Does the Heavy Electron Maintain its Integrity at Quantum Critical Point?

This talk will discuss non-Fermi liquid and quantum critical behavior in heavy fermion materials, focussing on the mechanism by which the electron mass appears to diverge at the quantum critical point. Is the quantum critical point merely a case of electron diffraction off a quantum critical spin density wave, or does it involve a fundamental break-down in the composite nature of the heavy electron place at the quantum critical point? We discuss the nature of the critical langrangian and show that the Hall constant changes continuously in the first scenario, but may "jump" discontinuously at a quantum critical point where the composite character of the electron quasiparticles changes.