arXiv subjects

Kentaro Kuga

Publications and source records attributed to Kentaro Kuga.

21 records · Page 2Linked to original sources

arXiv2012

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

beta-YbAlB4 is a heavy fermion superconductor that exhibits a quantum criticality without tuning at zero field and under ambient pressure. We have succeeded in substituting Fe for Al in beta-YbAlB4 as well as the polymorphous compound alpha-YbAlB4, which in contrast has a heavy Fermi liquid ground state. Full structure determination by single crystal X-ray diffraction confirmed no change in crystal structure for both alpha- and beta-YbAlB4, in addition to volume contraction with Fe substitution. Our measurements of the magnetization and specific heat indicate that both alpha-YbAl0.93Fe0.07B4 and beta-YbAl0.94Fe0.06B4 exhibit a magnetic order, most likely of a canted antiferromagnetic type, at $7\sim 9$ K. The increase in the entropy as well as the decrease in the antiferromagnetic Weiss temperature with the Fe substitution in both systems indicates that the chemical pressure due to the Fe substitution suppresses the Kondo temperature and induces the magnetism.

cond-mat.str-el↗

arXiv2012

Superconductivity in the Ferroquadrupolar State in the Quadrupolar Kondo Lattice PrTi$_2$Al$_{20}$

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 $4f$ and conduction electrons. Our study using high-purity single crystal reveals that PrTi$_2$Al$_{20}$ exhibits type-II superconductivity at $T_{\rm c} = 200$ mK in the nonmagnetic ferroquadrupolar state. The superconducting critical temperature and field phase diagram suggests moderately enhanced effective mass of $m^*/m_0 \sim 16$.

cond-mat.str-el↗

arXiv2011

Quantum Criticality without Tuning in the Mixed Valence Compound beta-YbAlB4

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 β-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.

cond-mat.str-el↗