States Of Opposite Parity Research Articles

Calculation of the optical absorption spectrum of ErCl3 in poly(ethylene oxide) (PEO)

The optical absorption spectrum for the rare-earth ion Er3+ in an amorphous polymer host poly(ethylene oxide) (PEO) has been calculated. A modified Judd–Ofelt theory has been exploited to calculate the oscillator strengths for the electric-dipole transitions within the 4 f11 configuration. Such transitions are allowed due to the admixing of opposite-parity states via the crystal field. Pertubation theory has been used to calculate the Stark level energies and the corresponding eigenstates using Racah algebra formalism. A simulated spectrum has then been constructed for this model system following molecular dynamics simulation generation of a sequence of physically representative environments for the rare-earth ions. These environments are then used to derive the crystal-field parameters needed to calculate spectral intensities and Stark energies. Molecular dynamics has also been used to probe such structurally interesting features as ion pairing, crystallization phenomena, coordination to the rare-earth ion, and radial distribution functions. Distinct qualitative trends were seen in the form of the spectral peaks for the different local Er3+ environments. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 80: 799–806, 2000

Lasing in Rare-Earth-Doped Semiconductors: Hopes and Facts

Semiconductors doped with rare-earth (RE) elements have attracted a lot of attention as alternative materials for producing electrically pumpe d semiconductor lasers whose emission wavelength is very weakly dependent on temperature. This prospect is especially attractive in the case of indirect-gap Silicon, whose photonic applications as the material for light emitters still remain more of a hope than a reality. In view of a desirable emission wavelength at 1.5 μm, a lot of research has concentrated on Si:Er (see Coffa et al. for a recent review). It is generally recognized that doping with Er ions presents one of the most promising approaches to Silicon photonics. However, despiteintensive investigations, stimulated emission has not been conclusively demonstrated for Si.Er or for any other RE-doped semiconductor. This is in striking contrast to optical amplifiers and lasers based on various erbium-doped glasses. In this article, which builds on recent articles in MRS Bulletin on Silicon photonics, we will address the issues relevant to efficient light generation by semiconductors doped with RE elements in general, and specifically by Si:Er-based structures.The intraimpurity electronic structure of RE ions is dominate d by electron-electron and spin-orbit interactions within the 4f shell. In the case of Er3+, they produce separated J-multiplets with 4I15/2 and 4I13/2 as the ground and the lowest-lying excited states, respectively. Due to the effective Screening of 4f electrons by the outer electron Shells, the host has a very limited influence and changes only slightly the relative positions of the levels. Depending on a particular site symmetry, the even terms of the crystal field split the free-ion J-multiplets into the Stark components typically by several meV for the ground State. The energy-level diagram of an Er3+ ion in a cubic crystal field is shown in Figure 1, where the energy transfer paths relevant for Si:Er are also schematically indicated. The odd terms of the crystal field potential admix the states of opposite parity to the 4f11 configuration of the Er3+ ion, thereby introducing a certain degree of electric-dipole strength into the otherwise forbidden intra-4f-shell transitions. This effect enhance s slightly the magnetic-dipole strength of the 4I15/2 ↔ 4I13/2 transition and is host- and site-dependent. There-fore, Er-related center s of different microstructure can be fairly easily identified.

Direct spectroscopic determination of the degree of orientation of parity-selected NO

If a polar molecule can be selected in a rotational state of definite parity, subsequent orientation of the molecule in an electric field mixes opposite parity states. The degree of mixing reflects the degree of orientation. Therefore, the intensity ratio of spectral lines that correspond to transitions starting from the two parity states being mixed, forms a sensitive and accurate probe of the molecular orientation. If saturation of the spectral lines of interest is avoided, the absolute degree of orientation can be determined, without recourse to other experimental data but line intensities. The method is illustrated for the case of the NO molecule.

Electronic structure of holes in modulation doped p-Si 1−xGe x/Si strained quantum wells in a magnetic field

The results of self-consistent calculations of hole energy levels in strained, symmetric and asymmetric, p-type modulation doped Si 1−xGe x/Si quantum wells in a magnetic field are reported. The band mixing is responsible for the enhanced effective g-factor of the opposite parity states. This leads to gaps at predominantly odd filling factors. The calculated filling factor dependent energy gaps are compared with gaps obtained from magneto-transport measurements.

