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We present the superconducting and normal state properties of CaPd2Ge2 single crystal investigated by magnetic susceptibility \chi, isothermal magnetization M, heat capacity C_p, in-plane electrical resistivity \rho and London penetration depth \lambda versus temperature T and magnetic field H measurements. Bulk superconductivity is inferred from the \rho(T) and C_p(T) data. The \rho(T) data exhibit metallic behavior and undergoes a superconducting transition with T_c onset = 1.98 K and zero resistivity state at T_c 0 = 1.67 K. The \chi(T) reveal the onset of superconductivity at 2.0 K. For T>2.0 K, the \chi(T) and M(H) are weakly anisotropic paramagnetic with \chi_ab > \chi_c. The C_p(T) confirm the bulk superconductivity below T_c = 1.69(3) K. The superconducting state electronic heat capacity is analyzed within the framework of a single-band \alpha-model of BCS superconductivity and various normal and superconducting state parameters are estimated. Within the \alpha-model, the C_p(T) data and the ab plane \lambda(T) data consistently indicate a moderately anisotropic s-wave gap with \Delta(0)/k_B T_c ~ 1.6, somewhat smaller than the BCS value of 1.764. The relationship of the heat capacity jump at T_c and the penetration depth measurement to the anisotropy in the s-wave gap is discussed., Comment: 12 pages, 9 figures, 2 Tables; Submitted to PRB

Constraints on the mass distribution in high-redshift clusters of galaxies are not currently very strong. We aim to constrain the mass profile, M(r), and dynamical status of the $z \sim 0.8$ LCDCS 0504 cluster of galaxies characterized by prominent giant gravitational arcs near its center. Our analysis is based on deep X-ray, optical, and infrared imaging, as well as optical spectroscopy. We model the mass distribution of the cluster with three different mass density profiles, whose parameters are constrained by the strong lensing features of the inner cluster region, by the X-ray emission from the intra-cluster medium, and by the kinematics of 71 cluster members. We obtain consistent M(r) determinations from three methods (dispersion-kurtosis, caustics and MAMPOSSt), out to the cluster virial radius and beyond. The mass profile inferred by the strong lensing analysis in the central cluster region is slightly above, but still consistent with, the kinematics estimate. On the other hand, the X-ray based M(r) is significantly below both the kinematics and strong lensing estimates. Theoretical predictions from $\Lambda$CDM cosmology for the concentration--mass relation are in agreement with our observational results, when taking into account the uncertainties in both the observational and theoretical estimates. There appears to be a central deficit in the intra-cluster gas mass fraction compared to nearby clusters. Despite the relaxed appearance of this cluster, the determinations of its mass profile by different probes show substantial discrepancies, the origin of which remains to be determined. The extension of a similar dynamical analysis to other clusters of the DAFT/FADA survey will allow to shed light on the possible systematics that affect the determination of mass profiles of high-z clusters, possibly related to our incomplete understanding of intracluster baryon physics., Comment: 13 pages, 14 figures, submitted to A&A, abstract shortened

The crystallographic, magnetic and thermal properties of BiMn2PO6 and BiZn2PO6 were investigated by x-ray diffraction, magnetic susceptibility \chi, heat capacity Cp, and 31P NMR measurements as well as by density-functional band-theory calculations. Both compounds show a strong monotonic lattice softening on cooling, where the Debye temperature decreases by a factor of two from \Theta_D=650K at T=300K to \Theta_D=300K at T=2K. The \chi(T) data for BiMn2PO6 above 150K follow a Curie-Weiss law with a Curie constant consistent with a S=5/2 with g=2 and an antiferromagnetic (AFM) Weiss temperature \theta_CW= -78K. The \chi data indicate long-range AFM ordering below TN=30K, confirmed by a sharp lambda-type peak in Cp(T) at 28.8K. The band-theory calculations indicate that BiMn2PO6 is an AFM compound with dominant interactions J1/kB= 6.7K and J3/kB= 5.6K along the legs and rungs of a two-leg spin-ladder, respectively. In addition to the long-range AFM ordering at TN=30K, a second transition at 10 K is observed from the \chi and NMR measurements but is not evident in the Cp data. The Cp data at low T suggest a significant contribution from AFM spin waves moving in three dimensions and the absence of a spin-wave gap. A detailed analysis of the NMR spectra indicates commensurate magnetic order between 10K and 30K and a possible incommensurate modulation and/or spin canting below 10K. The commensurate order is consistent with microscopic simulations that yield a collinear Neel-type AFM spin arrangement both within and between the ladders, despite the presence of multiple weak interactions frustrating this magnetic structure. Frustration for AFM ordering and 1D spatial anisotropy of the 3D spin interactions are manifested in the frustration ratio f=|{\theta}CW|/TN=2.6, indicating a suppression of TN from 68K in the absence of these effects to 30K in BiMn2PO6., Comment: 20 pages, 19 figures, 3 tables, 61 references; submitted to Phys. Rev. B

We report studies of CaCo{1.86}As2 single crystals. The electronic structure is probed by angle-resolved photoemission spectroscopy (ARPES) measurements of CaCo{1.86}As2 and by full-potential linearized augmented-plane-wave calculations for the supercell Ca8Co15As16 (CaCo{1.88}As2). Our XRD crystal structure refinement is consistent with the previous combined refinement of x-ray and neutron powder diffraction data showing a collapsed-tetragonal ThCr2Si2-type structure with 7(1)% vacancies on the Co sites corresponding to the composition CaCo{1.86}As2 [D. G. Quirinale et al., Phys. Rev. B 88, 174420 (2013)]. The anisotropic magnetic susceptibility chi(T) data are consistent with the magnetic neutron diffraction data of Quirianale et al. that demonstrate the presence of A-type collinear antiferromagnetic order below the Neel temperature TN = 52(1) K with the easy axis being the tetragonal c axis. However, no clear evidence from the resistivity rho(T) and heat capacity Cp(T) data for a magnetic transition at TN is observed. A metallic ground state is demonstrated from band calculations and the rho(T), Cp(T) and ARPES data, and spin-polarized calculations indicate a competition between the A-type AFM and FM ground states. The Cp(T) data exhibit a large Sommerfield electronic coefficient reflecting a large density of states at the Fermi energy D(EF), consistent with the band structure calculations which also indicate a large D(EF) arising from Co 3d bands. At 1.8 K the M(H) data for H|| c exhibit a well-defined first-order spin-flop transition at an applied field of 3.5 T. The small ordered moment of 0.3 muB/Co obtained from the M(H) data at low T, the large exchange enhancement of chi and the lack of a self-consistent interpretation of the chi(T) and M(H,T) data in terms of a local moment Heisenberg model together indicate that the magnetism of CaCo{1.86}As2 is itinerant., Comment: 18 pages, 15 figures, 4 tables, 61 references; v2: extended the fits of experimental data by additional electronic structure calculations; published version

