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Register a new userQuantum Criticality and Inhomogeneous Magnetic Order in Fe-doped alpha-YbAlB4
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Douglas E. MacLaughlin
Publication date
2016
fields
Physics
and research's language is
English
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The intermediate-valent polymorphs $alpha$- and $beta$-YbAlB$_4$ exhibit quantum criticality and other novel properties not usually associated with intermediate valence. Iron doping induces quantum criticality in $alpha$-YbAlB$_4$ and magnetic order in both compounds. We report results of muon spin relaxation ($mu$SR) experiments in the intermediate-valent alloys $alpha$-YbAl$_{1-x}$Fe$_x$B$_4$, $x = 0.014$ and 0.25. For $x = 0.014$ we find no evidence for magnetic order down to 25 mK@. The dynamic muon spin relaxation rate $lambda_d$ exhibits a power-law temperature dependence $lambda_d propto T^{-a}$, $a = 0.40(4)$, in the temperature range 100 mK--2 K, in disagreement with predictions by theories of antiferromagnetic (AFM) or valence quantum critical behavior. For $x = 0.25$, where AFM order develops in the temperature range 7.5--10 K, where we find coexistence of meso- or macroscopically segregated paramagnetic and AFM phases, with considerable disorder in the latter down to 2 K.
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Fermi liquid theory, the standard theory of metals, has been challenged by a number of observations of anomalous metallic behavior found in the vicinity of a quantum phase transition. The breakdown of the Fermi liquid is accomplished by fine-tuning the material to a quantum critical point using a control parameter such as the magnetic field, pressure, or chemical composition. Our high precision magnetization measurements of the ultrapure f-electron based superconductor {beta}-YbAlB4 demonstrate a scaling of its free energy indicative of zero-field quantum criticality without tuning in a metal. The breakdown of Fermi-liquid behavior takes place in a mixed-valence state, in sharp contrast with other known examples of quantum critical f-electron systems that are magnetic Kondo lattice systems with integral valence.
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