Detection of a Disorder-Induced Bose-Einstein Condensate in a Quantum Spin Material at High Magnetic Fields.

The coupled spin-1 chains material NiCl_{2}-4SC(NH_{2})_{2} (DTN) doped with Br impurities is expected to be a perfect candidate for observing many-body localization at high magnetic field: the so-called "Bose glass," a zero-temperature bosonic fluid, compressible, gapless, incoherent, and short-range correlated. Using nuclear magnetic resonance, we critically address the stability of the Bose glass in doped DTN, and find that it hosts a novel disorder-induced ordered state of matter, where many-body physics leads to an unexpected resurgence of quantum coherence emerging from localized impurity states. An experimental phase diagram of this new "order-from-disorder" phase, established from nuclear magnetic resonance T_{1}^{-1} relaxation rate data in the 13±1% Br-doped DTN, is found to be in excellent agreement with the theoretical prediction from large-scale quantum Monte Carlo simulations.

Real space imaging of spin polarons in Zn-doped SrCu(2)(BO(3))(2).

We report on the real space profile of spin polarons in the quasi-two-dimensional frustrated dimer spin system SrCu(2)(BO(3))(2) doped with 0.16% of Zn. The (11)B nuclear magnetic resonance spectrum exhibits 15 additional boron sites near nonmagnetic Zn impurities. With the help of exact diagonalizations of finite clusters, we have deduced from the boron spectrum, the distribution of local magnetizations at the Cu sites with fine spatial resolution, providing direct evidence for an extended spin polaron. The results are confronted with those of other experiments performed on doped and undoped samples of SrCu(2)(BO(3))(2).

Contribution of copy number variations in CMT1X: a retrospective study.

BACKGROUND AND PURPOSE: Charcot-Marie-Tooth disease type 1X (CMT1X) is an X-linked dominant hereditary motor-sensory peripheral neuropathy, which results from mutations in the Gap Junction B1 (GJB1) gene. In a few cases, gene deletions have been linked to the disease, but their relative contribution in the pathogenesis of CMT1X has not been assessed yet. Herein a retrospective study to establish the incidence of gene deletions is described. METHODS: Copy number variation analysis was performed by multiplex ligation-dependent probe amplification, whilst the breakpoints were defined by Sanger sequencing. RESULTS: A novel GJB1 deletion was identified in a family presenting with a classical CMT1X phenotype. The rearrangement includes the coding and the regulatory regions of GJB1. CONCLUSIONS: GJB1 deletions appear to be a rare but not insignificant cause of CMT1X and are associated with a typical disease phenotype. Accordingly, patients negative for point mutations whose pedigree and clinical records strongly suggest the possibility of CMT1X should be tested for GJB1 copy number variations.

The free volume of poly(vinyl methylether) as computed in a wide temperature range and at length scales up to the nanoregion.

In the present work, we focus on the free volume evaluations from different points of view, including the aspect of probe sizes, temperature, and cavity threshold. The free volume structure is analyzed on structures of poly(vinyl methylether) prepared by fully atomistic molecular dynamics. At first, the temperature behavior of an overall free volume and a free volume separated into individual cavities is shown. The origin of large free volume cavities is explained. A complex view on the cavity number is provided, while a complicated behavior previously observed is now explained. The number of large cavities remained almost constant with the temperature. Oppositely, the number of small cavities related to the atomic packing changes with temperature in a distinct way for glassy and supercooled regions. The cavity number maxima determine a percolation threshold according to percolation theory. The change in polymer properties with temperature can be related to a percolation of the free volume according to the free volume theory, when proper probe radii ∼0.8 Å are used for its observation. A construction of probabilistic distribution of free volume sizes is suggested. The free volume distributions reported here are bimodal. The bimodal character is explained by two different packings--atomic and segmental--forming a prepeak and a main peak on the distribution. Further attention is dedicated to comparisons of the computed free volume sizes and the ortho-positronium (o-Ps) lifetimes. The prepeak of the free volume distribution is probably unseen by o-Ps because of a cavity threshold limit. The effect of the shape factor on the computed o-Ps lifetimes is tested. The quasicavities obtained by redistributing the free volume maintain the ratio of the main dimensions with temperature. Finally, novel data on the cavity environment are provided, while it is suggested how these can be useful with the recent developments in the positron annihilation methods. The coordination number of large cavities with the polymer segments is around 1, as predicted in the free volume theory. Similarly to the percolation and the cavity number, the coordination number exhibits a change when explored by a suitable probe radius ∼0.8 Å. The insightful visualizations showed properties of interest investigated within the actual work.

Quasielastic neutron scattering study of hydrogen motions in an aqueous poly(vinyl methyl ether) solution.

