RESUMO
The effect of compression on the magnetic ground state of Sr_{2}IrO_{4} is studied with x-ray resonant techniques in the diamond anvil cell. The weak interlayer exchange coupling between square-planar 2D IrO_{2} layers is readily modified upon compression, with a crossover between magnetic structures around 7 GPa mimicking the effect of an applied magnetic field at ambient pressure. Higher pressures drive an order-disorder magnetic phase transition with no magnetic order detected above 17-20 GPa. The persistence of strong exchange interactions between J_{eff}=1/2 magnetic moments within the insulating IrO_{2} layers up to at least 35 GPa points to a highly frustrated magnetic state in compressed Sr_{2}IrO_{4}, opening the door for realization of novel quantum paramagnetic phases driven by extended 5d orbitals with entangled spin and orbital degrees of freedom.
RESUMO
We report the first measurements of phonon dispersion curves on the (001) surface of the strong three-dimensional topological insulator Bi2Se3. The surface phonon measurements were carried out with the aid of coherent helium beam surface scattering techniques. The results reveal a prominent signature of the exotic metallic Dirac fermion quasiparticles, including a strong Kohn anomaly. The signature is manifest in a low energy isotropic convex dispersive surface phonon branch with a frequency maximum of 1.8 THz and having a V-shaped minimum at approximately 2kF that defines the Kohn anomaly. Theoretical analysis attributes this dispersive profile to the renormalization of the surface phonon excitations by the surface Dirac fermions. The contribution of the Dirac fermions to this renormalization is derived in terms of a Coulomb-type perturbation model.
RESUMO
The electronic structure and magnetism of Ir 5d5 states in nonmetallic, weakly ferromagnetic BaIrO3 are probed with x-ray absorption techniques. Contrary to expectation, the Ir 5d orbital moment is found to be ~1.5 times larger than the spin moment. This unusual, atomiclike nature of the 5d moment is driven by a strong spin-orbit interaction in heavy Ir ions, as confirmed by the nonstatistical large branching ratio at Ir L(2,3) absorption edges. As a consequence, orbital interactions cannot be neglected when addressing the nature of magnetic ordering in BaIrO3. The local moment behavior persists even as the metallic-paramagnetic phase boundary is approached with Sr doping or applied pressure.
RESUMO
The hydrocarbon-degrading bacterium Micrococcus luteus strain Modasa was isolated from contaminated soil from Modasa, North Gujarat, India. Whole-genome sequencing and analysis provide an insight into the potentially important genes responsible for bioremediation.
RESUMO
The spin-valve effect is a quantum phenomenon so far only realized in multilayer thin films or heterostructures. Here we report a strong spin-valve effect existing in bulk single crystals of Ca3(Ru1-xCrx)2O7 having an anisotropic, bilayered crystal structure. This discovery opens new avenues to understand the underlying physics of spin valves, and fully realize its potential in practical devices.