Weyl nodes in periodic structures of superconductors and spin active materials

Motivated by recent progress in epitaxial growth of proximity structures of s-wave superconductors (S) and spin-active materials (M), we show that the periodic structure of S and M can behave effectively as a superconductor with pairs of point nodes, near which the low energy excitations are Weyl fermions. A simple toy model, where M is described by a Kronig-Penney potential with both spin-orbit coupling and exchange field, is proposed and solved to obtain the phase diagram of the nodal structure, the spin texture of the Weyl fermions, as well as the zero energy surface states in the form of open Fermi lines ("Fermi arcs"). Going beyond the simple model, a lattice model with alternating layers of S and magnetic $Z_2$ topological insulators (M) is solved. The calculated spectrum confirms previous prediction of Weyl nodes based on tunneling Hamiltonian of Dirac electrons. Our results provide further evidence that periodic structures of S and M are well suited for engineering gapless topological superconductors.Comment: Research article, contribution to theme issue "Andreev bound states" ed. Laura H. Greene and James A. Saul

Absence of long-range order in a triangular spin system with dipolar interactions

Antiferromagnetic Heisenberg model on the triangular lattice is perhaps the best known example of frustrated magnets, but it orders at low temperatures. Recent density matrix renormalization group (DMRG) calculations find that next nearest neighbor interaction $J_2$ enhances the frustration and leads to a spin liquid for $J_2/J_1\in (0.08,0.15)$. In addition, DMRG study of a dipolar Heisenberg model with longer range interactions gives evidence for a spin liquid at small dipole titling angle $\theta\in[0,10^\circ)$. In both cases, the putative spin liquid region appears to be small. Here, we show that for the triangular lattice dipolar Heisenberg model, a robust quantum paramagnetic phase exists in a surprisingly wide region, $\theta\in [0,54^\circ)$, for dipoles tilted along the lattice diagonal direction. We obtain the phase diagram of the model by functional renormalization group (RG) which treats all magnetic instabilities on equal footing. The quantum paramagnetic phase is characterized by a smooth continuous flow of vertex functions and spin susceptibility down to the lowest RG scale, in contrast to the apparent breakdown of RG flow in phases with stripe or spiral order. Our finding points to a promising direction to search for quantum spin liquids in ultracold dipolar molecules.Comment: 5 pages, 2 figures and the supplementary material

Scrambling dynamics and many-body chaos in a random dipolar spin model

Is there a quantum many-body system that scrambles information as fast as a black hole? The Sachev-Ye-Kitaev model can saturate the conjectured bound for chaos, but it requires random all-to-all couplings of Majorana fermions that are hard to realize in experiments. Here we examine a quantum spin model of randomly oriented dipoles where the spin exchange is governed by dipole-dipole interactions. The model is inspired by recent experiments on dipolar spin systems of magnetic atoms, dipolar molecules, and nitrogen-vacancy centers. We map out the phase diagram of this model by computing the energy level statistics, spectral form factor, and out-of-time-order correlation (OTOC) functions. We find a broad regime of many-body chaos where the energy levels obey Wigner-Dyson statistics and the OTOC shows distinctive behaviors at different times: Its early-time dynamics is characterized by an exponential growth, while the approach to its saturated value at late times obeys a power law. The temperature scaling of the Lyapunov exponent $\lambda_L$ shows that while it is well below the conjectured bound $2\pi T$ at high temperatures, $\lambda_L$ approaches the bound at low temperatures and for large number of spins.Comment: 7 pages, 8 figures with updated reference

Theory of interacting fermions in shaken square optical lattice

We develop a theory of weakly interacting fermionic atoms in shaken optical lattices based on the orbital mixing in the presence of time-periodic modulations. Specifically, we focus on fermionic atoms in circularly shaken square lattice with near resonance frequencies, i.e., tuned close to the energy separation between $s$-band and the $p$-bands. First, we derive a time-independent four-band effective Hamiltonian in the non-interacting limit. Diagonalization of the effective Hamiltonian yields a quasi-energy spectrum consistent with the full numerical Floquet solution that includes all higher bands. In particular, we find that the hybridized $s$-band develops multiple minima and therefore non-trivial Fermi surfaces at different fillings. We then obtain the effective interactions for atoms in the hybridized $s$-band analytically and show that they acquire momentum dependence on the Fermi surface even though the bare interaction is contact-like. We apply the theory to find the phase diagram of fermions with weak attractive interactions and demonstrate that the pairing symmetry is $s+d$-wave. Our theory is valid for a range of shaking frequencies near resonance, and it can be generalized to other phases of interacting fermions in shaken lattices.Comment: 12 pages with 5 figures. Comments and reference suggestions are welcom

Renormalization group analysis of dipolar Heisenberg model on square lattice

We present a detailed functional renormalization group analysis of spin-1/2 dipolar Heisenberg model on square lattice. This model is similar to the well known $J_1$-$J_2$ model and describes the pseudospin degrees of freedom of polar molecules confined in deep optical lattice with long-range anisotropic dipole-dipole interactions. Previous study of this model based on tensor network ansatz indicates a paramagnetic ground state for certain dipole tilting angles which can be tuned in experiments to control the exchange couplings. The tensor ansatz formulated on a small cluster unit cell is inadequate to describe the spiral order, and therefore the phase diagram at high azimuthal tilting angles remains undetermined. Here we obtain the full phase diagram of the model from numerical pseudofermion functional renormalization group calculations. We show that an extended quantum paramagnetic phase is realized between the N\'{e}el and stripe/spiral phase. In this region, the spin susceptibility flows smoothly down to the lowest numerical renormalization group scales with no sign of divergence or breakdown of the flow, in sharp contrast to the flow towards the long-range ordered phases. Our results provide further evidence that the dipolar Heisenberg model is a fertile ground for quantum spin liquids.Comment: 9 pages, 4 figure

