engleski

Quantum criticality of α-YbAlB4

α-YbAlB4 is a structural isomorph of the heavy fermion compound β-YbAlB4, in which quantum criticality [1, 2] marked by non-Fermi-liquid properties and low-temperature superconductivity [2], has recently been discovered at zero magnetic field. Although both compounds show similar fluctuating valence value of Yb2+/Yb3+ ions, α-YbAlB4 shows Fermi-liquid properties with no signs of quantum critical behaviour. Such large variation of ground states has been ascribed to the difference in the local symmetry of boron rings around Yb which modify the energy spectrum of the system. We look for signatures of magnetic field-induced quantum criticality by nuclear magnetic resonance. At low temperatures, the spin-lattice relaxation rate (1/T1) shows a clear departure from the Fermi-liquid behaviour. This increase of spin excitations is sensitive to magnetic field and close to 3.5 T shows divergent temperature dependence down to 50 mK, indicating the vicinity of a quantum critical point. We discuss the properties of the new emerging phase and compare it to existing models on heavy fermion systems. [1] S. Nakatsuji et al., Nature Phys. 4, 603 (2008). [2] Y. Matsumoto, S. Nakatsuji et al., Science 331, 316 (2011).

criticality; heavy fermion; nmr

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