Exactly solving a spinless fermionic system in two and three dimensions, we investigate the scaling behavior of the block entropy in critical and non-critical phases. The scaling of the block entropy crucially depends on the nature of the excitation spectrum of the system and on the topology of the Fermi surface. Noticeably, in the critical phases the scaling violates the area law and acquires a logarithmic correction only when a well defined Fermi surface exists in the system. When the area law is violated, we accurately verify a conjecture for the prefactor of the logarithmic correction, proposed by D. Gioev The nature of many-body entanglement in various solid-state models has been the focus of recent interest. The motivation for this effort is two-fold. On the one side, these systems are of interest for the purpose of quantum information processing and quantum computation [1]. At a fundamental level, the study of entanglement represents a purely quantum way of understanding and characterizing quantum phases and quantum phase transitions in many-body physics [2,3,4,5].A striking feature of entangled states |Ψ is that a local accurate description of such states is impossible, namely each subsystem A of the total system U can have a finite entropy, quantified as the von-Neumann entropy S A = −Trρ A log 2 ρ A of its reduced density matrix ρ A = T r U\A |Ψ Ψ|, whereas the total system clearly has zero entropy. The entropy of entanglement S A of the subsystem is a reliable estimate of the entanglement between the subsystem A and the rest, U \ A. Assuming that the system U corresponds to the whole universe in d dimensions, a fundamental question concerns the scaling behavior of the entropy of entanglement S L of an hypercubic subsystem L d (hereafter denoted as a block ) with its size L. Indeed, such scaling probes directly the spatial range of entanglement: when the block size exceeds the characteristic length over which two sites are entangled, the block entropy should become subadditive, and scale at most as the area of the block boundaries, following a so-called area law :A crucial question is then if and how the scaling of the block entropy changes when the nature of the quantum many-body state evolves in a critical way by passing through a quantum phase transition, and how the characteristic spatial extent of entanglement relates to the correlation length of the system. This question has been extensively addressed in the case of one-dimensional spin systems [5,6,7,8], in chains of harmonic oscillators [9,10] and in related conformal field theories (CFT) [11,12]. Here it is found unambiguosly that in states with exponentially decaying (connected) correlators S L follows the area law S L ∼ L 0 , saturating to a finite value, whereas for critical states, displaying power-law decaying correlations, a logarithmic correction to the area is always present: S L = [(c +c)/6] log 2 L, where c is the central charge of the related CFT. The asymptotic value of the block entropy is found to diverge logarithmically with t...

We report the detailed phase diagram and anomalous transport properties of Fe-based high-T_{c} superconductors SmFeAsO1-xFx. It is found that superconductivity emerges at x approximately 0.07, and optimal doping takes place in the x approximately 0.20 sample with the highest T_{c} approximately 54 K. T_{c} increases monotonically with doping; the anomaly in resistivity from structural phase or spin-density-wave order is rapidly suppressed, suggesting a quantum critical point around x approximately 0.14. As manifestations, a linear temperature dependence of the resistivity shows up at high temperatures in the x<0.14 regime but at low temperatures just above T_{c} in the x>0.14 regime; a drop in carrier density evidenced by a pronounced rise in the Hall coefficient is observed below the temperature of the anomaly peak in resistivity. A scaling behavior is observed between the Hall angle and temperature: cottheta_{H} proportional, variantT;{1.5} for all samples with different x in SmFeAsO1-xFx system.

The in-plane thermal conductivity of the iron selenide superconductor FeSe x ͑T c = 8.8 K͒ was measured down to 120 mK and up to 14.5 T ͑Ӎ3 / 4H c 2 ͒. In zero field, the residual linear term 0 / T at T → 0 is only about 16 W K −2 cm −1 , less than 4% of its normal-state value. Such a small 0 / T does not support the existence of nodes in the superconducting gap. More importantly, the field dependence of 0 / T in FeSe x is very similar to that in NbSe 2 , a typical multigap s-wave superconductor. We consider our data as strong evidence for multigap nodeless ͑at least in ab plane͒ superconductivity in FeSe x . This kind of superconducting gap structure may be generic for all Fe-based superconductors.

