Classical theories of alpha to gamma phase transition

1. Luttinger Ward functional NCA volumes exp. LDA LDA+U a 28Å3 24.7Å3 g 34.4Å3 35.2Å3 •  Various phases : • isostructural phase transition (T=298K, P=7kbar) •  (fcc) phase • [ magnetic moment • (Curie-Wiess law), • large volume, • stable high-T, low-p] •   (fcc) phase • [ loss of magnetic • moment (Pauli-para), • smaller volume, • stable low-T, high-p] • with large • volume collapse • v/v  15 • Electron configuration of Ce • Atom : [Xe]4f25d06s2 • Solid or compounds : • trivalent [Xe]4f1(5d6s)3, • tetravalent [Xe]4f0(5d6s)4 promotional model (Ramirez, Falicov 1971) • Mott transition (B. Johansson, 1974): Hubbard model changes and causes Mott tr. • Kondo volume colapse (J.W. Allen, R.M. Martin, 1982): Anderson (impurity) model changes → chnange of TK either constant or taken from LDA and rescaled bath LDA+DMFT is self-consistently determined bath for AIM ab initio calculation contains tff and Vfd hopping • Kondo volume colapse model resembles DMFT picture: • Solution of the Anderson impurity model → Kondo physics • Difference: with DMFT the lattice problem is solved (and therefore Δ must self-consistently determined)while in KVC Δ is calculated for a fictious impurity (and needs to be rescaled to fit exp.) LDA+DMFT formalism solution AIM 4f DMFT SCC mapping fermionic bath 5d 6s local in localized LMTO base Impurity problem (14x14): OCA TCA Using a novel approach to calculate optical properties of stronglycorrelated systems, we address the old question of the physicalorigin of the alpha to gamma transition in Cerium. Wefind that the Kondo collapse model, involving both the f and thespd electrons, describes the optical data better than a Motttransition picture involving the f electrons only. Our resultscompare well with existing experiments on thin films. We predictthe full temperature dependence of the optical spectra and findthe development of a hybridizationpseudogap in the vicinity ofthe alpha to gamma phase transition. LDA+DMFT results: Photoemission The alpha to gamma transition in Cerium: a theoretical view from optical spectroscopyKristjan Haulea,b and Gabriel KotliarbaJožef Stefan Institute, Ljubljana, SloveniabDepartment of Physics and Center for Material Theory, Rutgers University, Piscataway, NJ, USA • Transition is 1.order • ends with CP very similar to gas-liquid condesation estimated TK(exp)=60-80K estimated TK(exp)=2000K Classical theories of alpha to gamma phase transition Optics calculation within LDA+DMFT LDA+DMFT results: Optics • partial density of states • comparison to experiment Impurity solvers (expansion in hybridization strength) • temperature dependence of optics • (developement of a hybridization pseudogap) local (eigen)state - full atomic base , where general AIM: LDA compared to LDA+DMFT TCA ( ) Tests of the impurity solver • Quasiparticle renormalization amplitude • Imaginary axis data two band Hubbard model, Bethe lattice, U=4D three band Hubbard model,Bethe lattice, U=5D, T=0.0625D orbitally resolved "fat" optics for alpha phase ff contribution to optics <<fd<<dd • Real axis data Conclusions • The main features of the optical spectra in Cerium are a consequenceof a different hybridization strength between f and spd orbitals in the two phases • Kondo peak in low T alpha phase appears due to hybridization with spd bands • Optics conductivity has mostly d character • Optics shows a narrow Drude peak, hybridization (pseudo)gap and mid infrared peak at 1eV in alpha phase • Optics in gamma phase show a broad Drude like response (of d bands only) • "Kondo volume collapse model"explains the Cerium properties better than the "Mott transition" scenario three band Hubbard model, Bethe lattice, U=5D, T=0.0625D