The physical properties of self-flux grown EuPd2As2 single crystals have been investigated by magnetization M, magnetic susceptibility chi, specific heat Cp, and electrical resistivity rho measurements versus temperature T and magnetic field H. The crystal structure was determined by powder x-ray diffraction measurements, which confirmed the ThCr2Si2-type body-centered tetragonal structure (space group I4/mmm) reported previously. The rho(T) data indicate that state of EuPd2As2 is metallic. Long-range antiferromagnetic (AFM) ordering is apparent from the chi(T), Cp(T), and rho(T) measurements. For H \parallel c the chi(T) indicates two transitions at TN1 = 11.0 K and TN2 = 5.5 K, whereas for H \perp c only one transition is observed at TN1 = 11.0 K. Between TN1 and TN2 the anisotropic chi(T) data suggest a planar noncollinear AFM structure, whereas at T < TN2 the chi(T) and M(H,T) data suggest a spin reorientation transition in which equal numbers of spins cant in opposite directions out of the ab plane. We estimate the critical field at 2 K at which all Eu moments become aligned with the field to be about 22 T. The magnetic entropy at 25 K estimated from the Cp(T) measurements is about $11\%$ smaller than expected, possibly due to an inaccuracy in the lattice heat capacity contribution. An upturn in rho at T < TN1 suggests superzone energy gap formation below TN1. This behavior of rho(T < TN1) is not sensitive to applied magnetic fields up to H = 12 T., Comment: 11 pages, 10 figures, 2 tables and 52 references; To appear in J. Phys.: Condens. Matter

Motivated by recent experiments on low-dimensional frustrated quantum magnets with competing nearest-neighbor exchange coupling J1 and next nearest-neighbor exchange coupling J2 we investigate the magnetic susceptibility of two-dimensional J1-J2 Heisenberg models with arbitrary spin quantum number s. We use exact diagonalization and high-temperature expansion up to order 10 to analyze the influence of the frustration strength J2/J1 and the spin quantum number s on the position and the height of the maximum of the susceptibility. The derived theoretical data can be used to get information on the ratio J2/J1 by comparing with susceptibility measurements on corresponding magnetic compounds., Comment: paper presented at the 'XVII. International Conference on Recent Progress in Many-Body Theories', Rostock Sept 2013, accepted for publication in J. Phys. Conf. Ser

The magnetic structure and metal-insulator transition in antiferromagnetic (AFM) BaMn2As2 and Ba1-xKxMn2As2 single crystals have been investigated by 55Mn and 75As nuclear magnetic resonance (NMR) measurements. In the parent AFM insulator BaMn2As2 with a Neel temperature TN = 625 K, we observed a 55Mn zero-field NMR (ZFNMR) spectrum and confirmed the G-type AFM structure from the field dependence of the 55Mn spectra and 75As-NMR spectra below TN. In hole-doped crystals with x > 0.01, similar 55Mn ZFNMR spectra were observed and the AFM state was revealed to be robust up to x = 0.4 with the ordered moment nearly independent of x. The nuclear spin-lattice relaxation rates (1/T1) for both nuclei in the doped samples follow the Korringa relation T1T = const., indicating a metallic state. This confirms the coexistence of AFM ordered localized Mn spins and conduction carriers from a microscopic point of view. From the x-dependence of (T1T)^(-1/2) for both nuclei, we conclude that this transition is caused by vanishing of the hole concentration as the transition is approached from the metallic side., Comment: 5 pages, 4 figures, submitted to Phys. Rev. B

Neutron and x-ray diffraction measurements are presented for powders and single crystals of CaCo{1.86}As2. The crystal structure is a collapsed-tetragonal ThCr2Si2-type structure as previously reported, but with 7(1)% vacancies on the Co sites corresponding to the composition CaCo{1.86(2)}As2. The thermal expansion coefficients for both the a- and c-axes are positive from 10 to 300 K. Neutron diffraction measurements on single crystals demonstrate the onset of A-type collinear antiferromagnetic order below the Neel temperature TN = 52(1) K with the ordered moments directed along the tetragonal c-axis, aligned ferromagnetically in the ab-plane and antiferromagnetically stacked along the c-axis., Comment: 8 pages, 5 figures, 2 tables; submitted to Phys. Rev. B

Nuclear magnetic resonance (NMR), neutron diffaction (ND), x-ray diffraction, magnetic susceptibility and specific heat measurements on the frustrated A-site spinel CoAl2O4 compound reveal a collinear antiferromagnetic ordering below Tn = 9.8(2) K. A high quality powder sample characterized by x-ray diffraction that indicates a relatively low Co-Al inversion parameter x = 0.057(20) in (Co1-xAlx)[Al2-xCox]O4, shows a broad maximum around 15 K in magnetic susceptibility and a sharp peak at Tn in heat capacity. The average ordered magnetic moment of Co^2+ (S = 3/2) ions at the A-site is estimated to be 2.4(1) Bohr magneton from NMR and 1.9(5) Bohr magneton from ND which are smaller than the expected value of 3 Bohr magneton for S = 3/2 and g = 2. Antiferromagnetic spin uctuations and correlations in the paramagnetic state are revealed from the magnetic susceptibility, NMR and ND measurements, which are due to spin frustration and site inversion effects in the system. The ND data also show short-range dynamic magnetic ordering that persists to a temperature that is almost twice Tn., Comment: 13 pages, 18 figures, 2 tables, submitted to Phys. Rev. B

The number of so-called invisible states which need to be added to the q-state Potts model to transmute its phase transition from continuous to first order has attracted recent attention. In the q=2 case, a Bragg-Williams, mean-field approach necessitates four such invisible states while a 3-regular, random-graph formalism requires seventeen. In both of these cases, the changeover from second- to first-order behaviour induced by the invisible states is identified through the tricritical point of an equivalent Blume-Emery-Griffiths model. Here we investigate the generalised Potts model on a Bethe lattice with z neighbours. We show that, in the q=2 case, r_c(z)=[4 z / 3(z-1)] [(z-1)/(z-2)]^z invisible states are required to manifest the equivalent Blume-Emery-Griffiths tricriticality. When z=3, the 3-regular, random-graph result is recovered, while the infinite z limit delivers the Bragg-Williams, mean-field result.

