arXiv subjects

H. S. Lim

Publications and source records attributed to H. S. Lim.

17 recordsLinked to original sources

arXiv2026

A study of neutrinoless double electron capture in $^{40}$Ca from the AMoRE experiment

The search for neutrinoless double electron capture ($0\nu\mathrm{2EC}$) provides a sensitive probe of lepton-number violation and the Majorana nature of neutrinos. We investigate the $0\nu\mathrm{2EC}$ decay of $^{40}$Ca using cryogenic detectors equipped with metallic magnetic calorimeters in the AMoRE-I experiment. The analysis is based on a physics dataset corresponding to a total exposure of 7.32 kg$\cdot$yr from thirteen $^{40}$Ca$^{100}$MoO$_4$ crystals. No significant excess is observed, and a lower limit on the half-life is obtained as $T^{0\nu}_{1/2} > 1.7 \times 10^{22}$ yr at 90$\%$ confidence level. An improved sensitivity is expected for the upcoming AMoRE-II experiment. These results demonstrate the potential of CaMoO$_4$ detectors to explore rare decay processes beyond the primary $^{100}$Mo $0\nu\beta\beta$ search program.

nucl-ex↗

arXiv2026

LiFE-SNS: LiF Experiment for keV-scale Sterile Neutrino Search

The LiF Experiment for keV-scale Sterile Neutrino Search (LiFE-SNS) aims to probe sterile neutrinos through precision measurements of the tritium $\beta$ spectrum. Tritium nuclei are produced and embedded in LiF crystals via the ${}^{6}\mathrm{Li}(n,\alpha){}^{3}\mathrm{H}$ reaction, allowing thermal calorimetric detection of $\beta$ decays with magnetic microcalorimeters (MMCs) operated at millikelvin temperatures. We present the detector configuration, background studies, and calibration method, including modeling of position-dependent response and characterization of detector nonlinearity. We also discuss potential sources of systematic uncertainty relevant to the sterile-neutrino search. While the first phase of LiFE-SNS has been completed, this paper focuses on calibration and detector characterization. The achieved performance enables precision $\beta$-spectrum measurements, and projected sensitivities indicate competitive reach in the keV mass region.

hep-ex↗

arXiv2025

Improved limit on neutrinoless double beta decay of $^{100}$Mo from AMoRE-I

AMoRE searches for the signature of neutrinoless double beta decay of $^{100}$Mo with a 100 kg sample of enriched $^{100}$Mo. Scintillating molybdate crystals coupled with a metallic magnetic calorimeter operate at milli-Kelvin temperatures to measure the energy of electrons emitted in the decay. As a demonstration of the full-scale AMoRE, we conducted AMoRE-I, a pre-experiment with 18 molybdate crystals, at the Yangyang Underground Laboratory for over two years. The exposure was 8.02 kg$\cdot$year (or 3.89 kg$_{\mathrm{^{100}Mo}}\cdot$year) and the total background rate near the Q-value was 0.025 $\pm$ 0.002 counts/keV/kg/year. We observed no indication of $0νββ$ decay and report a new lower limit of the half-life of $^{100}$Mo $0νββ$ decay as $ T^{0ν}_{1/2}>2.9\times10^{24}~\mathrm{yr}$ at 90\% confidence level. The effective Majorana mass limit range is $m_{ββ}<$(210--610) meV using nuclear matrix elements estimated in the framework of different models, including the recent shell model calculations.

