1,615 research outputs found
Linear-in-frequency optical conductivity in GdPtBi due to transitions near the triple points
The complex optical conductivity of the half-Heusler compound GdPtBi is
measured in a frequency range from 20 to 22 000 cm (2.5 meV - 2.73 eV)
at temperatures down to 10 K in zero magnetic field. We find the real part of
the conductivity, , to be almost perfectly linear in
frequency over a broad range from 50 to 800 cm ( 6 - 100 meV) for
K. This linearity strongly suggests the presence of
three-dimensional linear electronic bands with band crossings (nodes) near the
chemical potential. Band-structure calculations show the presence of triple
points, where one doubly degenerate and one nondegenerate band cross each other
in close vicinity of the chemical potential. From a comparison of our data with
the optical conductivity computed from the band structure, we conclude that the
observed nearly linear originates as a cumulative effect
from all the transitions near the triple points.Comment: 5+ pages, 5 figures, band-structure and optical-conductivity
calculations adde
Two-channel conduction in YbPtBi
We investigated transport, magnetotransport, and broadband optical properties
of the half-Heusler compound YbPtBi. Hall measurements evidence two types of
charge carriers: highly mobile electrons with a temperature-dependent
concentration and low-mobile holes; their concentration stays almost constant
within the investigated temperature range from 2.5 to 300 K. The optical
spectra (10 meV - 2.7 eV) can be naturally decomposed into contributions from
intra- and interband absorption processes, the former manifesting themselves as
two Drude bands with very different scattering rates, corresponding to the
charges with different mobilities. These results of the optical measurements
allow us to separate the contributions from electrons and holes to the total
conductivity and to implement a two-channel-conduction model for description of
the magnetotransport data. In this approach, the electron and hole mobilities
are found to be around 50000 and 10 cm/Vs at the lowest temperatures (2.5
K), respectively.Comment: 6 page
Large zero-field cooled exchange-bias in bulk Mn2PtGa
We report a large exchange-bias (EB) effect after zero-field cooling the new
tetragonal Heusler compound Mn2PtGa from the paramagnetic state. The
first-principle calculation and the magnetic measurements reveal that Mn2PtGa
orders ferrimagnetically with some ferromagnetic (FM) inclusions. We show that
ferrimagnetic (FI) ordering is essential to isothermally induce the exchange
anisotropy needed for the zero-field cooled (ZFC) EB during the virgin
magnetization process. The complex magnetic behavior at low temperatures is
characterized by the coexistence of a field induced irreversible magnetic
behavior and a spin-glass-like phase. The field induced irreversibility
originates from an unusual first-order FI to antiferromagnetic transition,
whereas, the spin-glass like state forms due to the existence of anti-site
disorder intrinsic to the material.Comment: 5 pages, 4 figures, supplementary material included in a separate
file; accepted for publication in PR
Nonclassical properties of states engineered by superpositions of quantum operations on classical states
We consider an experimentally realizable scheme for manipulating quantum
states using a general superposition of products of field annihilation
() and creation () operators of the type (), with . Such an
operation, when applied on states with classical features, is shown to
introduce strong nonclassicality. We quantify the generated degree of
nonclassicality by the negative volume of Wigner distribution in the phase
space and investigate two other observable nonclassical features,
sub-Poissonian statistics and squeezing. We find that the operation introduces
negativity in the Wigner distribution of an input coherent state and changes
the Gaussianity of an input thermal state. This provides the possibility of
engineering quantum states with specific nonclassical features.Comment: 19 pages, IOPclass(iopart.cls
Spin-lattice coupling mediated giant magnetodielectricity across the spin reorientation in Ca2FeCoO5
The structural, phonon, magnetic, dielectric, and magneto dielectric
responses of the pure bulk Brownmillerite compound Ca2FeCoO5 are reported. This
compound showed giant magneto dielectric response (10%-24%) induced by strong
spin-lattice coupling across its spin reorientation transition (150-250 K). The
role of two Debye temperatures pertaining to differently coordinated sites in
the dielectric relaxations is established. The positive giant
magneto-dielectricity is shown to be a direct consequence of the modulations in
the lattice degrees of freedom through applied external field across the spin
reorientation transition. Our study illustrates novel control of
magneto-dielectricity by tuning the spin reorientation transition in a material
that possess strong spin lattice coupling.Comment: 7 pages, 12 figure
Effect of La Doping on Microstructure and Critical Current Density of MgB2
In the present study, La-doped MgB_2 superconductors with different doping
level (Mg1-xLaxB2; x=0.00, 0.01, 0.03 & 0.05) have been synthesized by
solid-state reaction route at ambient pressure. Effect of La doping have been
investigated in relation to microstructural characteristics and superconducting
properties, particularly intragrain critical current density (Jc). The
microstructural characteristics of the as synthesized Mg(La)B2 compounds were
studied employing transmission electron microscopic (TEM) technique. The TEM
investigations reveal inclusion of LaB6 nanoparticles within the MgB2 grains
which provide effective flux pinning centres. The evaluation of intragrain Jc
through magnetic measurements on the fine powdered version of the as
synthesized samples reveal that Jc of the samples change significantly with the
doping level. The optimum result on Jc is obtained for Mg0.97La0.03B2 at 5K,
the Jc reaches ~1.4x107A/cm2 in self field, ~2.1 x 106A/cm2 at 1T, ~2.5 x
105A/cm2 at 2.5T and ~1.8 x 104 A/cm2 at 4.5T. The highest value of intragrain
Jc in Mg0.97La0.03B2 superconductor has been attributed to the inclusion of
LaB6 nanoparticles which are capable of providing effective flux pinning
centres
Geometry versus Entanglement in Resonating Valence Bond Liquids
We investigate the behavior of bipartite as well as genuine multipartite
entanglement of a resonating valence bond state on a ladder. We show that the
system possesses significant amounts of bipartite entanglement in the steps of
the ladder while no substantial bipartite entanglement is present in the rails.
