arXiv subjects

Kyo-Hoon Ahn

Publications and source records attributed to Kyo-Hoon Ahn.

21 records · Page 2Linked to original sources

arXiv2014

Strain and Spin-Orbit Coupling Induced Orbital-Ordering in Mott Insulator BaCrO3

Using ab initio calculations, we have investigated an insulating tetragonally distorted perovskite BaCrO$_3$ with a formal $3d^2$ configuration, the volume of which is apparently substantially enhanced by a strain due to SrTiO$_3$ substrate. Inclusion of both correlation and spin-orbit coupling (SOC) effects leads to a metal-insulator transition and in-plane zigzag orbital-ordering (OO) of alternating singly filled $d_{xz}+id_{yz}$ and $d_{xz}-id_{yz}$ orbitals, which results in a large orbital moment $M_L$ ~ -0.78 $μ_B$ antialigned to the spin moment $M_S$ ~ $2|M_L|$ in Cr ions. Remarkably, this ordering also induces a considerable $M_L$ for apical oxygens. Our findings show metal-insulator and OO transitions, driven by an interplay among strain, correlation, and SOC, which is uncommon in 3d systems.

cond-mat.str-el↗

arXiv2012

Electron and phonon band-structure calculations for the antipolar SrPt$_{3}$P antiperovskite superconductor: Evidence of low-energy two-dimensional phonons

SrPt3P has recently been reported to exhibit superconductivity with Tc = 8.4 K. To explore its superconducting mechanism, we have performed electron and phonon band calculations based on the density functional theory, and found that the superconductivity in SrPt3P is well described by the strong coupling phonon-mediated mechanism. We have demonstrated that superconducting charge carriers come from pdπ-hybridized bands between Pt and P ions, which couple to low energy (~ 5 meV) phonon modes confined on the ab in-plane. These in-plane phonon modes, which do not break antipolar nature of SrPt3P, enhance both the electron-phonon coupling constant λand the critical temperature Tc. There is no hint of a specific phonon softening feature in the phonon dispersion, and the effect of the spin-orbit coupling on the superconductivity is found to be negligible.

cond-mat.supr-con↗

arXiv2012

Evaluation of Half-metallic Antiferromagnetism in ${\cal A}_2$CrFeO$_6$ ({$\cal A$}=La, Sr

The nearly well-ordered double perovskite La$_2$CrFeO$_6$ has been synthesized recently. Contrary to previous theoretical predictions, but in agreement with experimental observations, our first principle calculations indicate an insulating ferrimagnet La$_2$CrFeO$_6$ with antialigned S=3/2 Cr$^{3+}$ and S=5/2 Fe$^{3+}$ ions,using the local spin density approximation (LSDA), a correlated band theory LDA+U, and a semilocal functional modified Becke-Johnson method. Additionally, we investigated the double perovskite Sr$_2$CrFeO$_6$, which is as yet unsynthesized. In LSDA calculations, this system shows formally tetravalent Cr and Fe ions both having antialigned $S$=1 moments, but is a simple metal. Once applying on-site Coulomb repulsion U on both Cr and Fe ions, this system becomes half-metallic and the moment of Fe is substantially reduced, resulting in zero net moment. These results are consistent with our fixed spin moment studies. Our results suggest a precisely compensated half-metallic Sr$_2$CrFeO$_6$.

cond-mat.mtrl-sci↗