2026 Spring Poster Competition
這是2026清華物理學生研究壁報比賽的線上系統。我們希望藉由這個線上系統，讓大家每年有機會與不同領域的夥伴分享自己的研究成果。刺激橫向的合作與討論。如果對於投稿摘要有任何問題，可以參考使用手冊。
This is the online system for the 2026 poster competition. Through this system and the annual event, we hope to stimulate interdiscplinary discussions and collaborations through different sub fields of physics. If you have any questions about the system, please check the manual.
"If you want to walk fast, walk alone. If you want to walk far, walk together."
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Poster Talks
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13:00
SPIIR Offline Search on CBC in SSM region 3m
In the poster, I will represent our recent work on gravitational wave physics. In particular, we are interested in the signals from compact binary coalescences in the sub-solar mass region. According to our knowledge, there are no formation channels for black holes and neutron stars in such mass region. Detection of such signals allows us to give hints to new physics and constraint some dark matter models. We will also present how our algorithm is developed and is deployed for detection.
Speaker: NGAI CHUN LUNG (NTHU) -
13:03
RIXS Evidence for the Order–Disorder Antiferroelectric Transition in CuCrP$_2$S$_6$ 3m
We report polarization-dependent resonant inelastic X-ray scattering (RIXS) measurements that reveal the order–disorder nature of the antiferroelectric (AFE)–paraelectric (PE) transition in the van der Waals multiferroic CuCrP$_2$S$_6$. The RIXS transition from the high-spin $^4A_{2g}$ ground state of the Cr$^{3+}$ ion to a state with $^{4}T_{1g}$ symmetry splits into two $dd$ excitations at 2.0 and 2.15 eV, arising from the splitting of $^{4}T_{1g}$ into $^{4}E$ and $^{4}A_2$ due to trigonal distortion. The excitation energies remain nearly unchanged across the AFE–PE transition, indicating that the average Cr-centered trigonal crystal-field strength is insensitive to the Cu positions within RIXS resolution. However, in the AFE phase, these two peaks exhibit a distinct polarization contrast between RIXS excitations with $\pi$ and $\sigma$ polarizations, which evolves strongly with temperature. This polarization contrast vanishes in the PE phase, indicating that while the local trigonal splitting persists, Cu$^{+}$-ion distribution becomes dynamically disordered, thereby washing out the RIXS polarization anisotropy. These observations support the Cu-driven order–disorder mechanism for the AFE–PE transition, rather than a displacive transition.
Speaker: Yun-Chuan Su (Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan) -
13:06
Probing Excitonic Transitions at Atomic-Scale Defects in Chemical Vapor Deposition-Grown $\text{MoS}_2$ and $\text{WSe}_2$ 3m
Transition metal dichalcogenides (TMDs), such as $\text{WSe}_2$ and $\text{MoS}_2$, have attracted considerable attention due to their distinctive excitonic properties and promising applications in optoelectronic devices. In this work, we investigate the optical transitions and defect-related excitonic states in chemical vapor deposition (CVD)-grown $\text{WSe}_2$ and $\text{MoS}_2$, where the defect density is controlled by the gas flow rate during growth. Low-temperature photoluminescence (PL) and differential reflectance (DR) spectroscopy are employed to accurately identify various band-to-band optical transitions, including neutral excitons, trions, and defect-bound excitons. Moreover, PL mapping combined with dielectric engineering is used to elucidate the microscopic mechanisms and charge states of defect-bound excitons. The energy separations between defect-related emissions and free excitons exhibit similar trends in both materials, indicating analogous defect origins. These findings offer critical insights into defect engineering, bandgap modulation, and essential parameters for optimizing crystal growth in two-dimensional semiconductors.
