Quantum criticality in a metallic spin liquid

Abstract

When magnetic order is suppressed by frustrated interactions, spins form a highly correlated fluctuating ‘spin liquid’ state down to low temperatures. The magnetic order of local moments can also be suppressed when they are fully screened by conduction electrons through the Kondo effect. Thus, the combination of strong geometrical frustration and Kondo screening may lead to novel types of quantum phase transition. We report low-temperature thermodynamic measurements on the frustrated Kondo lattice Pr2Ir2O7, which exhibits a chiral spin liquid state below 1.5 K as a result of the frustrated interaction between Ising 4f local moments and their interplay with Ir conduction electrons. Our results provide a first clear example of zero-field quantum critical scaling that emerges in a spin liquid state of a highly frustrated metal.

Figure 1: Schematic phase diagram for geometrically frustrated Kondo lattice systems.
Figure 2: Low-temperature specific heat and entropy of Pr2Ir2O7.
Figure 3: Divergent behaviour of the magnetic Grüneisen ratio, ΓH, of Pr2Ir2O7 as function of temperature.
Figure 4: Evidence of a zero-field quantum critical point in Pr2Ir2O7.
Figure 5: Colour-coded contour plot of the Grüneisen ratio divided by magnetic field, ΓH/H, of Pr2Ir2O7 inH–T phase space.

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Acknowledgements

The authors acknowledge discussions with L. Balents, M. Brando, J.G. Donath, M. Garst, Yong-Baek Kim, K. Kimura, Q. Si, C. Stingl, M. Vojta and K. Winzer. This work has been supported by the German Science Foundation through FOR 960 (Quantum phase transitions), the Helmholtz Virtual Institute VH521, and by Grants-in-Aid for Scientific Research (No. 25707030) from JSPS, and by PRESTO of JST. The use of the Materials Design and Characterization Laboratory at ISSP is gratefully acknowledged. This work was supported also in part by the National Science Foundation under Grant No. PHYS-1066293 and the hospitality of the Aspen Center for Physics.

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Y.T., S.N. and P.G. planned the project. Measurements and analysis of the specific heat and magnetocaloric effect were performed by Y.T. The samples were synthesized and characterized by J.J.I. and S.N. Y.T., S.N. and P.G. discussed the results and prepared the manuscript.

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Correspondence to Y. Tokiwa or P. Gegenwart.

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The authors declare no competing financial interests.

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Tokiwa, Y., Ishikawa, J., Nakatsuji, S. et al. Quantum criticality in a metallic spin liquid. Nature Mater 13, 356–359 (2014). https://doi.org/10.1038/nmat3900

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