arXiv subjects

D. -H. Kim

Publications and source records attributed to D. -H. Kim.

At least 19 recordsLinked to original sources

arXiv2026

First-order phase transitions in the three-dimensional Blume-Capel ferromagnet

We investigate first-order phase transitions in the three-dimensional Blume-Capel ferromagnet on the simple cubic lattice by combining multicanonical simulations with two-parameter Wang-Landau sampling. The generalized-ensemble approach enables a detailed characterization of the coexistence region over a broad range of temperatures and crystal-field couplings, extending from the vicinity of the tricritical point deep into the first-order regime. We analyze the finite-size scaling behavior of thermodynamic observables, with particular emphasis on the energy probability density function, free-energy barriers, and interfacial properties. The evolution of the double-peaked energy distributions reveals a gradual crossover from weak to strong first-order behavior as the temperature is lowered. From the scaling of the free-energy barrier we determine the interface tension along the coexistence line and characterize its approach to the tricritical region through its vanishing behavior. In parallel, a field-mixing analysis based on the joint density of states obtained from two-parameter Wang-Landau simulations is employed to locate first-order transition points and probe tricritical behavior. While this approach has been highly successful in two-dimensional realizations of the Blume-Capel model, we find that in three dimensions its practical implementation becomes increasingly sensitive in the vicinity of the tricritical region, where the shallow structure of the relevant scaling variable distribution limits the ability to resolve coexistence conditions for the system sizes currently accessible. These results delineate the range of applicability of the method in three dimensions and provide a consistent picture of the first-order regime of the model.

cond-mat.stat-mech↗

arXiv2025

Asteroid sizes determined with thermophysical model and stellar occultations

Context. The sizes of many asteroids, especially slowly rotating, low-amplitude targets, remain poorly constrained due to selection effects. These biases limit the availability of high-quality data, leaving size estimates reliant on spherical shape assumptions. Such approximations introduce significant uncertainties propagating, e.g. into density determinations or thermophysical and compositional studies, affecting our understanding of asteroid properties. Aims. This work targets poorly studied main-belt asteroids, most of which lacked shape models. Using only high-quality dense light curves, thermal IR observations (incl. WISE), and stellar occultations, we aimed to produce reliable shape models and scale them via two independent techniques, allowing size comparison. We conducted two campaigns to obtain dense photometric light curves and to acquire multi-chord stellar occultations. Methods. Shape and spin models were reconstructed using lightcurve inversion. Sizes were determined by (1) thermophysical modeling with the Convex Inversion Thermophysical Model (CITPM), optimizing spin and shape models to visible lightcurve and IR data, and (2) scaling shape models with stellar occultations. Results. We obtained precise sizes and shape models for 15 asteroids. CITPM- and occultation-derived sizes agree within 5% in most cases, demonstrating the modeling's reliability. Larger discrepancies usually stem from incomplete occultation chord coverage. The study also gives insights into surface properties incl. albedo, roughness and thermal inertia. Conclusions. Using high-quality data and an advanced TPM integrating thermal and visible data with shape adjustment enabled precise size estimates comparable to those from multi-chord stellar occultations. We resolved major inconsistencies in previous size estimates, providing solid input for future studies on asteroid densities and surfaces.

astro-ph.EP↗

arXiv2023

Scaling slowly rotating asteroids by stellar occultations

As evidenced by recent survey results, majority of asteroids are slow rotators (P>12 h), but lack spin and shape models due to selection bias. This bias is skewing our overall understanding of the spins, shapes, and sizes of asteroids, as well as of their other properties. Also, diameter determinations for large (>60km) and medium-sized asteroids (between 30 and 60 km) often vary by over 30% for multiple reasons. Our long-term project is focused on a few tens of slow rotators with periods of up to 60 hours. We aim to obtain their full light curves and reconstruct their spins and shapes. We also precisely scale the models, typically with an accuracy of a few percent. We used wide sets of dense light curves for spin and shape reconstructions via light-curve inversion. Precisely scaling them with thermal data was not possible here because of poor infrared data: large bodies are too bright for WISE mission. Therefore, we recently launched a campaign among stellar occultation observers, to scale these models and to verify the shape solutions, often allowing us to break the mirror pole ambiguity. The presented scheme resulted in shape models for 16 slow rotators, most of them for the first time. Fitting them to stellar occultations resolved previous inconsistencies in size determinations. For around half of the targets, this fitting also allowed us to identify a clearly preferred pole solution, thus removing the ambiguity inherent to light-curve inversion. We also address the influence of the uncertainty of the shape models on the derived diameters. Overall, our project has already provided reliable models for around 50 slow rotators. Such well-determined and scaled asteroid shapes will, e.g. constitute a solid basis for density determinations when coupled with mass information. Spin and shape models continue to fill the gaps caused by various biases.

