engleski

Quantum critical behavior in transport properties of i-AuAlYb

Point in phase diagram where second order phase transition temperature is suppressed to zero temperature is called quantum critical point (QCP). Physical properties of the system near QCP are governed by quantum fluctuations that become important even at higher temperatures indicating critical point occurrence. Recently, quantum critical phenomena was observed for the first time in quasiperiodic crystal in magnetic susceptibility and specific heat. [1] Icosahedral i-Au-Al-Yb is intermediate valence compound [2] with majority of Yb ions in trivalent high spin state (J=7/2) compared to divalent (J=0) Yb ions. Although approximant phase with very similar local structure and composition shows intermediate valence character but with larger asymmetry among amount of divalent and trivalent ions it does not show quantum criticality at low temperatures. Recently we have measured electrical resistivity and thermopower down to 1.5 K and investigated stabilization mechanisms.[3] Here we present magnetic field influence on thermoelectric transport properties. It turned out that anomalous low-temperature behavior of electrical resistivity below 50 K tend to vanish in magnetic field. Thermopower is positive at high temperatures but at 12 K changes sign and near 4 K has minimum. It seems that this minimum and change of sign is somehow connected to quantum criticality since it disappears in magnetic field. We propose some kind of magnetic ordering of high spin Yb ions as ground state of i-Au-Al-Yb.

i-AuAlYb; transport properties

The paper was presented as a poster by Petar Popčević. This work was done within the activities of the European Integrated Center for the Development of New Metallic Alloys and Compounds - C-MAC.