Level Anticrossing Spectroscopy Research Articles

Conversion factors and widths of avoided crossings in Rydberg Stark states of K

In the experiment concerning the level anticrossing spectroscopy, the experimental widths are measured in the unit of V/cm, but the theoretical ones are presented in the unit of 1/cm. To facilitate the comparison of the experimental data with theoretical values, it is necessary to know the conversion factors that give the relation between the units of V/cm and 1/cm. In this paper, the results are presented for the conversion factors of Rydberg potassium based on the theory of the anticrossing signals and a kind of potential model, which make it possible to directly compare the theoretical widths with experimental ones. The method described here for obtaining the conversion factors of Rydberg potassium is suitable for any alkaline metal atom.

Fine structure of excitons and e-hpairs in GaAs/AlAs superlattices at the X-Γ crossover

Optically detected magnetic resonance (ODMR) and levelanticrossing spectroscopy were applied to study g-factors andexchange splittings of localized excitons and separatelylocalized electrons and holes at the Xz-Γ crossoverof the conduction band states in a GaAs/AlAs superlattice witha composition gradient. g-factors, exchange splittings and theorder of the exciton radiative levels were determined. In thetransition region we clearly observed the disappearance of type IIexcitons created by the Xz electron in AlAs and a heavyhole in GaAs layers. Appearance of type I excitons with an order of magnitude larger exchange was verified by LACspectroscopy. Intermediate `type II-like' and `type I-like'excitons were found in the transition region by ODMR and LACwith different exchange splittings and luminescence decay times.Besides ODMR of excitons with a definite value of exchangesplitting, ODMR ascribed to separately localized electrons and holes with a distribution of exchange splittings was detected.

Magnetic resonance in micro- and nanostructures

GaAs/AlAs and GaAs/AlGaAs quantum wells and superlattices were grown by molecularbeam epitaxy and self-organized oriented silver halide micro- and nanocrystals were embedded in crystalline alkali halide matrix. We report the results of the application of optically detected magnetic resonance (ODMR) and level anticrossing (LAC) spectroscopy for the investigations of these two classes of nanostructures. ODMR and LAC spectroscopy are shown to be very suitable for obtaining important physical parameters of low-dimensional systems and for a local diagnostics of nanostructures.

From Röntgen to Ioffe, from Giessen to Saint Petersburg — Relations between Russian and German physics

Two former professors of physics at Giessen university contributed significantly to the development of the Ioffe Institute: Wilhelm Conrad Rontgen as a teacher of Abram Ioffe, and Wilhelm Hanle, whose effect found various applications, e.g., in the spectroscopy of hot electrons in low-dimensional structures. A few examples will illustrate how topics of their scientific work found a continuation in the research activities at Giessen, but also in the collaboration between Giessen and Saint Petersburg. They range from sodium chloride, the old Rontgen/Ioffe material where we could prove the existence of an unusual isotope effect in nickel-doped crystals, over level-crossing experiments in gases, to GaAs/AlAs superlattices, where level-anticrossing spectroscopy of excitons reveals detailed information about recombination processes and interface quality. A short summary of the efforts to keep the traditionally close and good relations between Russian and German physics vital completes the report.

Optically detected magnetic resonance study of the transition from pseudodirect type-II to type-I GaAs/AlAs superlattices

Optically detected magnetic resonance and level anticrossing spectroscopy have been applied for the first time for a study of GaAs/AlAs superlattices (SL) in the transistion region type-II SL (Γ hole in the GaAs layer and X electron in the AlAs layer)—type I SL (Γ hole and Γ electron both in the GaAs layer). Three kinds of heavy-hole excitons which are typical for type-II SL, for the transition type-II/type-I and for type-I SL with the lifetime down to 300 ps have been evidenced in the transition region and their g-factors and exchange splitting parameters have been measured.

S 1-T 1 coupling in propynal by level anticrossing spectroscopy

Using level anticrossing spectroscopy we have measured the T 1 level density and the distribution of S 1-T 1 coupling matrix elements V st in propynal for the six S 1 vibrational levels: 0 0, 9 1, 12 1, 6 1, 5 1 and the lowest member of a Fermi resona triad 4 1/5 19 1/?, which possess 2036 to 3335 cm −1 excess energy with respect to the 0 0 T 1 vibrational level. We show that at l in the 0 0 state the coupling is vibronic spin-orbit. Parallel to the behaviour of the similar molecule glyoxal, the average 〈 V st〉 was found to remain constant in that energy range, a challenging result for the theories of singlet-triplet couplings and radiationless transitions.

