# Synopsis: Thrown out of the nest

Calculations reveal the effect of dimensionality in a prototypical charge-density-wave material.

Electrons in a material can collectively organize into ordered states at low temperatures. One such state is a charge-density wave (CDW), which is a periodic spatial modulation of the electronic charge. It is commonly believed that the phenomenon is tied to Fermi-surface nesting, that is, if it is possible to match segments of the Fermi surface upon translation by a fixed vector $\mathbf{\text{q}}$, then the charge-density wave that is created has a spatial periodicity $2\pi /|\mathbf{\text{q}}|$. But because this picture fails even for minor deviations from perfect nesting, it is questionable if this is the mechanism for CDWs forming in some materials.

In a Rapid Communication appearing in Physical Review B, Matteo Calandra and Francesco Mauri from the Institut de Minéralogie et de Physique des Milieux Condensés in France and Igor Mazin of the Naval Research Laboratory in the US perform density-functional-theory calculations on a prototypical CDW material: layered ${\text{NbSe}}_{2}$. Calandra et al. contrast calculations for a bilayer and a monolayer of ${\text{NbSe}}_{2}$ to find a different periodicity for the CDW in each case, which rules out Fermi-surface nesting as the cause. In this textbook example of CDW-forming material, one would have expected better nesting for the purely two-dimensional Fermi surface of the monolayer, and consequently the same ordering vector. Instead, they predict that an enhanced electron-phonon interaction drives the formation of the CDW.

Calandra et al. also find that the different CDW in the monolayer compared to the one in the bulk leads to a dramatic variation in conductivity, similar to what is seen in experiments. – Alex Klironomos

More Features »

### Announcements

More Announcements »

Cosmology

Nuclear Physics

## Related Articles

Materials Science

### Synopsis: A Crystal Ball for 2D Materials

Researchers predict new two-dimensional materials whose structures differ from their three-dimensional counterparts. Read More »

Atomic and Molecular Physics

### Viewpoint: Electron Pulses Made Faster Than Atomic Motions

Electron pulses have shattered the 10-femtosecond barrier at which essentially all atomic motion is frozen in materials. Read More »

Strongly Correlated Materials

### Viewpoint: Sensing Magnetic Fields with a Giant Quantum Wave

A refined version of a Bose-Einstein-condensate microscope detects static magnetic fields near the surface of a chip with unprecedented sensitivity and over a wide temperature range. Read More »