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Surface plasmon polariton (SPP) propagation on a Au thin film has been observed by tip-enhanced Rayleigh scattering. The interference pattern has been observed around the edge of the film. The interference is due to the near-field scattering light at the tip and SPP radiation from the edge of the film. From the interference width, we evaluated the wave number of SPP on the Au film. By changing the wavelength of the incidence light, we have obtained the dispersion relation of the SPP. The experimentally obtained dispersion relation is well corresponding to the calculated one using bulk Au parameters.

Europium (III) (Eu(3+))-doped nanoporous silica spheres were synthesized, and the states of Eu(3+) ions in the silica framework structure were investigated. The ordered nanopores were preserved with the doping at the Eu(3+) molar concentration to Si up to 10 mol%, and the O-Si-O and Si-OH groups in the structures were clearly rearranged with the doping, indicating the interaction of Eu(3+) with the O atoms. The significant morphological changes in the spheres were observed with the doping. The photoluminescence spectral shapes due to the transitions of (5)D(0)-(7)F(1) and (5)D(0)-(7)F(2) were indicative of the presence of the Eu(3+) in an environment of a low symmetry. It was found that the Eu(3+) was located inside the silica framework to electrostatically interact with the environmental O atoms, which would prevent the aggregation among Eu(3+) ions to show the efficient luminescence. Therefore, the interactions between the Eu(3+) ions and silica framework structures in the spheres were successfully clarified.

Europium (III) (Eu 3+ )-containing nanoporous silicas were successfully synthesized by two different loading methods (adsorption or doping), and the states of the Eu 3+ in the structure were investigated. The Eu 3+ -adsorption indicated that the Eu 3+ interacts with hydroxyl groups on the pore surface and H 2 O molecules to enhance the quenching, whereas the Eu 3+ -doping indicated that the Eu 3+ was located inside the structure framework that produced the efficient luminescence. The interaction between the Eu 3+ and silica structure depended on the loading method.

We have studied micro-photoluminescence spectra of self-assembled single GaAs/AlGaAs quantum dots (QDs). Under non-resonant optical excitation, a single GaAs QD exhibits several sharp peaks in the PL spectra whose origins are the recombination of neutral or charged multi-excitonic complexes. In single photon correlation measurements, photons emitted from charged biexcitons and charged excitons show bunching which indicates that photon pairs are generated from the cascade recombination of the charged biexcitons. The result of polarization correlation measurements shows that each photon of the pairs is polarized linearly and orthogonally. These polarization features can be understood by the superposition of elliptically polarized photons affected by the electron–hole exchange interaction in the anisotropic QD.

We have studied micro-photoluminescence spectra of a self-assembled single GaAs quantum dot under 8 K. With strong pulsed excitation, the micro-photoluminescence spectrum shows bright emission lines originated from an exciton, a positively charged exciton, and a biexciton, together with weak lower energy emissions reflecting multi-excitonic structures with more carriers. We have identified the origins of these weak emission lines, and showed the existence of charged biexciton states, through single photon correlation measurements and excitation power dependence of the photoluminescence intensity. In addition, investigating the radiative recombination process of the charged biexciton, we have determined the electron–hole exchange energy in the GaAs quantum dot.

A simple but flexible 2D lattice model is proposed to discuss localization and tunneling of a dressed photon in disordered nanomaterial systems. It is shown that a 1D finite disordered system with site-dependent masses is obtained after the contraction from 2D to 1D. A dressed photon description for a photon-electronic polarization–phonon interacting system is used to examine the spatial distribution of a dressed photon associated with coherent phonons in such a system. The temporal and tunneling behaviors of a dressed photon between two closely separated nanosystems are also investigated numerically. The model proposed is applicable to an arbitrary shape of nanostructure, and photon localization and tunneling inherent in the shape of the nanostructure is expected to be applied to the local manipulation of quantum states of nanostructure in excitation transfer processes, including spin and phonon degrees of freedom.

