Successive magnetic phase transitions and multiferroicity in the spin-one triangular-lattice antiferromagnet Ba3NiNb2O9.

We report the magnetic and electric properties of Ba3NiNb2O9, which is a quasi-two-dimensional spin-one triangular-lattice antiferromagnet with trigonal structure. At low T and with increasing magnetic field, the system evolves from a 120 degree magnetic ordering phase (A phase) to an up-up-down (uud) phase (B phase) with a change of slope at 1/3 of the saturation magnetization, and then to an "oblique" phase (C phase). Accordingly, the ferroelectricity switches on at each phase boundary with appearance of spontaneous polarization. Therefore, Ba3NiNb2O9 is a unique triangular-lattice antiferromagnet exhibiting both uud phase and multiferroicity.

Negative volume thermal expansion via orbital and magnetic orders in Ca2Ru1-(x)Cr(x)O4(0 < x < 0.13).

Ca2RuO4 undergoes a metal-insulator transition at T(MI)=357 K, followed by a well-separated transition to antiferromagnetic order at T(N)=110 K. Dilute Cr doping for Ru reduces the temperature of the orthorhombic distortion at T(MI) and induces ferromagnetic behavior at T(C). The lattice volume V of Ca2Ru1-(x)Cr(x)O4 (0 < x < 0.13) abruptly expands with cooling at both T(MI) and T(C), giving rise to a total volume expansion ΔV/V ≈ 1%, which sharply contrasts the smooth temperature dependence of the few known examples of negative volume thermal expansion driven by anharmonic phonon modes. In addition, the near absence of volume thermal expansion between T(C) and T(MI) represents an Invar effect. The two phase transitions, which surprisingly mimic the classic freezing transition of water, suggest an exotic ground state driven by an extraordinary coupling between spin, orbit, and lattice degrees of freedom.

Bound fermion states in pinned vortices in the surface states of a superconducting topological insulator.

By analytically solving the Bogoliubov-de Gennes equations we study the fermion bound states at the center of the core of a vortex in a two-dimensional superconductor. The superconducting states are induced via proximity effect between ans-wave superconductor and the surface states of a strong topological insulator. The strong spin-orbit coupling locks the spin perpendicular to the momentum (Rashba interaction). A zero-energy Majorana state arises together with an equally spaced (Δ∞2/EF) sequence of fermion excitations. The spin-momentum locking is key to the formation of the Majorana state. We present analytical expressions for the energy spectrum and the wave functions of the bound states. The wave functions fall off exponentially with the distanceρfrom the core of the vortex asexp[-∫0ρdρ'Δ(ρ')/vF]. An analytic expression for the local density of states (LDOS) for the bound states is obtained. The particle-hole symmetry is broken in the LDOS as a consequence of the spin-orbit coupling. The spin-polarization of the bound states is discussed. We also obtain the energy shifts of the bound states in a small magnetic field. A unitary transformation relating the model with Rashba interaction to the Dirac Hamiltonian is presented.

Clinical and biochemical effects of the E139K missense mutation in the TIMP3 gene, associated with Sorsby fundus dystrophy.

PURPOSE: To determine the phenotypic and biochemical characteristics of the p.E139K missense variant in tissue inhibitor of metalloproteinase 3 (TIMP3) associated with Sorsby fundus dystrophy (SFD). METHODS: The coding regions and adjacent intronic sequence of TIMP3 were amplified by polymerase chain reaction and then analyzed by bidirectional sequencing. Allele-specific PCR was used to determine the minimum allele frequency of the mutant allele in ethnically matched controls. Clinical examination and imaging of affected individuals with color fundus photography, scanning laser ophthalmoscope (fundal autofluorescence), and optical coherence tomography was performed. A mutant construct of the TIMP3 protein was created and expressed in human retinal pigment epithelium (ARPE19) cells, which were then assayed for oligomerization and intrinsic matrix metalloproteinase (MMP) inhibitory activity. RESULTS: Three affected individuals from a family of Welsh origin each harbored one allele of the TIMP3 missense variant c.415 G>A, (p.E139K), which was not identified in 534 ethnically matched control chromosomes and thus presumed pathogenic. The mutant protein was shown to dimerize in culture cells and retain its MMP inhibitory activity. Retinal examination was variable between eyes of affected individuals and between family members. Drusen-like deposits were common to all three affected individuals and yellow subretinal deposits, exudative maculopathy, and geographic atrophy were also observed. Optical coherence tomography (OCT) images of affected individuals demonstrated hyperreflectivity of the RPE-photoreceptor-choroid complex. CONCLUSIONS: The TIMP3 p.E139K mutation is another cause of SFD. It is the second TIMP3 sequence variant reported that does not affect the number of cysteine residues in the mutant protein yet dimerizes in vitro. The clinical presentation of this family is in keeping with previous clinical reports of this disorder.

Switching to ranibizumab in diabetic macular oedema refractory to bevacizumab treatment. / Cambio a ranibizumab en edema macular diabético refractario al tratamiento con bevacizumab.

