arXiv subjects

Jinwoong Kim

Publications and source records attributed to Jinwoong Kim.

42 records · Page 3Linked to original sources

arXiv2016

Revealing the Hidden Structural Phases of FeRh

${\it Ab}$ ${\it initio}$ electronic structure calculations reveal that tetragonal distortion has a dramatic effect on the relative stability of the various magnetic structures (C-, A-, G-, A$'$-AFM, and FM) of FeRh giving rise to a wide range of novel stable/metastable structures and magnetic phase transitions between these states. We predict that the ${\it cubic}$ G-AFM structure, which was believed thus far to be the ground state, is metastable and that the ${\it tetragonally}$ expanded G-AFM is the stable structure. The low energy barrier separating these states suggests phase coexistence at room temperature. We propose a novel A$'$-AFM phase to be the ${\it global}$ ground state among all magnetic phases which arises from the strain-induced tuning of the exchange interactions. The results elucidate the underlying mechanism for the recent experimental findings of electric-field control of magnetic phase transition driven via tetragonal strain. The novel magnetic phase transitions open interesting prospects for exploiting strain engineering for the next-generation memory devices.

cond-mat.mtrl-sci↗

arXiv2015

GdN thin-film: Chern Insulating State on Square Lattice

Using first-principles calculations, we predict a Chern insulating phase in thin films of the ferromagnetic semi-metal GdN. In contrast to previously proposed Chern insulator candidates, which mostly rely on honeycomb lattices, this system affords a great chance to realize the quantum anomalous Hall Effect on a square lattice without either a magnetic substrate or transition metal doping, making synthesis easier. The band inversion between 5d-orbitals of Gd and 2p-orbitals of N is verified by first-principles calculation based on density functional theory, and the band gap can be as large as 100 meV within GdN trilayer. With further increase of film thickness, the band gap tends to close and the metallic bulk property becomes obvious.

cond-mat.mtrl-sci↗

arXiv2015

Two dimensional topological insulators with tunable band gaps: HgTe and HgSe monolayers

Employing ab initio electronic calculations, we propose a new type of two-dimensional (2D) topological insulator (TI), monolayer (ML) low buckled (LB) mercury telluride (HgTe) and mercury selenide (HgSe), with tunable band gaps. Monolayer LB HgTe undergoes a transition to a topological nontrivial phase under the appropriate in-plane tensile strain (ε > 2.6%) due to the combination effects of strain and spin orbital coupling (SOC). Under the 2.6%< ε <4.2% tensile strain, the band inversion and topological nontrivial gap are induced by the SOC. For ε >4.2%, the band inversion is already realized by strain but the topological gap is induced by SOC. The band gap of monolayer LB HgTe TI phase can be tuned over a wide range from 0 eV to 0.20 eV as the tensile strain increases from 2.6% to 7.4%. Similarly, the topological phase transition of monolayer LB HgSe is induced by strain and SOC as the strain ε >3.1%. The topological band gap can be 0.05 eV as the strain increases to about 4.6%. The large band gap of 2D LB HgTe and HgSe monolayers make this type of material suitable for practical applications at room-temperature.

cond-mat.mes-hall↗

arXiv2013

Phonon-induced topological insulating phases in group IV-VI semiconductors

Development of topological insulating phases in IV-VI compounds under dynamic lattice deformations is studied using first-principles methods. Unlike the static state of topological phases at equilibrium conditions, we show that non-trivial topological phases are induced in the compounds by the dynamic lattice deformations from selective phonon modes. Calculations of the time-reversal polarization show that the Z2 invariant of the compounds is flipped by the atomic displacements of selective phonon modes and that the compounds exhibit oscillating topological phases upon dynamic lattice deformations. Our results indicate that the elementary excitations in solids can trigger topological phases in trivial band insulators.

cond-mat.mtrl-sci↗

arXiv2012

Topological phase transition in Dirac fermionic heterostructures

Materials with non-trivial topology in their electronic structures enforce the existence of helical Dirac fermionic surface states. We discovered emergent topological phases in the stacked structures of topological insulator and band insulator layers where the surface Dirac fermions interact to each other with particular helicity ordering. Using first-principles calculations and a model Lagrangian, we explicitly demonstrated that such helicity ordering occurs in real materials of ternary chalcogen compounds and determines their topological insulating phase. Our results reveal the rich collective nature of interacting surface Dirac fermions, and pave the way for utilizing topological phases for technological devices such as non-volatile memories.

cond-mat.mtrl-sci↗

arXiv2010

Topological insulating behaviour in conducting property of crystalline Ge-Sb-Te

We report a discovery, through first-principles calculations, that crystalline Ge-Sb-Te (GST) phase-change materials exhibit the topological insulating property. Our calculations show that the materials become topological insulator or develop conducting surface-like interface states depending on the layer stacking sequence. It is shown that the conducting interface states originate from topological insulating Sb2Te3 layers in GSTs and can be crucial to the electronic property of the compounds. These interface states are found to be quite resilient to atomic disorders but sensitive to the uniaxial strains. We presented the mechanisms that destroy the topological insulating order in GSTs and investigated the role of Ge migration that is believed to be responsible for the amorphorization of GSTs.

cond-mat.mtrl-sci↗