nucl-ex↗

arXiv2025

Development of MMC-based lithium molybdate cryogenic calorimeters for AMoRE-II

The AMoRE collaboration searches for neutrinoless double beta decay of $^{100}$Mo using molybdate scintillating crystals via low temperature thermal calorimetric detection. The early phases of the experiment, AMoRE-pilot and AMoRE-I, have demonstrated competitive discovery potential. Presently, the AMoRE-II experiment, featuring a large detector array with about 90 kg of $^{100}$Mo isotope, is under construction. This paper discusses the baseline design and characterization of the lithium molybdate cryogenic calorimeters to be used in the AMoRE-II detector modules. The results from prototype setups that incorporate new housing structures and two different crystal masses (316 g and 517 - 521 g), operated at 10 mK temperature, show energy resolutions (FWHM) of 7.55 - 8.82 keV at the 2.615 MeV $^{208}$Tl $γ$ line, and effective light detection of 0.79 - 0.96 keV/MeV. The simultaneous heat and light detection enables clear separation of alpha particles with a discrimination power of 12.37 - 19.50 at the energy region around $^6$Li(n, $α$)$^3$H with Q-value = 4.785 MeV. Promising detector performances were demonstrated at temperatures as high as 30 mK, which relaxes the temperature constraints for operating the large AMoRE-II array.

physics.ins-det↗

arXiv2024

Development of decay energy spectroscopy for radio impurity analysis

We present the development of a decay energy spectroscopy (DES) method for the analysis of radioactive impurities using magnetic microcalorimeters (MMCs). The DES system was designed to analyze radionuclides, such as Ra-226, Th-228, and their daughter nuclides, in materials like copper, commonly used in rare-event search experiments. We tested the DES system with a gold foil absorber measuring 20x20x0.05 mm^3, large enough to accommodate a significant drop of source solution. Using this large absorber and an MMC sensor, we conducted a long-term measurement over ten days of live time, requiring 11 ADR cooling cycles. The combined spectrum achieved an energy resolution of 45 keV FWHM, sufficient to identify most alpha and DES peaks of interest. Specific decay events from radionuclide contaminants in the absorber were identified. This experiment confirms the capability of the DES system to measure alpha decay chains of Ra-226 and Th-228, offering a promising method for radio-impurity evaluation in ultra-low background experiments.

physics.ins-det↗

arXiv2024

Projected background and sensitivity of AMoRE-II

AMoRE-II aims to search for neutrinoless double beta decay with an array of 423 Li$_2$$^{100}$MoO$_4$ crystals operating in the cryogenic system as the main phase of the Advanced Molybdenum-based Rare process Experiment (AMoRE). AMoRE has been planned to operate in three phases: AMoRE-pilot, AMoRE-I, and AMoRE-II. AMoRE-II is currently being installed at the Yemi Underground Laboratory, located approximately 1000 meters deep in Jeongseon, Korea. The goal of AMoRE-II is to reach up to $T^{0νββ}_{1/2}$ $\sim$ 6 $\times$ 10$^{26}$ years, corresponding to an effective Majorana mass of 15 - 29 meV, covering all the inverted mass hierarchy regions. To achieve this, the background level of the experimental configurations and possible background sources of gamma and beta events should be well understood. We have intensively performed Monte Carlo simulations using the GEANT4 toolkit in all the experimental configurations with potential sources. We report the estimated background level that meets the 10$^{-4}$counts/(keV$\cdot$kg$\cdot$yr) requirement for AMoRE-II in the region of interest (ROI) and show the projected half-life sensitivity based on the simulation study.

physics.ins-det↗

arXiv2024

Background study of the AMoRE-pilot experiment

We report a study on the background of the Advanced Molybdenum-Based Rare process Experiment (AMoRE), a search for neutrinoless double beta decay (\znbb) of $^{100}$Mo. The pilot stage of the experiment was conducted using $\sim$1.9 kg of \CAMOO~ crystals at the Yangyang Underground Laboratory, South Korea, from 2015 to 2018. We compared the measured $β/γ$ energy spectra in three experimental configurations with the results of Monte Carlo simulations and identified the background sources in each configuration. We replaced several detector components and enhanced the neutron shielding to lower the background level between configurations. A limit on the half-life of $0νββ$ decay of $^{100}$Mo was found at $T_{1/2}^{0ν} \ge 3.0\times 10^{23}$ years at 90\% confidence level, based on the measured background and its modeling. Further reduction of the background rate in the AMoRE-I and AMoRE-II are discussed.