Three Cu(2+)-containing coordination polymers were synthesized and characterized by experimental (X-ray diffraction, magnetic susceptibility, pulsed-field magnetization, heat capacity, and muon-spin relaxation) and electronic structure studies (quantum Monte Carlo simulations and density functional theory calculations). [Cu(HF(2))(pyz)(2)]SbF(6) (pyz = pyrazine) (1a), [Cu(2)F(HF)(HF(2))(pyz)(4)](SbF(6))(2) (1b), and [CuAg(H(3)F(4))(pyz)(5)](SbF(6))(2) (2) crystallize in either tetragonal or orthorhombic space groups; their structures consist of 2D square layers of [M(pyz)(2)](n+) that are linked in the third dimension by either HF(2)(-) (1a and 1b) or H(3)F(4)(-) (2). The resulting 3D frameworks contain charge-balancing SbF(6)(-) anions in every void. Compound 1b is a defective polymorph of 1a, with the difference being that 50% of the HF(2)(-) links are broken in the former, which leads to a cooperative Jahn-Teller distortion and d(x(2))(-y(2)) orbital ordering. Magnetic data for 1a and 1b reveal broad maxima in chi at 12.5 and 2.6 K and long-range magnetic order below 4.3 and 1.7 K, respectively, while 2 displays negligible spin interactions owing to long and disrupted superexchange pathways. The isothermal magnetization, M(B), for 1a and 1b measured at 0.5 K reveals contrasting behaviors: 1a exhibits a concave shape as B increases to a saturation field, B(c), of 37.6 T, whereas 1b presents an unusual two-step saturation in which M(B) is convex until it reaches a step near 10.8 T and then becomes concave until saturation is reached at 15.8 T. The step occurs at two-thirds of M(sat), suggesting the presence of a ferrimagnetic structure. Compound 2 shows unusual hysteresis in M(B) at low temperature, although chi vs T does not reveal the presence of a magnetic phase transition. Quantum Monte Carlo simulations based on an anisotropic cubic lattice were applied to the magnetic data of 1a to afford g = 2.14, J = -13.4 K (Cu-pyz-Cu), and J(perpendicular) = -0.20 K (Cu-F...H...F-Cu), while chi vs T for 1b could be well reproduced by a spin-1/2 Heisenberg uniform chain model for g = 2.127(1), J(1) = -3.81(1), and zJ(2) = -0.48(1) K, where J(1) and J(2) are the intra- and interchain exchange couplings, respectively, which considers the number of magnetic nearest-neighbors (z). The M(B) data for 1b could not be satisfactorily explained by the chain model, suggesting a more complex magnetic structure in the ordered state and the need for additional terms in the spin Hamiltonian. The observed variation in magnetic behaviors is driven by differences in the H...F hydrogen-bonding motifs.

The in-plane thermal conductivity κ of electron-doped iron-arsenide superconductor BaFe1.9Ni0.1As2 (Tc = 20.3 K) single crystal was measured down to 70 mK. In zero field, the absence of a residual linear term κ0/T at T → 0 is strong evidence for nodeless superconducting gap. In magnetic field, κ0/T shows a slow field dependence up to H = 14.5 T (≈ 30% Hc 2 ). This is consistent with the superconducting gap structure demonstrated by angle-resolved photoemission spectroscopy experiments in BaFe1.85Co0.15As2 (Tc = 25.5 K), where isotropic superconducting gaps with similar size on hole and electron pockets were observed.

Two sister chromatids must be held together by a cohesion process from their synthesis during S phase to segregation in anaphase. Despite its pivotal role in accurate chromosome segregation, how cohesion is established remains elusive. Here, we demonstrate that yeast Rtt101-Mms1, Cul4 family E3 ubiquitin ligases are stronger dosage suppressors of loss-of-function mutants than PCNA The essential cohesion reaction, Eco1-catalyzed Smc3 acetylation is reduced in the absence of Rtt101-Mms1. One of the adaptor subunits, Mms22, associates directly with Eco1. Point mutations (L61D/G63D) in Eco1 that abolish the interaction with Mms22 impair Smc3 acetylation. Importantly, an double mutant displays additive Smc3ac reduction. Moreover, Smc3 acetylation and cohesion defects also occur in the mutants of other replication-coupled nucleosome assembly (RCNA) factors upstream or downstream of Rtt101-Mms1, indicating unanticipated cross talk between histone modifications and cohesin acetylation. These data suggest that fork-associated Cul4-Ddb1 E3s, together with PCNA, coordinate chromatin reassembly and cohesion establishment on the newly replicated sister chromatids, which are crucial for maintaining genome and chromosome stability.

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We numerically evaluate the entanglement spectrum (singular value decomposition of the wavefunction) of paired states of fermions in two dimensions that break parity and time-reversal symmetries, focusing on the spin-polarized px + ipy case. The entanglement spectrum of the weak-pairing (BCS) phase contains a Majorana zero mode, indicating non-Abelian topological order. In contrast, for the strong-pairing (BEC) phase, we find no such mode, consistent with Abelian topological order.