astro-ph.EP↗

arXiv2022

Refinement of the convex shape model and tumbling spin state of (99942) Apophis using the 2020-2021 apparition data

Context. The close approach of the near-Earth asteroid (99942) Apophis to Earth in 2029 will provide a unique opportunity to examine how the physical properties of the asteroid could be changed due to the Earth's gravitational perturbation. As a result, the Republic of Korea is planning a rendezvous mission to Apophis. Aims. Our aim was to use photometric data from the apparitions in 2020-2021 to refine the shape model and spin state of Apophis. Methods. Using thirty-six 1 to 2-m class ground-based telescopes and the Transiting Exoplanet Survey Satellite, we performed a photometric observation campaign throughout the 2020-2021 apparition. The convex shape model and spin state were refined using the light-curve inversion method. Results. According to our best-fit model, Apophis is rotating in a short axis mode with rotation and precession periods of 264.178 hours and 27.38547 hours, respectively. The angular momentum vector orientation of Apophis was found as (275$^\circ$, -85$^\circ$) in the ecliptic coordinate system. The ratio of the dynamic moments of inertia of this asteroid was fitted to $I_a:I_b:I_c=0.64:0.97:1$, which corresponds to an elongated prolate ellipsoid. These findings regarding the spin state and shape model could be used to not only design the space mission scenario but also investigate the impact of the Earth's tidal force during close encounters.

astro-ph.EP↗

arXiv2021

Properties of slowly rotating asteroids from the Convex Inversion Thermophysical Model

Results from the TESS mission showed that previous studies strngly underestimated the number of slow rotators, revealing the importance of studying those asteroids. For most slowly rotating asteroids (P > 12), no spin and shape model is available because of observation selection effects. This hampers determination of their thermal parameters and accurate sizes. We continue our campaign in minimising selection effects among main belt asteroids. Our targets are slow rotators with low light-curve amplitudes. The goal is to provide their scaled spin and shape models together with thermal inertia, albedo, and surface roughness to complete the statistics. Rich multi-apparition datasets of dense light curves are supplemented with data from Kepler and TESS. In addition to data in the visible range, we also use thermal data from infrared space observatories (IRAS, Akari and WISE) in a combined optimisation process using the Convex Inversion Thermophysical Model (CITPM). This novel method has so far been applied to only a few targets, and in this work we further validate the method. We present the models of 16 slow rotators. All provide good fits to both thermal and visible data. The obtained sizes are on average accurate at the 5% precision, with diameters in the range from 25 to 145 km. The rotation periods of our targets range from 11 to 59 hours, and the thermal inertia covers a wide range of values, from 2 to <400 SI units, not showing any correlation with the period. With this work we increase the sample of slow rotators with reliable spin and shape models and known thermal inertia by 40%. The thermal inertia values of our sample do not display a previously suggested increasing trend with rotation period, which might be due to their small skin depth.

astro-ph.EP↗

arXiv2021

Quasi-static strain governing ultrafast spin dynamics

The quasi-static strain (QSS) is the product generated by the lattice thermal expansion after ultrafast photo-excitation and the effects of thermal and QSS are inextricable. Nevertheless, the two phenomena with the same relaxation timescale should be treated separately because of their different fundamental actions to the ultrafast spin dynamics. By employing ultrafast Sagnac interferometry and magneto-optical Kerr effect, we quantitatively prove the existence of QSS, which has been disregarded, and decouple two effects counter-acting each other. Through the magnetoelastic energy analysis, rather we show that QSS in ferromagnets plays a governing role on ultrafast spin dynamics, which is opposite to what have been known on the basis of thermal effect. Our demonstration provides an essential way of analysis on ultrafast photo-induced phenomena.

cond-mat.other↗

arXiv2019

Typical growth behavior of the out-of-time-ordered commutator in many-body localized systems

We investigate the typicality of the growth behavior of the out-of-time-ordered commutator (OTOC) in the many-body localized (MBL) quantum spin chains across random disorder realizations. In the MBL phase of the Heisenberg XXZ chain, we find that the estimate of the OTOC fluctuates significantly with the disorder realizations at the intermediate times of the main growth. Despite the consequent failure of the disorder average in the MBL phase, we argue that the characteristic behavior of the OTOC growth can still be identified by going through individual disorder realizations. We find that a power-law-type growth behavior appears typically after a disorder-dependent relaxation period, which is very close to the $t^2$ form derived in the effective Hamiltonian of a fully MBL system. The characteristic growth behavior observed at an individual disorder realization is robust in our tests with various state preparations and also verified in another MBL system of the random-transverse-field quantum Ising chain in a uniform longitudinal field.

