Lower Doublet Research Articles

Electronic structure of the frustrated diamond lattice magnet NiRh2O4

The $A$-site spinel ${\mathrm{NiRh}}_{2}{\mathrm{O}}_{4}$ is the only known realization of a spin-1 diamond lattice magnet and is predicted to host unconventional magnetic phenomena driven by frustrated nearest and next-nearest neighbor exchange as well as orbital degeneracy. Previous works found no sign of magnetic order but found a gapped dispersive magnetic excitation indicating a possible valence bond magnetic ground state. However, the presence of many competing low energy degrees of freedom and limited empirical microscopic constraints complicates further analysis. Here we carry out resonant inelastic x-ray scattering (RIXS), x-ray absorption spectroscopy (XAS), and inelastic neutron scattering (INS) to characterize the local electronic structure and lattice dynamics of ${\mathrm{NiRh}}_{2}{\mathrm{O}}_{4}$. The RIXS data can be partly described by a single-ion model for tetrahedrally coordinated ${\mathrm{Ni}}^{2+}$ and indicates a tetragonal distortion $\mathrm{\ensuremath{\Delta}}{t}_{2}=70$ meV that splits the ${t}_{2}$ orbitals into a high energy orbital singlet and lower energy orbital doublet. We identify features of the RIXS spectra that are consistent with a Rh-Ni two-site excitation indicating strong metal-metal hybridization mediated by oxygen in ${\mathrm{NiRh}}_{2}{\mathrm{O}}_{4}$. We also identify signatures of electron-phonon coupling through the appearance of phonon sidebands that dress crystal field excitations. These results establish the key energy scales relevant to the magnetism in ${\mathrm{NiRh}}_{2}{\mathrm{O}}_{4}$ and further demonstrate that covalency and lattice dynamics play essential roles in controlling the magnetic ground states of $A$-site spinels.

Influence of magnesium oxide on the physical and spectroscopic properties of manganese doped sodium tetra borate glasses

The effect of alkaline earth oxide on sodium tetraborate was analyzed by fabricating a range of glasses depicted by the formula x MgO-(40-x)ZnO-59.5Na2B4O7-0.5MnO2. Basic character was analyzed and confirmed by XRD tests.Decline in density is attributed to the replacement of high molecular mass ZnO by a relatively less molecular mass MgO. The volume enlargement is discussed in terms of increased bond lengths and induced non- bridging oxygen atoms. Parameters like refractive index, reflection loss, molar refractivity, electron polarizability are obtained from existing relations. All these are indirectly depends on density and molar volume and hence their nature. Optical studies revealed indirect kind of transitions in these glasses ranging the values of optical energy gap between 2.913–3.15 eV and Urbach energy (ΔE) 0.342–0.276 eV showing greater stability of glasses.Mn2 +ion in its d5 state revealed a well resolved sextet centered around g"2.032 indicating Mn2+ ions are in octahedral (Oh) environment resulted from jumps between lower doublet energy states. The resonance of g≈ 2.99 and g≈ 4.22 are related to rhombic surroundings of the Mn2+ and jumps between middle kramers doublets. The value of hyperfine split ‘A′ and Δg= (ge-g) are indicative of ionic bonding between Mn2 + ions and oxygens. Zero field splitting parameter ‘D′ decreases from x = 0 to x = 30 mol% and then increased for x = 40 mol%. Magnitude of unpaired spins(N) participating in the resonance and paramagnetic susceptibility(c) are calculated. FTIR and Raman studies are conducted. FTIR spectra revealed the structural changes from BO4 to BO3 by increasing MgO content. From FTIR and Raman studies it is established that MgO is acting as modifier in the given glass composition.