Speaker: Hsuan-Yi Chen (Department of Physics, National Tsing Hua University, Hsinchu 300044, Taiwan) -
13:09
Resolving Superconducting Vortices in Pb Monolayer and Thin Films on Si(111) 3m
We have investigated the superconducting vortices in Pb monolayer and thin films on Si(111) by using
scanning tunneling microscopy and spectroscopy (STM/STS). In the monolayer case, zero-bias
conductance (ZBC) mapping indicates that each vortex carries a single magnetic flux quantum (Φ₀) and
arranges into a hexagonal lattice, consistent with Abrikosov’s prediction. The experimentally determined
upper critical field (Hc₂) agrees well with the value predicted by Ginzburg–Landau theory. In multilayer
Pb films, the measured vortex density deviates from theoretical expectations due to the limited lateral
dimensions and flux penetration at the island edges. Moreover, the zero-bias conductance intensity at
the vortex core in even-layer islands is stronger than that in odd-layer ones, suggesting a layer-
dependent modulation of the vortex electronic states.Speaker: YUAN-MIN LAI (National Tsing Hua University) -
13:12
Testing the Polarization-Intensity Gradient Method for Magnetic Field Strength Estimation in Dense Core Simulations 3m
Magnetic fields play an important role in the star formation process and collapsing dense
cores. However, it is difficult to directly measure the magnetic field strength in observation. The polarization–intensity gradient method is a new approach to estimate the magnetic field strength using polarization angle and intensity gradient, which can provide the map of position-dependent magnetic field strength estimates. In this project, we evaluate the applicability of this method to real observational data and to determine whether it can provide robust magnetic field strength estimates in realistic star-forming environments. We first simulate collapsing dense cores with RAMSES and apply the polarization–intensity gradient method to estimate their magnetic field strength. Then we compare the estimated field strengths and the model to calculate the uncertainty. The results suggest that the polarization–intensity gradient method can well estimate the magnetic field strength in collapsing dense cores with an uncertainty smaller than a factor of 3.Speaker: Jo-Shui Kao (NTHU/ASIAA) -
13:15
Spatial distribution of blue quantum emitters in hexagonal boron nitride induced by electron beam irradiation. 3m
Hexagonal boron nitride (hBN) has emerged as a promising host for stable quantum emitters, with blue emission centers offering potential for applications in quantum photonics and nanoscale sensing. A key advantage of these emitters is their ability to release one photon at a time, which is essential for secure quantum communication and scalable photonic quantum technologies. Achieving precise control over the spatial positioning of such single-photon sources is therefore crucial for integrated quantum devices and photonic circuits. In this work, we employ confocal photoluminescence (PL) mapping to investigate the spatial distribution of blue emission centers in hBN flakes created by electron beam irradiation. By classifying different emitters, we aim to compare their spatial localization and distribution characteristics, providing insights into the controlled generation and deterministic placement of single-photon sources in hBN. Our work shows that these quantum emitters are highly promising candidates for integration into future quantum photonic circuits.
Speaker: Zong-Syun Li -
13:18
Density Matrices and Entanglement Properties of the Kitaev Spin Liquid 3m
We give an exact form of the density matrix of the spin-1/2 Kitaev spin liquid represented in terms of spin operators and study the entanglement properties of the Kitaev model within the spin framework. With the explicit form of the density matrix, plus the exact Gauss law of the emergent gauge theory and the exact 1-form Wilson symmetry in the Kitaev model, we demonstrate the existence of the underlying block-diagonal structure of the reduced density matrix, which gives rise to the extensive degeneracy in the entanglement spectrum. The block-diagonal structure is then proven to be responsible for the separability of the entanglement entropy into the gauge and matter parts. Furthermore, the method for applying our theory to cases with an odd number of lattice sites is also discussed. It also demonstrates a relation between the entanglement spectrum and the fermion parity, which is seldom mentioned in the literature.
Speaker: Mr Chen-Chih Wang (Department of physics, National Tsing Hua University) -
13:21
Exploring Kondo Physics and Yu–Shiba–Rusinov States in MnPc Molecules on Superconducting Pb(001) Surface 3m
We investigate the electronic and magnetic properties of manganese phthalocyanine (MnPc) molecules adsorbed on the Pb(001) surface, extending previous studies on MnPc/Pb(111). In contrast to the isotropic Fermi surface of Pb(111), Pb(001) exhibits pronounced anisotropy, providing a unique platform to explore anisotropy-driven effects in impurity–superconductor systems. Using scanning tunneling microscopy and spectroscopy, we observe well-defined Yu–Shiba–Rusinov (YSR) states associated with magnetic impurities. The spatial and energy-resolved spectra reveal clear anisotroic features, reflecting the underlying electronic structure of the substrate. Our results demonstrate that the anisotropic Fermi surface of Pb(001) plays a crucial role in shaping the spectral characteristics and spatial distribution of YSR states. In addition, the relationship between YSR states and the Kondo effect is systematically characterized. These findings provide new insights into the influence of substrate anisotropy on impurity-induced bound states in superconductors and contribute to a deeper understanding of magnetic adsorbates on anisotropic superconducting surfaces.
Speaker: YU-SHENG LUO -
13:24
Electrical Control of Hybridized Exciton in Moiré WS$_2$ /MoSe$_2$ Heterostructures 3m
Two-dimensional semiconductor heterostructures provide a rich platform for exploring strongly bound excitons and interlayer coupling phenomena. In particular, moiré superlattices formed by stacking transition metal dichalcogenide (TMD) monolayers enable tunable hybridization between excitonic states across layers. We investigate the electrical-driven band evolution in WS$_2$/ MoSe$_2$ heterobilayers using photoluminescence (PL) and differential reflectance (DR) spectroscopy on dual-gate devices. Because the conduction band edges of WS$_2$/ MoSe$_2$ are nearly degenerate, the applied electricity strongly mixes their electronic states. As a result, the DR spectra exhibit pronounced Stark redshifts and clear splitting of the MoSe$_2$ exciton resonances, evidencing the formation of hybridized inter- and intralayer excitons. These excitons further experience moiré potential modulation, giving rise to additional fine structures and localization behavior within the superlattice. Our findings highlight the moiré superlattice as a versatile platform for engineering hybridized excitonic states with tunable coupling, offering new opportunities for exploring correlated exciton physics and electrical-controllable quantum optoelectronic phenomena.
