b'Matter at Extreme StatesContinued38 Distorted Structure Could Advance Electronics. . . thenewly created Viktor Struzkhin, Jianjun Ying, and team foundstructurecould provide novel unusual structural changes in the semiconductor tin diselenide, SnSe 2 , when it was subjected toresearch opportunities for these pressure. Electrical conductivity can be turned onpromising materials.and off in semiconductors, a powerful property for electronics. Tin diselenide is a very thin, one-atom layered semiconductor, with a regular, repeating crystalline arrangement of atoms. It is called aAt pressures above 170,000 atmospheres they transition metal dichalcogenide (TMD) and canfound periodic distortions to the lattice structure be used to create smaller, cheaper transistors,that were related to the so-called charge density solar cells, LEDs, photodetectors, and more. Thewave. This wave is an ordered quantum fluid of researchers observations contrast with findings inelectrons that forms a wave pattern and can carry other metallic TMDs, so the newly created structurean electric current similar to the superconducting may provide novel research opportunities for thesestate wherein there is no resistance to electron flow. promising materials.But unlike a superconductor, the electric charge density wave current can be interrupted or distorted The team subjected tin diselenide to pressuresmaking a superlattice of atoms, which can be useful exceeding 170,000 times atmospheric pressurefor many applications.(17 gigapascals). They performed X-ray diffraction to see structural changes, Raman spectroscopyThe theoretical work suggests the charge density to observe vibrational changes, and electronicwaves occur from a special arrangement of transport measurements. They combined theirelectronic states called Fermi nesting conditions. observations with theoretical calculations on theThese conditions occur in the momentum space of materials behavior. electrons, a different kind of space than we are used P (r) P (r)At left, the electron density (below the red line) is uniform. At right, when the researchers applied pressure, the regular, repeating arrangement was changed, forming a charge density wave with gaps between atoms in the distorted arrangement. Image courtesy Viktor Struzhkin'