12,526 research outputs found
Localized reversible nanoscale phase separation in Pr_0.63Ca_0.37MnO_3 single crystal using a scanning tunneling microscope tip
We report the destabilization of the charge ordered insulating (COI) state in
a localized region of Pr_0.63Ca_0.37MnO_3 single crystal by current injection
using a scanning tunneling microscope tip. This leads to controlled phase
separation and formation of localized metallic nanoislands in the COI matrix
which have been detected by local tunneling conductance mapping. The metallic
regions thus created persist even after reducing the injected current to lower
values. The original conductance state can be restored by injecting a current
of similar magnitude but of opposite polarity. We thus achieve reversible
nanoscale phase separation that gives rise to the possibility to "write, read,
and erase" nanosized conducting regions in an insulating matrix with high
spatial resolution.Comment: 8 pages, 4 figures, Appl. Phys. Lett (accepted for publication
Black Hole Geometries in Noncommutative String Theory
We obtain a generalized Schwarzschild (GS-) and a generalized
Reissner-Nordstrom (GRN-) black hole geometries in (3+1)-dimensions, in a
noncommutative string theory. In particular, we consider an effective theory of
gravity on a curved -brane in presence of an electromagnetic (EM-) field.
Two different length scales, inherent in its noncommutative counter-part, are
exploited to obtain a theory of effective gravity coupled to an U(1)
noncommutative gauge theory to all orders in . It is shown that the
GRN-black hole geometry, in the Planckian regime, reduces to the GS-black hole.
However in the classical regime it may be seen to govern both
Reissner-Nordstrom and Schwarzschild geometries independently. The emerging
notion of 2D black holes evident in the frame-work are analyzed. It is argued
that the -string in the theory may be described by the near horizon 2D black
hole geometry, in the gravity decoupling limit. Finally, our analysis explains
the nature of the effective force derived from the nonlinear EM-field and
accounts for the Hawking radiation phenomenon in the formalism.Comment: 30 pages, 2 figure
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