Breakdown of Traditional Many-Body Theories for Correlated Electrons.

Starting from the (Hubbard) model of an atom, we demonstrate that the uniqueness of the mapping from the interacting to the noninteracting Green function, G→G_{0}, is strongly violated, by providing numerous explicit examples of different G_{0} leading to the same physical G. We argue that there are indeed infinitely many such G_{0}, with numerous crossings with the physical solution. We show that this rich functional structure is directly related to the divergence of certain classes of (irreducible vertex) diagrams, with important consequences for traditional many-body physics based on diagrammatic expansions. Physically, we ascribe the onset of these highly nonperturbative manifestations to the progressive suppression of the charge susceptibility induced by the formation of local magnetic moments and/or resonating valence bond (RVB) states in strongly correlated electron systems.

Efficacy of the nanoparticle-drug conjugate CRLX101 in combination with bevacizumab in metastatic renal cell carcinoma: results of an investigator-initiated phase I-IIa clinical trial.

BACKGROUND: Anti-angiogenic therapies are effective in metastatic renal cell carcinoma (mRCC), but resistance is inevitable. A dual-inhibition strategy focused on hypoxia-inducible factor (HIF) is hypothesized to be active in this refractory setting. CRLX101 is an investigational camptothecin-containing nanoparticle-drug conjugate (NDC), which durably inhibits HIF1α and HIF2α in preclinical models and in gastric cancer patients. Synergy was observed in the preclinical setting when combining this NDC and anti-angiogenic agents, including bevacizumab. PATIENTS AND METHODS: Patients with refractory mRCC were treated every 2 weeks with bevacizumab (10 mg/kg) and escalating doses of CRLX101 (12, 15 mg/m(2)) in a 3 + 3 phase I design. An expansion cohort of 10 patients was treated at the recommended phase II dose (RP2D). Patients were treated until progressive disease or prohibitive toxicity. Adverse events (AEs) were assessed using CTCAE v4.0 and clinical outcome using RECIST v1.1. RESULTS: Twenty-two patients were response-evaluable in an investigator-initiated trial at two academic medical centers. RCC histologies included clear cell (n = 12), papillary (n = 5), chromophobe (n = 2), and unclassified (n = 3). Patients received a median of two prior therapies, with at least one prior vascular endothelial tyrosine kinase inhibitor therapy (VEGF-TKI). No dose-limiting toxicities were observed. Grade ≥3 AEs related to CRLX101 included non-infectious cystitis (5 events), fatigue (3 events), anemia (2 events), diarrhea (2 events), dizziness (2 events), and 7 other individual events. Five of 22 patients (23%) achieved partial responses, including 3 of 12 patients with clear cell histology and 2 of 10 patients (20%) with non-clear cell histology. Twelve of 22 patients (55%) achieved progression-free survival (PFS) of >4 months. CONCLUSIONS: CRLX101 combined with bevacizumab is safe in mRCC. This combination fulfilled the protocol's predefined threshold for further examination with responses and prolonged PFS in a heavily pretreated population. A randomized phase II clinical trial in mRCC of this combination is ongoing.

Self-energy behavior away from the Fermi surface in doped Mott insulators.

We analyze self-energies of electrons away from the Fermi surface in doped Mott insulators using the dynamical cluster approximation to the Hubbard model. For large onsite repulsion, U, and hole doping, the magnitude of the self-energy for imaginary frequencies at the top of the band ([Formula: see text]) is enhanced with respect to the self-energy magnitude at the bottom of the band ([Formula: see text]). The self-energy behavior at these two [Formula: see text]-points is switched for electron doping. Although the hybridization is much larger for (0, 0) than for [Formula: see text], we demonstrate that this is not the origin of this difference. Isolated clusters under a downward shift of the chemical potential, [Formula: see text], at half-filling reproduce the overall self-energy behavior at (0, 0) and [Formula: see text] found in low hole doped embedded clusters. This happens although there is no change in the electronic structure of the isolated clusters. Our analysis shows that a downward shift of the chemical potential which weakly hole dopes the Mott insulator can lead to a large enhancement of the [Formula: see text] self-energy for imaginary frequencies which is not associated with electronic correlation effects, even in embedded clusters. Interpretations of the strength of electronic correlations based on self-energies for imaginary frequencies are, in general, misleading for states away from the Fermi surface.

Fluctuation Diagnostics of the Electron Self-Energy: Origin of the Pseudogap Physics.