Fin Whale Song Patterns Shift Over Time in the Central North Pacific

Male fin whales sing by producing 20-Hz pulses in regular patterns of inter-note intervals. While singing, fin whales may also alternate the frequency ranges of their notes. Different song patterns have been observed in different regions of the world's oceans. New song patterns suddenly emerging in an area have been hypothesized to either be indicators of new groups of whales in the area or signs of cultural transmission between groups. Since the status of fin whales around Hawaii is unknown and visual surveys are expensive and difficult to conduct in offshore areas, passive acoustic monitoring has been proposed as a way to monitor these whales. We used passive acoustic recordings from an array of 14 hydrophones to analyze the song patterns of 115 fin whale encounters made up of 50,034 unique notes off Kauai, Hawaii from 2011--2017. Fin whale singing patterns were more complicated than previously described. Fin whales off Hawaii sang in five different patterns made of two 20-Hz note types and both singlet and doublet inter-note interval patterns. The inter-note intervals present in their songs were 28/33 s for the lower frequency doublet, 30 s for the lower frequency singlet, 17/24 s for the higher frequency doublet, 17 s for the higher frequency singlet, and 12/20 s for the doublet that alternated between both note types. Some of these song patterns were unique to these fin whales in Hawaiian waters, while others were similar to song patterns recorded from fin whales off the U.S. west coast. Individual fin whales often utilized several different song patterns which suggests that multiple song patterns are not necessarily indicators of different individuals or groups. The dominant song pattern also changed over these years. Cultural transmission may have occurred between fin whales in Hawaiian waters and off the U.S. west coast, which has resulted in similar songs being present at both locations but on lagged timescales. Alternatively, groups occupying the Hawaiian waters could shift over time resulting in different song patterns becoming dominant. This work has implications for the population structure and behavior of Hawaii fin whales.

Emergent D6 symmetry in fully relaxed magic-angle twisted bilayer graphene

We present a tight-binding calculation of a twisted bilayer graphene at magic angle $\theta\sim 1.08^\circ$, allowing for full, in- and out-of-plane, relaxation of the atomic positions. The resulting band structure displays as usual four narrow mini bands around the neutrality point, well separated from all other bands after the lattice relaxation. A thorough analysis of the mini-bands Bloch functions reveals an emergent $D_6$ symmetry, despite the lack of any manifest point group symmetry in the relaxed lattice. The Bloch functions at the $\Gamma$ point are degenerate in pairs, reflecting the so-called valley degeneracy. Moreover, each of them is invariant under C$_{3z}$, i.e., transforming like one-dimensional, in-plane symmetric irreducible representation of an "emergent" $D_6$ group. Out of plane, the lower doublet is even under C$_{2x}$, while the upper doublet is odd, which implies that at least eight Wannier orbitals, two $s$-like and two $p_z$-like for each of the two supercell sublattices AB and BA are necessary, probably not sufficient, to describe the four mini bands. This unexpected one-electron complexity is likely to play an important role in the still unexplained metal-insulator-superconductor phenomenology of this system.

Amplifying ultraweak transitions in collective systems via quantum interference

We investigate laser-induced quantum interference phenomena in superradiance processes and in an ensemble of initially excited $\Lambda-$type closely packed three-level emitters. The lower doublet levels are pumped with a coherent laser field. Due to constructive quantum interference effects, the superradiance occurs on a much weaker atomic transition which is not the case in the absence of the coherent driving. This result may be of visible relevance for enhancing ultraweak transitions in atomic or atomic-like systems, respectively, or for high-frequency lasing effects.

Spectroscopic and theoretical studies of some 2-(2′-haloacetyl)-5-substituted: 1-Methylpyrrole, furan and thiophene

The conformational study of some 2-(2′-haloacetyl)-5-substituted five-membered heteroaromatic compounds Z-CH2C(O)(C4H2X)Y bearing a halogen (Z = Cl or Br) at the 2′-position and (Y = NO2, H, Me or Cl) substituents at the 5-position of the heteroaromatic ring for X = NMe, O and S was performed by IR carbonyl stretching band (νCO) analysis supported by the harmonic frequency, NBO and PCM calculations on the minima and saddle-point structures obtained at the M05-2X/aug-cc-pVTZ level. The computational results predicted the presence of four stable conformers, classified by the orientation of the Xring–CCO (syn/anti) and the OCC–Z (anticlinal/ synperiplanar) moieties as ac(syn), sp(syn), ac(anti) and sp(anti). The anti/syn equilibrium controls the relative stabilities of the conformers to a large extent while the anticlinal/synperiplanar accounts for the observed trend of the IR carbonyl band components. The computed νCO frequencies and the PCM trend of the relative abundance in solvents of increasing permittivity allowed the pairs of ac(syn)/ac(anti) and sp(syn)/sp(anti) conformers to be assigned to the lower and higher νCO frequency IR carbonyl doublet components, respectively. The PCM data failed to reproduce the experimental carbonyl triplet found in chloroform. However, the additional component could be justified by assuming the formation of complexes constituted by one chloroform molecule hydrogen bonded to the conformers in a PCM chloroform continuum.The NBO and short contact analysis suggested that the syn/anti conformational equilibrium is governed mainly by electrostatic interactions, while the anticlinal/synperiplanar depends to different extents on both orbital and electrostatic interactions.

