Related papers: Kondo hybridization and quantum criticality in $\b…

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…

Unconventional quantum criticality in heavy-fermion systems has been extensively analyzed in terms of a critical destruction of the Kondo effect. Motivated by a recent demonstration of quantum criticality in a mixed-valent heavy-fermion…

We present the high-precision magnetization data of the valence fluctuating heavy fermion superconductor $\beta$-YbAlB$_4$ in a wide temperature range from 0.02 K to 320 K spanning four orders of magnitude. We made detailed analyses of the…

Unconventional quantum critical phenomena observed in Yb-based periodic crystals such as YbRh$_2$Si$_2$ and $\beta$-YbAlB$_4$ have been one of the central issues in strongly correlated electron systems. The common criticality has been…

$\alpha$-YbAlB$_4$ is the locally isostructural polymorph of $\beta$-YbAlB$_4$, the first example of an Yb-based heavy fermion superconductor which exhibits pronounced non-Fermi-liquid behavior above $T_{\rm c}$. Interestingly, both…

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…

We have performed an angle resolved photoemission spectroscopy (ARPES) study of lightly-doped to underdoped YBa2Cu3Oy (YBCO) untwinned single crystals and a core-level x-ray photoemission spectroscopy (XPS) study of YBCO single and…

We present the first angle-resolved photoemission (ARPES) measurement of Fermi Surface in the "misfit" cobaltate [Bi2Ba2O4].[CoO2]~2. This compound contains the same triangular Co planes as Na cobaltates, but in a different 3D environment.…

We propose a model for the intrinsic quantum criticality of {\beta}-YbAlB4, in which a vortex in momentum space gives rise to a new type of Fermi surface singularity. The unquenched angular momentum of the |J = 7/2,m_J = \pm5/2> Yb…

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…

Intermetallic compounds containing $f$-electron elements have been prototypical materials for investigating strong electron correlations and quantum criticality (QC). Their heavy fermion ground state evoked by the magnetic $f$-electrons is…

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…

Hybridization of Bogoliubov quasiparticles (BQPs) between the CuO$_2$ layers in the triple-layer cuprate high-temperature superconductor Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+\delta}$ is studied by angle-resolved photoemission spectroscopy…

A detailed low-energy electronic structure of a Kondo insulator YbB$_{12}$ was revealed by a synergetic combination of ultrahigh-resolution laser photoemission spectroscopy (PES) and time-resolved PES. The former confirmed a 25-meV…

We studied the electronic structure of the Kondo lattice system Ce2Co0.8Si3.2 by angle-resolved photoemission spectroscopy (ARPES). The spectra obtained below the coherence temperature consist of a Kondo resonance, its spin-orbit partner…

Heavy fermion metals provide a prototype setting to study quantum criticality. Experimentally, quantum critical points have been identified and studied in a growing list of heavy fermion compounds. Theoretically, Kondo destruction has…

We have probed the crystalline electric-field ground states of pure $|J = 7/2, J_z = \pm 5/2\rangle$ as well as the anisotropic $c$-$f$ hybridization in both valence fluctuating systems $\alpha$- and $\beta$-YbAlB$_4$ by linear polarization…

Progress of theories and experiments of the quantum valence criticality is overviewed focusing on recent discoveries of direct evidence of quantum critical point of valence transitions in periodic crystal $\alpha$-YbAl$_{1-x}$Fe$_x$B$_4$ at…

The origin of intrinsic quantum criticality in the heavy-fermion superconductor $\beta$-YbAlB$_4$ has been attributed to strong Yb valence fluctuations and its peculiar crystal structure. Here, we assess these contributions individually by…

Angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM) have become indispensable tools in the study of correlated quantum materials. Both probe complementary aspects of the single-particle excitation…