This is a supplementary material to our Comment arXiv:0909.4265 on M. Stern, V. Garmider, E. Segre, M. Rappaport, V. Umansky, Y. Levinson, and I. Bar-Joseph, Phys. Rev. Lett. 101, 257402 (2008).
We study the photoluminescence from a near-surface quantum well in the regime of ambipolar tunneling to the surface states. Under steady-state excitation an electric field develops self-consistently due to the condition of equal tunneling currents for electrons and holes. The field induces a Stark shift of the photoluminescence signal which compares well with experimental data from near-surface GaAs/AlGaAs single quantum wells.
The formation and possible decay processes of neutral and charged excitonic complexes in electronic integral and fractional quantum Hall systems are discussed. The excitonic complexes are bound states of a small number of the relevant negatively and positively charged quasiparticles (e.g., conduction electrons and valence holes, reversed-spin electrons and spin holes, Laughlin quasielectrons and quasiholes, composite Fermions) that can occur in a 2D electron in the presence of a strong magnetic field. Examples of such bound states are interband neutral and charged excitons, fractionally charge…
Opto-spintronics is an emerging field where ultra-thin magnetic-semiconductors having high spin-valley coupling play an important role. Here, we demonstrate substitutional vanadium (V) doping in MoS$_2$ lattice in different extent, leading to the coexistence of photoluminescence (PL), valleypolarization (~32%), and valley splitting (~28 meV shift in PL with helicity $σ^+$ and $σ^-$ of light excitation). A large V doping causes semiconductor to metal transition in MoS$_2$ but with medium level causing the existence of photoluminescence with high spin polarization. The ambipolar nature of medium…
We present a self-consistent approach to describe ambipolar tunneling in asymmetrical double quantum wells under steady-state excitation and extend the results to the case of tunneling from a near-surface quantum well to surface states. The results of the model compare very well with the behavior observed in photoluminescence experiments in $InGaAs/InP$ asymmetric double quantum wells and in near-surface $AlGaAs/GaAs$ single quantum wells.
Despite having outstanding electrical properties, graphene is unsuitable for optical devices because of its zero band gap. Here, we report two-dimensional excitonic photoluminescence (PL) from graphene grown on Cu(111) surface, which shows an unexpected remarkably sharp and strong emission near 3.16 eV (full-width at half-maximum $\leq$ 3meV) and multiple emissions around 3.18 eV. As temperature increases, these emissions blue-shift, showing the characteristic negative thermal coefficient of graphene. Observed PLs originate from significantly suppressed dispersion of excited electrons in graph…
We propose an unconventional scheme of photoluminescence in a semiconductor thin film, where the nonlocal correlation between an excitonic wave and a light wave prominently enhances the exciton-light coupling beyond the long-wavelength approximation (the so-called excitonic superradiance regime). On the basis of the developed method extending input-output theory, we elucidate atypical photoluminescence effects due to the strong wave-wave correlation. In particular, the up-converted photoluminescence based on the coherent superposition of excitons is found to be highly efficient, i.e., it can b…
The energy and photoluminescence (PL) spectra of a two-dimensional electron gas (2DEG) interacting with a valence-band hole are studied in the high-magnetic-field limit as a function of the filling factor nu and the separation $d$ between the electron and hole layers. For d smaller than the magnetic length lambda, the hole binds one or more electrons to form neutral (X) or charged (X-) excitons, and PL probes the lifetime and binding energies of these complexes rather than the original correlations of the 2DEG. The low-lying states can be understood in terms of Laughlin-type correlations among…
We show that new low-energy photoluminescence (PL) bands can be created in semiconducting single-walled carbon nanotubes by intense pulsed excitation. The new bands are attributed to PL from different nominally dark excitons that are "brightened" due to defect-induced mixing of states with different parity and/or spin. Time-resolved PL studies on single nanotubes reveal a significant reduction of the bright exciton lifetime upon brightening of the dark excitons. The lowest energy dark state has longer lifetimes and is not in thermal equilibrium with the bright state.