Emergent Chiral Symmetry: Parity and Time Reversal Doubles

There are numerous examples of approximately degenerate states of opposite parity in molecular physics. Theory indicates that these doubles can occur in molecules that are reflection-asymmetric. Such parity doubles occur in nuclear physics as well, among nuclei with odd A ~ 219–229. We have also suggested elsewhere that such doubles occur in particle physics for baryons made up of cbu and cbd quarks. In this article, we discuss the theoretical foundations of these doubles in detail, demonstrating their emergence as a surprisingly subtle consequence of the Born–Oppenheimer approximation, and emphasizing their bundle-theoretic and topological underpinnings. Starting with certain "low energy" effective theories in which classical symmetries like parity and time reversal are anomalously broken on quantization, we show how these symmetries can be restored by judicious inclusion of "high-energy" degrees of freedom. This mechanism of restoring the symmetry naturally leads to the aforementioned doublet structure. A novel byproduct of this mechanism is the emergence of an approximate symmetry (corresponding to the approximate degeneracy of the doubles) at low energies which is not evident in the full Hamiltonian. We also discuss the implications of this mechanism for Skyrmion physics, monopoles, anomalies and quantum gravity.

Search for parity nonconservation in atomic dysprosium

Results of a search for parity nonconservation (PNC) in a pair of nearly degenerate opposite-parity states in atomic dysprosium are reported. The sensitivity to PNC mixing is enhanced in this system by the small energy separation between these levels, which can be crossed by applying an external magnetic field. The metastable odd-parity sublevel of the nearly crossed pair is first populated. A rapidly oscillating electric field is applied to mix this level with its even-parity partner. By observing time-resolved quantum beats between these sublevels, we look for interference between the Stark-induced mixing and the much smaller PNC mixing. To guard against possible systematic effects, reversals of the signs of the electric field, the magnetic field, and the decrossing of the sublevels are employed. We report a value of $|{H}_{w}|=|2.3\ifmmode\pm\else\textpm\fi{}2.9$ (statistical)\ifmmode\pm\else\textpm\fi{}0.7(systematic)| Hz for the magnitude of the weak-interaction matrix element. A detailed discussion is given of the apparatus, data analysis, and systematic effects.

Population inversion using laser and quasistatic magnetic field pulses

We show how, using a combination of a radiative pulse and a pulsed quasistatic magnetic field, it is possible to obtain complete population inversion between two states in a multistate system. The population transfer occurs between states of opposite parity, and does not require either careful control of pulse area nor frequency chirp. When the pulses are applied in counter-intuitive order the method is dynamically equivalent to stimulated Raman adiabatic passage (STIRAP). Complete inversion is also possible for intuitively ordered pulses, with robustness equivalent to that of STIRAP.

Parity Doublets in Quark Physics

There are numerous examples of very nearly degenerate states of opposite parity in molecular physics. The ammonia maser is based on one such doublet. Theory shows that these parity doublets can occur if the nuclear shape in the molecule is reflection asymmetric because the time scales of the shape and the electronic cloud are well separated. Parity doublets occur in nuclear physics as well for odd $A\ensuremath{\sim}219--229$. We discuss the theoretical foundation of these doublets and on that basis suggest that parity doublets should occur in particle physics too. In particular they should occur among baryons composed of $\mathrm{cbu}$ and $\mathrm{cbd}$ quarks.

Structure of low-lying levels in220Ac

The low-lying level structure of the odd-odd nucleus220Ac has been observed for the first time following the alpha decay of 0.8 s224Pa produced by the reaction209Bi (18O, 3n). Alpha-gamma and alpha-electron coincidence measurements were used in the construction of the220Ac level scheme. Opposite parity states with energy splittings similar to those in the recent high-spin nuclear study were observed. However, no levels or gamma transitions were observed in common with those of the high-spin work.

Vibronic transitions of Tm 3+ in various lattices

Vibronic transition probabilities have been derived for Tm 3+ in LiYF 4, YOCl and Na 5La(WO 4) 4. Determination of the vibronic transition probabilities for Tm 3+ is not easy, but, as far as they can be determined, it is shown that they have the same order of magnitude as those for Pr 3+ and are significantly larger than those of Gd 3+. These results give an indication that the electron-phonon coupling strength is large in the beginning and at the end of the trivalent lanthanide ion series and small in the centre. To explain the variation in vibronic transition probabilities for Pr 3+, Gd 3+ and Tm 3+, the position of the opposite parity states, the lanthanide contraction and the shielding of the 4 f electrons are considered.

PNC effects in neutron-232Th scattering: a window to class II or new states of nuclei?

