We present a theoretical framework for biexciton dynamics in molecular aggregates that explicitly treats populations and coherences across excitation manifolds within a reduced density-matrix formalism. By extending kinetic descriptions beyond the weak-coupling limit, the approach captures the influence of exciton delocalization and exciton-exciton annihilation while remaining computationally tractable within a Markovian description of environmental relaxation. Using this framework, we investigate how the spatial profile and momentum composition of the initial biexciton state govern fluorescence decay and transport. Incoherent initial conditions lead to strongly non-exponential relaxation and time-dependent diffusion driven by nonlinear population kinetics. In contrast, coherently prepared biexciton states exhibit pronounced early-time coherent transport, whose character depends sensitively on whether the initial state is prepared as a standing-wave or traveling-wave superposition of single-exciton modes. Despite nearly identical emission dynamics for J and H aggregate, biexciton transport properties differ markedly due to band structure-dependent interference effect. Our results demonstrate that biexciton dynamics remains strongly influenced by initial-state coherence and momentum composition. Besides initial-state preparation, the coherent-to-incoherent crossover and the diffusive spreading of the exciton density are sensitive to internal conversion processes such as exciton fusion and the decay to the first excited state. The present work establishes initial-state preparation as a key control parameter for many-exciton transport in excitonic systems and provides a general framework for interpreting nonlinear optical experiments beyond population-based descriptions.
A comprehensive experimental investigation of exciton and biexciton recombination in GaAs/AlGaAs quantum wells is presented. Exciton and biexciton recombination times are found to be 16 and 55 ps, respectively. A method of determining the dynamics of the exciton temperature is developed. It is shown that both exciton and biexciton recombination processes increase the exciton temperature by an amount as high as $\sim 10$ K. These processes impose a new restriction on the possibility of exciton Bose-Einstein condensation and make impossible its achievement in a system of direct excitons in GaAs …
Microscopic simulations of the coupled dynamics of cavity photons, excitons, and biexcitons
Institute for Photonic Quantum Systems (PhoQS), Paderborn University（帕德博恩大学光子量子系统研究所）；Department of Physics and Center for Optoelectronics and Photonics Paderborn (CeOPP), Paderborn University（帕德博恩大学物理系与光电光子学中心）；Wyant College of Optical Sciences, University of Arizona（亚利桑那大学怀特光学学院）
We calculate the near-field optical spectra of excitons and biexcitons in semiconductor quantum dots naturally occurring at interface fluctuations in GaAs-based quantum wells, using a non-local description of the response function to a spatially modulated electro-magnetic field. The relative intensity of the lowest, far-field forbidden excitonic states is predicted; the spatial extension of the ground biexciton state is found in agreement with recently published experiments.
We report on single InGaAs quantum dots embedded in a lateral electric field device. By applying a voltage we tune the neutral exciton transition into resonance with the biexciton using the quantum confined Stark effect. The results are compared to theoretical calculations of the relative energies of exciton and biexciton. Cascaded decay from the manifold of single exciton-biexciton states has been predicted to be a new concept to generate entangled photon pairs on demand without the need to suppress the fine structures splitting of the neutral exciton.
The exciton and biexciton binding energy have been studied for a ZnSe/ZnS core/shell quantum dot using WKB (Wentzel-Kramers-Brillouin) approximation. The exciton binding energy increases for small shell thickness and for large thickness, the binding energy again starts decreasing. A similar result is obtained for biexcitons where for thicker shells, the biexciton attains antibonding.
