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We find evidence that superconductivity intrudes into the paramagnetic-to-magnetic transition of the Kondo lattice model if magnetic frustration is added. Specifically, we study by the variational method the model on a square lattice in the presence of both nearest-neighbor (t) and next-nearest-neighbor (t') hopping of the conduction electrons. We find that, when t'/t > 0, a d-wave superconducting dome emerges between the magnetic and paramagnetic metal phases and close to the compensated regime, i.e., the number of conduction electrons equals the number of localized spin-1 /2 moments. Superconductivity is further strengthened by a direct antiferromagnetic exchange, JH, between the localized moments, to such an extent that we observe coexistence with magnetic order. [ABSTRACT FROM AUTHOR]

The damaging effect of strong electron-electron repulsion on regular, electron-phonon superconductivity is a standard tenet. In spite of that, an increasing number of compounds such as fullerides and more recently alkali-doped aromatics exhibit superconductivity despite very narrow bands and very strong electron repulsion. Here, we explore superconducting solutions of a model Hamiltonian inspired by the electronic structure of alkali-doped aromatics. The model is a two-site, two-narrow-band metal with a single intersite phonon, leading to attraction-mediated, two-order parameter superconductivity. On top of that, the model includes a repulsive onsite Hubbard U, whose effect on the superconductivity we study. Starting within mean field, we find that s± superconductivity is the best solution surviving the presence of U, whose effect is canceled out by the opposite signs of the two order parameters. The correlated Gutzwiller study that follows is necessary because without electron correlations, the superconducting state would in this model be superseded by an antiferromagnetic insulating state with lower energy. The Gutzwiller correlations lower the energy of the metallic state, with the consequence that the s± superconducting state is stabilized and even strengthened for small Hubbard U. [ABSTRACT FROM AUTHOR]

Several examples of metallic electron-doped polycyclic aromatic hydrocarbons (PAHs) molecular crystals have recently been experimentally proposed. Some of them have superconducting components, but most other details are still unknown beginning with structure and the nature of metallicity. We carried out ab initio density functional calculations for La-Phenanthrene (La-PA), here meant to represent a generic case of three-electron doping, to investigate structure and properties of a conceptually simple case. To our surprise we found first of all that the lowest energy state is not metallic but band insulating, with a disproportionation of two inequivalent PA molecular ions and a low PI symmetry, questioning the common assumption that three electrons will automatically metallize a PAH crystal. Our best metallic structure is metastable and slightly higher in energy, and retains equivalent PA ions and a higher P21 symmetry-the same generally claimed for metallic PAHs. We show that a "dimerizing" periodic distortion opens very effectively a gap in place of a symmetry related degeneracy of all P21 structures near the Fermi level, foreshadowing a possible role of that special intermolecular phonon in superconductivity of metallic PAHs. A Hubbard-Frohlich model describing that situation is formulated for future studies. [ABSTRACT FROM AUTHOR]

We show how to include the Jahn–Teller coupling of moiré phonons to the electrons in the continuum model formalism which describes small-angle twisted bilayer graphene. These phonons, which strongly couple to the valley degree of freedom, are able to open gaps at most integer fillings of the four flat bands around the charge neutrality point. Moreover, we derive the full quantum mechanical expression of the electron–phonon Hamiltonian, which may allow accessing phenomena such as the phonon-mediated superconductivity and the dynamical Jahn–Teller effect. [ABSTRACT FROM AUTHOR]

Stellar mergers and accretion events have been crucial in shaping the evolution of the Milky Way (MW). These events have been dynamically identified and chemically characterized using red giants and main-sequence stars. RR Lyrae (RRL) variables can play a crucial role in tracing the early formation of the MW since they are ubiquitous, old (t ≥ 10 Gyr) low-mass stars and accurate distance indicators. We exploited Data Release 3 of the GALAH survey to identify 78 field RRLs suitable for chemical analysis. Using synthetic spectra calculations, we determined atmospheric parameters and abundances of Fe, Mg, Ca, Y, and Ba. Most of our stars exhibit halo-like chemical compositions, with an iron peak around [Fe/H] ≈ −1.40, and enhanced Ca and Mg content. Notably, we discovered a metal-rich tail, with [Fe/H] values ranging from −1 to approximately solar metallicity. This sub-group includes almost 1/4 of the sample, it is characterized by thin disc kinematics and displays sub-solar α-element abundances, marginally consistent with the majority of the MW stars. Surprisingly, they differ distinctly from typical MW disc stars in terms of the s-process elements Y and Ba. We took advantage of similar data available in the literature and built a total sample of 535 field RRLs for which we estimated kinematical and dynamical properties. We found that metal-rich RRLs (1/3 of the sample) likely represent an old component of the MW thin disc. We also detected RRLs with retrograde orbits and provided preliminary associations with the Gaia–Sausage–Enceladus, Helmi, Sequoia, Sagittarius, and Thamnos stellar streams. [ABSTRACT FROM AUTHOR]

