重费米子超磁体YbAgGe的量子双临界性
Quantum bicriticality in the heavy-fermion metamagnet YbAgGe
摘要：
双临界点是自旋翻转变磁性的典型特征，在双临界点处，两个不同的非线性破碎相同时变得不稳定。有趣的是，重费米子化合物YbAgGe也具有这样一个双临界点，在磁场为μ H_BCP ~ 4.5 T时，其低温T_BCP ~ 0.3 K。在它的附近，YbAgGe表现出反常的行为，我们归因于量子双临界点（QBCP）的影响，这是接近参数空间，但可以达到进一步调整T_BCP为零。使用高分辨率的磁热效应的测量，我们证明，磁Grueneisen参数伽玛_H确实都改变了符号和发散所需的量子临界性。此外，Gamma_H显示出特征标度行为，但仅在低场侧，H < H_BCP，表明相对于临界场的显著不对称性。我们推测T_BCP的小值与YbAgGe的近藤晶格的几何挫挫有关。
英文摘要：
Bicritical points, at which two distinct symmetry-broken phases become simultaneously unstable, are typical for spin-flop metamagnetism. Interestingly, the heavy-fermion compound YbAgGe also possesses such a bicritical point (BCP) with a low temperature T_BCP ~ 0.3 K at a magnetic field of mu_0 H_BCP ~ 4.5 T. In its vicinity, YbAgGe exhibits anomalous behavior that we attribute to the influence of a quantum bicritical point (QBCP), that is close in parameter space yet can be reached by tuning T_BCP further to zero. Using high-resolution measurements of the magnetocaloric effect, we demonstrate that the magnetic Grueneisen parameter Gamma_H indeed both changes sign and diverges as required for quantum criticality. Moreover, Gamma_H displays a characteristic scaling behavior but only on the low-field side, H < H_BCP, indicating a pronounced asymmetry with respect to the critical field. We speculate that the small value of T_BCP is related to the geometric frustration of the Kondo-lattice of YbAgGe.
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