Scanning tunneling microscopy reveals the exotic properties of an unusual type of electron

November 14, 2014, RIKEN
Figure 1: Using scanning tunneling miscopy and spectroscopy, the distribution of massless Dirac electrons in different Landau levels can be imaged on the surface of bismuth selenide. Credit: Tetsuo Hanaguri, RIKEN Center for Emergent Matter Science

The unusual properties of electrons responsible for the exotic conduction states on the surface of a class of materials known as topological insulators have been imaged by RIKEN researchers. The imaging technique promises a more complete understanding of such systems and could aid the development of novel spintronic devices.

In some unusual material systems, such as graphene and , can sometimes behave as if they have no mass. These massless Dirac electrons, as they are known, differ from standard electrons in that they are mathematically described by a wavefunction with two components, rather than the usual single component.

This difference in wavefunction causes the particles to behave slightly differently under a magnetic field. Both standard and Dirac electrons move in a circular motion under a magnetic field, following any one of a discrete set of orbits. Each orbit has a characteristic energy, known as a Landau-level energy, that depends on the strength of the . The precise orbits, however, differ between Dirac and standard electrons.

To observe these Landau orbits, Tetsuo Hanaguri and colleagues from the RIKEN Center for Emergent Matter Science and the Tokyo Institute of Technology imaged the surface of a bismuth selenide crystal using a scanning tunneling microscope. "Using scanning tunneling microscopy and spectroscopy, it is possible to image wavefunctions by measuring electron distributions," says Hanaguri.

Scanning tunneling microscopy involves bringing an atomically sharp metal tip to within nanometers of the film's surface and applying a voltage. The measured current provides detailed information about the electrons in the vicinity of the tip. "In this way, we succeeded in imaging the distribution of massless Dirac electrons in various Landau levels," explains Hanaguri (Fig. 1). "The electron distribution of a Dirac electron could only be reproduced by superimposing the distributions for two neighboring levels, which proved that the massless Dirac electron consists of two components."

Bismuth selenide is the most prominent example of a topological insulator—an exotic class of materials that are electrically insulating internally but have highly conductive two-dimensional surfaces due to the formation of Dirac electrons. In such materials, the two components of the wavefunction of Dirac electrons are associated with spin. Beyond research, the imaging tool developed by Hanaguri's team could also be used to manipulate spins in these materials. "We plan to search for new methods to control Dirac electrons, such as by introducing magnetic impurities to actively modify the magnetic environment," says Hanaguri.

Explore further: Researchers demonstrate and explain surface conduction in a topological insulator

More information: Fu, Y.-S., Kawamura, M., Igarashi, K., Takagi, H., Hanaguri, T. & Sasagawa, T. "Imaging the two-component nature of Dirac–Landau levels in the topological surface state of Bi2Se3." Nature Physics advance online publication, 14 September 2014 DOI: 10.1038/nphys3084

Related Stories

Research brings new control over topological insulator

March 20, 2014

An international team of scientists investigating the electronic properties of ultra-thin films of new materials – topological insulators (TIs) - has demonstrated a new method to tune their unique properties using strain.

Novel topological crystalline insulator shows mass appeal

August 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 ...

The secrets of tunneling through energy barriers

November 7, 2011

Electrons moving in graphene behave in an unusual way, as demonstrated by 2010 Nobel Prize laureates for physics Andre Geim and Konstantin Novoselov, who performed transport experiments on this one-carbon-atom-thick material. ...

Recommended for you

Researchers capture an image of negative capacitance in action

January 21, 2019

For the first time ever, an international team of researchers imaged the microscopic state of negative capacitance. This novel result provides researchers with fundamental, atomistic insight into the physics of negative capacitance, ...

Toward ultrafast spintronics

January 21, 2019

Electronics have advanced through continuous improvements in microprocessor technology since the 1960s. However, this process of refinement is projected to stall in the near future due to constraints imposed by the laws of ...

New thermoelectric material delivers record performance

January 17, 2019

Taking advantage of recent advances in using theoretical calculations to predict the properties of new materials, researchers reported Thursday the discovery of a new class of half-Heusler thermoelectric compounds, including ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

movementiseternal
Nov 15, 2014
This comment has been removed by a moderator.

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.