We demonstrate how to identify which physical processes dominate the low-energy spectral functions of correlated electron systems. We obtain an unambiguous classification through an analysis of the equation of motion for the electron self-energy in its charge, spin, and particle-particle representations. Our procedure is then employed to clarify the controversial physics responsible for the appearance of the pseudogap in correlated systems. We illustrate our method by examining the attractive and repulsive Hubbard model in two dimensions. In the latter, spin fluctuations are identified as the origin of the pseudogap, and we also explain why d-wave pairing fluctuations play a marginal role in suppressing the low-energy spectral weight, independent of their actual strength.

Origin of the pseudogap in cuprate superconductors from quantum cluster theories.

We analyze the origin of the pseudogap present in cuprate superconductors. We elucidate the mechanism of pseudogap formation close to the Mott localization within the dynamical cluster approach (DCA) to the Hubbard model. As the Coulomb interaction is increased, cluster-bath Kondo states are destroyed and a nondegenerate bound cluster state is formed, leading to a pseudogap. This occurs first at the antinodal point due to its weaker coupling to the bath, explaining the momentum dependence of the pseudogap. We find that the character of the pseudogap is related to breaking d-wave pairs.

Divergent precursors of the Mott-Hubbard transition at the two-particle level.

Identifying the fingerprints of the Mott-Hubbard metal-insulator transition may be quite elusive in correlated metallic systems if the analysis is limited to the single particle level. However, our dynamical mean-field calculations demonstrate that the situation changes completely if the frequency dependence of the two-particle vertex functions is considered: The first nonperturbative precursors of the Mott physics are unambiguously identified well inside the metallic regime by the divergence of the local Bethe-Salpeter equation in the charge channel. In the low-temperature limit this occurs for interaction values where incoherent high-energy features emerge in the spectral function, while at high temperatures it is traceable up to the atomic limit.

Dynamical vertex approximation for nanoscopic systems.

With an increasing complexity of nanoscopic systems and the modeling thereof, new theoretical tools are needed for a reliable calculation of complex systems with strong electronic correlations. To this end, we propose a new approach based on the recently introduced dynamical vertex approximation. We demonstrate its reliability already on the one-particle vertex (i.e., dynamical mean field theory) level by comparison with the exact solution. Modeling a quantum point contact with 110 atoms, we show that the contact becomes insulating already before entering the tunneling regime due to a local Mott-Hubbard transition occurring on the atoms which form the point contact.

Factors associated with elevated or blunted PTH response in vitamin D insufficient adults.

OBJECTIVES: The purpose of this study was to examine factors associated with high or low parathyroid hormone (PTH) levels in relationship to vitamin D insufficiency. DESIGN: This was a cross-sectional study consisting of 516 healthy men and women, aged 30-85, all Caucasians with vitamin D insufficiency [serum 25(OH)D<45 nmol L(-1)]. The group was divided into quartiles by PTH levels and the highest and lowest quartiles were compared with regard to various factors likely to affect calcium metabolism. We used stepwise multivariable logistic regression to determine the independent association between PTH levels and other variables for men and women separately. RESULTS: We found that men in the lowest PTH quartile were significantly younger, had less energy intake, lower body mass index (BMI) and better kidney function compared with the highest PTH quartile. They had also higher ionized calcium, insulin-like growth factor (IGF1) and testosterone and were more likely to smoke. Women within the lowest PTH quartile were younger, had lower BMI and magnesium values and higher IGF1 levels and were more likely to smoke. Stepwise multivariate regression showed that IGF1, testosterone and BMI were significantly associated with PTH in men (R(2)=0.472) but smoking, BMI and kidney function in women (R(2)=0.362). CONCLUSIONS: Our results indicate that during vitamin D insufficiency, factors other than calcium and vitamin D may modify PTH response. These factors may be different between sexes and we have identified novel factors, IGF1 and testosterone in men which may be compensatory in nature and confirmed previous factors such as smoking, BMI and kidney function in women.

Electron-phonon interaction and antiferromagnetic correlations.

We study effects of the Coulomb repulsion on the electron-phonon interaction (EPI) in the Holstein-Hubbard model, using the antiferromagnetic (AF) dynamical mean-field approximation. AF correlations strongly enhance EPI effects on the electron Green's function with respect to the paramagnetic correlated system, but the net effect of the Coulomb interaction is a moderate suppression of the EPI. Doping leads to additional suppression. In contrast, the Coulomb interaction strongly suppresses EPI effects on phonons, but the suppression weakens with doping.

Polaronic behavior of undoped high-T(c) cuprate superconductors from angle-resolved photoemission spectra.

