Kentaro Kuga

Quantum Criticality Without Tuning in the Mixed Valence Compound β-YbAlB4

A quantum phase transition is observed in a stoichiometric compound at ambient pressure and in zero magnetic field. 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 by 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 β-YbAlB4 demonstrate a scaling of its free energy that is indicative of zero-field quantum criticality without tuning in a metal. The breakdown of Fermi liquid behavior takes place in a mixed-valence state, which is in sharp contrast with other known examples of quantum critical f-electron systems that are magnetic Kondo lattice systems with integral valence.

Superconductivity in the Ferroquadrupolar State in the Quadrupolar Kondo Lattice PrTi2Al20

The cubic compound PrTi 2 Al 20 is a quadrupolar Kondo lattice system that exhibits quadrupolar ordering due to the non-Kramers Γ 3 ground doublet and has strong hybridization between 4 f and conduction electrons. Our study using high-purity single crystals reveals that PrTi 2 Al 20 exhibits type-II superconductivity at T c = 200 mK in the nonmagnetic ferroquadrupolar state. The superconducting critical temperature and field phase diagram indicates clean limit superconductivity with moderately enhanced effective mass of m * / m 0 ∼16.

Magnetic order induced by Fe substitution of Al site in the heavy-fermion systems α-YbAlB4 and β-YbAlB4

\alpha

Field Evolution of Quantum Critical and Heavy Fermi-Liquid Components in the Magnetization of the Mixed Valence Compound β-YbAlB4

-YbAlB

High Pressure Measurements of the Resistivity of β-YbAlB4

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Low-temperature magnetization of the quantum critical heavy fermion superconductor β-YbAlB4

is the locally isostructural polymorph of

Quantum valence criticality in a correlated metal

\beta

Quantum criticality and inhomogeneous magnetic order in Fe-doped α − YbAlB 4

-YbAlB

Pressure-Induced Local Structural Changes in Heavy Fermion β-YbAlB4

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