Renormalization-group theory of correlated electron systems

The thesis applies position-space renormalization-group theory to a variety of correlated electron systems, determining finite-temperature phase diagrams and thermodynamic properties for electron densities both at and away from half-filling. We begin by assessing the effectiveness of the Suzuki-Takano quantum decimation method on a d = 1 Hubbard model in an external magnetic field, where exact results for the specific heat, magnetic and charge susceptibilities are available at various electron densities. We find that our approach converges to the exact values at high temperature, and agrees well even at moderate-to-low temperatures. We then extend the decimation through the Migdal-Kadanoff procedure to a Hubbard model in d = 3. Phase diagrams are calculated for a range of Coulomb couplings, and two new "" phases are found for hole-dopings of 10 - 18% and 30 - 35%. The electron hopping strength renormalizes to infinity at the T phase sinks, possibly indicating superconductivity, an interpretation further supported by features of the specific heat. The next part turns to the tJ model in d = 3, where the phase was originally observed. In the vicinity of this phase we see a sharp peak in the superfluid weight, and a suppressed low temperature specific heat indicating gap formation. The doping dependence of the free carrier density is similar to that found experimentally in cuprate superconductors. Since strong anisotropy is a key aspect of high-T, materials, we also consider a d = 3 tJ model with distinct in-plane and out-of-plane couplings. We examine the evolution of the phase diagram as the interplane coupling is weakened, and find that the T phase persists even in the quasi-two-dimensional regime.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Physics.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2005

Author dc:creator

• Hinczewski, Michael, 1979-

Advisor dc:contributor.advisor

• A. Nihat Berker.

• Physics.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/34392

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/34392