High-pressure effects on structural, magnetic, and vibrational properties of van der Waals antiferromagnet MnPS₃

The crystal structure, vibrational spectra, and magnetic structure of quasi-two-dimensional layered van der Waals material MnPS3 were studied using x-ray diffraction and Raman spectroscopy at high pressures up to 28 GPa, and neutron diffraction up to 3.6 GPa, respectively. A structural phase transition between two monoclinic modifications of the same C2/m symmetry was observed, evolving gradually in the pressure range of about 1–6 GPa. The transition is accompanied by abrupt shortening of lattice parameters, significant reduction of the monoclinic distortion, and anomalies in the pressure behavior of several Raman-mode frequencies. No more structural phase transitions were revealed in the studied pressure range. The antiferromagnetic (AFM) state with a propagation vector k= (0, 0, 0) remains stable in ambient pressure and high-pressure structural phases of MnPS3 at least up to 3.6 GPa. The Néel temperature increases noticeably with a pressure coefficient of dTN/dP=6.7 K/GPa, leading to modification of the dominant first-neighbor magnetic interaction exchange parameter with a relevant coefficient dJ1/dP≈−0.6 meV/GPa. This observation is in contrast to the pressure behavior of FePS3, demonstrating modification of the AFM state from 2D-like to 3D-like at the similar pressure-induced structural phase transition. The different pressure response of the magnetic states of MnPS3 and FePS3 is analyzed in terms of competing in-plane and interplane magnetic interactions

High-pressure effects on structural, magnetic, and vibrational properties of van der Waals antiferromagnet MnPS₃

The crystal structure, vibrational spectra, and magnetic structure of quasi-two-dimensional layered van der Waals material MnPS3 were studied using x-ray diffraction and Raman spectroscopy at high pressures up to 28 GPa, and neutron diffraction up to 3.6 GPa, respectively. A structural phase transition between two monoclinic modifications of the same C2/m symmetry was observed, evolving gradually in the pressure range of about 1–6 GPa. The transition is accompanied by abrupt shortening of lattice parameters, significant reduction of the monoclinic distortion, and anomalies in the pressure behavior of several Raman-mode frequencies. No more structural phase transitions were revealed in the studied pressure range. The antiferromagnetic (AFM) state with a propagation vector k= (0, 0, 0) remains stable in ambient pressure and high-pressure structural phases of MnPS3 at least up to 3.6 GPa. The Néel temperature increases noticeably with a pressure coefficient of dTN/dP=6.7 K/GPa, leading to modification of the dominant first-neighbor magnetic interaction exchange parameter with a relevant coefficient dJ1/dP≈−0.6 meV/GPa. This observation is in contrast to the pressure behavior of FePS3, demonstrating modification of the AFM state from 2D-like to 3D-like at the similar pressure-induced structural phase transition. The different pressure response of the magnetic states of MnPS3 and FePS3 is analyzed in terms of competing in-plane and interplane magnetic interactions

Resonant dipole-dipole interaction in the presence of dispersing and absorbing surroundings

Within the framework of quantization of the macroscopic electromagnetic field, equations of motion and an effective Hamiltonian for treating both the resonant dipole-dipole interaction between two-level atoms and the resonant atom-field interaction are derived, which can suitably be used for studying the influence of arbitrary dispersing and absorbing material surroundings on these interactions. The theory is applied to the study of the transient behavior of two atoms that initially share a single excitation, with special emphasis on the role of the two competing processes of virtual and real photon exchange in the energy transfer between the atoms. In particular, it is shown that for weak atom-field interaction there is a time window, where the energy transfer follows a rate regime of the type obtained by ordinary second-order perturbation theory. Finally, the resonant dipole-dipole interaction is shown to give rise to a doublet spectrum of the emitted light for weak atom-field interaction and a triplet spectrum for strong atom-field interaction.Comment: 15 pages, 1 figure, RevTE

Study of KS KL Coupled Decays and KL -Be Interactions with the CMD-2 Detector at VEPP-2M Collider

The integrated luminosity about 4000 inverse nanobarn of around phi meson mass ( 5 millions of phi mesons) has been collected with the CMD-2 detector at the VEPP-2M collider. A latest analysis of the KS KL coupled decays based on 30 % of available data is presented in this paper. The KS KL pairs from phi meson decays were reconstructed in the drift chamber when both kaons decayed into two charged particles. From a sample of 1423 coupled decays a selection of candidates to the CP violating KL into pi+ pi- decay was performed. CP violating decays were not identified because of the domination of events with a KL regenerating at the Be beam pipe into KS and a background from KL semileptonic decays. The regeneration cross section of 110 MeV/c KL mesons was found to be 53 +- 17 mb in agreement with theoretical expectations. The angular distribution of KS mesons after regeneration and the total cross section of KL for Be have been measured.Comment: 14 pages, 8 figure