Magnetization, nuclear magnetic resonance, high-resolution x-ray diffraction and magnetic field-dependent neutron diffraction measurements reveal a novel magnetic ground state of Ba{0.60}K{0.40}Mn2As2 in which itinerant ferromagnetism (FM) below a Curie temperature TC = 100 K arising from the doped conduction holes coexists with collinear antiferromagnetism (AFM) of the Mn local moments that order below a Neel temperature TN = 480 K. The FM ordered moments are aligned in the tetragonal ab-plane and are orthogonal to the AFM-ordered Mn moments that are aligned along the c-axis. The magnitude and nature of the low-T FM ordered moment correspond to complete polarization of the doped-hole spins (half-metallic itinerant FM) as deduced from magnetization and ab-plane electrical resistivity measurements., Comment: 6 pages, 6 figures, including Supplemental Material; v2: minor revisions, published version

Inelastic neutron scattering measurements of paramagnetic SrCo$_{2}$As$_{2}$ at T=5 K reveal antiferromagnetic (AFM) spin fluctuations that are peaked at a wavevector of $\textbf{Q}_{\mathrm{AFM}}=(1/2,1/2,1)$ and possess a large energy scale. These stripe spin fluctuations are similar to those found in $A$Fe$_{2}$As$_{2}$ compounds, where spin-density wave AFM is driven by Fermi surface nesting between electron and hole pockets separated by $\textbf{Q}_{\mathrm{AFM}}$. SrCo$_{2}$As$_{2}$ has a more complex Fermi surface and band structure calculations indicate a potential instability towards either a ferromagnetic or stripe AFM ground state. The results suggest that stripe AFM magnetism is a general feature of both iron and cobalt-based arsenides and the search for spin fluctuation-induced unconventional superconductivity should be expanded to include cobalt-based compounds., Comment: This is a companion paper to arXiv:1306.5222 with journal reference Phys. Rev. B 88, 014526 (2013)

In tetragonal SrCo2As2 single crystals, inelastic neutron scattering measurements demonstrated that strong stripe-type antiferromagnetic (AFM) correlations occur at a temperature T = 5 K [W. Jayasekara et al., arXiv:1306.5174] that are the same as in the isostructural AFe2As2 (A = Ca, Sr, Ba) parent compounds of high-Tc superconductors. This surprising discovery suggests that SrCo2As2 may also be a good parent compound for high-Tc superconductivity. Here, structural and thermal expansion, electrical resistivity rho, angle-resolved photoemission spectroscopy (ARPES), heat capacity Cp, magnetic susceptibility chi, 75As NMR and neutron diffraction measurements of SrCo2As2 crystals are reported together with LDA band structure calculations that shed further light on this fascinating material. The c-axis thermal expansion coefficient alpha_c is negative from 7 to 300 K, whereas alpha_a is positive over this T range. The rho(T) shows metallic character. The ARPES measurements and band theory confirm the metallic character and in addition show the presence of a flat band near the Fermi energy E_F. The band calculations exhibit an extremely sharp peak in the density of states D(E_F) arising from a flat d_{x^2 - y^2} band. A comparison of the Sommerfeld coefficient of the electronic specific heat with chi(T = 0) suggests the presence of strong ferromagnetic itinerant spin correlations which on the basis of the Stoner criterion predicts that SrCo2As2 should be an itinerant ferromagnet, in conflict with the magnetization data. The chi(T) does have a large magnitude, but also exhibits a broad maximum at 115 K suggestive of dynamic short-range AFM spin correlations, in agreement with the neutron scattering data. The measurements show no evidence for any type of phase transition between 1.3 and 300 K and we propose that metallic SrCo2As2 has a gapless quantum spin-liquid ground state., Comment: 24 pages, 18 figures, 4 tables, 97 references; v2: updated Ref. 23 and corrected several typos; v3: minor revisions, published version. This is a companion paper to arXiv:1306.5174

We use angle-resolved photoemission spectroscopy and full-potential linearized augmented-plane-wave (FP-LAPW) calculations to study the electronic structure of BaCo2As2. The Fermi surface (FS) maps and the corresponding band dispersion data (at 90 K and 200 K) reveal a small electron pocket at the center and a large electron pocket at the corner of the Brillouin zone. Therefore the nesting between electron and hole FS pockets is absent in this compound, in contrast to the parent compounds of FeAs-based high-T_c superconductors. The electronic structure at about 500 meV binding energy is very similar to features at the chemical potential in BaFe2As2. This indicates that complete substitution of Co for Fe causes a nearly rigid shift in the Fermi energy by adding two electrons per formula unit without significant changes in the band dispersions. The experimental FS topology as well as band dispersion data are in reasonable agreement with the FP-LAPW calculations., Comment: 13 pages, 6 figures

The synthesis and crystallography, magnetic susceptibility chi, magnetization M, specific heat Cp, in-plane electrical resistivity rho and in-plane magnetic penetration depth measurements are reported for single crystals of APd2As2 (A = Ca, Sr, Ba) versus temperature T and magnetic field H. The crystals were grown using PdAs self-flux. CaPd2As2 and SrPd2As2 crystallize in a collapsed body-centered tetragonal ThCr2Si2-type structure (I4/mmm), whereas BaPd2As2 crystallizes in the primitive tetragonal CeMg2Si2-type structure (P4/mmm), in agreement with literature data. The rho(T) data exhibit metallic behavior for all three compounds. Bulk superconductivity is reported for CaPd2As2 and SrPd2As2 below Tc = 1.27 and 0.92 K, respectively, whereas only a trace of superconductivity is found in BaPd2As2. No other phase transitions were observed. The chi(T) and M(H) data reveal anisotropic diamagnetism in the normal state, with chi_c > chi_ab for CaPd2As2 and BaPd2As2, and chi_c < chi_ab for SrPd2As2. The normal and superconducting state data indicate that CaPd2As2 and SrPd2As2 are conventional type-II nodeless s-wave electron-phonon superconductors. The electronic superconducting-state heat capacity data for CaPd2As2, which has an extremely sharp heat capacity jump at Tc, are analyzed using our recent elaboration of the alpha-model of the BCS theory of superconductivity, which indicates that the s-wave gap in this compound is anisotropic in momentum space., Comment: 25 two-column typeset pages, 21 figures, 8 tables, 81 references; v2: minor changes, published version

