Papers

We derive a rigorous sufficient condition for the absence of spin-glass order in the Ising spin glass with symmetric binary couplings on Migdal–Kadanoff (MK) hierarchical lattices with even branching number. The key observation is that a single exact renormalization-group step creates zero effective bonds with positive probability, thereby reducing the problem to bond percolation on the corresponding hierarchical lattice. When the induced dilution exceeds the percolation threshold, both spin-glass order and stiffness are absent at all temperatures, including zero temperature. As a consequence, our criterion gives a rigorous proof that the Ising spin glass on the square lattice does not exhibit a spin-glass phase within the MK approximation. More unexpectedly, by choosing sufficiently large scale factors and branching numbers, we construct MK hierarchical lattices whose fractal dimensions are arbitrarily close to three from below but still exhibit no spin-glass order. This sharply contrasts with numerical estimates obtained for MK hierarchical lattices with relatively small scale factors and branching numbers, which placed the lower critical dimension near \(2.52\).

Copropagating quantum Hall edge channels provide a promising platform for compact electron interferometry and flying quantum states. In silicon, the valley degree of freedom offers a natural alternative to spin-resolved edge channels because spin-flip scattering is strongly suppressed by the weak spin-orbit interaction. Here, we investigate interchannel transitions between copropagating valley edge channels in a double-layer-gated silicon metal-oxide-semiconductor field-effect transistor. With the bulk filling factor set to $\nu=2$, two spin-polarized valley edge channels are brought into close proximity near a depleted side gate. We observe strong intervalley mixing, with a transition probability close to 1/2, indicating nearly complete equilibration between the two valley edge channels. In contrast, interchannel transport between edge channels with different spin orientations shows negligible transition probability, consistent with suppressed spin-flip scattering in silicon. These results demonstrate that intervalley coupling at a Si/SiO$_2$ interface can provide a beam-splitter-like operation for copropagating valley edge channels, establishing a key building block toward compact silicon quantum Hall interferometers.

We study the singularities of some selected integrable lattice equations and show they all admit three types of singularities: one of finite and two of infinite extent. In particular, we show that all the equations we study possess a recently discovered, strip-like, singularity which is known under the moniker of ”taishi”. We study in detail the interaction of these taishi with the remaining two types of singularities and show that the rich behaviour first obtained in the case of the Korteweg-deVries equation is also present for other equations. Moreover, we find that in all cases this behaviour can be encoded in terms of simple symbolic dynamics which are just the dynamics governing a Box & Ball cellular automaton.

Continuous-variable quantum key distribution (CVQKD) has attracted extensive attention due to its compatibility and low costs. However, bandwidth mismatch exists to varying degrees between the transmitter and receiver. This may prevent frequency components carrying modulation information from being fully perceived by the legitimate party. In this paper, we identify a practical security loophole caused by bandwidth mismatch and propose a corresponding spectral attack scheme. Different from previous approaches that exploit security loopholes to conceal the excess noise introduced by intercept-resend attacks, this scheme can directly obtain raw-key information without introducing additional disturbances. A proof-of-principle attack on a CVQKD system with filtering operation is constructed to verify the feasibility. Experimental results indicate that Eve can obtain enough information to render the system insecure if this practical security loophole is ignored. Based on the identified security loophole, corresponding defense strategies are proposed. This work helps bridge the gap between theoretical models and practical implementations, providing a reference for defense design in practical quantum communication systems.

We review the present status of observations of the Cosmic Microwave Background. This book chapter is an update to an earlier review "Physics of the Cosmic Microwave Background Anisotropy" that appeared a decade ago in the compilation "One Hundred Years of General Relativity: From Genesis and Empirical Foundations to Gravitational Waves, Cosmology and Quantum Gravity." The earlier contribution summarized the state of the field then as well as the underlying cosmology and gravitational physics. This contribution reports on what new has occurred in the field during the intervening time 2015-2025. We also review future prospects.

We consider a periodically driven transverse field Ising model and study the long-time behavior of the correlations between the excitations in the spin chain. We show that the longest correlation length is defined by the interference between the topological defects induced by the analog of the Kibble-Zurek mechanism and those induced by the Floquet resonance. We show that although the correlations always have a finite correlation length since the system is integrable, the correlation length can be made arbitrarily large by tuning the drive period.