Inversionless Superradiance and the Duffing Model

Superradiance of three-level optical systems with a doublet in the ground state (Λ-scheme) placed in a high-Q cavity is studied theoretically. The conservation laws are obtained, which allow to considerably reduce the dimension of the phase space of the examined model (R11→R5). In the particular case of a degenerate doublet, a mapping that makes it possible to reduce the problem of the three-level superradiance to a Duffing oscillator model (R5→R2) is found. It is shown the possibility to initiate the superradiance generation even in the case when the population of the upper level is smaller than the total population of the lower doublet, i.e., without population inversion on the whole.

Spectroscopic and theoretical studies of some 4′-substituted-phenyl 2-(ethanesulfonyl)acetates. Structure of 4′-nitrophenyl 2-(ethanesulfonyl)acetate

Abstract An analysis of carbonyl bands in the infrared spectra of some 2-ethylsulfonyl 4′-substituted phenylacetates bearing substituents NO2 (1), H (2) and OMe (3), supported by B3LYP/6-31G(d,p) and SM5.42R at PM3 level calculations, along with natural bond orbital analysis (NBO) and X-ray diffraction (for 1) was performed. Theoretical data indicated the existence of two stable gauche conformations (g 1 and g 2). The g 1 conformer is the most stable, least polar and has the lowest νCO frequency. The more intense, lower frequency carbonyl doublet component found in CCl4 solution is assigned to the g 1 conformer. As the solvent dielectric constant increases (going from CCl4 to MeCN) the higher frequency νCO doublet increases in intensity. This behaviour is reproduced by the solvation free energy calculations, supporting the conformer assignments. NBO calculations indicate that the most important orbital interaction is LPO9 → π*C7=O8 for both conformers, which corresponds to [C=O ↔ C+–O-] conjugation. This stabilises the g 1 conformer to a greater extent and is responsible for the lower νCO frequency. The sum of the selected NBO delocalisation energies for 1–3 indicates that the g 1 conformer is more stable. It is concluded that the calculated greater stability of the g 1 conformer is due to a balance of attractive electrostatic and orbital interactions along with relevant hydrogen bonds. The X-ray crystal structure analysis of 1 shows the presence of two crystallographic independent but almost superimposable molecules each which adopt a cis geometry. The molecules are consolidated into the three-dimensional crystal packing by C–H…O interactions as well as by nitro- N–O…π(phenyl) contacts.

Electromagnetically Induced Entanglement.

Quantum entanglement provides an essential resource for quantum computation, quantum communication, and quantum network. How to conveniently and efficiently produce entanglement between bright light beams presents a challenging task to build realistic quantum information processing networks. Here, we present an efficient and convenient way to realize a novel quantum phenomenon, named electromagnetically induced entanglement, in the conventional Λ-type three-level atomic system driven by a strong pump field and a relatively weak probe field. Nearly perfect entanglement between the two fields can be achieved with a low coherence decay rate between the two lower levels, high pump-field intensity, and large optical depth of the atomic ensemble. The physical origin is quantum coherence between the lower doublet produced by the pump and probe fields, similar to the well-known electromagnetically induced transparency. This method would greatly facilitate the generation of nondegenerate narrow-band continuous-variable entanglement between bright light beams by using only coherent laser fields, and may find potential and broad applications in realistic quantum information processing.

Generation of multipartite continuous-variable entanglement via atomic spin wave: Heisenberg-Langevin approach

We conduct theoretical studies on the effects of various parameters on generation of multipartite continuous-variable entanglement via atomic spin wave induced by the strong coupling and probe fields in the Λ-type electromagnetically induced transparency configuration in a realistic atomic ensemble by using the Heisenberg-Langevin formalism. It is shown that the increase of the atomic density and/or Rabi frequencies of the scattering fields, as well as the decrease of the coherence decay rate of the lower doublet would strengthen the degree of multipartite entanglement. This provides a clear evidence that the creation of multicolor multipartite entangled narrow-band fields to any desired number with a long correlation time can be achieved conveniently by using atomic spin wave in an atomic ensemble with large optical depth, which may find interesting applications in quantum information processing and quantum networks.

