Browsing by Author "Luo, Yongkang"

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    Heavy-fermion quantum criticality and destruction of the Kondo effect in a nickelﾠoxypnictide
    (Nature Publishing Group, 2014) Luo, Yongkang; Pourovskii, Leonid; Rowley, S.E.; Li, Yuke; Feng, Chunmu; Georges, Antoine; Dai, Jianhui; Cao, Guanghan; Xu, Zhuﾒan; Si, Qimiao; Ong, N.P.
    A quantum critical point arises at a continuous transformation between distinct phases of matter at zero temperature. Studies in antiferromagnetic heavy-fermion materials have revealed that quantum criticality has several classes, with an unconventional type that involves a critical destruction of the Kondo entanglement [1,2]. To understand such varieties, it is important to extend the materials basis beyond the usual setting of intermetallic compounds. Here we show that a nickel oxypnictide, CeNiAsO, exhibits a heavy-fermion antiferromagnetic quantum critical point as a function of either pressure or P/As substitution. At the quantum critical point, non-Fermi-liquid behaviour appears, which is accompanied by a divergent effective carrier mass. Across the quantum critical point, the low-temperature Hall coefficient undergoes a rapid sign change, suggesting a sudden jump of the Fermi surface and a destruction of the Kondo effect [3,4]. Our results imply that the enormous materials basis for the oxypnictides, which has been so crucial in the search for high-temperature superconductivity, will also play a vital role in the effort to establish the universality classes of quantum criticality in strongly correlated electron systems.
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    Unconventional and conventional quantum criticalities in CeRh0.58Ir0.42In5
    (Springer Nature, 2018) Luo, Yongkang; Lu, Xin; Dioguardi, Adam P.; Rosa, Priscila S.F.; Bauer, Eric D.; Si, Qimiao; Thompson, Joe D.
    An appropriate description of the state of matter that appears as a second order phase transition is tuned toward zero temperature, viz. quantum-critical point (QCP), poses fundamental and still not fully answered questions. Experiments are needed both to test basic conclusions and to guide further refinement of theoretical models. Here, charge and entropy transport properties as well as AC specific heat of the heavy-fermion compound CeRh0.58Ir0.42In5, measured as a function of pressure, reveal two qualitatively different QCPs in aﾠsinglematerial driven by a single non-symmetry-breaking tuning parameter. A discontinuous sign-change jump in thermopower suggests an unconventional QCP atﾠpc1ﾠaccompanied by an abrupt Fermi-surface reconstruction that is followed by a conventional spin-density-wave critical point atﾠpc2ﾠacross which the Fermi surface evolves smoothly to a heavy Fermi-liquid state. These experiments are consistent with some theoretical predictions, including the sequence of critical points and the temperature dependence of the thermopower in their vicinity.