Quantum transitions of nematic phases in a spin-1 bilinear-biquadratic model and their implications for FeSe
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2-dimenional systems↗
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Laboratory detection of the C3N an C4H free radicals
The millimeter-wave spectra of the linear carbon chain free radicals C3N and C4H, first identified in IRC + 10216 and hitherto observed only in a few astronomical sources, have been detected with a Zeeman-modulated spectrometer in laboratory glow discharges through low pressure flowing mixtures of N2 + HC3N and He + HCCH, respectively. Four successive rotational transitions between 168 and 198 GHz have been measured for C3N, and five rotational transitions between 143 and 200 GHz for C4H; each is a well-resolved spin doublet owing to the unpaired electron present in both species. Precise values for the rotational, centrifugal distortion, and spin doubling constants have been obtained, which, with hyperfine constants derived from observations of the lower rotational transitions in the astronomical source TMC 1, allow all the rotational transitions of C3N and C4H at frequencies less than 300 GHz to be calculated to an absolute accuracy exceeding 1 ppm.
Gottlieb, C. A.↗
Dynamics of the Venus atmosphere
The superrotation of the Venus atmosphere is a major unanswered problem in planetary science. At cloud-top levels (65-70 km altitude) the atmosphere rotates with a five-day period, corresponding to an equatorial wind speed of 90 m/s. Angular velocity is roughly constant on spherical shells, and decreases linearly with altitude to zero at the surface. The direction of rotation is the same as that of the solid planet, which is retrograde--opposite to the direction of orbital motion, but the 5-day period is short compared to the 243-day spin period of the solid planet or to the mean solar day, which is 117 Earth-days at the surface. The problem with the superrotation is that shearing stresses tend to transfer angular momentum downward, and would slow the atmosphere until it is spinning with the solid planet. Some organized circulation pattern is counteracting the tendency, but the pattern has not been identified. A simple Hadley-type circulation cannot do it because such a circulation is zonally symmetric and Hide's Theorem states that in an axisymmetric circulation an extremum in angular momentum per unit mass M can exist only at the surface. Venus violates the last condition, having a maximum of retrograde M on the equator at 70-80 km altitude. This leaves waves and eddies to maintain the superrotation but the length scales and forcing mechanisms for these motions need to be specified. Possible forcing mechanisms associated with waves, eddies and tides are discussed.
Ingersoll, A. P.↗
Compressive strain turns 𝑠 ± - into 𝑑-wave pairing in a one-unit-cell La 3 Ni 2 O 7 thin film via substrate-induced hole doping
Motivated by recent reports of ambient-pressure superconductivity in La 3 Ni 2 O 7 films grown on LaSrAlO 4 , we investigate the superconducting instability in a one-unit-cell (1UC) thin film using ab initio and random-phase approximation techniques. Compared to the high-pressure bulk system, the ratio of interlayer 𝑑 3𝑧 2 −𝑟 2 hopping to intralayer 𝑑 𝑥 2 −𝑦 2 hopping is suppressed in the 1UC thin film, and the crystal-field splitting of the 𝑒 𝑔 orbitals is increased. Here, our calculation indicates that spin-fluctuation-driven pairing correlations are weak for the stoichiometric case at ambient pressure, but increase significantly under hole doping. The leading pairing symmetry is also found to change by hole doping. Specifically, we obtain a leading 𝑑 𝑥 2 −𝑦 2 pairing state at moderate hole doping, followed by a 𝑑 𝑥𝑦 state at higher doping. These states are driven by intraband spin-fluctuation scattering within the 𝛾 hole pocket centered around the 𝑀 point, and arise primarily from states in the Ni layer farther from the substrate. These results strongly suggest that the thin-film superconducting samples are hole-doped and that pairing in this system predominantly arises in the layer, as opposed to the interlayer pairing in the pressurized bulk system.