Strong Coulomb interactions in single-layer transition metal dichalcogenides (TMDs) result in the emergence of strongly bound excitons, trions and biexcitons. These excitonic complexes possess the valley degree of freedom, which can be exploited for quantum optoelectronics. However, in contrast to the good understanding of the exciton and trion properties, the binding energy of the biexciton remains elusive, with theoretical calculations and experimental studies reporting discrepant results. In this work, we resolve the conflict by employing low-temperature photoluminescence spectroscopy to id…
Our goal is to provide a physical understanding of the elementary coupling between photon and biexciton and to derive the physical characteristics of the biexciton oscillator strength, following the procedure we used for trion. Instead of the more standard two-photon absorption, this work concentrates on molecular biexciton created by photon absorption in an exciton gas. We first determine the appropriate set of coordinates in real and momentum spaces to describe one biexciton as two interacting excitons. We then turn to second quantization and introduce the "Fourier transform in the exciton s…
Microscopic approach to the quantized light-matter interaction in semiconductor nanostructures: Complex coupled dynamics of excitons, biexcitons, and photons
Paderborn University（帕德博恩大学）；University of Arizona（亚利桑那大学）
We demonstrate the simultaneous dressing of both vacuum-to-exciton and exciton-to-biexciton transitions of a single semiconductor quantum dot in a high-Q micropillar cavity, using photoluminescence spectroscopy. Resonant two-photon excitation of the biexciton is achieved by spectrally tuning the quantum dot emission with respect to the cavity mode. The cavity couples to both transitions and amplifies the Rabi-frequency of the likewise resonant cw laser, driving the transitions. We observe strong-field splitting of the emission lines, which depend on the driving Rabi field amplitude and the cav…
We present a first-principle path integral Monte-Carlo (PIMC) study of the binding energy of excitons, trions (positively and negatively charged excitons) and biexcitons bound to single-island interface defects in quasi-two-dimensional GaAs/Al$_{x}$Ga$_{1-x}$As quantum wells. We discuss in detail the dependence of the binding energy on the size of the well width fluctuations and on the quantum-well width. The numerical results for the well width dependence of the exciton, trions and biexciton binding energy are in good quantitative agreement with the available experimental data.
The multivalley band structure of monolayer transition metal dichalcogenides (TMDs) gives rise to intravalley and intervalley excitons. Much knowledge of these excitons has been gained, but fundamental questions remain, such as how to describe them all in a unified picture with their correlations, how are those from different valleys coupled to form the intervalley biexciton? To address the issues, we derive an exciton Hamiltonian from interpair correlations between the constituent carriers-fermions of two excitons. Identifying excitons by irreducible representations of their point symmetry gr…
We observe excited exciton and biexciton states of localised excitons in an anisotropic quantum ring, where large polarisation asymmetry supports the presence of a crescent-like localised structure. We also find that saturation of the localised ground state exciton with increasing excitation can be attributed to relatively fast dissociation of biexcitons (? 430 ps) compared to slow relaxation from the excited state to the ground state (? 1000 ps). As no significant excitonic Aharonov-Bohm oscillations occur up to 14 T, we conclude that phase coherence around the rim is inhibited as a consequen…
The influence of a perpendicular magnetic field on the binding energy and structural properties of excitons, trions, and biexcitons in monolayers of semiconducting transition metal dichalcogenides (TMDs) is investigated. The stochastic variational method (SVM) with a correlated Gaussian basis is used to calculate the different properties of these few-particle systems. In addition, we present a simplified variational approach which supports the SVM results for excitons as a function of magnetic field. The exciton diamagnetic shift is compared with recent experimental results and we extend this …
A recent single quantum wire is of sufficient quality to reveal new details of the photoluminescence (PL) evolution with increasing electron--hole (e--h) pair density. At a pair density of 3.6 $\times$ 10$^{3}$ cm$^{-1}$, the PL is characteristic of biexcitons shifted below the exciton peak by the 2.8-meV biexciton binding. At the pair density of 1.2 $\times$ 10$^{5}$ cm$^{-1}$, the biexciton peak broadens without energy shift to an e--h plasma. At all pair densities up to 30 K, neither the exciton peak nor the one-dimensional (1D) continuum edge shows any shift. In contrast to prevailing theo…