Vanadium sesquioxide (V2O3) is an antiferromagnetic insulator below TN≈55K. The magnetic order does not consist of only antiferromagnetic nearest-neighbor bonds, possibly excluding the interplane vanadium pairs, as one would infer from the bipartite character of the hexagonal basal plane in the high-temperature corundum structure. In fact, a magnetic structure with one ferromagnetic bond and two antiferromagnetic ones in the honeycomb plane is known experimentally to be realized, accompanied by a monoclinic distortion that makes the ferromagnetic bond inequivalent from the other two. We show here that the magnetic ordering, the accompanying monoclinic structural distortion, the magnetic anisotropy, and also the recently discovered high-pressure nonmagnetic monoclinic phase, can all be accurately described by conventional electronic structure calculations within GGA and GGA+U. Remarkably, our calculations yield that the corundum phase would be unstable to a monoclinic distortion even without magnetic ordering, thus suggesting that magnetism and lattice distortion are independent phenomena, though they reinforce each other. By means of GGA+U, we find a metal-to-insulator transition at a critical Uc. Both metal at U ≤ Uc and insulator above Uc have the same magnetic order as that actually observed below TN, but different monoclinic distortions. Reassuringly, the distortion on the insulating side agrees with the experimental one. Our results are in line with DMFT calculations for the paramagnetic phase [A. I. Poteryaev et al., Phys. Rev. B 76, 085127 (2007)], which predict that the insulating character is driven by a correlation-enhanced crystal-field splitting between egπ and a1g orbitals that pushes the latter above the chemical potential. We find that the a1g orbital, although almost empty in the insulating phase, is actually responsible for the unusual magnetic order as it leads to magnetic frustration whose effect is similar to a next-nearest-neighbor exchange in a Heisenberg model on a honeycomb lattice. [ABSTRACT FROM AUTHOR]

We study the phase diagram of the Kondo lattice model with nearest-neighbor hopping in the square lattice by means of the variational Monte Carlo technique. Specifically, we analyze a wide class of variational wave functions that allow magnetic and superconducting order parameters, so as to assess the possibility that superconductivity might emerge close to the magnetic instability, as is often observed in heavy-fermion systems. Indeed, we do find evidence of d-wave superconductivity in the paramagnetic sector, i.e., when magnetic order is not allowed in the variational wave function. However, when magnetism is allowed, it completely covers the superconducting region, which thus disappears from the phase diagram. [ABSTRACT FROM AUTHOR]

We exploit exact inequalities that refer to the entropy of a distribution to derive a simple variational principle at finite temperature for trial density matrices of Gutzwiller and Jastrow type. We use the result to extend at finite temperature the Gutzwiller approximation, which we apply to study a two-orbital model that we believe captures some essential features of V2O3. We indeed find that the phase diagram of the model bears many similarities to that of real vanadium sesquioxide. In addition, we show that in a Bethe lattice, where the finite-temperature Gutzwiller approximation provides a rigorous upper bound of the actual free energy, the results compare well with the exact phase diagram obtained by dynamical mean-field theory. [ABSTRACT FROM AUTHOR]

