一级相变附近量子三临界点的自旋涨落理论：应用于重费米子系统、YbRh2Si2、CeRu2Si2和beta-YbAlB4
Spin Fluctuation Theory for Quantum Tricritical Point Arising in Proximity to First-Order Phase Transitions: Applications to Heavy-Fermion Systems, YbRh2Si2, CeRu2Si2, and beta-YbAlB4
摘要：
提出了反铁磁量子三临界点（QTCP）的自旋涨落唯象理论，其中一级相变在零温时变为连续相变。在磁场作用下，除了反铁磁量子临界点外，反铁磁量子临界点附近还出现了铁磁量子临界涨落，这与传统的反铁磁量子临界点形成了鲜明的对比.对于巡游电子系统，我们证明了在反铁磁有序（铁磁）波数q=Q（q=0）下，QTCP周围临界磁涨落的温度依赖性为chiQ \propto T ^{-3/2}（chi 0 \propto T^{-3/4}）。chi 0 ^{-1}的凸温度依赖性是QTCP的特征，这在传统的自旋涨落理论中是从未见过的。我们提出，量子三临界性的一般理论，与特定的近藤物理本身无关，解决了量子临界性的难题，广泛观察到的重费米子系统，如YbRh 2Si 2，CeRu 2Si 2，和β-YbAlB 4。对于YbRh_2Si_2，通过合理选择唯象参数，我们的理论成功地再现了实验铁磁磁化率和磁化曲线的定量行为.量子三临界性与比热、核磁弛豫时间1/T_1T、霍尔系数等物理性质的奇异性也是一致的。对于CeRu_2Si_2和β-YbAlB_4，我们指出量子三临界性是在这些材料中观察到的均匀磁化率的异常发散增强的可能起源。
英文摘要：
We propose a phenomenological spin fluctuation theory for antiferromagnetic quantum tricritical point (QTCP), where the first-order phase transition changes into the continuous one at zero temperature. Under magnetic fields, ferromagnetic quantum critical fluctuations develop around the antiferromagnetic QTCP in addition to antiferromagnetic ones, which is in sharp contrast with the conventional antiferromagnetic quantum critical point. For itinerant electron systems,} we show that the temperature dependence of critical magnetic fluctuations around the QTCP are given as chiQ \propto T^{-3/2} (chi0\propto T^{-3/4}) at the antiferromagnetic ordering (ferromagnetic) wave number q=Q (q=0). The convex temperature dependence of chi0^{-1} is the characteristic feature of the QTCP, which is never seen in the conventional spin fluctuation theory. We propose that the general theory of quantum tricriticality that has nothing to do with the specific Kondo physics itself, solves puzzles of quantum criticalities widely observed in heavy-fermion systems such as YbRh2Si2, CeRu2Si2, and beta-YbAlB4. For YbRh2Si2, our theory successfully reproduces quantitative behaviors of the experimental ferromagnetic susceptibility and the magnetization curve by choosing the phenomenological parameters properly. The quantum tricriticality is also consistent with singularities of other physical properties such as specific heat, nuclear magnetic relaxation time 1/T_1T, and Hall coefficient. For CeRu2Si2 and beta-YbAlB4, we point out that the quantum tricriticality is a possible origin of the anomalous diverging enhancement of the uniform susceptibility observed in these materials.
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