Spectroscopic and Theoretical Studies of Some 3-(4′-Substituted phenylsulfanyl)-1-methyl-2-piperidones

The analysis of the IR carbonyl bands of some 3-(4′-substituted phenylsulfanyl)-1-methyl-2-piperidones 1–6 bearing substituents: NO2 (compound 1), Br (compound 2), Cl (compound 3), H (compound 4) Me (compound 5) and OMe (compound 6) supported by B3LYP/6-31+G(d,p) and PCM calculations along with NBO analysis (for compound 4) and X-ray diffraction (for 2) indicated the existence of two stable conformations, i.e., axial (ax) and equatorial (eq), the former corresponding to the most stable and the least polar one in the gas phase calculations. The sum of the energy contributions of the orbital interactions (NBO analysis) and the electrostatic interactions correlate well with the populations and the νCO frequencies of the ax and eq conformers found in the gas phase. Unusually, in solution of the non-polar solvents n-C6H14 and CCl4, the more intense higher IR carbonyl frequency can be ascribed to the ax conformer, while the less intense lower IR doublet component to the eq one. The same νCO frequency trend also holds in polar solvents, that is νCO (eq) < νCO (ax). However, a reversal of the ax/eq intensity ratio occurs going from non-polar to polar solvents, with the ax conformer component that progressively decreases with respect to the eq one in CHCl3 and CH2Cl2, and is no longer detectable in the most polar solvent CH3CN. The PCM method applied to compound 4 supports these findings. In fact, it predicts the progressive increase of the eq/ax population ratio as the relative permittivity of the solvent increases. Moreover, it indicates that the computed νCO frequencies of the ax and eq conformers do not change in the non–polar solvents n-C6H14 and CCl4, while the νCO frequencies of the eq conformer become progressively lower than that of the ax one going from CHCl3 to CH2Cl2 and to CH3CN, in agreement with the experimental IR values. The analysis of the geometries of the ax and eq conformers shows that the carbonyl oxygen atom of the eq conformer is free for solvation, while the O[CO]…H[o-Ph] hydrogen bond that takes place in the ax conformer partially hinders the approach of the solvent molecules to the carbonyl oxygen atom. Therefore, the larger solvation that occurs in the carbonyl oxygen atom of the eq conformer is responsible for the observed and calculated decrease of the corresponding frequency. The X-ray single crystal analysis of 2 indicates that this compound adopts the most polar eq geometry in the solid. In fact, in order to obtain the largest energy gain, the molecules are arranged in the crystal in a helical fashion due to dipole moment coupling along with C-H…O and C-H…πPh hydrogen bonds.

Superradiance of the system comprised of two parallel resonant thin layers

A cavity-like regime of superradiance for a double-layer medium populated by atoms with the A-scheme of transitions is considered in a semiclassical approximation under the condition that the layers are arranged symmetrically with respect to initial characteristics of the field and atomic system populating the layers. An analytical law for the linear stage of the superradiance process is found that agrees well with numerical solution of the differential equations of the model under consideration for any initial conditions nearly up to the peak of the appropriate characteristic of the field intensity module. For the case of degenerate lower doublet, the resonant character of the dependence of the superradiance pulse time delay on the distance between the layers is studied.

Heart of the Beat (the Flagellar Beat, that Is)

Heart of the Beat (the Flagellar Beat, that Is)

RECK Forms Cowbell-shaped Dimers and Inhibits Matrix Metalloproteinase-catalyzed Cleavage of Fibronectin

The membrane-anchored protease regulator RECK plays important roles in mammalian development and tumor suppression. The biochemical bases of these bioactivities, however, remain poorly understood. Here we report on the properties of a recombinant RECK protein expressed in mouse fibroblasts and purified to near homogeneity. Multiple lines of evidence indicate that RECK forms dimers. Single particle reconstruction using transmission electron microscopy revealed a unique cowbell-like shaped RECK dimer. RECK is cleaved by MMP-2 and MMP-7 and competitively inhibits MMP-7-catalyzed cleavage of fibronectin. Forced RECK expression in HT1080 cells, whose endogenous RECK expression is minimal, leads to an increase in the amount of fibronectin associated with the cell. Our data demonstrate the ability of RECK to protect fibronectin from MMP-mediated degradation.

Coherent population trapping in a specific model

Coherent population trapping is shown to occur in a driven symmetric double-well potential. In the model of the ammonia molecule, for a molecule initially prepared in its lower doublet, under certain circumstances, the upper level remains unpopulated, this occurs in spite of the fact that the laser field is resonant with the |2〉→|3〉 trasition. This is a coherent population trapping phenomenon which cannot be accounted for with the convential models.

