5,122 research outputs found
Nanoscale Defect Formation on InP(111) Surfaces after MeV Sb Implantation
We have studied the surface modifications as well as the surface roughness of
the InP(111) surfaces after 1.5 MeV Sb ion implantations. Scanning Probe
Microscope (SPM) has been utilized to investigate the ion implanted InP(111)
surfaces. We observe the formation of nanoscale defect structures on the InP
surface. The density, height and size of the nanostructures have been
investigated here as a function of ion fluence. The rms surface roughness, of
the ion implanted InP surfaces, demonstrates two varied behaviors as a function
of Sb ion fluence. Initially, the roughness increases with increasing fluence.
However, after a critical fluence the roughness decreases with increasing
fluence. We have further applied the technique of Raman scattering to
investigate the implantation induced modifications and disorder in InP. Raman
Scattering results demonstrate that at the critical fluence, where the decrease
in surface roughness occurs, InP lattice becomes amorphous.Comment: 18 pages, 9 figure
Singular Effects of Impurities near the Ferromagnetic Quantum-Critical Point
Systematic theoretical results for the effects of a dilute concentration of
magnetic impurities on the thermodynamic and transport properties in the region
around the quantum critical point of a ferromagnetic transition are obtained.
In the quasi-classical regime, the dynamical spin fluctuations enhance the
Kondo temperature. This energy scale decreases rapidly in the quantum
fluctuation regime, where the properties are those of a line of critical points
of the multichannel Kondo problem with the number of channels increasing as the
critical point is approached, except at unattainably low temperatures where a
single channel wins out.Comment: 4 pages, 2 figure
Universality in heavy-fermion systems with general degeneracy
We discuss the relation between the T^{2}-coefficient of electrical
resistivity and the T-linear specific-heat coefficient for
heavy-fermion systems with general , where is the degeneracy of
quasi-particles. A set of experimental data reveals that the Kadowaki-Woods
relation; , collapses
remarkably for large-N systems, although this relation has been regarded to be
commonly applicable to the Fermi-liquids. Instead, based on the Fermi-liquid
theory we propose a new relation;
with and .
This new relation exhibits an excellent agreement with the data for whole the
range of degenerate heavy-fermions.Comment: 2 figures, to appear in Phys. Rev. Let
Effect of Strain Relaxation on Magnetotransport properties of epitaxial La_0.7Ca_0.3MnO_3 films
In this paper, we have studied the effect of strain relaxation on
magneto-transport properties of La_0.7Ca_0.3MnO_3 epitaxial films (200 nm
thick), which were deposited by pulsed laser deposition technique under
identical conditions. All the films are epitaxial and have cubic unit cell. The
amount of strain relaxation has been varied by taking three different single
crystal substrates of SrTiO_3, LaAlO_3 and MgO. It has been found that for
thicker films the strain gets relaxed and produces variable amount of disorder
depending on the strength of strain relaxation. The magnitude of lattice
relaxation has been found to be 0.384, 3.057 and 6.411 percent for film
deposited on SrTiO_3, LaAlO_3 and MgO respectively. The films on LaAlO_3 and
SrTiO_3 show higher T_{IM} of 243 K and 217 K respectively as compared to
T_{IM} of 191 K for the film on MgO. Similarly T_C of the films on SrTiO_3 and
LaAlO_3 is sharper and has value of 245 K and 220 K respectively whereas the TC
of the film on MgO is 175 K. Higher degree of relaxation creates more defects
and hence TIM (T_C) of the film on MgO is significantly lower than of SrTiO_3
and LaAlO_3. We have adopted a different approach to correlate the effect of
strain relaxation on magneto-transport properties of LCMO films by evaluating
the resistivity variation through Mott's VRH model. The variable presence of
disorder in these thick films due to lattice relaxation which have been
analyzed through Mott's VRH model provides a strong additional evidence that
the strength of lattice relaxation produces disorder dominantly by increase in
density of defects such as stacking faults, dislocations, etc. which affect the
magneto-transport properties of thick epitaxial La_0.7Ca_0.3MnO_3 films
High-bias stability of monatomic chains
For the metals Au, Pt and Ir it is possible to form freely suspended
monatomic chains between bulk electrodes. The atomic chains sustain very large
current densities, but finally fail at high bias. We investigate the breaking
mechanism, that involves current-induced heating of the atomic wires and
electromigration forces. We find good agreement of the observations for Au
based on models due to Todorov and coworkers. The high-bias breaking of atomic
chains for Pt can also be described by the models, although here the parameters
have not been obtained independently. In the limit of long chains the breaking
voltage decreases inversely proportional to the length.Comment: 7 pages, 5 figure
Signatures of valence fluctuations in CeCu2Si2 under high pressure
Simultaneous resistivity and a.c.-specific heat measurements have been
performed under pressure on single crystalline CeCu2Si2 to over 6 GPa in a
hydrostatic helium pressure medium. A series of anomalies were observed around
the pressure coinciding with a maximum in the superconducting critical
temperature, . These anomalies can be linked with an abrupt change
of the Ce valence, and suggest a second quantum critical point at a pressure
GPa, where critical valence fluctuations provide the
superconducting pairing mechanism, as opposed to spin fluctuations at ambient
pressure. Such a valence instability, and associated superconductivity, is
predicted by an extended Anderson lattice model with Coulomb repulsion between
the conduction and f-electrons. We explain the T-linear resistivity found at
in this picture, while other anomalies found around can be
qualitatively understood using the same model.Comment: Submitted to Phys. Rev.
When grassroots innovation movements encounter mainstream institutions: implications for models of inclusive innovation
Grassroots innovation movements (GIMs) can be regarded as initiators or advocates of alternative pathways of innovation. Sometimes these movements engage with more established science, technology and innovation (STI) institutions and development agencies in pursuit of their goals. In this paper, we argue that an important aspect to encounters between GIMs and mainstream STI institutions is the negotiation of different framings of grassroots innovation and development of policy models for inclusive innovation. These encounters can result in two different modes of engagement by GIMs; what we call insertion and mobilization. We illustrate and discuss these interrelated notions of framings and modes of engagement by drawing on three case studies of GIMs: the Social Technologies Network in Brazil, and the Honey Bee Network and People's Science Movements in India. The cases highlight that inclusion in the context of GIMs is not an unproblematic, smooth endeavour, and involves diverse interpretations and framings, which shape what and who gets included or excluded. Within the context of increasing policy interest, the analysis of encounters between GIMs and STI institutions can offer important lessons for the design of models of inclusive innovation and development
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