
MottHubbard MetalInsulator Transition
 Thermopower in a system with spincharge separation . Using an asymptotic Bethe ansatz for holons and spinons, the lowtemperature thermopower of the onedimensional Hubbard model was evaluated for the case of repulsive interactions. The competition between the entropy carried by the holons and that carried by the backflow of the spinons gives rise to an unusual temperature and doping dependence of the thermopower which is qualitatively similar to that observed in the normal state of high T c superconductors and certain quasionedimensional organic conductors. In particular, it is shown that the sign of the thermopower near the metalinsulator transition is opposite to that of noninteracting electrons, consistent with the notion of a ``doped Mott insulator.''
 Scaling theory of the MottHubbard metalinsulator transition in one dimension , with Andrew Millis and Sriram Shastry. The persistent current I of a mesoscopic Hubbard ring with commensurate electron density was calculated analytically via an asymptotic finitesize solution of the Bethe ansatz equations. The exponential decrease of I with the circumference of the ring allows one to define the correlation length xi(U) in the insulating phase of the model. We showed that in the vicinity of the zero temperature critical point of the MottHubbard metalinsulator transition the doping, systemsize, and interactionstrength dependence of the frequencydependent conductivity scale with the correlation length xi . These results confirm the applicability of the hyperscaling ansatz to this system, and suggest that the scaling function for the conductivity which we calculated is universal.
Publications
 C. A. Stafford, A. J. Millis, and B. S. Shastry,
Finitesize effects on the optical conductivity of a halffilled Hubbard ring,
Phys. Rev. B 43, 13660 (1991).
 C. A. Stafford and A. J. Millis,
Scaling theory of the MottHubbard metalinsulator transition in one dimension,
Phys. Rev. B 48, 1409 (1993).
 C. A. Stafford,
Unusual lowtemperature thermopower in the onedimensional Hubbard model,
Phys. Rev. B 48, 8430 (1993).
 C. A. Stafford and S. Das Sarma,
Collective Coulomb Blockade in an Array of Quantum Dots: A MottHubbard Approach,
Phys. Rev. Lett. 72, 3590 (1994).