The single-band alpha-model of superconductivity [H. Padamsee, et al., J. Low Temp. Phys. {\bf 12}, 387 (1973)] is a popular model that was adapted from the single-band Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity mainly to allow fits to electronic heat capacity versus temperature T data that deviate from the BCS prediction. The model assumes that the normalized superconducting order parameter Delta(T)/Delta(0) and therefore the normalized London penetration depth lambda_L(T)/lambda_L(0) are the same as in BCS theory, calculated using the BCS value alpha_BCS = 1.764 of alpha = Delta(0)/(kB Tc), where kB is Boltzmann's constant and Tc is the superconducting transition temperature. On the other hand, to calculate the electronic free energy, entropy, heat capacity and thermodynamic critical field versus T, the alpha-model takes alpha to be an adjustable parameter. Here we write the BCS equations and limiting behaviors for the superconducting state thermodynamic properties explicitly in terms of alpha, as needed for calculations within the alpha-model, and present plots of the results versus T and alpha that are compared with the respective BCS predictions. Mechanisms such as gap anisotropy and strong coupling that can cause deviations of the thermodynamics from the BCS predictions, especially the heat capacity jump at Tc, are considered. Extensions of the alpha-model that have appeared in the literature such as the two-band model are also discussed. Tables of values of Delta(T)/Delta(0) and lambda_L(T)/lambda_L(0) calculated from the BCS theory using alpha = alpha_BCS are provided, which are the same in the alpha-model by assumption. Tables of values of the entropy, heat capacity and thermodynamic critical field versus T for seven values of alpha including alpha_BCS are also presented., Comment: 19 two-column pages, 9 figures, 7 tables

BaMn2As2 is a local-moment antiferromagnetic insulator with a N\'eel temperature of 625 K and a large ordered moment of 3.9 Bohr magneton per Mn. Remarkably, this compound can be driven metallic by the substitution of as little as 1.6% K for Ba while retaining essentially the same ordered magnetic moment and N\'eel temperature, as previously reported. Here, using both powder and single crystal neutron diffraction we show that the local moment antiferromagnetic order in Ba(1-x)KxMn2As2 remains robust up to x = 0.4. The ordered moment is nearly independent of x for 0 < x < 0.4 and the N\'eel transition temperature decreases to 480 K at x = 0.4., Comment: 5 pages, 5 figures

The order of a phase transition is usually determined by the nature of the symmetry breaking at the phase transition point and the dimension of the model under consideration. For instance, q-state Potts models in two dimensions display a second order, continuous transition for q = 2,3,4 and first order for higher q. Tamura et al recently introduced Potts models with "invisible" states which contribute to the entropy but not the internal energy and noted that adding such invisible states could transmute continuous transitions into first order transitions. This was observed both in a Bragg-Williams type mean-field calculation and 2D Monte-Carlo simulations. It was suggested that the invisible state mechanism for transmuting the order of a transition might play a role where transition orders inconsistent with the usual scheme had been observed. In this paper we note that an alternative mean-field approach employing 3-regular random ("thin") graphs also displays this change in the order of the transition as the number of invisible states is varied, although the number of states required to effect the transmutation, 17 invisible states when there are 2 visible states, is much higher than in the Bragg-Williams case. The calculation proceeds by using the equivalence of the Potts model with 2 visible and r invisible states to the Blume-Emery-Griffiths (BEG) model, so a by-product is the solution of the BEG model on thin random graphs., Comment: (2) Minor typos corrected, references updated

We study a class of arrangements of lines with multiplicities on the plane which admit the Chalykh-Veselov Baker-Akhiezer function. These arrangements are obtained by adding multiplicity one lines in an invariant way to any dihedral arrangement with invariant multiplicities. We describe all the Baker-Akhiezer arrangements when at most one line has multiplicity higher than 1. We study associated algebras of quasi-invariants which are isomorphic to the commutative algebras of quantum integrals for the generalized Calogero-Moser operators. We compute the Hilbert series of these algebras and we conclude that the algebras are Gorenstein. We also show that there are no other arrangements with Gorenstein algebras of quasi-invariants when at most one line has multiplicity bigger than 1., Comment: 38 pages

The synthesis and crystallographic and physical properties of polycrystalline EuNiGe3 are reported. EuNiGe3 crystallizes in the noncentrosymmetric body-centered tetragonal BaNiSn3-type structure. The physical property data consistently demonstrate that this is a metallic system in which Eu spins S = 7/2 order antiferromagnetically at a temperature TN = 13.6 K. Magnetic susceptibility chi data for T > TN indicate that the Eu atoms have spin 7/2 with g = 2, that the Ni atoms are nonmagnetic, and that the dominant interactions between the Eu spins are ferromagnetic. Thus we propose that EuNiGe3 has a collinear A-type antiferromagnetic structure. A fit of chi(T < TN) by our molecular field theory is consistent with a collinear magnetic structure. Electrical resistivity rho data from TN to 350 K are fitted by the Bloch-Gruneisen model for electron-phonon scattering, yielding a Debye temperature of 265(2) K. A strong decrease in rho occurs below TN due to loss of spin-disorder scattering. Heat capacity data at 25 K < T < 300 K are fitted by the Debye model, yielding the same Debye temperature 268(2) K as found from rho(T). The extracted magnetic heat capacity is consistent with S = 7/2. The magnetic entropy at TN = 13.6 K is 83% of the expected asymptotic high-T value, with the remainder recovered by 30 K., Comment: 10 pages, 7 figures; submitted to Phys. Rev. B

We investigate the partially asymmetric exclusion process (PASEP) with open boundaries when the reverse hopping rate of particles q=-1, using a representation of the PASEP algebra related to the al-Salam Chihara polynomials. When q=-1 the representation is two-dimensional, which allows for straightforward calculation of the normalization, current and density. We note that these quantities behave in an a priori reasonable manner in spite of the apparently unphysical value of q as the input, alpha, and output, beta, rates are varied over the physical range of 0 to 1. As is well known, another two dimensional representation exists when 0

We present the structural, magnetic, thermal and ab-plane electronic transport properties of single crystals of CaCu1.7As2 grown by the self-flux technique that were investigated by powder x-ray diffraction, magnetic susceptibility chi, isothermal magnetization M, specific heat Cp, and electrical resistivity rho measurements as a function of temperature T and magnetic field H. X-ray diffraction analysis of crushed crystals at room temperature confirm the collapsed tetragonal ThCr2Si2-type structure with \sim 15% vacancies on the Cu sites as previously reported, corresponding to the composition CaCu1.7As2. The chi(T) data are diamagnetic, anisotropic and nearly independent of T. The chi is larger in the ab-plane than along the c-axis, as also observed previously for SrCu2As2 and for pure and doped BaFe2As2. The Cp(T) and rho(T) data indicate metallic sp-band character. In contrast to the chi(T) and Cp(T) data that do not show any evidence for phase transitions below 300 K, the rho(T) data exhibit a sharp increase in slope on cooling below a temperature Tt = 54-56 K, depending on the crystal. The \rho(T) data show no hysteresis on warming and cooling through Tt and the transition appears to be second order. The phase transition may arise from spatial ordering of the vacancies on the Cu sublattice. The Tt is found to be independent of H for H \leq 8 T. A positive magnetoresistance is observed below Tt that increases with decreasing T and attains a value in H = 8.0 T of 8.7% at T = 1.8 K., Comment: 9 pages, 7 figures, 4 tables, 38 references; v2: Added discussion of Fe vacancies in AFe2Se2 compounds. Added new resistivity data for CaCu1.7As2 and new discussion of them; v3: minor changes, published version

