Synopsis: The space between

LaAlO3/SrTiO3 interfaces grown by different methods all show a metal-insulator transition, but the observed interfacial electric field strength is not consistent with a widely studied model.
Synopsis figure
Illustration: Y. Segal et al., Phys. Rev. B (2009)

Recent experiments have shown that a metal-insulator transition occurs at the interface between a LaAlO3 layer and a SrTiO3 substrate. As the LaAlO3 thickness approaches four unit cells, a sharp jump in conductivity is observed when an additional single unit cell is added, but for thinner layers the interface is insulating. This behavior is believed to be the consequence of an electron gas appearing suddenly at the interface, but its origin is controversial. Mechanisms intrinsic to the structure, as well as extrinsic effects related to defects and oxygen vacancies, have been proposed.

In a Rapid Communication appearing in Physical Review B, Yaron Segal and colleagues at Yale University, US, report their investigation of LaAlO3/SrTiO3 structures grown by molecular beam epitaxy, which avoids the problem of defects produced by the laser deposition methods used in previous studies. With x-ray photoemission spectroscopy, the Yale group has been able to measure the strength of the electric field at the interface by looking for offsets in the electronic band structure.

Segal et al. find that the metal-insulator transition is present regardless of the growth method, suggesting that deposition-induced defects are not playing a role in the increase in conductivity. Moreover, the photoemission data reveal smaller electric fields than expected, casting doubt on the applicability of models that rely on intense charge discontinuities at the interface and indicating that the theoretical understanding of these unusual materials will need further refinement. – David Voss


More Announcements »

Subject Areas

MesoscopicsNanophysicsMaterials Science

Previous Synopsis

Next Synopsis

Atomic and Molecular Physics

Opening the gate to quantum computation

Read More »

Related Articles

Synopsis: Measuring Spin One Atom at a Time

Synopsis: Measuring Spin One Atom at a Time

Electron microscopy experiments have measured the spin state of individual metal atoms on a graphene layer, characterizing their potential for information storage applications.   Read More »

Synopsis: Through a Glass Densely

Synopsis: Through a Glass Densely

A new model for light scattering explains why an unexpected amount of light propagates through materials containing densely packed scattering objects.   Read More »

Synopsis: Light Sees Electronic Bands

Synopsis: Light Sees Electronic Bands

An all-optical alternative to photoemission spectroscopy can probe the electronic band structure of a solid. Read More »

More Articles