Time-delayed detection in level anticrossing spectroscopy

In the present paper we discuss the time-delayed detection of the fluorescence signal in a level anticrossing experiment showing that, unlike what occurs in other methods, it does not lead, in general, to a signal profile narrowing as the delay time increases. However, we find conditions under which this technique provides the possibility of enhanced spectral resolution, as well as gives a direct measurement of the difference between the decay rates of the levels involved.

Steady-state level-anticrossing spectra for bound-exciton triplets associated with complex defects in semiconductors.

A detailed analysis of magnetically induced level-anticrossing (LAC) effects for bound-exciton (BE) triplets associated with isoelectronic complex defects in semiconductors is presented, using rate equations and a spin Hamiltonian approach. It is shown that the observation of the LAC effects is due to nonvanishing microscopic interactions coupling the approaching states. In addition there exists an inequivalency between these states, due to a steady-state excitation mechanism. The hyperfine interactions are proved to be the main static interaction responsible for the LAC effects. Characteristic distinctions between different BE systems (from thermalized to unthermalized) are shown to exist in the vicinity of the LAC field region as well as for high magnetic fields. A good agreement between the treatment developed in the present work and experimental LAC spectra for several complex defects in GaP has been obtained. Useful information about the bound excitons and their associated defects can be extracted by simple steady-state level-anticrossing spectroscopy, i.e., in complete absence of external perturbing radiofrequency or microwave fields.

Study of singlet-triplet coupling in glyoxal by level anticrossing spectroscopy. VII. Complete assignment of the 0 0, 8 1, 6 17 1 and 4 1 anticrossing spectra

In paper VI of this series, we have made the statistical analysis of the singlet-triplet coupling matrix elements for ten N S = 0 singlet vibrational levels of glyoxal, without determining the triplet quantum numbers. In this paper we present the complete assignment (triplet rotational quantum numbers and vibrational symmetry) of each anticrossing observed from four singlet vibrational levels: 0 0, 8 1, 6 17 1 and 4 1 (which give respectively 36, 76, 155 and 145 anticrossings by 0 to 7.5 T scans). Therefore we determine the zero-field energy origin of most of the triplet vibrational levels which are located within 7 cm −1 of the four singlet levels studied. Two kinds of selection rules are found: the first stemming from direct vibronic spin-orbit interactions and the second from indirect ones (involving an intermediate triplet state). About half of the anticrossings are due to direct vibronic spin-orbit interactions, the mean value of their matrix elements is more than ten times larger than indirect matrix elements and thus are dominant in ϱ〈 V st〉. In conclusion, we confirm that ISC in glyoxal is governed by direct vibronic spin-orbit interactions.

Study of singlet-triplet coupling in glyoxal by level anticrossing spectroscopy. VI. Vibrational density and statistics of matrix elements versus energy

By laser excitation of the rotationless level (J = 0) of ten vibrational levels of the S1 (Au) state (00, 72, 51, 81, 6171, 41, 8172, 21, 8141 and 2172) of supersonic jet cooled glyoxal, we have obtained S1-T1 anticrossing spectra using the homogeneous, high magnetic field (0–8 T) of a Bitter coil. As explained previously, Vst is readily obtained from the width of an anticrossing. As triplet vibrational energy increases from 2776 (00 of S1) to 4636 cm−1 (2172 of S1), the number of anticrossings increases from 38 (00) to 871 (2172). The anticrossing density is related to the vibrational density of T1. The Vst histrograms obtained for each vibrational level are very similar: p(Vst) ∝ V−1−αst with 0.4 ⩽ α ⩽ 0.7. The more significant and surprising result is that <Vst > is independent of vibrational energy, even though the corresponding vibrational overlaps predicted a decrease in <Vst >, of at least two orders of magnitude between 00 and 2172. From Vst statistics we determine ϱ<Vst > and ϱ<V2st > which are the dominant factors for ISC (intersystem crossing). We predict that strong S-T mixing should occur above 6900 ± 500 cm−1.