We present optical study of MAPbBr3 single crystals grown from solution by inverse temperature crystallization method. Photoluminescence temperature dependence of narrow and isolated exciton resonance showed encouragingly low inhomogeneous broadening Γ ~ 0.5 meV, which is comparable to those of MBE-grown III-V heterostructures, indicating high quality of the solution-grown perovskite. Excitonic origin of the resonance was proved by its superlinear pump intensity dependence in contrast to the linear behavior of the defect-assisted recombination bands. In addition, for the first time phonon repl…
The optical properties of monolayer transition metal dichalcogenides are dominated by tightly-bound excitons. They form at distinct valleys in reciprocal space, and can interact via the valley-exchange coupling, modifying their dispersion considerably. Here, we predict that angle-resolved photoluminescence can be used to probe the changes of the excitonic dispersion. The exchange-coupling leads to a unique angle dependence of the emission intensity for both circularly and linearly-polarised light. We show that these emission characteristics can be strongly tuned by an external magnetic field d…
Strain engineering is a powerful tool for tuning physical properties of 2D materials, including monolayer transition metal dichalcogenides (TMD) -- direct bandgap semiconductors with strong excitonic response. Here, we demonstrate an approach for local characterization of strain-induced modification of excitonic photoluminescence in TMD-based materials. We reversibly stress a monolayer of MoSe$_2$ with an AFM tip and perform spatio-spectral mapping of the excitonic photoluminescence in the vicinity of the indentation point. To fully reproduce the experimental data, we introduce the linear depe…
We study the theory of intrinsic photoluminescence of two-dimensional electron systems in the vicinity of the $ν=1$ quantum Hall state. We focus predominantly on the recombination of a band of initial ``excitonic states'' that are the low-lying energy states of our model at $ν=1$. It is shown that the recombination of excitonic states can account for recent observations of the polarization-resolved spectra of a high-mobility GaAs quantum well. The asymmetric broadening of the spectral line in the $σ_-$ polarization is explained to be the result of the ``shake-up'' of spin-waves upon radiative …
Recently lead halide nanocrystals (quantum dots) have been reported with potential for photovoltaic and optoelectronic applications due to their excellent luminescent properties. Herein excitonic photoluminescence (PL) excited by two-photon absorption in perovskite CsPbBr3 quantum dots (QDs) have been studied across a broad temperature range from 80K to 380K. Two-photon absorption has been investigated with absorption coefficient up to 0.085 cm/GW at room temperature. Moreover, the photoluminescence excited by two-photon absorption shows a linear blue-shift (0.25meV/K) below temperature of ~22…
The remarkably strong Coulomb interaction in atomically thin transition metal dichalcogenides (TMDs) results in an extraordinarily rich many-particle physics including the formation of tightly bound excitons. Besides optically accessible bright excitonic states, these materials also exhibit a variety of dark excitons. Since they can even lie below the bright states, they have a strong influence on the exciton dynamics, lifetimes, and photoluminescence. While very recently, the presence of dark excitonic states has been experimentally demonstrated, the origin of these states, their formation, a…
We report a photoluminescence observation of robust excitonic polarons due to strong coupling of exciton and longitudinal optical (LO) phonon as well as Fano-type interference in high quality ZnO crystal. At low enough temperatures, the strong coupling of excitons and LO phonons leads to not only traditional Stokes lines (SLs) but also up to second-order anti-Stokes lines (ASLs) besides the zero-phonon line (ZPL). The SLs and ASLs are found to be not mirror symmetric with respect to the ZPL, strongly suggesting that they are from different coupling states of exciton and phonons. It is more int…
The effect of an external electric field F on the excitonic photoluminescence (PL) spectra of a symmetric coupled double quantum well (DQW) is investigated both theoretically and experimentally. We show that the variational method in a two-particle electron-hole wave function approximation gives a good agreement with measurements of PL on a narrow DQW in a wide interval of F including flat-band regime. The experimental data are presented for an MBE-grown DQW consisting of two 5 nm wide GaAs wells, separated by a 4 monolayers (MLs) wide pure AlAs central barrier, and sandwiched between Ga_{0.7}…
We present optical spectroscopy (photoluminescence and reflectance) studies of thin layers of the transition metal dichalcogenide WSe2, with thickness ranging from mono- to tetra-layer and in the bulk limit. The investigated spectra show the evolution of excitonic resonances as a function of layer thickness, due to changes in the band structure and, importantly, due to modifications of the strength of Coulomb interaction as well. The observed temperature-activated energy shift and broadening of the fundamental direct exciton are well accounted for by standard formalisms used for conventional s…
We study the photoluminescence dynamics of ultra-cold indirect excitons optically created in a double quantum well heterostructure. Above a threshold laser excitation, our experiments reveal the apparition of the so-called inner photoluminescence ring. It is characterized by a ring shaped photoluminescence which suddenly collapses once the laser excitation is terminated. We show that the spectrally resolved dynamics is in agreement with an excitonic origin for the inner-ring which is formed due to a local heating of indirect excitons by the laser excitation. To confirm this interpretation and …
Taking into account the tetrahedral shape of a quantum dot quantum well (QDQW) when describing excitonic states, phonon modes and the exciton-phonon interaction in the structure, we obtain within a non-adiabatic approach a quantitative interpretation of the photoluminescence (PL) spectrum of a single CdS/HgS/CdS QDQW. We find that the exciton ground state in a tetrahedral QDQW is bright, in contrast to the dark ground state for a spherical QDQW.