Previous investigations of dynamical quantum phase transition (DQPT) have predominantly focused on sudden quench protocols. In this work, we systematically explore the fate of DQPT from the sudden to the slow quench regime. We establish that DQPT remains robust under slow quenching when the protocol crosses an equilibrium quantum phase transition. Conversely, we show that accidental DQPTs,which occur when the pre and post quench Hamiltonians reside in the same equilibrium phase, can be filtered out in the slow quench limit. This demonstrates that slow quenches can reveal the intrinsic connection between DQPT and equilibrium quantum phase transitions, thereby enabling DQPT to serve as a dynamical probe for identifying equilibrium quantum critical points. We illustrate these findings with examples from the XY chain, the Aubry-André model, and the trimer Su-Schrieffer-Heeger model.

The Sun was almost certainly born in a stellar cluster, implying some degree of external forcing from neighboring stars during the Solar System's infancy. Published estimates of the strongest relevant stellar encounter, however, span a broad range, from relatively gentle perturbations to violently disruptive flybys. The modest inclination dispersion of the distant trans-Neptunian population has previously been used to argue that strong primordial encounters were unlikely and that the outer Solar System was not violently stirred at birth. In this work, we independently examine this constraint and ask whether this conclusion holds in the presence of Planet Nine. Because Planet Nine can reshape the distant trans-Neptunian population over gigayear timescales, the extent to which the present-day inclination distribution preserves a direct record of primordial cluster excitation is a priori unclear. To address this question, we compare long-term N-body integrations in which distant test particles begin either in strongly cluster-perturbed configurations or in comparatively quiescent ones, and are then evolved under the influence of the known giant planets, the Galactic tide, the effects of passing stars, and Planet Nine. We find that Planet Nine does not transform a highly excited primordial population into one resembling the observed low-inclination distant sample. Instead, comparisons between the simulated and the observed distant TNO populations indicate that the observed distant TNOs are most consistent with a relatively mildly perturbed birth environment, even in the presence of Planet Nine. If this comparatively low inclination dispersion is confirmed to be an intrinsic feature of the distant TNO population, rather than an artifact of observational bias, it constitutes a robust constraint on the severity of primordial cluster perturbations.

Partially coherent beams have attracted considerable attention due to their intrinsic resilience against complex environmental perturbations. However, the intrinsic wavefront fluctuations make it fundamentally challenging to preserve well-defined orbital angular momentum during propagation. In this work, we propose and experimentally demonstrate a class of radially correlated, partially coherent beams that carry deterministic vortex structures, generated via optical conformal mapping from Cartesian to log-polar coordinates. The resulting beams exhibit a ring-shaped coherence distribution, characterized by low coherence in the radial direction and high coherence in the azimuthal direction. This unique feature of such a beam supports a well-defined deterministic vortex phase, thereby enabling the beam to preserve its ring-shaped coherence distribution during propagation through a focusing system. Our results provide new insights into the design of new partially coherent beams and may facilitate the development of applications in optical encoding, free-space information transmission, and ultrafast light-matter interactions.

We present synthetic images of galaxies that are in the stages of star formation quenching for the Cosmological Advanced Survey Telescope for Optical and UV Research (CASTOR) and Nancy Grace Roman Space Telescope (NGRST), based on simulations coming from the IllustrisTNG suite, as processed using the stellar population synthesis library galaxev. We account for the effects of dust and various sources of noise to produce mock observations that should mirror real observations. Using these synthetic images, we fit photometric observations in binned circular annuli using FAST++ and a flexible star formation history, and recover well the spatially resolved stellar mass and star formation rate. We thereby measure various indicators (morphological metrics) of spatially resolved star formation activity in the context of galaxy quenching. We find that we are able to distinguish quenching galaxies from a mass-matched control sample of normal star forming galaxies. We additionally find that we can distinguish various quenching mechanisms, where galaxies consistent with an inside-out quenching signature can be separated from galaxies that display an outside-in signature. Using machine learning techniques the accuracy of this classification is reliable, and the progress through the quenching episode can be estimated for the different populations of quenching galaxies. We make predictions for the abundance of the various quenching populations in proposed surveys for CASTOR and NGRST, and find that these surveys will enable the classifications of thousands of quenching galaxies out to intermediate redshifts, and more when considering higher redshifts.