Zhang, Yang [Oak Ridge National Laboratory (ORNL),↗
Binary collisions of dark matter blobs
We describe the model-independent mechanism by which dark matter and dark matter structures heavier than ~ 8 × 10 11 GeV form binary pairs in the early Universe that spin down and merge both in the present and throughout the Universe’s history, producing potentially observable signals. Sufficiently dense dark objects will dominantly collide through binary mergers instead of random collisions. We detail how one would estimate the merger rate accounting for finite size effects, multibody interactions, and friction with the thermal bath. We predict how mergers of dark dense objects could be detected through gravitational and electromagnetic signals, noting that such mergers could be a unique source of high frequency gravitational waves. We rule out objects whose presence would contradict observations of the CMB and diffuse gamma-rays.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Observations of interplanetary plasma waves, spacecraft noise, and sheath phenomena on Imp 7
The Imp 7 plasma wave instrument measures electric and magnetic wave components of plasma oscillations over the frequency range from 10 Hz to 100 kHz. The instrumentation and relevant external characteristics of the spacecraft that appear to be responsible for some in-flight disturbance effects are briefly described. It is shown that as each one of the 16 solar panel flats rotates into shadow or sunlight, the array transients produce fluctuating magnetic fields that are detected on the magnetic loop mounted 3.4 m from the spacecraft. These transients occur 16 times per spin period, and the corresponding magnetic noise has a high frequency on the rapidly spinning Imp 7 spacecraft. The analysis suggests that some Imp magnetic threshold levels measured 3-4 m from the spacecraft are determined by the solar array current transient effects associated with the discrete 16-sided geometry of the spacecraft. The geometry also influences the response of the electric dipole antenna by modulating the sheath.
Scarf, F. L.↗
Equation of State and Spin Crossover of (Al, Fe)–Phase H
The transport of hydrogen into Earth's deep interior may have an impact on lower mantle dynamics as well as on the seismic signature of subducted material. Due to the stability of the hydrous phases δ-AlOOH (delta phase), MgSiO 2 (OH) 2 (phase H), and ε-FeOOH at high temperatures and pressures, their solid solutions may transport significant amounts of hydrogen as deep as the core-mantle boundary. Here we have constrained the equation of state, including the effects of a spin crossover in the Fe 3+ atoms, of (Al, Fe)-phase H: Al 0.84 Fe 3+ 0.07 Mg 0.02 Si 0.06 OOH, using powder X-ray diffraction measurements to 125 GPa, supported by synchrotron Mössbauer spectroscopy measurements on (Al, Fe)-phase H and δ-(Al, Fe)OOH. The changes in spin state of Fe 3+ in (Al, Fe)-phase H results in a significant decrease in bulk sound velocity and occurs over a different pressure range (48–62 GPa) compared with δ-(Al, Fe)OOH (32–40 GPa). Changes in axial compressibilities indicate a decrease in the compressibility of hydrogen bonds in (Al, Fe)-phase H near 30 GPa, which may be associated with hydrogen bond symmetrization. The formation of (Al, Fe)-phase H in subducted oceanic crust may contribute to scattering of seismic waves in the mid-lower mantle (~1,100–1,550 km). Accumulation of 1–4 wt.% (Al, Fe)-phase H could reproduce some of the seismic signatures of large, low seismic-velocity provinces. Our results suggest that changes in the electronic structure of phases in the (δ-AlOOH)-(MgSiO 2 (OH) 2 )-(ε-FeOOH) solid solution are sensitive to composition and that the presence of these phases in subducted oceanic crust could be seismically detectable throughout the lower mantle.
