Pressure-Induced Hydration and Formation of Bilayer Ice in Nacrite, a Kaolin-Group Clay
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99 GENERAL AND MISCELLANEOUS↗
Engineering topics
Lee, Y.
Publications and source records attributed to Lee, Y..
Role of nonlocality in exchange correlation for magnetic two-dimensional van der Waals materials
To obtain accurate independent-particle descriptions for ferromagnetic two-dimensional van der Waals materials, we apply the quasiparticle self-consistent G W (QSGW) method to VI 3 , CrI 3 , CrGeTe 3 , and Fe 3 GeTe 2 . QSGW provides a description of the nonlocal exchange-correlation term in the one-particle Hamiltonian. The nonlocal term is important not only as the U of density functional theory ( DFT ) + U but also for differentiating occupied and unoccupied states in semiconductors. Finally, we show the limitations of DFT + U in mimicking QSGW.
36 MATERIALS SCIENCE↗
OGLE-2018-BLG-0677Lb: A Super-Earth Near the Galactic Bulge
We report the analysis of the microlensing event OGLE-2018-BLG-0677. A small feature in the light curve of the event leads to the discovery that the lens is a star–planet system. Although there are two degenerate solutions that could not be distinguished for this event, both lead to a similar planet-host mass ratio. We perform a Bayesian analysis based on a Galactic model to obtain the properties of the system and find that the planet corresponds to a super-Earth/sub-Neptune with a mass of M{sub planet}=3.96{sub −2.66}{sup +5.88}M{sub ⊕}. The host star has a mass of M{sub host}=0.12{sub −0.08}{sup +0.14} M{sub ⊙}. The projected separation for the inner and outer solutions are 0.63{sub −0.17}{sup +0.20} au and 0.72{sub −0.19}{sup +0.23} au respectively. At Δχ{sup 2}=χ{sup 2}(1L1S)−χ{sup 2}(2L1S)=46, this is by far the lowest Δχ {sup 2} for any securely detected microlensing planet to date, a feature that is closely connected to the fact that it is detected primarily via a “dip” rather than a “bump.”.
79 ASTRONOMY AND ASTROPHYSICS↗
Noncollinear magnetic structure and anisotropic magnetoelastic coupling in cobalt pyrovanadate $\mathrm{Co_2V_2O_7}$
$\mathrm{Co_2V_2O_7}$ was recently reported to exhibit remarkable magnetic-field-induced magnetization plateaus and ferroelectricity, but its magnetic ground state remains ambiguous. Magnetometry measurements and time-of-flight neutron powder diffraction (NPD) have been employed to study the structural and magnetic properties of $\mathrm{Co_2V_2O_7}$, which includes two nonequivalent Co sites. Upon cooling below the Néel temperature $T_N = 6.0(2)$ K, we observe magnetic Bragg peaks at 2 K in NPD, which indicates the formation of long-range magnetic order of $\mathrm{Co^{2+}}$ moments. After symmetry analysis and magnetic structure refinement, we demonstrate that $\mathrm{Co_2V_2O_7}$ possesses a complicated noncollinear magnetic ground state with Co moments mainly located in the b-c plane and forming a noncollinear spin-chain-like structure along the c -axis. The ab initio calculations demonstrate that the noncollinear magnetic structure is more stable than various ferromagnetic states at low temperature. The noncollinear magnetic structure with a canted ↑↑↓↓ spin configuration is considered to be the origin of magnetoelectric coupling in$\mathrm{Co_2V_2O_7}$ because the inequivalent exchange striction induced by the spin-exchange interaction between the neighboring spins could be the driving force of ferroelectricity. Finally, it is also found that the deviation of lattice parameters a and b is opposite below $T_N$, while the lattice parameter c and $β$ stay almost constant below $T_N$, evidencing the anisotropic magnetoelastic coupling in $\mathrm{Co_2V_2O_7}$.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Dirac nodal lines protected against spin-orbit interaction in IrO 2
The interplay between strong spin-orbit coupling and electron correlations has recently been the subject of intense investigation, due to a number of theoretically predicted phases such as quantum spin liquids, unconventional superconductivity, complex magnetic orders, and correlated topological phases of matter. In particular, iridates have been proposed as a promising family of materials which could host a number of these phases. In this paper, we report the existence of Dirac nodal lines in the binary oxide IrO 2 , through a combination of reactive oxide molecular beam epitaxy and angle-resolved photoemission spectroscopy. Unlike in other such materials reported to date, these Dirac nodal lines have the unique property of being simultaneously (i) robust against spin-orbit coupling, as they are protected by the nonsymmorphic symmetry of the rutile structure, and (ii) only partially occupied, since they cross the Fermi level. This should have direct implications on the low-energy physics properties tied to the band velocity such as magnetoresistance and spin Hall effect.
