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Understanding quantum materials—solids in which interactions among constituent electrons yield a great variety of novel emergent quantum phenomena—is a forefront challenge in modern condensed matter physics. This goal has driven the invention and refinement of several experimental methods, which can spectroscopically determine the elementary excitations and correlation functions that determine material properties. Here we focus on the future experimental and theoretical trends of resonant inelastic x-ray scattering (RIXS), which is a remarkably versatile and rapidly growing technique for probing different charge, lattice, spin, and orbital excitations in quantum materials. We provide a forward-looking introduction to RIXS and outline how this technique is poised to deepen our insight into the nature of quantum materials and of their emergent electronic phenomena. Published by the American Physical Society2024 

Abstract Magnetic van der Waals (vdW) materials have opened new frontiers for realizing novel many-body phenomena. Recently NiPS₃has received intense interest since it hosts an excitonic quasiparticle whose properties appear to be intimately linked to the magnetic state of the lattice. Despite extensive studies, the electronic character, mobility, and magnetic interactions of the exciton remain unresolved. Here we address these issues by measuring NiPS₃with ultra-high energy resolution resonant inelastic x-ray scattering (RIXS). We find that Hund’s exchange interactions are primarily responsible for the energy of formation of the exciton. Measuring the dispersion of the Hund’s exciton reveals that it propagates in a way that is analogous to a double-magnon. We trace this unique behavior to fundamental similarities between the NiPS₃exciton hopping and spin exchange processes, underlining the unique magnetic characteristics of this novel quasiparticle. 

ABSTRACT We conducted a GPU-accelerated reprocessing of $$\sim 87~{{\ \rm per\ cent}}$$ of the archival data from the High Time Resolution Universe South Low Latitude (HTRU-S LowLat) pulsar survey by implementing a pulsar search pipeline that was previously used to reprocess the Parkes Multibeam Pulsar Survey (PMPS). We coherently searched the full 72-min observations of the survey with an acceleration search range up to $$|50|\, \rm m\, s^{-2}$$, which is most sensitive to binary pulsars experiencing nearly constant acceleration during 72 min of their orbital period. Here we report the discovery of 71 pulsars, including six millisecond pulsars, of which five are in binary systems, and seven pulsars with very high dispersion measures (DM $$\gt 800 \, \rm pc \, cm^{-3}$$). These pulsar discoveries largely arose by folding candidates to a much lower spectral signal-to-noise ratio than in previous surveys and by exploiting the coherence of folding over the incoherent summing of the Fourier components to discover new pulsars as well as candidate classification techniques. We show that these pulsars could be fainter and on average more distant as compared with both the previously reported 100 HTRU-S LowLat pulsars and the background pulsar population in the survey region. We have assessed the effectiveness of our search method and the overall pulsar yield of the survey. We show that through this reprocessing we have achieved the expected survey goals, including the predicted number of pulsars in the survey region, and discuss the major causes why these pulsars were missed in previous processing of the survey. 

Researchers have been aggressively investigating group-IV (Ge, SiGeSn, GeSn) optoelectronic materials to realize tunable wavelength lasers, photodetectors, and transistors. By exploiting strain and bandgap engineering of these materials via choice of substrate orientation and intelligent buffer engineering as well as precise control of Sn alloy composition during material synthesis, it will offer widespread device applications. There is an opportunity to improve the device-level quality of GeSn material systems along with higher Sn incorporation that face growth challenges during epitaxy. The current research work presents the substrate orientation and misorientation (100)/2˚, (100)/6˚, (110), (111) mediated epitaxial GeSn and Ge optoelectronic materials synthesized via MBE and analyzed using several analytical tools. X-ray analysis demonstrated high quality GeSn materials with less broadening and good symmetricity on (100) compared to (110) GeSn materials. Minority carrier lifetimes of these GeSn epilayers were extracted as > 400 ns for the (100) substrate misoriented by 6˚ towards [110] direction. Raman spectroscopy measurements were performed to study the vibrational properties, where the LO phonon wavenumber shifts at ωLO = 301.11 ± 0.8 cm¬–1 from (100)/2˚, (100)/6˚ and (110) oriented GeSn epilayers that were synthesized in equivalent growth conditions. Cross-sectional TEM of (100)/2˚ GeSn sample was performed that revealed good quality GeSn material on GaAs. Elimination of the interfaced electronic dipole charge effects, that destabilize the group-IV/group III-V heterointerface and further layer growths, is attributed to aid in achieving superior quality GeSn epitaxial materials over a (100) substrate that is misoriented by 6˚ towards the [110] direction. This substrate offcut will enable to annihilate antiphase domains due to polar-on-non-polar epitaxial growth, which further reduce non-radiative recombination centers in GeSn material. Hence, growth of GeSn material on misoriented (100) substrate offers two-fold benefits: (i) reduced active defects at the GeSn/III-V heterointerface, and (ii) self-annihilation of the antiphase domain boundaries for enhancing the efficiency of optical devices. 

