1,294 research outputs found
Electric field induced biaxiality and the electro-optic effect in a bent-core nematic liquid crystal
We report the observation of a biaxial nematic phase in a bent-core molecular system using polarizing microscopy, electro-optics, and dielectric spectroscopy, where we find that the biaxiality exists on a microscopic scale. An application of electric field induces a macroscopic biaxiality and in consequence gives rise to electro-optic switching. This electro-optic effect shows significant potential in applications for displays due to its fast high-contrast response. The observed electro-optic switching is explained in terms of the interaction of the ferroelectric clusters with the electric field
Berry curvature unravelled by the Nernst effect in MnGe
The discovery of topological quantum materials represents a striking
innovation in modern condensed matter physics with remarkable fundamental and
technological implications. Their classification has been recently extended to
topological Weyl semimetals, i.e., solid state systems which exhibit the
elusive Weyl fermions as low-energy excitations. Here we show that the Nernst
effect can be exploited as a sensitive probe for determining key parameters of
the Weyl physics, applying it to the non-collinear antiferromagnet MnGe.
This compound exhibits anomalous thermoelectric transport due to enhanced Berry
curvature from Weyl points located extremely close to the Fermi level. We
establish from our data a direct measure of the Berry curvature at the Fermi
level and, using a minimal model of a Weyl semimetal, extract for the first
time the Weyl point energy and their distance in momentum-space
Diode laser assisted surface nitriding of Ti-6Al-4v: properties of the nitrided surface
In the present study, a detailed investigation of mechanical and electrochemical properties of laser-surface-nitrided Ti-6Al-4V has been carried out. Laser treatment is carried out by melting the surface of Ti-6Al-4V substrate using a high power CW diode laser with nitrogen as shrouding environment. The effect of laser parameters (applied power and gas flow rate) on the properties of the nitrided surface was evaluated. The microhardness of the nitrided surface was improved to a maximum of 1175 VHN in the present set of laser processing conditions as compared to 280 VHN of as-received substrate. Surface nitriding increased the potential for pit formation (E pit) significantly as compared to as-received Ti-6Al-4V. Immersion in Hank's solution showed calcium phosphate deposition from the solution. The optimum process parameters for laser surface nitriding were derived
Power spectra of self-organized critical sandpiles
We analyze the power spectra of avalanches in two classes of self-organized
critical sandpile models, the Bak-Tang-Wiesenfeld model and the Manna model. We
show that these decay with a power law, where the exponent value
is significantly smaller than 2 and equals the scaling exponent
relating the avalanche size to its duration. We discuss the basic ingredients
behind this result, such as the scaling of the average avalanche shape.Comment: 7 pages, 3 figures, submitted to JSTA
Sequential Infiltration Synthesis of Silicon Dioxide in Polymers with Ester Groups─Insight from In Situ Infrared Spectroscopy
New strategies to synthesize nanometer-scale silicon dioxide (SiO2) patterns have drawn much attention in applications such as microelectronic and optoelectronic devices, membranes, and sensors, as we are approaching device dimensions shrinking below 10 nm. In this regard, sequential infiltration synthesis (SIS), a two-step gas-phase molecular assembly process that enables localized inorganic material growth in the targeted reactive domains of polymers, is an attractive process. In this work, we performed in situ Fourier transform infrared spectroscopy (FTIR) measurements during SiO2 SIS to investigate the reaction mechanism of trimethylaluminum (TMA) and tri(tert-pentoxy) silanol (TPS) precursors with polymers having ester functional groups (poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), polycaprolactone (PCL), and poly(t-butyl methacrylate) (PBMA)), for the purpose of growing patterned nanomaterials. The FTIR results show that for PMMA and PEMA, a lower percentage of functional groups participated in the reactions and formed weak and unstable complexes. In contrast, almost all functional groups in PCL and PBMA participated in the reactions and showed stable and irreversible interactions with TMA. We discovered that the amount of SiO2 formed is not directly correlated with the number of interacting functional groups. These insights into the SiO2 SIS mechanism will enable nanopatterning of SiO2 for low-dimensional applications
Extremely high magnetoresistance and conductivity in the type-II Weyl semimetals WP2 and MoP2