Abstract The sign correlation of parity-non-conserving ( pnc ) asymmetries observed in neutron 232 Th scattering at the peak of p-wave resonances is examined. Assuming that it is a real effect, the conditions that this implies for a theoretical explanation are determined. It is shown that it has to rely on the existence of two states of opposite parity, which act as “doorway states”, different from those recently considered in the present field. The location of these states, their energy difference and their spreading width are estimated. It is shown that experimental data on 232 Th favor the location of both “doorway states” in the low energy region ( E s 0 , E p 0 ∼0–1 keV). In this case, the asymmetry exhibits a different sign depending on whether the energy of the p-wave resonance is below or above E s 0 . Candidates for such states are then considered, including the well known parity doublet built on a pear-shape nucleus, a more exotic one based on a structure where spins of nucleons align along their momentum ( σ · p correlation), and finally an accidental one in the second well of the potential energy surface. The evidence for a sign correlation in a limited energy range partly depends on the size of the random contribution to the observed pnc effects. The examination of the root mean square value of the pnc matrix element between states of the compound nucleus shows that the range of predictions is quite large and does not provide any constraint at present.

Two-photon spectroscopy between states of opposite parities.

Magnetic and electric dipole two-photon absorption (MED-TPA), recently introduced as a spectroscopic technique for studying transitions between states of opposite parities, is investigated from a theoretical point of view. An approximation referred to as weak quasiclosure approximation is used together with symmetry adaptation techniques to calculate the transition amplitude between states having well-defined symmetry properties. Selection rules for MED-TPA are derived and compared to selection rules for parity-forbidden electric dipole two-photon absorption.

Three-body halos. III. Effects of finite core spin.

We investigate effects of finite core spin in two-neutron halos in the three-body model consisting of two neutrons and a core. The states in the neutron-core subsystem can then have an additional splitting due to the coupling of the neutron and core spins. The connection between the structure of the total system and the states of the neutron-core subsystem depends strongly on this spin splitting. However, the spatial structure is essentially unchanged. The neutron momentum distribution in a nuclear dissociation reaction will consist of a broad and a narrow distribution arising from the two spin split neutron-core virtual states. The large distance behavior is investigated and the conditions for the Efimov effect turn out to be more restrictive. The magnetic moment is equal to the core value independent of spin splitting and energies of the neutron-core states. The excited states of opposite parity depend strongly on the spin splitting. The parameters in our numerical examples are chosen to be appropriate for $^{11}\mathrm{Li}$ and $^{19}\mathrm{B}$.

Experimental investigation of excited states in atomic dysprosium.

A pair of closely lying states of opposite parity and the same total electronic angular momentum (J=10) at 19797.96 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ in dysprosium is experimentally investigated with the goal of evaluating parameters relevant to parity and parity--time-reversal violation experiments. An atomic beam apparatus is used. The states of interest are populated with a sequence of two laser pulses, and a third laser pulse and fluorescence detection are used to probe the state population. Their lifetimes are determined from the dependence of the fluorescence signal on the time delay between the pump and probe pulses. The lifetime of the even-parity state was also measured by a different method involving detection of cascade fluorescence. Spectroscopy of radio-frequency E1 transitions between the opposite-parity states is performed when one of the states is populated and the population of the other is probed. This determines precise energy separations between various isotope and hyperfine structure components, and allows extraction of the corresponding isotope shift and hyperfine structure parameters. Electric polarizability is determined from radio-frequency line shapes in the presence of a dc electric field. As part of the preparation of a parity violation experiment, level-crossing signals which occur when various Zeeman components of the closest hyperfine components (isotope 163, F=10.5; initial separation 3.1 MHz) are brought together in the presence of collinear electric and magnetic fields were studied. These measurements provide an independent determination of the E1 matrix element between the opposite-parity states. In addition, lifetimes, isotope, and hyperfine structure of other dysprosium states are obtained and a number of narrow autoionization resonances (\ensuremath{\Gamma}10 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) are observed.

Operator dependence of hadron masses for Kogut-Susskind quarks on the lattice

Operator dependence of hadron masses for the Kogut-Susskind fermion action is studied with a quenched simulation at β = 6.0 on a 24 3 × 40 lattice at the quark mass m q a = 0.01 and 0.02. With an improved wall source masses are extracted for all 64 meson and 120 baryon operators local in time. For mesons hadron masses are separated into two levels corresponding to π and ϱ. The results confirm the spin-flavor assignment in the literature. At a finer level, however, the spectrum shows some fine structure for π whereas a good degeneracy is observed for ϱ. The spectrum of baryons is also basically divided into the nucleon and Δ. However, one set of operators theoretically assigned to the nucleon in fact couples to Δ. We also find a substantial operator dependence in the nucleon mass. This gives rise to a large uncertainty in m N m ϱ depending on which operators are used to extract hadron masses. A brief discussion is also made for the characteristic of the opposite parity states.

