Ji Hoon Shim

Pohang University of Science and Technology

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Changhoon Lee

Pohang University of Science and Technology

B. I. Min

Pohang University of Science and Technology

Bo Gyu Jang

Los Alamos National Laboratory

Jisook Hong

Lawrence Berkeley National Laboratory

Jun Sung Kim

Institute for Basic Science

Changyoung Kim

Institute for Basic Science

Ina Park

Pohang University of Science and Technology

Geunsik Lee

Ulsan National Institute of Science and Technology

Duck Young Kim

Center for High Pressure Science and Technology Advanced Research

Gabriel Kotliar

Rutgers, The State University of New Jersey

Cooperative Institutions

Pohang University of Science and Technology

229

Seoul National University

150

Institute for Basic Science

129

Yonsei University

108

Government of the Republic of Korea

Sungkyunkwan University

Korea Advanced Institute of Science and Technology

Samsung (South Korea)

Lawrence Berkeley National Laboratory

Korea University

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Kondo interaction in FeTe and its potential role in the magnetic order

Nature Communications (2023)

Younsik Kim Minseok Kim Dongwook Kim Minjae Kim Minsoo Kim

Finding d-electron heavy fermion (HF) states has been an important topic as the diversity in d-electron materials can lead to many exotic Kondo effect-related phenomena or new states of matter such as correlation-driven topological Kondo insulator or cooperation between long-range magnetism and Kondo lattice behavior. Yet, obtaining direct spectroscopic evidence for a d-electron HF system has been elusive to date. Here, we report the observation of Kondo lattice behavior in an antiferromagnetic metal, FeTe, via angle-resolved photoemission spectroscopy (ARPES) and transport properties measurements. The Kondo lattice behavior is represented by the emergence of a sharp quasiparticle at low temperatures. The transport property measurements confirm the low-temperature Fermi liquid behavior and reveal successive coherent-incoherent crossover upon increasing temperature. We interpret the Kondo lattice behavior as a result of hybridization between localized Fe 3dxy and itinerant Te 5pz orbitals. Our interpretation is further evidenced by Fano-type tunneling spectra which accompany a hybridization gap. Our observations strongly suggest unusual cooperation between Kondo lattice behavior and long-range magnetic order.

Kondo insulator

Magnetism

Strongly correlated material

Lattice (music)

10.1038/s41467-023-39827-1

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Citations (8)

Ultrafast Infrared Photoresponse from Heavily Hydrogen-Doped VO₂ Single Crystalline Nanoparticles

Nano Letters (2020)

Minwoo Kim Yong‐Ryun Jo Changhoon Lee Won‐Jin Moon Ji Hoon Shim

Infrared photodetectors are sought for diverse applications and their performance relies on photoactive materials and photocurrent generation mechanisms. Here, we fabricate IR photodetectors with heavily hydrogen-doped VO2 (i.e., HVO2) single-crystalline nanoparticles which show two orders greater resistivities than pure VO2. The I–V plots obtained under IR light irradiation are expressed by space charge limited current mechanism and the increase in photocurrent occurs due to the increase in the number of photoinduced trap sites. This phenomenon remarkably improves the key parameters at λ = 780 nm of high responsivity of 35280 A/W, high detectivity of 1.12 × 1013 Jones, and strikingly fast response times of 0.6–2.5 ns, that is, 3 orders of magnitude faster than the best records of two-dimensional structures and heterostructures. Density functional theory calculations illustrate that the generation of photoinduced trap sites is attributed to the movement of hydrogen atoms to less stable interstitial sites in VO2 under light exposure.

Photocurrent

Photoconductivity

10.1021/acs.nanolett.0c00358

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Citations (19)

Large anomalous Hall current induced by topological nodal lines in a ferromagnetic van der Waals semimetal

Nature Materials (2018)

Kyoo Kim Junho Seo Eunwoo Lee Kyung‐Tae Ko Beom Seok Kim

Topological insulator

10.1038/s41563-018-0132-3

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Citations (443)

Ultrafast Energy Transfer Process in Confined Gold Nanospheres Revealed by Femtosecond X-ray Imaging and Diffraction

Nano Letters (2023)

Jaeyong Shin Chul-Ho Jung Yungok Ihm Seung-Phil Heo Daewoong Nam

Femtosecond laser pulses drive nonequilibrium phase transitions via reaction paths hidden in thermal equilibrium. This stimulates interest to understand photoinduced ultrafast melting processes, which remains incomplete due to challenges in resolving accompanied kinetics at the relevant space-time resolution. Here, by newly establishing a multiplexing femtosecond X-ray probe, we have successfully revealed ultrafast energy transfer processes in confined Au nanospheres. Real-time images of electron density distributions with the corresponding lattice structures elucidate that the energy transfer begins with subpicosecond melting at the specimen boundary earlier than the lattice thermalization, and proceeds by forming voids. Two temperature molecular dynamics simulations uncovered the presence of both heterogeneous melting with the melting front propagation from surface and grain boundaries and homogeneous melting with random melting seeds and nanoscale voids. Supported by experimental and theoretical results, we provide a comprehensive atomic-scale picture that accounts for the ultrafast laser-induced melting and evaporation kinetics.

