1. The alpha to gamma transition in Cerium: a theoretical view from optical spectroscopy Kristjan Haule a,b and Gabriel Kotliar b a Jožef Stefan Institute, Ljubljana, Slovenia b Department of Physics and Center for Material Theory, Rutgers University, Piscataway, NJ, USA Classical theories of alpha to gamma phase transition estimated T K (exp)=2000K estimated T K (exp)=60-80K 4f 5d 6s orbitally resolved "fat" optics for alpha phase LDA compared to LDA+DMFT ff contribution to optics <<fd<<dd Conclusions  The main features of the optical spectra in Cerium are a consequence of 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 TC A Luttinger Ward functional local (eigen)state - full atomic base, where general AIM: ( ) two band Hubbard model, Bethe lattice, U=4D three band Hubbard model, Bethe lattice, U=5D, T=0.0625D three band Hubbard model, Bethe lattice, U=5D, T=0.0625D Using a novel approach to calculate optical properties of strongly correlated systems, we address the old question of the physical origin of the alpha to gamma transition in Cerium. We find that the Kondo collapse model, involving both the f and the spd electrons, describes the optical data better than a Mott transition picture involving the f electrons only. Our results compare well with existing experiments on thin films. We predict the full temperature dependence of the optical spectra and find the development of a hybridization pseudogap in the vicinity of the alpha to gamma phase transition. solution AIM DMFT SCC local in localized LMTO base Impurity problem (14x14): Impurity solvers (expansion in hybridization strength) Mott transition (B. Johansson, 1974):Mott transition (B. Johansson, 1974): Hubbard model changes and causes Mott tr. Kondo volume colapse (J.W. Allen, R.M. Martin, 1982):Kondo volume colapse (J.W. Allen, R.M. Martin, 1982): Anderson (impurity) model changes → chnange of T K bath either constant or taken from LDA and rescaled ab initio calculation contains t ff and V fd hopping is self-consistently determined bath for AIM 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 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 NCA OCA T CA Tests of the impurity solver Quasiparticle renormalization amplitude Imaginary axis data Real axis data Electron configuration of Ce Atom : [Xe]4f 2 5d 0 6s 2 Solid or compounds : trivalent [Xe]4f 1 (5d6s) 3, tetravalent [Xe]4f 0 (5d6s) 4 promotional model (Ramirez, Falicov 1971) Transition is 1.order ends with CP very similar to gas-liquid condesation  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  35.2Å 3 34.4Å 3  24.7Å 3 28Å 3  LDA+ULDAexp.volumes fermionic bath mapping LDA+DMFT formalism LDA+DMFT results: Photoemission Optics calculation within LDA+DMFT LDA+DMFT results: Optics comparison to experimentcomparison to experiment partial density of statespartial density of states temperature dependence of opticstemperature dependence of optics (developement of a hybridization pseudogap) (developement of a hybridization pseudogap)