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arXiv 1808.09240cond-mat.str-el
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亚铁磁交替链的磁场-温度phase diagram:全极化真空的自旋波理论

Magnetic field - temperature phase diagram of ferrimagnetic alternating chains: spin-wave theory from a fully polarized vacuum

W. M. da Silva, R. R. Montenegro-Filho

摘要:

量子临界(QC)现象可以通过研究在外加磁场($B$)下的量子磁体来获得。QC点位于磁化平台的端点处,并且分离有间隙和无间隙阶段。在一个维度上,无隙相的低能量激发形成Luttinger液体(LL),并且交叉线界定绝缘(平台)和LL区域,以及QC区域。交替亚铁磁链在$T=0$处具有自发磁化,在零场处具有带隙激发。除了在完全极化(FP)磁化处的平台之外;由于间隙,在亚铁磁(FRI)磁化处存在另一磁化平台。我们发展了自旋波理论来研究这些链在外加磁场下的热性质:一个来自FRI经典态,另一个来自FP态,将它们的结果与量子Monte Carlo数据进行比较。我们从FP态开始深化理论,得到了$T$与$B$低$T$相图中的交叉线。特别是,从局部极值点的磁化率和磁化强度曲线,我们确定了一个LL制度之间的交叉形成的FRI状态的激发到另一个建立从FP状态的激发。这两个LL制度是由一个不对称的圆顶状的交叉线,观察到的其他量子磁体在施加磁场的相图。

英文摘要:

Quantum critical (QC) phenomena can be accessed by studying quantum magnets under an applied magnetic field ($B$). The QC points are located at the endpoints of magnetization plateaus and separate gapped and gapless phases. In one dimension, the low-energy excitations of the gapless phase form a Luttinger liquid (LL), and crossover lines bound insulating (plateau) and LL regimes, as well as the QC regime. Alternating ferrimagnetic chains have a spontaneous magnetization at $T=0$ and gapped excitations at zero field. Besides the plateau at the fully polarized (FP) magnetization; due to the gap, there is another magnetization plateau at the ferrimagnetic (FRI) magnetization. We develop spin-wave theories to study the thermal properties of these chains under an applied magnetic field: one from the FRI classical state, and other from the FP state, comparing their results with quantum Monte Carlo data. We deepen the theory from the FP state, obtaining the crossover lines in the $T$ vs. $B$ low-$T$ phase diagram. In particular, from local extreme points in the susceptibility and magnetization curves, we identify the crossover between an LL regime formed by excitations from the FRI state to another built from excitations of the FP state. These two LL regimes are bounded by an asymmetric dome-like crossover line, as observed in the phase diagram of other quantum magnets under an applied magnetic field.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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