Impurities and transport in fractionalized states of strongly correlated electrons

• Applicant: Dr. Lars Fritz
• Subject Area: Theoretical Condensed Matter Physics
• Term: from 2007 to 2010
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 39317888

The physics of Mott insulators is commonly associated with spin physics described in terms of a general Heisenberg model. Such models allow for a huge variety of different ground states which can in principle be antiferromagnetic (ordered) or paramagnetic (disordered). Particularly interesting are materials with one spin S = ½ per unit cell. The paramagnetic phase of such systems can be spontaneously dimerized breaking translational invariance, or can break no symmetry at all, the latter being called spin liquid. The elementary excitations of spin liquids are electrically neutral excitations which carry spin S = ½ and are commonly referred to as spinons. In a gauge field description such spinons carry an emergent gauge charge Q.In the first part of the project I intend to study the physics of impurities, which carry both spin and gauge charge, embedded in bulk systems in a spin liquid state using a phenomenological description in terms of a gauge theory. This will lead to predictions for observables which could be used to detect and discriminate such states.In a second part I study electromagnetic transport in systems, where a neutral spin liquid is coupled to charged fermionic quasiparticles. Such a situation naturally appears near the breakdown of the Kondo effect in heavy fermion materials. The interplay of the emergent internal gauge field with the external electromagnetic field promises to have very interesting effects on transport properties. Furthermore, I will investigate whether such models can be realized in optical lattices.

• DFG Programme: Research Fellowships
• International Connection: USA
• Host: Professor Dr. Subir Sachdev