nucl-ex↗

arXiv2022

Status and performance of the AMoRE-I experiment on neutrinoless double beta decay

AMoRE is an international project to search for the neutrinoless double beta decay of $^{100}$Mo using a detection technology consisting of magnetic microcalorimeters (MMCs) and molybdenum-based scintillating crystals. Data collection has begun for the current AMORE-I phase of the project, an upgrade from the previous pilot phase. AMoRE-I employs thirteen $^\mathrm{48depl.}$Ca$^{100}$MoO$_4$ crystals and five Li$_2$$^{100}$MoO$_4$ crystals for a total crystal mass of 6.2 kg. Each detector module contains a scintillating crystal with two MMC channels for heat and light detection. We report the present status of the experiment and the performance of the detector modules.

physics.ins-det↗

arXiv2022

A lab scale experiment for keV sterile neutrino search

We developed a simple small-scale experiment to measure the beta decay spectrum of $^{3}$H. The aim of this research is to investigate the presence of sterile neutrinos in the keV region. Tritium nuclei were embedded in a 1$\times$1$\times$1 cm$^3$ LiF crystal from the $^6$Li(n,$α$)$^3$H reaction. The energy of the beta electrons absorbed in the LiF crystal was measured with a magnetic microcalorimeter at 40 mK. We report a new method of sample preparation, experiments, and analysis of $^3$H beta measurements. The spectrum of a 10-hour measurement agrees well with the expected spectrum of $^3$H beta decay. The analysis results indicate that this method can be used to search for keV-scale sterile neutrinos.

physics.ins-det↗

arXiv2014

Tuning the Band Structures of a 1D Width-Modulated Magnonic Crystal by a Transverse Magnetic Field

Theoretical studies, based on three independent techniques, of the band structure of a one-dimensional width-modulated magnonic crystal under a transverse magnetic field are reported. The band diagram is found to display distinct behaviors when the transverse field is either larger or smaller than a critical value. The widths and center positions of bandgaps exhibit unusual non-monotonic and large field-tunability through tilting the direction of magnetization. Some bandgaps can be dynamically switched on and off by simply tuning the strength of such a static field. Finally, the impact of the lowered symmetry of the magnetic ground state on the spin-wave excitation efficiency of an oscillating magnetic field is discussed. Our finding reveals that the magnetization direction plays an important role in tailoring magnonic band structures and hence in the design of dynamic spin-wave switches.

cond-mat.mtrl-sci↗

arXiv2013

Comment on "Physical Origin and Generic Control of Magnonic Band Gaps of Dipole-Exchange Spin Waves in Width-Modulated Nanostrip Waveguides" [K.-S. Lee, D.-S. Han, and S.-K. Kim, PRL 102, 127202 (2009), arXiv:0811.0411]

In Ref. [PRL 102, 127202 (2009)] Lee et al. reported the existence of large magnonic bandgaps in one-dimensional width-modulated Permalloy nanostripe waveguides based on OOMMF simulations. However, as the symmetry of the magnetic field pulse they applied to excite the spin waves (SWs) was not general, the entire set of SW branches with A symmetry was omitted from the magnonic band structures (see below). This omission has unfortunately led to misleading conclusions of, for instance, the number, width and position of the bandgaps. We present here the full band structure based on three different theoretical approaches that gave consistent predictions, thus corroborating the methods employed, namely, a microscopic approach, OOMMF simulations, and a method based on the linearized Landau-Lifshitz equation. Further, we provide a physical interpretation using group theory.

cond-mat.mes-hall↗

arXiv2008

Micro-Brillouin Study of the Eigenvibrations of Single Isolated Polymer Nanospheres

