arXiv subjects

Chul Hong Park

Publications and source records attributed to Chul Hong Park.

9 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

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↗

arXiv2025

Coexistence of 3D and quasi-2D Fermi surfaces driven by orbital selective Kondo scattering in UTe$_2$

The 3D Fermi surface, along with a chiral in-gap state and a Majorana zero energy state, is suggested to play a crucial role in the topologically nontrivial superconductivity in UTe$_2$. However, conflicting experimental observations of the 2D Fermi surface raise questions about topological superconductivity. By combining ab initio many-body perturbation GW theory and dynamical mean-field theory based on Feynman diagrams, we discovered the coexistence of two orbital dependent Fermi surfaces, both centered at the $Γ$ point in the Brillouin zone, which are heavily influenced by the orbital-selective Kondo effect. At high temperature, both Fermi surfaces exhibit 3D nature with weak spectral weight due to incoherent Kondo hybridization. Upon cooling down to 25 K, due to the pronounced Kondo coherence, while one Fermi surface remains a robust 3D Fermi surface, the other transforms surprisingly into a quasi-2D Fermi surface, which should be responsible for the experimental observation of 2D character. Our results suggest that the 3D Fermi surface should exist at low temperature for the topological superconductivity. Our findings call for further investigation of the interplay between the two orbital-dependent $Γ$-centered Fermi surfaces.

cond-mat.str-el↗

arXiv2024

Topological singularity-induced Mott-like self-energy and its impact on Kondo cloud formation

We discovered that abnormal Mott physics can emerge even in weakly correlated 4f fermions through their interplay with topological singularity. Employing ab initio many-body perturbation theory combined with dynamical mean field theory, we show that 4f electrons near the topological singular point experience strong effective Coulomb repulsion, as the hybridization channels are blocked near the singularity. As a result, Mott-like self-energy emerges, forbidding the coexistence of 4f quasiparticles and the topological singularity at the same energy level in HoPtBi, PrPtBi, and PrAlGe. The formation of 4f quasiparticles is highly dependent on the energy of topological singularity relative to the Fermi level. This effect is suggested to be responsible for the selective quantum phenomena observed between heavy fermion behavior from Kondo resonance and anomalous transport from nontrivial topological states.

cond-mat.str-el↗

arXiv2023

Mott transition and abnormal instability of electronic structure in FeSe

FeSe has been extensively explored as a quantum material, primarily due to the observed highest superconducting transition temperature among Fe-based unconventional superconductors. Nonetheless, the electronic structure and the electron correlations responsible for the remarkable diversity of physical properties in FeSe remain elusive. We undertook a comprehensive investigation of the electronic structure of FeSe, known as a Hund metal, and found that it is not uniquely defined. Through accounting for all two-particle irreducible diagrams constructed from electron Green's function $G$ and screened Coulomb interaction $W$ in a self-consistent manner, a Mott-insulator phase of FeSe is unveiled. The metal-insulator transition is driven by the strong on-site Coulomb interaction in its paramagnetic phase, accompanied by the weakening of both local and non-local screening effects on the Fe-3$d$ orbitals. Our results suggest that Mott physics may play a pivotal role in shaping the electronic, optical, and superconducting properties of monolayer or nanostructured FeSe.

cond-mat.str-el↗

arXiv2022

Impacts of f-d Kondo cloud on superconductivity of nickelates

The discovery of superconducting nickelates reignited hope for elucidating the high-$T_{\textrm{c}}$ superconductivity mechanism in the isostructural cuprates. While in the cuprates, the superconducting gap opens up on a single-band of the quasi-2D Fermi surface, the nickelates are known to have 3D nature of electronic structure with multi-band. This raises a serious question about the role of 2D nature for the high-$T_{\textrm{c}}$ superconductivity. Here, employing dynamical mean field theory combined with GW method, we found the Kondo effect driven by the strong correlation of Nd-4$f$ and Ni-3$d$ electrons emerging at low temperature. The Kondo effect modifies the topology of the Fermi surface leading to 3D multi-band nature. Remarkably, the Kondo effect is easily destroyed by lattice modulation, leading to the quasi-2D nature. Our findings clearly explain the inconsistent occurrence of superconductivity and distinct electrical resistivity behavior between NdNiO$_{2}$ bulk and films.