We investigate the dynamical symmetry of the Sasaki-Mukhanov equation, which governs the evolution of primordial perturbations during inflation. By mapping the Sasaki-Mukhanov equation to a constant-frequency harmonic oscillator via an auxiliary Ermakov field satisfying the Ermakov-Pinney equation, we construct the associated $sl(2, R)$ generators and derive the Ermakov-Lewis invariant. We apply this framework to de Sitter space and slow-roll inflation, demonstrating that the Bunch-Davies vacuum gives $I_{EL} = 1/2$, conserved non-perturbatively at all orders in slow-roll.

Over the past 30 years, the special limiting procedure known as ultradiscretisation has become the tool of choice in the field of infinite dimensional integrable systems for constructing cellular automata that exhibit solitonic behaviour, as e.g. in the Korteweg-de Vries equation. A lesser known fact is that, in many cases, ultradiscretisation can also be used to construct cellular automata that retain the essential dynamical features (such as the existence of limit cycles etc.) of a dynamical system expressed in terms of ordinary differential equations (ODEs). In its standard application, the ultradiscretisation procedure relies on the prior construction of a `good' discretisation of the dynamical system at hand, that shares the essential dynamical features of the ODE and which is sign-free, making it amenable to the ultradiscrete limit. In this paper we show, on a simple but generic model, that even if one starts from a discrete system with different dynamical features than the ODE one obtains as its continuum limit, the ultradiscrete limit can be tweaked such that the dynamics of the resulting cellular automaton is closer to that of the continuum limit than to that of the discrete model itself.

We present the scattering modes of the oscillon, to the first three orders in the Fodor expansion, in terms of elementary functions. In the case of relativistic modes, these results are new. We use them to fully decompose the field and also to analytically invert the decomposition. In quantum field theory, this allows us to show that the corresponding creation and annihilation operators satisfy the usual oscillator algebra, extending to relativistic modes the demonstration that, at a fixed order in the Fodor expansion, a periodic oscillon state exists.

Radiative heat transfer at subwavelength distances is generally understood as enhanced energy exchange mediated by photon tunnelling between neighboring bodies. While near-field interactions can dramatically increase mutual heat transfer, whether they also modify the thermal radiation emitted by the bodies themselves remains an open question. Here we experimentally show that near-field electromagnetic coupling reshapes far-field thermal emission through a distance-dependent dressed emissivity. Using a dual-probe calorimetric platform, we independently monitor the radiative balance of two borosilicate microspheres over separations ranging from 120 micrometers to a few hundred nanometers, spanning the transition from the far field to the near field. Nanowatt-resolved differential radiometry reveals asymmetric heat fluxes and a non-monotonic response of the hotter sphere, demonstrating that thermal radiation is governed not only by emitter-bath interactions but also by coupling to the surrounding photonic environment. By analyzing the total power exchanged between the coupled system and the external thermal bath, we directly extract a dressed emissivity and show that near-field interactions renormalize the far-field thermal emission of the pair through a redistribution of the electromagnetic modes available to thermal fluctuations. These observations provide direct experimental evidence that thermal emitters are dressed by their electromagnetic environment, establishing a thermal analogue of the Purcell effect.

A nonequilibrium Green's function approach to heavy-quark transport is discussed within the framework of the Kadanoff-Baym equation. One- and two-loop self-energy diagrams with hard-thermal-loop resummed propagators are calculated in the real-time formalism. Under the quasiparticle approximation, the kinetic equation reduces to the Boltzmann equation that accounts for elastic scattering and medium-induced gluon emission from a single scattering. Numerical studies suggest that off-shell and memory effects in quark-gluon plasmas influence heavy-quark dynamics, particularly near the critical temperature.

We consider whether every quantum random access code (QRAC) with density-operator encodings and arbitrary decoding measurements obeys the conjectured bound $p\leq(1+\sqrt{m/n})/2$, where $n$ classical bits are encoded into $m$ qubits and $p$ is the worst-case success probability. We find that classical random access codes with private randomness, which form a subclass of this QRAC model, violate the bound. We embed these classical codes as QRACs with diagonal encoding states and commuting decoding measurements, and construct pure-state realizations with identical decoding statistics. The achievability theorem of Ambainis, Nayak, Ta-Shma, and Vazirani then yields violations for every fixed $p\in(1/2,1)$ at sufficiently large input length. The counterexamples span the full open interval between the conjectured and Nayak bounds at each fixed compression rate. A finite-blocklength analysis further yields order-optimal logarithmic qubit scaling for a recovery bias scaling as $\sqrt{\log_2 n/n}$ with a sufficiently large prefactor. These results identify the classical coding rate as the source of the separation and motivate restricted bounds based on quantitative spectral properties of decoding measurements.

