Spinon Confinement in the One-Dimensional Ising-Like Antiferromagnet SrCo2V2O8

For quasi-one dimensional quantum spin systems theory predicts the occurrence of a confinement of spinon excitation due to interchain couplings. Here we investigate the system SrCo2V2O8, a realization of the weakly-coupled Ising-like XXZ antiferromagnetic chains, by terahertz spectroscopy with and without applied magnetic field. At low temperatures a series of excitations is observed, which split in a Zeeman-like fashion in an applied magnetic field. These magnetic excitations are identified as the theoretically predicted spinon-pair excitations. Using a one dimensional Schr\"odinger equation with a linear confinement potential imposed by weak interchain couplings, the hierarchy of the confined spinons can be fully described.Comment: 4 pages, 3 figure

Field Induced Magnetic Ordering and Single-ion Anisotropy in the Quasi-1D Haldane Chain Compound SrNi2V2O8: A Single Crystal investigation

Field-induced magnetic ordering in the Haldane chain compound SrNi$_{2}$V$_{2}$O$_{8}$ and effect of anisotropy have been investigated using single crystals. Static susceptibility, inelastic neutron scattering, high-field magnetization, and low temperature heat-capacity studies confirm a non-magnetic spin-singlet ground state and a gap between the singlet ground state and triplet excited states. The intra-chain exchange interaction is estimated to be $J \sim 8.9{\pm}$0.1 meV. Splitting of the dispersions into two modes with minimum energies 1.57 and 2.58 meV confirms the existence of single-ion anisotropy $D(S^z){^2}$. The value of {\it D} is estimated to be $-0.51{\pm}0.01$ meV and the easy axis is found to be along the crystallographic {\it c}-axis. Field-induced magnetic ordering has been found with two critical fields [$\mu_0H_c^{\perp c} = 12.0{\pm}$0.2 T and $\mu_0H_c^{\parallel c} = 20.8{\pm}$0.5 T at 4.2 K]. Field-induced three-dimensional magnetic ordering above the critical fields is evident from the heat-capacity, susceptibility, and high-field magnetization study. The Phase diagram in the {\it H-T} plane has been obtained from the high-field magnetization. The observed results are discussed in the light of theoretical predictions as well as earlier experimental reports on Haldane chain compounds

Evolution of antiferromagnetic domains in the all-in-all-out ordered pyrochlore Nd2_2Zr2_2O7_7

We report the observation of magnetic domains in the exotic, antiferromagnetically ordered all-in-all-out state of Nd$_2$Zr$_2$O$_7$, induced by spin canting. The all-in-all-out state can be realized by Ising-like spins on a pyrochlore lattice and is established in Nd$_2$Zr$_2$O$_7$ below 0.31 K for external magnetic fields up to 0.14 T. Two different spin arrangements can fulfill this configuration which leads to the possibility of magnetic domains. The all-in-all-out domain structure can be controlled by an external magnetic field applied parallel to the [111] direction. This is a result of different spin canting mechanism for the two all-in-all-out configurations for such a direction of the magnetic field. The change of the domain structure is observed through a hysteresis in the magnetic susceptibility. No hysteresis occurs, however, in case the external magnetic field is applied along [100].Comment: Accepted for publication in Phys. Rev. B, 6 pages, 6 figure