58 GEOSCIENCES↗
Measurement of single- and double-polarization observables in the photoproduction of 𝜋 + 𝜋 − meson pairs off the proton using CLAS at Jefferson Laboratory
The photoproduction of 𝜋 + 𝜋 − meson pairs off the proton has been studied in the reaction 𝛾𝑝→𝑝𝜋 + 𝜋 − using the CEBAF Large Acceptance Spectrometer (CLAS) and the frozen-spin target (FROST) in Hall B at the Thomas Jefferson National Accelerator Facility. For the first time, the beam and target asymmetries, 𝐼 𝑠,𝑐 and 𝑃 𝑥,𝑦 , have been measured along with the beam-target double-polarization observables, 𝑃$^{𝑠,𝑐}_{𝑥,𝑦}$, using a transversely polarized target with center-of-mass energies ranging from 1.51 GeV up to 2.04 GeV. These data and additional 𝜋𝜋 photoproduction observables from CLAS and experiments elsewhere were included in a partial-wave analysis within the Bonn-Gatchina framework. Significant contributions from 𝑠-channel resonance production are observed in addition to 𝑡-channel exchange processes. The data indicate significant contributions from 𝑁* and Δ* resonances in the third and fourth resonance regions.
QCD phenomenology↗
Shock-induced effects in calcite from Cactus Crater
The paper discusses shock metamorphism of calcite from coralline limestone samples retrieved from a borehole drilled into rocks beneath Cactus Crater, a nuclear explosion crater at Eniwetok Atoll. The metamorphism was detected and quantified using electron spin resonance (ESR); the ESR spectra of Mn(+) present as a trace constituent in the coral samples, show a consistent decrease in hyperfine peak splitting with decreasing depth of sample. It is suggested that the decrease in hyperfine peak splitting reflects a decrease in crystal field splitting, and therefore, small increases on cation-anion distances produced by mechanical energy input during the shock process. Two alternative crater models suggested by the ESR results are a depiction of a steady decay of the shock wave, and a delineation of a breccia lens with a breccia-bedrock interface at 20 plus or minus 5 m.
Vizgirda, J.↗
Modeling the Spin Equilibrium of Neutron Stars in LMXBs Without Gravitational Radiation
In this paper we discuss the spin-equilibrium of accreting neutron stars in LMXBs. We demonstrate that, when combined with a naive spin-up torque, the observed data leads to inferred magnetic fields which are at variance with those of galactic millisecond radiopulsars. This indicates the need for either additional spin-down torques (eg. gravitational radiation) or an improved accretion model. We show that a simple consistent accretion model can be arrived at by accounting for radiation pressure in rapidly accreting systems (above a few percent of the Eddington accretion rate). In our model the inner disk region is thick and significantly sub-Keplerian, and the estimated equilibrium periods are such that the LMXB neutron stars have properties that accord well with the galactic millisecond radiopulsar sample. The implications for future gravitational-wave observations are also discussed briefly.
Andersson, N.↗
Nanoscale Defects as Probes of Time-Reversal Symmetry Breaking
Nanoscale defects such as nitrogen-vacancy (NV) centers can serve as sensitive and noninvasive probes of electromagnetic fields and fluctuations from materials, which in turn can be used to characterize these systems. Here we specifically discuss how NV centers can probe time-reversal symmetry breaking (TRSB) phenomena in low-dimensional electronic systems. We argue that the difference in relaxation rates Γ$_{±\hat{z}}$ of NV centers starting from 𝑚 = ±1 spin states to the ground state with 𝑚 = 0 directly probes TRSB. The effect arises from the difference in the fluctuation spectrum of left- and right-polarized electromagnetic fields emanating from such materials. In the quantum Hall setting, the NV center experiences (nearly zero) large additional contribution to its relaxation due to the presence of the material when its magnetic dipole (anti)aligns with the external field. More generally, the difference in the relaxation rates is sensitive to the imaginary part of the wave-vector-dependent Hall conductivity. We argue that this can be used to determine the Hall viscosity, which can potentially distinguish candidate fractional quantum Hall states and be used to infer the pairing angular momentum in TRSB superconductors. We compute the average relaxation rate [Γ$_{+\hat{z}}$ + Γ$_{-\hat{z}}$] near thin film superconductors and find that it exhibits a Hebel-Slichter-like enhancement below 𝑇 𝑐 . The difference Γ$_{+\hat{z}}$ −Γ$_{-\hat{z}}$ also inherits this peak but is only nonzero for 𝑇 < 𝑇 𝑐 and only if the superconductivity is chiral. We provide concrete estimates for observing this effect in stacked twisted bismuth strontium calcium copper oxide flakes.
