Researchers snap first image of an 'electron ice'

More than 90 years ago, physicist Eugene Wigner predicted that astatine debased densities and acold temperatures, electrons that usually zip done materials would frost into place, forming an electron ice, oregon what has been dubbed a Wigner crystal.

While physicists person obtained indirect grounds that Wigner crystals exist, nary 1 has been capable to drawback a representation of one—until now.

UC Berkeley physicists published past week successful the diary Nature an representation of conscionable specified an electron crystal sandwiched betwixt 2 semiconductor layers. The representation is impervious affirmative that these crystals exist.

"If you accidental you person an electron crystal, amusement maine the crystal," elder writer Feng Wang, Berkeley prof of physics, told Nature.

The Berkeley and Berkeley Lab team, involving physicists from the labs of Wang, Michael Crommie and Alex Zettl, developed a caller method for visualizing the crystals, which thin to "melt" erstwhile probed. By placing a graphene expanse implicit the semiconductor sandwich, the squad was capable to probe the Wigner crystal with a scanning tunneling microscope without melting the illustration and show the crystalline lattice structure, arsenic Wigner predicted.

According to doctoral campaigner Hongyuan Li and erstwhile postdoctoral chap Shaowei Li, co-first authors of the paper, the survey not lone lays a coagulated instauration for knowing electron Wigner crystals, but besides provides an attack that is mostly applicable for imaging correlated electron lattices successful different systems.

"The method is non-invasive to the authorities you privation to probe. To me, it is simply a precise clever idea," physicist Kin Fai Mak of Cornell University told Nature.

Imaging electron clouds with graphene

Electrons wrong materials behave successful galore unusual ways, but astir ever zip astir astatine precocious speed. Wigner predicted that if they could beryllium slowed down, their earthy repulsion—particles with the aforesaid electric charge repel 1 another—would let them to presume a uniformly spaced arrangement, fundamentally a crystal structure.

The squad created the Wigner crystals making a sandwich of single-atom layers of 2 akin semiconductors: tungsten disulfide and tungsten diselenide. The researchers utilized an electrical tract to tune the density of the electrons betwixt the 2 layers and past cooled the full instrumentality to a somesthesia of astir 5 Kelvin, adjacent implicit zero.

Their archetypal effort to measurement the electron density successful the two-dimensional crystal sandwich with a scanning tunneling microscope (STM) destroyed the crystal. The squad suggested covering the instrumentality with a graphene sheet, which acts similar a expanse of photograph insubstantial to grounds the determination of the electrons. The scientists utilized the STM to work the electron representation connected the graphene—as predicted, the electrons settled into a crystal statement with a separation astir 100 times greater than the separation of atoms successful the semiconductor sheets.

Other co-authors of the insubstantial are Emma Regan, Danqing Wang, Wenyu Zhao and Salman Kahn of Berkeley; Kentaro Yumigeta, Mark Blei and Sefaattin Tongay of Arizona State University successful Tempe; and Takashi Taniguchi and Kenji Watanabe of the National Institute for Materials Science successful Tsukuba, Japan.

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