cond-mat.str-el↗

arXiv2019

Thermal properties of slowly rotating asteroids: Results from a targeted survey

Context. Earlier work suggests that slowly rotating asteroids should have higher thermal inertias than faster rotators because the heat wave penetrates deeper into the sub-surface. However, thermal inertias have been determined mainly for fast rotators due to selection effects in the available photometry used to obtain shape models required for thermophysical modelling (TPM). Aims. Our aims are to mitigate these selection effects by producing shape models of slow rotators, to scale them and compute their thermal inertia with TPM, and to verify whether thermal inertia increases with the rotation period. Methods. To decrease the bias against slow rotators, we conducted a photometric observing campaign of main-belt asteroids with periods longer than 12 hours, from multiple stations worldwide, adding in some cases data from WISE and Kepler space telescopes. For spin and shape reconstruction we used the lightcurve inversion method, and to derive thermal inertias we applied a thermophysical model to fit available infrared data from IRAS, AKARI, and WISE. Results. We present new models of 11 slow rotators that provide a good fit to the thermal data. In two cases, the TPM analysis showed a clear preference for one of the two possible mirror solutions. We derived the diameters and albedos of our targets in addition to their thermal inertias, which ranged between 3$^{+33}_{-3}$ and 45$^{+60}_{-30}$ Jm$^{-2}$s$^{-1/2}$K$^{-1}$. Conclusions. Together with our previous work, we have analysed 16 slow rotators from our dense survey with sizes between 30 and 150 km. The current sample thermal inertias vary widely, which does not confirm the earlier suggestion that slower rotators have higher thermal inertias.

astro-ph.EP↗

arXiv2014

Moving perturbation in a one-dimensional Fermi gas

We simulate a balanced attractively interacting two-component Fermi gas in a one-dimensional lattice perturbed with a moving potential well or barrier. Using the time-evolving block decimation method, we study different velocities of the perturbation and distinguish two velocity regimes based on clear differences in the time evolution of particle densities and the pair correlation function. We show that, in the slow regime, the densities deform as particles are either attracted by the potential well or repelled by the barrier, and a wave front of hole or particle excitations propagates at the maximum group velocity. Simultaneously, the initial pair correlations are broken and coherence over different sites is lost. In contrast, in the fast regime, the densities are not considerably deformed and the pair correlations are preserved.

cond-mat.quant-gas↗

arXiv2014

Non-local quantum fluctuations and fermionic superfluidity in the imbalanced attractive Hubbard model

We study fermionic superfluidity in strongly anisotropic optical lattices with attractive interactions utilizing the cluster DMFT method, and focusing in particular on the role of non-local quantum fluctuations. We show that non-local quantum fluctuations impact the BCS superfluid transition dramatically. Moreover, we show that exotic superfluid states with delicate order parameter structure, such as the Fulde-Ferrell-Larkin-Ovchinnikov phase driven by spin population imbalance, can emerge even in the presence of such strong fluctuations.

cond-mat.quant-gas↗

arXiv2012

Complexity Characterization in a Probabilistic Approach to Dynamical Systems Through Information Geometry and Inductive Inference

Information geometric techniques and inductive inference methods hold great promise for solving computational problems of interest in classical and quantum physics, especially with regard to complexity characterization of dynamical systems in terms of their probabilistic description on curved statistical manifolds. In this article, we investigate the possibility of describing the macroscopic behavior of complex systems in terms of the underlying statistical structure of their microscopic degrees of freedom by use of statistical inductive inference and information geometry. We review the Maximum Relative Entropy (MrE) formalism and the theoretical structure of the information geometrodynamical approach to chaos (IGAC) on statistical manifolds. Special focus is devoted to the description of the roles played by the sectional curvature, the Jacobi field intensity and the information geometrodynamical entropy (IGE). These quantities serve as powerful information geometric complexity measures of information-constrained dynamics associated with arbitrary chaotic and regular systems defined on the statistical manifold. Finally, the application of such information geometric techniques to several theoretical models are presented.

math-ph↗

arXiv2011

Information Geometric Modeling of Scattering Induced Quantum Entanglement

We present an information geometric analysis of entanglement generated by an s-wave scattering between two Gaussian wave packets. We conjecture that the pre and post-collisional quantum dynamical scenarios related to an elastic head-on collision are macroscopic manifestations emerging from microscopic statistical structures. We then describe them by uncorrelated and correlated Gaussian statistical models, respectively. This allows us to express the entanglement strength in terms of scattering potential and incident particle energies. Furthermore, we show how the entanglement duration can be related to the scattering potential and incident particle energies. Finally, we discuss the connection between entanglement and complexity of motion.