36 MATERIALS SCIENCE↗
Seasonal, Solar Zenith Angle, and Solar Flux Variations of O+ in the Topside Ionosphere of Mars
Using observations from Mars Atmosphere and Volatile EvolutioN's Neutral Gas and Ion Mass Spectrometer, we characterize the seasonal, solar zenith angle (SZA), and solar flux dependent variations of the O+ peak and the O+/O+2 ratio in the topside ionosphere of Mars.We find that the O+ peak is between 220 and 300 km and forms at a roughly constant neutral atmospheric pressure level of 10(−8.7±0.4) Pa. The O+ peak altitude also decreases with increasing SZA near the terminator and varies sinusoidally with an amplitude of 26 km over a period of one Mars year in response to the changing solar insolation. The O+ peak altitude reaches a maximum near Northern Winter solstice and Mars perihelion. The O+ peak density on the dayside has an average value of (1.1 ± 0.5) × 103 cm−3, has no dependence on SZA for SZAs up to ∼90◦, and is mainly controlled by the thermospheric O/CO2 ratio as predicted by photochemical theory. Above the O+ peak, the O+/O+2 ratio in the dayside ionosphere approaches a constant value of 1.1 ± 0.6, decreases with increasing SZA, and is highly variable on timescales of days or less.We discuss why the O+ peak is different than the main (M2) peak at Mars and why it is similar to the F2 peak at Earth.
Girazian, Z.↗
Two Jupiter-mass Planets Discovered by the KMTNet Survey in 2017
We report two microlensing events, KMT-2017-BLG-1038 and KMT-2017-BLG-1146, that are caused by planetary systems. These events were discovered by Korea Microlensing Telescope Network survey observations from the 2017 bulge season. The discovered systems consist of a planet and host star with mass ratios of 5.3{sub −0.4}{sup +0.2}×10{sup −3} and 2.0{sub −0.1}{sup +0.6}×10{sup −3}, respectively. Based on a Bayesian analysis assuming a Galactic model without stellar remnant hosts, we find that the planet KMT-2017-BLG-1038Lb is a super-Jupiter-mass planet (M{sub p} =2.04{sub −1.15}{sup +2.02} M{sub J}) orbiting a mid-M dwarf host (M{sub h}=0.37{sub −0.20}{sup +0.36} M{sub ⊙}) that is located at 6.01{sub −1.72}{sup +1.27} kpc toward the Galactic bulge. The other planet, KMT-2017-BLG-1146Lb, is a sub-Jupiter-mass planet (M{sub p}=0.71{sub −0.42}{sup +0.80} M{sub J}) orbiting a mid-M dwarf host (M{sub h}=0.33{sub −0.20}{sup +0.36} M{sub ⊙}) at a distance of 6.50{sub −2.00}{sup +1.38} kpc toward the Galactic bulge. Both are potentially gaseous planets that are beyond their hosts’ snow lines. These typical microlensing planets will be routinely discovered by second-generation microlensing surveys, rapidly increasing the number of detections.
79 ASTRONOMY AND ASTROPHYSICS↗
Large tunable intrinsic gap in rhombohedral-stacked tetralayer graphene at half filling
At half filling, the very flat energy bands in rhombohedral-stacked tetralayer graphene are unstable to electronic interactions, giving rise to electronic states with spontaneous broken symmetries. Using transport measurements on suspended dual-gated devices, we observe an insulating ground state with a large interaction-induced transport gap up to 80 meV, which can be enhanced by a perpendicular magnetic field, and suppressed by an interlayer potential, carrier density, or a critical temperature of ~40 K. This insulating gapped state is proposed to be a layer antiferromagnet with broken time reversal symmetry.