Genuine multipartite entanglement present in the system is negligible. The
results are in stark contrast with the entanglement properties of the same
state on isotropic lattices in two and higher dimensions, indicating that the
geometry of the lattice can have important implications on the quality of
quantum information and other tasks that can be performed by using multiparty
states on that lattice.Comment: 6 pages, 8 figures, RevTeX
Development of 0.2C-CrMnMoV Ultra High Strength Steel
A study was carried out to develop a low alloy ultra high
strength steel by induction melting and thermomechanical
treatment (TMT) containing alloying elements like carbon,
manganese, molybdenum, chromium and vanadium. A
base alloy was prepared with 0.24%C, 1.16% Mn, 0.23%
Si, 5.61% Cr, 0.42%V, 1.01% Mo, 0.026%S and 0.032%P.
It showed tensile strength of 1467 MPa, yield strength of
about 1180 MPa, impact strength of 6.3J and elongation of
5.9% in as-tempered condition. Other alloy was prepared
by addition of 0.054% titanium with the base composition.
It displayed tensile strength, yield strength, impact
toughness and % elongation of 1615 MPa, 1240 MPa,
8.2J and 6.15%, respectively. The optical, SEM and TEM
microstructures confirmed that the base alloy and the
titanium alloy consisted with tempered lath martensites.
The remaining part of the ingot was further processed by
the thermomechanical treatment. The ingots were rolled in
two passes, initially at 950 C and subsequently at 850 C
followed by immediate cooling in oil. The TMT plates of
the base alloy confirmed the tensile strength of 1755 MPa,
yield strength in excess of 1460 MPa and impact strength
of 9.1J. The titanium added TMT plate displayed tensile
strength of 1860 MPa, yield strength of 1580 MPa and
impact strength of 10.1J. Microstructures of titanium
added alloy consisted finer lath martensite and precipitates
of titanium carbides/carbonitrides. It was observed that the
addition of titanium significantly improved the mechanical
properties of 0.2C-Cr Mn Mo V alloys and the mechanical
properties were also improved significantly by
thermomechanical treatment
Fabrication of Resorcinol-Formaldehyde Xerogel based High Aspect Ratio 3-D Hierarchical C-MEMS Structures
We demonstrate a novel method to fabricate arrays of resorcinol-
formaldehyde xerogel (RFX) based high aspect ratio (HAR) three-
dimensional (3-D) hierarchical C-MEMS structures. Starting from
a master pattern of HAR 3-D posts fabricated in SU-8 negative
photoresist by photolithography, a negative PDMS stamp with
arrays of holes was prepared by micromolding. The PDMS stamp
was then used to fabricate HAR 3-D RFX posts by replica molding.
The 3-D RFX posts thus fabricated were electrosprayed with SU-8
or an RF sol in the form of submicron or nano sized droplets and
followed by pyrolysis to yield HAR 3-D hierarchical carbon posts.
To characterize their use in C-MEMS based batteries,
galvanostatic (charge and discharge) experiments on RFX derived
carbon showed that it can be reversibly intercalated with Li ions
and possesses superior intercalation properties as compared to SU-
8 derived carbon which is a widely used material in C-MEMS
Nontransgenic models of breast cancer
Numerous models have been developed to address key elements in the biology of breast cancer development and progression. No model is ideal, but the most useful are those that reflect the natural history and histopathology of human disease, and allow for basic investigations into underlying cellular and molecular mechanisms. We describe two types of models: those that are directed toward early events in breast cancer development (hyperplastic alveolar nodules [HAN] murine model, MCF10AT human xenograft model); and those that seek to reflect the spectrum of metastatic disease (murine sister cell lines 67, 168, 4T07, 4T1). Collectively, these models provide cell lines that represent all of the sequential stages of progression in breast disease, which can be modified to test the effect of genetic changes
- …