진호섭 교수

We investigated the electronic structure of 5d transition-metal oxide Sr2IrO4 using angle-resolved photoemission, optical conductivity, x-ray absorption measurements, and first-principles band calculations. The system was found to be well described by novel effective total angular momentum Jeff states, in which the relativistic spin-orbit coupling is fully taken into account under a large crystal field. Despite delocalized Ir 5d states, the Jeff states form such narrow bands that even a small co

The Rashba effect is spin degeneracy lift originated from spin-orbit coupling under inversion symmetry breaking and has been intensively studied for spintronics applications. However, easily implementable methods and corresponding materials for directional controls of Rashba splitting are still lacking. Here, we propose organic-inorganic hybrid metal halide perovskites as 3D Rashba systems driven by bulk ferroelectricity. In these materials, it is shown that the helical direction of the angular

Halide perovskite solar cells are a recent ground-breaking development achieving power conversion efficiencies exceeding 18%. This has become possible owing to the remarkable properties of the AMX3 perovskites, which exhibit unique semiconducting properties. The most efficient solar cells utilize the CH3NH3PbI3 perovskite whose band gap, Eg, is 1.55 eV. Even higher efficiencies are anticipated, however, if the band gap of the perovskite can be pushed deeper in the near-infrared region, as in the

Semiconductor materials for efficient hard radiation detection are identified by combining a powerful chemical concept called dimensional reduction and precise theoretical electronic structure calculations. After more than 50 years of research and development in the field, this constitutes a significant step forward in the search for new detector materials. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy

We investigated the temperature-dependent evolution of the electronic structure of the ${J}_{\text{eff}}=\frac{1}{2}$ Mott insulator ${\text{Sr}}_{2}{\text{IrO}}_{4}$ using optical spectroscopy. The optical conductivity spectra $\ensuremath{\sigma}(\ensuremath{\omega})$ of this compound has recently been found to exhibit two $d\text{\ensuremath{-}}d$ transitions associated with the transition between the ${J}_{\text{eff}}=\frac{1}{2}$ and ${J}_{\text{eff}}=\frac{3}{2}$ bands due to the cooperati

By using a first-principles method employing the local density approximation plus Hubbard parameter approach, we study point defects in NiO and interactions between them. The defect states associated with nickel or oxygen vacancies are identified within the energy gap. It is found that nickel vacancies introduce shallow levels in the density of states for the spin direction opposite to that of the removed Ni atom, while the oxygen vacancy creates more localized in-gap states. The interaction pro

Abstract Two-dimensional materials equipped with strong spin–orbit coupling can display novel electronic, spintronic, and topological properties originating from the breaking of time or inversion symmetry. A lot of interest has focused on the valley degrees of freedom that can be used to encode binary information. By performing ab initio time-dependent density functional simulation on MoS 2 , here we show that the spin is not only locked to the valley momenta but strongly coupled to the optical

Topological insulators are a novel quantum state of matter that reveals their properties and shows exotic phenomena when combined with other phases. Hence, priority has been given to making a good quality topological insulator interface with other compounds. From the applications point of view, the topological insulator phase in perovskite structures could be important to provide the various heterostructure interfaces with multifunctional properties. Here, by performing a tight-binding analysis

We present a microscopic model for the anisotropic exchange interactions in ${\text{Sr}}_{2}{\text{IrO}}_{4}$. A direct construction of Wannier functions from first-principles calculations proves the ${j}_{\text{eff}}=1/2$ character of the spin-orbit integrated states at the Fermi level. An effective ${j}_{\text{eff}}$-spin Hamiltonian explains the observed weak ferromagnetism and anisotropy of antiferromagnetically ordered magnetic state, which arise naturally from the ${j}_{\text{eff}}=1/2$ st

We theoretically predict that the series of Pb-based layered chalcogenides, Pb${}_{n}$Bi${}_{2}$Se${}_{n+3}$and Pb${}_{n}$Sb${}_{2}$Te${}_{n+3}$, are possible new candidates for topological insulators, and the topological phases are changed from a topological insulator to a band insulator with increasing $n$. Among the new topological insulators, we found a large bulk band gap of 0.40 eV in PbBi${}_{2}$Se${}_{4}$, and that of Pb${}_{2}$Sb${}_{2}$Te${}_{5}$ is located near the phase boundary betw

The emergence of topologically protected conducting states with the chiral spin texture is the most prominent feature at the surface of topological insulators. On the application side, large band gap and high resistivity to distinguish surface from bulk degrees of freedom should be guaranteed for the full usage of the surface states. Here, we suggest that the oxide cubic perovskite YBiO3, more than just an oxide, defines itself as a new three-dimensional topological insulator exhibiting both a l

We study the electronic properties of a new planar carbon crystal formed through networking biphenylene molecules. Novel electronic features among carbon materials such as zone-center saddle point and peculiar type-II Dirac fermionic states are shown to exist in the low-energy electronic spectrum. The type-II state here has a nearly flat branch and is close to a transition to type I. Possible magnetic instabilities related to low-energy bands are discussed. Furthermore, with a moderate uniaxial

Abstract Defect engineering is one of the key technologies in materials science, enriching the modern semiconductor industry and providing good test-beds for solid-state physics. While homogenous doping prevails in conventional defect engineering, various artificial defect distributions have been predicted to induce desired physical properties in host materials, especially associated with symmetry breakings. Here, we show layer-by-layer defect-gradients in two-dimensional PtSe 2 films developed

When topological insulators meet broken time-reversal symmetry, they bring forth many novel phenomena, such as topological magnetoelectric, half-quantum Hall, and quantum anomalous Hall effects. From the well-known quantum spin Hall state in Bi${}_{2}$Se${}_{3}$ thin films, we predict various topological and magnetic phases when the time-reversal symmetry is broken by magnetic ion doping. As the magnetic ion density increases, the system undergoes successive topological or magnetic phase transit