16 research outputs found
Imaging anomalous nematic order and strain in optimally doped BaFe(As,P)
We present the strain and temperature dependence of an anomalous nematic
phase in optimally doped BaFe(As,P). Polarized ultrafast optical
measurements reveal broken 4-fold rotational symmetry in a temperature range
above in which bulk probes do not detect a phase transition. Using
ultrafast microscopy, we find that the magnitude and sign of this nematicity
vary on a m length scale, and the temperature at which it
onsets ranges from 40 K near a domain boundary to 60 K deep within a domain.
Scanning Laue microdiffraction maps of local strain at room temperature
indicate that the nematic order appears most strongly in regions of weak,
isotropic strain. These results indicate that nematic order arises in a genuine
phase transition rather than by enhancement of local anisotropy by a strong
nematic susceptibility. We interpret our results in the context of a proposed
surface nematic phase
Imaging anomalous nematic order and strain in optimally doped BaFe(As,P)
We present the strain and temperature dependence of an anomalous nematic
phase in optimally doped BaFe(As,P). Polarized ultrafast optical
measurements reveal broken 4-fold rotational symmetry in a temperature range
above in which bulk probes do not detect a phase transition. Using
ultrafast microscopy, we find that the magnitude and sign of this nematicity
vary on a m length scale, and the temperature at which it
onsets ranges from 40 K near a domain boundary to 60 K deep within a domain.
Scanning Laue microdiffraction maps of local strain at room temperature
indicate that the nematic order appears most strongly in regions of weak,
isotropic strain. These results indicate that nematic order arises in a genuine
phase transition rather than by enhancement of local anisotropy by a strong
nematic susceptibility. We interpret our results in the context of a proposed
surface nematic phase
Monitoring of microplastic pollution in the Arctic: Recent developments in polymer identification, quality assurance and control (QA/QC), and data reporting
The pollution of the environment with plastics is of growing concern worldwide, including the Arctic region. While larger plastic pieces are a visible pollution issue, smaller microplastics are not visible with the naked eye. These particles are available for interaction by Arctic biota and have become a concern for animal and human health. The determination of microplastic properties includes several methodological steps, i.e. sampling, extraction, quantification and chemical identification. This review discusses suitable analytical tools for the identification, quantification and characterization of microplastics in the context of monitoring in the Arctic. It further addresses quality assurance and quality control (QA/QC) which is particularly important for the determination of microplastic in the Arctic, as both contamination and analyte losses can occur. It presents specific QA/QC measures for sampling procedures and for the handling of samples in the laboratory, either on land or on ship, and considering the small size of microplastics as well as the high risk of contamination. The review depicts which data should be mandatory to report, thereby supporting a framework for harmonized data reporting.publishedVersio
Resonance-enhanced optical nonlinearity in the Weyl semimetal TaAs
While all media can exhibit first-order conductivity describing current
linearly proportional to electric field, , the second-order conductivity,
, relating current to , is nonzero only when inversion
symmetry is broken. Second order nonlinear optical responses are powerful tools
in basic research, as probes of symmetry breaking, and in optical technology as
the basis for generating currents from far-infrared to X-ray wavelengths. The
recent surge of interest in Weyl semimetals with acentric crystal structures
has led to the discovery of a host of -related phenomena in this
class of materials, such as polarization-selective conversion of light to dc
current (photogalvanic effects) and the observation of giant second-harmonic
generation (SHG) efficiency in TaAs at photon energy 1.5 eV. Here, we present
measurements of the SHG spectrum of TaAs revealing that the response at 1.5 eV
corresponds to the high-energy tail of a resonance at 0.7 eV, at which point
the second harmonic conductivity is approximately 200 times larger than seen in
the standard candle nonlinear crystal, GaAs. This remarkably large SHG response
provokes the question of ultimate limits on , which we address
by a new theorem relating frequency-integrated nonlinear response functions to
the third cumulant (or "skewness") of the polarization distribution function in
the ground state. This theorem provides considerable insight into the factors
that lead to the largest possible second-order nonlinear response, specifically
showing that the spectral weight is unbounded and potentially divergent when
the possibility of next-neighbor hopping is included.Comment: 7 pages, 4 figure
Large magneto-optical Kerr effect and imaging of magnetic octupole domains in an antiferromagnetic metal
When a polarized light beam is incident upon the surface of a magnetic
material, the reflected light undergoes a polarization rotation. This
magneto-optical Kerr effect (MOKE) has been intensively studied in a variety of
ferro- and ferrimagnetic materials because it provides a powerful probe for
electronic and magnetic properties as well as for various applications
including magneto-optical recording. Recently, there has been a surge of
interest in antiferromagnets (AFMs) as prospective spintronic materials for
high-density and ultrafast memory devices, owing to their vanishingly small
stray field and orders of magnitude faster spin dynamics compared to their
ferromagnetic counterparts. In fact, the MOKE has proven useful for the study
and application of the antiferromagnetic (AF) state. Although limited to
insulators, certain types of AFMs are known to exhibit a large MOKE, as they
are weak ferromagnets due to canting of the otherwise collinear spin structure.