36 MATERIALS SCIENCE↗
Persistent Correlation between Superconductivity and Antiferromagnetic Fluctuations near a Nematic Quantum Critical Point in FeSe 1-x S x
Here, we present 77 Se-NMR measurements on FeSe 1-x S x samples with sulfur content x = 0 %, 9%, 15%, and 29 %. Twinned nematic domains are observed in the NMR spectrum for all samples except x = 29 % . The NMR spin-lattice relaxation rate shows that antiferromagnetic (AFM) fluctuations are initially enhanced between x = 0 % and x = 9 % , but are strongly suppressed for higher x values. The observed behavior of the AFM fluctuations parallels the superconducting transition temperature T c in these materials, providing strong evidence for the primary importance of AFM fluctuations for superconductivity, despite the presence of nematic quantum criticality in the FeSe 1-x S x system.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Hidden Magnetic States Emergent Under Electric Field, In A Room Temperature Composite Magnetoelectric Multiferroic
The ability to control a magnetic phase with an electric field is of great current interest for a variety of low power electronics in which the magnetic state is used either for information storage or logic operations. Over the past several years, there has been a considerable amount of research on pathways to control the direction of magnetization with an electric field. More recently, an alternative pathway involving the change of the magnetic state (ferromagnet to antiferromagnet) has been proposed. In this paper, we demonstrate electric field control of the Anomalous Hall Transport in a metamagnetic FeRh thin film, accompanying an antiferromagnet (AFM) to ferromagnet (FM) phase transition. This approach provides us with a pathway to “hide” or “reveal” a given ferromagnetic region at zero magnetic field. By converting the AFM phase into the FM phase, the stray field, and hence sensitivity to external fields, is decreased or eliminated. Using detailed structural analyses of FeRh films of varying crystalline quality and chemical order, we relate the direct nanoscale origins of this memory effect to site disorder as well as variations of the net magnetic anisotropy of FM nuclei. Our work opens pathways toward a new generation of antiferromagnetic – ferromagnetic interactions for spintronics.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Magnetic fluctuations and superconducting properties of CaKFe 4 As 4 studied by As 75 NMR
In this paper, we report 75 As nuclear magnetic resonance (NMR) studies on a new iron-based superconductor, CaKFe 4 As 4 , with T c = 35 K. 75 As NMR spectra show two distinct lines corresponding to the As(1) and As(2) sites close to the K and Ca layers, respectively, revealing that K and Ca layers are well ordered without site inversions. We found that nuclear quadrupole frequencies ν Q of the As(1) and As(2) sites show an opposite temperature T dependence. Nearly T independent behavior of the Knight shifts K is observed in the normal state, and a sudden decrease in K in the superconducting (SC) state suggests spin-singlet Cooper pairs. 75 As spin-lattice relaxation rates 1/T 1 show a power-law T dependence with different exponents for the two As sites. The isotropic antiferromagnetic spin fluctuations characterized by the wave vector q = (π, 0) or (0, π) in the single-iron Brillouin zone notation are revealed by 1/T 1 T and K measurements. Such magnetic fluctuations are necessary to explain the observed temperature dependence of the 75 As quadrupole frequencies, as evidenced by our first-principles calculations. Finally, in the SC state, 1/T 1 shows a rapid decrease below T c without a Hebel-Slichter peak and decreases exponentially at low T, consistent with an s ± nodeless two-gap superconductor.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
OGLE-2016-BLG-1469L: Microlensing Binary Composed of Brown Dwarfs
We report the discovery of a binary composed of two brown dwarfs, based on the analysis of the micro lensing event OGLE-2016-BLG-1469. Thanks to the detection of both finite-source and micro lens-parallax effects, we are able to measure both the masses M(sub 1) ~ 0.05 Solar Mass and M(sub 2) ~ 0.01 Solar Mass, and the distance D(sub L) ~ 4.5 kpc, as well as the projected separation a(sub perpendicular) ~ 0.33 au. This is the third brown-dwarf binary detected using the micro lensing method, demonstrating the usefulness of micro lensing in detecting field brown-dwarf binaries with separations of less than 1 au.
OGLE-2016-BLG-1469↗
OGLE-2016-BLG-1469L: Microlensing Binary Composed of Brown Dwarfs
We report the discovery of a binary composed of two brown dwarfs, based on the analysis of the microlensing event OGLE-2016-BLG-1469. Thanks to the detection of both finite-source and microlens-parallax effects, we are able to measure both the masses M{sub 1}∼0.05 M{sub ⊙} and M{sub 2}∼0.01 M{sub ⊙}, and the distance D{sub L}∼4.5 kpc, as well as the projected separation a{sub ⊥}∼0.33 au. This is the third brown-dwarf binary detected using the microlensing method, demonstrating the usefulness of microlensing in detecting field brown-dwarf binaries with separations of less than 1 au.