We demonstrate that the exciton and biexciton emission energies as well as exciton fine structure splitting (FSS) in single (In,Ga)As/GaAs quantum dots (QDs) can be efficiently tuned using hydrostatic pressure in situ in an optical cryostat at up to 4.4 GPa. The maximum exciton emission energy shift was up to 380 meV, and the FSS was up to 180 $μ$eV. We successfully produced a biexciton antibinding-binding transition in QDs, which is the key experimental condition that generates color- and polarization-indistinguishable photon pairs from the cascade of biexciton emissions and that generates en…
The photoluminescence spectrum of a single quantum dot was recorded as a secondary resonant laser optically dressed either the vacuum-to-exciton or the exciton-to-biexciton transitions. High-resolution polarization-resolved measurements using a scanning Fabry-Perot interferometer reveal splittings of the linearly-polarized fine-structure states that are non-degenerate in an asymmetric quantum dot. These splittings manifest as either triplets or doublets and depend sensitively on laser intensity and detuning. Our approach realizes complete resonant control of a multi-excitonic system in emissio…
Multiply-excited states in semiconductor quantum dots feature intriguing physics and play a crucial role in nanocrystal-based technologies. While photoluminescence provides a natural probe to investigate these states, room temperature single-particle spectroscopy of their emission has so far proved elusive due to the temporal and spectral overlap with emission from the singly-excited and charged states. Here we introduce biexciton heralded spectroscopy, enabled by a single-photon avalanche diode array based spectrometer. This allows us to directly observe biexciton-exciton emission cascades an…
We present the phase diagram of free charges (electrons and holes), excitons, and biexcitons in highly excited CdSe nanoplatelets that predicts a crossover to a biexciton-dominated region at easily attainable low temperatures or high photoexcitation densities. Our findings extend previous work describing only free charges and excitons by introducing biexcitons into the equation of state, while keeping the exciton and biexciton binding energies constant in view of the relatively low density of free charges in this material. Our predictions are experimentally testable in the near future and offe…
It is demonstrated how the exciton and the biexciton state of a quantum dot can be prepared with high fidelity on a picosecond time-scale by driving the dot with a strong laser pulse that is tuned above the exciton resonance for exciton preparation and in resonance with the exciton transition for biexciton preparation. The proposed schemes make use of the phonon-induced relaxation towards photon dressed states in optically driven quantum dots and combine the simplicity of Rabi flopping with the robustness of adiabatic rapid passage schemes. Our protocols allow for an on-demand, fast and almost…
We present a detailed investigation into the optical characteristics of individual InAs quantum dots (QDs) grown by metalorganic chemical vapor deposition, with low temperature emission in the telecoms window around 1300 nm. Using micro-photoluminescence (PL) spectroscopy we have identified neutral, positively charged, and negatively charged exciton and biexciton states. Temperature-dependent measurements reveal dot-charging effects due to differences in carrier diffusivity. We observe a pronounced linearly polarized splitting of the neutral exciton and biexciton lines (~250 ueV) resulting fro…
Interactions between two excitons can result in the formation of bound quasiparticles, known as biexcitons. Their properties are determined by the constituent excitons, with orbital and spin states resembling those of atoms. Monolayer transition metal dichalcogenides (TMDs) present a unique system where excitons acquire a new degree of freedom, the valley pseudospin, from which a novel intervalley biexciton can be created. These biexcitons comprise two excitons from different valleys, which are distinct from biexcitons in conventional semiconductors and have no direct analogue in atomic and mo…
Pulsed resonant fluorescence is used to probe ultrafast phonon-assisted exciton and biexciton preparation in individual self-assembled InGaAs quantum dots. By driving the system using large area ($\geq10π$) near resonant optical pulses, we experimentally demonstrate how phonon mediated dissipation within the manifold of dressed excitonic states can be used to prepare the neutral exciton with a fidelity $\geq 70\%$. By comparing the phonon-assisted preparation with resonant Rabi oscillations we show that the phonon-mediated process provides the higher fidelity preparation for large pulse areas …
We performed spectroscopic studies of a single GaAs quantum ring with an anisotropy in the rim height. The presence of an asymmetric localised state was suggested by the adiabatic potential. The asymmetry was investigated in terms of the polarization dependence of excitons and biexcitons, where a large energy di erence (0.8 meV) in the exciton emission energy for perpendicular polarizations was observed and the oscillator strengths were also compared using the photoluminescence decay rate. For perpendicular polarizations the biexciton exhibits twice the energy di erence seen for the exciton, a…