The localized acoustic modes of single isolated polymethyl methacrylate (PMMA) and polystyrene nanospheres have been studied by micro-Brillouin light scattering. The measured mode frequencies are analyzed on the basis of the Lamb theory formulated for a sphere under free boundary conditions. By measuring light scattering from single isolated particles, placed atop a piece of polished silicon wafer, the free-surface conditions are almost experimentally realized. The observed spectral peaks are attributed to localized eigenvibrations whose frequencies scale as inverse sphere diameter, in accordance with Lamb's theory. The Young's moduli and Poisson ratios of the polymer spheres studied have been evaluated from fits to the experimental data. We have demonstrated that micro-Brillouin spectroscopy is a powerful technique for probing the acoustic dynamics and mechanical properties of nanostructures.

cond-mat.other↗

arXiv2008

Selection rules for Brillouin light scattering from eigenvibrations of a sphere

Selection rules governing Brillouin light scattering from the vibrational eigenmodes of a homogeneous, free-surface submicron sphere have been derived using group theory. The derivation is for the condition where the sphere diameter is of the order of the excitation light wavelength. Well-resolved spectral data obtained from Brillouin light scattering from submicron silica spheres provide experimental verification of the selection rules.

cond-mat.other↗

arXiv2004

Theory of Upper Critical Field without Energy Quantization

Conventional theories for determining upper critical fields are inevitably related to the lowest eigenvalues of appropriate equations. In this Letter, a new theory of upper critical fields is designed and justified. Using MgB$_2$ as modeling prototype, our computations are in excellent agreement with the Ginzburg-Landau theory. The long-standing issue, the upward curvature of the upper critical field, is found to be a manifestation of the crossover of the order parameter. The current theory is an alternative to the traditional technique of energy quantization in determining upper critical fields.

cond-mat.supr-con↗

arXiv2003

Determinations of upper critical field in continuous Ginzburg-Landau model

Novel procedures to determine the upper critical field $B_{c2}$ have been proposed within a continuous Ginzburg-Landau model. Unlike conventional methods, where $B_{c2}$ is obtained through the determination of the smallest eigenvalue of an appropriate eigen equation, the square of the magnetic field is treated as eigenvalue problems so that the upper critical field can be directly deduced. The calculated $B_{c2}$ from the two procedures are consistent with each other and in reasonably good agreement with existing theories and experiments. The profile of the order parameter associated with $B_{c2}$ is found to be Gaussian-like, further validating the methodology proposed. The convergences of the two procedures are also studied.

cond-mat.supr-con↗

arXiv2002

Determinations of upper critical field in the c-a plane

Within a continuous Ginzburg-Landau model for layered superconductors, two procedures are proposed to determine the upper critical field parallel to the $c$-$a$ crystal plane with an angle $θ$ tilted from the c-axis. For an intrinsically layered superconductor, the upper critical fields for $θ\to 90^\circ$, as determined by the two procedures, are consistent with each other and in reasonably good agreement with those determined by similar procedures suited for the parallel upper critical field ($θ= 90^\circ$). The profile of the order parameter obtained at $B_{c2}$ is Gaussian-like, indicating the plausibility of the procedures proposed.

cond-mat.supr-con↗

arXiv2002

Properties of parallel upper critical field within Continuous Ginzburg-Landau model

In this paper, we employ a continuous Ginzburg-Landau model to study the behaviors of the parallel upper critical field of an intrinsically-layered superconductor. Near $T_c$ where the order parameter is nearly homogeneous, the parallel upper critical field is found to vary as $(1-T/T_c)^{1/2}$. With a well-localized order parameter, the same field temperature dependence holds over the whole temperature range. The profile of the order parameter at the parallel upper critical field may be of a Gaussian type, which is consistent with the usual linear Ginzburg-Landau theory. In addition, the influences of the unit cell dimension and the average effective masses on the parallel upper critical field and the associated order parameter are also addressed.

cond-mat.supr-con↗