Speaker: Ping-Hau Chen (National Tsing Hua University) -
13:27
Defect Activation and Stabilization in Hexagonal Boron Nitride for Room-Temperature Single-Photon Sources 3m
Single-photon emitters (SPEs) are key building blocks for next-generation quantum communication and information technologies. Hexagonal boron nitride (hBN), with its graphene-like layered structure, wide bandgap, and van der Waals bonding, has emerged as a promising host material for stable, room-temperature single-photon emission. In this study, we significantly enhance the density and stability of defect-based quantum emitters in thin hBN layers by immersing the material in selected organic solvents, followed by thermal annealing in an argon (Ar) gas environment. Comprehensive photoluminescence (PL) spectroscopy and surface analyses confirm the activation and improved emission stability of defect centers. This approach provides a robust and scalable route toward the fabrication of bright and reliable single-photon sources based on hBN.
Speaker: 林 郁晨 -
13:30
$H$-linear magnetoresistance in the $T^2$ resistivity regime of overdoped infinite-layer nickelate La$_{1-x}$Sr$_x$NiO$_2$ 5m
We report a systematic magnetotransport study on high-crystallinity overdoped La$_{(1-x)}$Sr$_x$NiO$_2$ (LSNO) thin films with x = 0.20-0.24. By conducting pulsed-field transport experiment up to 62 T, we reveal two salient features of the normal-state transport in this LSNO thin films: (1) the magnetoresistivity does not follow the Kohler's scaling rule but exhibit a H-linear behavior in the high H/T limit and (2) the normal-state resistivity below 30 K consistently follows a $T^2$ behavior across the overdoped regime. Our results demonstrate a coexistence of strange-metal and Fermi-liquid transport features in the unconventional superconductor and provide new information on the transport characteristics of the normal ground state that host superconductivity in infinite-layer nickelates.
Speaker: Yong-Cheng Pan -
13:35
Atomic-Scale Characterization of Iron Oxide Thin Film on Ag(001) by Scanning Tunneling Microscopy 3m
High resolution scanning tunneling microscopy has been used to characterize the structural properties and growth mechanism of iron oxide thin film deposited on an Ag(001) substrate. Our experimental results show that the FeO(111) monolayer exhibits a c(2 × 10)/p(2 × 11)/c(2 × 12) unit cell due to lattice matching between the hexagonal overlayer and square substrate lattices. Besides, line defects with locally square atomic coordination are formed due to the excess oxygen in FeO thin film. Our findings provide a platform for understanding the metal oxide-substrate interactions down to atomic scale.
Speaker: Yi-Chun Huang (Department of Physics, National Tsing Hua University, Hsinchu, Taiwan) -
13:38
Properties and Implications of Milling Behavior in Active Particles with Anisotropic Vision 3m
Milling behavior—such as the vortex-like motion observed in reindeer herds, fish schools, and army ant colonies—represents a striking example of collective dynamics in nature. The milling structure is formed spontaneously and maintained continuously, but the underlying mechanisms are still unclear. We think that animals' anisotropic perception or attention is important; therefore, we account for the vision range, depicted by a vision angle and the vision distance, of each particle when it is aligned with others in active Brownian particle (ABP) simulations. By varying the vision angle and activity, we reproduce the milling motion and also obtain aster and flocking states. The aster state typically occurs for small vision angles, but it hardly exists in the macroscopic world, implying that animals' sensing angles have a lower bound. For the transition from flocking to milling, our model may provide insight that individuals become hyper-aroused and their vision narrows under threat, leading to the formation of a milling structure to defend against the predator. In addition, we propose an approximation method that may relate the milling morphology observed in nature to its corresponding vision range of the species. Furthermore, we show that the spatial distribution of particles within the milling structure depends on individuals' activity, which sheds light on the evolutionary advantage of the defensive strategy.
Speaker: Hsin-Yu Chen (Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan) -
13:41
Doping evolution of thermodynamic properties across the antiferromagnetic endpoint in Mott insulator Sr2(Ir,Rh)O4 3m
Sr₂IrO₄ is a 5d Mott insulator that shares the defining characteristics with the high-temperature cuprate superconductors. The absence of superconductivity in doped Sr₂IrO₄ makes it an attractive platform to study the low-temperature electronic properties and manifestation of quantum criticality therein. In this study, we synthesize a series of Sr₂(Ir,Rh) O₄ polycrystalline samples with 0 < x < 0.26 and measure their magnetic susceptibility and specific heat down to 2K. In combination with complementary Hall effect measurements, we study the change in electronic properties across the putative quantum critical point at x Rh ≈ 0.15, at which the long-range antiferromagnetic order is fully suppressed, and discuss the evolution of electronic ground state in Sr₂(Ir,Rh)O₄.
Speaker: tzuning Yen -
13:44
Epitaxial growth of MnTe/Bi₂Te₃ heterostructures on Si(111) 3m
Here we report preliminary results of expixial growth of MnTe/Bi₂Te₃ heterostructures on Si(111).