A 3D Ising model with a purely plaquette, 4-spin interaction displays a planar flip symmetry intermediate between a global and a gauge symmetry and as a consequence has a highly degenerate low temperature phase and no standard magnetic order parameter. This plaquette Hamiltonian is a particular case of a family of 3D Gonihedric Ising models defined by Savvidy and Wegner. An anisotropic variant of the the purely plaquette Gonihedric model, originally discussed as the "Fuki-Nuke" model by Suzuki, is non-trivially equivalent to a stack of 2D Ising models, each of which can magnetize independently at the phase transition point. Consideration of this anisotropic model suggests that a suitable order parameter in the isotropic case may also be constructed using a form of planar magnetization, in which nearest neighbour correlators summed over planes replace a sum over spin values. We conduct Monte-Carlo simulations to investigate this and related candidate order parameters in a toy model of Gonihedric ground states, the Fuki-Nuke model and the isotropic plaquette Gonihedric model itself.

Predictions of the anisotropic magnetic susceptibility chi below the antiferromagnetic (AFM) ordering temperatures TN of local moment Heisenberg AFMs have been made previously using molecular field theory (MFT) but are very limited in their applicability. Here a MFT calculation of chi(T<=TN) is presented for a wide variety of collinear and noncollinear Heisenberg AFMs containing identical crystallographically equivalent spins without recourse to magnetic sublattices. The results are expressed in terms of directly measurable experimental parameters and are fitted with no adjustable parameters to experimental chi(T<=TN) data from the literature for several collinear and noncollinear AFMs. The influence of spin correlations and fluctuations beyond MFT is quantified by the deviation of the theory from the data. The origin of the universal chi(T<=TN) observed for triangular lattice AFMs exhibiting coplanar noncollinear 120 degree AFM ordering is clarified., Comment: 5 pages, 5 figures

The Fermi surfaces (FS's) and band dispersions of EuRh2As2 have been investigated using angle-resolved photoemission spectroscopy. The results in the high-temperature paramagnetic state are in good agreement with the full potential linearized augmented plane wave calculations, especially in the context of the shape of the two-dimensional FS's and band dispersion around the Gamma (0,0) and X (pi,pi) points. Interesting changes in band folding are predicted by the theoretical calculations below the magnetic transition temperature Tn=47K. However, by comparing the FS's measured at 60K and 40K, we did not observe any signature of this transition at the Fermi energy indicating a very weak coupling of the electrons to the ordered magnetic moments or strong fluctuations. Furthermore, the FS does not change across the temperature (~ 25K) where changes are observed in the Hall coefficient. Notably, the Fermi surface deviates drastically from the usual FS of the superconducting iron-based AFe2As2 parent compounds, including the absence of nesting between the Gamma and X FS pockets., Comment: 4 pages, 4 figures

We report the growth of single crystals of SrCu2As2, SrCu2Sb2, SrCu2(As{0.84}Sb{0.16})2 and BaCu2Sb2 using the self-flux technique and their structural, magnetic, thermal and transport properties that were investigated by powder x-ray diffraction (XRD), magnetic susceptibility chi, specific heat Cp and electrical resistivity rho measurements versus temperature T from 1.8 to 350 K. Rietveld refinements of XRD patterns for crushed crystals confirm that SrCu2As2 crystallizes in the ThCr2Si2-type structure and SrCu2Sb2 crystallizes in the CaBe2Ge2-type structure. However, BaCu2Sb2 is found to have a large unit cell consisting of three blocks. Here a ThCr2Si2-type block is sandwiched between two CaBe2Ge2-type blocks along the c-axis, as reported, but likely with a monoclinic distortion. The chi data of all these compounds are diamagnetic and reveal nearly T-independent anisotropic behavior. The finite values of the Sommerfeld linear specific heat coefficients gamma and the T dependences of rho reveal metallic character of all four compounds. The electronic and magnetic properties indicate that these compounds are sp metals with Cu in the 3d^{10} electronic configuration corresponding to the oxidation state Cu^{+1}, as previously predicted theoretically for (Sr,Ba)Cu2As2 by D. J. Singh. We find that SrCu2As2 has a collapsed-tetragonal structure. The electronic character of the Cu and the strength of the As-As interlayer bonding are both expected to drastically change between weakly Cu-substituted BaFe2As and pure BaCu2As2., Comment: 26 pages, 23 figures, 8 tables, 105 references; v2: substantially expanded the discussion about collapsed tetragonal phases and transition metal doping of BaFe2As2. Submitted to PRB

Polycrystalline samples of LaNi2(Ge{1-x}P{x})2 (x = 0, 0.25, 0.50, 0.75, 1) were synthesized and their properties investigated by x-ray diffraction (XRD), heat capacity Cp, magnetic susceptibility chi, and electrical resistivity rho measurements versus temperature T. These compounds all crystallize in the body-centered-tetragonal ThCr2Si2-type structure. The rho(T) measurements indicate that all compositions in this system are metallic. The low-T Cp measurements yield a rather large Sommerfeld coefficient gamma = 12.4(2) mJ/mol K^2 for x = 0 reflecting a large density of states at the Fermi energy that is comparable with the largest values found for the AFe2As2 class of materials with the same crystal structure. The gamma decreases approximately linearly with x to 7.4(1) mJ/mol K^2 for x = 1. The chi measurements show nearly temperature-independent paramagnetic behavior across the entire range of compositions except for LaNi2Ge2, where a broad peak is observed at 300 K from chi(T) measurements up to 1000 K that may arise from short-range antiferromagnetic correlations in a quasi-two-dimensional magnetic system. High-accuracy Pade approximants representing the Debye lattice heat capacity and Bloch-Gruneisen electron-phonon resistivity functions versus T are presented and are used to analyze our experimental Cp(T) and rho(T) data, respectively. The T-dependences of rho for all samples are well-described by the Bloch-Gruneisen model, although the observed rho(300 K) values are larger than calculated from this model. A significant T-dependence of the Debye temperature determined from the Cp(T) data was observed for each composition. No clear evidence for bulk superconductivity or any other long-range phase transition was found for any of the compositions studied., Comment: 21 pages, 22 figures, 7 tables; v2: minor revisions, published version