The standard approach for generating deeply degenerate quantum gases is evaporative or sympathetic cooling in a harmonic trap, after which the gas has reached its minimum entropy. All subsequent state transformations rely on adiabatic changes of a closed system, and coupling to the environment or non-adiabatic processes monotonically increase the entropy. Here, we demonstrate that this experimental paradigm can be bypassed by utilizing species-selective trapping with a low-dissipation optical tune-out trap in a dual-species mixture. We successfully reduce the entropy of a two-component fermionic quantum gas via isothermal compression within a bosonic bath, reaching deep quantum degeneracy of $T/T_F = 0.024^{+0.007}$, with $T_F$ the Fermi temperature. By characterizing the cross-dimensional relaxation and thermalization, we demonstrate that cooling light fermions with heavy bosons remains efficient and fast, even deep in the degenerate regime, where the thermalization time is found to be independent of $T/T_F$. Our results pave the way for direct cooling within optical lattices, box traps, or other complex potentials, thereby eliminating the reliance on adiabatic state transformations to reach strongly interacting many-body regimes.

Geometric phase in metasurfaces is conventionally realized using spatially rotated linearly birefringent meta-atoms under circularly polarized illumination. Here we demonstrate that full $\sim2\pi$ geometric phase modulation can be achieved through circular birefringence and observed under linear polarization excitation. We introduce a plasmonic metasurface composed of spatially rotated chiral spiral unit cells designed to produce space-variant circular retardance. This generates a geometric phase ramp equivalent to a blazed grating, leading to $\pm1$ diffraction orders in momentum space. Using leakage radiation microscopy, we directly resolve these orders and show how their intensities depend upon the input linear polarization confirming the geometric origin of the phase. We theoretically analyze the phenomenon using a rotated Poincaré space and confirm our results by direct Stokes parameters measurement. These results establish basis-independent approach to geometric phase accumulation in circularly birefringent plasmonic metasurfaces.

Although hidden-photon dark matter with masses above $10^{-4}\,\mathrm{eV}$ is well motivated by inflationary production, it remains largely unexplored by terrestrial experiments. Through kinetic mixing, hidden photons induce a weak oscillating electric field above $10\,\mathrm{GHz}$. We propose to amplify this signal using a compact high-frequency distributed cavity and detect it with chip-scale Rydberg-atom superheterodyne spectroscopy. Combining resonant enhancement, large dipole moments of Rydberg atoms, and long-term stable integration, this approach can probe hidden-photon dark matter in the mass range $5 \times 10^{-5}\text{--}7\times 10^{-4}\,\mathrm{eV}$ with sensitivities $3$–$4$ orders of magnitude beyond existing limits.

Recent observations of superconductivity in twisted bilayer WSe$_2$ (tWSe$_2$) have motivated theoretical proposals for unconventional pairing mechanisms. A central question is whether band topology plays an essential role in the system's correlation physics. In this letter, we develop a first-principles-based description of the top moiré valence bands in tWSe$_2$. Using density functional theory (DFT) calculations, we identify the bands in the relevant range of twist angles to be topologically non-trivial, with the top valence bands carrying Chern numbers $C=(+1,+1)$ for the $K$ valley. In order to treat the strong correlation physics, we construct compact molecular orbitals directly from the DFT wave functions through a partial Wannierization procedure and with the guidance of spinful $C_{3z}$ symmetry representations. This yields a localized $f$ orbital together with a complementary topological $c$ orbital, allowing us to extract hopping and hybridization amplitudes from first principles. The resulting parameters provide an ab initio benchmark for the effective Hamiltonian. Our work establishes a foundation for understanding superconductivity in moiré TMDs and highlights tWSe$_2$ as a promising platform for exploring topological superconductivity.