In depositing Bi₂Te₃ on Si(111), we observe clear RHEED oscillation, indicating layer-by-layer growth. The measured lattice constant of Bi₂Te₃ thin films is around 4.38Å, consistent with theliterature. On the other hand, the RHEED pattern from MnTe layer, which is grown on top of Bi₂Te₃/Si(111), shows a more diffused feature. This suggests that the parameters for growing MnTe need to be further optimized in order to achieve better epitaxial quality. The high-quality MnTe/Bi₂Te₃ ultrathin film heterostructure would constitute an essential system for exploring the complex interplay between altermagnetism and topological insulator in low dimensionality.Speaker: 偉軒 高 -
13:47
Neutrinos from Superradiant Primordial Black Holes 3m
Black hole superradiance provides a unique mechanism for probing particle production. In this work, we investigate the extragalactic neutrino flux produced by quenched superradiance around Primordial Black Holes (PBHs).
We calculate and compare the neutrino flux and peak energy across various coupling constants and light boson masses for both the scalar and vector cases. On our poster, we showcase examples of the extragalactic flux components for the scalar superradiance clouds. By superimposing these signals onto known neutrino backgrounds—including Solar, Reactor, and Geoneutrinos—our numerical results reveal a distinct, clean neutrino signal in the MeV-GeV energy range.
As a next step, we aim to construct exclusion plots to constrain the parameter space using extragalactic and galactic neutrino spectra.Speaker: Ms Yixuan Lin (NTHU) -
13:50
Pulse compression and autocorrelation signal analysis of a non-collinear optical parametric amplifier 3m
Non-collinear optical parametric amplifier (NOPA) belongs to ultrafast laser technology and generates high-power, frequency-tunable pulses by mixing a pump beam and a white-light seed at an angle within a nonlinear optical crystal. Our home-built NOPA features a dual-beam configuration: one path utilizes a green pump to generate tunable infrared output, while the other employs an ultraviolet pump to produce visible and ultraviolet light. The output pulses are temporally broadened due to dispersion and nonlinear processes. To enhance the temporal resolution of NOPA, a pair of SF10 prisms is installed to provide negative group delay dispersion (GDD) to compensate for the broadening. On this poster a detailed analysis of our pulse compression for the infrared light, demonstrating a minimal pulse duration of 27.2 ± 0.3 fs, will be presented.
Speaker: Yen-Chen Chiang -
13:53
The JCMT BISTRO Survey: Magnetic Fields in the Massive Star-Forming Region Onsala 2 3m
We investigate the magnetic field in the massive star-forming region Onsala 2 (ON2) in Cygnus-X complex using the polarization observations at 850µm performed as part of the James Clerk Maxwell Telescope (JCMT) B-Fields In Star-Forming Region Observations survey (BISTRO) with the POL-2 instrument. Our data cover the entire ON2 complex at a resolution of ~0.12 pc, allowing us to spatially resolve the polarized emission from the filamentary structures. We identify five clumps within ON2 and calculate the magnetic field strength via the Davis-Chandrasekhar-Fermi (DCF) method in each region. We analyze the energy budgets through the mass-to-flux ratio, plasma beta, and Alfvén Mach number to quantify the relative contributions of magnetic, gravitational, thermal, and turbulent energies, respectively. The results indicate that the magnetic field is less dominant than gravity but more influential than thermal pressure and turbulence. Additionally, we estimate the star formation rate (SFR) in the southern part of ON2, providing a quantitative reference for the star formation activity in this region.
Speaker: Meng-Zhe Yang (National Tsing Hua University) -
13:56
Searching for triple-detection Planet Nine candidates using far-infrared all-sky survey data 3m
The outer solar system is theoretically predicted to harbor an undiscovered planet, often referred to as Planet Nine (P9). Simulations suggest that its gravitational influence could explain the unusual clustering of distant Kuiper Belt Objects. However, no observational evidence for P9 has been found so far, as its predicted orbit lies far beyond Neptune, where it reflects only a faint amount of sunlight. A feasible solution is to detect thermal emission from P9 in the far-infrared, rather than using optical surveys. Extended from our recent study (Phan T. L. et al., 2025, PASA, 42, e064), this work aims to find P9 in the far-infrared all-sky survey data from IRAS catalogs and AKARI Monthly Unconfirmed Source List (MUSL). After applying the positional and flux criteria, we produced all possible pairs of IRAS and AKARI sources whose 23-year angular separations were limited between 42' and 166', corresponding to the orbital motion of P9 at 280 - 700 AU. For each pair, we continued to search for the third detection in AKARI data based on the expected parallax motion of P9 over 6 months. We present the preliminary results after manually checking their IRAS/AKARI cutout images. Multiple-detection P9 candidates are important in estimating orbital parameters and comparing them to the simulation results.
