Hyeon‐Woo Jeong
A5049176677- Astrophysics and Cosmic Phenomena
- Radio Astronomy Observations and Technology
- Graphene research and applications
- Neutrino Physics Research
- 2D Materials and Applications
- Molecular Junctions and Nanostructures
- Electronic and Structural Properties of Oxides
- Topological Materials and Phenomena
- Quantum and electron transport phenomena
- Particle Accelerators and Free-Electron Lasers
- Advanced Battery Materials and Technologies
- Computational Physics and Python Applications
- Magnetic and transport properties of perovskites and related materials
- Advanced Battery Technologies Research
- Magnetic properties of thin films
- Radio Wave Propagation Studies
- Ferroelectric and Piezoelectric Materials
- Advancements in Battery Materials
- ZnO doping and properties
- Semiconductor materials and devices
- Surface Chemistry and Catalysis
- Gyrotron and Vacuum Electronics Research
- Graphene and Nanomaterials Applications
- Quantum-Dot Cellular Automata
- Particle accelerators and beam dynamics
Korea Astronomy and Space Science Institute
2023-2024
Pohang University of Science and Technology
2019-2024
Korea University of Science and Technology
2023-2024
University College Cork
2023
Sungkyunkwan University
2013
Seoul National University
2013
Current-induced control of magnetization in ferromagnets using spin-orbit torque (SOT) has drawn attention as a new mechanism for fast and energy efficient magnetic memory devices. Energy-efficient spintronic devices require spin-current source with large SOT efficiency (ξ) electrical conductivity (σ), an spin injection across transparent interface. Herein, single crystals the van der Waals (vdW) topological semimetal WTe2 vdW ferromagnet Fe3 GeTe2 are used to satisfy requirements their...
Abstract Hexagonal boron nitride (hBN) is a van der Waals semiconductor with wide bandgap of ~ 5.96 eV. Despite the indirect characteristics hBN, charge carriers excited by high energy electrons or photons efficiently emit luminescence at deep-ultraviolet (DUV) frequencies via strong electron-phonon interaction, suggesting potential DUV light emitting device applications. However, electroluminescence from hBN has not been demonstrated so far. In this study, we report and photocurrent...
Abstract The lower-energy peak of the spectral energy distribution blazars has commonly been ascribed to synchrotron radiation from relativistic particles in jets. Despite consensus regarding jet emission processes, particle acceleration mechanism is still debated. Here, we present first X-ray polarization observations PG 1553+113, a high-synchrotron-peak blazar observed by Imaging Polarimetry Explorer (IXPE). We detect an degree (10 ± 2)% along electric-vector position angle ψ X = 86° 8°....
Abstract We report the first >99% confidence detection of X-ray polarization in BL Lacertae. During a recent X-ray/ γ -ray outburst, 287 ks observation (2022 November 27–30) was taken using Imaging Polarimetry Explorer (IXPE), together with contemporaneous multiwavelength observations from Neil Gehrels Swift observatory and XMM-Newton soft X-rays (0.3–10 keV), NuSTAR hard (3–70 optical Calar Alto Perkins Telescope observatories. Our data suggest that IXPE energy band is at crossover...
Aims. We aim to probe the magnetic field geometry and particle acceleration mechanism in relativistic jets of supermassive black holes. Methods. conducted a polarimetry campaign from radio X-ray wavelengths high-synchrotron-peak (HSP) blazar Mrk 421, including Imaging Polarimetry Explorer (IXPE) measurements 2022 December 6–8. During IXPE observation, we also monitored 421 using Swift -XRT obtained single observation with XMM-Newton improve spectral analysis. The time-averaged polarization...
We report the X-ray polarization properties of high-synchrotron-peaked (HSP) blazar PKS 2155−304 based on observations with Imaging Polarimetry Explorer (IXPE). observed source between Oct 27 and Nov 7, 2023. also conducted an extensive contemporaneous multiwavelength (MW) campaign. find that during first half ( T 1 ) IXPE pointing, exhibited highest degree detected for HSP thus far, (30.7 ± 2.0)%; this dropped to (15.3 2.1)% second 2 ). The angle remained stable pointing at 129.4° ±1.8°...
Defects in wide bandgap materials have emerged as promising candidates for solid-state quantum optical technologies. Electrical excitation of single emitters may lead to scalable on-chip devices and therefore is highly sought after. However, most are not amenable efficient doping, posing challenges electrical integration. Here, we demonstrate narrowband electroluminescence from visible near-infrared color centers hexagonal boron nitride (hBN). We harness van der Waals tunnel junctions...
CTA 102 is a $\gamma$-ray bright blazar that exhibited multiple flares in observations by the Large Area Telescope on board Fermi Gamma-Ray Space during period of 2016-2018. We present results from analysis multi-wavelength light curves aiming at revealing nature relativistic jet blazar. analyse radio, optical, X-ray, and data obtained 2012 September 29 to 2018 October 8. identify six curve, showing harder-when-brighter-trend spectra. perform cross-correlation curves. find nearly zero time...
CTA 102 is a γ-ray bright blazar that exhibited multiple flares in observations by the Large Area Telescope on board Fermi Gamma-Ray Space during period of 2016--2018. We present results from analysis multi-wavelength light curves with aim revealing nature relativistic jet blazar. analysed radio, optical, X-ray, and data obtained 2012 September 29 to 2018 October 8. identified six curve, showing harder-when-brighter trend spectra. performed cross-correlation curves. found nearly zero time...
