DOE Pulse
  • Number 453  |
  • November 30, 2015

Unstoppable, one-dimensional electron waves

XCBikeRacer by Daniel Plunkett. Licensed under CC BY-SA 3.0 via Commons -

XCBikeRacer by Daniel Plunkett. Licensed
under CC BY-SA 3.0 via Commons -

In certain nanomaterials, electrons are able to race through custom-built roadways just one atom wide. To achieve excellent efficiency, these one-dimensional paths must be paved with absolute perfection—a single errant atom can stop racing electrons in their tracks or even launch it backwards. Unfortunately, such imperfections are inevitable.

Now, a pair of scientists from Brookhaven Lab and Ludwig Maximilian University in Munich has proposed the first solution to such subatomic stoppage: a novel way to create a more robust electron wave by binding together the electron's direction of movement and its spin. The trick, as described in a paper published November 16 in Physical Review Letters and featured as an Editor's Selection, is to exploit magnetic ions lacing the electron racetrack. The theory could drive advances in nanoscale engineering for data- and energy-storage technologies. 

"One-dimensional materials can only be very good conductors if they are defect-free, but nothing in this world is perfect," said Brookhaven physicist Alexei Tsvelik, one of two authors on the paper. "Our theory, the first of its kind, lays out a way to protect electron waves and optimize these materials."

The work relies on a model system called a Kondo chain, where flowing electrons interact with local magnetic moments within a material. Properly harnessed, this powerful interaction could allow materials to behave like perfect conductors and offer high efficiency.

"As the electrons flow, they interact with magnetic moments embedded in the material—these pockets of intrinsic magnetism are the key to producing the bound state," said Ludwig Maximilian University physicist Oleg Yevtushenko, the other collaborator on the paper. "The magnetic moments bind spin and direction tightly together, so any disturbance would need to flip the electron's spin in order to change its direction," making it much more difficult to stop the wave.

To understand why, imagine walking along a narrow path barely wide enough for both feet. In such a simple system, turning around is easy—one can pivot around at the slightest provocation. "But what if we give our pedestrian a bicycle?" Tsvelik said. "It suddenly becomes very difficult to break that angular momentum and change directions—especially on such a narrow path. This bound spin-direction state is like our electron's bicycle, keeping it rolling along powerfully enough to overcome bumps in the one-dimensional road. – by Justin Eure

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[Karen McNulty Walsh, 631.344.8350,]