Speaker: Mr Terry Long Phan (Institute of Astronomy, National Tsing Hua University, Hsinchu, Taiwan) -
13:59
Observation of Bright Intralayer Moiré Excitons in Mg(OH)₂/MoSe₂ Heterostructure 3m
Recent studies of moiré physics in bilayer transition-metal dichalcogenides (TMDs) have largely focused on interlayer excitons, whose photoluminescence (PL) is typically weak and thus less suitable for quantum photonics applications. Here, we demonstrate that intralayer moiré excitons can be formed in a heterostructure composed of insulating Mg(OH)$_2$ and monolayer(ML) MoSe$_2$. Zero twist-angle PL and differential reflectance (DR) spectra reveal distinct moiré exciton features, signifying the formation of intralayer moiré states. Further experiments, including spatial mapping, power-dependent, and polarization-resolved PL spectroscopy, confirm that these moiré excitons exhibit robust interband optical transitions and high emission brightness. Our results establish intralayer moiré excitons as a promising and tunable light-emitting platform, paving the way for future optoelectronic and quantum photonic applications.
Speaker: Yu-Cheng Lin (NTHU) -
14:02
Modeling Multi-Peak Patterns in Cell Polarity: The Role of an Intermediate Species' Retention Rate in Reduced Two-Component Activator-Substrate Model 3m
Cell polarity provides a classic example of spatial self-organization in biological systems, where proteins accumulate asymmetrically on the cell membrane. This phenomenon can be modeled by the mass-conserved activator–substrate (MCAS) model, which is formulated as a set of reaction–diffusion equations describing the exchange between membrane-bound and cytosolic species. In the standard two-species MCAS model, multiple localized peaks typically compete and coarsen into a single steady-state peak. However, previous studies have shown that introducing an intermediate diffusive species, which forms an indirect conversion pathway, can yield equalized multi-peak patterns. Building on this framework, our work demonstrates how equalization can also occur within a two-species MCAS model when the effect of the intermediate species is represented by balanced sink and source terms in the reaction–diffusion equations. With these terms, the reduced model exhibits both competition and equalization regimes. We further investigate how the retention rate of the intermediate species controls the transition between these patterning modes.
Speaker: Ren Hao Lee (Department of Physics, National Tsing Hua University, Hsinchu City, Taiwan) -
14:05
Strain-dependent optical properties in Janus MoSSe monolayer 3m
Recently, Janus Transition Metal Dichalcogenide (TMD) monolayer MoSSe, with a sandwiched S–Mo–Se structure, has been synthesized by replacing the top S atomic layer in MoS2 with Se atoms. Compared with MoS2, Janus TMDs MoSSe exhibit superior electron mobility as well as enhanced nonlinear optical responses. These characteristics make Janus TMDs highly promising for applications in device fabrication and flexible electronics. Understanding the strain-dependent properties of MoSSe monolayer is fundamentally important to its applications of flexible devices. In this work, we investigated the strain photoluminescence (PL) and angle-resolved second harmonic generation (SHG) responses of a Janus MoSSe monolayer under different uniaxial-strain conditions. Additionally, we used first-principles calculations to investigate the band structure, strain dependence of the SHG susceptibilities and SHG anisotropic patterns. In our PL measurements, applying strain along either the armchair or the zigzag direction causes a red shift in the emission energy, consistent with the band structure simulation results. The SHG measurements show a reduction in SHG intensity under strain applied in different directions.
Speaker: Ms Yi−Syun Hsieh (Department of Physics, National Tsing Hua University, Hsinchu 300044, Taiwan) -
14:08
Uncertainty-aware Neural Networks for Fuzzy Dark Matter Model Selection from xHI Measurements 3m
Fuzzy dark matter (FDM) provides an alternative to the standard cold dark matter picture by suppressing small-scale structure formation through quantum pressure effects. In this work, we test whether FDM can better reproduce the high neutral hydrogen fractions inferred from recent JWST observations at redshifts z > 8. We generate 21 cm reionization histories with 21cmFirstCLASS over a grid of FDM masses and fractions, and incorporate JWST $x_{HI}$ constraints using Bayesian inference that preserves their full non-Gaussian uncertainty distributions. To compare simulations with observations, we use a hybrid neural-network framework that combines convolutional layers for spatial features with recurrent layers for redshift evolution. We find that models near $m_{FDM}$ ~ $10^{-22}$ eV and $f_{FDM}$ ~ 0.04 provide the best agreement with the current data, while lighter masses are more strongly constrained. These results suggest that FDM can delay early structure formation and produce a later, more gradual reionization history, in better agreement with current high-redshift observations.
Speaker: Bahareh Soleimanpour Salmasi (National Tsing Hua University) -
14:11
Tuning the Growth Mode of Bi on Cu(111) via a Co Interlayer 3m
This study about the growth of Bi on a Co-covered Cu(111) surface . Revealing that distinct surface superstructures such as √3 ×√3 R30° surface alloy and [2012] phase can be selectively fabricated by controlling the deposition parameters. The atomic arrangements and local electronic properties of these structures were characterized using scanning tunneling microscopy (STM) and spectroscopy (STS). Analysis shows that the formation of these specific phases is governed by a complex interaction between the Co interlayer thickness and the Bi coverage. This work demonstrates the high tunability and potential of the Bi/Co/Cu(111) system for atomic-scale structural design.
