On the Existence of Pure,Broadband Toroidal Sources in Electrodynamics

Multipoles are paramount for describing electromagnetic fields in many areas of nanoscale optics, playing an essential role in the design of devices in plasmonics and all-dielectric nanophotonics. Challenging the traditional division into electric and magnetic moments, toroidal moments are proposed as a physically distinct family of multipoles with significant contributions to the properties of matter. However, the apparent impossibility of separately measuring their response sheds doubt on their true physical significance. Here, the possibility of selectively exciting toroidal moments is confirmed without any other multipole. A set of general conditions is developed that any current distribution must fulfill to be entirely described by toroidal moments and prove the results in an analytically solvable case. The new theory allows to design and verify experimentally an artificial structure supporting a pure broadband toroidal dipole response in the complete absence of the electric dipole and other “ordinary” multipole contributions. In addition, a structure capable of supporting a novel type of non-radiating source is proposed- a “toroidal anapole,” originating from the destructive interference of the toroidal dipole with the unconventional electromagnetic sources known as mean square radii. The results in this work provide conclusive evidence on the independent excitation of toroidal moments in electrodynamics.     

Synthesis and Properties of Nitrozoruthenium Thiocarbamide Complex

The [RuNO(Thio)₄Cl]Cl₂ compound (where Thio is thiocarbamide) was synthesized by reacting nitrozochloro complexes of Ru with thiocarbamide. Its structure and properties in solutions were studied by IR, EAS, EPR, pH-metric, and electrical conductivity methods. The complex was found to have octahedral structure, with the chlorine atom in the trans-position relative to the nitrozo group, and four Thio groups coordinated through the sulfur atom and lying in the equatorial plane. This compound is labile in solutions. The mechanism and rate constants of the first hydrolysis stage were determined at 25, 50, and 75°C, and the enthalpy of the reaction was estimated. With a Thio excess, the nitrozo group is replaced to form the Ru(III) and Ru(II) thiocarbamide complexes.