ABSTRACT The HTRU-S Low Latitude survey data within 1° of the Galactic Centre (GC) were searched for pulsars using the Fast Folding Algorithm (FFA). Unlike traditional Fast Fourier Transform (FFT) pipelines, the FFA optimally folds the data for all possible periods over a given range, which is particularly advantageous for pulsars with low-duty cycles. For the first time, a search over acceleration was included in the FFA to improve its sensitivity to binary pulsars. The steps in dispersion measure (DM) and acceleration were optimized, resulting in a reduction of the number of trials by 86 per cent. This was achieved over a search period range from 0.6 to 432-s, i.e. 10 per cent of the observation time (4320s), with a maximum DM of 4000 pc cm−3 and an acceleration range of ±128 m s−2. The search resulted in the re-detections of four known pulsars, including a pulsar that was missed in the previous FFT processing of this survey. This result indicates that the FFA pipeline is more sensitive than the FFT pipeline used in the previous processing of the survey within our parameter range. Additionally, we discovered a 1.89-s pulsar, PSR J1746-2829, with a large DM, located 0.5 from the GC. Follow-up observations revealed that this pulsar has a relatively flat spectrum (α = −0.9 ± 0.1) and has a period derivative of ∼1.3 × 10−12 s s−1, implying a surface magnetic field of ∼5.2 × 1013 G and a characteristic age of ∼23 000 yr. While the period, spectral index, and surface magnetic field strength are similar to many radio magnetars, other characteristics such as high linear polarization are absent. 

Abstract The microscopic origins of emergent behaviours in condensed matter systems are encoded in their excitations. In ordinary magnetic materials, single spin-flips give rise to collective dipolar magnetic excitations called magnons. Likewise, multiple spin-flips can give rise to multipolar magnetic excitations in magnetic materials with spin S ≥ 1. Unfortunately, since most experimental probes are governed by dipolar selection rules, collective multipolar excitations have generally remained elusive. For instance, only dipolar magnetic excitations have been observed in isotropic S = 1 Haldane spin systems. Here, we unveil a hidden quadrupolar constituent of the spin dynamics in antiferromagnetic S = 1 Haldane chain material Y 2 BaNiO 5 using Ni L 3 -edge resonant inelastic x-ray scattering. Our results demonstrate that pure quadrupolar magnetic excitations can be probed without direct interactions with dipolar excitations or anisotropic perturbations. Originating from on-site double spin-flip processes, the quadrupolar magnetic excitations in Y 2 BaNiO 5 show a remarkable dual nature of collective dispersion. While one component propagates as non-interacting entities, the other behaves as a bound quadrupolar magnetic wave. This result highlights the rich and largely unexplored physics of higher-order magnetic excitations. 

Abstract We studied the magnetic excitations in the quasi-one-dimensional (q-1D) ladder subsystem of Sr 14−x Ca x Cu 24 O 41 (SCCO) using Cu L 3 -edge resonant inelastic X-ray scattering (RIXS). By comparing momentum-resolved RIXS spectra with high ( x  = 12.2) and without ( x  = 0) Ca content, we track the evolution of the magnetic excitations from collective two-triplon (2 T) excitations ( x  = 0) to weakly-dispersive gapped modes at an energy of 280 meV ( x  = 12.2). Density matrix renormalization group (DMRG) calculations of the RIXS response in the doped ladders suggest that the flat magnetic dispersion and damped excitation profile observed at x  = 12.2 originates from enhanced hole localization. This interpretation is supported by polarization-dependent RIXS measurements, where we disentangle the spin-conserving Δ S  = 0 scattering from the predominant Δ S  = 1 spin-flip signal in the RIXS spectra. The results show that the low-energy weight in the Δ S  = 0 channel is depleted when Sr is replaced by Ca, consistent with a reduced carrier mobility. Our results demonstrate that off-ladder impurities can affect both the low-energy magnetic excitations and superconducting correlations in the CuO 4 plaquettes. Finally, our study characterizes the magnetic and charge fluctuations in the phase from which superconductivity emerges in SCCO at elevated pressures. 

{"Abstract":["Data files for the manuscript "Quadrupolar magnetic excitations in an isotropic spin-1 antiferromagnet".<\/p>\n\nReference: A. Nag, A. Nocera, S. Agrestini, M. Garcia-Fernandez, A. C. Walters, Sang-Wook Cheong, S. Johnston, and Ke-Jin Zhou, "Quadrupolar magnetic excitations in an isotropic spin-1 antiferromagnet". arXiv:2111.03625 (2021).<\/p>\n\nPreprint: arXiv:2111.03625 (2021), URL: https://arxiv.org/abs/2111.03625<\/p>"]}