cond-mat.str-el↗

arXiv2020

Ferromagnetic Weyl Fermions in Two-Dimensional Layered Electride Gd$_2$C

Recently, two-dimensional layered electrides have emerged as a new class of materials which possess anionic electron layers in the interstitial spaces between cationic layers. Here, based on first-principles calculations, we discover a time-reversal-symmetry-breaking Weyl semimetal phase in a unique two-dimensional layered ferromagnetic (FM) electride Gd$_2$C. It is revealed that the crystal field mixes the interstitial electron states and Gd 5$d$ orbitals near the Fermi energy to form band inversions. Meanwhile, the FM order induces two spinful Weyl nodal lines (WNLs), which are converted into multiple pairs of Weyl nodes through spin-orbit coupling. Further, we not only identify Fermi-arc surface states connecting the Weyl nodes but also predict a large intrinsic anomalous Hall conductivity due to the Berry curvature produced by the gapped WNLs. Our findings demonstrate the existence of Weyl fermions in the room-temperature FM electride Gd$_2$C, therefore offering a new platform to investigate the intriguing interplay between electride materials and magnetic Weyl physics.

cond-mat.mtrl-sci↗

arXiv2019

Hidden Weyl Fermions in Paramagnetic Electride Y$_2$C

Recent experimental observations of Weyl fermions in materials opens a new frontier of condensed matter physics. Based on first-principles calculations, we here discover Weyl fermions in a two-dimensional layered electride material Y$_2$C. We find that the Y 4$d$ orbitals and the anionic $s$-like orbital confined in the interstitial spaces between [Y$_2$C]$^{2+}$ cationic layers are hybridized to give rise to van Have singularities near the Fermi energy $E_{\rm F}$, which induce a ferromagnetic (FM) order via the Stoner-type instability. This FM phase with broken time-reversal symmetry hosts the rotation-symmetry protected Weyl nodal lines near $E_{\rm F}$, which are converted into the multiple pairs of Weyl nodes by including spin-orbit coupling (SOC). However, we reveal that, due to its small SOC effects, Y$_2$C has a topologically nontrivial drumhead-like surface state near $E_{\rm F}$ as well as a very small magnetic anisotropy energy with several $μ$eV per unit cell, consistent with the observed surface state and paramagnetism at low temperatures below ${\sim}$2 K. Our findings propose that the Brillouin zone coordinates of Weyl fermions hidden in paramagnetic electride materials would fluctuate in momentum space with random orientations of the magnetization direction.

cond-mat.mtrl-sci↗

arXiv2016

Stacking-sequence-independent band structure and shear exfoliation of two-dimensional electride materials

The electronic band structure of crystals is generally influenced by the periodic arrangement of their constituent atoms. Specifically, the emerging two-dimensional (2D) layered structures have shown different band structures with respect to their stacking configurations. Here, based on first-principles density-functional theory calculations, we demonstrate that the band structure of the recently synthesized 2D Ca$_2$N electride changes little for the stacking sequence as well as the lateral interlayer shift. This intriguing invariance of band structure with respect to geometrical variations can be attributed to a complete screening of [Ca$_2$N]$^{+}$ cationic layers by anionic excess electrons delocalized between the cationic layers. The resulting weak interactions between 2D dressed cationic layers give rise to not only a shallow potential barrier for bilayer sliding but also an electron-doping facilitated shear exfoliation. Our findings open a route for exploration of the peculiar geometry-insensitive electronic properties in 2D electride materials, which will be useful for future thermally stable electronic applications.

cond-mat.mtrl-sci↗