ff-wave superfluidity from repulsive interaction in Rydberg-dressed Fermi gas

Interacting Fermi gas provides an ideal model system to understand unconventional pairing and intertwined orders relevant to a large class of quantum materials. Rydberg-dressed Fermi gas is a recent experimental system where the sign, strength, and range of the interaction can be controlled. The interaction in momentum space has a negative minimum at $q_c$ inversely proportional to the characteristic length-scale in real space, the soft-core radius $r_c$. We show theoretically that single-component (spinless) Rydberg-dressed Fermi gas in two dimensions has a rich phase diagram with novel superfluid and density wave orders due to the interplay of the Fermi momentum $p_F$, interaction range $r_c$, and interaction strength $u_0$. For repulsive bare interactions $u_0>0$, the dominant instability is $f$-wave superfluid for $p_Fr_c\lesssim 2$, and density wave for $p_Fr_c\gtrsim 4$. The $f$-wave pairing in this repulsive Fermi gas is reminiscent of the conventional Kohn-Luttinger mechanism, but has a much higher $T_c$. For attractive bare interactions $u_0<0$, the leading instability is $p$-wave pairing. The phase diagram is obtained from functional renormalization group that treats all competing many-body instabilities in the particle-particle and particle-hole channels on equal footing.Comment: 6 pages with 2 figures and reference

Pulmonary embolism presenting as syncope: a case report

<p>Abstract</p> <p>Introduction</p> <p>Despite the high incidence of pulmonary embolism its diagnosis continues to be difficult, primarily because of the vagaries of symptoms and signs in presentation. Conversely, syncope is a relatively easy clinical symptom to detect, but has varied etiologies that lead to a documented cause in only 58% of syncopal events. Syncope as the presenting symptom of pulmonary embolism has proven to be a difficult clinical correlation to make.</p> <p>Case presentation</p> <p>We present the case of a 26-year-old Caucasian man with pulmonary embolism induced-syncope and review the pathophysiology and diagnostic considerations.</p> <p>Conclusions</p> <p>Pulmonary embolism should be considered in the differential diagnosis of every syncopal event that presents at an emergency department.</p

Performance of Anatolian Merino and Akkaraman Lambs Fed Triticale, Hungarian Vetch or a Mixture of the Two Forages

Forages from Hungarian vetch and triticale monocultures or mixtures that can be produced with relatively low cost are important feed sources for ruminants in spring particularly in the arid and semiarid regions. The feed intake and the response of different sheep breeds (Fraser et al. 2009) to forage resources that vary in feeding value may differ. Therefore it is critical to match forage to animal and crop production needs for more efficient production in integrated crop livestock farming system

Relationship between serum interleukin-1β levels and acute phase response proteins in patients with familial Mediterranean fever

Introduction: The aim of this study was to investigate whether serum levels of interleukin-1β (IL–1β) has any possible correlation on inflammatory parameters such as C-reactive protein (CRP), erythrocyte sedimentation rate (ESR) and fibrinogen concentration in patients with familial Mediterra-nean fever (FMF) patients during attack-free period. Materials and methods: The serum levels of IL-1β, as an indicator of cytokines status, and the acute phase response proteins, CRP, ESR and fibrinogen levels were evaluated in 35 attack-free patients with FMF and 25 healthy volunteers. Results: Serum IL-1β levels were significantly higher in patients with FMF than control subjects (P = 0.018). There was no statistically significant difference in the serum levels of ESR, CRP and fibrino-gen between two groups (P = 0.181, P = 0.816, P = 0.686, respectively). There was a significant cor-relation between IL-1β and CRP (r = 0.513, P = 0.002) values of FMF group. Conclusions: In conclusion, our results confirm the presence of increased IL-1β levels in FMF pati-ents during attack-free period. Serum IL-1β values seems to correlate with CRP levels. The elevation of IL-1β levels may be important in monitoring subclinical inflammation of attack free period in FMF patients

Protective effects of silymarin on methotrexate-induced damages in rat testes

The present study aimed to investigate the protective effects of silymarin (SMN), an antioxidant, on methotrexate (MTX)-induced damage in rat testes. Thirty-two Wistar albino rats were divided into four groups (n = 8): control, MTX (20 mg/kg, i.p. on days 1 and 5), SMN (200 mg/kg, orally), and MTX + SMN (20 mg/kg, i.p. on days 1 and 5 and SMN 200 mg/kg orally) groups. At the end of the 6-week trial period, histopathological, immunohistochemical, biochemical, and spermatological analyses were performed on testes tissues. Histopathologically, MTX-induced damage, including depletion of germ cell and loos of spermatozoa, was significantly improved with SMN treatment. Immunohistochemically, the immunoreactivity of glutathione peroxidase 1 (GPx1) and manganese superoxide dismutase 2 (SOD2) were detected more intensely in the MTX + SMN group than in the MTX group. Biochemical examinations revealed that SMN supplementation decreased the lipid peroxidation and increased enzymatic antioxidants in the SMN-treated rats. Spermatologically, significant differences were found in the density, motility, dead-to-live sperm ratio, and abnormal sperm rate in the MTX + SMN group compared to the MTX group. In conclusion, SMN seems to have protective effects as an antioxidant against MTX-induced damage in rat testes