Absence of spin liquid in nonfrustrated correlated systems.

The question of the existence of a spin liquid state in the half-filled Hubbard model on the honeycomb (also known as graphene) lattice is revisited. The variational cluster approximation, the cluster dynamical mean field theory, and the cluster dynamical impurity approximation are applied to various cluster systems. Assuming that the spin liquid phase coincides with the Mott insulating phase in this nonfrustrated system, we find that the Mott transition is preempted by a magnetic transition occurring at a lower value of the interaction U, and therefore the spin liquid phase does not occur. This conclusion is obtained using clusters with two bath orbitals connected to each boundary cluster site. We argue that using a single bath orbital per boundary site is insufficient and leads to the erroneous conclusion that the system is gapped for all nonzero values of U.

Stable algebraic spin liquid in a Hubbard model.

We show the existence of a stable algebraic spin liquid (ASL) phase in a Hubbard model defined on a honeycomb lattice with spin-dependent hopping that breaks time-reversal symmetry. The effective spin model is the Kitaev model for large on-site repulsion. The gaplessness of the emergent Majorana fermions is protected by the time-reversal invariance of this model. We prove that the effective spin model is time-reversal invariant in the entire Mott phase, thus ensuring the stability of the ASL. The model can be physically realized in cold atom systems, and we propose experimental signals of the ASL.

Optimal transport technique to understand peptide conformations.

Using Protein Data Bank (PDB), the distribution of backbone torsional angle for dipeptides and tripeptides has been obtained and analyzed in several past works. However, the more extended peptides distributions are difficult to obtain due to the data sparsity. In this paper, we introduce a technique based on Optimal Transport theory to understand peptide conformations. This technique renders a computational method to determine the multi-point distribution of the backbone torsional angles of the peptide. Applying this technique, we study tetrapeptide conformations, presenting a detailed analysis of tetrapeptides distributions composed of Ala and Gly amino acids, and compare it with PDB data. Our study shows that tetrapeptides such as AAAA, AAAG, AGAA, and GAAA prefer right-handed alpha-helix secondary structure formations and beta-turns in GGGG, GAGG, AAGG, and AAGA.

Determinants of Pre-Hospital Delay after Myocardial Infarction in Bangladesh: A Rural Center Experience.

Determinants of pre-hospital delay after myocardial infarction, strictly among South-Asian rural community, till now is largely unknown. And Bangladesh is not an exception. It is a fact that though around two third of its population still live in villages, we do not know what factors are having influence on such delay. To find out these primers of time consumption before seeking medical help, this is a picture of a medical college hospital situated in a rural precinct. This cross-sectional analytical study was conducted among 98 patients came with Myocardial Infarction (MI) who had met inclusion and exclusion criteria from July 2019 and December 2019. Both STEMI & NSTEMI patients were selected as they have similar attributes. Data was collected in the coronary care unit using a preformed questionnaire. Among 98 MI patients, where 16 female and 82 male patients had average age 53±12 years. Average income rural community was around 100 USD. Almost 50% of sample were illiterate or below 5th grade. On average 6.6 hours (95% CI: 3.5-12.3) were required to reach CCU after symptom onset, whereas distance to first medical contact (FMC) was about 10.2 Km (95% CI: 6.4-16.2). Median distance to nearest PCI-capable hospital was 140 Km (IQR- 20 Km). Only 28% of patients could reach hospital within 2 hours, where 85% had onset of symptom while they were at home. Tertiary level medical college (74.5%) followed by Upazilla (Sub-urban) government health complex (22.4%) were frequent site of FMC. Principle mode of transport to hospital was CNG-three-wheeler (75% of cases). Logistic regression analysis showed only low literacy was as significant predictor about more than 2 hours pre-hospital delay (OR=2.58; p=0.043). Other factors such as low income (OR=2.51; p=0.126), diabetes mellitus (OR=2.99; p=0.059), female sex (OR=1.56; p=0.753), house wife (OR=1.88; p=0.547), previous MI (OR=1.52; p=1.000), symptom ignorance (OR=2.14; p=0.455) increases pre-hospital delay and distance to FMC <10 Km (OR=0.44; p=0.079) no significant prediction of pre-hospital delay after myocardial infarction. As rural community has less access to education low literacy has a significant impact on pre-hospital delay after myocardial infarction. So measures should be taken in rural areas through patient education and social awareness program regarding MI symptom and danger of delayed medical attention.

Can disorder act as a chemical pressure? An optical study of the Hubbard model.

The optical properties have been studied using the dynamical mean-field theory on a disordered Hubbard model. Despite the fact that disorder turns a metal to an insulator in high dimensional correlated materials, we notice that it can enhance certain metallic behavior as if a chemical pressure is applied to the system resulting in an increase of the effective lattice bandwidth (BW). We study optical properties in such a scenario and compare results with experiments where the BW is changed through isovalent chemical substitution (keeping electron filling unaltered) and obtain remarkable similarities vindicating our claim. We also make the point that these similarities differ from some other forms of BW tuned optical effects.

Orbital-selective Mott transition out of band degeneracy lifting.

We outline a general mechanism for orbital-selective Mott transition, the coexistence of both itinerant and localized conduction electrons, and show how it can take place in a wide range of realistic situations, even for bands of identical width and correlation, provided a crystal field splits the energy levels in manifolds with different degeneracies and the exchange coupling is large enough to reduce orbital fluctuations. The mechanism relies on the different kinetic energy in manifolds with different degeneracy. This phase has Curie-Weiss susceptibility and non-Fermi-liquid behavior, which disappear at a critical doping, all of which is reminiscent of the physics of the pnictides.

Sound velocity anomaly at the mott transition: application to organic conductors and V2O3.

Close to the Mott transition, lattice degrees of freedom react to the softening of electron degrees of freedom. This results in a change of lattice spacing, a diverging compressibility, and a critical anomaly of the sound velocity. These effects are investigated within a simple model, in the framework of dynamical mean-field theory. The results compare favorably to recent experiments on the layered organic-conductor kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Cl. We predict that effects of a similar magnitude are expected for V(2)O(3), despite the much larger value of the elastic modulus of this material.

Interaction-induced adiabatic cooling and antiferromagnetism of cold fermions in optical lattices.

We propose an interaction-induced cooling mechanism for two-component cold fermions in an optical lattice. It is based on an increase of the spin entropy upon localization, an analogue of the Pomeranchuk effect in liquid helium 3. We discuss its application to the experimental realization of the antiferromagnetic phase. We illustrate our arguments with dynamical mean-field theory calculations.

Theory of insulator metal transition and colossal magnetoresistance in doped manganites.

The persistent proximity of insulating and metallic phases, a puzzling characteristic of manganites, is argued to arise from the self-organization of the twofold degenerate e(g) orbitals of Mn into localized Jahn-Teller (JT) polaronic levels and broad band states due to the large electron-JT phonon coupling present in them. We describe a new two band model with strong correlations and a dynamical mean-field theory calculation of equilibrium and transport properties. These explain the insulator metal transition and colossal magnetoresistance quantitatively, as well as other consequences of two state coexistence.