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Results for “symmetry”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Continuous symmetry breaking in a trapped-ion spin chain
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Four-component protein nanocages designed by programmed symmetry breaking
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Orientation-dependent production of normal Archimedean and dynamical spirals for revealing orbital symmetries in diatomic multi-orbital molecules
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Evidence of symmetry breaking in a Gd 2 di-nuclear molecular polymer
A chiral 3D coordination compound, [Gd 2 (L) 2 (ox) 2 (H 2 O) 2 ], arranged around a dinuclear Gd unit has been characterized by X-ray photoemission and X-ray absorption measurements in the context of density functional theory studies.
The evolution of solvation symmetry and composition in Zn halide aqueous solutions from dilute to extreme concentrations
Valence-to-core X-ray emission spectroscopy is combined with electronic structure theory and molecular dynamics simulations to quantify contact ion pairing in Zn halide aqueous electrolytes.
Why the electron chooses one of two symmetry-related paths in the type II bacterial photosynthetic reaction centers
A series of electron and proton transfer reactions are carried out in photosynthetic reaction centers that convert the energy of light into high energy reduced products and add to the proton gradient. All photosynthetic reaction centers (photosystems I, II, and different bacterial reaction centers (bRCs)) have their charge separating cofactors arranged with two, c 2 -symmetric paths from a primary donor to a terminal acceptor. In Type II reaction centers (PSII and bRCs), electrons utilize only one active branch. In bRCs the electron transfer occurs in the A branch from the excited state of the bacteriochlorophyll (BChl) dimer P 860 through BChl A , bacteriopheophytin A (BPh A ), to ubiquinone Q A , and then to the B-branch Q B . B-branch BChl B and BPh B do not participate. A similar path is found in PSII. These proteins challenge our understanding of how proteins can turn on or turn off the activity of bound ligands. The shift of the electrochemical midpoint potential (E m ) of each cofactor by the protein environment is calculated using continuum electrostatics within the Multi-Conformation Continuum Electrostatic (MCCE) program. In bRCs from Rhodobacter sphaeroides, the electrostatic potentials favor reduction of the active branch cofactors. The residues that contribute to a more positive potential on the A branch are identified. These are often distant from the cofactors. The large difference of the potential at the competing BChls may direct the electron transfer to the A branch. Residues TyrM210 and PheL181 are at symmetrical positions on the A and B branches, near P 860 , between BChl A and BChl B . Mutated bRCs, that swap the Tyr and Phe (YF mutant), have been shown to support some electron transfer to the B-branch cofactors. Here, the calculated E m s with the YF swap show more positive B-branch potentials, which help explain why there is now electron transfer along the B branch.
Topological field theory with Haagerup symmetry
Here, we construct a (1 + 1)d topological field theory (TFT) whose topological defect lines (TDLs) realize the transparent Haagerup $\mathscr{H}$ 3 fusion category. This TFT has six vacua, and each of the three non-invertible simple TDLs hosts three defect operators, giving rise to a total of 15 point-like operators. The TFT data, including the three-point coefficients and lasso diagrams, are determined by solving all the sphere four-point crossing equations and torus one-point modular invariance equations. We further verify that the Cardy states furnish a non-negative integer matrix representation under TDL fusion. While many of the constraints we derive are not limited to this particular TFT with six vacua, we leave open the construction of TFTs with two or four vacua. Finally, TFTs realizing the Haagerup $\mathscr{H}$ 1 and $\mathscr{H}$ 2 fusion categories can be obtained by gauging algebra objects. This article makes a modest offering in our pursuit of exotica and the quest for their eventual conformity.
Replica symmetry breaking for the integrable two-site Sachdev–Ye–Kitaev model
We analyze a two-body non-Hermitian two-site Sachdev–Ye–Kitaev (SYK) model with the couplings of one site complex conjugated to the other site. This model, with no explicit coupling between the sites, shows an infinite number of second-order phase transitions, which is a consequence of the factorization of the partition function into a product over Matsubara frequencies. We calculate the quenched free energy in two different ways: first in terms of the single-particle energies and second by solving the Schwinger–Dyson equations of the two-site model. The first calculation can be done entirely in terms of a one-site model. The conjugate replica enters due to non-analyticities when Matsubara frequencies enter the spectral support of the coupling matrix. The second calculation is based on the replica trick of the two-site partition function. Both methods give the same result. The free-fermion partition function can also be rephrased as a matrix model for the coupling matrix. Up to minor details, this model is the random matrix model that describes the chiral phase transition of QCD, and the order parameter of the two-body model corresponds to the chiral condensate of QCD. Comparing to the corresponding four-body model, we are able to determine which features of the free energy are due to the chaotic nature of the four-body model. The high-temperature phase of both models is entropy dominated, and in both cases, the free energy is determined by the spectral density. The chaotic four-body SYK model has a low-temperature phase whose free energy is almost temperature-independent, signaling an effective gap of the theory even though the actual spectrum does not exhibit a gap. On the other hand, the low-temperature free energy of the two-body SYK model is not flat; in fact, it oscillates to arbitrarily low temperature. This indicates a less desirable feature that the entropy of the two-body model is not always positive in the low-temperature phase, which most likely is a consequence of the non-hermiticity.