The compound BaMn2As2 with the tetragonal ThCr2Si2 structure is a local-moment antiferromagnetic insulator with a Neel temperature TN = 625 K and a large ordered moment mu = 3.9 mu_B/Mn. We demonstrate that this compound can be driven metallic by partial substitution of Ba by K, while retaining the same crystal and antiferromagnetic structures together with nearly the same high TN and large mu. Ba_{1-x}K_xMn2As2 is thus the first metallic ThCr2Si2-type MAs-based system containing local 3d transition metal M magnetic moments, with consequences for the ongoing debate about the local moment versus itinerant pictures of the FeAs-based superconductors and parent compounds. The Ba_{1-x}K_xMn2As2 class of compounds also forms a bridge between the layered iron pnictides and cuprates and may be useful to test theories of high Tc superconductivity., Comment: 5 two-column typeset pages, 5 figures, 20 references; v2: minor revisions, 4 new references, published version

The study of intracluster light can help us to understand the mechanisms taking place in galaxy clusters, and to place constraints on the cluster formation history and physical properties. However, owing to the intrinsic faintness of ICL emission, most searches and detailed studies of ICL have been limited to redshifts z<0.4.We search for ICL in a subsample of ten clusters detected by the ESO Distant Cluster Survey (EDisCS), at redshifts 0.4

We note that two formulations of dual gonihedric Ising models in 3d, one based on using Wegner's general framework for duality to construct a dual Hamiltonian for codimension one surfaces, the other on constructing a dual Hamiltonian for two-dimensional surfaces, are related by a variant of the standard decoration/iteration transformation. The dual Hamiltonian for two-dimensional surfaces contains a mixture of link and vertex spins and as a consequence possesses a gauge invariance which is inherited by the codimension one surface Hamiltonian. This gauge invariance ensures the latter is equivalent to a third formulation, an anisotropic Ashkin-Teller model. We describe the equivalences in detail and discuss some Monte-Carlo simulations which support these observations.

The gonihedric Ising Hamiltonians defined in three and higher dimensions by Savvidy and Wegner provide an extensive, and little explored, catalogue of spin models on (hyper)cubic lattices with many interesting features. In three dimensions the kappa=0 gonihedric Ising model on a cubic lattice has been shown to possess a degenerate low-temperature phase and a first order phase transition, as well as interesting dynamical properties. The dual Hamiltonian to this may be written as an anisotropic Ashkin-Teller model and also has a degenerate low-temperature phase as a result of similar symmetries to the original plaquette action. It is possible to write an alternative dual formulation which utilizes three flavours of spins, rather than the two of the Ashkin-Teller model. This still possesses anisotropic couplings, but all the interaction terms are now four spin couplings and it acquires an additional, local gauge symmetry. We investigate this alternative dual Hamiltonian using zero temperature and mean-field methods together with Monte-Carlo simulations and discuss its properties and the relation to the Ashkin-Teller variant.

BaMn2As2 is unique among BaT2As2 compounds crystallizing in the body-centered-tetragonal ThCr2Si2 structure, which contain stacked square lattices of 3d transition metal T atoms, since it has an insulating large-moment (3.9 muB/Mn) G-type (checkerboard) antiferromagnetic AF ground state. We report measurements of the anisotropic magnetic susceptibility chi versus temperature T from 300 to 1000 K of single crystals of BaMn2As2, and magnetic inelastic neutron scattering measurements at 8 K and 75As NMR measurements from 4 to 300 K of polycrystalline samples. The Neel temperature determined from the chi(T) measurements is TN = 618(3) K. The measurements are analyzed using the J1-J2-Jc Heisenberg model. Linear spin wave theory for G-type AF ordering and classical and quantum Monte Carlo simulations and molecular field theory calculations of chi(T) and of the magnetic heat capacity Cmag(T) are presented versus J1, J2 and Jc. We also obtain band theoretical estimates of the exchange couplings in BaMn2As2. From analyses of our chi(T), NMR, neutron scattering, and previously published heat capacity data for BaMn2As2 on the basis of the above theories for the J1-J2-Jc Heisenberg model and our band-theoretical results, our best estimates of the exchange constants in BaMn2As2 are J1 = 13 meV, J2/J1 = 0.3 and Jc/J1 = 0.1, which are all antiferromagnetic. From our classical Monte Carlo simulations of the G-type AF ordering transition, these exchange parameters predict TN = 640 K for spin S = 5/2, in close agreement with experiment. Using spin wave theory, we also utilize these exchange constants to estimate the suppression of the ordered moment due to quantum fluctuations for comparison with the observed value and again obtain S = 5/2 for the Mn spin., Comment: 48 pages, 33 figures, 11 tables, 86 references; v2: Added discussion to introduction, additional classical Monte Carlo data added; published version

We present ACS, NICMOS, and Keck AO-assisted photometry of 20 Type Ia supernovae SNe Ia from the HST Cluster Supernova Survey. The SNe Ia were discovered over the redshift interval 0.623 < z < 1.415. Fourteen of these SNe Ia pass our strict selection cuts and are used in combination with the world's sample of SNe Ia to derive the best current constraints on dark energy. Ten of our new SNe Ia are beyond redshift $z=1$, thereby nearly doubling the statistical weight of HST-discovered SNe Ia beyond this redshift. Our detailed analysis corrects for the recently identified correlation between SN Ia luminosity and host galaxy mass and corrects the NICMOS zeropoint at the count rates appropriate for very distant SNe Ia. Adding these supernovae improves the best combined constraint on the dark energy density \rho_{DE}(z) at redshifts 1.0 < z < 1.6 by 18% (including systematic errors). For a LambdaCDM universe, we find \Omega_\Lambda = 0.724 +0.015/-0.016 (68% CL including systematic errors). For a flat wCDM model, we measure a constant dark energy equation-of-state parameter w = -0.985 +0.071/-0.077 (68% CL). Curvature is constrained to ~0.7% in the owCDM model and to ~2% in a model in which dark energy is allowed to vary with parameters w_0 and w_a. Tightening further the constraints on the time evolution of dark energy will require several improvements, including high-quality multi-passband photometry of a sample of several dozen z>1 SNe Ia. We describe how such a sample could be efficiently obtained by targeting cluster fields with WFC3 on HST., Comment: 27 pages, 11 figures. Submitted to ApJ. This first posting includes updates in response to comments from the referee. See http://www.supernova.lbl.gov for other papers in the series pertaining to the HST Cluster SN Survey. The updated supernova Union2.1 compilation of 580 SNe is available at http://supernova.lbl.gov/Union

