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arXiv 0808.2127cond-mat.str-elcond-mat.stat-mech
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强磁场中二维反铁磁体的集体激发

Collective excitations in two-dimensional antiferromagnet in strong magnetic field

A. V. Syromyatnikov

摘要:

本文讨论了在强磁场H中,在饱和值$H_c$附近,T=0时正方晶格上自旋$\frac12$二维海森堡反铁磁体(AF)。本文提出了一种微扰方法,在小参数$(H_c-H)/H_c$中,得到了动量不太接近AF矢量的首阶磁振子谱。我们发现,磁振子是定义良好的准粒子在$H>0.9H_c$,虽然阻尼是相当大的区域边界附近。在${\bf k}=(π,0)$处观察到一个特征性的类圆局部极小值,并伴随着$(π,0)$附近阻尼的减小。所提出的方法可用于讨论其他二维玻色气体中的短波长激发。

英文摘要:

We discuss spin-$\frac12$ two-dimensional (2D) Heisenberg antiferromagnet (AF) on a square lattice at T=0 in strong magnetic field H near its saturation value $H_c$. A perturbation approach is proposed to obtain spectrum of magnons with momenta not very close to AF vector in the leading order in small parameter $(H_c-H)/H_c$. We find that magnons are well-defined quasi-particles at $H>0.9H_c$ although the damping is quite large near the zone boundary. A characteristic rotonlike local minimum in the spectrum is observed at ${\bf k}=(π,0)$ accompanied by decrease of the damping near $(π,0)$. The suggested approach can be used in discussion of short-wavelength excitations in other 2D Bose gases of particles or quasi-particles.

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