NV centers↗
A Systematic, Polynomial-Cost Approach to Exact Correlation Energies (Final Technical Report)
The full configuration interaction (FCI) wave function provides the exact solution to the Schrödinger equation in a given basis set. While FCI is intractable due to exponential computational costs, the many-body expansion (or the method of increments) can reduce scaling to a low-order polynomial with system size. This project entailed advances in the incremental FCI (iFCI) approach, designed to allow iFCI to reach larger system sizes and maintain its intrinsic high accuracy. This document describes advances in solvers for iFCI, strategies to treat multiple charge and spin states, and virtual state management methods to reduce memory requirements. Overall, this project allows iFCI to correlate (for the first time) 142 valence electrons in 444 orbitals in a realistic model of a transition metal complex.
74 ATOMIC AND MOLECULAR PHYSICS↗
Large amplitude wave packets observed in the ionosphere in association with transverse ion acceleration
Very short duration, large amplitude bursts of monochromatic waves ('spikelets') were detected by the electric field experiment on the sounding rocket MARIE, launched in February 1985 from Churchill, Manitoba. About 35 events were detected, with an average time scale of 5 ms and an average amplitude of 100-150 mV/m. Their frequency varied between 7 and 18 kHz, and there is some evidence that the frequency is a decreasing function of altitude. The bursts are not correlated with any events on the payload, and their occurrence is not related to the rocket's spin or coning. The events were confined to the altitude range 450-650 kilometers. This coincides exactly with the altitude range for which perpendicular (90 deg) ion conics were detected by the particle experiment on the same payload. The 'spikelets' were also correlated one-to-one with small (10-100 mV/m) double-layerlike or shocklike features of similar time scale in the dc electric field data.
Labelle, J.↗
IrRep: Symmetry eigenvalues and irreducible representations of ab initio band structures
Here, we present IrRep – a Python code that calculates the symmetry eigenvalues of electronic Bloch states in crystalline solids and the irreducible representations under which they transform. As input it receives bandstructures computed with state-of-the-art Density Functional Theory codes such as VASP, Quantum Espresso, or Abinit, as well as any other code that has an interface to Wannier90. Our code is applicable to materials in any of the 230 space groups and double groups preserving time-reversal symmetry with or without spin-orbit coupling included, for primitive or conventional unit cells. This makes IrRep a powerful tool to systematically analyze the connectivity and topological classification of bands, as well as to detect insulators with non-trivial topology, following the Topological Quantum Chemistry formalism: IrRep can generate the input files needed to calculate the (physical) elementary band representations and the symmetry-based indicators using the [CheckTopologicalMat: https://www.cryst.ehu.es/cgi-bin/cryst/programs/magnetictopo.pl] routine of the Bilbao Crystallographic Server. It is also particularly suitable for interfaces with other plane-waves based codes, due to its flexible structure.
97 MATHEMATICS AND COMPUTING↗
Unitary Bethe-Salpeter Methods in Two- and Three-Body Systems
The study of resonances, unstable particles formed in particle scattering, is motivated by the questions about the strong interaction and the composition of hadrons. In order to advance this study in the intermediate energy region, a variety of techniques are used. In this thesis, we present work done on two different analyses that use the principle of unitarity and the Bethe-Salpeter equation to study the resonances Lambda(1405), Sigma(1385), and a1(1260). Firstly, we perform a simultaneous analysis of Sand P-waves of the Strangeness = -1 two-body meson-baryon scattering amplitude using all low-energy data. For the first time, differential cross section data are included for chiral unitary coupled-channel models. From this model, S- and P-wave amplitudes are extracted and we observe both well-known I(JP)=0(1/2^-) S-wave states as well as a new I(JP)=1(1/2^+) state absent in quark models and lattice QCD results. Multiple statistical and phenomenological tests suggest that, while the data clearly require an I =1 P-wave resonance, the new state just accounts for the absence of the decuplet Sigma(1385)3/2+ in the model which is subsequently included in the parameterization. Secondly, we formulate the final state interaction of the a1(1260) resonance decay in a manifestly three-body-unitary parameterization and fit it to the a1(1260) lineshape measured by the ALEPH experiment. Dalitz plots calculated from this fit are presented. The work demonstrates the feasibility to numerically solve a previously derived amplitude and its generalization to isobars with spin and coupled channels. The model is a good test case because it can also be applied to other meson decays including exotic states and modified for the finite-volume problem as it arises in lattice QCD due to its manifest unitarity. The understanding of the resonances being analyzed in both the two-body work and the three-body work gives a better understanding of intermediate energy QCD.