In self-assembled multilayer arrays of micrometer-sized spheres which include small amount of fluorescent particles, unique six-dot-triangular and seven-dot-hexagonal patterns have been known to appear in the fluorescence microscopic image. Although it has been suggested that these patterns correspond to local domain structures, i.e., face centered cubic (fcc) or hexagonal closed packing (hcp), no convincing evidence has been presented. In this study, we fabricated well-controlled photonic clusters by use of micromanipulation and investigated the relation between the propagation patterns and the domain structures. While the minimum fcc and hcp clusters exhibited the triangular and hexagonal patterns, respectively, it was also found that the propagation patterns are dependent on the size of the clusters.

Four-wave mixing (FWM) technique is used to study the phonon induced dephasing of the excitons in CdTe self-assembled quantum dots. The FWM signals show two different decay structures with fast and slow decay components, indicating a non-Lorentzian line-shape with a zero-phonon line and a broadband from exciton–acoustic phonon interaction in the spectral region. The dephasing of the zero-phonon line and the sideband components both show non-linear characteristics with respect to temperature. The experimental data are reproduced well by a theoretical model taking into account the carrier–acoustic phonon coupling.

The qubits can be entangled when they interact with a common Ohmic reservoir. We analyze how the reservoir-induced entanglement of qubits can be observed as the beat signal in the decay curve of the macroscopic polarization. The origin of this effect is the Lamb phase shift on the qubit array. We quantify the amount of the reservoir-induced entanglement and show how to experimentally evaluate it from the decay curve of the macroscopic polarization. We discuss how the beat signal can be discriminated from the other kinds of beat signals. We also show that our analysis can be used to estimate the reservoir characteristics.

We measured time-resolved photon echo signals by using the heterodyne detection technique on GaAs multiple quantum wells. Oscillation structure with a period of about 0.8 ps is observed when the time interval (delay time) of two pulses which generate the photon echo signal is shorter than 0.4 ps. The oscillating structure disappears when the delay time is longer than 0.6 ps. Temperature and excitation density dependence indicate that the origin of this oscillation is the interaction between a normal exciton and an exciton coupled with a specific acoustic phonon mode which is identified by calculating the Rytov model.

The phase characteristics of transmitted optical pulses in a three-dimensional photonic crystal were investigated in both energy and time domains by using a spectrally-resolved cross-correlation technique. The temporal evolution of femtosecond pulses passing through polystyrene colloidal crystals exhibits a large phase distortion near the stop bands. The dispersion curve estimated from the phase shift shows good correspondence with that calculated from a photonic band calculation. The group velocity significantly slows down near the stop bands. These results are in good agreement with a photonic band theory.

The phonon bottleneck effect is studied in InAs/GaInP quantum dots (QDs). The time-resolved photoluminescence spectra from the lowest ( n =1) and second lowest ( n =2) exciton states in QDs are measured in the temperature range of 5– 200 K . We find that the rise time of the n =1 level is about 500 ps when the excitation energy is in resonance with the n =2 level. This is a long time compared to about 200 ps in non-resonant excitation, and therefore the bottleneck effect exists between the levels n =2 and 1. In order to understand the source of the bottleneck, the temperature dependence of carrier relaxation time between the exciton levels is investigated in the assigned temperature range. With increasing temperature, the relaxation time decreases to 200 ps at 200 K . The data are in good agreement with the theoretical fit of the relaxation probability for multi-phonon processes.

The signals due to six-wave mixing (SWM) processes are observed for two-dimensional excitons and biexcitons. The signal intensity of the SWM process strongly depends on the pulse area of the excitation light. The pulse area is estimated by comparing the intensities of four-wave mixing (FWM) signals in two different directions. The photon echo and the transient-grating signals due to the biexcitonic state of GaSe were observed by SWM. When we change the order of the excitation pulses in our SWM experiments, the excitonic phase relaxation process can be observed in the negative delay-time region.