We measure the top quark mass (mt) in ppbar collisions at a center of mass energy of 1.96 TeV using dilepton ttbar->W+bW-bbar->l+nubl-nubarbbar events, where l denotes an electron, a muon, or a tau that decays leptonically. The data correspond to an integrated luminosity of 5.4 fb-1 collected with the D0 detector at the Fermilab Tevatron Collider. We obtain mt = 174.0 +- 1.8(stat) +- 2.4(syst) GeV, which is in agreement with the current world average mt = 173.3 +- 1.1 GeV. This is currently the most precise measurement of mt in the dilepton channel., Comment: 7 pages, 4 figures

Crystal structure, electronic structure, and magnetic behavior of the spin-1/2 quantum magnet Na1.5VOPO4F0.5 are reported. The disorder of Na atoms leads to a sequence of structural phase transitions revealed by synchrotron x-ray powder diffraction and electron diffraction. The high-temperature second-order alpha <--> beta transition at 500 K is of the order-disorder type, whereas the low-temperature beta <--> gamma+gamma' transition around 250 K is of the first order and leads to a phase separation toward the polymorphs with long-range (gamma) and short-range (gamma') order of Na. Despite the complex structural changes, the magnetic behavior of Na1.5VOPO4F0.5 probed by magnetic susceptibility, heat capacity, and electron spin resonance measurements is well described by the regular frustrated square lattice model of the high-temperature alpha-polymorph. The averaged nearest-neighbor and next-nearest-neighbor couplings are J1 ~ -3.7 K and J2 ~ 6.6 K, respectively. Nuclear magnetic resonance further reveals the long-range ordering below TN = 2.6 K in low magnetic fields. Although the experimental data are consistent with the simplified square-lattice description, band structure calculations suggest that the ordering of Na atoms introduces a large number of inequivalent exchange couplings that split the square lattice into plaquettes. Additionally, the direct connection between the vanadium polyhedra induces an unusually strong interlayer coupling having effect on the transition entropy and the transition anomaly in the specific heat. Peculiar features of the low-temperature crystal structure and the relation to isostructural materials suggest Na1.5VOPO4F0.5 as a parent compound for the experimental study of tetramerized square lattices as well as frustrated square lattices with different values of spin., Comment: 18 pages, 22 figures, 7 tables + supplementary information and cif files

We investigate the dual of the kappa=0 Gonihedric Ising model on a 3D cubic lattice, which may be written as an anisotropically coupled Ashkin-Teller model. The original kappa=0 Gonihedric model has a purely plaquette interaction, displays a first order transition and possesses a highly degenerate ground state. We find that the dual model admits a similar large ground state degeneracy as a result of the anisotropic couplings and investigate the coupled mean field equations for the model on a single cube. We also carry out Monte Carlo simulations which confirm a first order phase transition in the model and suggest that the ground state degeneracy persists throughout the low temperature phase. Some exploratory cooling simulations also hint at non-trivial dynamical behaviour., Comment: 17 pages, 12 figures

Reducing the scatter between cluster mass and optical richness is a key goal for cluster cosmology from photometric catalogs. We consider various modifications to the red-sequence matched filter richness estimator of Rozo et al. (2009), and evaluate their impact on the scatter in X-ray luminosity at fixed richness. Most significantly, we find that deeper luminosity cuts can reduce the recovered scatter, finding that sigma_lnLX|lambda=0.63+/-0.02 for clusters with M_500c >~ 1.6e14 h_70^-1 M_sun. The corresponding scatter in mass at fixed richness is sigma_lnM|lambda ~ 0.2-0.3 depending on the richness, comparable to that for total X-ray luminosity. We find that including blue galaxies in the richness estimate increases the scatter, as does weighting galaxies by their optical luminosity. We further demonstrate that our richness estimator is very robust. Specifically, the filter employed when estimating richness can be calibrated directly from the data, without requiring a-priori calibrations of the red-sequence. We also demonstrate that the recovered richness is robust to up to 50% uncertainties in the galaxy background, as well as to the choice of photometric filter employed, so long as the filters span the 4000 A break of red-sequence galaxies. Consequently, our richness estimator can be used to compare richness estimates of different clusters, even if they do not share the same photometric data. Appendix 1 includes "easy-bake" instructions for implementing our optimal richness estimator, and we are releasing an implementation of the code that works with SDSS data, as well as an augmented maxBCG catalog with the lambda richness measured for each cluster., Comment: Submitted to ApJ. 20 pages in emulateapj format

The compounds BaMn2As2 and BaFe2As2 both crystallize in the body-centered-tetragonal ThCr2Si2-type (122-type) structure at room temperature but exhibit quite different unit cell volumes and very different magnetic and electronic transport properties. Evidently reflecting these disparities, we have discovered a large miscibility gap in the system Ba(Mn_xFe_{1-x})2As2. Rietveld refinements of powder x-ray diffraction (XRD) measurements on samples slow-cooled from 1000 C to room temperature (RT) reveal a two-phase mixture of BaMn2As2 and Ba(Mn_{0.12}Fe_{0.88})2As2 phases together with impurity phases for x = 0.2, 0.4, 0.5, 0.6 and 0.8. We infer that there exists a miscibility gap in this system at 300 K with composition limits 0.12 < x < 1. For samples quenched from 1000 C to 77 K, the refinements of RT XRD data indicate that the miscibility gap at RT narrows at 1000 C to 0.2 < x < 0.8. Samples with x=0.4, 0.5 and 0.6 quenched from 1100-1400 C to 77 K contain a single 122-type phase together with significant amounts of Fe_{1-x}Mn_xAs and FeAs2 impurity phases. These results indicate that the system is not a pseudo-binary system over the whole composition range and that the 122-type phase has a significant homogeneity range at these temperatures. Magnetic susceptibility, electrical resistivity and heat capacity measurements versus temperature of the single-phase quenched polycrystalline samples with x = 0.2 and 0.8 and for lightly doped BaMn2As2 crystals are reported., Comment: 14 pages, 16 figures, 3 tables; published version

We present a measurement of the helicity of the W boson produced in top quark decays using ttbar decays in the l+jets and dilepton final states selected from a sample of 5.4 fb^-1 of collisions recorded using the D0 detector at the Fermilab Tevatron ppbar collider. We measure the fractions of longitudinal and right-handed W bosons to be f_0 = 0.669 +- 0.102 [ +- 0.078 (stat.) +- 0.065 (syst.)] and f_+ = 0.023 +- 0.053 [+- 0.041 (stat.) +- 0.034 (syst.)], respectively. This result is consistent at the 98% level with the standard model. A measurement with f_0 fixed to the value from the standard model yields f_+ = 0.010 +- 0.037 [+- 0.022 (stat.) +- 0.030 (syst.) ]., Comment: To be submitted to Phys. Rev. D

We report the result of a search for the pair production of the lightest supersymmetric partner of the top quark ($\tilde{t}_1$) in $p\bar{p}$ collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider corresponding to an integrated luminosity of 5.4 fb$^{-1}$. The scalar top quarks are assumed to decay into a $b$ quark, a charged lepton, and a scalar neutrino ($\tilde{\nu}$), and the search is performed in the electron plus muon final state. No significant excess of events above the standard model prediction is detected, and improved exclusion limits at the 95% C.L. are set in the the ($M_{\tilde{t}_1}$,$M_{\tilde{\nu}}$) mass plane.

