Magnetic behavior of single crystalline Ho2_2PdSi3_3

The magnetic behavior of single-crystal Ho$_2$PdSi$_3$, crystallizing in an AlB$_2$-derived hexagonal structure, is investigated by magnetic susceptibility ($\chi$) and electrical resistivity ($\rho$) measurements along two directions. There is no dramatic anisotropy in the high temperature Curie-Weiss parameter or in the $\rho$ and isothermal magnetization data, though there is a noticeable anisotropy in the magnitude of $\rho$ between two perpendicular orientations. The degree of anisotropy is overall less prominent than in the Gd (which is an S-state ion!) and Tb analogues. A point of emphasis is that this compound undergoes long range magnetic ordering below 8 K as in the case of analogous Gd and Dy compounds. Considering this fact for these compounds with well-localised f-orbital, the spin glass freezing noted for isomorphous U compounds in the recent literature could be attributed to the role of the f-ligand hybridization, rather than just Pd-Si disorder.Comment: Physical Review B, in pres

Frustrated antiferromagnetic quantum spin chains for spin length S > 1

We investigate frustrated antiferromagnetic Heisenberg quantum spin chains at T=0 for S=3/2 and S=2 using the DMRG method. We localize disorder and Lifshitz points, confirming that quantum disorder points can be seen as quantum remnants of classical phase transitions. Both in the S=3/2 and the S=2 chain, we observe the disappearance of effectively free S=1/2 and S=1 end spins respectively. The frustrated spin chain is therefore a suitable system for clearly showing the existence of free end spins S'=[S/2] also in half-integer antiferromagnetic spin chains with S>1/2. We suggest that the first order transition found for S=1 in our previous work is present in all frustrated spin chains with S>1/2, characterized by the disappearance of effectively free end spins with S'=[S/2].Comment: 6 pages, 8 ps figures, uses RevTeX, submitted to PR

Longer Duration of Diabetes Strongly Impacts Fracture Risk Assessment: The Manitoba BMD Cohort

Context: Type 2 diabetes is associated with a higher risk for major osteoporotic fracture (MOF) and hip fracture than predicted by the World Health Organization fracture risk assessment (FRAX) tool. Objective: The objective of the study was to examine the impact of diabetes duration on fracture risk. Methods: Using a clinical dual-energy x-ray absorptiometry registry linked with the Manitoba administrative databases, we identified all women age 40 years or older with 10 or more years of prior health care coverage undergoing hip dual-energy x-ray absorptiometry measurements (1996 –2013). Incident MOF and incident hip fractures were each studied over 7 years. Cox proportional hazards models were adjusted for FRAX (FRAX adjusted) and then FRAX plus comorbidity, falls, osteoporosis therapy, or insulin (fully adjusted). FRAX calibration was assessed comparing observed vs predicted probabilities. Results: There were 49 098 women without and 8840 women with diabetes (31.4%10 y duration; 20.1% 5–10 y; 23.7%5 y; 24.8% new onset). In FRAX-adjusted analyses, only duration longer than 10 years was associated with a higher risk for MOF (hazard ratio [HR] 1.47, 95% confidence interval [CI] 1.30 –1.66), and this was similar in the fully adjusted models (HR 1.34, 95% CI 1.17–1.54). In contrast, a higher risk for hip fracture was seen for all durations in a dose-dependent fashion (eg, FRAX adjusted HR 2.10, 95% CI 1.71–2.59 for duration 10 y vs HR 1.32, 95% CI 1.03–1.69 for new onset). FRAX significantly underestimated the MOF risk (calibration ratio 1.24, 95% CI 1.08 –1.39) and hip fracture risk (1.93, 95% CI 1.50 –2.35) in those with a diabetes duration longer than 10 years. Conclusion: Diabetes is a FRAX-independent risk factor for MOF only in women with a long duration of diabetes, but diabetes increases hip fracture risk, regardless of duration. Those with diabetes longer than 10 years are at particularly high risk of fracture, and this elevated risk is currently underestimated by FRAX

Dimerization and Incommensurate Spiral Spin Correlations in the Zigzag Spin Chain: Analogies to the Kondo Lattice

Using the density matrix renormalization group and a bosonization approach, we study a spin-1/2 antiferromagnetic Heisenberg chain with near-neighbor coupling $J_1$ and frustrating second-neighbor coupling $J_2$, particularly in the limit $J_2 >> J_1$. This system exhibits both dimerization and incommensurate spiral spin correlations. We argue that this system is closely related to a doped, spin-gapped phase of the one-dimensional Kondo lattice.Comment: 18 pages, with 13 embedded encapsulated Postscript figures, uses epsf.sty. Corrects a misstatement about the pitch angle, and contains additional reference