Excitonic Molecule in CuCl Crystal

count the detailed band structure of CuCl. The fine structure of the excitonic molecule is clarified with the effective electron—hole exchange effect taken into account beyond the effective mass approximation. The electron-hole exchange interaction mixes the states of opposite parities with respect to the permutation of electrons and holes. Two trial envelope functions, sym- metric and antisymmetric under the permutation of two electrons or two holes, were used in the numerical minimization of the ground state energy of the biexciton. The obtained binding energy of the biexciton, as well as, the ratio of the mixing of the trial envelope functions of opposite parities are presented.

Investigation of nearly degenerate opposite parity states in atomic dysprosium.

A pair of closely lying states of opposite parity and the same angular momentum J=10 at 19797 96 cm{sup {minus}1} in dysprosium were experimentally investigated with the goal of evaluating parameters relevant to experiments searching for P and P,T violation effects. These effects are enhanced due to extreme proximity of the opposite parity levels. Additional advantages arise because both states have relatively long lifetimes. Measurements of these lifetimes, electric polarizability and energy intervals between isotope and hyperfine components are presented. The experiment utilized an atomic beam. The states of interest were populated from the ground state (J=8) by using two consecutive transitions induced by pulsed lasers. To determine the lifetimes, a third laser pulse was used to excite a transition from the populated level and fluorescence from the upper state of this transition was detected. The lifetimes were determined from the fluorescence signal dependence on the time delay between pulses with a fixed spatial separation between the pump and the probe region. To determine energy separations between various isotope and hyperfine components, the even parity state was populated, E1 rf transitions were induced to the odd parity state and the population of this state was probed. From an analysis ofmore » the observed transitions, precise isotope shifts and hfs parameters for both states were determined. In order to determine the electric polarizability, the shifts and line shapes of the lowes frequency transitions (at 3.10 and 68.83 MHz) were studied when a dc electric field was applied along with the rf field. The obtained information will be used in a parity violation experiment which currently is in preparation in our laboratory.« less

Hyperfine lifting of parity degeneracy and the question of inversion in a rigid molecule.

This Letter demonstrates that the parity degeneracy of isolated vibration-rotation states of a rigid molecule can be removed by hyperfine interactions. Hyperfine structures of infrared transitions in ${\mathrm{PH}}_{3}$ are obtained, by saturation spectroscopy around 10 \ensuremath{\mu}m. One of these is used to demonstrate unequivocally that degenerate states of opposite parity are separated by the proton hyperfine interactions. We show that alternative explanations involving the physical inversion of the molecule are completely inconsistent with the details of the spectra obtained. In addition to the splitting conclusion, which has very wide generality, new confidence limits are placed on the possible inversion splitting.

An experimental search for enhanced parity non-conserving optical rotation in samarium

The authors have made a preliminary study of several allowed M1 transitions within the 4f66s2 ground state configuration of samarium with the aim of observing enhanced parity non-conserving (PNC) optical rotation. No evidence for R=Im(E1)PNC/(M1) greater than 10-6 has been found. They conclude that, although opposite parity states are comparatively close (ca 200 cm-1) in the cases studied, the strength of the admixed E1 transitions is low thereby reducing any potential enhancement. This also complicates any theoretical analysis since there is no single dominant E1 component in the admixture, and in any case calculations of oscillator strengths for samarium with its complicated level structure are notoriously difficult. Finally, the reactivity of metallic samarium poses considerable experimental difficulties in achieving sufficiently high vapour pressures.

Even-odd anomalous tunneling effect.

The analysis of the interacting fermion models with the SU(2) symmetry indicates the different behavior of the splittings of opposite-parity lowest-energy eigenstates for even and odd numbers of fermions. The imaginary time-dependent mean-field approach reproduces the average results only. For the odd particle numbers, an introduction of the universal logarithmic term to the action integral is needed. The even-odd effect appears in a wide class of models with the SU(2) symmetry and is connected with the crossing of the energy surfaces of opposite-parity states for an odd number of fermions.