Metal-Insulator transitions in the periodic Anderson model

We solve the Periodic Anderson model in the Mott-Hubbard regime, using Dynamical Mean Field Theory. Upon electron doping of the Mott insulator, a metal-insulator transition occurs which is qualitatively similar to that of the single band Hubbard model, namely with a divergent effective mass and a first order character at finite temperatures. Surprisingly, upon hole doping, the metal-insulator transition is not first order and does not show a divergent mass. Thus, the transition scenario of the single band Hubbard model is not generic for the Periodic Anderson model, even in the Mott-Hubbard regime.Comment: 5 pages, 4 figure

Asymmetry between the electron- and hole-doped Mott transition in the periodic Anderson model

We study the doping driven Mott metal-insulator transition (MIT) in the periodic Anderson model set in the Mott-Hubbard regime. A striking asymmetry for electron or hole driven transitions is found. The electron doped MIT at larger U is similar to the one found in the single band Hubbard model, with a first order character due to coexistence of solutions. The hole doped MIT, in contrast, is second order and can be described as the delocalization of Zhang-Rice singlets.Comment: 18 pages, 19 figure

Pseudogap temperature as a Widom line in doped Mott insulators

The pseudogap refers to an enigmatic state of matter with unusual physical properties found below a characteristic temperature $T^*$ in hole-doped high-temperature superconductors. Determining $T^*$ is critical for understanding this state. Here we study the simplest model of correlated electron systems, the Hubbard model, with cluster dynamical mean-field theory to find out whether the pseudogap can occur solely because of strong coupling physics and short nonlocal correlations. We find that the pseudogap characteristic temperature $T^*$ is a sharp crossover between different dynamical regimes along a line of thermodynamic anomalies that appears above a first-order phase transition, the Widom line. The Widom line emanating from the critical endpoint of a first-order transition is thus the organizing principle for the pseudogap phase diagram of the cuprates. No additional broken symmetry is necessary to explain the phenomenon. Broken symmetry states appear in the pseudogap and not the other way around.Comment: 6 pages, 4 figures and supplementary information; published versio

Mott physics and first-order transition between two metals in the normal state phase diagram of the two-dimensional Hubbard model

For doped two-dimensional Mott insulators in their normal state, the challenge is to understand the evolution from a conventional metal at high doping to a strongly correlated metal near the Mott insulator at zero doping. To this end, we solve the cellular dynamical mean-field equations for the two-dimensional Hubbard model using a plaquette as the reference quantum impurity model and continuous-time quantum Monte Carlo method as impurity solver. The normal-state phase diagram as a function of interaction strength $U$, temperature $T$, and filling $n$ shows that, upon increasing $n$ towards the Mott insulator, there is a surface of first-order transition between two metals at nonzero doping. That surface ends at a finite temperature critical line originating at the half-filled Mott critical point. Associated with this transition, there is a maximum in scattering rate as well as thermodynamic signatures. These findings suggest a new scenario for the normal-state phase diagram of the high temperature superconductors. The criticality surmised in these systems can originate not from a T=0 quantum critical point, nor from the proximity of a long-range ordered phase, but from a low temperature transition between two types of metals at finite doping. The influence of Mott physics therefore extends well beyond half-filling.Comment: 27 pages, 16 figures, LaTeX, published versio

Oncological safety of stromal vascular fraction enriched fat grafting in two-stage breast reconstruction after nipple sparing mastectomy: long-term results of a prospective study

OBJECTIVE: Autologous fat transfer (AFT) is commonly used to treat implant palpability and prevent fibrosis and thinning in mastectomy skin flaps. A major limit to this procedure is volume retention over time, leading to the introduction of fat enrichment with stromal vascular fraction (SVF+AFT). Oncological concerns have been raised over the injection of an increased concentration of progenitors cells (ASCs) in the SVF. The aim of the study is to evaluate the long-term cancer recurrence risk of SVF+AFT cases compared to AFT, in patients undergoing Nipple Sparing Mastectomy (NSM). PATIENTS AND METHODS: A prospective study was designed to compare three groups of patients undergoing NSM followed by SVF+AFT, AFT or none (control group), after a two-stage breast reconstruction. Patients were strictly followed-up for at least 5-years from the second stage reconstructive procedure. Loco-regional and systemic recurrence rate were evaluated over time as the primary outcome. Logistic regression was used to investigate which factors were associated with recurrence events and independent variables of interest were: surgical technique, age above 50 years old, lympho-vascular invasion, oncological stage, adjuvant or neoadjuvant chemotherapy, adjuvant radiotherapy and adjuvant hormone therapy. RESULTS: 41 women were included in G1 (SVF+AFT), 64 in G2 (AFT), and 64 in G3 (control group). Loco-regional recurrence rate was 2.4% for G1, 4.7% for G2, and 1.6% for G3. Systemic recurrence was 7.3%, 3.1%, and 3.1%, respectively. Among the variables included, there were no significant risk factors influencing a recurrence event, either loco-regional or systemic. In particular, SVF+AFT (G1) did not increase the oncological recurrence. CONCLUSIONS: Our data suggest that both centrifuged and SVF-enhanced fat transfer have a similar safety level in comparison to patients who did not undergo fat grafting in breast reconstruction after NSM