Quantum spin dynamics

Abstract:

Magnetoactive elastomers may display magnetic hysteresis, even if they are filled only with magnetically soft particles. In this work we discuss application of the first-order reversal curve (FORC) analysis to identify and study hysteresis of that kind. To obtain theoretical magnetization curves and FORC diagrams for the composites in question, a simple model comprising two magnetically soft particles embedded in an elastic environment is proposed. Elucidation of the features present in FORC diagrams is conducted using computer simulation. Despite the simplicity of the model, it allows one to explain the origin of diagonal ridge patterns, which turn up in the FORC diagrams of elastomer composites with magnetically soft filler, and to quantify the experimental results. As the ridge pattern of the diagrams is inherently exclusive to such types of materials, it could be useful for their diagnostics.

Abstract:

The properties of organic conductors are often tuned by the application of chemical or external pressure, which change orbital overlaps and electronic bandwidths while leaving the molecular building blocks virtually unperturbed. Here, we show that, unlike any other method, light can be used to manipulate the local electronic properties at the molecular sites, giving rise to new emergent properties. Targeted molecular excitations in the charge-transfer salt κ−(BEDT−TTF)2 Cu[N(CN)2] Br induce a colossal increase in carrier mobility and the opening of a superconducting optical gap. Both features track the density of quasiparticles of the equilibrium metal and can be observed up to a characteristic coherence temperature T∗≃50K, far higher than the equilibrium transition temperature TC=12.5K. Notably, the large optical gap achieved by photoexcitation is not observed in the equilibrium superconductor, pointing to a light-induced state that is different from that obtained by cooling. First-principles calculations and model Hamiltonian dynamics predict a transient state with long-range pairing correlations, providing a possible physical scenario for photomolecular superconductivity.