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

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

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

Plagioclase preferred orientation and induced seismic anisotropy in mafic igneous rocks

Fractional crystallization and crystal segregation controlled by settling or floating of minerals during the cooling of magma can lead to layered structures in mafic and ultramafic intrusions in continental and oceanic settings in the lower crust. Thus, the seismic properties and fabrics of layered intrusions must be calibrated to gain insight into the origin of seismic reflections and anisotropy in the deep crust. To this end, we have measured P and S wave velocities and anisotropy in 17 plagioclase-rich mafic igneous rocks such as anorthosite and gabbro at hydrostatic pressures up to 650 MPa. Anorthosites and gabbroic anorthosites containing >80 vol% plagioclase and gabbros consisting of nearly equal modal contents of plagioclase and pyroxene display distinctive seismic anisotropy patterns: Vp(Z)/Vp(Y) ≥ 1 and Vp(Z)/Vp(X) ≥ 1 for anorthosites while 0.8 Vp(Y) than the gabbros. Laminated anorthosites with Vp(X) ≈ Vp(Y)≪ Vp(Z) display a strong crystal preferred orientation (CPO) of plagioclase whose (010) planes and [100] and [001] directions parallel to the foliation. For the gabbros and amphibolites characterized by Vp(X) ≈ Vp(Y) > Vp(Z) and Vp(X) > Vp(Y) > Vp(Z), respectively, pyroxene and amphibole play a dominant role over plagioclase in the formation of seismic anisotropy. The Poisson's ratio calculated using the average P and S wave velocities from the three principal propagation-polarization directions (X, Y, and Z) of a highly anisotropic anorthosite cannot represent the value of a true isotropic equivalent. The CPO-induced anisotropy enhances and decreases the foliation-normal incidence reflectivity at gabbro-peridotite and anorthosite-peridotite interfaces, respectively.25 page(s