New compound shows unusual conducting properties

Nov 26, 2013
Fig. 1: Crystal structure and successfully grown single crystals of BiTeCl.

A new compound developed at Tokyo Tech shows highly unusual conducting properties that could be used in future electronic components.

Ordinary insulating solids, such as diamond, have energy bands that are fully occupied by electrons. The conducting band is so far away from the valence band in diamond that electrons do not have sufficient energy to move - the 'band gap' is large - therefore no electric current can be carried.

In recent years, researchers have become interested in materials called (TIs), which act as insulators on the inside, but are highly conductive on their surfaces. In TIs, an exceptionally strong spin-orbit interaction inverts the energy gap between occupied and empty states, so that electrons at the surface can flow across the gap. These properties are intrinsic to the material, meaning a TI remains conductive even if its surface is not perfect.

Now, an international team of scientists from Japan, the UK and the USA, led by Takao Sasagawa at Tokyo Institute of Technology, have successfully developed a new TI from bismuth, tellurium and chlorine (BiTeCl). Their new TI is inversion asymmetric, meaning it has different electronic states, and therefore different polarities, on each crystal surface. As a result, it exhibits many topological effects that have not been seen experimentally before.

"The metallic surface state of a TI is similar to graphene in that the electron mobility is remarkably high due to zero-mass electrons, or Dirac fermions," explains Sasagawa. " The Dirac fermions have a characteristic spin and in this context they can host a wide range of exotic quantum phenomena. Symmetry-breaking is the best way of inducing these fascinating topological effects."

Fig. 2: Electronic structures of BiTeCl's top and bottom crystal surfaces observed by photoemission spectroscopy.

Sasagawa and his team optimised their laboratory growing conditions to produce single crystals of BiTeCl. They then split each single crystal to obtain two different surfaces - one Te and one Cl - and observed their electronic structures using spectroscopy. The composition of the TI's top and bottom crystal surfaces are such that their charge carriers are opposite, leading to polarization. The TI can therefore be used as a diode, allowing current flow in only one direction. It also exhibits pyroelectric capabilities, meaning that it can generate a temporary voltage when heated or cooled.

BiTeCl shows promise as a platform for other topological phenomena, and may have applications at high temperatures. The discovery could also have significant implications for the development of quantum-based technologies in future, as Sasagawa explains: " We would like to discover a topological superconductor whose surface can host Majorana fermions - particles which are their own antiparticles, and could be used for the development of topological quantum computing."

Explore further: Pseudoparticles travel through photoactive material

More information: Y.L.Chen, M. Kanou, Z.-X. Shen, T. Sasagawa et al. Discovery of a single topological Dirac fermion in the strong inversion asymmetric compound BiTeCl. Nature Physics Published online: 6 October 2013 DOI: 10.1038/NPHYS2768

Related Stories

Blocking infinity in a topological insulator

Feb 08, 2013

(Phys.org)—In bulk, topological insulators (TIs) are good insulators, but on their surface they act as metals, with a twist: the spin and direction of electrons moving across the surface of a TI are locked ...

Researchers forward quest for quantum computing

May 23, 2013

Research teams from UW-Milwaukee and the University of York investigating the properties of ultra-thin films of new materials are helping bring quantum computing one step closer to reality.

Novel topological crystalline insulator shows mass appeal

Aug 29, 2013

Disrupting the symmetrical structure of a solid-state topological crystalline insulator creates mass in previously mass-less electrons and imparts an unexpected level of control in this nascent class of materials, an international ...

Recommended for you

Pseudoparticles travel through photoactive material

Apr 23, 2015

Researchers of Karlsruhe Institute of Technology (KIT) have unveiled an important step in the conversion of light into storable energy: Together with scientists of the Fritz Haber Institute in Berlin and ...

From metal to insulator and back again

Apr 22, 2015

New work from Carnegie's Russell Hemley and Ivan Naumov hones in on the physics underlying the recently discovered fact that some metals stop being metallic under pressure. Their work is published in Physical Re ...

Electron spin brings order to high entropy alloys

Apr 22, 2015

Researchers from North Carolina State University have discovered that electron spin brings a previously unknown degree of order to the high entropy alloy nickel iron chromium cobalt (NiFeCrCo) - and may play ...

Expanding the reach of metallic glass

Apr 22, 2015

Metallic glass, a class of materials that offers both pliability and strength, is poised for a friendly takeover of the chemical landscape.

Electrons move like light in three-dimensional solid

Apr 22, 2015

Electrons were observed to travel in a solid at an unusually high velocity, which remained the same independent of the electron energy. This anomalous light-like behavior is found in special two-dimensional ...

Quantum model helps solve mysteries of water

Apr 20, 2015

Water is one of the most common and extensively studied substances on earth. It is vital for all known forms of life but its unique behaviour has yet to be explained in terms of the properties of individual ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.