Study of the radiative decay ϕ→ηγ\phi \to \eta \gamma with CMD-2 detector

Using the $1.9 pb^{-1}$ of data collected with the CMD-2 detector at VEPP-2M the decay mode $\phi \to \eta \gamma$, $\eta \to \pi^+\pi^-\pi^0$ has been studied. The obtained branching ratio is B($\phi \to \eta \gamma) = (1.18 \pm 0.03 \pm 0.06)$.Comment: 13 pages, 5 figures, LaTex2e, to be published in Phys. Lett.

Observation of KS0K_S^0 semileptonic decays with CMD-2 detector

The decay $K_S^0 \to \pi e \nu$ has been observed by the CMD-2 detector at the e^+e^- collider VEPP-2M at Novosibirsk. Of 6 million produced $K_L^0K_S^0$ pairs, $75 \pm 13$ events of the $K_S^0 \to \pi e \nu$ decay were selected. The corresponding branching ratio is $B(K_S^0 \to \pi e \nu)=(7.2 \pm 1.4)\times10^{-4}$. This result is consistent with the evaluation of $B(K_S^0 \to \pi e \nu)$ from the $K_L^0$ semileptonic rate and $K_S^0$ lifetime assuming $\Delta S=\Delta Q$ .Comment: 7 pages, 6 figures, LaTex2e. Submitted to Phys.Lett.

Measurement of omega meson parameters in pi^+pi^-pi^0 decay mode with CMD-2

About 11 200 e^+e^- -> omega -> pi^+pi^-pi^0 events selected in the center of mass energy range from 760 to 810 MeV were used for the measurement of the \omega meson parameters. The following results have been obtained: sigma _{0}=(1457 \pm 23 \pm 19)nb, m_{\omega}=(782.71 \pm 0.07 \pm 0.04) MeV/c^{2}, \Gamma_{\omega}=(8.68 \pm 0.23 \pm 0.10) MeV, \Gamma_{e^+e^-}\cdot Br (\omega -> pi^+pi^-pi^0)= (0.528 \pm 0.012 \pm 0.007) \cdot 10^{-3} MeV.Comment: 8 pages, 4 figure

Study of the process e+e- to pi+pi-pi+pi-pi0 with CMD-2 detector

The process e+e- to pi+ pi- pi+ pi- pi0 has been studied in the center of mass energy range 1280 -- 1380 MeV using 3.0 1/pb of data collected with the CMD-2 detector in Novosibirsk. Analysis shows that the cross section of the five pion production is dominated by the contributions of the eta pi+pi- and omega pi+pi- intermediate states.Comment: 8 pages, 3 figure. Submitted to Phys. Lett.

Observation of the conversion decay ϕ→π0e+e−\phi\to\pi^0e^+e^- at CMD-2

Using 15.1^{-1} of data collected by CMD-2 in the $\phi$-meson energy range, the branching ratio of the conversion decay $\phi\to\pi^0e^+e^-$ has been measured for the first time: B(\phi\to\pi^0e^+e^-) = (1.22 \pm 0.34 \pm 0.21) \cdot 10 ^{-5}.Comment: 13 pages, 6 PostScript figures, uses refmerge.sty. To be published in Phys. Lett.

Cross section of the reaction e+e−→π+π−π+π−e^+ e^- \to \pi^+\pi^-\pi^+\pi^- below 1 GeV at CMD-2

Using 3.07 ${pb}^{-1}$ of data collected in the energy range 0.60-0.97 GeV by CMD-2, about 150 events of the process \epm \to \pch have been selected. The energy dependence of the cross section agrees with the assumption of the $a_1(1260) \pi$ intermediate state which is dominant above 1 GeV. For the first time \fourpi events are observed at the $\rho$ meson energy. Under the assumption that all these events come from the $\rho$ meson decay, the value of the cross section at the $\rho$ meson peak corresponds to the following decay width: \Gamma(\rho^0 \to \fourpi) = (2.8 \pm 1.4 \pm 0.5) {keV} or to the branching ratio B(\rho^0 \to \fourpi) = (1.8 \pm 0.9 \pm 0.3) \cdot 10 ^{-5}.Comment: 15 pages, 5 figure