math-ph↗

arXiv2011

Information Geometry of Quantum Entangled Gaussian Wave-Packets

Describing and understanding the essence of quantum entanglement and its connection to dynamical chaos is of great scientific interest. In this work, using information geometric (IG) techniques, we investigate the effects of micro-correlations on the evolution of maximal probability paths on statistical manifolds induced by systems whose microscopic degrees of freedom are Gaussian distributed. We use the statistical manifolds associated with correlated and non-correlated Gaussians to model the scattering induced quantum entanglement of two spinless, structureless, non-relativistic particles, the latter represented by minimum uncertainty Gaussian wave-packets. Knowing that the degree of entanglement is quantified by the purity P of the system, we express the purity for s-wave scattering in terms of the micro-correlation coefficient r - a quantity that parameterizes the correlated microscopic degrees of freedom of the system; thus establishing a connection between entanglement and micro-correlations. Moreover, the correlation coefficient r is readily expressed in terms of physical quantities involved in the scattering, the precise form of which is obtained via our IG approach. It is found that the entanglement duration can be controlled by the initial momentum p_{o}, momentum spread σ_{o} and r. Furthermore, we obtain exact expressions for the IG analogue of standard indicators of chaos such as the sectional curvatures, Jacobi field intensities and the Lyapunov exponents. We then present an analytical estimate of the information geometric entropy (IGE); a suitable measure that quantifies the complexity of geodesic paths on curved manifolds. Finally, we present concluding remarks addressing the usefulness of an IG characterization of both entanglement and complexity in quantum physics.

math-ph↗

arXiv2011

Exotic superfluid states of lattice fermions in elongated traps

We present real-space dynamical mean-field theory calculations for attractively interacting fermions in three-dimensional lattices with elongated traps. The critical polarization is found to be 0.8, regardless of the trap elongation. Below the critical polarization, we find unconventional superfluid structures where the polarized superfluid and Fulde-Ferrell-Larkin-Ovchinnikov-type states emerge across the entire core region.

cond-mat.quant-gas↗

arXiv2010

Reexamination of an Information Geometric Construction of Entropic Indicators of Complexity

Information geometry and inductive inference methods can be used to model dynamical systems in terms of their probabilistic description on curved statistical manifolds. In this article, we present a formal conceptual reexamination of the information geometric construction of entropic indicators of complexity for statistical models. Specifically, we present conceptual advances in the interpretation of the information geometric entropy (IGE), a statistical indicator of temporal complexity (chaoticity) defined on curved statistical manifolds underlying the probabilistic dynamics of physical systems.

math-ph↗

arXiv2010

The Effect Of Microscopic Correlations On The Information Geometric Complexity Of Gaussian Statistical Models

We present an analytical computation of the asymptotic temporal behavior of the information geometric complexity (IGC) of finite-dimensional Gaussian statistical manifolds in the presence of microcorrelations (correlations between microvariables). We observe a power law decay of the IGC at a rate determined by the correlation coefficient. It is found that microcorrelations lead to the emergence of an asymptotic information geometric compression of the statistical macrostates explored by the system at a faster rate than that observed in absence of microcorrelations. This finding uncovers an important connection between (micro)-correlations and (macro)-complexity in Gaussian statistical dynamical systems.

math-ph↗

arXiv2009

Induced interactions for ultracold Fermi gases in optical lattices

We investigate the effect of optical lattices on the BCS superfluidity by using the Gorkov--Melik-Barkhudarov (GMB) correction for a two-component Fermi gas. We find that the suppression of the order parameter is strongly enhanced by the lattice effects. The predictions made by the GMB corrections are in qualitative and, for the cases studied, quantitative agreement with previous quantum Monte Carlo results. We discuss how the GMB correction extends the validity of the mean-field theory to a wider range of tunable optical lattice systems in different dimensions.

cond-mat.quant-gas↗

arXiv2007

Incommensurate Charge Order Phase in Fe2OBO3 due to Geometrical Frustration

The temperature dependence of charge order in Fe2OBO3 was investigated by resistivity and differential scanning calorimetry measurements, Mossbauer spectroscopy, and synchrotron x-ray scattering, revealing an intermediate phase between room temperature and 340 K, characterized by coexisting mobile and immobile carriers, and by incommensurate superstructure modulations with temperature-dependent propagation vector (1/2,0,tau). The incommensurate modulations arise from specific anti-phase boundaries with low energy cost due to geometrical charge frustration.

cond-mat.str-el↗