Pressure-tuned quantum criticality in the antiferromagnetic Kondo semi-metal CeNi${}_{2-\delta }$As${}_2$

Abstract

The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi${}_{2-\delta }$As${}_2$ ($\delta$$\approx$0.28) as its antiferromagnetic order is tuned by pressure and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of $\sim$0.032 $e^{-}$/f.u. in CeNi${}_{2-\delta }$As${}_2$ leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo lattice state with decreasing temperature. The small carrier density and associated semi-metallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raise the specter of Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening.

15+7 pages, 4+5 figures in Proc. Natl. Acad. Sci. USA (2015)

References in corpus (4)

• Fermi-liquid instabilities at magnetic quantum phase transitions
• Quantum Criticality in Heavy Fermion Metals
• Heavy Fermion Quantum Criticality and Destruction of the Kondo Effect in a Nickel Oxypnictide
• Magnetic property and crystalline electric field effect in ThCr${}_2$Si${}_2$-type CeNi${}_2$As${}_2$

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