The photoluminescence from localized excitons in In 0.25 Ga 0.75 N was enhanced up to 6.6 times by approaching a gold nano-particle to nano-meter vicinity. Mapping images of enhanced photoluminescence and topological images were measured simultaneously with a spatial resolution of 100 nm. With an improved measurement system and selection of relatively flat area of the sample, we propose that the segregated metallic In droplet ought to play an important role for the present tip-enhance effect.

The phase characteristics of transmitted optical pulses were investigated in the energy- and the temporal domain using the spectrally resolved cross-correlation technique. The temporal evolution of fs pulses passing through GaAs/AlGaAs quantum wells indicates a long tail due to the coherent emission from the exciton. The phase discontinuity was observed in the time-domain data. The phase of the coherent emission signal is found to differ by 180° from that of the incident light field. Furthermore, we report the pulse propagation effect when the pre-excited coherent exciton exists in the sample. The resultant data shows that the ultrashort optical pulses are strongly affected by the phase difference between the coherent emission and the coherent exciton polarization.

The polarization rotation induced by the light pulse excitation is investigated on GaAs heterostructures. The temporal profile of the rotation angle shows an exponential decay reflecting the spin relaxation of excitons. The spectrally resolved transients exhibit not only the magnitude but the direction of the polarization rotation varies with the detection energy. The spectral features are in quantitative agreement with a calculation, where the saturation, the energy shift and the damping of the spin-polarized exciton resonance are taken into account.

Time-resolved three-pulse photon echoes of the exciton in layered semiconductor GaSe are investigated by using up-conversion technique. The time-resolved echo signal depends on the separation time between the first and second pulses. The shape of the echo signal changes as the separation time increases. The time-resolved signal also depends on the waiting time between the second and third pulses. For a short waiting time, the temporal evolution of the echo signal shows an ideal photon-echo-like (Gaussian-like) shape. On the other hand, for longer waiting times, the temporal shape of the echo signal changes dramatically and has an extra peak at the arrival time of the third pulse. This behavior can be explained by spectral diffusion in the three-pulse photon echo process.

The coherent emission in the direction of the reflection has been investigated under the Brewster angle of incidence by using phase-locked pulse pairs to excite resonantly the excitons in the anisotropic crystal GaSe. The interferogram of the reflected pulse has a long tail corresponding to the free induction decay signal. We also observed the phase difference between the coherent emission from the Γ4 and Γ6 excitonic polarizations in the direction of the reflection.

Excitation intensity dependence of photoluminescence signals is observed in Cd 0.9 Mn 0.1 Te at 2 K with varying exciton density from 10 14 to 10 19 cm −3 . For intermediate density regime ( 16 cm −3 ) , the transient spectral shift reflecting the magnetic polaron formation is found to decrease with an increase in density. For high-density regime (>10 17 cm −3 ) , the polaron shift disappears, and the density-dependent red shift caused by the band-gap renormalization is observed. The experimental findings demonstrate that the magnetic polaron is unstable at high-density condition.

Magneto-optical studies on self-organized quantum dots (QDs) of Cd 1− x Mn x Te were reported. Cd 1− x Mn x Te QDs with Mn composition less than 10% were grown successfully on the ZnTe(1 0 0) surface by atomic layer epitaxy. A typical dot size of 20 nm in diameter and 2 nm in height and density of the order of 10 11 cm −2 were confirmed by atomic force microscope (AFM) measurement. In photoluminescence (PL) measurements on capped QDs, the excitonic emission from Cd 1− x Mn x Te dots was observed but the spectra were composed of two lines with a separation of 20–26 meV at low temperatures. In the dependence on the temperature, the excitation intensity and the magnetic field, the PL line at the lower-energy side exhibited peculiar behaviors, compared to that in the higher-energy side — rapid quenching with an increase of temperature up to 20 K, much smaller Zeeman shift under magnetic fields, and the saturation of the circular polarization at low magnetic fields. These features of the lower-energy line were discussed in relation to the excitonic magnetic polaron in QDs. Preliminary results of time-resolved PL and spatial-resolved PL using the far-field microscope are also shown.

