Static impurities in the kagome lattice: dimer freezing and mutual repulsion

We consider the effects of doping the S = 1/2 kagome lattice with static impurities. We demonstrate that impurities lower the number of low-lying singlet states, induce dimer-dimer correlations of considerable spatial extent, and do not generate free spin degrees of freedom. Most importantly, they experience a highly unconventional mutual repulsion as a direct consequence of the strong spin frustration. These properties are illustrated by exact diagonalization, and reproduced to semi-quantitative accuracy within a dimer resonating-valence-bond description which affords access to longer length scales. We calculate the local magnetization induced by doped impurities, and consider its implications for nuclear magnetic resonance measurements on known kagome systems.Comment: 9 pages, 12 figure

Interaction between static holes in a quantum dimer model on the kagome lattice

A quantum dimer model (QDM) on the kagome lattice with an extensive ground-state entropy was recently introduced [Phys. Rev. B 67, 214413 (2003)]. The ground-state energy of this QDM in presence of one and two static holes is investigated by means of exact diagonalizations on lattices containing up to 144 kagome sites. The interaction energy between the holes (at distances up to 7 lattice spacings) is evaluated and the results show no indication of confinement at large hole separations.Comment: 6 pages, 3 figures. IOP style files included. To appear in J. Phys.: Condens. Matter, Proceedings of the HFM2003 conference, Grenobl

Static impurities in the S=(3/2) kagome lattice: Exact diagonalization calculations on small clusters

We consider the effects of doping the S=(3/2) kagome lattice with static, nonmagnetic impurities. By exact-diagonalization calculations on small clusters, we deduce the local spin correlations and magnetization distribution around a vacancy. As in the S=(1/2) kagome lattice, in the vicinity of the impurity, we find an extended region where the spin correlations are altered as a consequence of frustration relief and no indications for the formation of local moments. We discuss the implications of our results for local-probe measurements on S=(3/2) kagome materials

Static impurities in the S=3/2 kagome lattice: Exact diagonalization calculations on small clusters

We consider the effects of doping the S=3/2 kagome lattice with static, nonmagnetic impurities. By exact-diagonalization calculations on small clusters, we deduce the local spin correlations and magnetization distribution around a vacancy. As in the S=1/2 kagome lattice, in the vicinity of the impurity, we find an extended region where the spin correlations are altered as a consequence of frustration relief and no indications for the formation of local moments. We discuss the implications of our results for local-probe measurements on S=3/2 kagome materials

Une cause de cardiomyopathie dilatée chez l'enfant: le déficit primaire en carnitine [A cause of dilated cardiomyopathy in child: primary carnitine deficiency].

AIM: The aim of this case report was to show the importance to research metabolic etiology, especially a carnitine deficiency in dilated cardiomyopathy of children. CASE REPORT: A three years old Togolese child presented muscular hypotonia, dyspnea. Examination showed left galop murmur and systolic murmur 2/6. Chest X-ray showed cardiomegaly (CTI: 0.66), electrocardiogram, a sinusal rythm, left ventricle hypertrophy and T wave abnormalities. Echocardiogram showed a markedly dilated left ventricle with reduced systolic function (EF: 0.43; reference range 0.55-0.80) and moderate mitral regurgitation. The inflammatory signs where negatives. Magnetic resonance imaging don't show signs of ischemic or myocarditis. The levels of free and total plasmatic carnitine decreased: 3μmol/L (N: 18-48μmol/L) and 5μmol/l (N: 29-70μmol/L) respectively. Mutation analysis of the gene SLC22A5 confirms the diagnosis of primary systemic carnitine deficiency. Treatment with oral carnitine was started at 200mg/kg per day. Within three weeks of treatment, we observed the decrease of all symptoms and the left ventricular size and function normalized (EF: 0.62). He has now been on oral carnitine for live. CONCLUSION: Primary carnitine deficiency is a cause of dilated cardiomyopathy in child. It must systematically be suspected when a child presents a primitive cardiomyopathy. The treatment with oral carnitine for live is simple, with excellent prognosis

GAUSSIAN ORTHOGONAL ENSEMBLE FOR THE LEVEL SPACING STATISTICS OF THE QUANTUM FOUR-STATE CHIRAL POTTS MODEL

International audienc

Correlations, spin dynamics, defects: the highly-frustrated Kagomé bilayer

21 pages, 24 figuresThe SrCr$_{9p}$Ga$_{12-9p}$O$_{19}$ and Ba$_{2}$Sn$_{2}$ZnGa$_{10-7p}$Cr$_{7p}$O$_{22}$ compounds are two highly-frustrated magnets possessing a quasi-two-dimensional Kagomé bilayer of spin $\frac{3}{2}$ chromium ions with antiferromagnetic interactions. Their magnetic susceptibility was measured by local Nuclear Magnetic Resonance and non-local (SQUID) techniques, and their low-temperature spin dynamics by Muon Spin Resonance. Consistent with the theoretical picture drawn for geometrically frustrated systems, the Kagomé bilayer is shown here to exhibit: (i) short range spin-spin correlations down to a temperature much lower than the Curie-Weiss temperature, no conventional long-range transition occurring; (ii) a Curie contribution to the susceptibility from paramagnetic defects generated by spin vacancies; (iii) low-temperature spin fluctuations, at least down to 30 mK, which are a trademark of a dynamical ground state. These properties point to a spin-liquid ground state, possibly built on Resonating Valence Bonds with unconfined spinons as the magnetic excitations