Sunspot oscillations probe magnetic-plasma interactions in the solar atmosphere. We investigate oscillation periods in six sunspot active regions observed in the 8-10 um band with the Accurate Infra-red Magnetic-field Solar Telescope (AIMS) at Lenghu Observatory. Light curves were extracted from umbra, penumbra, and quiet Sun regions. Wavelet analysis was applied using four methods: pixel-wise with mean/median aggregation, and spatial mean/median prior to analysis. The weighted mean period is more physically meaningful than the dominant period, better representing multi-mode oscillations. A consistent period sequence holds across all datasets: umbra (U) < penumbra (P) < quiet Sun (Q), with typical values of 260-313 s, 286-374 s, and 294-382 s. This pattern is recovered with 100% consistency by pixel-wise mean/median and spatial median methods. Spatial mean shows 1/6 full, 3/6 partial, and 2/6 inconsistency. Spatial smoothing increases periods by up to 21%, most strongly in the umbra. All peak ratios are below 0.3 (mean 0.14 +/- 0.03), confirming multi-mode oscillations. These results establish the 8-10 um band as a valuable diagnostic window for sunspot magneto-convection and wave propagation.

Neutral-atom arrays and trapped-ion crystals offer complementary strengths for fault-tolerant quantum computing but lack a fast way to deterministically interact. Here we propose a controlled-$Z$ gate generated by the charge-induced-dipole ($C_4$) force between a Rydberg-excited atom and a trapped ion, balanced by a spin-dependent optical Magnus force on the ion that closes phase-space trajectories within a few microseconds. Toggling the Rydberg state extends the scheme to multi-ion crystals at negligible overhead. The resulting ${\sim}5\,$kHz atom shuttle accelerates short-distance QCCD links and enables hybrid qLDPC memories in which atom logical qubits are written onto an ion block treated as a passive storage zone. We perform circuit-level Monte Carlo simulations and find that the hybrid architecture supports orders of magnitude more operations than atom-only or ion-only architectures at fixed code distance and logical error rate.

We present the first blind search for OH 18-cm absorption with the Five-hundred-meter Aperture Spherical Telescope (FAST), conducted alongside the HI 21-cm absorption search. Our previous FAST blind HI absorption search identified 34 systems. In this work, we extend the search using 2024 and part of the 2025 CRAFTS and FASHI data (394.4 hr and 1622.1 deg$^{2}$) together with FATHOMER observations, yielding four known and three new HI absorbers, for a total of 41 HI absorption systems. We search for OH absorption in 19 HI absorption systems whose OH redshifted frequencies fall within the FAST band. The known OH absorber towards PKS 1413+135 was re-detected, making our survey the first blind survey to detect OH absorption. No new OH absorbers were identified. We examine the relationship between $N_{\rm{OH}}$ and $N_{\rm{HI}}$, applying survival analysis to account for upper limits. The analysis does not provide statistically significant evidence for either an $N_{\rm{OH}}$-$N_{\rm{HI}}$ correlation or redshift evolution of $N_{\rm{OH}}$/$N_{\rm{HI}}$. Finally, spectral stacking sets 3$\sigma$ OH column density upper limits of 4.93, 1.64, and 1.72 $T_{\rm{ex}}$/$c_{\rm{f,OH}}\times$10$^{12}$cm$^{-2}$K$^{-1}$ for associated, intervening, and combined samples, corresponding to [\rm{OH}]/[\rm{HI}] ratios of $<$1.66$\times$10$^{-8}$, $<$1.42$\times$10$^{-8}$, and $<$0.90$\times$10$^{-8}$, assuming $T_{\rm{ex}}$=10K for OH and $T_{\rm{s}}$=100K for HI. These results place the strongest constraints to date on the OH content in radio-selected HI absorbers and establish a blind-survey benchmark for future studies of molecular gas in HI-selected systems. They also demonstrate that known HI 21-cm absorbers provide an effective parent sample for systematic OH absorption searches, paving the way for future larger surveys.

