Magnonic superradiant phase transition

In the superradiant phase transition (SRPT), coherent light and matter fields are expected to appear spontaneously in a coupled light–matter system in thermal equilibrium. However, such an equilibrium SRPT is forbidden in the case of charge-based light–matter coupling, known as no-go theorems. Here, we show that the low-temperature phase transition of ErFeO3 at a critical temperature of approximately 4 K is an equilibrium SRPT achieved through coupling between Fe3+ magnons and Er3+ spins. By verifying the efficacy of our spin model using realistic parameters evaluated via terahertz magnetospectroscopy and magnetization experiments, we demonstrate that the cooperative, ultrastrong magnon–spin coupling causes the phase transition. In contrast to prior studies on laser-driven non-equilibrium SRPTs in atomic systems, the magnonic SRPT in ErFeO3 occurs in thermal equilibrium in accordance with the originally envisioned SRPT, thereby yielding a unique ground state of a hybrid system in the ultrastrong coupling regime.

Low-temperature phase transition and magnetic properties of K3YbSi2O7

The new ambient-temperature hexagonal (space group P63 /mmc) polymorph of tripotassium ytterbium(III) disilicate (β-K3YbSi2O7) has been synthesized by the high-temperature flux method and subsequently structurally characterized. In the course of the temperature-dependent single-crystal diffraction experiments, a phase transformation of β-K3YbSi2O7 to a novel low-temperature orthorhombic phase (β′-K3YbSi2O7, space group Cmcm) has been observed at about 210 K. β-K3YbSi2O7 is isostructural with K3ErSi2O7, whereas β′-K3YbSi2O7 adopts a new type of structure. Both compounds can be built up from a regular alternation of layers of two types, which are parallel to the (001) plane. In the octahedral layer, YbO6 octahedra are isolated and linked by K1O6+3 polyhedra. The second, slightly thicker sorosilicate layer is formed by a combination of Si2O7 dimers and K2O6+3 polyhedra. The boundary between the layers is a pseudo-kagome oxide sheet based on 3.6.3.6 meshes. The phase transition is due to a tilt of the two SiO4 tetrahedra forming a single dimer which induces a decrease of the Si—O—Si angle between bridging Si—O bonds from 180° (dictated by symmetry in space group P63/mmc) to ≃164°. Magnetic characterization indicates that K3YbSi2O7 remains paramagnetic down to 2 K, showing no apparent influence of the phase transformation on its magnetic properties. Analysis of the magnetization data revealed the positions of the three lowest crystal field levels of the Yb3+ cations, as well as the corresponding projections of their angular momentum on the direction of the magnetic field.

Ferroelectric Property, Narrow Band Gap and Ultra-Large Reversible Entropy Change in a Novel Nonlinear Ionic Chromium (VI) Compound

A novel chromium (VI)-based compound: [(CH3CH2)3N(CH2Cl)] [CrO3Cl] (1), has undergone a high-temperature phase transition around 340.9 K, accompanied by ultra-large entropy change of 63.49 J·mol-1·K-1. 1 exhibits a moderate ferroelectric...

NONLINEAR MODEL OF THE THREE-COMPONENTS COMPETITIVE ADSORPTION USING LANGMUIR EQUILIBRIUM

A basis for the mathematical modeling of non-isothermal gas competitive adsorption in a porous solid using Langmuir equilibrium is given. High-performance analytical solutions of considered adsorption models based on the Heaviside operating method and Landau’s decom- position and linearization approach of Langmuir equilibrium by expanding into a convergent series in the temperature phase transition point are proposed. Numerical experiments results based on high-speed computations on multicore computers are presented.

A high-Tc organic-ionic phase transition crystal obtained from a trivalent cation

The organic-ionic crystal of [1,4,7-triazacyclononammonium] Cl3, containing a trivalent cation, shows a high-temperature phase transition coupled with dielectric switching.