Eun-Ah Kim, Stanford University

2/7/08 – 4:30 p.m., 700 Clark Hall

In the last several years, experimental evidence has accumulated in a variety of highly correlated electronic systems of new quantum phases which (for purely electronic reasons) spontaneously break the rotational (point group) symmetry of the underlying crystal.  Such “nematic” phases have been seen in quantum Hall systems, in the metamagnetic SrRuO, and more recently in magnetic neutron scattering studies of the high temperature superconductor, YBCO.

The quantum dynamics of the nematic order parameter, especially near a putative quantum critical point, naturally couples strongly to low energy fermionic excitations (quasiparticles).  Such coupling can affect the nature and even the fate of quasiparticles making a study of nematic quantum criticality a   highly nontrivial problem. In this talk, I will discuss our recent results on one case in which this problem can be attacked in a tractable manner: the nodal nematic quantum criticality. Deep inside a d-wave superconducting state in a two-dimensional tetragonal crystal, the phase space for the low energy fermions reduce from the entire Fermi surface to four nodal points. The limited phase space for scattering allows for a controlled analysis of the nematic quantum criticality for nodal fermions.

We study the character of this quantum phase transition.  We investigated the problem by solving a model system with $N$ flavors of quasiparticles in the large N limit.   We find the transition to be continuous in this limit and the critical nematic fluctuations to have drastic effects on the nature of nodal quasiparticles.  To leading order in 1/N, quantum fluctuations enhance the dispersion anisotropy of the nodal excitations, and cause strongly angle dependent scattering leading to a nontrivial structure in the single particle spectral function. I will discuss possible implications of our results for cuprate physics from the spectral function of the nematic mode and the single fermion spectral function.