Study of singlet—triplet coupling in glyoxal by level anticrossing spectroscopy. V. Nature of singlet—triplet interaction

Abstract We observe in glyoxal cooled in a supersonic free jet the fluorescence of individual rotational levels of the S 1 state excited by a cw laser. We use the technique of singlet—triplet magnetic resonance near an anticrossing to measure matrix elements V 31 as a function of rotational quantum numbers N s , N t , K s , K t . The experimental results are compared with theoretical models of singlet—triplet couplings and we show that the spin-vibronic interaction is the dominant singlet—triplet interaction in glyoxal.

Study of singlet-triplet coupling in glyoxal by level anticrossing spectroscopy. IV. Theory of anticrossing position. Application to the measurement of triplet quantum numbers and rotational constants

We have performed anticrossing experiments in high magnetic fields on several rotational and vibrational singlet levels of glyoxal in a supersonic jet. We show that by analysis of these experiments, we can determine rotational quantum numbers, vibrational symmetry and rotational constants of the triplet level most efficiently coupled to the singlet laser-excited ones.

Study of singlet-triplet coupling in glyoxal by level anticrossing spectroscopy. II. Theory of the positions of double resonances near a singlet-triplet anticrossing. Application to the precise measurement of singlet-triplet coupling and of fine and hyperfine structure parameters of the triplet of glyoxal

We set the theory for the position of double resonance signals near an anticrossing point. We use this theory to interpret our experimental results for anticrossings between the (K ≈ 6, J = 13) rotational level of the vibrationless 0° 1Au state of glyoxal and five sample rovibrational triplet levels, leading to very precise (up to a few 10−4 on relative value) measurements of singlet-triplet coupling and fine and hyperfine structure parameters. The zero field singlet-triplet coupling matrix elements measured vary from 11.4±0.14 to 300.0±0.8 MHz. The hyperfine structure constant (82 MHz) is constant to within ±2% for the five triplet levels. The two fine structure parameters to the contrary vary by a factor of roughly two.

Study of singlet-triplet coupling in glyoxal by level anticrossing spectroscopy. III. Theory of widths and intensities of double resonances near a singlet-triplet anticrossing. Application to the measurement of relaxation parameters of glyoxal

We set the theory for the amplitude and widths of double resonance signals near an anticrossing. This theory is used to discuss the possibility of measuring singlet, triplet and coherence relaxation parameters in our experiments on anticrossings between the (K = 6, J = 13) rotational level of vibrationless 0° 1Au state of glyoxal and a sample rovibrational triplet level.

Study of the singlet-triplet coupling in glyoxal trans and cis by level-anticrossing spectroscopy

Anticrossing experiments were performed on both cis and trans isomers of glyoxal. The comparison of the widths and intensities of these signals confirms the predominance of indirect spin-orbit coupling and the assignment of the1 A u−3 A u coupling in glyoxal to the small-molecule weak-coupling limit.

Study of the singlet—triplet coupling in glyoxal by level-anticrossing spectroscopy. I. Experimental techniques and results

Level anticrossing and a new optical-radiofrequency double resonance technique were applied to a study of the singlet—triplet interactions for single rotational levels of the vibrationless 1A u state of glyoxal. The density and spectral distribution of triplet rotational levels virtually coupled to the ( K = 6, J = 13) and ( K = 7, J = 35) singlet states were determined. The values of the singlet—triplet coupling constants V st for some selected level pairs were measured. The assignment to the weak-coupling limit is confirmed.

Electric dipole moment of the A 2Π state of CN as measured by level anticrossing spectroscopy

The dipole moment of the electronically excited A 2Π state of the CN radical has been measured as 0.56±0.03 D by analyzing the electric field dependence of the level anticrossing spectral linewidth. The theory of the Stark effect in this system is developed and it is shown that the broadening depends upon two parameters: the A 2Π dipole moment and the electric dipole transition moment between the A 2Π and B 2Σ+ states. The spectral linewidth is rather insensitive to the value of the transition moment and this quantity is not well determined from the experimental data.