AIM: To determine the efficacy of switching to ranibizumab in patients with diabetic macular oedema refractory to treatment with bevacizumab, and to evaluate the outcomes when switching back to bevacizumab. METHODS: A prospective study was conducted that included 43 eyes of 31 patients refractory to previous bevacizumab treatment. The patients were switched to ranibizumab, and optical coherence tomography was performed one month post-injection. Patients showing improvement (>10% reduction in central sub-field thickness) were switched back to bevacizumab, and optical coherence tomography was performed one month post-switch back. RESULTS: The 34 eyes switched to ranibizumab showed a statistically significant improvement in mean best corrected visual acuity from 0.67±0.39 logMAR to a mean of 0.55±0.36 logMAR (P<.05). In addition, there was a statistically significant decrease in central subfield thickness (CST) from a mean of 475.3±122.8 to a mean of 417.3±109.1 (P<.05). In the 21 eyes that were switched back to bevacizumab, there was no significant difference either in the change in CST or in the change in best corrected visual acuity post-switch back. CONCLUSION: Switching to ranibizumab in patients improves both the best corrected visual acuity and CST in diabetic patients refractory to previous bevacizumab treatment. This effect is pronounced in patients with increased CST prior to the switch. Switching back to bevacizumab adds no further improvement.

Decoupling of magnetism and electric transport in single-crystal (Sr1-x A x )2IrO4 (A = Ca or Ba).

We report a systematical structural, transport and magnetic study of Ca or Ba doped Sr2IrO4 single crystals. Isoelectronically substituting Ca2+ (up to 15%) or Ba2+ (up to 4%) ion for the Sr2+ ion provides no additional charge carriers but effectively changes the lattice parameters in Sr2IrO4. In particular, 15% Ca doping considerably reduces the c-axis and the unit cell by nearly 0.45% and 1.00%, respectively. These significant, anisotropic compressions in the lattice parameters conspicuously cause no change in the Néel temperature which remains at 240 K, but drastically reduces the electrical resistivity by up to five orders of magnitude or even precipitates a sharp insulator-to-metal transition at lower temperatures, i.e. the vanishing insulating state accompanies an unchanged Néel temperature in (Sr1-x A x )2IrO4. This observation brings to light an intriguing difference between chemical pressure and applied pressure, the latter of which does suppress the long-range magnetic order in Sr2IrO4. This difference reveals the importance of the Ir1-O2-Ir1 bond angle and homogenous volume compression in determining the magnetic ground state. All results, along with a comparison drawn with results of Tb and La doped Sr2IrO4, underscore that the magnetic transition plays a nonessential role in the formation of the charge gap in the spin-orbit-tuned iridate.

Quantification of optic nerve head topography in optic neuritis: a pilot study.

AIMS: To investigate optic nerve head topography in patients with optic neuritis compared to controls using the Heidelberg retina tomograph-II (HRT-II) and to determine if detected changes are related to visual function and electrophysiology. METHODS: 25 patients with a previous single episode of unilateral optic neuritis and 15 controls were studied with HRT-II, visual evoked potentials, and pattern electroretinogram. Patients also had testing of visual acuity, visual field, and colour vision. RESULTS: In affected eyes compared to fellow eyes, there was reduction of both the mean retinal nerve fibre layer (RNFL) thickness at the disc edge (p = 0.009) and the neuroretinal rim volume (p = 0.04). In affected eyes compared to control eyes, the three dimensional optic cup shape measure was increased (p = 0.01), indicative of an abnormal cup shape. There were no other significant differences in HRT-II measures. Within patient interocular difference correlation was used to investigate the functional relevance of these changes and demonstrated associations between RNFL thickness change and changes in visual acuity, visual field, and colour vision. Colour vision change was also associated with change in neuroretinal rim volume. CONCLUSIONS: HRT detects functionally relevant changes in RNFL thickness and neuroretinal rim volume between eyes affected by optic neuritis and unaffected fellow eyes.

Orbital two-channel Kondo effect in epitaxial ferromagnetic L1(0)-MnAl films.

The orbital two-channel Kondo effect displaying exotic non-Fermi liquid behaviour arises in the intricate scenario of two conduction electrons compensating a pseudo-spin-1/2 impurity of two-level system. Despite extensive efforts for several decades, no material system has been clearly identified to exhibit all three transport regimes characteristic of the two-channel Kondo effect in the same sample, leaving the interpretation of the experimental results a subject of debate. Here we present a transport study suggestive of a robust orbital two-channel Kondo effect in epitaxial ferromagnetic L1(0)-MnAl films, as evidenced by a magnetic field-independent resistivity upturn with a clear transition from logarithmic- to square-root temperature dependence and deviation from it in three distinct temperature regimes. Our results also provide an experimental indication of the presence of two-channel Kondo physics in a ferromagnet, pointing to considerable robustness of the orbital two-channel Kondo effect even in the presence of spin polarization of the conduction electrons.

Macular microholes: pathogenesis and natural history.

