engleski

Exotic H−T phase diagram of a-YbAlB4 detected by nuclear magnetic resonance

Research of mixed-valence compounds has recently been advanced by the discovery of quantum critical (QC) behaviour in β -YbAlB4 where, at low-temperature, a quantum critical point emerges at ambient pressure and zero magnetic field [1]. It has been suggested that here gapless excitations emerge through a line node in the hybridization between 4f and conduction electrons [2], creating a diverging DOS centred at kx, ky = 0 point of the Fermi surface. While at high temperature the sister compound α- YbAlB4 shows equivalent properties to its QC counterpart, its ground state displays all the characteristics of a Fermi liquid. However, nuclear magnetic resonance has found signatures [3] of magnetic-field induced quantum criticality close to 3.8 T, followed by a gradual suppression of the heavy fermion state at higher magnetic fields. We continue to explore the H-T phase diagram of α- YbAlB4 by NMR, and find several other fieldinduced phenomena describing the low-energy properties of this system. We detect a jump in the quadrupolar coupling of 27Al close to 3.8 T indicating a change in the quasistatic electronic environment, and an additional critical behaviour for magnetic field value close to 2.0 T. The diverging nuclear spin-lattice relaxation rate (1/T1 ) show clear power-law temperature dependence down to 70 mK, revealing excitations of a vanishingly small energy scale. We present our findings as well as their possible interpretations in the scope of current theoretical models. [1] S. Nakatsuji et al, Nat. Phys., 4, 603 (2008). [2] A. Ramires, P. Coleman, A. H. Nevidomskyy, A. M. Tsvelik, Phys. Rev. Lett., 109, 176404 (2012). [3] M. S. Grbic, M. Yoshida, K. Kimura, K. Kuga, S. Nakatsuji, M. Takigawa, SCES conference 2013.

critical; heavy fermion; mixed valence magnetic field

nije evidentirano