Using light to put a twist on electrons

Some molecules, including the majority of those found in living things, can have two distinct mirror-image shapes.Sometimes, the properties of the right-handed and left-handed versions differ, and only one of them can carry out the molecule’s functions.

Using a particular kind of light beam to stimulate the material, a group of physicists have now discovered that a pattern that is similarly asymmetrical can be induced and measured at will in exotic materials.In this instance, the phenomenon of “handedness,” also known as chirality, is caused by a patterning in the density of electrons within the material rather than by the structure of the molecules themselves.

Shining a circularly polarized mid-infrared light at an unusual material, a form of transition-metal dichalcogenide semimetal known as TiSe2, or titanium diselenide, produced this asymmetric patterning, the researchers discovered.