pdf, 9 MiB - Infoscience - EPFL
pdf, 9 MiB - Infoscience - EPFL
pdf, 9 MiB - Infoscience - EPFL
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Contents<br />
1 Introduction 15<br />
1.1 History of high temperature superconductivity . . . . . . . . . . . 15<br />
1.2 The phase diagram . . . . . . . . . . . . . . . . . . . . . . . . . . 17<br />
1.3 Theoretical approaches to superconductivity . . . . . . . . . . . . 18<br />
1.4 Microscopic models for the cuprates . . . . . . . . . . . . . . . . . 20<br />
1.4.1 Three band Hubbard model . . . . . . . . . . . . . . . . . 20<br />
1.4.2 Hubbard and t-J models . . . . . . . . . . . . . . . . . . . 22<br />
1.4.3 Anderson’s Resonating valence-bond theory . . . . . . . . 24<br />
1.5 Scope of the Dissertation . . . . . . . . . . . . . . . . . . . . . . . 29<br />
2 Numerical Methods 31<br />
2.1 Variational Monte Carlo . . . . . . . . . . . . . . . . . . . . . . . 31<br />
2.1.1 Degenerate open shell . . . . . . . . . . . . . . . . . . . . 34<br />
2.1.2 Pfaffian variational Monte Carlo . . . . . . . . . . . . . . . 36<br />
2.2 Jastrow factors, Gutzwiller projection . . . . . . . . . . . . . . . . 38<br />
2.3 Stochastic minimization . . . . . . . . . . . . . . . . . . . . . . . 39<br />
2.3.1 Implementation of the minimization . . . . . . . . . . . . . 40<br />
2.3.2 Derivative of degenerate eigenvectors . . . . . . . . . . . . 41<br />
2.3.3 Correlated measurement minimization . . . . . . . . . . . 42<br />
2.3.4 Multi - Determinant/Pfaffian wavefunctions . . . . . . . . 43<br />
2.4 Lanczos Step . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44<br />
2.5 Physical observables . . . . . . . . . . . . . . . . . . . . . . . . . 45<br />
2.6 Auxiliary-field Quantum Monte Carlo . . . . . . . . . . . . . . . . 45<br />
2.6.1 Particle-hole transformation . . . . . . . . . . . . . . . . . 49<br />
3 t-J Model on the triangular lattice 51<br />
3.1 Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51<br />
3.2 Superconductivity in the Cobaltites . . . . . . . . . . . . . . . . . 51<br />
3.3 Variational Monte Carlo . . . . . . . . . . . . . . . . . . . . . . . 55<br />
3.3.1 Variational wavefunction . . . . . . . . . . . . . . . . . . . 55<br />
3.3.2 Commensurate order . . . . . . . . . . . . . . . . . . . . . 58<br />
3.3.3 Characterization of the encountered instabilities . . . . . . 59<br />
3.3.4 Short-Range RVB wavefunction . . . . . . . . . . . . . . . 60<br />
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