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Abstract Optical phonon engineering through nonlinear effects has been utilized in ultrafast control of material properties. However, nonlinear optical phonons typically exhibit rapid decay due to strong mode-mode couplings, limiting their effectiveness in temperature or frequency sensitive applications. Here we report the observation of long-lived nonlinear optical phonons through the spontaneous formation of phonon frequency combs in the van der Waals material CrXTe₃(X=Ge, Si) using high-resolution Raman scattering. Unlike conventional optical phonons, the highestA_gmode in CrGeTe₃splits into equidistant, sharp peaks forming a frequency comb that persists for hundreds of oscillations and survives up to 200K. These modes correspond to localized oscillations of Ge₂Te₆clusters, isolated from Cr hexagons, behaving as independent quantum oscillators. Introducing a cubic nonlinear term to the harmonic oscillator model, we simulate the phonon time evolution and successfully replicate the observed comb structure. Similar frequency comb behavior is observed in CrSiTe₃, demonstrating the generalizability of this phenomenon. Our findings demonstrate that Raman scattering effectively probes high-frequency nonlinear phonon modes, offering insight into the generation of long-lived, tunable phonon frequency combs with potential applications in ultrafast material control and phonon-based technologies. 

Abstract The recent Far-Infrared Polarimetric Large-Area Central Molecular Zone Exploration (FIREPLACE) survey with SOFIA has mapped plane-of-sky magnetic field orientations within the Central Molecular Zone (CMZ) of the Milky Way. Applying the Histogram of Relative Orientations analysis to the FIREPLACE data, we find that the relative orientation between magnetic fields and column density structures is random in low-density regions ( $2\times 10^{22}\lesssim N_{{\mathrm{H}}_2}\lesssim 10^{23}{\mathrm{cm}}^{-2}$) but becomes preferentially parallel in high-density regions (≳10²³cm⁻²). This trend is in contrast with that of the nearby molecular clouds, where the relative orientation transitions from parallel to perpendicular with increasing column densities. However, the relative orientation varies between individual CMZ clouds. Comparisons with magnetohydrodynamic simulations specific to the CMZ conditions suggest that the observed parallel alignment is intrinsic, rather than artifacts caused by the projection effect. The origin of this parallel configuration may arise from the fact that most dense structures in the CMZ are not self-gravitating, as they are in supervirial states, except for the ministarburst region Sgr B2. These findings are consistent with the low star formation efficiency observed in the CMZ compared to that in the Galactic disk. 

Abstract We report the first arcsecond-resolution observations of the magnetic field in the ministarburst complex Sgr B2. SMA polarization observations revealed magnetic field morphology in three dense cores of Sgr B2 N(orth), M(ain), and S(outh). The total plane-of-sky magnetic field strengths in these cores are estimated to be 4.3–10.0 mG, 6.2–14.7 mG, and 1.9–4.5 mG derived from the angular dispersion function method after applying the correction factors of 0.21 and 0.5. Combining with analyses of the parsec-scale polarization data from Stratospheric Observatory for Infrared Astronomy, we found that a magnetically supercritical condition is present from the cloud scale (∼10 pc) to core scale (∼0.2 pc) in Sgr B2, which is consistent with the burst of star formation activities in the region likely resulting from a multiscale gravitational collapse from the cloud to dense cores. 

Abstract The Galactic center (GC) is an extreme region of the Milky Way that is host to a complex set of thermal and nonthermal structures. In particular, the GC contains high-density gas and dust that is collectively referred to as the Central Molecular Zone (CMZ). In this work, we study a subset of HNCO filaments identified in Band 3 Atacama Large Millimeter/submillimeter Array (ALMA) observations of the GC obtained by the ALMA CMZ Exploration Survey that are comparable to high-density filaments identified in the Galactic disk. We compare the orientation of the magnetic field derived from 214μm Stratospheric Observatory for Infrared Astronomy and 850μm James Clerk Maxwell Telescope observations with the filament orientation to determine which mechanisms dominate the formation of these filaments. We observe a large range of magnetic orientations in our observed filaments indicating the complex environments the filaments are located in. We also compare the observational results to synthetic datasets created using an MHD model of the GC. Our analysis reveals that the dominant mechanisms local to the HNCO filaments vary throughout the GC with some filaments being dominated by supersonic turbulence and others by subsonic turbulence. The comparison to synthetic observations indicates that the observed filaments are in magnetically dominated environments that could be supporting these filaments against collapse. Our results on the CMZ filaments are also compared to results obtained on similar filaments located in the Galactic disk, and we find that the filaments studied here are possible CMZ analogs to the dense filamentary “bones” observed previously in the Galactic disk. 

