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AWP-ODC is a 4th-order finite difference code used by the SCEC community for linear wave propagation, Iwan-type nonlinear dynamic rupture and wave propagation, and Strain Green Tensor simulation. We have ported and verified the CUDA-version of AWP-ODC-SGT, a reciprocal version used in the SCEC CyberShake project, to HIP so that it can also run on AMD GPUs. This code achieved sustained 32.6 Petaflop/s performance and 95.6% parallel efficiency at full scale on Frontier, a Leadership Computing Facility at Oak Ridge National Laboratory. The readiness of this community software on AMD Radeon Instinct GPUs and EPYC CPUs allows SCEC to take advantage of exascale systems to produce more realistic ground motions and accurate seismic hazard products. We have also deployed AWP-ODC to Azure to leverage the array of tools and services that Azure provides for tightly coupled HPC simulation on commercial cloud. We collaborated with Internet 2/Azure Accelerator supporting team, as part of Microsoft Internet2/Azure Accelerator for Research Fall 2022 Program, with Azure credits awarded through Cloudbank, an NSF-funded initiative. We demonstrate the AWP performance with a benchmark of ground motion simulation on various GPU based cloud instances, and a comparison of the cloud solution to on-premises bare-metal systems. AWP-ODC currently achieves excellent speedup and efficiency on CPU and GPU architectures. The Iwan-type dynamic rupture and wave propagation solver faces significant challenges, however, due to the increased computational workload with the number of yield surfaces chosen. Compared to linear solution, the Iwan model adds 10x-30x more computational time plus 5x-13x more memory consumption that require substantial code changes to obtain excellent performance. Supported by NSF’s Characteristic Science Applications (CSA) program for the Leadership-Class Computing Facility (LCCF) at Texas Advanced Computing Center (TACC), we are porting and improving the performance of this nonlinear AWP-ODC software, preparing for the next generation NSF LCCF system called Horizon, to be installed at TACC. During Texascale days on the current TACC’s Frontera, we carried out an Iwan-type nonlinear dynamic rupture and wave propagation simulation of a Mw7.8 scenario earthquake on the southern San Andreas fault. This simulation modeled 83 seconds of rupture with a grid spacing of 25 m to resolve frequencies up to 4 Hz with a minimum shear-wave velocity of 500 m/s. 

Spin liquids are quantum phases of matter with a variety of unusual features arising from their topological character, including “fractionalization”—elementary excitations that behave as fractions of an electron. Although there is not yet universally accepted experimental evidence that establishes that any single material has a spin liquid ground state, in the past few years a number of materials have been shown to exhibit distinctive properties that are expected of a quantum spin liquid. Here, we review theoretical and experimental progress in this area. 

Abstract Amongst the rare-earth perovskite nickelates, LaNiO 3 (LNO) is an exception. While the former have insulating and antiferromagnetic ground states, LNO remains metallic and non-magnetic down to the lowest temperatures. It is believed that LNO is a strange metal, on the verge of an antiferromagnetic instability. Our work suggests that LNO is a quantum critical metal, close to an antiferromagnetic quantum critical point (QCP). The QCP behavior in LNO is manifested in epitaxial thin films with unprecedented high purities. We find that the temperature and magnetic field dependences of the resistivity of LNO at low temperatures are consistent with scatterings of charge carriers from weak disorder and quantum fluctuations of an antiferromagnetic nature. Furthermore, we find that the introduction of a small concentration of magnetic impurities qualitatively changes the magnetotransport properties of LNO, resembling that found in some heavy-fermion Kondo lattice systems in the vicinity of an antiferromagnetic QCP. 

Abstract We present the results of a search for gravitational-wave transients associated with core-collapse supernova SN 2023ixf, which was observed in the galaxy Messier 101 via optical emission on 2023 May 19, during the LIGO–Virgo–KAGRA 15th Engineering Run. We define a five-day on-source window during which an accompanying gravitational-wave signal may have occurred. No gravitational waves have been identified in data when at least two gravitational-wave observatories were operating, which covered ∼14% of this five-day window. We report the search detection efficiency for various possible gravitational-wave emission models. Considering the distance to M101 (6.7 Mpc), we derive constraints on the gravitational-wave emission mechanism of core-collapse supernovae across a broad frequency spectrum, ranging from 50 Hz to 2 kHz, where we assume the gravitational-wave emission occurred when coincident data are available in the on-source window. Considering an ellipsoid model for a rotating proto-neutron star, our search is sensitive to gravitational-wave energy 1 × 10⁻⁴M_⊙c²and luminosity 2.6 × 10⁻⁴M_⊙c²s⁻¹for a source emitting at 82 Hz. These constraints are around an order of magnitude more stringent than those obtained so far with gravitational-wave data. The constraint on the ellipticity of the proto-neutron star that is formed is as low as 1.08, at frequencies above 1200 Hz, surpassing past results. 

Abstract Continuous gravitational waves (CWs) emission from neutron stars carries information about their internal structure and equation of state, and it can provide tests of general relativity. We present a search for CWs from a set of 45 known pulsars in the first part of the fourth LIGO–Virgo–KAGRA observing run, known as O4a. We conducted a targeted search for each pulsar using three independent analysis methods considering single-harmonic and dual-harmonic emission models. We find no evidence of a CW signal in O4a data for both models and set upper limits on the signal amplitude and on the ellipticity, which quantifies the asymmetry in the neutron star mass distribution. For the single-harmonic emission model, 29 targets have the upper limit on the amplitude below the theoretical spin-down limit. The lowest upper limit on the amplitude is 6.4 × 10⁻²⁷for the young energetic pulsar J0537−6910, while the lowest constraint on the ellipticity is 8.8 × 10⁻⁹for the bright nearby millisecond pulsar J0437−4715. Additionally, for a subset of 16 targets, we performed a narrowband search that is more robust regarding the emission model, with no evidence of a signal. We also found no evidence of nonstandard polarizations as predicted by the Brans–Dicke theory.