The peculiar band structure of semimetals exhibiting Dirac and Weyl crossings
can lead to spectacular electronic properties such as large mobilities
accompanied by extremely high magnetoresistance. In particular, two closely
neighbouring Weyl points of the same chirality are protected from annihilation
by structural distortions or defects, thereby significantly reducing the
scattering probability between them. Here we present the electronic properties
of the transition metal diphosphides, WP2 and MoP2, that are type-II Weyl
semimetals with robust Weyl points. We present transport and angle resolved
photoemission spectroscopy measurements, and first principles calculations. Our
single crystals of WP2 display an extremely low residual low-temperature
resistivity of 3 nohm-cm accompanied by an enormous and highly anisotropic
magnetoresistance above 200 million % at 63 T and 2.5 K. These properties are
likely a consequence of the novel Weyl fermions expressed in this compound. We
observe a large suppression of charge carrier backscattering in WP2 from
transport measurements.Comment: Appeared in Nature Communication
Laser surface nitriding of Ti-6Al-4V for bio-implant application
The present study aims at enhancing the biocompatibility of Ti-6Al-4V by laser surface nitriding. Laser surface nitriding has been carried out by melting of sand blasted Ti-6Al-4V substrate using a high power continuous wave DIODE laser with nitrogen as shrouding environment (at a pressure of 5l/min). Following laser treatment, a detailed characterization of the surface has been conducted. Microhardness and biocompatibility have been evaluated. Laser surface nitriding led to formation of dendrites of TiN on the surface. The microhardness is improved to 900- 950 VHN (in laser surface nitriding) as compared to 260 VHN of as-received substrate. Biocompatibility behavior showed a better cell viability in laser surface nitrided Ti-6Al-4V sample as compared to as-received one
The iridium double perovskite Sr2YIrO6 revisited: A combined structural and specific heat study
Recently, the iridate double perovskite SrYIrO has attracted
considerable attention due to the report of unexpected magnetism in this
Ir (5d) material, in which according to the J model, a
non-magnetic ground state is expected. However, in recent works on
polycrystalline samples of the series BaSrYIrO no indication of
magnetic transitions have been found. We present a structural, magnetic and
thermodynamic characterization of SrYIrO single crystals, with emphasis
on the temperature and magnetic field dependence of the specific heat. Here, we
demonstrate the clue role of single crystal X-ray diffraction on the structural
characterization of the SrYIrO double perovskite crystals by reporting
the detection of a supercell, where ,
and are the unit cell dimensions of the reported monoclinic subcell. In
agreement with the expected non-magnetic ground state of Ir (5d) in
SrYIrO, no magnetic transition is observed down to 430~mK. Moreover,
our results suggest that the low temperature anomaly observed in the specific
heat is not related to the onset of long-range magnetic order. Instead, it is
identified as a Schottky anomaly caused by paramagnetic impurities present in
the sample, of the order of \%. These impurities lead to
non-negligible spin correlations, which nonetheless, are not associated with
long-range magnetic ordering.Comment: 20 pages, 10 figure
Size dependent tunneling and optical spectroscopy of CdSe quantum rods
Photoluminescence excitation spectroscopy and scanning tunneling spectroscopy
are used to study the electronic states in CdSe quantum rods that manifest a
transition from a zero dimensional to a one dimensional quantum confined
structure. Both optical and tunneling spectra show that the level structure
depends primarily on the rod diameter and not on length. With increasing
diameter, the band-gap and the excited state level spacings shift to the red.
The level structure was assigned using a multi-band effective-mass model,
showing a similar dependence on rod dimensions.Comment: Accepted to PRL (nearly final version). 4 pages in revtex, 4 figure
Multifractal scaling in the Bak-Tang-Wiesenfeld Sandpile and edge events
An analysis of moments and spectra shows that, while the distribution of
avalanche areas obeys finite size scaling, that of toppling numbers is
universally characterized by a full, nonlinear multifractal spectrum. Rare,
large avalanches dissipating at the border influence the statistics very
sensibly. Only once they are excluded from the sample, the conditional toppling
distribution for given area simplifies enough to show also a well defined,
multifractal scaling. The resulting picture brings to light unsuspected, novel
physics in the model.Comment: 5 pages, 4 figure
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