Twisted van der Waals heterostructures provide a platform for studying wide range of electron correlation phenomena, including unconventional superconductivity and correlated insulating states. However, fabricating such devices is challenging due to the difficulty in achieving maintaining homogeneous twist-angles. Here, we present fabrication method preserve twist-angle with minimal deformation. We fabricated marginally twisted double-bilayer graphene (mTDBG) stacks directly imaged resulting...
The blazar 3C 454.3 (z=0.859) has been extensively investigated using multiwavelength high-resolution polarization studies, showing variations on milliarcsecond scales. This study investigates the polarimetric characteristics of at 22--129 GHz decadal (2011--2022) data sets. In addition, we also delve into origin flare observed in 2019. corresponding sets were obtained from single-dish mode observations Korean VLBI Network (KVN) and 43 Very Long Baseline Array (VLBA). Using those data,...
Abstract We present multiwavelength polarization measurements of the luminous blazar Mrk 501 over a 14 month period. The 2–8 keV X-ray was measured with Imaging Polarimetry Explorer (IXPE) six 100 ks observations spanning from 2022 March to 2023 April. Each IXPE observation accompanied by simultaneous data NuSTAR, Swift/XRT, and/or XMM-Newton. Complementary optical–infrared were also available in B , V R I and J bands, as radio 4.85 GHz 225.5 GHz. Among first five observations, we did not...
Abstract We present X-ray polarimetry observations from the Imaging Polarimetry Explorer (IXPE) of three low spectral peak and one intermediate blazars, namely 3C 273, 279, 454.3, S5 0716+714. For none these objects was IXPE able to detect polarization at 3 σ level. However, we placed upper limits on degree ∼10%–30%. The undetected polarizations favor models where band is dominated by unpolarized photons upscattered relativistic electrons in jets although hadronic are not completely...
Recently, lattice dynamics of the highly strained europium monoxide, as a promising candidate for strong ferroelectric-ferromagnet material, applied in next-generation storage devices, attracted huge attention solid-state electronics.Here, authors investigate effect tensile strain on dielectric properties pulsed laser deposited EuO thin films from 10 to 200 K.A nearly 3% out-of-plane compression is observed film thickness was reduced ~ 8 nm, which could originate mismatch between and LaAlO3...
We present the results of a radio multi-frequency ($\rm 3-340~GHz$) study blazar 3C~454.3. After subtracting quiescent spectrum corresponding to optically thin emission, we found two individual synchrotron self-absorption (SSA) features in wide-band spectrum. The one SSA had relatively low turnover frequency ($\nu_{\rm m}$) range $\rm 3-37~GHz$ (lower $\nu_{\rm m}$ spectrum, LSS), and other high 55-124~GHz$ (higher HSS). Using parameters, estimated magnetic field strengths at surface where...
We report, for the first time, that oxidation of bilayer graphene (BLG) can be reversibly and stacking-specifically controlled. The infrared (IR) absorption, IR nanoscopy, Raman spectroscopy measurements on BLG consistently show reversible changes in spectra images upon exposure to O2 H2 at elevated temperatures. also obtain spectroscopic theoretical evidence stacking orders layers have a profound influence oxide structures: AB-BLG reacting with singlet triplet oxygen results endoperoxides...
We present the results of a spectral analysis using simultaneous multifrequency (22, 43, 86, and 129 GHz) very long baseline interferometry (VLBI) observations Korean VLBI Network (KVN) on BL Lac object, Markarian 421 (Mrk 421). The data we used was obtained from January 2013 to June 2018. light curves showed several flux enhancements with global decreases. To separate variable quiescent components in for milliarcsecond-scale emission regions, assumed that radiation comes regions radiating...
Abstract We present the results of a spectral analysis using simultaneous multifrequency (22, 43, 86, and 129 GHz) very long baseline interferometry (VLBI) observations Korean VLBI Network on BL Lac object, Markarian 421. The data we used were obtained from 2013 January to 2018 June. light curves showed several flux enhancements with global decreases. To separate variable quiescent components in for milliarcsecond-scale emission regions, assumed that radiation comes regions radiating...
We report the X-ray polarization properties of high-synchrotron-peaked (HSP) blazar PKS 2155$-$304 based on observations with Imaging Polarimetry Explorer (IXPE). observed source between Oct 27 and Nov 7, 2023. also conducted an extensive contemporaneous multiwavelength (MW) campaign. find that during first half ($T_1$) IXPE pointing, exhibited highest degree detected for HSP thus far, (30.7$\pm$2.0)%, which dropped to (15.3$\pm$2.1)% second ($T_2$). The angle remained stable pointing at...
We present multiwavelength polarization measurements of the luminous blazar Mrk~501 over a 14-month period. The 2--8 keV X-ray was measured with Imaging Polarimetry Explorer (IXPE) six 100-ks observations spanning from 2022 March to 2023 April. Each IXPE observation accompanied by simultaneous data NuSTAR, Swift/XRT, and/or XMM-Newton. Complementary optical-infrared were also available in B, V, R, I, and J bands, as radio 4.85 GHz 225.5 GHz. Among first five observations, we did not find...
First demonstration of electroluminescence from quantum emitters in hexagonal boron nitride by utilizing a novel excitation mechanism that is distinct traditional p-n junctions. We unveil stable isolated narrowband even at room temperature.