Here we report the first observation of a large MOKE signal in an AF metal at
room temperature. In particular, we find that despite a vanishingly small
magnetization of 0.002 /Mn, the non-collinear AF metal
MnSn exhibits a large zero-field MOKE with a polar Kerr rotation angle of
20 milli-degrees, comparable to ferromagnetic metals. Our first-principles
calculations have clarified that ferroic ordering of magnetic octupoles in the
non-collinear Neel state may cause a large MOKE even in its fully compensated
AF state without spin magnetization. This large MOKE further allows imaging of
the magnetic octupole domains and their reversal induced by magnetic field. The
observation of a large MOKE in an AF metal should open new avenues for the
study of domain dynamics as well as spintronics using AFMs.Comment: 30 pages, 4 figure
Efficient Sample and Data Processing for Chemical and Physical Characterization of Urban Environmental Microplastics
Recommended from our members
Nonlinear optical properties and spectroscopy of Weyl semimetals
Nonlinear optical properties of materials are useful both for their practical applications, but also as a characterization tool for symmetry in novel systems. However, the nonlinear optical response of a material is often not as one of its fundamental properties, along with band structure, linear conductivity, etc. This has particularly been the case with the recent interest in “quantum materials”: materials such as high-Tc superconductors, topological materials, and exotic magnets. Weyl semimetals are a class of materials where band-touching points have divergent Berry curvature, and are host to a number of unique physical phenomena such as the chiral anomaly and Fermi arc surface states. From the nonlinear optics perspective, Weyl semimetals are interesting since inversion-symmetry breaking Weyl semimetals have been experimentally realized, and breaking of inversion-symmetry is crucial for second order nonlinear optical phenomena.In this dissertation, I present results from a number of studies of the Weyl semimetal TaAs and related compounds using nonlinear optical techniques. As detailed here, TaAs was discovered to have the largest measured nonlinear optical susceptibility of any material, and further, this susceptibility was found to be caused by a resonance in the spectrum of nonlinear optical conductivity. TaAs was also measured to have a photogalvanic effect that has qualitatively different characteristics depending on the direction of measurement. These nonlinear optical properties of the TaAs family of materials may lead to interesting applications in near-field nonlinear optics, and optical pulse shaping below the diffraction limit
Recommended from our members
Nonlinear optical properties and spectroscopy of Weyl semimetals
Nonlinear optical properties of materials are useful both for their practical applications, but also as a characterization tool for symmetry in novel systems. However, the nonlinear optical response of a material is often not as one of its fundamental properties, along with band structure, linear conductivity, etc. This has particularly been the case with the recent interest in “quantum materials”: materials such as high-Tc superconductors, topological materials, and exotic magnets. Weyl semimetals are a class of materials where band-touching points have divergent Berry curvature, and are host to a number of unique physical phenomena such as the chiral anomaly and Fermi arc surface states. From the nonlinear optics perspective, Weyl semimetals are interesting since inversion-symmetry breaking Weyl semimetals have been experimentally realized, and breaking of inversion-symmetry is crucial for second order nonlinear optical phenomena.In this dissertation, I present results from a number of studies of the Weyl semimetal TaAs and related compounds using nonlinear optical techniques. As detailed here, TaAs was discovered to have the largest measured nonlinear optical susceptibility of any material, and further, this susceptibility was found to be caused by a resonance in the spectrum of nonlinear optical conductivity. TaAs was also measured to have a photogalvanic effect that has qualitatively different characteristics depending on the direction of measurement. These nonlinear optical properties of the TaAs family of materials may lead to interesting applications in near-field nonlinear optics, and optical pulse shaping below the diffraction limit