We extract the total width of the top quark, Gamma_t, from the partial decay width Gamma(t -> W b) measured using the t-channel cross section for single top quark production and from the branching fraction B(t -> W b) measured in ttbar events using up to 2.3 fb^-1 of integrated luminosity collected by the D0 Collaboration at the Tevatron ppbar Collider. The result is Gamma_t = 1.99 +0.69 -0.55 GeV, which translates to a top-quark lifetime of tau_t = (3.3 +1.3 -0.9) x 10^-25 s. Assuming a high mass fourth generation b' quark and unitarity of the four-generation quark-mixing matrix, we set the first upper limit on |Vtb'| < 0.63 at 95% C.L., Comment: submitted to Phys. Rev. Letters

As a contribution to the understanding of the dark energy concept, the Dark energy American French Team (DAFT, in French FADA) has started a large project to characterize statistically high redshift galaxy clusters, infer cosmological constraints from Weak Lensing Tomography, and understand biases relevant for constraining dark energy and cluster physics in future cluster and cosmological experiments. The purpose of this paper is to establish the basis of reference for the photo-z determination used in all our subsequent papers, including weak lensing tomography studies. This project is based on a sample of 91 high redshift (z>0.4), massive clusters with existing HST imaging, for which we are presently performing complementary multi-wavelength imaging. This allows us in particular to estimate spectral types and determine accurate photometric redshifts for galaxies along the lines of sight to the first ten clusters for which all the required data are available down to a limit of I_AB=24/24.5 with the LePhare software. The accuracy in redshift is of the order of 0.05 for the range 0.2

Single crystals of superconducting OsB_2 [T_c = 2.10(5) K] have been grown using a Cu-B eutectic flux. We confirm that OsB_2 crystallizes in the reported orthorhombic structure (space group Pmmn) at room temperature. Both the normal and superconducting state properties of the crystals are studied using various techniques. Heat capacity versus temperature C(T) measurements yield the normal state electronic specific heat coefficient \gamma = 1.95(1) mJ/mol K^2 and the Debye temperature \Theta_D = 539(2) K. The measured frequencies of Shubnikov-de Haas oscillations are in good agreement with those predicted by band structure calculations. Magnetic susceptibility \chi(T,H), electrical resistivity \rho(T) and C(T,H) measurements (H is the magnetic field) demonstrate that OsB_2 is a bulk low-\kappa [\kappa(T_c) = 2(1)] Type-II superconductor that is intermediate between the clean and dirty limits [\xi(T=0)/\ell = 0.97)] with a small upper critical magnetic field H_c2(T = 0) = 186(4) Oe. The penetration depth is \lambda(T = 0) = 0.300 \mu m. An anomalous (not single-gap BCS) T dependence of \lambda was fitted by a two-gap model with \Delta_1(T = 0)/k_BT_c = 1.9 and \Delta_2(T = 0)/k_BT_c = 1.25, respectively. The discontinuity in the heat capacity at T_c, \Delta C/\gamma T_c = 1.32, is smaller than the weak-coupling BCS value of 1.43, consistent with the two-gap nature of the superconductivity in OsB_2. An anomalous increase in \Delta C at T_c of unknown origin is found in finite H; e.g., \Delta C/\gamma T_c \approx 2.5 for H \approx 25 Oe., Comment: 15 pages, 18 figures, 4 tables

The application of information geometric ideas to statistical mechanics using a metric on the space of states, pioneered by Ruppeiner and Weinhold, has proved to be a useful alternative approach to characterizing phase transitions. Some puzzling anomalies become apparent, however, when these methods are applied to the study of black hole thermodynamics. A possible resolution was suggested by Quevedo et al. who emphasized the importance of Legendre invariance in thermodynamic metrics. They found physically consistent results for various black holes when using a Legendre invariant metric, which agreed with a direct determination of the properties of phase transitions from the specific heat. Recently, information geometric methods have been employed by Wei et al. to study the Kehagias-Sfetsos (KS) black hole in Horava-Lifshitz gravity. The formalism suggests that a coupling parameter in this theory plays a role analogous to the charge in Reissner-Nordstrom (RN) black holes or angular momentum in the Kerr black hole and calculation of the specific heat shows a singularity which may be interpreted as a phase transition. When the curvature of the Ruppeiner metric is calculated for such a theory it does not, however, show a singularity at the phase transition point. We show that the curvature of a particular Legendre invariant ("Quevedo") metric for the KS black hole is singular at the phase transition point. We contrast the results for the Ruppeiner, Weinhold and Quevedo metrics and in the latter case investigate the consistency of taking either the entropy or mass as the thermodynamic potential., Comment: v2: some references added

Polycrystalline samples of Sr2Mn2CuAs2O2, Sr2Mn3As2O2, and Sr2Zn2MnAs2O2 were synthesized. Their temperature- and applied magnetic field-dependent structural, transport, thermal, and magnetic properties were characterized by means of x-ray and neutron diffraction, electrical resistivity rho, heat capacity, magnetization and magnetic susceptibility measurements. These compounds have a body-centered-tetragonal crystal structure (space group I4/mmm) that consists of MO2 (M = Zn and/or Mn) oxide layers similar to the CuO2 layers in high superconducting transition temperature Tc cuprate superconductors, and intermetallic MAs (M = Cu and/or Mn) layers similar to the FeAs layers in high-Tc pnictides. These two types of layers alternate along the crystallographic c-axis and are separated by Sr atoms. The site occupancies of Mn, Cu and Zn were studied using Rietveld refinements of x-ray and neutron powder diffraction data. The temperature dependences of rho suggest metallic character for Sr2Mn2CuAs2O2 and semiconducting character for Sr2Mn3As2O2 and Sr2Zn2MnAs2O2. Sr2Mn2CuAs2O2 is inferred to be a ferrimagnet with a Curie temperature TC = 95(1) K. Remarkably, we find that the magnetic ground state structure changes from a G-type antiferromagnetic structure in Sr2Mn3As2O2 to an A-type ferrimagnetic structure in Sr2Mn2CuAs2O2 in which the Mn ions in each layer are ferromagnetically aligned, but are antiferromagnetically aligned between layers., Comment: 18 pages, 16 figures, 6 tables; submitted to Phys. Rev. B