Quantum bicriticality in the heavy-fermion metamagnet YbAgGe

TL;DR

This study investigates quantum bicriticality in the heavy-fermion compound YbAgGe, revealing divergence and sign change in the magnetic Grueneisen parameter near a bicritical point, indicating quantum critical behavior influenced by geometric frustration.

Contribution

The paper provides experimental evidence of quantum bicriticality in YbAgGe through magnetocaloric measurements, highlighting asymmetric scaling behavior near the bicritical point.

Findings

Magnetic Grueneisen parameter diverges and changes sign near the bicritical point.

Asymmetric scaling behavior observed only on the low-field side.

Possible link between low T_BCP and geometric frustration.

Abstract

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.