The spectral diffusion across the exciton line in GaSe is observed in two types of four-wave-mixing experiments. In the stimulated photon echo experiment, the signal shows a non-exponential decay as the waiting time between the second and third pulses increases. This behavior begins clearly from a few 10 ps of the waiting time. The deformation of the signal profile depending on the delay time of first two pulses is also observed in the transient grating-type signal. These results are in good agreement with the result of a theoretical calculation based on a stochastic model.

We report on micro photoluminescence (μ-PL) experiments in CdTe and CdMnTe quantum dots (QDs). PL spectra of the CdTe QDs indicate an ensemble of discrete narrow lines, each of which arises from a single dot emission. High emission efficiency of the present QDs allows the time resolving of the μ-PL signal. Dependence of the PL decay time on the QD size shows the evidence for the quantum size effect of the radiative recombination process. For CdMnTe QDs, it is found that the discrete spectral feature disappears in the μ-PL spectrum, reflecting the fast relaxation kinetics of excitons in the manganese doped QDs.

We have studied the effect of oxygen incorporation into AlGaInP on carrier recombination in GaInP/AlGaInP double heterostructures (DH) grown by MBE using a solid phosphorus valved cell. It was found that photoluminescence efficiency and interfacial recombination velocity of the DH were determined by residual oxygen concentration in the AlGaInP layers. The non-radiative recombination rate in AlGaInP was proportional to the oxygen concentration. We achieved AlGaInP with oxygen concentrations below 4 × 10 16 cm -3 (the detection limit of the SIMS measurement), nonetheless decay of the carriers in the DH was still governed by interfacial recombination. There was a discrepancy in interfacial recombination velocity as a function of oxygen concentration between samples previously grown by MOCVD and our samples currently grown by MBE.

We demonstrate the decoherence control of excitons on a layered compound semiconductor GaSe by using successive femtosecond pulses. The intermediate pulses act as π pulses, which reverse the time evolution of non-Markovian dynamics. By changing the incident timing of the π pulses, we determine the effective pulse interval condition for suppressing the decoherence of excitons by optical pulse irradiation.

We performed a three-pulse six-wave mixing (SWM) measurement on a gallium arsenide (GaAs) multiple quantum well and observed the time-resolved SWM signal using the heterodyne detection technique. The second pulse acts as a π pulse that reverses the time evolution of the non-Markovian dynamics. By changing the pulse interval conditions, we confirmed the suppression of exciton decoherence by π pulse irradiation (bang–bang control).

Single-photon emitters and detectors are key devices for realizing secure communications by single-photon-based cryptography and single-photon-based quantum computing. For the establishment of these technologies, we need to understand the electronic structures of single and multiple excitons. Therefore, we have studied their emissions via the micro-photoluminescence (μ-PL) spectra of strain-free GaAs/AlGaAs single quantum dots, using excitation power dependence, time-resolved, and single-photon correlation measurements. Under pulsed excitation, we observed clear photon antibunching and bunching by auto- and cross-correlation measurements. From these results, we found that the emission peaks observed in the μ-PL spectra originated from exciton, charged exciton, and biexciton states.

By using a tightly focused laser beam, we have studied light propagation in two-dimensional photonic crystals consisting of closed-packed hexagonal arrays of polystyrene particles with diameter of 1∼5 μm. The light propagation is found to depend strongly on the focal point positioning, the incident beam polarization and the interaction between particles and glass substrates.

Oscillation behavior with periods of 0.56 and 0.88 ps has been observed by time-integrated four-wave-mixing measurements in GaAs multiple quantum wells. Temperature and excitation density dependence shows that the oscillations are caused by the quantum kinetic interactions between excitons and phonons. The energies of the phonons correspond exactly to those of the folded acoustic phonons calculated by the Rytov model.