We present angle-resolved photoemission spectroscopy (ARPES) data on undoped La2CuO4, indicating polaronic coupling between bosons and charge carriers. Using a shell model, we calculate the electron-phonon coupling and find that it is strong enough to give self-trapped polarons. We develop an efficient method for calculating ARPES spectra in undoped systems. Using the calculated couplings, we find the width of the phonon sideband in good agreement with experiment. We analyze reasons for the observed dependence of the width on the binding energy.

Apparent electron-phonon interaction in strongly correlated systems.

We study the interaction of electrons with phonons in strongly correlated solids, having high-T(c) cuprates in mind. Using sum rules, we show that the apparent strength of this interaction strongly depends on the property studied. If the solid has a small fraction (doping) delta of charge carriers, the influence of the interaction on the phonon self-energy is reduced by a factor delta, while there is no corresponding reduction of the coupling seen in the electron self-energy. This supports the interpretation of recent photoemission experiments, assuming a strong coupling to phonons.

Role of surface States in scanning tunneling spectroscopy of (111) metal surfaces with Kondo adsorbates.

A nearly free-electron model to describe scanning tunneling spectroscopy of (111) metal surfaces with Kondo impurities is presented. Surface states are found to play an important role giving a larger contribution to the conductance of Cu(111) and Au(111) than Ag(111) surfaces. The different line shapes observed when Co is adsorbed on the different substrates are mainly determined by the position of the surface band onset relative to the Fermi energy and the decay length of the surface state into the substrate. The lateral dependence of the line shape amplitude is found to be bulklike for R|| < or approximately 3-5 A and surfacelike at larger distances, in agreement with experimental data.

Electron-phonon interaction in the t-J model.

We derive a t-J model with electron-phonon coupling from the three-band model, considering modulation of both hopping and Coulomb integrals by phonons. While the modulation of the hopping integrals dominates, the modulation of the Coulomb integrals cannot be neglected. The model explains the experimentally observed anomalous softening of the half-breathing mode upon doping and a weaker softening of the breathing mode. It is shown that other phonons are not strongly influenced, and, in particular, the coupling to a buckling mode is not strong in this model.

Strong superconductivity with local Jahn-Teller phonons in C60 solids.

We analyze fulleride superconductivity at experimental doping levels, treating the electron-electron and electron-phonon interactions on an equal footing, and demonstrate that the Jahn-Teller phonons create a local (intramolecular) pairing which is surprisingly resistant to the Coulomb repulsion, despite the weakness of retardation in these low-bandwidth systems. The requirement for coherence throughout the solid then yields a very strong doping dependence to T(c), one consistent with experiment and much stronger than expected from standard Eliashberg theory.

Velocity training induces power-specific adaptations in highly functioning older adults.

OBJECTIVE: To test the efficacy of high-velocity training in healthy older persons. DESIGN: A 12-week randomized trial, with subjects blocked for gender and residence, comparing high-velocity resistance training with a self-paced walking program. SETTING: Retirement community. PARTICIPANTS: Forty-three volunteers over the age of 70 years. INTERVENTION: Power group: high-velocity leg exercises 3 times weekly with weekly increases in resistance combined with 45 minutes of moderate, nonresistance exercise weekly. Walking group: moderate intensity exercise 30 minutes daily, 6 days weekly. MAIN OUTCOME MEASURES: Variables measured included leg press peak power and leg extensor strength. Functional performance outcomes included: 6-minute walk distance, Short Physical Performance Battery, Physical Performance Test, and Medical Outcomes Study Short-Form Health Survey. RESULTS: Peak power improved 22% (p =.004) in the power group (3.7 +/- 1.0 W/kg to 4.5 +/- 1.4 W/kg) but did not change in the walking group (3.99 +/-.76 W/kg to 3.65 +/-.94 W/kg). Leg extensor power at resistance of 50%, 60%, and 70% of body weight increased 50%, 77%, and 141%, respectively, in the power group (p <.0001, repeated-measures analysis of variance). Strength improved 22% in the power-trained individuals and 12% in the walkers (p <.0001). Training did not improve functional task performance in either group. One subject developed a radiculopathy during training. CONCLUSIONS: Resistance training focusing on speed of movement improved leg power and maximal strength substantially, but did not improve functional performance in healthy high-functioning older volunteers.

Saturation of electrical resistivity in metals at large temperatures.

We present a microscopic model for systems showing resistivity saturation. An essentially exact quantum Monte Carlo calculation demonstrates that the model describes saturation. We give a simple explanation for saturation, using charge conservation and considering the limit where thermally excited phonons have destroyed the periodicity. Crucial model features are phonons coupling to the hopping matrix elements and a unit cell with several atoms. We demonstrate the difference to a model of alkali-doped C60 with coupling to the level positions, for which there is no saturation.