System Bits: Nov. 18

Phase transitions between liquid, gas
Researchers from the University of Tokyo and Tokyo Institute of Technology reminded that materials change their form between three states — solid, liquid, and gas — depending on factors such as temperature and pressure. However, a phase transition does not necessarily occur between liquid and gas, and they can continuously transform from the one to the other.

With regard to spins — microscopic magnets associated with electrons in magnetic solids — there are three similar states. The solid corresponds to, for instance, a ferromagnetic state in which all the spins point the same direction, while the gas corresponds to a paramagnetic state in which the spin directions are random. On the other hand, for the spin liquid, although the concept of the “quantum spin liquid” has been proposed in analogy with liquid helium that does not solidify even down to the lowest temperatures, its existence and nature have remained as an enigma for a long time, they said.

Recently the team discovered that there is always a phase transition between quantum spin liquids and a paramagnetic state: they cannot continuously transform into each other, contrary to the common belief. This was shown by large-scale numerical simulations for a theoretical spin model called the Kitaev model. The transition they discovered is of new type, not explained by the conventional theory for phase transitions. The researchers also clarified that the novel transition is regarded as a change of the topological nature of the system.

As such, they urge a reconsideration of recent experimental studies that suggest the existence of quantum spin liquids by the absence of phase transitions.

Schematic of the novel gas-liquid transition in quantum magnets. (Source: University of Tokyo)

This is expected to have an impact on the field of quantum information, in which topological nature is used for data processing.

Synthesizing inexpensive liquid crystal compound
Liquid crystal compounds possessing tetrafluoroethylene-bridging structures are sought after as materials for next-generation liquid displays made from tetrafluoroethylene, fluorine-based resin and key industrial materials.

To this end, a group of researchers affiliated with Osaka University-Daikin Industries (Fluorine Chemistry) Joint Research Course have developed a new reaction for developing a liquid crystal compound possessing a tetrafluoroethylene-bridging structure in a short-step process.

Industrially, tetrafluoroethylenes is a very inexpensive chemical compound with many applications. One product employing tetrafluoroethylene is known by the trade name Teflon, but the applications of tetrafluoroethylene have been limited to the production of a fluorine-based resin and have never been used as a manufacturing material in a broad range of chemical products such as medicines or agricultural chemicals, the researchers explained.

But, a liquid crystal compound bearing a tetrafluoroethylene-bridging structure has been sought after as a material for next-generation liquid crystal displays. If a method of synthesizing such a liquid crystal compound in large quantities at a low price can be developed, it will give momentum to the practical use and diffusion of high-performance optical devices. However, typical synthesis methods of chemical compounds lack versatility and cost a lot or use highly toxic fluorinating agents for the synthesis, so environmentally friendly and inexpensive synthesis methods have been sought.

The discovery is expected to further promote the development of new fluoline-containing functional materials at a low cost and the practical use and dissemination of high-performance optical devices.

Mixing light at the nanoscale
While currently requiring too much space and power when done with light, researchers at the University of Pennsylvania have engineered a nanowire system that could pave the way for photonics systems that combines two light waves to produce a third with a different frequency and using an optical cavity to amplify the intensity of the output to a usable level.

Light emitted from the underside of the cavity. The dotted outline represents the orientation of the cadmium sulfide nanowire. (Source: University of Pennsylvania)