Quasi-Two-Dimensional Fermi Surfaces and Coherent Interlayer Transport in KFe2_2As2_2

We report the results of the angular-dependent magnetoresistance oscillations (AMROs), which can determine the shape of bulk Fermi surfaces in quasi-two-dimensional (Q2D) systems, in a highly hole-doped Fe-based superconductor KFe$_2$As$_2$ with $T_c \approx$ 3.7 K. From the AMROs, we determined the two Q2D FSs with rounded-square cross sections, corresponding to 12% and 17% of the first Brillouin zone. The rounded-squared shape of the FS cross section is also confirmed by the analyses of the interlayer transport under in-plane fields. From the obtained FS shape, we infer the character of the 3d orbitals that contribute to the FSs.Comment: 4 pages, 4 figures, accepted in Phys. Rev. Let

Integer spin-chain antiferromagnetism of the 4d oxide CaRuO3 with post-perovskite structure

A quasi-one dimensional magnetism was discovered in the post-perovskite CaRuO3 (Ru4+: 4d4, Cmcm), which is iso-compositional with the perovskite CaRuO3 (Pbnm). An antiferromagnetic spin-chain function with -J/kB = 350 K well reproduces the experimental curve of the magnetic susceptibility vs. temperature, suggesting long-range antiferromagnetic correlations. The anisotropic magnetism is probably owing to the dyz - 2p- dzx and dzx - 2p- dyz superexchange bonds along a-axis. The Sommerfeld coefficient of the specific heat is fairly small, 0.16(2) mJ mol-1 K-2, indicating that the magnetism reflects localized nature of the 4d electrons. As far as we know, this is the first observation of an integer (S = 1) spin-chain antiferromagnetism in the 4d electron system.Comment: Accepted for publication in Phys. Rev.

Interplay between magnetism and conductivity in the one-dimensional organic conductor TPP[Fe(Pc)(CN)2]2

The strongly nonlinear current-voltage (I-V) characteristics and the large negative magnetoresistance (MR) are observed at low temperatures in the one-dimensional organic conductor TPP[Fe(Pc)(CN)2]2. The nonlinear I-V curves are interpreted as the transport of the electrons and holes excited from the charge ordered state on the Fe(Pc)(CN)2 chains, whose energy gap strongly depends on electric fields. The negative MR is enhanced as temperature decreases, and the resistance steeply changes over four orders of magnitude around 15 T at 1.5 K. This decrease is associated with a magnetic torque anomaly, and the energy gap is rapidly reduced around 15 T. The detailed analyses of the I-V curves show that the electric flux distribution, i.e., the dimensionality of the Coulomb interaction between the carriers, also changes around 15 T

Seismic properties of peridotite xenoliths as a clue to imaging the lithospheric mantle beneath NE Tasmania, Australia

Peridotite xenoliths from Northeast Tasmania, Australia, consist of spinel lherzolites and minor dunites that originated from the uppermost mantle at depths of less than 40 km, based on the geothermal gradient beneath Tasmania, where the depth of the Moho is 29. km. The crystal preferred orientations (CPOs) of olivine and pyroxene were measured in 5 of 13 collected samples (1 dunite and 4 lherzolites) that were large enough to enable measurements. Olivine CPOs indicate the dominance of (010) [100] slip. Geothermobarometric analyses of the xenoliths yield temperatures of 950-1050 °C and pressures of 0.7-1.1 GPa. Using these data, we calculated changes in the seismic properties of a rock with ideal volume fractions of olivine and pyroxene under conditions of 1000 °C and 1 GPa, for various orientations of the structural reference frame in the case of three geodynamic models (extension, shear, and upwelling). The model of horizontal extension performs best in explaining the structure of the uppermost lithospheric mantle beneath Northeast Tasmania.6 page(s

1{^{1}}H-NMR analysis of the SDW properties of (TMTSF)2{_{2}}NO3{_{3}}

SDW properties of (TMTSF)$_{2}$NO$_{3}$ have been investigated by means of $^{1}$H-NMR analysis on a single crystal sample. The SDW wave number is incommensurate and incommensurate and very near a commensurate value (1/2, 1/4, 0) which is almost the same as that of the PF$_{6}$ salt, while the SDW amplitude is ~0.4 $\mu_{B}$/molecule which is about one-half of the latter. We found that $T_{1}^{-1}$ in the SDW state exhibits anomalies. Key words. Bechgaard salt, $^{1}$H-NMR, incommensurate SDW, Second peak

A database of plagioclase crystal preferred orientations (CPO) and microstructures - implications for CPO origin, strength, symmetry and seismic anisotropy in gabbroic rocks

