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Researchers Create Zigzag Wigner Crystal

Researchers at National Cheng Kung University developed Wigner crystal using a nanowire with controllable width

A Wigner crystal is the solid phase of electrons that was first predicted by Eugene Wigner in 1934. As the potential energy dominates the kinetic energy at low densities, a gas of electrons moving in 2D or 3D in a uniform, inert, neutralizing background will crystallize. This leads to formation of a lattice when the electron density is less than a critical value. The electrons form a body-centered cubic lattice in 3D, a triangular lattice in 2D, and an evenly spaced lattice in 1D, which minimizes the potential energy. Such spatially ordered arrangement of electrons is evident in certain 2D systems and can be possible in 1D systems.

Now, researchers from National Cheng Kung University and University College London observed a zigzag Wigner crystal, which is an intermediate case between a 1D and a 2D crystal. The researchers used a nanowire with tunable width to generate such chain of electrons. The measurements revealed polarization in the electron spin, which in turn suggests application of zigzag Wigner crystals in spintronics. Although prior research with nanowires revealed hints of 1D Wigner crystals, the data were inconclusive due to similar signatures gained from other noncrystalline states. Several theories predicted that weakening the confinement of electrons trapped in a 1D potential could create such a crystal. The electrons therefore, could expand in a second dimension and form a zigzag Wigner phase with unique spin properties.

In the current experiment, researchers used a nanowire whose effective width can be controlled electronically. A magnetic device focused electrons at the end of the nanowire that were emitted from the nanowire onto a detector. Researchers expanded the effective width of the nanowire by weakening the 1D confinement. The single peak observed at the detector turned into two peaks that signifies formation of zigzag Wigner crystal. The team measured the spins of the electrons to confirm these interpretation and revealed that the electrons were polarized exactly as theoretical models predicted for such a Wigner crystal. The research was published in Physical Review Letters on September 06, 2018.