We report the demonstration of decoherence control of excitons on a layered compound semiconductor GaSe by using successive three femtosecond pulses, i.e., the six-wave mixing configuration. The second pulse acts as a π pulse which reverses the time evolution of non-Markovian dynamics. By changing the pulse interval conditions, we confirmed for the first time the suppression of exciton decoherence by π pulse irradiation.

We have studied time-resolved photoluminescence (PL) of type-II GaP/AlP/GaP quantum wells with different well widths and acquired detailed information concerning the mechanisms of the radiative recombination. At low temperatures, the PL spectra consist mainly of a no-phonon line. The decay of the no-phonon line was slow and nonexponential. The decay curves could be fitted to a model which assumes that the radiative recombination occurs as the result of both incoherent and coherent Γ-X scattering due to disorder at the interface. The fit revealed that the dominant Γ-X mixing mechanism was random scattering caused by fluctuations in the potential at the interface. Based on simple perturbation theory, the observed increase in the radiative decay rate with decreasing well width was explained by the increase of overlap of the electron envelope wave functions as well as the decrease of Γ-X energy separation. The model suggests that the magnitude of the potential responsible for the Γ-X mixing is considerably greater than those observed in the type II GaAs AlAs heterostructures.

We present results on the acoustical phonon dephasing for a single GaAs quantum dot. Micro photoluminescence ( μ -PL) is used to observe the temperature dependence of the exciton line in self-assembled GaAs semiconductor single quantum dots (QDs). The observation of the PL with temperature shows that there are two different states within the PL emission, namely the zero-phonon line and the phonon sidebands. When the temperature increases, the effect of the sidebands become clearer and show substantial broadening. In the present experiments, PL and μ -PL spectra have been measured at temperatures of 5 K≤ T ≤90 K for GaAs self-assembled QD samples.

We present firm evidence for biexciton formation in ZnSe ZnS x Se 1−x (x = 0.18) multiple quantum wells through transient four-wave-mixing technique. The signal shows a new emission at 4.6 meV below the lowest exciton line, arising from two-photon resonant four-wave-mixing process involving exciton and biexciton levels. Results provide a dephasing time, for the first time, as well as a binding energy for the biexciton.

Changes of the dimensionality and Tc through iodine intercalation and oxidation have been studied in Bi2Sr2CaCu2O8+δ single crystals. Both intercalation and oxidation change the dimensionality of the physical properties from pseudo-two-dimensional to three-dimensional and decrease Tc. These effects are explained by the multilayer model, where a high-Tc cuprate is regarded as an alternating stack of CuO2 layers (superconducting layers) and block layers (normal layers), taking into account the proximity effect. The Tc-suppression by Cu-site substitution has also been studied for iodine-intercalated and pristine Bi2Sr2Ca(Cu1−zCoz)2O8+δ polycrystals with different δ-values.

The polarization dependence of 3-pulse four wave mixing (FWM) at the exciton resonance has been studied in GaSe. A quantum beat modulation can be observed in 3-pulse FWM signals. The polarization dependence of the quantum beat has also been studied. The quantum beat and the polarization interference can be experimentally distinguished by the time-integrated 3-pulse FWM.

The polarization dependence of the stimulated photon echo due to excitons has been studied in GaSe. A quantum beat modulation can be observed in the stimulated photon echo signals. The polarization dependence of the quantum beat is also studied. The quantum beat and the polarization interference are experimentally distinguished by the time-integrated stimulated photon echo.

We confirm the existence of a biexciton in ZnSe-based quantum wells using transient four-wave-mixing spectroscopy. It is found that a new spectral line appears below the heavy-hole-related exciton resonance, corresponding to the exciton-biexciton transition. Through the analysis, we have determined the dephasing time of the biexciton, as well as the biexciton binding energy.