Criterion for Weak Spin–Orbit Coupling in Heavy-Fermion Superconductivity: Numerical Renormalization-Group Study

A criterion for effective irrelevancy of the spin-orbit coupling in the heavy-fermion superconductivity is discussed on the basis of the impurity Anderson model with two sets of Kramers doublets. Using Wilson's numerical renormalization-group method, we demonstrate a formation of the quasiparticle as well as the renormalization of the rotational symmetry-breaking interaction in the lower Kramers doublet (quasispin) space. A comparison with the quasispin conserving interaction exhibits the effective irrelevancy of the symmetry-breaking interaction for the splitting of two doublets Delta larger than the characteristic energy of the local spin fluctuation T_K. The formula for the ratio of two interactions is also determined.

On the origin of the splittings of the [formula omitted](SO 42−) modes in the specular reflectance IR spectra of gypsum

The IR polarized spectra of gypsum CaSO 4·2H 2O were recorded at incidence angles of approximately 10 and 16 degrees. Band singlet or doublet was observed for the higher frequency ν 3 (SO 4 2−) mode of B u symmetry type, depending on polarization ( n or p). A doublet was observed for the lower frequency ν 3 (SO 4 2−) mode of B u symmetry type too, irrespectively of the type of polarization. In order to give an explanation for the doublets origin, a model permittivity function was constructed. Quite good agreement exists between the reflectance based on the model permittivity function and the experimentally measured one for the high-frequency doublet. The origin of the lower frequency doublet could not be explained in this way, but may be speculated to result from an Evans type interaction between a combination of a water libration and ν 2 (SO 4 2−), with the lower frequency ν 3 (SO 4 2−) mode.

Nonperturbative coherent population trapping: an analytic model.

Coherent population trapping is shown to occur in a driven symmetric double-well potential in the strong-field regime. The system parameters have been chosen to reproduce the 0(-) <--> 3(+) transition of the inversion mode of the ammonia molecule. For a molecule initially prepared in its lower doublet we find that, under certain circumstances, the 3(+) level remains unpopulated, and this occurs in spite of the fact that the laser field is resonant with the 0(-) <--> 3(+) transition and intense enough so as to strongly mix the 0(+) and 0(-) ground states. This counterintuitive result constitutes a coherent population trapping phenomenon of nonperturbative origin which cannot be accounted for with the usual models.

Effect of the near-lying level on the kinetics of populations in the superradiance of a thin layer: Local-field regime

The effect of the local field on the competition of transitions in the superradiance of an incompletely excited thin layer of three-level atoms Λ-diagram of working transitions) is studied. The analysis made proves that the upper sublevel of the lower doublet is initially unpopulated. It is shown that the Raman transition, in the local-field regime, is ahead of the development of the superradiance pulse and causes the transfer of populations between sublevels of the lower doublet.

Vaccinia virus telomeres: interaction with the viral I1, I6, and K4 proteins.

The 192-kb linear DNA genome of vaccinia virus has covalently closed hairpin termini that are extremely AT rich and contain 12 extrahelical bases. Vaccinia virus telomeres have previously been implicated in the initiation of viral genome replication; therefore, we sought to determine whether the telomeres form specific protein-DNA complexes. Using an electrophoretic mobility shift assay, we found that extracts prepared from virions and from the cytoplasm of infected cells contain telomere binding activity. Four shifted complexes were detected using hairpin probes representing the viral termini, two of which represent an interaction with the "flip" isoform and two with the "flop" isoform. All of the specificity for protein binding lies within the terminal 65-bp hairpin sequence. Viral hairpins lacking extrahelical bases cannot form the shifted complexes, suggesting that DNA structure is crucial for complex formation. Using an affinity purification protocol, we purified the proteins responsible for hairpin-protein complex formation. The vaccinia virus I1 protein was identified as being necessary and sufficient for the formation of the upper doublet of shifted complexes, and the vaccinia virus I6 protein was shown to form the lower doublet of shifted complexes. Competition and challenge experiments confirmed that the previously uncharacterized I6 protein binds tightly and with great specificity to the hairpin form of the viral telomeric sequence. Incubation of viral hairpins with extracts from infected cells also generates a smaller DNA fragment that is likely to reflect specific nicking at the apex of the hairpin; we show that the vaccinia virus K4 protein is necessary and sufficient for this reaction. We hypothesize that these telomere binding proteins may play a role in the initiation of vaccinia virus genome replication and/or genome encapsidation.