Excitonic effects play a particularly important role in the optoelectronic behavior of two-dimensional semiconductors. To facilitate the interpretation of experimental photoabsorption and photoluminescence spectra we provide (i) statistically exact diffusion quantum Monte Carlo binding-energy data for a Mott-Wannier model of (donor/acceptor-bound) excitons, trions, and biexcitons in two-dimensional semiconductors in which charges interact via the Keldysh potential, (ii) contact pair-distribution functions to allow a perturbative description of contact interactions between charge carriers, and …
We have closely examined the emission spectrum at the heavy-hole exciton resonance in a high-quality GaAs multi-quantum well (MQW) sample using picosecond excitation-correlation photoluminescence (ECPL) spectroscopy. Dynamics of the ECPL signal at low and high energy sides of the excitonic photoluminescence (PL) peak shows complementary behavior. The ECPL signal is positive (negative) below (above) the PL peak and it changes sign within a narrow band of energy lying between excitonic absorption and emission peaks. The energy at which this sign change takes place is interpreted as the excitonic…
The pumping intensity (I) dependence of the photoluminescence (PL) spectra of perfectly laterally two-dimensionally ordered SiGe quantum dots on Si(001) substrates was studied. The PL results from recombinations of holes localized in the SiGe quantum dots and electrons localized due to the strain field in the surrounding Si matrix. The analysis of the spectra revealed several distinct bands, attributed to phonon-assisted recombination and no-phonon recombination of the excitonic ground state and of the excited excitonic states, which all exhibit a linear I dependence of the PL intensity. At ap…
We present a comprehensive photoluminescence study of exchange interaction in self-assembled CdTe/ZnTe quantum dots. We exploit the presence of multiple charge states in the photoluminescence spectra of single quantum dots to analyze simultaneously fine structure of different excitonic transitions, including recombination of neutral exciton/biexciton, doubly charged negative exciton and negatively charged biexciton. We demonstrate that the fine structure results from electron-hole exchange interaction and that spin Hamiltonians with effective exchange constants $δ_i$ can provide a good descrip…
The formation and various possible decay processes of neutral and charged excitonic complexes in electronic integral and fractional quantum Hall systems are discussed. The excitonic complexes are bound states of a small number of the relevant negatively and positively charged quasiparticles (e.g., conduction electrons and valence holes, reversed-spin electrons and spin holes, Laughlin quasielectrons and quasiholes, composite fermions) that occur in an electron system under specific conditions (e.g., electron density, well width, electric and magnetic fields, or hydrostatic pressure). The examp…
Taking into account the tetrahedral shape of a quantum dot quantum well (QDQW) when describing excitonic states, phonon modes and the exciton-phonon interaction in the structure, we obtain within a non-adiabatic approach a quantitative interpretation of the photoluminescence spectrum of a single CdS/HgS/CdS QDQW. We find that the exciton ground state in a tetrahedral QDQW is bright, in contrast to the dark ground state for a spherical QDQW. The position of the phonon peaks in the photoluminescence spectrum is attributed to interface optical phonons. We also show that the experimental value of …
We report on a magneto-photoluminescence study of isotopically pure 70Ge/Si self-assembled type-II quantum dots. Oscillatory behaviors attributed to the Aharonov-Bohm effect are simultaneously observed for the emission energy and intensity of excitons subject to an increasing magnetic field. When the magnetic flux penetrates through the ring-like trajectory of an electron moving around each quantum dot, the ground state of an exciton experiences a change in its angular momentum. Our results provide the experimental evidence for the phase coherence of a localized electron wave function in group…
Characteristics of GaAs/In$_{x}$Ga$_{1-x}$As/GaAs heterostructures with a single quantum well, which were obtained at various growth parameters, are evaluated according to the results of measurements of low-temperature photoluminescence spectra and their corresponding theoretical analysis.
