Jae-Joon Yoo

Body-centered tetragonal ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$ is shown to have its electronic structure and properties dominated by the layered in-plane Cu-3d--O-2p interactions. A strong Fermi surface instability along [110] with \ensuremath{\Vert}q\ensuremath{\Vert}=2${k}_{\mathrm{F}}$ leads, via a soft-phonon mode, to the observed orthorhombic phase and accounts for its semiconducting properties. The addition of divalent metals, i.e., Ba, Sr, suppresses the instability and stabilizes the t

The origin of the electric-field gradients (EFG) at nuclear sites in the high-${\mathit{T}}_{\mathit{c}}$ superconductor ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ is investigated theoretically by means of highly precise local-density full-potential linearized-augmented-plane-wave calculations. In all cases considered (i.e., at Cu, O, Ba, and Y nuclei), the theoretical predictions for the principal axis ${\mathit{V}}_{\mathit{z}\mathit{z}}$ and the anisotropy parameter \ensuremath

With one of the highest intrinsic magnetic moments $(10.6\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{B}/\mathrm{atom})$ among the heavy rare-earth elements, dysprosium exhibits a rich magnetic phase diagram, including several modulated magnetic phases. Aided by the Ruderman-Kittel-Kasuya-Yosida interaction, the magnetic modulations propagate coherently over a long range. Neutron diffraction experiments were performed to determine the microscopic magnetic origin of the field induced phases in

Abstract Based on first-principles density-functional theory (DFT) calculations, we report that the transition-metal bis-dithiolene, M 3 C 12 S 12 ( M = Mn and Fe), complexes can be a two-dimensional (2D) ferromagnetic insulator with nontrivial Chern number. Among various synthetic pathways leading to metal bis-dithiolenes, the simplest choice of ligand, Benzene-hexathiol, connecting metal cations to form a Kagome lattice is studied following the experimental report of time-reversal symmetric is

Using elastic neutron scattering on single crystals of ${\text{La}}_{1\ensuremath{-}x}{A}_{x}{\text{CoO}}_{3}$ ($A={\text{Ca}}^{2+}$, ${\text{Sr}}^{2+}$, and ${\text{Ba}}^{2+}$), we found the development of magnetic superstructures below the global magnetic transition to be strongly dependent on the size of the $A$-site dopant, $⟨{r}_{A}⟩$, in an unusual way. Upon reducing the $⟨{r}_{A}⟩$ (i.e., as with Ca doping), only a commensurate ferromagnetic cluster phase is evident. On expanding the $⟨{r

We mapped spatially varying intramolecular electronic structures on a pentacene-gold interface using scanning tunneling spectroscopy. Along with ab initio calculations based on density functional theory, we found that the directional nature of the d orbitals of Au atoms plays an important role in the interaction at the pentacene-gold contact. The gold-induced interface states are broadened and shifted by various pentacene-gold distances determined by the various registries of a pentacene molecul