# Synopsis: The space between

${\text{LaAlO}}_{3}/{\text{SrTiO}}_{3}$ 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.

Recent experiments have shown that a metal-insulator transition occurs at the interface between a ${\text{LaAlO}}_{3}$ layer and a ${\text{SrTiO}}_{3}$ substrate. As the ${\text{LaAlO}}_{3}$ 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 ${\text{LaAlO}}_{3}/{\text{SrTiO}}_{3}$ 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

### Announcements

More Announcements »

Optics

## Next Synopsis

Atomic and Molecular Physics

## Related Articles

Materials Science

### Viewpoint: Relaxons Heat Up Thermal Transport

A recasting of the theory that underlies thermal transport in electrical insulators relies on new vibrational modes called relaxons. Read More »

Photonics

### Synopsis: Decoding the Light from Ten Million Quantum Dots

A spectroscopy method can identify quantum dots within an ensemble based on their size and emission frequency. Read More »

Materials Science

### Viewpoint: Improving Electronic Structure Calculations

A new approach to calculating the properties of molecules and solids may offer higher accuracy at reasonable computational cost, accelerating the discovery of useful materials. Read More »