We report on the observation of spin dependent optically dressed states and optical Stark effect on an individual Mn spin in a semiconductor quantum dot. The vacuum-to-exciton or the exciton-to-biexciton transitions in a Mn-doped quantum dot are optically dressed by a strong laser field and the resulting spectral signature is measured in photoluminescence. We demonstrate that the energy of any spin state of a Mn atom can be independently tuned using the optical Stark effect induced by a control laser. High resolution spectroscopy reveals a power, polarization and detuning dependent Autler-Town…
In this work we study theoretically and experimentally the multi-particle structure of the so-called type-II quantum dots with spatially separated electrons and holes. Our calculations based on customarily developed full configuration interaction approach reveal that exciton complexes containing holes interacting with two or more electrons exhibit fairly large antibinding energies. This effect is found to be the hallmark of the type-II confinement. In addition, an approximate self-consistent solution of the multi-exciton problem allows us to explain two pronounced phenomena: the blue-shift of …
The energy spectrum of a two-dimensional electron gas (2DEG) interacting with a valence-band hole is studied in the high magnetic field limit as a function of the filling factor nu and the separation d between the electron and hole layers. For d smaller than the magnetic length lambda, the hole binds one or more electrons to form neutral (X) or charged (X-) excitons. The low-lying states can be understood in terms of Laughlin-like correlations among the constituent charged fermions (electrons and X-). For d comparable to lambda, the electron-hole interaction is not strong enough to bind a full…
The exciton states in strained (In,Ga)As nanorings embedded in a GaAs matrix are computed. The strain distribution is extracted from the continuum mechanical model, and the exact diagonalization approach is employed to compute the exciton states. Weak oscillations of the ground exciton state energy with the magnetic field normal to the ring are an expression of the excitonic Aharonov-Bohm effect. Those oscillations arise from anticrossings between the ground and the second exciton state and can be enhanced by increasing the ring width. Simultaneously, the oscillator strength for exciton recomb…
If the Zeeman energy is small, the lowest energy excitations of a two dimensional electron gas at filling factor nu=1 are spin waves (spin flip excitations). At nu slightly larger (smaller) than unity, reversed spin electrons (spin holes) can form bound states with K spin waves that are known as skyrmions, S_K^- (antiskyrmions, S_K^+). It is suggested in this work that a valence hole can also bind K spin waves to form an excitonic complex X_K^+, analogous to the S_K^+. One spin hole of the S_K^+ is simply replaced by the valence hole. At nu<=1, a small number of S_K^+'s are present before intr…
We present a comparative study of two self-assembled quantum dot (QD) systems based on II-VI compounds: CdTe/ZnTe and CdSe/ZnSe. Using magneto-optical techniques we investigated a large population of individual QDs. The systematic photoluminescence studies of emission lines related to the recombination of neutral exciton X, biexciton XX, and singly charged excitons (X$^+$, X$^-$) allowed us to determine average parameters describing CdTe QDs (CdSe QDs): X-XX transition energy difference 12 meV (24 meV); fine-structure splitting $δ_{1}=$0.14 meV ($δ_{1}=$0.47 meV); $g$-factor $g=$2.12 ($g=$1.71…
The separation dependence of the interaction between two resonant groups of CdSe/ZnS nanocrystallite quantum dots is studied at room temperature. A near-field scanning optical microscope is used to bring a group of mono-disperse ~6.5 nm diameter nanocrystallite quantum dots which are attached to the microscope probe, into close proximity of `~8.5 nm diameter group of nanocrystallite quantum dots which are deposited on a solid immersion lens. Information extracted from photoluminescence, photoluminescence excitation and absorption curves as well as numerical calculations of the energy levels, s…
We report on stacked multiple quantum dots (QDs) formed inside inverted pyramidal recesses, which allow for the precise positioning of the QDs themselves. Specifically we fabricated double QDs with varying inter-dot distance and ensembles with more than two nominally highly symmetric QDs. For each, the effect of the interaction between QDs is studied by characterizing a large number of QDs through photoluminescence spectroscopy. A clear red-shift of the emission energy is observed together with a change in the orientation of its polarization, suggesting an increasing interaction between the QD…
We report on molecular beam epitaxy growth of symmetric InAs/InP quantum dots (QDs) emitting at telecom C-band (1.55 $μ$m) with ultra-small excitonic fine-structure splitting of ~2 $μ$eV. The QDs are grown on distributed Bragg reflector and systematically characterized by micro-photoluminescence ($μ$-PL) measurements. One order of magnitude of QD PL intensity enhancement is observed in comparison with as-grown samples. Combination of power-dependent and polarization-resolved measurements reveal background-free exciton, biexciton and dark exciton emission with resolution-limited linewidth below…
