Mott-Hubbard Metal-Insulator Transition

• Thermopower in a system with spin-charge separation . Using an asymptotic Bethe ansatz for holons and spinons, the low-temperature thermopower of the one-dimensional 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 quasi-one-dimensional organic conductors. In particular, it is shown that the sign of the thermopower near the metal-insulator transition is opposite to that of noninteracting electrons, consistent with the notion of a ``doped Mott insulator.''
  
  
• Scaling theory of the Mott-Hubbard metal-insulator 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 finite-size 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 Mott-Hubbard metal-insulator transition the doping, system-size, and interaction-strength dependence of the frequency-dependent 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

1. C. A. Stafford, A. J. Millis, and B. S. Shastry,
   Finite-size effects on the optical conductivity of a half-filled Hubbard ring,
   Phys. Rev. B 43, 13660 (1991).
   
   
2. C. A. Stafford and A. J. Millis,
   Scaling theory of the Mott-Hubbard metal-insulator transition in one dimension,
   Phys. Rev. B 48, 1409 (1993).
   
   
3. C. A. Stafford,
   Unusual low-temperature thermopower in the one-dimensional Hubbard model,
   Phys. Rev. B 48, 8430 (1993).
   
   
4. C. A. Stafford and S. Das Sarma,
   Collective Coulomb Blockade in an Array of Quantum Dots: A Mott-Hubbard Approach,
   Phys. Rev. Lett. 72, 3590 (1994).