Fractional S^z excitation and its bound state around the 1/3 plateau of the S=1/2 Ising-like zigzag XXZ chain

We present the microscopic view for the excitations around the 1/3 plateau state of the Ising-like zigzag XXZ chain. We analyze the low-energy excitations around the plateau with the degenerating perturbation theory from the Ising limit, combined with the Bethe-form wave function. We then find that the domain-wall particles carrying $S^z=\pm 1/3$ and its bound state of $S^z=\pm 2/3$ describe well the low-energy excitations around the 1/3 plateau state. The formation of the bound state of the domain-walls clearly provides the microscopic mechanism of the cusp singularities and the even-odd behavior in the magnetization curve.Comment: 13 pages, 15 figure

Phase Transitions Between Topologically Distinct Gapped Phases in Isotropic Spin Ladders

We consider various two-leg ladder models exhibiting gapped phases. All of these phases have short-ranged valence bond ground states, and they all exhibit string order. However, we show that short-ranged valence bond ground states divide into two topologically distinct classes, and as a consequence, there exist two topologically distinct types of string order. Therefore, not all gapped phases belong to the same universality class. We show that phase transitions occur when we interpolate between models belonging to different topological classes, and we study the nature of these transitions.Comment: 11 pages, 16 postscript figure

The phase diagram of the extended anisotropic ferromagnetic-antiferromagnetic Heisenberg chain

By using Density Matrix Renormalization Group (DMRG) technique we study the phase diagram of 1D extended anisotropic Heisenberg model with ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor interactions. We analyze the static correlation functions for the spin operators both in- and out-of-plane and classify the zero-temperature phases by the range of their correlations. On clusters of $64,100,200,300$ sites with open boundary conditions we isolate the boundary effects and make finite-size scaling of our results. Apart from the ferromagnetic phase, we identify two gapless spin-fluid phases and two ones with massive excitations. Based on our phase diagram and on estimates for the coupling constants known from literature, we classify the ground states of several edge-sharing materials.Comment: 12 pages, 13 figure

Thermodynamics of the incommensurate state in Rb_2WO_4: on the Lifshitz point in A`A``BX_4 compounds

We consider the evolution of the phase transition from the parent hexagonal phase $P6_{3}/mmc$ to the orthorhombic phase $Pmcn$ that occurs in several compounds of $A'A''BX_{4}$ family as a function of the hcp lattice parameter $c/a$. For compounds of $K_{2}SO_{4}$ type with $c/a$ larger than the threshold value 1.26 the direct first-order transition $Pmcn-P6_{3}/mmc$ is characterized by the large entropy jump $Rln2$. For compounds $Rb_{2}WO_{4}$, $K_{2}MoO_{4}$, $K_{2}WO_{4}$ with $c/a<1.26$ this transition occurs via an intermediate incommensurate $(Inc)$ phase. DSC measurements were performed in $Rb_{2}WO_{4}$ to characterize the thermodynamics of the $Pmcn-Inc-P6_{3}/mmc$ transitions. It was found that both transitions are again of the first order with entropy jumps $0.2Rln2 and$0.3Rln2$. Therefore, at$c/a ~ 1.26$the$A'A''BX_{4}$compounds reveal an unusual Lifshitz point where three first order transition lines meet. We propose the coupling of crystal elasticity with$BX_{4}$ tetrahedra orientation as a possible source of the transitions discontinuity.Comment: 13 pages,1 Postscript figure. Submitted as Brief Report to Phys. Rev. B, this paper reports a new work in Theory and Experiment, directed to Structural Phase Transition

Angular profile of emission of non-zero spin fields from a higher-dimensional black hole

Recent works have included the effect of rotation on simulations of black hole events at the LHC, showing that the angular momentum of the black hole cannot be ignored and it makes a non-trivial contribution for most of the lifetime of the black hole. A key consequence of the rotation of the black hole is that the Hawking radiation is no longer isotropic, making it more difficult to infer space–time parameters from measurements of the emitted particles. In this Letter we study the angular distribution of the Hawking emission of non-zero spin particles with specific helicity on the brane. We argue that the shape of the distribution could be used as a measure of the angular momentum of the black hole

Minimal configurations and sandpile measures

We give a new simple construction of the sandpile measure on an infinite graph G, under the sole assumption that each tree in the Wired Uniform Spanning Forest on G has one end almost surely. For, the so called, generalized minimal configurations the limiting probability on G exists even without this assumption. We also give determinantal formulas for minimal configurations on general graphs in terms of the transfer current matrix.Comment: 16 pages; the introduction has been expanded and minor corrections have been mad