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$beta$-YbAlB$_4$ is the first Yb-based heavy fermion superconductor with $T_{rm c} = 80$ mK. We measured low temperature magnetization of high-purity single crystals down to $T=$ 25 mK. The measurements have revealed a considerable amount of volume fractions of the superconductivity and the upper critical field $B_{c2}$ curve under field along the c axis, consistent with the previous results. In the normal state, the previously observed divergent behavior in the temperature dependence of the magnetization has been confirmed using higher quality samples and under a low field of 22 mT. In addition, the measurements have revealed a power law behavior, namely, $dM/dTpropto T^{3/2}$, which has a slightly higher exponent than the previous results.
Measurements of the electric resistivity $rho(T)$ under pressure up to 8 GPa were performed on high-quality single-crystals of the Yb-based heavy fermion system $beta$-YbAlB$_4$ in the temperature range $2<T<$ 300 K. In the resistivity data, we obser
We analyze the key origin of quantum valence criticality in the heavy electron metal $beta$-YbAlB$_4$ evidenced in the sister compound $alpha$-YbAl$_{0.986}$Fe$_{0.014}$B$_4$. By constructing a realistic canonical model for $beta$-YbAlB$_4$, we evalu
Density functional theory methods are applied to investigate the properties of the new superconductor $beta$-YbAlB$_4$ and its polymorph $alpha$-YbAlB$_4$. We utilize the generalized gradient approximation + Hubbard U (GGA+U) approach with spin-orbit
Electronic structures of the quantum critical superconductor beta-YbAlB4 and its polymorph alpha-YbAlB4 are investigated by using bulk-sensitive hard x-ray photoemission spectroscopy. From the Yb 3d core level spectra, the values of the Yb valence ar
We report an angle-resolved photoemission (ARPES) study of $beta$-YbAlB$_4$, which is known to harbor unconventional quantum criticality (QC) without any tuning. We directly observe a quasiparticle peak (QP), emerging from hybridization, characterize