Two kinds of novel spectroscopic methods of two-photon resonant second-harmonic generation (SHG) and Brewster-angle reflection were investigated for exploring the electronic structure in strained ZnSe/GaAs thin films. A line splitting into two, which is caused by in-plane tensile strain, in the excitation spectrum of the normally forbidden SHG signal was observed in resonance with the 2P exciton, whereas three lines in resonance were observed with the 1S exciton polaritons. In the Brewster-angle reflection spectrum, on the other hand, only one broad line with the width presumably broadened inhomogeneously, was observed in the 1S exciton region. Next, Brewster-angle reflection spectroscopy was also investigated in a few samples of ZnSe/ZnS quantum wells. For those, two split lines were distinctly observed in the 1S exciton region, as it should be. Comparison between those spectral lines and the one-photon excitation spectrum of luminescence indicates that they are consistent. Thus, it is concluded that both methods should serve as a simple and novel tool for characterizing II–VI thin films.

We have studied the electronic structure of strained-layer ZnSe/ZnS superlattices by using two kinds of two-photon spectroscopy: two-photon absorption spectroscopy and resonant second-harmonic generation. The exciton binding energy is found to exhibit a blue shift as compared to the bulk value due to the exciton confinement effect. Based on the observed subband energies, we derive a conduction-band offset of ∼ 70 meV and a valence-band offset of ∼ 800 meV.

We report temperature dependence of the electronic Raman scattering in high-Tc copper oxide Bi2Sr2CaCu2O2+δ. The variation of the electronic Raman spectrum below Tc reflects not only the superconducting gap, hut also the condensation of thermally excited quasiparticles to the superconductinggroundstate. The former exhibits a significant variation only just below Tc, which is quite different from the temperature dependence of the gap predicted from weak-coupling BCS theory. In contrast, the superconducting condensation occurs almost over the whole temperature region of the superconducting phase. Further, we report the electronic Raman scattering in oxygen-deficient Bi2Sr2CaCu2O2+δ. Both tetragonal A1g and B1g scatterings exhibit a continuum spectrum with a broad peak at low temperatures. As compared to the spectrum of Tc~90K Bi2Sr2CaCu2O2 + δ, the redistribution of the continuum is incomplete, suggesting the existence of normal-state carriers. Remarkably, the A1g peak energy does not depend significantly on oxygen content, which is basically inconsistent with behaviour of the gap expected from BCS theory. We discuss the oxygenconcentration dependence of the electronic Raman scattering.

Dynamics of quasi-two-dimensional excitons in layered compound GaSe was investigated in the femtosecond regime through time-resolved degenerate four-wave-mixing: stimulated photon-echo and transient grating methods. The mechanisms of phase, population and orientational relaxations of the excitons were considered on the basis of their temperature dependences.

Tunneling spectroscopic measurement was carried out in the superconducting phase of Bi 2 Sr 2 CaCu 2 O 8 with use of a low temperature scanning tunneling microscope. Both the cleaved Bi-O surface and the lateral surface of a single crystal were investigated. The tunneling conductance shows an explicit superconducting gap structure at both surfaces. For the lateral surface the conductance curve is independent of the tip distance from the sample surface and gives directly the electronic density of states in the superconducting phase. The obtained gap structure is in good agreement with the BCS prediction, although it seems that the gap is slightly anisotropic. The obtained gap-ratio 2Δ/k B T c =6.1 indicates the strong-coupling nature of this superconductor. For the Bi-O surface, on the other hand, the normalized differential conductance increases with increasing the tip distance, especially at the outside of the superconducting gap as reported by Hasegawa et al . Such a dependence on the tip distance is attributed to series barriers of Bi-O, Sr-O layers and vacuum for the tunneling between the Cu-O layer and the tip metal.

