530 research outputs found
Jakob Ruf: Leben, Werk und Studien, hg. von Hildegard Elisabeth Keller, 2008
No abstract availabl
Spin-1/2 Triangular Lattice with Orbital Degeneracy in a Metallic Oxide Ag2NiO2
A novel metallic and magnetic transition metal oxide Ag2NiO2 is studied by
means of resistivity, magnetic susceptibility, specific heat and X-ray
diffraction. The crystal structure is characterized by alternating stacking of
a Ni3+O2 layer and a (Ag2)+ layer, the former realizing a spin-1/2 triangular
lattice with eg orbital degeneracy and the latter providing itinerant
electrons. It is found that the NiO2 layer exhibits orbital ordering at Ts =
260 K and antiferromagnetic spin ordering at TN = 56 K. Moreover, a moderately
large mass enhancement is found for the itinerant electrons, suggesting a
significant contribution from the nearly localized Ni 3d state to the Ag 5s
state that forms a broad band.Comment: 9 pages, 5 figures, to be published in Rapid Communications, Phys.
Rev.
Impact of elasticity on the piezoresponse of adjacent ferroelectric domains investigated by scanning force microscopy
As a consequence of elasticity, mechanical deformations of crystals occur on
a length scale comparable to their thickness. This is exemplified by applying a
homogeneous electric field to a multi-domain ferroelectric crystal: as one
domain is expanding the adjacent ones are contracting, leading to clamping at
the domain boundaries. The piezomechanically driven surface corrugation of
micron-sized domain patterns in thick crystals using large-area top electrodes
is thus drastically suppressed, barely accessible by means of piezoresponse
force microscopy
Low-voltage nanodomain writing in He-implanted lithium niobate crystals
A scanning force microscope tip is used to write ferroelectric domains in
He-implanted single-crystal lithium niobate and subsequently probe them by
piezoresponse force microscopy. Investigation of cross-sections of the samples
showed that the buried implanted layer, \,\textmu m below the surface,
is non-ferroelectric and can thus act as a barrier to domain growth. This
barrier enabled stable surface domains of \,\textmu m size to be written
in 500\,\textmu m-thick crystal substrates with voltage pulses of only 10\,V
applied to the tip
Anomalous temperature evolution of the internal magnetic field distribution in the charge-ordered triangular antiferromagnet AgNiO2
Zero-field muon-spin relaxation measurements of the frustrated triangular
quantum magnet AgNiO2 are consistent with a model of charge disproportionation
that has been advanced to explain the structural and magnetic properties of
this compound. Below an ordering temperature of T_N=19.9(2) K we observe six
distinct muon precession frequencies, due to the magnetic order, which can be
accounted for with a model describing the probable muon sites. The precession
frequencies show an unusual temperature evolution which is suggestive of the
separate evolution of two opposing magnetic sublattices.Comment: 4 pages, 3 figure
Contrast Mechanisms for the Detection of Ferroelectric Domains with Scanning Force Microscopy
We present a full analysis of the contrast mechanisms for the detection of
ferroelectric domains on all faces of bulk single crystals using scanning force
microscopy exemplified on hexagonally poled lithium niobate. The domain
contrast can be attributed to three different mechanisms: i) the thickness
change of the sample due to an out-of-plane piezoelectric response (standard
piezoresponse force microscopy), ii) the lateral displacement of the sample
surface due to an in-plane piezoresponse, and iii) the electrostatic tip-sample
interaction at the domain boundaries caused by surface charges on the
crystallographic y- and z-faces. A careful analysis of the movement of the
cantilever with respect to its orientation relative to the crystallographic
axes of the sample allows a clear attribution of the observed domain contrast
to the driving forces respectively.Comment: 8 pages, 8 figure
Comparing and characterizing some constructions of canonical bases from Coxeter systems
The Iwahori-Hecke algebra of a Coxeter system has a
"standard basis" indexed by the elements of and a "bar involution" given by
a certain antilinear map. Together, these form an example of what Webster calls
a pre-canonical structure, relative to which the well-known Kazhdan-Lusztig
basis of is a canonical basis. Lusztig and Vogan have defined a
representation of a modified Iwahori-Hecke algebra on the free
-module generated by the set of twisted involutions in
, and shown that this module has a unique pre-canonical structure satisfying
a certain compatibility condition, which admits its own canonical basis which
can be viewed as a generalization of the Kazhdan-Lusztig basis. One can modify
the parameters defining Lusztig and Vogan's module to obtain other
pre-canonical structures, each of which admits a unique canonical basis indexed
by twisted involutions. We classify all of the pre-canonical structures which
arise in this fashion, and explain the relationships between their resulting
canonical bases. While some of these canonical bases are related in a trivial
fashion to Lusztig and Vogan's construction, others appear to have no simple
relation to what has been previously studied. Along the way, we also clarify
the differences between Webster's notion of a canonical basis and the related
concepts of an IC basis and a -kernel.Comment: 32 pages; v2: additional discussion of relationship between canonical
bases, IC bases, and P-kernels; v3: minor revisions; v4: a few corrections
and updated references, final versio
Impact of the tip radius on the lateral resolution in piezoresponse force microscopy
We present a quantitative investigation of the impact of tip radius as well
as sample type and thickness on the lateral resolution in piezoresponse force
microscopy (PFM) investigating bulk single crystals. The observed linear
dependence of the width of the domain wall on the tip radius as well as the
independence of the lateral resolution on the specific crystal-type are
validated by a simple theoretical model. Using a Ti-Pt-coated tip with a
nominal radius of 15 nm the so far highest lateral resolution in bulk crystals
of only 17 nm was obtained
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