Changhee Sohn

superlattices on THE from a chiral spin texture. By additively engineering the interfacial inversion symmetry with atomic-scale precision, we directly link the competition between interfacial collinear ferromagnetic interactions and DMIs to an enhanced THE. The ability to control the DMI and resulting THE points to a pathway for harnessing interfacial structures to maximize the density of chiral spin textures useful for developing high-density information storage and quantum magnets for quantum

Charge transfer in superlattices consisting of SrIrO 3 and SrMnO 3 is investigated using density functional theory. Despite the nearly identical work function and nonpolar interfaces between SrIrO 3 and SrMnO 3, rather large charge transfer was experimentally reported at the interface between them. Here, we report a microscopic model that captures the mechanism behind this phenomenon, providing a qualitative understanding of the experimental observation. This leads to unique strain dependence of

Strongly correlated vanadium dioxide (VO2) is one of the most promising materials that exhibits a temperature-driven, metal–insulator transition (MIT) near room temperature. The ability to manipulate the MIT at nanoscale offers both insight into understanding the energetics of phase transition and a promising potential for nanoelectronic devices. In this work, we study nanoscale electrochemical modifications of the MIT in epitaxial VO2 thin films using a combined approach with scanning probe mic

Determining the origin of the insulating gap in the monoclinic V O2(M1) is a long-standing issue. The difficulty of this study arises from the simultaneous occurrence of structural and electronic transitions upon thermal cycling. Here, we compare the electronic structure of the M1 phase with that of single crystalline insulating V O2(A) and V O2(B) thin films to better understand the insulating phase of VO2. As these A and B phases do not undergo a structural transition upon thermal cycling, we

Abstract Spin-phonon coupling (SPC) plays a critical role in numerous intriguing phenomena of transition metal oxides (TMOs). In 3d and 4 d TMOs, the coupling between spin and lattice degrees of freedom is known to originate from the exchange interaction. On the other hand, the origin of SPC in 5 d TMOs remains to be elucidated. To address this issue, we measured the phonon spectra of the 5 d pyrochlore iridate Y 2 Ir 2 O 7 using optical spectroscopy. Three infrared-active phonons soften below t

Abstract Oxygen defect control has long been considered an important route to functionalizing complex oxide films. However, the nature of oxygen defects in thin films is often not investigated beyond basic redox chemistry. One of the model examples for oxygen-defect studies is the layered Ruddlesden–Popper phase La 2 − x Sr x CuO 4 − δ (LSCO), in which the superconducting transition temperature is highly sensitive to epitaxial strain. However, previous observations of strain-superconductivity co

We report a temperature-dependent optical spectroscopic study of the Heisenberg-Kitaev magnet $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{RuCl}}_{3}$. Our measurements reveal anomalies in the optical response near the magnetic ordering temperature. At higher temperatures, we observe a redistribution of spectral weight over a broad energy range that is associated with nearest-neighbor spin-spin correlations. This finding is consistent with highly frustrated magnetic interactions and in agre

Abstract Oxygen defects are essential building blocks for designing functional oxides with remarkable properties, ranging from electrical and ionic conductivity to magnetism and ferroelectricity. Oxygen defects, despite being spatially localized, can profoundly alter global properties such as the crystal symmetry and electronic structure, thereby enabling emergent phenomena. In this work, we achieved tunable metal–insulator transitions (MIT) in oxide heterostructures by inducing interfacial oxyg

Abstract Artificial heterostructures composed of dissimilar transition metal oxides provide unprecedented opportunities to create remarkable physical phenomena. Here, we report a means to deliberately control the orbital polarization in LaNiO 3 (LNO) through interfacing with SrCuO 2 (SCO), which has an infinite-layer structure for CuO 2 . Dimensional control of SCO results in a planar-type (P–SCO) to chain-type (C–SCO) structure transition depending on the SCO thickness. This transition is explo

The slow kinetics of the oxygen reduction reaction (ORR) is one of the key challenges in developing high performance energy devices, such as solid oxide fuel cells. Straining a film by growing on a lattice-mismatched substrate has been a conventional approach to enhance the ORR activity. However, due to the limited choice of electrolyte substrates to alter the degree of strain, a systematic study in various materials has been a challenge. Here, we explore the strain modulation of the ORR kinetic

Altermagnets exhibit characteristics akin to antiferromagnets, with spin-split anisotropic bands in momentum space. RuO_{2} has been considered as a prototype altermagnet; however, recent reports have questioned altermagnetic ground state in this material. In this Letter, we demonstrate spin-dependent tunneling magnetoresistance (TMR) in RuO_{2}-based magnetic tunnel junctions, which suggests the spin-splitted anisotropic band structure of our RuO_{2} films. The observed TMR is contingent on the

Abstract 5 d pyrochlore oxides with all-in-all-out magnetic order are prime candidates for realizing strongly correlated, topological phases of matter. Despite significant effort, a full understanding of all-in-all-out magnetism remains elusive as the associated magnetic excitations have proven difficult to access with conventional techniques. Here we report a Raman spectroscopy study of spin dynamics in the all-in-all-out magnetic state of the 5 d pyrochlore Cd 2 Os 2 O 7 . Through a comparison

Tin titanate ($\mathrm{SnTi}{\mathrm{O}}_{3}$) has been notoriously impossible to prepare as a thin-film ferroelectric, probably because high-temperature annealing converts much of the $\mathrm{S}{\mathrm{n}}^{2+}$ to $\mathrm{S}{\mathrm{n}}^{4+}$. In the present paper, we show two things: first, perovskite phase $\mathrm{SnTi}{\mathrm{O}}_{3}$ can be prepared by atomic-layer deposition directly onto $p$-type Si substrates; and second, these films exhibit ferroelectric switching at room temperat

Abstract Ferromagnetic insulators (FMIs) are one of the most important components in developing dissipationless electronic and spintronic devices. However, FMIs are innately rare to find in nature as ferromagnetism generally accompanies metallicity. Here, novel room‐temperature FMI films that are epitaxially synthesized by deliberate control of the ratio between two B‐site cations in the double perovskite Sr 2 Fe 1+ x Re 1‐ x O 6 (−0.2 ≤ x ≤ 0.2) are reported. In contrast to the known FM metalli

Authors present optical spectroscopy measurements of 5d transition metal oxide Sr${}_{2}$IrO${}_{4}$. The results are interpreted in terms of orbital-dependent electron-phonon interaction and are essential for understanding the physics of this material.