Condensed Matter Seminar

Austen Lamacraft
University of Virginia

Thursday, October 2, 2008
1:00 pm in SPL 52

Motion of an impurity in a one-dimensional quantum liquid

Abstract: The study of systems in which one or a few distringuished degrees of freedom are simultaneously coupled to a 'bath' consisting of an infinite number more finds applications in all branches of physics. In condensed matter physics, such situations are often called 'impurity' problems, since the canonical examples describe the dynamics of a defect in an otherwise perfect crystal lattice, or a foreign atom in a pure fluid. The latter arises naturally in the field of ultracold atomic physics.

In this talk I consider the motion of an impurity particle in a general one-dimensional quantum fluid at zero temperature. The dispersion relation of the impurity is strongly affected by interactions with the fluid as the particle's wavelength approaches twice the interparticle separation (corresponding to the Fermi momentum in a fermionic gas). This behavior is caused by singular backward scattering processes and can be understood by analogy to the Kondo effect, both at strong and weak coupling, with the possibility of a quantum phase transition where the group velocity at this momentum jumps to zero with increasing coupling. The low energy singularities in the impurity spectral function can be understood on the same footing.