exchange and Random-Field xy- Chain for S=1/2

清美 岡本, Kiyomi Okamoto

Oleg Derzhko, Taras Krokhmalskii

Wai Pang Sze, Xiaohui Li, Tai Kai Ng

Taras Verkholyak, Oleg Derzhko, Taras Krokhmalskii +1 more

We examine dynamic quantities of a random spin-1/2 isotropic XY chain in a transverse field.The randomness is related to the sign of the nearest-neighbor exchange interaction and can be eliminated by a suitable transformation.As a result, the dynamic quantities for the random spin chain are related to the same dynamic quantities for the homogeneous spin chain.We use the available results for the latter model to discuss the effect of randomness on the dynamic structure factors of the quantum spin chain.

L.L. Gonçalves, André P. Vieira

Dario Cabib, S. D. Mahanti

Thermodynamic properties of one-dimensional Ising chains with random nearest neighbor exchange interaction J are studied exactly in the case of distributions of the type P(J) = A|J|ν for Jmin ≤J ≤Jmax and P(J) = 0, otherwise. The results are compared with those for a periodic chain. We find that the specific heat C ∼Tν+1 for Jmin = 0 and kT ≪Jmax. The dependence of spin-spin correlation function on distance and temperature is discussed. The absence of the peak in the zero field χ⊥ as a function of temperature when ν = 0 is noted in contrast to the case of the periodic chain. The effect of randomness on the low temperature behaviour of these thermodynamic quantities is different. For instance whereas C becomes analytic at T = 0, χ|| either remains singular (ferromagnetic) or becomes analytic (antiferromagnetic). The effect of random xy interaction (∑iJi⊥(SixSi + 1x + SiySi + 1y)) on the high temperature behaviour of χ|| and χ⊥ is discussed.