Speaker: Fang-Tzu Chang (Department of Physics, National Tsing Hua University, Hsinchu, Taiwan) -
14:14
Random spin-3/2 antiferromagnetic Heisenberg chains revisited 3m
We employ a tree-tensor-network strong-disorder renormalization group (tSDRG) to study the disordered antiferromagnetic spin-$3/2$ Heisenberg chain with bond-alternations. Extended SDRG predicts two distinct random-singlet regimes in the weak- and strong-disorder limits, characterized by different effective-spin structures ($S_{\mathrm{eff}}=1/2$ and $S_{\mathrm{eff}}=3/2$), separated by an intervening multicritical point $P_4$.[Ref:1,2] Here we locate $P_4$ using the distribution of spin correlations and the theoretical prediction of the critical exponent is verified via finite-size scaling. With bond alternation, we further map the phase boundaries between distinct VBS phases; notably, these boundaries converge toward the $P_4$ location. In the weak-disorder regime, however, our tSDRG results deviate from theoretical expectations, which we attribute to the reduced scale separation that undermines the strong-disorder assumption and renders the local decimation approximation less reliable. Overall, our results validate the predicted multicriticality and clarify the practical regime of applicability of tSDRG, motivating refinements or complementary approaches in the weak-disorder limit.
Speaker: yentung lin -
14:17
JWST COSMOS-Web DR1: Identifying z∼9−10 protocluster candidates through photometry 3m
It is important to find and study protoclusters in the distant Universe during their formative stages in order to understand the formation and evolution of present-day galaxy clusters. In the pre-JWST era, protocluster candidates were primarily identified up to z ≲ 7, limited by optical wavelength coverage and survey area. With deep JWST
near-infrared surveys such as CEERS and JADES have enabled the identification of protocluster candidates at z > 7. By taking advantage of JWST COSMOS-Web’s near-infrared sensitivity, spatial resolution, and wide survey area, Wu et al. (2025) identified seven z ≈ 9–10 protocluster candidates using COSMOS-Web DR0.5 (FOV: 0.27 deg²). In this work, we present an extended search for high-redshift (z ≈ 9–10) protocluster candidates using the full DR1.0 dataset (FOV:0.54 deg²). We apply F115W-dropout color selection and spectral energy distribution (SED) fitting to isolate high-redshift galaxy candidates, and compute local overdensities to identify protocluster regions. The identification of protoclusters at z > 9 provides new constraints on the formation and early evolution of the most massive structures in the Universe.Speaker: Srivardini Ayyappan (NTHU, Macquarie University) -
14:20
Tracing AGN Contribution and Number Fraction Across Cosmic Time with JWST 3m
Active galactic nuclei (AGN) are pivotal drivers of galaxy evolution, yet many remain undetected in ultraviolet and optical surveys due to heavy dust obscuration. In these systems, dust absorbs the high-energy accretion disk emission and re-radiates it at longer wavelengths, making mid-infrared (IR) observations essential for uncovering the full population of obscured AGN. Tracking the AGN IR contribution and number fraction provides insight into the dominance of AGN activity within galaxies and how common AGNs are across cosmic time. Historically, the AKARI space telescope provided key insights into these populations; however, JWST’s 6.5m mirror offers $\sim$90 times the sensitivity of AKARI’s 0.68m aperture, allowing for the detection of much fainter objects during early stages of galaxy growth. Utilizing the JWST Systematic Mid-infrared Instrument Legacy Extragalactic Survey (SMILES) and the JWST Advanced Deep Extragalactic Survey (JADES), we leverage continuous optical to mid-IR coverage (0.4–25.5 $\mu$m) in the GOODS-S field to identify obscured AGN via multi-wavelength SED fitting with CIGALE. Our sample includes 290 AGN across 0 $<$ z $<$ 10.5, a seven-fold increase over previous JWST Cosmic Evolution Early Release Science (CEERS) survey studies due to the larger 15-pointing SMILES MIRI footprint. We find that both the AGN IR contribution and number fraction increase significantly with redshift, while decreasing as a function of total IR luminosity. These results highlight JWST’s capacity to reveal previously hidden populations, suggesting that AGN activity was more prevalent and energetically dominant in the early universe.
Speaker: Angel Rodriguez Barbosa (National Tsing Hua University) -
14:23
Do Astrophysical Hazards Solve the Fermi Paradox? 3m
The Fermi Paradox underscores the lack of evidence for advanced extraterrestrial life despite the Galaxy’s age and scale. While interstellar distances are often seen as barriers to communication and migration, Galactic rotation could shorten travel times and enable expansion. Yet most models overlook destructive astrophysical hazards. Hazardous astrophysical events—asteroid impacts, supernovae (SNe), and giant molecular cloud (GMC) encounters—may extinguish advanced civilizations before colonization spreads. We simulate Galactic-scale migration of advanced civilizations with these hazards included: asteroid impacts are probabilistic, while SNe and GMCs impose extinction within defined radii. In hazard-free cases, up to 72% of stars at the Solar radius (8.2 kpc) are colonized. With hazards, colonization collapses entirely within 830 Myr. These results suggest astrophysical hazards may provide a physical resolution to the Fermi Paradox.
