Special Condensed Matter Seminar, Simon Trebst, U. of Cologne, "Spin liquids and (Majorana) metals"

Fri, Jun 2, 2017, 1:15 pm
PCTS Seminar Room

Spin liquids are often dichotomous states, where an electronic Mott insulator harbors emergent itinerant degrees of freedom that form a metal. Three-dimensional Kitaev models, relevant to the physics of certain spin-orbit entangled Mott insulators, stand out as prototypical examples that allow to analytically track the emergence of such spin liquids — the elementary spin degrees of freedom fractionalize into a gapped Z2 gauge field and itinerant Majorana fermions. The latter form a Majorana metal whose precise nature depends on the geometry of the underlying lattice and can be captured by their nodal manifolds including the possibility of Majorana Fermi surfaces, nodal lines, and topologically protected Weyl nodes. In this talk, I will also discuss a second example that in many ways is opposite to the above — a classical spin liquid where the manifold of degenerate zero-temperature spin spiral states is captured by a “spiral surface”. I will show that by doubling the classical spin model to a free fermion model the latter can be understood as Fermi surfaces of a closely related metallic state.