Where Electrons Hide: A Puzzle in a Crystal ⚡ экспресс
By scanning tunneling microscopy (STM) on tungsten diselenide (WSe2) crystals — a typical semiconducting transition metal dichalcogenide — the exact position of the valence band Wannier center was determined. Using substitutional doping with point defects, the atomic lattice sites were first identified in STM images, after which it was shown that the density of states maximum at the K point of the Brillouin zone is located between atoms, whereas at the Γ point it lies directly on the atoms. This inversion of maximum positions proves that WSe2 is a topologically obstructed atomic insulator, which cannot be adiabatically transformed to the trivial atomic limit. This finding is important for understanding topological properties of layered materials and designing devices based on them.
Usually electrons in crystals, like honey in a honeycomb, cluster around atoms. But in tungsten diselenide — a layered material, resembling a honeycomb of carbon — the picture is different. Physicists used spectroscopy — a method that, like a supersensitive probe, feels the electron clouds. To mark the positions of atoms, they added a few 'foreign' atoms to the lattice, and then measured where electrons feel more 'comfortable' at different energies.
It turned out: at low energies, electrons crowd not on atoms, but in the voids between them — as if the honey had leaked out of the cells. At slightly higher energy, they, on the contrary, return to the atoms. And the transition occurs abruptly, like a switch click, rather than a smooth flow.
This is not just a fun phenomenon. The twisted states of electrons are resistant to interference, which opens the way to reliable quantum computers.
🎯 The most amazing part: electrons move from atoms to voids not gradually, but in a leap, like a switch between two realities.