Femtochemistry

10.1021/acs.nanolett.2c04920

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Citations (7)

Two roles of salicylic acid in the accumulation of polyhydroxyalkanoic acid in Pseudomonas fluorescens BM07 grown with mixtures of fructose and 11-phenoxyundecanoic acid

한국생물공학회 학술대회 (2005)

Ji Hoon Shim Jong Kook Rho Mun Hwan Choi Sung Chul Yoon

Pseudomonas fluorescens

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High-performance rechargeable metal–air batteries enabled by efficient charge transport in multielement random alloy electrocatalyst

Applied Catalysis B Environment and Energy (2023)

Chandran Balamurugan Changhoon Lee Kyusang Cho Jehan Kim Byoungwook Park

The integration of bifunctionally active sites of multielement random alloy catalysts with other metal oxide electrocatalysts is a promising strategy for efficient electrochemical reactions. In this study, a novel combination of virtual crystal approximation and hydrothermal synthesis was used to investigate the composition-dependent structure and electrical property in a Ag1−xNix catalyst. The combination showed that a hexagonal closed-packed structure of Ag1−xNix with a compositional ratio of 6:4 (Ag:Ni) had electrical conductivity of ∼2 × 107 S∙cm−1 and an ionization potential of − 5.4 eV. Furthermore, the bifunctional oxygen electrocatalytic efficiencies of Ag0.6Ni0.4 were improved by forming a heterointerface with the CoNb2O6 electrocatalyst, resulting in a discharge-charge voltage gap of 0.81 V over 587 h, peak power density of 178.9 mW∙cm−2, and specific capacity of 806.8 mA∙h∙g−1 in a zinc–air battery. This approach was applied to pouch-type zinc–air batteries, resulting in long-term stability of over 158.6 h at 10 mA∙cm−2.

10.1016/j.apcatb.2023.122631

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Observation of a kink during the formation of the Kondo resonance band in a heavy-fermion system

Physical Review B (2013)

Hong Chul Choi Kristjan Haule Gabriel Kotliar B. I. Min Ji Hoon Shim

We have shown that the kink behavior in the spectral function of a heavy fermion can appear during the formation of the Kondo resonance (KR) band and the hybridization gap. We have investigated the heavy fermion compound CeCoGe${}_{2}$, using a combined approach of the density functional theory and the dynamical mean field theory. Low temperature $T$ spectral functions show dispersive KR states, similarly to the recent experimental observation. During the evolution from the $\text{non-}f$ conduction band state at high $T$ to the dispersive KR band state at low $T$, which have topologically different band shapes, we have found the existence of kinks in the $\text{non-}f$ spectral function near the Fermi level ${E}_{F}$. The observation of kink is clearly in correspondence with the multiple temperature scales of the formation of the KR band.

Spectral function

Kondo insulator

Anderson impurity model

10.1103/physrevb.88.125111

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Citations (16)

Vacancy-suppressed lattice conductivity of high-ZTIn4Se3−x

Physical Review B (2013)

Hyo Seok Ji Hyoungchul Kim Changhoon Lee Jong‐Soo Rhyee Moo Hwan Kim

Anomalous, vacancy-induced anisotropic thermal conductivity is one of the important properties in the recently discovered high-$ZT$ In${}_{4}$Se${}_{3\ensuremath{-}x}$ compound. In this work, the lattice thermal conductivity of In${}_{4}$Se${}_{3\ensuremath{-}x}$ is investigated using equilibrium molecular dynamics simulation, the point-defect model, and ab initio calculations. The charge density distribution shows highly anisotropic structure with strong bonding along In-Se-In chain direction. Se vacancy strongly suppresses the phonon propagation along the chain direction, with little change in other directions. We show that suppressed long-range acoustic phonon transport caused by the vacancy results in anisotropic change of lattice conductivity. We suggest controlling of vacancy in intrinsic low-dimensional compounds is critical in achieving optimal lattice thermal conductivity and other thermoelectric properties.

Lattice (music)

10.1103/physrevb.87.125111

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Citations (36)

Thermophysical properties of liquid UO2, ZrO2 and corium by molecular dynamics and predictive models

Journal of Nuclear Materials (2017)

Woong Kee Kim Ji Hoon Shim Massoud Kaviany

Corium

10.1016/j.jnucmat.2017.04.030

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Citations (38)

Oxygen-driven enhancement of electron correlation in hexagonal iron at Earth's inner core conditions

arXiv (Cornell University) (2021)

Bo Gyu Jang Yu He Ji Hoon Shim Ho‐kwang Mao Duck Young Kim

Earth's inner core consists of mainly iron with a bit of light elements. Understanding of its structure and related physical properties has been elusive for both experiment and theory due to its required extremely high pressure and temperature conditions. Here, using density functional theory plus dynamical mean field theory, we demonstrate that oxygen atoms energetically stabilize hexagonal structured iron at the inner core condition. Electrical resistivity is much enhanced compared with pure hcp-Fe, supporting the conventional thermal convection model. Moreover, our calculated seismic velocity shows a quantitative match with geologically observed Preliminary Reference Earth Model data.

Outer core

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