Sadasivan, Daniel↗
Resolution of zigzag magnetic correlations in Na-deficient Na x IrO 3 without long-range ordering
The materials search for Kitaev quantum spin liquids led to the discovery of many honeycomb lattice materials. Much attention has been paid to materials without magnetic order down to the lowest temperatures. The newly synthesized Na-deficient Na x IrO 3 has been found to bear no sign of long-range magnetic order above 1 K from physical property measurements. In this paper, we report momentum-and energy-resolved excitation spectra in Na-deficient Na x IrO 3 measured using a resonant inelastic x-ray scattering spectrometer. Orbital excitation spectra show that the octahedral and trigonal crystal field splittings are larger in Na x IrO 3 than in Na 2 IrO 3 . On the other hand, the low-energy spectrum at low temperature shows a wave-vector dispersion and a spectral weight distribution that are similar to those of Na 2 IrO 3 , revealing that the two-dimensional zigzag magnetic correlations in Na x IrO 3 are similar to those in Na 2 IrO 3 in terms of the ordered magnetic moment direction and three dynamically fluctuating zigzag orders. The azimuth angle dependence of the low-energy spectrum corroborates these results. The two-dimensional zigzag magnetic correlations rapidly weaken until 50 K. At high temperatures, the spectral weight distribution of the low-energy excitation resembles that of the pure Kitaev model, indicating that the Kitaev interaction dominates the dynamic magnetic response at high temperature. Here we suggest that the larger crystal field and distortion and the weakened longer-range Heisenberg exchange interactions due to the Na deficiency in Na x IrO 3 contribute to bring Na x IrO 3 away from the zigzag long-range magnetic order phase.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Toward Full Configuration Interaction for Transition-Metal Complexes
In this work, an efficacious approximation to full configuration interaction (FCI) is adapted to calculate singlet-triplet gaps for transition-metal complexes. This strategy, incremental FCI (iFCI), uses a many-body expansion to systematically add correlation to a simple reference wave function and therefore achieves greatly reduced computational costs compared to FCI. iFCI through the 3-body expansion is demonstrated on four model transition-metal complexes involving the metals Zn, V, and Cu. Screening techniques to increase the computational efficiency of iFCI are proposed and tested, showing reduction in the number of 3-body terms by more than 90% with controlled errors. The largest complex treated by iFCI has 142 valence electrons, all of which are correlated among the full set of 444 active orbitals. Computed spin gaps approach experimental results for the four complexes, though room for improvement remains.
74 ATOMIC AND MOLECULAR PHYSICS↗
The Submillimeter-Wave Spectrum of Isotopic Methyl Cyanide
The laboratory submillimeter-wave rotational spectrum of the 13 CH 3 CN, CH 3 13 CN, and the CH 3 C 15 N isotopomers of methyl cyanide has been observed in natural abundance in the 294 to 607 GHz region. The maximum J and K values are 34 an 14, respectively. Fifteen additional CH 3 CN transitions up to K=21 were also measured. The transitions of all four species are fitted to a symmetric top Hamiltonian and the rotation and distortion constants are determined. The 14 N quadropole and spin rotation are also calculated and presented. Suggested values for many other parameters which could not be directly determined from the isotope spectra are calculated from the normal species values and isotope relationships. The determined and calculated constants should predict the spectrum of the three isotopomers to well over 1 THz accurately enough for astronomical assignments.
methyl↗