High-resolution energy data is increasingly central to Industry 4.0, where electrical signals such as three-phase voltage and current carry rich information about machine condition, tool wear, and process dynamics. Capturing this information in practice remains difficult: commercial power analysis are largely proprietary, offer limited or no access to high-sampling rate data for transient analysis, restrict access to raw waveform data, and offer no customization, while general-purpose open hardware lacks the front-end accuracy, isolation, and robustness required for industrial measurement. This paper presents Autonomous Energy Monitoring System (AEMS), an open-source, low-cost, and modular platform supported by a host, edge-gateway, and optional cloud software stack that enables autonomous, long-duration acquisition independent of a continuously connected host and thereby closes this gap by combining research-grade fidelity with industrial deployability. The system acquires three-phase voltage and current through an isolated front-end and a 24-bit, simultaneously sampling analog-to-digital converter, managed by a dual-core architecture that separates deterministic acquisition and on-board logging from host communication and control. Industrial interfaces (Ethernet, RS-485/Modbus, and BLE) together with hardware-level synchronization enable scalable, time-aligned acquisition across multiple machines, supported by a complete host, edge-gateway, and optional cloud software stack. We validate the platform on a three-axis CNC machining center, where it resolves spindle, feed-drive, rapid-traverse, and material-removal energy states and detects feed-rate changes as small as 50 mm/min. By releasing the full hardware and firmware openly, this work aims to democratize access to high-fidelity energy monitoring for both researchers and small and medium-sized manufacturers.

The density dependence of the speed of sound in cold neutron star matter remains poorly constrained and is central to determining the high-density equation of state (EOS). While binary neutron star (BNS) merger simulations increasingly incorporate detailed microphysics, the direct impact of the sound-speed in the neutron star core on observable signatures has not been systematically explored. We address this by introducing a simplified parametrization that suppresses microphysics while allowing controlled variation of the sound speed at supranuclear densities through its derivative with respect to the baryon chemical potential. Using the WhiskyTHC code, we perform a suite of fully relativistic BNS merger simulations and identify correlations between the sound-speed slope parameter and key merger outcomes, including remnant properties and post-merger GW frequencies. These results demonstrate that multimessenger observables are sensitive to the behavior of matter at the highest densities reached in neutron star cores. We further analyze gravitational-wave signals from the CoRe database of binary neutron star merger simulations employing more realistic equations of state. Our analysis reveals approximately EOS-independent relations between the derivative of the sound speed and the peak post-merger gravitational-wave frequency. Although these relations cannot be considered truly quasi-universal, they nonetheless indicate that post-merger gravitational waves retain measurable information about the EOS at he highest densities. At the same time, the remaining EOS dependence highlights the difficulty of isolating the underlying high-density physics and motivates the development of targeted parameterized frameworks for interpreting future multimessenger observations.

Two-dimensional (2D) nanomaterials derived from non-van der Waals (non-vdW) solids offer exceptional physicochemical properties, yet their synthesis is impeded by intrinsic covalent/metallic bonding and high surface reactivity of the precursors. Here, we report a general vapor-phase etching and transformation platform for producing a library of 36 2D carbides, nitrides, and carbonitrides, exhibiting electrical conductivities spanning six orders of magnitude. Using reactive vapors like hydrogen chloride, we selectively remove A-layers from MAX phases to yield well-defined layers (MXenes), including previously inaccessible semiconducting Hf2CTx. By varying the reactive vapor environment, MXenes can be engineered at X-site and surface-termination site and even be transformed into non-vdW layers such as 2D MAX phases. This general and scalable vapor-phase platform reframes 2D material synthesis, opening new avenues for various applications.

The recent synthesis of pentagonal PdTe$_2$ monolayer motivates broader research interests in transition-metal ditellurides whose electronic phases are governed by symmetry and structural reconstruction. The pentagonal phase of transition-metal ditellurides exhibits electronic properties that are dramatically different from those of its hexagonal counterpart due to its lower crystalline symmetry. Using first-principles calculations, we study monolayer $X$Te$_2$ ($X=\mathrm{Pd},\mathrm{Pt},\mathrm{Ni}$) in both hexagonal and pentagonal polymorphs. By constructing a continuous structural interpolation between the hexagonal and pentagonal phases, we show that the semimetal (hex)-to-semiconductor (penta) transition occurs only after an intermediate structural threshold rather than at the onset of symmetry reduction. The gap opening coincides with the formation of Te–Te dimers, which drive the bonding–antibonding splitting of the Te $p$ states and reorganize the band edges. In addition, the nonsymmorphic symmetry of the pentagonal phase enforces band degeneracies at the Brillouin-zone boundary, leading to symmetry-protected two-dimensional (2D) Dirac states. These results establish pentagonal $X$Te$_2$ monolayers as a new class of 2D semiconductors in which symmetry constraints and local bonding collectively shape the unconventional semiconducting electronic structure.

