We report the temperature dependence of the Yb valence in the geometrically frustrated compound
Using polarized optical and magnetooptical spectroscopy, we have demonstrated universal aspects of electrodynamics associated with Dirac nodal lines that are found in several classes of unconventional intermetallic compounds. We investigated anisotropic electrodynamics of
 NSFPAR ID:
 10081684
 Publisher / Repository:
 Proceedings of the National Academy of Sciences
 Date Published:
 Journal Name:
 Proceedings of the National Academy of Sciences
 Volume:
 116
 Issue:
 4
 ISSN:
 00278424
 Page Range / eLocation ID:
 p. 11681173
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
More Like this

Abstract from 12 to 300 K using resonant xray emission spectroscopy at the Yb ${\mathrm{Y}\mathrm{b}\mathrm{B}}_{4}$ transition. We find that the Yb valence, ${L}_{{\alpha}_{1}}$v , is hybridized between thev = 2 andv = 3 valence states, increasing from at 12 K to $v=2.61\pm 0.01$ at 300 K, confirming that $v=2.67\pm 0.01$ is a Kondo system in the intermediate valence regime. This result indicates that the Kondo interaction in ${\mathrm{Y}\mathrm{b}\mathrm{B}}_{4}$ is substantial, and is likely to be the reason why ${\mathrm{Y}\mathrm{b}\mathrm{B}}_{4}$ does not order magnetically at low temperature, rather than this being an effect of geometric frustration. Furthermore, the zeropoint valence of the system is extracted from our data and compared with other Kondo lattice systems. The zeropoint valence seems to be weakly dependent on the Kondo temperature scale, but not on the valence change temperature scale ${\mathrm{Y}\mathrm{b}\mathrm{B}}_{4}$T _{v}. 
SubNeptunes are common among the discovered exoplanets. However, lack of knowledge on the state of matter in
${\mathrm{H}}_{2}$ Orich setting at high pressures and temperatures ($PT$ ) places important limitations on our understanding of this planet type. We have conducted experiments for reactions between${\mathrm{S}\mathrm{i}\mathrm{O}}_{2}$ and${\mathrm{H}}_{2}$ O as archetypal materials for rock and ice, respectively, at high$PT$ . We found anomalously expanded volumes of dense silica (up to 4%) recovered from hydrothermal synthesis above ∼24 GPa where the${\mathrm{C}\mathrm{a}\mathrm{C}\mathrm{l}}_{2}$ type (Ct) structure appears at lower pressures than in the anhydrous system. Infrared spectroscopy identified strong OH modes from the dense silica samples. Both previous experiments and our density functional theory calculations support up to 0.48 hydrogen atoms per formula unit of (${\mathrm{S}\mathrm{i}}_{1x}{\mathrm{H}}_{4x}$ )${\mathrm{O}}_{2}\hspace{0.17em}\left(x=0.12\right)$ . At pressures above 60 GPa,${\mathrm{H}}_{2}$ O further changes the structural behavior of silica, stabilizing a niccolitetype structure, which is unquenchable. From unitcell volume and phase equilibrium considerations, we infer that the niccolitetype phase may contain H with an amount at least comparable with or higher than that of the Ct phase. Our results suggest that the phases containing both hydrogen and lithophile elements could be the dominant materials in the interiors of waterrich planets. Even for fully layered cases, the large mutual solubility could make the boundary between rock and ice layers fuzzy. Therefore, the physical properties of the new phases that we report here would be important for understanding dynamics, geochemical cycle, and dynamo generation in waterrich planets. 