Corrigendum to this article was published in Solid Earth, 5, 509-509, 2014, doi:10.5194/se-5-509-2014. This study presents a unique database of 172 plagioclase Crystallographic Preferred Orientations (CPO) of variously deformed gabbroic rocks. The CPO characteristics as a function of the deformation regime (magmatic or crystal-plastic) are outlined and discussed. The studied samples are dominantly from slow-and fast-spread present-day ocean crust, as well as from the Oman ophiolite. Plagioclase is the dominant mineral phase in the studied samples. Plagioclase CPOs are grouped into three main categories: Axial-B, a strong point alignment of (010) with a girdle distribution of [100]; Axial-A, a strong point maximum concentration of [100] with parallel girdle distributions of (010) and (001); and P-type, point maxima of [100], (010), and (001). A majority of CPO patterns are Axial-B and P-type, in samples showing either magmatic or crystal-plastic deformation textures. Axial-A CPOs are less common; they represent 21% of the samples deformed by crystal-plastic flow. Although fabric strength (ODF J index) does not show any consistent variation as a function of the CPO patterns, there is a significant difference in the relationship between the ODF and pole figures J indices; the magmatic type microstructures have high (010) pole figures J indices, which increase linearly with ODF J index, whereas the high [100] pole figures J indices of plastically deformed samples vary in a more scattered manner with ODF J index. The multistage nature of plastic deformation superposed on a magmatic structure compared with magmatic flow, and the large number of possible slip-systems in plagioclase probably account for these differences. Calculated seismic properties (P wave and S wave velocities and anisotropies) of plagioclase aggregates show that anisotropy (up to 12% for P wave and 14% for S wave) tends to increase as a function of ODF J index. In comparison with the olivine 1998 CPO database, the magnitude of P wave anisotropy for a given J index is much less than olivine, whereas it is similar for S wave anisotropy. Despite a large variation of fabric patterns and geodynamic setting, seismic properties of plagioclase-rich rocks have similar magnitudes of anisotropy. There is a small difference in the aggregate elastic symmetry, with magmatic microstructures having higher orthorhombic and hexagonal components, whereas plastic deformation microstructures have a slightly higher monoclinic component, possibly correlated with predominant monoclinic simple shear flow in plastically deformed samples. Overall, plots for CPO strength (ODF J index), pole figure strength, CPO symmetry and seismic anisotropy show significant scattering. This could be related to sampling statistics, although our database is a factor of ten higher than the olivine database of 1998, or it could be related to the low symmetry (triclinic) structure of plagioclase resulting in the addition of degrees of freedom in the processes creating the CPOs.32 page(s

Seismic Anisotropy of the Uppermost Mantle Beneath the Rio Grande Rift: Evidence from Kilbourne Hole Peridotite Xenoliths, New Mexico

Peridotite xenoliths from the Kilbourne Hole maar, New Mexico, consist of spinel lherzolite, harzburgite, and dunite. Because Kilbourne Hole erupted at approximately 10 ka, these xenoliths represent essentially current conditions beneath the Rio Grande rift. In this study, we present detailed petrofabric data and seismic properties obtained from peridotite xenoliths from Kilbourne Hole to illuminate the origin and significance of shear-wave splitting in the uppermost mantle beneath this active rift. Using phase relations and the temperature of equilibration, we infer that these xenoliths were derived from the uppermost mantle, from depths of 35-60 km. Their crystallographic preferred orientations indicate the preservation of olivine b-axis fiber fabrics with a strong concentration of [010] with girdles of [100] and [001]. We consider three geodynamic models for the source region of these xenoliths: horizontal extension, lateral shear, and upwelling. After calculating seismic properties using a volume fraction of olivine, orthopyroxene and clinopyroxene appropriate to each model, we conclude that these xenoliths are derived from a lateral shear zone (vertical foliation (XY plane) and horizontal lineation within the plane of the foliation (X-axis)). However, the degree of seismic anisotropy generated by peridotite xenoliths alone is limited, so that the existence of melt in thin cracks or dikes could be required to cause a significant increase; the orientation of such melt pockets parallel to the XY plane in either model would result in an increase in anisotropy. These results indicate that the shear-wave splitting observed in the Rio Grande rift is a reflection of the lithospheric fabric and the presence of melts as thin cracks or dikes

Spin and anion dynamics on (TMTSF)2{_{2}}FSO3{_{3}}, studied by NMR

In order to characterise the electronic properties in sub-phases of (TMTSF)$_{2}$FSO$_{3}$ under pressure, $^{77}$Se, and $^{19}$F NMR Knight shift ($K)$ and relaxation rate (1/$T_{1})$ measurements were performed at ambient and 0.82 GPa pressure. The insulating phase below the metal-insulator transition (MIT) at 89 K at ambient pressure (AP) was confirmed as a nonmagnetic state with a gap of $\Delta$/$k_{B}\sim 420$ K. This MIT is strongly coupled with anion ordering. The MIT temperature decreases under pressure, and many electronic anomalies (or transitions) have been observed from transport measurements. The reduction of density of states in the metallic state by applying pressure was confirmed by the analysis of $K$ and Korringa constant (1/$T_{1}T)$. A nonmagnetic insulating transition corresponding to the MIT at AP at 89 K, was observed at $\sim$45 K at 0.82 GPa. A spin (charge) gap in the insulating state at 0.82 GPa is smaller ($\Delta$/$k_{B}\sim 90$ K) than that at AP. Key words. metal insulator transition – NMR