Abstract The nature of the magnetic field structure throughout the Galactic Center (GC) has long been of interest. The recent Far-InfraREd Polarimetric Large-Area Central Molecular Zone (CMZ) Exploration (FIREPLACE) Survey reveals preliminary connections between the seemingly distinct vertical and horizontal magnetic field distributions previously observed in the GC. We use the statistical techniques of the Histogram of Relative Orientation and the Projected Rayleigh Statistic to assess whether the CMZ magnetic field preferentially aligns with the structure of the CMZ molecular clouds or the morphology of the nonthermal emission of the GC nonthermal filament (NTF) population. We find that there is a range of magnetic field orientations throughout the population of CMZ molecular clouds, ranging from parallel to perpendicular orientation. We posit these orientations depend on the prevalence of gravitational shear in the GC, in contrast with what is observed in Galactic Disk star-forming regions. We also compare the magnetic field orientation from dust polarimetry with individual prominent NTFs, finding a preferred perpendicular relative orientation. This perpendicular orientation indicates that the vertical field component found in the FIREPLACE observations is not spatially confined to the NTFs, providing evidence for a more pervasive vertical field in the GC. From dynamical arguments, we estimate an upper limit on the magnetic field strength for this vertical field, findingB≤ 4 mG. A field close to this upper limit would indicate that the NTFs are not local enhancements of a weaker background field and that the locations of the NTFs depend on proximity to sites of cosmic-ray production. 

Abstract The nonlinear Hall effect (NLHE) with time‐reversal symmetry has emerged as a transformative phenomenon within the Hall effect family, attracting significant interest due to its profound implications for both fundamental physics and technological applications. While prior studies have predominantly focused on NLHE in 2D materials, advancements in practical applications have been constrained by low operating temperatures and limited responsivity, typically below 10⁻⁴m/V. Achieving significant responsivity at room temperature (RT) in 3D systems has proven challenging, particularly for scattering‐induced NLHE. Here, the discovery of disorder scattering‐induced NLHE in chalcopyrite‐type CdGeAs₂bulk single crystals is reported, demonstrating a remarkable responsivity of up to 10⁻³m/V at RT. The studies reveal that NLHE not only facilitates ac‐driven second harmonic and rectification Hall responses but also induces an exceptionally large anomalous Hall angle. Through band structure measurements by ARPES, DFT calculations, as well as symmetry and nonlinear Hall conductivity scaling analyses, disorder scattering is identified as the dominant mechanism for the NLHE in CdGeAs₂. Leveraging the observed strong responsivity of NLHE at RT, its broadband electronic frequency mixing capability in the MHz range is further demonstrated. This work sets the foundation for integrating scattering‐induced NLHE in 3D materials into very high‐frequency mixing technologies. 

eal-time systems with hard timing constrains require known upper bounds on each task’s worst-case execution time (WCET) to determine if all deadlines can be met. One challenge in predictable execution is that Dynamic Random Access Memory (DRAM) cells must be refreshed periodically to maintain data validity, yet memory remains blocked during refresh, which results in overly pessimistic WCET bounds. This work contributes “Colored Refresh” to hide DRAM refresh overhead while preserving real-time schedulability for cyclic executives, which are widely used in highly critical systems. Colored Refresh partitions DRAM memory at rank granularity such that refreshes rotate round-robin from rank to rank. Real-time tasks are assigned different ranks via colored memory allocation. By cooperatively scheduling real-time tasks and refresh operations, memory requests no longer suffer from refresh interference. This reduces memory access latencies for tasks irrespective of DRAM density and size. Hence, Colored Refresh reduces a task’s WCET and makes its execution more predictable. 

Bounding each task’s worst-case execution time (WCET) accurately is essential for real-time systems to determine if all deadlines can be met. Yet, access latencies to Dynamic Random Access Memory (DRAM) vary significantly due to DRAM refresh, which blocks access to memory cells. Variations further increase as DRAM density grows. This work contributes the “Colored Refresh Server” (CRS), a uniprocessor scheduling paradigm that partitions DRAM in two distinctly colored groups such that refreshes of one color occur in parallel to the execution of real-time tasks of the other color. By executing tasks in phase with periodic DRAM refreshes with opposing colors, memory requests no longer suffer from refresh interference. Experimental results confirm that refresh overhead