The transconductance $g_m = dI_D/dV_G$ of a field-effect transistor (FET) is conventionally read as a proxy for carrier density. We show that it is instead a spectroscopic probe of the carrier distribution: because $g_m$ weights the spectral current $j(E)$ by the gate-voltage derivative $\partial f(E)/\partial V_G$ and integrates over energy, it is sensitive to the shape of $f(E)$, not merely its integrated weight $n$. We develop an energy-resolved transport framework for two-dimensional (2D) FETs and, within a gate-independent spectral-kernel approximation, derive the decomposition $g_m = g_m^{(n)} + g_m^{(\alpha)}$ into the conventional density-modulation term $g_m^{(n)}$ and a distribution-shape-driven term $g_m^{(\alpha)}$. The latter, obtained as the residual after subtracting the smooth density-modulation background from the measured $g_m$, exhibits a characteristic anomalous peak at a gate voltage $V_G^{\rm pk}$. This peak has no counterpart in equilibrium transport and cannot be explained by carrier density modulation alone. With the spectral kernel calibrated, the peak position and height – extracted from standard DC/lock-in $g_m$ sweeps – constrain the hot-carrier energy $E_0$, spectral width $\sigma$, and generation threshold $n_c$, realizing a steady-state, all-electrical spectroscopy of the carrier distribution. An optional time-resolved extension further recovers the carrier relaxation time $\tau$ from the transient response following a pump excitation, establishing the 2D FET as a distribution-function spectrometer that requires no optical readout.

We present a data-driven measurement of galaxy bias and scale-dependent relative bias for elliptical and spiral galaxies using angular auto- and cross-power spectra from DES and DESI Legacy Imaging Surveys DR8. We introduce the cross-tracer clustering ratio (CTCR), the ratio of auto- to cross-power spectra, which isolates the relative clustering of morphological tracers as a function of angular multipole $\ell$. Across both surveys, ellipticals are more strongly clustered than spirals; the cleanest constraints come from DESI, where the two redshift distributions are well matched. The difference is scale dependent: the relative bias is near unity on large scales ($\ell \lesssim 50$) and rises toward smaller scales, reaching $2.9$–$4.0\sigma$ per bin at $\ell = 200$ with an inverse-variance-weighted amplitude $\Delta b = +0.56 \pm 0.06$. A complementary linear-bias analysis confirms that ellipticals are positively biased relative to the matter field, while spirals are consistent with weak bias or anti-bias. The results are robust to two covariance estimators, contamination tests, luminosity splits, and comparisons with two N-body mock catalogs. Throughout, we present the CTCR as an effective clustering ratio that is an upper bound on the physical bias ratio, adopting an assumption-light strategy appropriate for a first measurement; the joint multi-spectrum decomposition required to extract the physical bias ratio is identified as future work. These findings provide empirical evidence that galaxy morphology imprints both the amplitude and scale dependence of galaxy bias, and establish the CTCR as a useful observable for testing halo occupation and assembly-bias models with future imaging surveys.

Background-Oriented Schlieren (BOS) has become a versatile quantitative diagnostic for density-varying flows, in which estimating the light-ray deflection from the measured displacement is the essential step linking the recorded images to the underlying refractive-index field. Two-dimensional BOS traditionally treats this through the intuitive deflection angle, whereas three-dimensional tomographic BOS relies on the rigorous deflection vector derived from the ray equation. These descriptions have evolved largely independently, and the assumptions bridging them, together with the systematic errors they introduce, have not been examined in a unified manner. Based on geometric optics, this study establishes a unified deflection estimation framework that reconciles the mainstream two- and three-dimensional methods into a single mathematical structure and exposes the hierarchy of approximations underlying each. By deconstructing four key assumptions, namely the thin phase object, the uniform boundary refractive index, the paraxial approximation, and the perpendicularity between the deflection vector and the optical axis, we derive rigorous unified deflection expressions in both two- and three-dimensional space and categorize the mainstream methods accordingly. Using phase objects constructed from one-dimensional chirp signals and two-dimensional turbulent fields from Direct Numerical Simulation, combined with high-fidelity nonlinear ray tracing as the ground truth, we quantitatively characterize and analytically interpret the deflection estimation error of each method under both uniform and non-uniform refractive-index boundary conditions. This work provides a theoretical toolkit for assessing and enhancing the accuracy of quantitative BOS diagnostics.