4,960 research outputs found
Antisymmetric magnetoresistance in magnetic multilayers with perpendicular anisotropy
While magnetoresistance (MR) has generally been found to be symmetric in
applied field in non-magnetic or magnetic metals, we have observed
antisymmetric MR in Co/Pt multilayers. Simultaneous domain imaging and
transport measurements show that the antisymmetric MR is due to the appearance
of domain walls that run perpendicular to both the magnetization and the
current, a geometry existing only in materials with perpendicular magnetic
anisotropy. As a result, the extraordinary Hall effect (EHE) gives rise to
circulating currents in the vicinity of the domain walls that contributes to
the MR. The antisymmetric MR and EHE have been quantitatively accounted for by
a theoretical model.Comment: 17 pages, 4 figure
Unusual Magnetization Reversal in [Co/Pt]\u3csub\u3e4\u3c/sub\u3e Multilayers with Perpendicular Anisotropy
Unusual magnetization reversal of [Co(4 Å)/Pt(10 Å)]4 multilayers with perpendicular magnetic anisotropy has been revealed macroscopically by magnetometry measurements and microscopically by magneto-optical Kerr effect microscopy and magnetic force microscopy (MFM) imaging. During the first-order reversal process, the magnetization first decreases, then reaches a plateau, and finally rises back to saturation, corresponding to expanding bubble domains, stationary domains, and fading contrast but unchanged boundary domains, respectively. MFM imaging reveals the existence of many submicron-scaled unreversed channels within the boundary of the “bubble” domains. The magnetization reversal behavior can be accounted for by the evolution of the unusual domain structures in different field regimes
Extended Impurity Potential in a d_{x^2-y^2} Superconductor
We investigate the role of a finite potential range of a nonmagnetic impurity
for the local density of states in a d_{x^2-y^2} superconductor. Impurity
induced subgap resonances are modified by the appearance of further scattering
channels beyond the --wave scattering limit. The structure of the local
density of states (DOS) in the vicinity of the impurity is significantly
enhanced and therefore improves the possibility for observing the
characteristic anisotropic spatial modulation of the local DOS in a d_{x^2-y^2}
superconductor by scanning tunneling microscopy.Comment: 4 pages, Revtex, with 4 embedded eps figures. Submitted to Phys. Rev.
Let
Unusual Magnetization Reversal in [Co/Pt]\u3csub\u3e4\u3c/sub\u3e Multilayers with Perpendicular Anisotropy
Unusual magnetization reversal of [Co(4 Å)/Pt(10 Å)]4 multilayers with perpendicular magnetic anisotropy has been revealed macroscopically by magnetometry measurements and microscopically by magneto-optical Kerr effect microscopy and magnetic force microscopy (MFM) imaging. During the first-order reversal process, the magnetization first decreases, then reaches a plateau, and finally rises back to saturation, corresponding to expanding bubble domains, stationary domains, and fading contrast but unchanged boundary domains, respectively. MFM imaging reveals the existence of many submicron-scaled unreversed channels within the boundary of the “bubble” domains. The magnetization reversal behavior can be accounted for by the evolution of the unusual domain structures in different field regimes
Quantum critical effects on transition temperature of magnetically mediated p-wave superconductivity
We determine the behavior of the critical temperature of magnetically
mediated p-wave superconductivity near a ferromagnetic quantum critical point
in three dimensions, distinguishing universal and non-universal aspects of the
result. We find that the transition temperature is non-zero at the critical
point, raising the possibility of superconductivity in the ferromagnetic phase.Comment: 4 pages, 4 figure
Fluctuation Exchange Analysis of Superconductivity in the Standard Three-Band CuO2 Model
The fluctuation exchange, or FLEX, approximation for interacting electrons is
applied to study instabilities in the standard three-band model for CuO2 layers
in the high-temperature superconductors. Both intra-orbital and near-neigbor
Coulomb interactions are retained. The filling dependence of the d(x2-y2)
transition temperature is studied in both the "hole-doped" and "electron-doped"
regimes using parameters derived from constrained-occupancy density-functional
theory for La2CuO4. The agreement with experiment on the overdoped hole side of
the phase diagram is remarkably good, i.e., transitions emerge in the 40 K
range with no free parameters. In addition the importance of the "orbital
antiferromagnetic," or flux phase, charge density channel is emphasized for an
understanding of the underdoped regime.Comment: REVTex and PostScript, 31 pages, 26 figures; to appear in Phys. Rev.
B (1998); only revised EPS figures 3, 4, 6a, 6b, 6c, 7 and 8 to correct
disappearance of some labels due to technical problem
Vortex Pull by an External Current
In the context of a dynamical Ginzburg-Landau model it is shown numerically
that under the influence of a homogeneous external current J the vortex drifts
against the current with velocity in agreement to earlier analytical
predictions. In the presence of dissipation the vortex undergoes skew
deflection at an angle with respect to the
external current. It is shown analytically and verified numerically that the
angle and the speed of the vortex are linked through a simple
mathematical relation.Comment: 19 pages, LATEX, 6 Postscript figures included in separate compressed
fil
On Existence and Properties of Approximate Pure Nash Equilibria in Bandwidth Allocation Games
In \emph{bandwidth allocation games} (BAGs), the strategy of a player
consists of various demands on different resources. The player's utility is at
most the sum of these demands, provided they are fully satisfied. Every
resource has a limited capacity and if it is exceeded by the total demand, it
has to be split between the players. Since these games generally do not have
pure Nash equilibria, we consider approximate pure Nash equilibria, in which no
player can improve her utility by more than some fixed factor through
unilateral strategy changes. There is a threshold (where
is a parameter that limits the demand of each player on a specific
resource) such that -approximate pure Nash equilibria always exist for
, but not for . We give both
upper and lower bounds on this threshold and show that the
corresponding decision problem is -hard. We also show that the
-approximate price of anarchy for BAGs is . For a restricted
version of the game, where demands of players only differ slightly from each
other (e.g. symmetric games), we show that approximate Nash equilibria can be
reached (and thus also be computed) in polynomial time using the best-response
dynamic. Finally, we show that a broader class of utility-maximization games
(which includes BAGs) converges quickly towards states whose social welfare is
close to the optimum
Quantum transport in ultracold atoms
Ultracold atoms confined by engineered magnetic or optical potentials are
ideal systems for studying phenomena otherwise difficult to realize or probe in
the solid state because their atomic interaction strength, number of species,
density, and geometry can be independently controlled. This review focuses on
quantum transport phenomena in atomic gases that mirror and oftentimes either
better elucidate or show fundamental differences with those observed in
mesoscopic and nanoscopic systems. We discuss significant progress in
performing transport experiments in atomic gases, contrast similarities and
differences between transport in cold atoms and in condensed matter systems,
and survey inspiring theoretical predictions that are difficult to verify in
conventional setups. These results further demonstrate the versatility offered
by atomic systems in the study of nonequilibrium phenomena and their promise
for novel applications.Comment: 24 pages, 7 figures. A revie
Differential Regulation of Trichome Formation on the Adaxial and Abaxial Leaf Surfaces by Gibberellins and Photoperiod in Arabidopsis thaliana (L.) Heynh
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