Abstract The family of transitionmetal dipnictides has been of theoretical and experimental interest because this family hosts topological states and extremely large magnetoresistance (MR). Recently,
, a member of this family, has been predicted to support a topological crystalline insulating state. Here, by using highresolution angleresolved photoemission spectroscopy (ARPES), we reveal both closed and open pockets in the metallic Fermi surface (FS) and linearly dispersive bands on the ( ${\mathrm{T}\mathrm{a}\mathrm{A}\mathrm{s}}_{2}$ ) surface, along with the presence of extreme MR observed from magnetotransport measurements. A comparison of the ARPES results with firstprinciples computations shows that the linearly dispersive bands on the measured surface of $\stackrel{\u203e}{2}01$ are trivial bulk bands. The absence of symmetryprotected surface state on the ( ${\mathrm{T}\mathrm{a}\mathrm{A}\mathrm{s}}_{2}$ ) surface indicates its topologically dark nature. The presence of open FS features suggests that the openorbit fermiology could contribute to the extremely large MR of $\stackrel{\u203e}{2}01$ . ${\mathrm{T}\mathrm{a}\mathrm{A}\mathrm{s}}_{2}$ 
Abstract One of the cornerstone effects in spintronics is spin pumping by dynamical magnetization that is steadily precessing (around, for example, the
z axis) with frequencyω _{0}due to absorption of lowpower microwaves of frequencyω _{0}under the resonance conditions and in the absence of any applied bias voltage. The twodecadesold ‘standard model’ of this effect, based on the scattering theory of adiabatic quantum pumping, predicts that component of spin current vector ${I}^{{S}_{z}}$ is timeindependent while $({I}^{{S}_{x}}(t),{I}^{{S}_{y}}(t),{I}^{{S}_{z}})\propto {\omega}_{0}$ and ${I}^{{S}_{x}}(t)$ oscillate harmonically in time with a single frequency ${I}^{{S}_{y}}(t)$ω _{0}whereas pumped charge current is zero in the same adiabatic $I\equiv 0$ limit. Here we employ more general approaches than the ‘standard model’, namely the timedependent nonequilibrium Green’s function (NEGF) and the Floquet NEGF, to predict unforeseen features of spin pumping: namely precessing localized magnetic moments within a ferromagnetic metal (FM) or antiferromagnetic metal (AFM), whose conduction electrons are exposed to spin–orbit coupling (SOC) of either intrinsic or proximity origin, will pump both spin $\propto {\omega}_{0}$ and charge ${I}^{{S}_{\alpha}}(t)$I (t ) currents. All four of these functions harmonically oscillate in time at both even and odd integer multiples of the driving frequency $N{\omega}_{0}$ω _{0}. The cutoff order of such high harmonics increases with SOC strength, reaching in the onedimensional FM or AFM models chosen for demonstration. A higher cutoff ${N}_{\mathrm{m}\mathrm{a}\mathrm{x}}\simeq 11$ can be achieved in realistic twodimensional (2D) FM models defined on a honeycomb lattice, and we provide a prescription of how to realize them using 2D magnets and their heterostructures. ${N}_{\mathrm{m}\mathrm{a}\mathrm{x}}\simeq 25$ 
Abstract We measure the thermal electron energization in 1D and 2D particleincell simulations of quasiperpendicular, lowbeta (
β _{p}= 0.25) collisionless ion–electron shocks with mass ratiom _{i}/m _{e}= 200, fast Mach number –4, and upstream magnetic field angle ${\mathcal{M}}_{\mathrm{ms}}=1$θ _{Bn}= 55°–85° from the shock normal . It is known that shock electron heating is described by an ambipolar, $\stackrel{\u02c6}{\mathit{n}}$ parallel electric potential jump, ΔB ϕ _{∥}, that scales roughly linearly with the electron temperature jump. Our simulations have –0.2 in units of the preshock ions’ bulk kinetic energy, in agreement with prior measurements and simulations. Different ways to measure $\mathrm{\Delta}{\varphi}_{\parallel}/(0.5{m}_{\mathrm{i}}{{u}_{\mathrm{sh}}}^{2})\sim 0.1$ϕ _{∥}, including the use of de Hoffmann–Teller frame fields, agree to tensofpercent accuracy. Neglecting offdiagonal electron pressure tensor terms can lead to a systematic underestimate ofϕ _{∥}in our lowβ _{p}shocks. We further focus on twoθ _{Bn}= 65° shocks: a ( ${\mathcal{M}}_{\mathrm{s}}\phantom{\rule{0.25em}{0ex}}=\phantom{\rule{0.25em}{0ex}}4$ ) case with a long, 30 ${\mathcal{M}}_{\mathrm{A}}\phantom{\rule{0.25em}{0ex}}=\phantom{\rule{0.25em}{0ex}}1.8$d _{i}precursor of whistler waves along , and a $\stackrel{\u02c6}{\mathit{n}}$ ( ${\mathcal{M}}_{\mathrm{s}}\phantom{\rule{0.25em}{0ex}}=\phantom{\rule{0.25em}{0ex}}7$ ) case with a shorter, 5 ${\mathcal{M}}_{\mathrm{A}}\phantom{\rule{0.25em}{0ex}}=\phantom{\rule{0.25em}{0ex}}3.2$d _{i}precursor of whistlers oblique to both and $\stackrel{\u02c6}{\mathit{n}}$ ;B d _{i}is the ion skin depth. Within the precursors,ϕ _{∥}has a secular rise toward the shock along multiple whistler wavelengths and also has localized spikes within magnetic troughs. In a 1D simulation of the , ${\mathcal{M}}_{\mathrm{s}}\phantom{\rule{0.25em}{0ex}}=\phantom{\rule{0.25em}{0ex}}4$θ _{Bn}= 65° case,ϕ _{∥}shows a weak dependence on the electron plasmatocyclotron frequency ratioω _{pe}/Ω_{ce}, andϕ _{∥}decreases by a factor of 2 asm _{i}/m _{e}is raised to the true proton–electron value of 1836.