79 ASTRONOMY AND ASTROPHYSICS↗
OGLE-2015-BLG-1482L: The First Isolated Low-mass Microlens in the Galactic Bulge
We analyze the single microlensing event OGLE-2015-BLG-1482 simultaneously observed from two ground-based surveys and from Spitzer. The Spitzer data exhibit finite-source effects that are due to the passage of the lens close to or directly over the surface of the source star as seen from Spitzer. Such finite-source effects generally yield measurements of the angular Einstein radius, which when combined with the microlens parallax derived from a comparison between the ground-based and the Spitzer light curves yields the lens mass and lens-source relative parallax. From this analysis, we find that the lens of OGLE-2015-BLG-1482 is a very low-mass star with a mass 0.10±0.02 M{sub ⊙} or a brown dwarf with a mass 55±9 M{sub J}, which are located at D{sub LS}=0.80±0.19 kpc and D{sub LS}=0.54±0.08 kpc, respectively, where D{sub LS} is the distance between the lens and the source, and thus it is the first isolated low-mass microlens that has been decisively located in the Galactic bulge. The degeneracy between the two solutions is severe (Δχ{sup 2}=0.3). The fundamental reason for the degeneracy is that the finite-source effect is seen only in a single data point from Spitzer, and this single data point gives rise to two solutions for ρ, the angular size of the source in units of the angular Einstein ring radius. Because the ρ degeneracy can be resolved only by relatively high-cadence observations around the peak, while the Spitzer cadence is typically ∼1 day{sup −1}, we expect that events for which the finite-source effect is seen only in the Spitzer data may frequently exhibit this ρ degeneracy. For OGLE-2015-BLG-1482, the relative proper motion of the lens and source for the low-mass star is μ{sub rel}=9.0±1.9 mas yr{sup −1}, while for the brown dwarf it is 5.5±0.5 mas yr{sup −1}. Hence, the degeneracy can be resolved within ∼10 years from direct-lens imaging by using next-generation instruments with high spatial resolution.
79 ASTRONOMY AND ASTROPHYSICS↗
Electron-ion collider: The next QCD frontier: Understanding the glue that binds us all
This White Paper presents the science case of an Electron-Ion Collider (EIC), focused on the structure and interactions of gluon-dominated matter, with the intent to articulate it to the broader nuclear science community. It was commissioned by the managements of Brookhaven National Laboratory (BNL) and Thomas Jefferson National Accelerator Facility (JLab) with the objective of presenting a summary of scientific opportunities and goals of the EIC as a follow-up to the 2007 NSAC Long Range plan. This document is a culmination of a community-wide effort in nuclear science following a series of workshops on EIC physics over the past decades and, in particular, the focused ten-week program on “Gluons and quark sea at high energies” at the Institute for Nuclear Theory in Fall 2010. It contains a brief description of a few golden physics measurements along with accelerator and detector concepts required to achieve them. It has been benefited profoundly from inputs by the users’ communities of BNL and JLab. Furthermore, this White Paper offers the promise to propel the QCD science program in the US, established with the CEBAF accelerator at JLab and the RHIC collider at BNL, to the next QCD frontier.
43 PARTICLE ACCELERATORS↗
Electronic properties of GeTe and Ag- or Sb-substituted GeTe studied by low-temperature Te 125 NMR
We have carried out 125 Te nuclear magnetic resonance (NMR) in a wide temperature range of 1.5–300 K to investigate the electronic properties of Ge 50 Te 50 , Ag 2 Ge 48 Te 50 , and Sb 2 Ge 48 Te 50 from a microscopic point of view. From the temperature dependence of the NMR shift (K) and nuclear spin lattice relaxation rate (1/T 1 ), we found that two bands contribute to the physical properties of the materials. One band overlaps the Fermi level providing the metallic state where no strong electron correlations are revealed by Korringa analysis. The other band is separated from the Fermi level by an energy gap of E g /k B ~67 K, which gives rise to semiconductorlike properties. First-principles calculation reveals that the metallic band originates from the Ge vacancy while the semiconductorlike band is related to the fine structure of the density of states near the Fermi level. We find low-temperature Te125 NMR data for the materials studied here clearly show that Ag substitution increases hole concentration while Sb substitution decreases it.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Physical properties of the Ce 2 M Al 7 Ge 4 heavy-fermion compounds ( M = Co , Ir , Ni , Pd )
Here, we report the synthesis, crystal structure, and characterization by means of single-crystal x-ray diffraction, neutron powder diffraction, and magnetic, thermal, and transport measurements of the new heavy-fermion compounds Ce 2 MAl 7 Ge 4 (M=Co,Ir,Ni,Pd). These compounds crystallize in a noncentrosymmetric tetragonal space group P$\bar{4}$2 1 m, consisting of layers of square nets of Ce atoms separated by Ge-Al and M-Al-Ge blocks. Ce 2 CoAl 7 Ge 4 ,Ce 2 IrAl 7 Ge 4 , and Ce 2 NiAl 7 Ge 4 order magnetically below TM=1.8, 1.6, and 0.8 K, respectively. There is no evidence of magnetic ordering in Ce 2 PdAl 7 Ge 4 down to 0.4 K. Furthermore, the small amount of entropy released in the magnetic state of Ce 2 MAl 7 Ge 4 (M = Co, Ir, Ni) and the reduced specific heat jump at T M suggest a strong Kondo interaction in these materials. Ce 2 PdAl 7 Ge 4 shows non-Fermi liquid behavior, possibly due to the presence of a nearby quantum critical point.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Structural characterization of solid lipoproteic colloid gels by ultra-small-angle X-ray scattering and the relation with sodium release
Not Available
Kuo, Wan-Yuan (ORCID:0000000300571009)↗