Consequences of critical interchain couplings and anisotropy on a Haldane chain

Effects of interchain couplings and anisotropy on a Haldane chain have been investigated by single crystal inelastic neutron scattering and density functional theory (DFT) calculations on the model compound SrNi$_2$V$_2$O$_8$. Significant effects on low energy excitation spectra are found where the Haldane gap ($\Delta_0 \approx 0.41J$; where $J$ is the intrachain exchange interaction) is replaced by three energy minima at different antiferromagnetic zone centers due to the complex interchain couplings. Further, the triplet states are split into two branches by single-ion anisotropy. Quantitative information on the intrachain and interchain interactions as well as on the single-ion anisotropy are obtained from the analyses of the neutron scattering spectra by the random phase approximation (RPA) method. The presence of multiple competing interchain interactions is found from the analysis of the experimental spectra and is also confirmed by the DFT calculations. The interchain interactions are two orders of magnitude weaker than the nearest-neighbour intrachain interaction $J$ = 8.7~meV. The DFT calculations reveal that the dominant intrachain nearest-neighbor interaction occurs via nontrivial extended superexchange pathways Ni--O--V--O--Ni involving the empty $d$ orbital of V ions. The present single crystal study also allows us to correctly position SrNi$_2$V$_2$O$_8$ in the theoretical $D$-$J_{\perp}$ phase diagram [T. Sakai and M. Takahashi, Phys. Rev. B 42, 4537 (1990)] showing where it lies within the spin-liquid phase.Comment: 12 pages, 12 figures, 3 tables PRB (accepted). in Phys. Rev. B (2015

Investigation of the magnetic structure and crystal field states of pyrochlore antiferromagnet Nd2Zr2O7

We present synchrotron x-ray diffraction, neutron powder diffraction and time-of-flight inelastic neutron scattering measurements on the rare earth pyrochlore oxide Nd2Zr2O7 to study the ordered state magnetic structure and cystal field states. The structural characterization by high-resolution synchrotron x-ray diffraction confirms that the pyrochlore structure has no detectable O vacancies or Nd/Zr site mixing. The neutron diffraction reveals long range all-in/all-out antiferromagnetic order below T_N ~ 0.4 K with propagation vector k = (0 0 0) and an ordered moment of 1.26(2) \mu_B/Nd at 0.1 K. The ordered moment is much smaller than the estimated moment of 2.65 \mu_B/Nd for the local Ising ground state of Nd3+ (J=9/2) suggesting that the ordering is partially suppressed by quantum fluctuations. The strong Ising anisotropy is further confirmed by the inelastic neutron scattering data which reveals a well-isolated dipolar-octupolar type Kramers doublet ground state. The crystal field level scheme and ground state wavefunction have been determined.Comment: 12 pages, 15 figures, 2 table

Effects of Acute Exercise on Affect in Females with Substance Use Disorder

International Journal of Exercise Science 16(5): 95-108, 2023. Negative mood states experienced during the withdrawal stage of substance dependence have been associated with relapse in persons suffering from substance use disorder (SUD). Exercise is gaining attention as an adjunct therapy for SUD due to its ability to alleviate negative mood states experienced during withdrawal. The purpose of this study was to investigate the effects of acute, controlled bouts of aerobic and resistance exercise versus sedentary control (quiet reading) on positive affect (PA) and negative affect (NA) in females undergoing SUD treatment at inpatient facilities. Females (n=11; 34 + 8 yrs) were randomly assigned to each condition in counterbalanced fashion. Aerobic exercise (AE) consisted of 20 minutes of steady-state moderate intensity (40-60% HRR) treadmill walking. Resistance exercise (RE) consisted of 20 minutes of standardized circuit weight training (1:1 work to rest ratio). The Positive and Negative Affect Scale (PANAS) was used to assess PA and NA pre- and post-interventions. Repeated measures ANOVAs indicated AE and RE significantly increased PA (p \u3c 0.05) versus control, with no significant difference between AE and RE. Friedman’s test revealed AE and RE significantly reduced NA (p \u3c 0.05) versus control. Results indicate short bouts of aerobic and resistance exercise are equally effective for acute mood regulation and superior to a sedentary control in females undergoing inpatient SUD treatment

Exciton-magnon transitions in the frustrated chromium antiferromagnets CuCrO2, alpha-CaCr2O4, CdCr2O4, and ZnCr2O4