Epitaxial Cd1-xMnxTe (x ≅ 1%) layers have been grown on a CdTe buffer layer on a GaAs (100) substrate, using molecular beam epitaxy (MBE). A comparison of the superimposed photoluminescence (PL) spectra in Cd1-xMnxTe and CdTe, observed by adjusting the thickness of the Cd1-xMnxTe layer, has made it easier to assign the excitonic origins of the Cd1-xMnxTe. A spectral-decomposition analysis has revealed that the free exciton emission is dominant in Cd1-xMnxTe grown at 350°C. This is in contrast to previous work where excitons bound to neutral acceptors are dominant in Cd1-xMnxTe at concentrations x less than 5%. A temporal energy shift of exciton emission is also observed in time-resolved measurements with and without an external magnetic field. The results are discussed in relation to magnetic polaron formation and the exciton localization effect arising from compositional inhomogeneity.

Two-photon absorption spectroscopy is used as a novel tool to study residual strain in ZnSe epitaxial layers grown on GaAs substrates. Taking advantage of the polarization selection rules, we find that ZnSe layers thicker than 2 μm suffer in-plane tensile strain of the order of 10 -4 , while the epilayer thinner than 1 μm undergoes biaxial compression. The measured thickness dependence of misfit strains is compared to that obtained from X-ray diffraction.

Strong signals of both hyper-Raman scattering by optic phonons and hyper-Rayleigh scattering (SHG), the latter of which is forbidden by the usual selection rules, were found to emerge in two-photon resonance with excitation energy of the 2P excitons in a thin film sample of ZnSe on GaAs substrate. Both excitation spectra, which are found to be basically similar to each other, indicate an energy-splitting of the 2P excitons. As a result, it is found that the sample of 5 μm thickness suffer in-plane strains due to lattice misfit between ZnSe and GaAs, an order of which has been estimated thereby as e ≈ 5 × 10-4. A similar resonant hyper-Raman scattering was also found in a bulk sample of CdS, and is utilized for gaining into insight the microscopic origin of the phenomenon. On the basis of the results, it is discussed that the present phenomena, found for the first time in solids, would serve as novel spectroscopic methods for characterizing sample quality of II–VI compounds recently developed by state-of-the-art methods, through the strain-induced structure of the 2P excitons free from polariton effects.

Temporal development of polarized luminescence signals in GaSe was investigated in a magnetic field. Reflecting the quantum beat effect between the Zeeman split exciton states, it was found that oscillatory features appear on the degree of circular or linear polarization of the luminescence. Different exciton g factors were observed in longitudinal and transverse magnetic fields, showing the magneto-optical anisotropy of the present sample.

We demonstrate that the 2P excitonic wave function in ZnSe can be manipulated coherently by a phase-locked pulse pair under two-photon excitation. The symmetry of the state is directly observed by changing the polarization of the phase-locked pulse pair.

Angle-resolved inverse photoemission spectroscopy was performed on a Bi 2 Sr 2 CaCu 2 O 8 single crystal to study the electronic structure in the vicinity of the Fermi level. Inverse photoemission intensity shows two maxima at about 0.21 ΓX and 0.6ΓX from the Γ point along the ΓX direction, suggesting that there are two bands crossing the Fermi level. The present experimental result was compared with angle-resolved photoemission results and band structure calculations.

The anisotropic resistivity in the a − b plane and Hall coefficient have been measured in a single-crystal Bi 2 Sr 2 CaCU 2 O y (BSCCO ) and their temperature dependences have been analyzed by a two-band model involving holes and electrons. It is confirmed that the calculated values of the resistivities and Hall coefficient reproduce well the data and the carrier concentrations, mobilities and mean-free-paths obtained from the model are reasonable values in physics. It is found that the hole concentration is smaller than the electron one, but the hole mobility is larger than the electron one. The transport properties of BSCCO are discussed in terms of two types of the hole and electron carrier.

The cw and time-resolved photoluminescence spectra of a [0 0 1]-(GaAs) 10 /(AlAs) 10 short-period superlattice are studied under [0 0 1] uniaxial stress. The superlattice is of the type-II and the lowest excited state is the “X z ” exciton. The stress dependence of the exciton decay time is found to be explained in terms of a thermally activated transition of excitons to the l'state. Results for the stress-induced change in the X-Γ mixing are also presented.