Symmetry-resolved CO desorption and oxidation dynamics on O/Ru(0001) probed at the C K-edge by ultrafast X-ray spectroscopy
In this work, we report on carbon monoxide desorption and oxidation induced by 400 nm femtosecond laser excitation on the O/Ru(0001) surface probed by time-resolved X-ray absorption spectroscopy (TR-XAS) at the carbon K-edge. The experiments were performed under constant background pressures of CO (6x10 -8 Torr) and O 2 (3x10 -8 Torr). Under these conditions, we detect two transient CO species with narrow 2π* peaks, suggesting little 2π* interaction with the surface. Based on polarization measurements, we find that these two species have opposing orientations: (1) CO favoring a more perpendicular orientation and (2) CO favoring a more parallel orientation with respect to the surface. We also directly detect gas-phase CO 2 using a mass spectrometer and observe weak signatures of bent adsorbed CO 2 at slightly higher X-ray energies than the 2π* region. These results are compared to previously reported TR-XAS results at the O K-edge where the CO background pressure was three times lower (2x10 -8 Torr) while maintaining the same O 2 pressure. At the lower CO pressure, in the CO 2π* region, we observed adsorbed CO and a distribution of OC-O bond lengths close to the CO oxidation transition state, with little indication of gas-like CO. The shift towards 'gas-like' CO species may be explained by the higher CO exposure, which blocks O adsorption, decreasing O coverage and increasing CO coverage. These effects decrease the CO desorption barrier through dipole-dipole interaction, while simultaneously increasing the CO oxidation barrier.
Symmetry progression and band vs Mott character of CdPS 3 under pressure
Complex chalcogenides are renowned for their tunable electronic, magnetic, and optical properties under external stimuli. The MPX 3 family (M = Mn, Ni, Co, V; X = S, Se) is a platform for many exciting discoveries—especially under compression—although CdPS3 is thought to be different because the Cd center possesses a filled 4d shell, which precludes Mottness. Here, we combine synchrotron-based infrared absorbance and Raman scattering spectroscopies with diamond anvil cell techniques, complementary lattice dynamics calculations, and an analysis of the energy landscape to reveal a series of structural phase transitions in CdPS 3 . We find four distinct pressure-driven transitions, with low frequency modes detectable over the full 35 GPa range of our investigation. A group–subgroup analysis along with our first-principles calculations allows us to partially unravel the space group sequence. For instance, the first critical pressure is a monoclinic C2/m to trigonal $\overline{R}$3 transition at 10 GPa. Despite the softness and overall sensitivity to pressure, we do not locate an insulator-to-metal transition in this pressure range, indicating that the energy scale for gap closure is significantly higher than expected. We discuss these findings in terms of force-induced color change and Mott vs band character in this system.
Gyrotropy-induced symmetry breaking in RF-specific plasma wall interaction: Mechanisms and mitigation strategies
Ion cyclotron range of frequencies (ICRF) heating is essential for creating plasma in next-generation fusion devices. ICRF antennas often produce localized wall erosion, reducing reliability, material survivability, and overall plasma performance. We show that the wave physics' gyrotropy is among the causes of toroidal and poloidal asymmetries in these erosion spots, and that this source of asymmetry can be compensated for either by controlling the poloidal phasing or by modifying the limiter shapes.
Connecting collisional and photofragmentation resonances in the ungerade symmetry states of H 2
A recently developed energy-dependent frame transformation theory that incorporates both ionisation and dissociation channels of the H 2 molecule, is extended to treat the ungerade states that occur both in dissociative recombination and as the final state in ground state photoabsorption. The theoretical treatment includes the rotational degrees of freedom and is benchmarked against a two-dimensional model that can be solved with high accuracy and also compared with photoabsorption experiments. Analysis of the resulting spectra demonstrates how the same resonances appear in very different observables, often with quite different line shapes.
Symmetry degeneration and room temperature ferroelectricity in ion-irradiated SrTiO 3
Polar phonon modes associated with room temperature ferroelectricity are observed in SrTiO 3 single crystals irradiated with Ti ions. Quantitative strain analysis reveals that irradiation-induced out-of-plane strain drives the centrosymmetric cubic SrTiO 3 to a tetragonal-like structure in the maximum damaged region. Energy transfer from ions to electrons during ion irradiation yields defects in SrTiO 3 that also plays an important role for the room temperature ferroelectricity. Different from thin film techniques, the ferroelectricity in the ion irradiated SrTiO 3 can occur for much larger thicknesses, depending on the energy and type of ion.
Emergent symmetry in TbTe 3 revealed by ultrafast reflectivity under anisotropic strain
Here, we report ultrafast reflectivity measurements of the dynamics of the order parameter of the charge density wave (CDW) in TbTe 3 under anisotropic strain. We observe an increase in the frequency of the amplitude mode with increasing tensile strain along the a-axis (which drives the lattice into a > c, with a and c the lattice constants), and similar behavior for tensile strain along c (c > a). This suggests that both strains stabilize the corresponding CDW order and further support the near equivalence of the CDW phases oriented in a- and c-axis, in spite of the orthorhombic space group. The results were analyzed within the time-dependent Ginzburg–Landau framework, which agrees well with the reflectivity dynamics. Our study presents an ultrafast approach to assess the stability of phases and order parameter dynamics in strained systems.
Behavior of solitary waves of coupled nonlinear Schrödinger equations subjected to complex external periodic potentials with odd-$\mathcal{PT}$ symmetry
In this work, we discuss the response of both moving and trapped solitary wave solutions of a two-component nonlinear Schrödinger system in 1 + 1 dimensions to an odd-$\mathcal{PT}$ external periodic complex potential. The dynamical behavior of perturbed solitary waves is explored by conducting numerical simulations of the nonlinear system and using a collective coordinate variational approximation. We present case examples corresponding to choices of parameter values and initial conditions involved therein. The results of the collective coordinate approximation are compared against numerical simulations where we observe qualitatively good agreement between the two. Unlike the case for a single-component solitary wave in a complex periodic $\mathcal{PT}$-symmetric potential, the collective coordinate equations do not have a small oscillation regime, and initially the height of the two components changes in opposite directions often causing instability. We find that the dynamic stability criteria we have used in the one-component case are a good indicator for the onset of dynamic instabilities in the present setup.