English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

We present a microscopic picture rationalizing the surprisingly steepdecrease of the band gap with temperature in insulators, crystalline orotherwise. The gap narrowing largely results from fluctuations oflong-wavelength optical phonons---when the latter are present---or theirdisordered analogs, if the material is amorphous. We elaborate on this notionto show that possibly with the exception of weakly bound solids made ofclosed-shell atoms, the existence of an insulating gap or pseudo-gap in aperiodic solid implies that optical phonons must be present, too. This meansthat in an insulating solid, the primitive cell must have at least two atomsand/or that a charge density wave is present. As a corollary, a (periodic)elemental solid whose primitive unit contains only one atom will ordinarily bea metal, possibly unless the element belongs to group 18 of the periodic table,consistent with observation. Some implications of the present results forquantum solids are briefly discussed, such as that the ground state of theWigner crystal must be anti-ferromagnetic. A simple field theory of themetal-insulator transition is constructed that ties long-wavelength opticalvibrations with fluctuations of an order parameter for the metal-insulatortransition; symmetry-breaking aspects of the latter transition are therebyhighlighted.

journal of chemical physics online/the journal of chemical physics/journal of chemical physics

Temperature-driven narrowing of the insulating gap as a precursor of the  insulator-to-metal transition: Implications for the electronic structure of  solids