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Topological semimetal in a fermionic optical lattice

Topological insulator in an optical lattice: Each atom in the lattice is represented by what looks like two dumbbells that cross. Here, this state is a property of higher orbitals and physicists represent orbitals with different shapes. To date, much of the atom-optical lattice experiments focused on physics of the lowest orbital or "s" band, represented by a sphere. Recently, scientists have been exploring physics associated with higher orbitals, like the dumbbell shaped "p" orbitals shown here.

Ultracold atomic gases trapped by laser light have become a playground for exploring quantum matter and even uncovering new phenomena not yet seen in nature.

PFC researchers at JQI have shown that this kind of optical lattice system can exhibit a never-before-seen quantum state called a topological semimetal. This state can also undergo a new type of phase transition to a topological insulator.

Harnessing the underlying phenomena of topological insulators, known as quantum hall physics, is important for developing new types of electronics and quantum information.

The team proposes an atom-optical lattice system as the ideal test bed. An ultracold gas may not sound like a solid, but under certain conditions, this unusual quantum matter behaves just like a crystal found in nature. Neutral atoms trapped by a checkerboard of laser light [lattice depicted above] are analogous to electrons in a crystalline solid.

If the atoms do not interact with each other, an energy band structure emerges that represents the semimetal. Allowing the particles to interact disrupts the system and forces a phase transition, turning the semimetal into a topological insulator. This topological insulator does not require adding any magnetic fields or even spin-orbit coupling. It arises from many-body interactions.

Kai Sun, W. Vincent Liu, Andreas Hemmerich, and S. Das Sarma
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