Speaker: Mr Deriyan Senjaya (Department of Physics NTHU Taiwan) -
14:26
Interpreting Optical Diffractive Neural Networks (ODNN) via Gradient-based Physical Activation Mapping (GPAM) 3m
Optical diffractive neural networks (ODNNs) perform computation through light propagation and diffraction, yet their internal physical decision mechanism remains difficult to interpret. In this work, we propose Gradient-based Physical Activation Mapping (GPAM), a method that quantifies the contribution of each diffractive neuron by back-propagating gradients through physical wave propagation. Beyond visualization, we establish a quantitative evaluation framework for optical neural network interpretability, including peak localization, foreground energy concentration, weakly-supervised segmentation, and faithfulness analysis based on mask ratio. Experiments on MNIST and Fashion-MNIST datasets show that GPAM relevance maps are spatially consistent with object regions and that masking high-relevance regions leads to significant confidence and accuracy drops. These results demonstrate that GPAM not only visualizes where the optical neural network focuses but also quantifies how accurate and faithful the explanations are. The proposed framework provides a practical tool for optical system analysis, alignment diagnosis, and interpretable optical neural network design.
Keywords: Optical diffractive neural networks, Interpretability, Optical computing, Saliency map, Optical neural networks
Speaker: Hong-Yueh Huang (NTHU PHYS) -
14:29
Estimating the Hubble Constant from Localized and Nonlocalized Fast Radio Bursts Using CHIME Data 3m
The Hubble constant (H₀) characterizes the present-day expansion rate of the universe. However, despite the significant decrease in measurement uncertainties, the discrepancy of more than 4𝜎 remains between two main methods —the Cosmic Microwave Background (CMB) and Cepheid-calibrated Type Ia supernovae (SNe Ⅰa), known as the Hubble tension. To address the Hubble tension, where the ΛCDM model yields a value of H₀ = 67.66 ± 0.42 km s⁻¹ Mpc⁻¹ while Cepheid-calibrated Type Ia supernovae give H₀ = 73.04 ± 1.04 km s⁻¹ Mpc⁻¹, it is essential to develop independent methods for measuring the Hubble constant. Fast radio bursts (FRBs) are short-lived, intense extragalactic signals that last only a few milliseconds in the radio band. The dispersion measure (DM) of an FRB is related to the integrated free-electron density along the line of sight and is correlated with redshift. This relation, known as the Macquart relation, links DM to redshift by tracing the number of free electrons along the path, thereby providing a probe of the distance-redshift relation and enabling constraints on the H₀. We present a new approach using FRB data from CHIME Catalog 2, including both localized and non-localized FRBs, with photometric redshifts from DESI. Our analysis is based on 4539 FRBs. We apply the Probabilistic Association of Transients to their Host (PATH) method to estimate the host-galaxy redshift probabilities for non-localized FRBs. We then derive the Macquart relation to estimate the value of H₀.
Speaker: YaLi Chu (IoA) -
14:32
Resolving Atomic Structures of Altermagnetic MnTe by Scanning Tunneling Microscopy 3m
Altermagnetic materials can generate spin-polarized currents for magnetic memory applications while remaining insensitive to external magnetic fields, leading to improved signal stability. MnTe is a representative altermagnetic semiconductor with zero net magnetization and anisotropic band splitting.
In this work, we use scanning tunneling microscopy and spectroscopy (STM/STS) to investigate the atomic structure and electronic properties of MnTe. Cleaved bulk MnTe reveals two distinct surface phases with lattice constants around 440 pm. For thin film growth on Bi₂Te₃, Mn deposition forms hexagonal islands attributed to monolayer MnTe₂, while co-deposition of Mn and Te produces monolayer MnTe with consistent lattice structures.
These results demonstrate atomic-scale characterization of altermagnetic MnTe and provide a foundation for future spin-polarized STM studies of its magnetic structure.
Speaker: Shao Chi Tu (Department of Physics, National Tsing Hua University) -
14:35
A Particle-Scale Continuum Model for Active Brownian Particles 3m
Active Brownian particles (ABPs) provide a minimal model for exploring collective dynamics in active matter. Recent studies suggest that active particle could have interesting elastic properties. While many continuum descriptions have been developed at the hydrodynamic scale, particle-scale mean-field approaches are more suitable for capturing emergent elastic properties. Motivated by this, we employ dynamical density functional theory (DDFT) to construct a continuum model with a structure similar to the phase field crystal framework, aiming to describe ABP behavior near the onset of clustering. Molecular dynamics simulations are carried out both to obtain pair distribution functions which used to determine effective interaction parameters in the theory.
