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1. Spin-Forbidden Excitations in the Magneto-optical Spectra of ${\mathrm{CrI}}_3$ Tuned by Covalency

   https://doi.org/10.1103/4km4-4rvn  

   Occhialini, Connor A; Nessi, Luca; Martins, Luiz_G P; Demir, Ahmet Kemal; Song, Qian; Hasse, Vicky; Shekhar, Chandra; Felser, Claudia; Watanabe, Kenji; Taniguchi, Takashi; et al (July 2025, Physical Review X)

   Spin-forbidden ( $\mathrm{\Delta }S\ne 0$ ) multiplet excitations and their coupling to magnetic properties are of increasing importance for magneto-optical studies of correlated materials. Nonetheless, the mechanisms for optically brightening these transitions and their generality remain poorly understood. Here, we report magnetic circular dichroism (MCD) spectroscopy on the van der Waals ferromagnet (FM) ${\mathrm{CrI}}_3$ . Previously unreported spin-forbidden ( $\mathrm{\Delta }S=1$ ) ${{}^{4}A}_{2\mathrm{g}}\to {{}^{2}E}_{\mathrm{g}}/{{}^{2}T}_{1\mathrm{g}}$ ${\mathrm{Cr}}^{3+}$ $dd$ excitations are observed near the ligand-to-metal charge-transfer excitation threshold. The assignment of these excitations and their ${\mathrm{Cr}}^{3+}$ multiplet character is established through complementary Cr $L_3$ -edge resonant inelastic x-ray scattering measurements along with charge-transfer multiplet calculations and chemical trends in the chromium trihalide series ( $\mathrm{Cr}{X}_3$ , $X=$ Cl, Br, I). We utilize the high sensitivity of MCD spectroscopy to study the thickness-dependent optical response. The spin-forbidden excitations remain robust down to the monolayer limit, and we observe a significant magnetic-field dependence of the MCD spectrum across the antiferromagnetic-to-FM transition in few-layer samples. We preliminarily attribute this behavior to changes in the metal-ligand covalency with magnetic state. Our results clarify the magneto-optical response of ${\mathrm{CrI}}_3$ and identify covalency as a central mechanism for the brightening and field tunability of spin-forbidden multiplet excitations. 

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2. Measurement of transverse $\mathrm{\Lambda }$ and $\overline{\mathrm{\Lambda }}$ hyperon polarization in $p\mathrm{Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$

   https://doi.org/10.1103/rc6r-zt9q  

   Aaij, R; Abdelmotteleb, A_S W; Abellan_Beteta, C; Abudinén, F; Ackernley, T; Adefisoye, A A; Adeva, B; Adinolfi, M; Adlarson, P; Agapopoulou, C; et al (December 2025, Physical Review D)

   The transverse polarization of $\mathrm{\Lambda }$ and $\overline{\mathrm{\Lambda }}$ hyperons is measured in $p\mathrm{Pb}$ collisions collected by the LHCb experiment at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The polarization is averaged over hyperon transverse momentum in the range $0.15<p_{\mathrm{T}}<6.00\mathrm{GeV}/c$ , and Feynman- $x$ in the ranges $0.005<x_{\mathrm{F}}<0.040$ (forward region) and $-0.10<x_{\mathrm{F}}<-0.01$ (backward region) defined relative to the proton beam direction. The transverse polarization is found to be compatible with zero for both $\mathrm{\Lambda }$ and $\overline{\mathrm{\Lambda }}$ hyperons. The results are also measured as a function of $p_{\mathrm{T}}$ and $x_{\mathrm{F}}$ with no significant dependence on these variables observed. The results are compared with previous experimental measurements at different center-of-mass energies and collision environments. 

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3. Magnetic properties of a staggered $S=1$ chain with an alternating single-ion anisotropy direction

   https://doi.org/10.1103/PhysRevB.111.014421  

   Vaidya, S; Curley, S_P M; Manuel, P; Stewart, J Ross; Le, M Duc; Balz, C; Shiroka, T; Blundell, S J; Wheeler, K A; Calderon-Lin, I; et al (January 2025, Physical Review B)

