Theory of spin-polarized scanning tunneling microscopy applied to local spins

We provide a theory for scanning tunneling microscopy and spectroscopy using a spin-polarized tip. It it shown that the tunneling conductance can be partitioned into three separate contributions, a background conductance which is independent of the local spin, a dynamical conductance which is proportional to the local spin moment, and a conductance which is proportional to the noise spectrum of the local spin interactions. The presented theory is applicable to setups with magnetic tip and substrate in non-collinear arrangement, as well as for non-magnetic situations. The partitioning of the tunneling current suggests a possibility to extract the total spin moment of the local spin from the dynamical conductance. The dynamical conductance suggests a possibility to generate very high frequency spin-dependent ac currents and/or voltages. We also propose a measurement of the dynamical conductance that can be used to determine the character of the effective exchange interaction between individual spins in clusters. The third contribution to the tunneling current is associated with the spin-spin correlations induced by the exchange interaction between the local spin moment and the tunneling electrons. We demonstrate how this term can be used in the analysis of spin excitations recorded in conductance measurements. Finally, we propose to use spin-polarized scanning tunneling microscopy for detailed studies of the spin excitation spectrum.Comment: 12 pages, 4 figure, updated to match the published version, to appear in the Phys. Rev.

Ecosystem engineering creates a direct nutritional link between 600-m deep cold-water coral mounds and surface productivity

Cold-water corals (CWCs) form large mounds on the seafloor that are hotspots of biodiversity in the deep sea, but it remains enigmatic how CWCs can thrive in this food-limited environment. Here, we infer from model simulations that the interaction between tidal currents and CWC-formed mounds induces downwelling events of surface water that brings organic matter to 600-m deep CWCs. This positive feedback between CWC growth on carbonate mounds and enhanced food supply is essential for their sustenance in the deep sea and represents an example of ecosystem engineering of unparalleled magnitude. This ’topographically-enhanced carbon pump’ leaks organic matter that settles at greater depths. The ubiquitous presence of biogenic and geological topographies along ocean margins suggests that carbon sequestration through this pump is of global importance. These results indicate that enhanced stratification and lower surface productivity, both expected consequences of climate change, may negatively impact the energy balance of CWCs

Electronic structure and magnetism of equiatomic FeN

In order to investigate the phase stability of equiatomic FeN compounds and the structure-dependent magnetic properties, the electronic structure and total energy of FeN with NaCl, ZnS and CsCl structures and various magnetic configurations are calculated using the first-principles TB-LMTO-ASA method. Among all the FeN phases considered, the antiferromagnetic NaCl structure with q=(00pi) is found to have the lowest energy at the theoretical equilibrium volume. However, the FM NaCl phase lies only 1mRyd higher. The estimated equilibrium lattice constant for nonmagnetic ZnS-type FeN agrees quite well with the experimental value, but for the AFM NaCl phase the estimated value is 6.7% smaller than that observed experimentally. For ZnS-type FeN, metastable magnetic states are found for volumes larger than the equilibrium value. On the basis of an analysis of the atom- and orbital-projected density of states and orbital-projected Crystal Orbital Hamilton Population, the iron-nitrogen interactions in NM ZnS, AFM NaCl and FM CsCl structures are discussed. The leading Fe-N interactions is due to the d-p iron-nitrogen hybridization, while considerable s-p and p-p hybridizations are also observed in all three phases. The iron magnetic moment in FeN is found to be highly sensitive to the nearest-neighboring Fe-N distance. In particular, the magnetic moment shows an abrupt drop from a value of about 2 muB to zero with the reduction of the Fe-N distance for the ZnS and CsCl structures.Comment: 12 pages, 6 figure

Measuring Client Experiences of Motivational Interviewing During a Lifestyle Intervention

The Client Evaluation of Motivational Interviewing was used to assess motivational interviewing experiences in a predominantly female, African American sample from the Southeastern United States who received motivational interviewing-based feedback during a multicomponent lifestyle intervention. Motivational interviewing was experienced differently than a primarily White, male, Northeastern mental health sample

Spontaneous separation of two-component Fermi gases in a double-well trap

The two-component Fermi gas in a double-well trap is studied using the density functional theory and the density profile of each component is calculated within the Thomas-Fermi approximation. We show that the two components are spatially separate in the two wells once the repulsive interaction exceeds the Stoner point, signaling the occurrence of the ferromagnetic transition. Therefore, the double-well trap helps to explore itinerant ferromagnetism in atomic Fermi gases, since the spontaneous separation can be examined by measuring component populations in one well.Comment: 6 pages, 6 figures, to appear in ep

Correlated metals and the LDA+U method

While LDA+U method is well established for strongly correlated materials with well localized orbitals, its application to weakly correlated metals is questionable. By extending the LDA Stoner approach onto LDA+U, we show that LDA+U enhances the Stoner factor, while reducing the density of states. Arguably the most important correlation effects in metals, fluctuation-induced mass renormalization and suppression of the Stoner factor, are missing from LDA+U. On the other hand, for {\it moderately} correlated metals LDA+U may be useful. With this in mind, we derive a new version of LDA+U that is consistent with the Hohenberg-Kohn theorem and can be formulated as a constrained density functional theory. We illustrate all of the above on concrete examples, including the controversial case of magnetism in FeAl.Comment: Substantial changes. In particular, examples of application of the proposed functional are adde