The structure of the ground state exciton of Cd(Se,Te) quantum dots embedded in ZnTe matrix is studied experimentally using photoluminescence spectroscopy and theoretically using ${\bf k}\cdot{\bf p}$ and configuration interaction methods. The experiments reveal a considerable reduction of fine-structure splitting energy of the exciton with increase of Se content in the dots. That effect is interpreted by theoretical calculations to originate due to the transition from spatially direct (type-I) to indirect (type-II) transition between electrons and holes in the dot induced by increase of Se. T…
We present experimental and theoretical study of single semiconductor quantum dots excited by two non-degenerate, resonantly tuned variably polarized lasers. The first laser is tuned to excitonic resonances. Depending on its polarization it photogenerates a coherent single exciton state. The second laser is tuned to biexciton resonances. By scanning the energy of the second laser for various polarizations of the two lasers, while monitoring the emission from the biexciton and exciton spectral lines, we map the biexciton photoluminescence excitation spectra. The resonances rich spectra of the s…
We have used magneto-photoluminescence measurements to establish that InP/GaAs quantum dots have a type-II (staggered) band alignment. The average excitonic Bohr radius and the binding energy are estimated to be 15nm and 1.5 meV respectively. When compared to bulk InP, the excitonic binding is weaker due to the repulsive (type-II) potential at the hetero-interface. The measurements are extended to over almost six orders of magnitude of laser excitation powers and to magnetic fields of up to 50 tesla. It is shown that the excitation power can be used to tune the average hole occupancy of the qu…
Photoluminescence from bulk HfS$_2$ grown by the chemical vapor transport method is reported. A series of emission lines is apparent at low temperature in the energy range of 1.4 - 1.5 eV. Two groups of the observed excitonic transitions followed by their replicas involving acoustic and optical phonons are distinguished using classical intensity correlation analysis. The emission is attributed to the recombination of excitons bound to iodine (I$_2$) molecules intercalated between layers of HfS$_2$. The I$_2$ molecules are introduced to the crystal during the growth as halogen transport agents …
The monolayer transition metal dichalcogenides are an emergent semiconductor platform exhibiting rich excitonic physics with coupled spin-valley degree of freedom and optical addressability. Here, we report a new series of low energy excitonic emission lines in the photoluminescence spectrum of ultraclean monolayer WSe2. These excitonic satellites are composed of three major peaks with energy separations matching known phonons, and appear only with electron doping. They possess homogenous spatial and spectral distribution, strong power saturation, and anomalously long population (> 6 $μ$s) and…
Rydberg excitons are, with their ultrastrong mutual interactions, giant optical nonlinearities, and very high sensitivity to external fields, promising for applications in quantum sensing and nonlinear optics at the single-photon level. To design quantum applications it is necessary to know how Rydberg excitons and other excited states relax to lower-lying exciton states. Here, we present photoluminescence excitation spectroscopy as a method to probe transition probabilities from various excitonic states in cuprous oxide, and we show giant Rydberg excitons at $T=38$ mK with principal quantum n…
We present a detailed investigation of different excitonic states weakly confined in single GaAs/AlGaAs quantum dots obtained by the Al droplet-etching method. For our analysis we make use of temperature-, polarization- and magnetic field-dependent $μ$-photoluminescence measurements, which allow us to identify different excited states of the quantum dot system. Besides that, we present a comprehensive analysis of g-factors and diamagnetic coefficients of charged and neutral excitonic states in Voigt and Faraday configuration. Supported by theoretical calculations by the Configuration interacti…
We investigate the lateral transport of excitons in ZnSe quantum wells by using time-resolved micro-photoluminescence enhanced by the introduction of a solid immersion lens. The spatial and temporal resolutions are 200 nm and 5 ps, respectively. Strong deviation from classical diffusion is observed up to 400 ps. This feature is attributed to the hot-exciton effects, consistent with previous experiments under cw excitation. The coupled transport-relaxation process of hot excitons is modelled by Monte Carlo simulation. We prove that two basic assumptions typically accepted in photoluminescence i…
School of Materials Science and Engineering, Ocean University of China(中国海洋大学材料科学与工程学院);University of Shanghai for Science and Technology(上海理工大学);South China Normal University(华南师范大学);Sichuan University(四川大学)
The fine structure of excited excitonic states in a quantum dot with an embedded magnetic ion is studied theoretically and experimentally. The developed theory takes into account the Coulomb interaction between charged carriers, the anisotropic long-range electron-hole exchange interaction in the zero-dimensional exciton, and the exchange interaction of the electron and the hole with the $d$-electrons of a Mn ion inserted inside the dot. Depending on the relation between the quantum dot anisotropy and the exciton-Mn coupling the photoluminescence excitation spectrum has a qualitatively differe…