arXiv subjects

Eunja Kim

Publications and source records attributed to Eunja Kim.

7 recordsLinked to original sources

arXiv2026

Strong electron correlations and ligand hybridization for altermagnetism

Spin-band splitting is a hallmark of altermagnetism, intrinsically linked to magnetic ordering driven by electron correlations. However, recent inconsistencies in the detection of altermagnetism in strongly correlated altermagnet candidates have cast doubt on the robustness of this phenomenon and its dependence on many-body effects. Here, density functional theory combined with dynamical mean-field theory (DFT+DMFT), we dissect the electronic origins of altermagnetism in three prototypical candidates: MnF$_2$, MnTe, and RuO$_2$. In MnF$_2$, we identify pronounced local electron correlations within Mn-3$d$ states and uncover a distinct Mott gap in the visible range. The strong correlations markedly localize the Mn-3$d$ electrons, leading to a narrowing of the spin-resolved bandwidth and, consequently, a suppression of spin-band splitting. By contrast, MnTe provides an ideal platform for altermagnetism, exhibiting substantial local Mn-3$d$ magnetic moments due to the strong correlations and pronounced spin-band splitting, enabled by robust Mn-3$d$--Te-5$p$ orbital hybridization. RuO$_2$ manifests as a Pauli paramagnet with vanishing local moments, even in its antiferromagnetic phase. Nonetheless, it exhibits significant spin-band splitting, indicative of itinerant altermagnetic behavior. Our results reveal that both strong local electron correlations and judicious ligand selection to promote orbital hybridization are key prerequisites to realizing altermagnetism in strongly correlated systems. These insights pave the way for the rational design and discovery of novel altermagnetic materials.

cond-mat.str-el↗

arXiv2025

Hund's physics extends to actinide f electron systems

Uranium 5f electrons often yield heavy-fermion behavior via Kondo screening. However, the pronounced bad-metallic transport of uranium mononitride (UN) defies an incoherent Kondo explanation. Using density-functional theory combined with dynamical mean-field theory, we show that UN is a strongly correlated bad metal. The dominant correlations arise from intra-atomic Hund's exchange interaction between two 5f electrons, which aligns local magnetic moments and produces large quasiparticle mass renormalization. This identifies UN as a 5f-electron analogue of a Hund's metal-a paradigm chiefly associated with transition-metal d systems. Our results motivate a re-examination of the interplay between Mott, Kondo, and Hund-driven correlations across actinide correlated materials.

cond-mat.str-el↗

arXiv2025

Lifshitz transition in correlated topological semimetals

Topological quasiparticles, arising when the chemical potential is near the band crossing, are pivotal for the development of next-generation quantum devices. They are expected to exist in half-Heusler correlated topological semimetals. However, the emergence of hole carriers, which alter the chemical potential away from the quadratic-band-touching points is not yet understood. Here, we investigated the electronic structure of YPtBi and GdPtBi through ab initio many-body perturbation GW theory combined with dynamical mean-field theory and revealed that the correlation effects of 4$d$ or 4$f$ electrons can lead to the formation of hole carriers. In YPtBi, the weakly correlated Y-4$d$ electrons constitute the topological bands, and the quadratic-band-touching point is at the Fermi level at high temperatures. At low temperatures, enhanced correlations of Y-4$d$ renormalize the topological bands, leading to the formation of hole pocket. In GdPtBi, the strongly correlated Gd-4$f$ electrons form the Hubbard-like bands originate from self-energy effects associated with a topological singularity. These local bands encompass itinerant 4$f$ bands, which hybridize with topological bands to induce pronounced hole bands. This concerted effect reduces the hole doping, bringing the chemical potential closer to the quadratic-band-touching points as the temperature is lowered. The temperature-induced Lifshitz transition should be responsible for the large hole bands observed in both topological semimetals in angle-resolved photoemission spectroscopy measurements at low temperatures. Our findings indicate that the integration of correlated fermions within a topological framework can modulate the energy landscape of topological bands.

cond-mat.str-el↗

arXiv2020

Strain-Controlled Magnetic Ordering in 2D Carbon Metamaterials

We use ab initio spin-polarized density functional theory to study the magnetic order in a Kagomé-like 2D metamaterial consisting of pristine or substitutionally doped phenalenyl radicals polymerized into a nanoporous, graphene-like structure. In this and in a larger class of related structures, the constituent polyaromatic hydrocarbon molecules can be considered as quantum dots that may carry a net magnetic moment. The structure of this porous system and the coupling between the quantum dots may be changed significantly by applying moderate strain, thus allowing to control the magnetic order and the underlying electronic structure.

cond-mat.mes-hall↗

arXiv2018

Enhanced Superconducting Transition Temperature in Electroplated Rhenium

We show that electroplated Re films in multilayers with noble metals such as Cu, Au, and Pd have an enhanced superconducting critical temperature relative to previous methods of preparing Re. The dc resistance and magnetic susceptibility indicate a critical temperature of approximately 6 K. Magnetic response as a function of field at 1.8 K demonstrates type-II superconductivity, with an upper critical field on the order of 2.5 T. Critical current densities greater than 10^7 A/m^2 were measured above liquid-helium temperature. Low-loss at radio frequency was obtained below the critical temperature for multilayers deposited onto resonators made with Cu traces on commercial circuit boards. These electroplated superconducting films can be integrated into a wide range of standard components for low-temperature electronics.

cond-mat.supr-con↗

arXiv2017

Phosphorous dimerization in GaP at high pressure

Using combined experimental and computational approaches we show that at 43 GPa and 1300 K gallium phosphide adopts the super-Cmcm structure, here indicated with its Pearson notation oS24. First-principles enthalpy calculations demonstrate that this oS24 structure is more thermodynamically stable above about 20 GPa than other proposed polymorphs, such as cubic ZB and SC16 or the ubiquitous orthorhombic Cmcm phase (oS8). It is found that oS24-structured GaP exhibits short P-P bonds, according to our high-resolution structural analysis. Such phosphorous dimerization in GaP, observed for the first time and confirmed by ab initio calculations, sheds light on the nature of the super-Cmcm structure and provides critical new insights into the high-pressure polymorphism of octet semiconductors. Bond directionality and anisotropy, in addition to 5-fold phosphorous coordination, explain the relatively low symmetry of this high-pressure structure.

cond-mat.mtrl-sci↗

arXiv2004

Novel Pressure Induced Structural Phase Transition in AgSbTe$_{2}$

We report a novel high pressure structural sequence for the functionally graded thermoelectric, narrow band gap semiconductor AgSbTe$_{2}$, using angle dispersive x-ray diffraction in a diamond anvil cell with synchrotron radiation at room temperature. The compound undergoes a B1 to B2 transition; the transition proceeds through an intermediate amorphous phase found between 17-26 GPa that is quenchable down to ambient conditions. The pressure induced structural transition observed in this compound is the first of its type reported in this ternary cubic family, and it is new for the B1-B2 transition pathway reported to date. Density Functional Theory (DFT) calculations performed for the B1 and B2 phases are in good agreement with the experimental results.

cond-mat.mtrl-sci↗