AIMS: To study the natural history and evaluate optical coherence tomography (OCT) and the retinal thickness analyser (RTA) in patients with macular microholes. METHODS: The medical records of 22 patients with a well demarcated red intraretinal foveal or juxtafoveal defect were reviewed. Fluorescein angiography (FA), RTA, and OCT were performed. The main outcome measures were visual acuity (VA), and OCT and RTA characteristics of microholes. Long term follow up was available in 13 eyes of 12 patients. RESULTS: The patients had a mean age of 50 years and a mean refractive error of -0.93 dioptres. The presenting symptom was a central scotoma in 14 eyes and metamorphopsia in eight eyes. All patients had a corrected VA ranging from 20/16 to 20/125, with 20 out of 24 eyes (83%) having a VA > or =20/40. Symptoms remained stable or improved in 16 out of 22 patients (72%). OCT 2 findings were normal but an abnormality of the outer retina and/or a defect of the retinal pigment epithelium (RPE) were demonstrated on OCT 3 in 15 of 18 eyes (83%). The RTA topographic map demonstrated a defect at the site of the microhole in two out of 12 eyes. CONCLUSION: Although biomicroscopic examination suggested an inner foveal defect, the OCT 3 scans demonstrated a localised abnormality of the outer retina and/or RPE which could not be resolved using OCT 2. Macular microholes have a favourable long term prognosis with stable VA. Bilateral involvement is uncommon.

Undercompensated kondo impurity with quantum critical point

The low-temperature properties of a magnetic impurity of spin S interacting with an electron gas via anisotropic spin exchange are studied via Bethe's ansatz. For S>1/2 the impurity is only partially compensated at T = 0, leaving an effective spin that is neither integer nor half integer. The entropy has an essential singularity at H = T = 0, and the susceptibility and the specific heat follow power laws of H and T with nonuniversal exponents, which are the consequence of a quantum critical point. The results for the generalization to an arbitrary number of channels are also reported.

Strong magnetic instability in correlated metallic Bi2Ir2O7.

We report an experimental/theoretical study of single-crystal Bi(2)Ir(2)O(7) that possesses a metallic state with strongly exchange-enhanced paramagnetism. The ground state of Bi(2)Ir(2)O(7) is characterized by the following features: (1) a divergent low-temperature magnetic susceptibility that indicates no long-range order down to 50 mK; (2) strongly field-dependent coefficients of the low-temperature T and T(3) terms of the specific heat; (3) a conspicuously large Wilson ratio R(W) ≈ 53.5; and (4) unusual temperature and field dependences of the Hall resistivity that abruptly change below 80 K, without any clear correlation with the magnetic behavior. All these unconventional properties suggest the existence of an exotic ground state in Bi(2)Ir(2)O(7).

Correlated giant dielectric peaks and antiferromagnetic transitions near room temperature in pure and alkali-doped BaMnO(3-δ).

We report structural, magnetic, dielectric and thermal properties of single-crystal BaMnO(2.99) and its derivatives BaMn(0.97)Li(0.03)O(3) and Ba(0.97)K(0.03)MnO(3). The hexagonal 15R-BaMnO(2.99) perovskite phase is a known antiferromagnetic insulator that orders at a Néel temperature T(N) = 220 K. We find dilute Li and K doping change the ratio of cubic to hexagonal layers and cause drastic changes in the dielectric and magnetic properties. Unusually large high-temperature magnetoelectric shifts (up to 85%) are observed near temperatures at which pronounced peaks in the dielectric constant are observed for applied electric fields along either the c or a axis, respectively. The temperatures of the dielectric peaks are strongly correlated with anomalies in the c- or a-axis magnetic susceptibility and the specific heat for all compositions studied. All our data suggest that the strongly anisotropic magnetic and dielectric anomalies (which occur near, or above room temperature) originate from the same Mn ion sites, which implies these materials form an exceptional class of magnetoelectrics.

A preliminary longitudinal study of the retinal nerve fiber layer in progressive multiple sclerosis.

Thinning of the retinal nerve fiber layer (RNFL) of clinically unaffected eyes is seen in patients with multiple sclerosis (MS). It is uncertain when this thinning occurs, and whether ongoing RNFL loss can be measured over time with optical coherence tomography (OCT). Using time-domain OCT, we studied 34 patients with progressive MS (16 primary progressive MS, 18 secondary progressive; 14 male; 20 female; mean age at study entry 51 years; median EDSS 6; mean disease duration at study entry 12 years) on two occasions with a median interval of 575 (range 411-895) days apart. Eighteen healthy controls (10 male; eight female; mean age at study entry 46 years) were also studied twice, with a median interval of 656 days (range 398-890). Compared to controls, the patients had significant decreases in the RNFL thickness and macular volume of their clinically unaffected eyes at study entry. No significant decrease in RNFL thickness was observed between baseline and follow-up in either patients or controls. Macular volume declined significantly in patients and controls, but there was no difference in this change between the two groups. The study findings suggest that time domain OCT detects little disease-related ongoing loss of retinal axons in progressive forms of MS and has limited use for monitoring potential neuroprotective therapies at this stage of disease. Further studies are needed using higher-resolution OCT systems and in larger groups of patients, to elucidate the timing and mechanism of RNFL loss that is observed in clinically unaffected nerves in MS.