   Materials composed of spin-1 antiferromagnetic (AFM) chains are known to adopt complex ground states that are sensitive to the single-ion-anisotropy (SIA) energy ( $D$ ), and intrachain ( $J_0$ ) and interchain ( $J_{1,2}^{\prime }$ ) exchange energy scales. While theoretical and experimental studies have extended this model to include various other energy scales, the effect of the lack of a common SIA axis is not well explored. Here we investigate the magnetic properties of $\mathrm{Ni}\left(\mathrm{pyrimidine}\right){\left({\mathrm{H}}_2\mathrm{O}\right)}_2{\left({\mathrm{NO}}_3\right)}_2$ , a chain compound where the tilting of Ni octahedra leads to a twofold alternation of the easy-axis directions along the chain. Muon-spin relaxation measurements indicate a transition to long-range order at $T_{\text{N}}=2.3\mathrm{K}$ and the magnetic structure is initially determined to be antiferromagnetic and collinear using elastic neutron diffraction experiments. Inelastic neutron scattering measurements were used to find $J_0=5.107\left(7\right)\mathrm{K}, D=2.79\left(1\right)\mathrm{K},J_1^{\prime }=0.00\left(5\right)\mathrm{K}, J_2^{\prime }=0.18\left(3\right)\mathrm{K}$ , and a rhombic anisotropy energy $E=0.19\left(9\right)\mathrm{K}$ . Mean-field modeling reveals that the ground state structure hosts spin canting of $\varphi \approx 6.5^{\circ }$ , which is not detectable above the noise floor of the elastic neutron diffraction data. Monte Carlo simulation of the powder-averaged magnetization, $M\left(H\right)$ , is then used to confirm these Hamiltonian parameters, while single-crystal $M\left(H\right)$ simulations provide insight into features observed in the data. Published by the American Physical Society2025 

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4. Dipolar-octupolar correlations and hierarchy of exchange interactions in ${\mathrm{Ce}}_2{\mathrm{Hf}}_2{\mathrm{O}}_7$

   https://doi.org/10.1103/j451-ztvr  

   Porée, Victor; Bhardwaj, Anish; Lhotel, Elsa; Petit, Sylvain; Gauthier, Nicolas; Yan, Han; Pomjakushin, Vladimir; Ollivier, Jacques; Quilliam, Jeffrey A; Nevidomskyy, Andriy H; et al (November 2025, Physical Review B)

   High-resolution neutron spectroscopy on ${\mathrm{Ce}}_2{\mathrm{Hf}}_2{\mathrm{O}}_7$ reveals a correlated state characterized by distinct dipolar scattering signals—quasielastic and inelastic contributions consistent with ‘photon’ and ‘spinon’ excitations in quantum spin ice. These signals coexist with weak octupolar scattering. Fits of thermodynamic data using numerical methods indicate a dominant octupolar exchange, $J_x$ or $J_y$ , with substantial dipolar $J_z$ and minute dipole-octupole $J_{xz}$ couplings. The $J_{xz}$ value is corroborated by an independent fit of the neutron scattering amplitude balance between dipolar and octupolar ‘photon’ contributions, highlighting its importance to understand neutron scattering results in this family. ${\mathrm{Ce}}_2{\mathrm{Hf}}_2{\mathrm{O}}_7$ enriches the landscape of dipole-octupole pyrochlore physics, and reveals a ‘quantum multipolar liquid’ where hybrid correlations involve multiple terms in the moment series expansion, opening questions regarding their intertwining and hierarchy in quantum phases. 

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5. Photoproduction of the ${\mathrm{\Sigma }}^{+}$ hyperon using linearly polarized photons with CLAS

   https://doi.org/10.1103/PhysRevC.111.025204  

   Clark, L; McKinnon, B; Ireland, D G; Glazier, D I; Livingston, K; Rönchen, D; Acar, A G; Achenbach, P; Alvarado, J S; Amaryan, M J; et al (February 2025, Physical Review C)

   Measurements of the polarization observables $\mathrm{\Sigma },\mathbf{P},\mathbf{T},{\mathbf{O}}_{\mathbf{x}},{\mathbf{O}}_{\mathbf{z}}$ for the reaction $\vec{\gamma }p\to K_S^0{\mathrm{\Sigma }}^{+}$ using a linearly polarized photon beam of energy 1.1 to 2.1 GeV are reported. The measured data provide information on a channel that has not been studied extensively, but is required for a full coupled-channel analysis in the nucleon resonance region. Observables have been simultaneously extracted using likelihood sampling with a Markov-Chain Monte Carlo process. Angular distributions in bins of photon energy $E_{\gamma }$ are produced for each polarization observable. $\mathbf{T},{\mathbf{O}}_{\mathbf{x}}$ , and ${\mathbf{O}}_{\mathbf{z}}$ are first time measurements of these observables in this reaction. The extraction of $\mathrm{\Sigma }$ extends the energy range beyond a previous measurement. The measurement of $\mathbf{P}$ , the recoil polarization, is consistent with previous measurements. The measured data are shown to be significant enough to affect the estimation of the nucleon resonance parameters when fitted within a coupled-channels model. Published by the American Physical Society2025 

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