Quantum bi-critical point in YbAgGe

Tokiwa, Yoshifumi  ; Garst, M.*; Gegenwart, P.*; Bud'ko, S. L.*; Canfield, P. C.*

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 0.3K at a magnetic field of 4.5T. In its vicinity, YbAgGe exhibits anomalous behavior that we attribute to the influence of a quantum bicritical point that is close in parameter space yet can be reached by tuning further to zero. Using high-resolution measurements of the magnetocaloric effect, we demonstrate that the magnetic Gruneisen parameter indeed both changes sign and diverges as required for quantum criticality. Moreover, displays a characteristic scaling behavior but only on the low-field side , indicating a pronounced asymmetry with respect to the critical field. We speculate that the small value of is related to the geometric frustration of the Kondo lattice of YbAgGe.