Speaker: Ping-Cheng Lu -
14:38
Exploring the Degree of Freedom Beyond Standard Model via Primordial Black Hole Evaporation with Memory Burden Effect 3m
Primordial black holes (PBHs) formed during the early universe provide a unique probe of physics beyond the Standard Model. In this study, we investigate the impact of additional degrees of freedom from supersymmetry (SUSY) particles and the memory burden effect (MBE) on the evaporation process of PBHs formed via first-order phase transitions. By analyzing how these factors influence the PBH lifetime, we aim to provide insights into potential new physics and constraints on early universe phase transitions. Our findings may offer indirect evidence supporting the existence of first-order phase transitions, contributing to a deeper understanding of high-energy physics and cosmology.
Speaker: Leah Ya-Ling Lin (National Tsing Hua University) -
14:41
Using Python and Raspberry Pi to efficiently capture (high-quality) LEED images and accurately extract lattice constants 3m
Accurate determination of surface atomic positions relies on high-quality LEED I(V) data. This study show how to use Python to control a Raspberry Pi camera for capture LEED data. Furthermore, it shows how to fit the data to accurately extract the positions of LEED spots. In addition to obtaining high-precision lattice constants, this method also obtain I(V) curves of the diffraction spots, effectively integrating with theoretical simulation tools such as SATLEED and ViPErLEED, optimizing the preprocessing workflow for surface structure analysis.
Speaker: KA WENG LEI (NTHU) -
14:44
Beyond Calabrese–Cardy Scaling: Exceptional-Point Sensitivity and its de Sitter RT Origin 3m
Entanglement entropy at one-dimensional criticality typically follows the Calabrese--Cardy scaling.
In non-unitary critical chains, however, we show that a finite system retains a universal sensitivity to a small spectral gap $\Delta$ away from the exceptional point.
Concretely, we find an additional contribution
\begin{equation}
S_A(\ell)=\frac{c}{3}\log!\Big[\frac{L}{\pi}\sin!\Big(\frac{\pi \ell}{L}\Big)\Big]+\log(\Delta L)+\cdots ,
\end{equation}
which appears as an $\ell$-independent offset when $\Delta L\lesssim 1$.
This behavior has no Hermitian analogue: gaps below the finite-size scale $1/L$ are invisible to entanglement in unitary critical chains, while here the entropy continues to resolve $\Delta$ through the combination $\Delta L$.
We give a holographic understanding in de Sitter space: the RT extremal curve generically extends to past infinity (the IR limit), so it necessarily probes the IR completion and yields the $\log(\Delta L)$ term.
We further confirm this interpretation in a circuit realization by showing that the same contribution is precisely the entanglement of the IR state at the end of a finite-depth RG flow, i.e. a residual entanglement left after finite-depth disentangling.Speaker: 鄺宏 周 (NTHU PHYS) -
14:47
Growth and Electronic Properties of Functionalized DAE Molecules on Au(111)/Ag(111) studied by STM/STS 3m
Over the past decade, On-Surface Synthesis rapidly emerged as a successful bottom-up method for synthesizing atomically precise, low-dimensional nanomaterials with tailored electronic, magnetic, and optical properties. A crucial yet unachieved goal toward single-molecule devices is the integration of reversible molecular bistability.
Here, we discuss first experimental results for an organic complex (DAE). DAE functions as a molecular switch and exhibits in solution a light-controlled ring-opening/ring-closing mechanism. Thereby, conductivity and spin-spin coupling are modulated. In our study, we investigate DAE molecules functionalized for coupling reactions. DAE molecules are prepared on different substrates (Ag(111),Au(111)) and their growth behavior and electronic characteristics are examined in dependence on the ligand structure, as revealed by Scanning Tunneling Microscopy (STM) and Scanning Tunneling Spectroscopy (STS).
Keywords: DAE, bistability, STM/STS, molecular switch
Speaker: Aaman Akhtar Ahmed (National Tsing Hua University) -
14:50
Interplay of charge density wave, pairing density wave and superconductivity in high Tc cuprate superconductors 3m
In this work, We study the interplay among charge density wave (CDW), pair density wave (PDW), and d-wave superconducting (SC) orders in high-temperature cuprate superconductors. Using the renormalized mean-field theory based on the t-J model formulated in real space, we derive self-consistent equations incorporating for CDW, PDW and d-wave SC order parameters with different doping. We focus on wavevectors Q=(Qx,Qy) and their multiples (nQx,mQy) with Qx=Qy=pi/4 and m, n=0,+/-1, +/-2…+/-7 . The results show that density waves are dominated by wavevectors being pi/4 and its multiples in the underdoped regime, and they are dominated by wavevectors being pi/4 and its multiples around the optimum doping regime. Furthermore, density waves continue to the overly doped regime and vanish at doping being around 0.19, displaying the quantum critical point at doping level 0.19.
Speaker: Mr SHIH-SI HSIAO (National Tsing Hua University)
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