We present a quasielastic neutron scattering (QENS) investigation of the component dynamics in an aqueous Poly(vinyl methyl ether) (PVME) solution (30% water content in weight). In the glassy state, an important shift in the Boson peak of PVME is found upon hydration. At higher temperatures, the diffusive-like motions of the components take place with very different characteristic times, revealing a strong dynamic asymmetry that increases with decreasing T. For both components, we observe stretching of the scattering functions with respect to those in the bulk and non-Gaussian behavior in the whole momentum transfer range investigated. To explain these observations we invoke a distribution of mobilities for both components, probably originated from structural heterogeneities. The diffusive-like motion of PVME in solution takes place faster and apparently in a more continuous way than in bulk. We find that the T-dependence of the characteristic relaxation time of water changes at T ≲ 225 K, near the temperature where a crossover from a low temperature Arrhenius to a high temperature cooperative behavior has been observed by broadband dielectric spectroscopy (BDS) [S. Cerveny, J. Colmenero and A. Alegría, Macromolecules, 38, 7056 (2005)]. This observation might be a signature of the onset of confined dynamics of water due to the freezing of the PVME dynamics, that has been selectively followed by these QENS experiments. On the other hand, revisiting the BDS results on this system we could identify an additional "fast" process that can be attributed to water motions coupled with PVME local relaxations that could strongly affect the QENS results. Both kinds of interpretations, confinement effects due to the increasing dynamic asymmetry and influence of localized motions, could provide alternative scenarios to the invoked "strong-to-fragile" transition.

Atomic motions in poly(vinyl methyl ether): A combined study by quasielastic neutron scattering and molecular dynamics simulations in the light of the mode coupling theory.

Quasielastic neutron scattering experiments (time-of-flight, neutron spin echo, and backscattering) on protonated poly(vinyl methyl ether) (PVME) have revealed the hydrogen dynamics above the glass-transition temperature. Fully atomistic molecular dynamics simulations properly validated with the neutron scattering results have allowed further characterization of the atomic motions accessing the correlation functions directly in real space. Deviations from Gaussian behavior are found in the high-momentum transfer range, which are compatible with the predictions of mode coupling theory (MCT). We have applied the MCT phenomenological version to the self-correlation functions of PVME atoms calculated from our simulation data, obtaining consistent results. The unusually large value found for the lambda-exponent parameter is close to that recently reported for polybutadiene and simple polymer models with intramolecular barriers.

Neuropsychological profile in Italian children with neurofibromatosis type 1 (NF1) and their relationships with neuroradiological data: Preliminary results.

BACKGROUND: Neurofibromatosis type 1 is a genetic disorder associated with cognitive deficits, learning disabilities and behavioral problems. These domains appear to have a still controversial debated association with local areas of T2-hyperintensities on MRI images, called unidentified bright objects (UBOs). METHODS: A cohort of 36 children (aged 7-11 years) included consecutively, underwent neuropsychological and behavioral assessment to determine their cognitive and neuropsychological profile, and the frequency of specific learning disabilities. MRI examination was used to determine the impact of UBOs' presence, number, and location on the cognitive, neuropsychological and behavioral profile, and also the presence of optic glioma. RESULTS: The mean full intelligence quotient was 104.6; only one child had mild intellectual disability. Forty one percent of children had a diagnosis of specific learning disabilities and reading was mainly involved. Twenty per cent had attention problems. All children had normal scores in visuo-motor and visuo-perceptual tests. UBOs were present in 94.0% of the MRI examinations. Two children had optic glioma. Children with UBOs in a specific location and children with UBOs elsewhere were statistically compared, no one of the location seemed to have an impact on general cognition measured with full intelligence quotient. The thalamus was associated with problems in calculation and striatum with behavioral problems. An inverse relationship between the number of UBOs and the full intelligence quotient was present, but without a statistical significance. CONCLUSIONS: In this study, the specific location of UBOs did not seem to influence the general cognitive profile and also the relationship between their number and the full intelligence quotient was not significant; these results are still controversial in literature. Finally, the presence of UBOs in the thalamus and striatum may represent a neuroradiological pattern that influences performances in calculation and behavior respectively in children with Neurofibromatosis type 1.

GDAP1 mutations in Italian axonal Charcot-Marie-Tooth patients: Phenotypic features and clinical course.