We report on optical transmission spectroscopy of the Cr-based frustrated triangular antiferromagnets CuCrO2 and alpha-CaCr2O4, and the spinels CdCr2O4 and ZnCr2O4 in the near-infrared to visible-light frequency range. We explore the possibility to search for spin correlations far above the magnetic ordering temperature and for anomalies in the magnon lifetime in the magnetically ordered state by probing exciton-magnon sidebands of the spin-forbidden crystal-field transitions of the Cr3+ ions (spin S = 3/2). In CuCrO2 and alpha-CaCr2O4 the appearance of fine structures below T_N is assigned to magnon sidebands by comparison with neutron scattering results. The temperature dependence of the line width of the most intense sidebands in both compounds can be described by an Arrhenius law. For CuCrO2 the sideband associated with the 4A2 -> 2T2 transition can be observed even above T_N. Its line width does not show a kink at the magnetic ordering temperature and can alternatively be described by a Z2 vortex scenario proposed previously for similar materials. The exciton-magnon features in alpha-CaCr2O4 are more complex due to the orthorhombic distortion. While for CdCr2O4 magnon sidebands are identified below T_N and one sideband excitation is found to persist across the magnetic ordering transition, only a weak fine structure related to magnetic ordering has been observed in ZnCr2O4.Comment: 14 pages, 10 figures, all comments are welcome and appreciated, accepted for publication in PR

Using particle size distributions to fingerprint suspended sediment sources Evaluation at laboratory and catchment scales

Applications of sediment source fingerprinting studies are growing globally despite the high costs and workloads associated with the analyses of conventional fingerprint properties on target sediment samples collected using traditional methods. To this end, there is a need to test new fingerprint properties that can overcome these challenges. Sediment particle size could potentially contribute here since it is relatively easy to measure but, until now, has rarely been deployed as a fingerprint itself. Instead, particle size has been used to ensure that source and target sediment samples are more directly comparable on the basis of the fingerprints used. Accordingly, this work examined whether particle size distributions (PSDs) could be used as a reliable fingerprint for apportioning sediment sources, in combination with a grain size un-mixing model. Application of PSDs as a fingerprint was tested at two scales: (i) in a laboratory setting where soil samples with known PSDs were used to generate artificial mixtures to evaluate un-mixing model results, and (ii) a catchment setting comparing PSDs in a confluence-based approach to test if downstream target sediment PSDs could be un-mixed into the contributions of sediment coming from an upstream and a tributary sampling site. Laboratory results showed that the known proportions of the two, three and four soil samples in the artificial mixtures were predicted accurately using the AnalySize grain size un-mixing model, giving average absolute errors of 9%, 8% and 6%, respectively. Catchment results showed variable performances when comparing un-mixing results with sediment budget estimations, with the best results obtained at higher discharge values during storm runoff events. Overall, our results suggest the potential of using PSDs for estimating contributions of sediment sources delivering SS with distinct PSDs when sources are located at short distance to the downstream sampling site

High frequency un-mixing of soil samples using a submerged spectrophotometer in a laboratory setting—implications for sediment fingerprinting

Purpose This study tests the feasibility of using a submersible spectrophotometer as a novel method to trace and apportion suspended sediment sources in situ and at high temporal frequency. Methods Laboratory experiments were designed to identify how absorbance at different wavelengths can be used to un-mix artificial mixtures of soil samples (i.e. sediment sources). The experiment consists of a tank containing 40 L of water, to which the soil samples and soil mixtures of known proportions were added in suspension. Absorbance measurements made using the submersible spectrophotometer were used to elucidate: (i) the effects of concentrations on absorbance, (ii) the relationship between absorbance and particle size and (iii) the linear additivity of absorbance as a prerequisite for un-mixing. Results The observed relationships between soil sample concentrations and absorbance in the ultraviolet visible (UV–VIS) wavelength range (200–730 nm) indicated that differences in absorbance patterns are caused by soil-specific properties and particle size. Absorbance was found to be linearly additive and could be used to predict the known soil sample proportions in mixtures using the MixSIAR Bayesian tracer mixing model. Model results indicate that dominant contributions to mixtures containing two and three soil samples could be predicted well, whilst accuracy for four-soil sample mixtures was lower (with respective mean absolute errors of 15.4%, 12.9% and 17.0%). Conclusion The results demonstrate the potential for using in situ submersible spectrophotometer sensors to trace suspended sediment sources at high temporal frequency