arXiv subjects

Gil-ho Lee

Publications and source records attributed to Gil-ho Lee.

3 recordsLinked to original sources

arXiv2019

Pulsed Laser Deposition of Rocksalt Magnetic Binary Oxides

Here we systematically explore the use of pulsed laser deposition technique (PLD) to grow three basic oxides that have rocksalt structure but different chemical stability in the ambient atmosphere: NiO (stable), MnO (metastable) and EuO (unstable). By tuning laser fluence, an epitaxial single-phase nickel oxide thin-film growth can be achieved in a wide range of temperatures from 10 to 750 °C. At the lowest growth temperature, the out-of-plane strain raises to 1.5%, which is five times bigger than that in a NiO film grown at 750 °C. MnO thin films that had long-range ordered were successfully deposited on the MgO substrates after appropriate tuning of deposition parameters. The growth of MnO phase was strongly influenced by substrate temperature and laser fluence. EuO films with satisfactory quality were deposited by PLD after oxygen availability had been minimized. Synthesis of EuO thin films at rather low growth temperature prevented thermally-driven lattice relaxation and allowed growth of strained films. Overall, PLD was a quick and reliable method to grow binary oxides with rocksalt structure in high quality that can satisfy requirements for applications and for basic research.

cond-mat.mtrl-sci↗

arXiv2019

Dielectric properties of strained NiO thin films

The dielectric properties of NiO thin films grown by pulsed laser deposition have been studied as a function of strain at temperature from 10 to 300 K. Above 150 K, the contribution of space-charge polarization to the dielectric permittivity of NiO films becomes dominant and the more defective films, which were grown at low temperatures show a drastical increase in the dielectric constant up to room temperature. While the atomically-ordered film, which was grown at high temperature doesn't show any considerable change in the dielectric constant in the range from 10 to 300 K. Below 100 K, the effect of strain on the dielectric constant becomes clear. An increase in dielectric permittivity is observed in the strained films while the relaxed film doesn't show any remarkable deviation from its bulk value. The low-temperature dielectric behavior of NiO thin film can be interpreted based on the effect of strain on the lattice dynamics of rocksalt binary oxides.

cond-mat.mtrl-sci↗

arXiv2018

Asymmetric Josephson Effect in Inversion Symmetry Breaking Topological Materials

Topological materials which possess topologically protected surface states have attracted much attention in recent years. In this work, we study the critical current of superconductor/inversion symmetry breaking topological material/superconductor junctions. We found surprisingly that, in topological materials with broken inversion symmetry, the magnitude of the critical Josephson currents $|I^{+}_c(B)|$ at fixed magnetic field $B$ is not the same for critical currents $|I^{-}_c(B)|$ flowing in the opposite direction. Moreover, the critical currents violate the $| I_{c}^{\pm}(B)| = |I_{c}^{\pm}(-B)|$ relation and give rise to asymmetric Fraunhofer patterns. We call this phenomenon asymmetric Josephson effect (AJE). AJE can be use to detect inversion symmetry breaking in topological materials such as in quantum spin Hall systems and Weyl semimetals.

cond-mat.supr-con↗