Mutations in the ganglioside-induced differentiation associated-protein 1 (GDAP1) gene have been associated with both autosomal recessive (AR) and dominant (AD) Charcot-Marie-Tooth (CMT) axonal neuropathy. The relative frequency of heterozygous, dominant mutations in Italian CMT is unknown. We investigated the frequency of dominant mutations in GDAP1 in a cohort of 109 axonal Italian patients by sequencing genomic DNA and search for copy number variations. We also explored correlations with clinical features. All cases had already been tested for variants in common axonal AD genes. Eight patients (7.3%) harbored five already reported heterozygous mutations in GDAP1 (p.Arg120Gly, p.Arg120Trp, p.His123Arg, p.Gln218Glu, p.Arg226Ser). Mutations had different penetrances in the families; the onset of symptoms is in the first decade and progression is slower than usually seen in GDAP1-related AR-CMT. We show that the relative frequency of mutations in GDAP was slightly higher than those observed in MFN2 and MPZ (7.3% vs 6.3% and 5.0%). The relatively milder clinical features and the quite indolent course observed are relevant for prognostic assessment. On the basis of our experience and the data reported here, we suggest GDAP1 as the first gene that should be analysed in Italian patients affected by CMT2.

Effective theory of magnetization plateaux in the Shastry-Sutherland lattice.

We use the nonperturbative Contractor-Renormalization method (CORE) in order to derive an effective model for triplet excitations on the Shastry-Sutherland lattice. For strong enough magnetic fields, various magnetization plateaux are observed, e.g., at 1/8, 1/4, 1/3 of the saturation, as found experimentally in a related compound. Moreover, other stable plateaux are found at 1/9, 1/6, or 2/9. We give a critical review of previous works and try to resolve some apparent inconsistencies between various theoretical approaches.

Thermal fluctuations of DNA enclosed by glycerol-water glassy matrices: an elastic neutron scattering investigation.

Through elastic neutron scattering measurements, we investigated the thermal fluctuations of DNA enclosed by glycerol-water glassy matrices, at different levels of hydration, over the wide temperature range from 20 to 300 K. For all the samples, the extracted hydrogen mean square displacements (MSD) show a purely vibrational harmonic trend at very low temperatures, and a first onset of anharmonic dynamics above approximately 100 K. Such onset is consistent with the activation of DNA methyl group rotational motions. Then, at a certain temperature Td, the MSD show a second onset of anharmonicity, which corresponds to the DNA dynamical transition. The Td values vary as a function of the hydration degree of the environment. The crucial role of the solvent mobility to activate the DNA thermal fluctuations is proposed, together with a preferential hydration effect of the DNA phosphate groups. Finally, a comparison between the average mobility of homologous samples of DNA and the lysozyme protein is considered.

Spin gap and string order parameter in the ferromagnetic spiral staircase heisenberg ladder: a quantum Monte Carlo study.

We consider a spin-1/2 ladder with a ferromagnetic rung coupling J perpendicular and inequivalent chains. This model is obtained by a twist (theta) deformation of the ladder and interpolates between the isotropic ladder (theta=0) and the SU(2) ferromagnetic Kondo necklace model (theta = pi). We show that the ground state in the (theta, J perpendicular) plane has a finite string order parameter characterizing the Haldane phase. Twisting the chain introduces a new energy scale, which we interpret in terms of a Suhl-Nakamura interaction. As a consequence we observe a crossover in the scaling of the spin gap at weak coupling from delta/J parallel proportional, variant J perpendicular/J parallel for theta < theta c approximately 8 pi/9 to delta/J parallel proportional, variant (J perpendicular/J parallel)2 for theta > theta c. Those results are obtained on the basis of large scale quantum Monte Carlo calculations.

Thermodynamics of the spin Luttinger liquid in a model ladder material.

The phase diagram in temperature and magnetic field of the metal-organic, two-leg, spin-ladder compound (C5H12N)2CuBr4 is studied by measurements of the specific heat and the magnetocaloric effect. We demonstrate the presence of an extended spin Luttinger-liquid phase between two field-induced quantum critical points and over a broad range of temperature. Based on an ideal spin-ladder Hamiltonian, comprehensive numerical modeling of the ladder specific heat yields excellent quantitative agreement with the experimental data across the entire phase diagram.

Zeeman effect in superconducting two-leg ladders: irrational magnetization plateaus and exceeding the Pauli limit.

The effect of a parallel magnetic field on superconducting two-leg ladders is investigated numerically. The magnetization curve displays an irrational plateau at a magnetization equal to the hole density. Remarkably, its stability is fundamentally connected to the existence of a well-known magnetic resonant mode. Once the zero-field spin gap is suppressed by the field, pairs acquire a finite momentum characteristic of a Fulde-Ferrell-Larkin-Ovchinnikov phase. In addition, Sz = 0 triplet superconducting correlations coexist with singlet ones above the irrational plateau. This provides a simple mechanism in which the Pauli limit is exceeded as suggested by recent experiments.

Antiholons in one-dimensional t-J models.

Using a newly developed hybrid Monte Carlo algorithm for the nearest-neighbor (nn) t-J model, we show that antiholons identified in the supersymmetric inverse squared (IS) t-J model are clearly visible in the electron-addition spectrum of the nn t-J model at J=2t and also for J=0.5t, a value of experimental relevance.