Keselman Anna, Balents Leon, Starykh Oleg A
Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106, USA.
Canadian Institute for Advanced Research, Toronto, Ontario M5G 1M1, Canada.
Phys Rev Lett. 2020 Oct 30;125(18):187201. doi: 10.1103/PhysRevLett.125.187201.
We study the transverse dynamical susceptibility of an antiferromagnetic spin-1/2 chain in the presence of a longitudinal Zeeman field. In the low magnetization regime in the gapless phase, we show that the marginally irrelevant backscattering interaction between the spinons creates a nonzero gap between two branches of excitations at small momentum. We further demonstrate how this gap varies upon introducing a second neighbor antiferromagnetic interaction, vanishing in the limit of a noninteracting "spinon gas." In the high magnetization regime, as the Zeeman field approaches the saturation value, we uncover the appearance of two-magnon bound states in the transverse susceptibility. This bound state feature generalizes the one arising from string states in the Bethe ansatz solution of the integrable case. Our results are based on numerically accurate, unbiased matrix-product-state techniques as well as analytic approximations.
我们研究了在纵向塞曼场存在下反铁磁自旋-1/2链的横向动态磁化率。在无隙相的低磁化强度区域，我们表明，自旋子之间的边缘无关背散射相互作用在小动量下的两个激发分支之间产生了一个非零能隙。我们进一步证明了在引入次近邻反铁磁相互作用时这个能隙是如何变化的，在非相互作用“自旋子气体”的极限情况下该能隙消失。在高磁化强度区域，随着塞曼场接近饱和值，我们在横向磁化率中发现了双磁振子束缚态的出现。这种束缚态特征推广了可积情形的贝塞耳假设解中由弦态产生的特征。我们的结果基于数值精确、无偏的矩阵乘积态技术以及解析近似。
