Scientists discover exotic quantum state of matter

Washington, April 25 : A team of scientists have discovered an exotic quantum state of matter, which could lead to advances in new kinds of fast quantum or "spintronic" computing devices, of potential use in future electronic technologies.

The scientists, who are from Princeton University, US, have found that one of the most intriguing phenomena in condensed-matter physics - known as the Quantum Hall effect - can occur in nature in a way that no one has ever seen before.

The quantum Hall effect has only been seen previously in atomically thin layers of semiconductors in the presence of a very high applied magnetic field.

Electrons, which are electrically charged particles, behave in a magnetic field like a cloud of mosquitoes in a crosswind.

In a material that conducts electricity, like copper, the magnetic "wind" pushes the electrons to the edges. An electrical voltage rises in the direction of this wind - at right angles to the direction of the current flow.

Edwin Hall discovered this unexpected phenomenon, which came to be known as the Hall effect, in 1879. The Hall effect has become a standard tool for assessing charge in electrical materials in physics labs worldwide.

Now, the team from Princeton has recorded this exotic behavior of electrons in a bulk crystal of bismuth-antimony without any external magnetic field being present.

"We had the right tool and the right set of ideas," said Zahid Hasan, an assistant professor of physics who led the research and propelled X-ray photons at the surface of the crystal to find the effect.

For this, Hasan's team decided to go beyond the conventional tools for measuring quantum Hall effects. They used a high-energy, accelerator-based technique called synchrotron photo-electron spectroscopy.

They took the bulk three-dimensional crystal of bismuth-antimony, zapped it with ultra-fast X-ray photons and watched as the electrons jumped out. By fine-tuning the X-rays, they could directly take pictures of the dancing patterns of the electrons on the edges of the sample.

The nature of the quantum Hall behavior in the bulk of the material was then identified by analyzing the unique dancing patterns observed on the surface of the material in their experiments.

The images observed by the Princeton group provide the first direct evidence for quantum Hall-like behavior without external magnetic fields.

"What is exciting about this new method of looking at the quantum Hall-like behavior is that one can directly image the electrons on the edges of the sample, which was never done before," said Hasan.

"This very direct look opens up a wide range of future possibilities for fundamental research opportunities into the quantum Hall behavior of matter," he added.

ANI