Background: The prognostic role of hyperglycemia in patients with myocardial infarction and obstructive coronary arteries (MIOCA) is acknowledged, while data on non-obstructive coronary arteries (MINOCA) are still lacking. Recently, we demonstrated that admission stress-hyperglycemia (aHGL) was associated with a larger infarct size and inflammatory response in MIOCA, while no differences were observed in MINOCA. We aim to investigate the impact of aHGL on short and long-term outcomes in MIOCA and MINOCA patients. Methods: Multicenter, population-based, cohort study of the prospective registry, designed to evaluate the prognostic information of patients admitted with acute myocardial infarction to S. Orsola-Malpighi and Maggiore Hospitals of Bologna metropolitan area. Among 2704 patients enrolled from 2016 to 2020, 2431 patients were classified according to the presence of aHGL (defined as admission glucose level ≥ 140 mg/dL) and AMI phenotype (MIOCA/MINOCA): no-aHGL (n = 1321), aHGL (n = 877) in MIOCA and no-aHGL (n = 195), aHGL (n = 38) in MINOCA. Short-term outcomes included in-hospital death and arrhythmias. Long-term outcomes were all-cause and cardiovascular mortality. Results: aHGL was associated with a higher in-hospital arrhythmic burden in MINOCA and MIOCA, with increased in-hospital mortality only in MIOCA. After adjusting for age, gender, hypertension, Killip class and AMI phenotypes, aHGL predicted higher in-hospital mortality in non-diabetic (HR = 4.2; 95% CI 1.9–9.5, p = 0.001) and diabetic patients (HR = 3.5, 95% CI 1.5–8.2, p = 0.003). During long-term follow-up, aHGL was associated with 2-fold increased mortality in MIOCA and a 4-fold increase in MINOCA (p = 0.032 and p = 0.016). Kaplan Meier 3-year survival of non-hyperglycemic patients was greater than in aHGL patients for both groups. No differences in survival were found between hyperglycemic MIOCA and MINOCA patients. After adjusting for age, gender, hypertension, smoking, LVEF, STEMI/NSTEMI and AMI phenotypes (MIOCA/MINOCA), aHGL predicted higher long-term mortality. Conclusions: aHGL was identified as a strong predictor of adverse short- and long-term outcomes in both MIOCA and MINOCA, regardless of diabetes. aHGL should be considered a high-risk prognostic marker in all AMI patients, independently of the underlying coronary anatomy. Trial registration data were part of the ongoing observational study AMIPE: Acute Myocardial Infarction, Prognostic and Therapeutic Evaluation. ClinicalTrials.gov Identifier: NCT03883711. [ABSTRACT FROM AUTHOR]

Dirac fermions play a central role in the study of topological phases, for they can generate a variety of exotic states, such as Weyl semimetals and topological insulators. The control and manipulation of Dirac fermions constitute a fundamental step toward the realization of novel concepts of electronic devices and quantum computation. By means of Angle-Resolved Photo-Emission Spectroscopy (ARPES) experiments and ab initio simulations, here, we show that Dirac states can be effectively tuned by doping a transition metal sulfide, BaNiS2, through Co/Ni substitution. The symmetry and chemical characteristics of this material, combined with the modification of the charge-transfer gap of BaCo1-xNixS2 across its phase diagram, lead to the formation of Dirac lines, whose position in k-space can be displaced along the Γ-MΓ-M symmetry direction and their form reshaped. Not only does the doping x tailor the location and shape of the Dirac bands, but it also controls the metal-insulator transition in the same compound, making BaCo1-xNixS2 a model system to functionalize Dirac materials by varying the strength of electron correlations. [ABSTRACT FROM AUTHOR]

Background: Hyperglycemia has been associated with increased inflammatory indexes and larger infarct sizes in patients with obstructive acute myocardial infarction (obs-AMI). In contrast, no studies have explored these correlations in non-obstructive acute myocardial infarction (MINOCA). We investigated the relationship between hyperglycemia, inflammation and infarct size in a cohort of AMI patients that included MINOCA. Methods: Patients with AMI undergoing coronary angiography between 2016 and 2020 were enrolled. The following inflammatory markers were evaluated: C-reactive protein, neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR) and neutrophil-to-platelet ratio (NPR). Myocardial infarct size was measured by peak high sensitivity troponin I (Hs-TnI) levels, left-ventricular-end-diastolic-volume (LVEDV) and left ventricular ejection fraction (LVEF). Results: The final study population consisted of 2450 patients with obs-AMI and 239 with MINOCA. Hyperglycemia was more prevalent among obs-AMI cases. In all hyperglycemic patients—obs-AMI and MINOCA—NLR, NPR, and LPR were markedly altered. Hyperglycemic obs-AMI subjects exhibited a higher Hs-TnI (p < 0.001), a larger LVEDV (p = 0.003) and a lower LVEF (p < 0.001) compared to normoglycemic ones. Conversely, MINOCA patients showed a trivial myocardial damage, irrespective of admission glucose levels. Conclusions: Our data confirm the association of hyperglycemic obs-AMI with elevated inflammatory markers and larger infarct sizes. MINOCA patients exhibited modest myocardial damage, regardless of admission glucose levels. [ABSTRACT FROM AUTHOR]