Tiny computer hard drives closer to reality

A new technique to study the interface between materials may pave way for miniature computer hard drives, better solar cells and novel superconductors, scientists say.
A team of scientists, led by Assistant Professor Andrivo Rusydi from the National University of Singapore, has successfully developed a technique to study the interface between materials.
With a better understanding of how materials interface, scientists can tweak the properties of different materials more easily, and this opens doors to the development of better solar cells, novel superconductors and smaller hard drives.
Some of the most exciting condensed matter physics problems are found at the interfaces of dissimilar materials.

"If you put two materials together, you can create completely new properties. For instance, two non-conducting, non-magnetic insulators can become conducting and in some cases ferromagnetic and superconducting at their interface," said Rusydi.
"The problem is that we do not fully understand what is happening at the interface yet," said Rusydi.

To resolve this long-standing mystery in the physics of condensed matter, the scientists investigated the interface between strontium titanate and lanthanum aluminate, two insulators that become conductors at their interface. In doing this, the team uncovered another mystery.
"For this interface, a theory predicts that the conductivity should be tenfold higher than what is observed. So, 90 per cent of the charge carriers - the electrons - are missing," said Rusydi.

To search for the missing electrons, the scientists employed high-energy reflectivity coupled with spectroscopic ellipsometry.
They utilised the bright synchrotron radiation source at the Singapore Synchrotron Light Source at NUS and Deutsches Elektronen-Synchrotron and floodlighted the interface of the two materials with a wide energy range.
The absorption of synchrotron radiation at specific wavelengths revealed the energy state of the corresponding electrons and unveiled their hiding place in the crystal lattice, researchers said.
It was found that only about 10 per cent of the expected electrons are free to migrate to the interface of the two materials to form a conduction band.

The remaining 90 per cent are bound in the molecular lattice at higher energy states that were not visible to light sources used in earlier searches.
"This came as a surprise. But it also explains why more than just one layer is necessary to fully unfold the interface properties," said Rusydi.
The finding was published in the journal Nature Communication.