We demonstrate control over the spin state of a semiconductor quantum dot exciton using a polarized picosecond laser pulse slightly detuned from a biexciton resonance. The control pulse follows an earlier pulse, which generates an exciton and initializes its spin state as a coherent superposition of its two non-degenerate eigenstates. The control pulse preferentially couples one component of the exciton state to the biexciton state, thereby rotating the exciton's spin direction. We detect the rotation by measuring the polarization of the exciton spectral line as a function of the time-differen…
Polarization-dependent two-dimensional Fourier-transform spectroscopy (2DFTS) is performed on excitons in strained bulk GaAs layers probing the coherent response for differing amounts of strain. Biaxial tensile strain lifts the degeneracy of heavy-hole (HH) and light-hole (LH) valence states, leading to an observed splitting of the associated excitons at low temperature. Increasing the strain increases the magnitude of the HH/LH exciton peak splitting, induces an asymmetry in the off-diagonal coherences, increases the difference in the HH and LH exciton homogenous linewidths, and increases the…
We report on a strong dependence of the phonon-induced damping of Rabi dynamics in an optically driven exciton-biexciton quantum dot system on the polarization of the exciting pulse. While for a fixed pulse intensity the damping is maximal for linearly polarized excitation, it decreases with increasing ellipticity of the polarization. This finding is most remarkable considering that the carrier-phonon coupling is spin-independent. In addition to simulations based on a numerically exact real-time path integral approach, we present an analysis within a weak coupling theory that allows for analyt…
The recent accessibility of high quality, charge neutral monolayer transition metal dichalcogenides with narrow exciton linewidths at the homogeneous limit provides an ideal platform to study excitonic many-body interactions. In particular, the possibility to manipulate coherent exciton-exciton interactions, which govern the ultrafast nonlinear optical response, by applying an external magnetic field has not been considered so far. We address this discrepancy by presenting a nonlinear microscopic theory in the coherent limit for optical excitations in the presence of out-of-plane, in-plane, an…
Single-layer WS$_2$ is a direct-gap semiconductor showing strong excitonic photoluminescence features in the visible spectral range. Here, we present temperature-dependent photoluminescence measurements on mechanically exfoliated single-layer WS$_2$, revealing the existence of neutral and charged excitons at low temperatures as well as at room temperature. By applying a gate voltage, we can electrically control the ratio of excitons and trions and assert a residual n-type doping of our samples. At high excitation densities and low temperatures, an additional peak at energies below the trion do…
We present results on both the intensity and phase-dynamics of the transient non-linear optical response of a single quantum dot (SQD). The time evolution of the Four Wave Mixing (FWM) signal on a subpicosecond time scale is dominated by biexciton effects. In particular, for the cross-polarized excitation case a biexciton bound state is found. In this latter case, mean-field results are shown to give a poor description of the non-linear optical signal at small times. By properly treating exciton-exciton effects in a SQD, coherent oscillations in the FWM signal are clearly demonstrated. These o…
Excitons, trions, biexcitons, and exciton-trion complexes in two-dimensional transition metal dichalcogenide sheets of MoS$_2$, MoSe$_2$, MoTe$_2$, WS$_2$ and WSe$_2$ are studied by means of density functional theory and path integral Monte Carlo method in order to accurately account for the particle-particle correlations. In addition, the effect of dielectric environment on the properties of these exciton complexes is studied by modifying the effective interaction potential between particles. Calculated exciton and trion binding energies are consistent with previous experimental and computati…
Strong light-matter interactions in layered transition metal dichalcogenides (TMDs) open up vivid possibilities for novel exciton-based devices. The optical properties of TMDs are dominated mostly by the tightly bound excitons and more complex quasiparticles, the biexcitons. Instead of physically exfoliated monolayers, the solvent-mediated chemical exfoliation of these 2D crystals is a cost-effective, large-scale production method suitable for real device applications. We explore the ultrafast excitonic processes in WS$_{2}$ dispersion using broadband femtosecond pump-probe spectroscopy at roo…
Single layers of WS2 are direct gap semiconductors with high photoluminescence (PL) yield holding great promise for emerging applications in optoelectronics. The spatial confinement in a 2D monolayer together with the weak dielectric screening lead to huge binding energies for the neutral excitons as well as other excitonic complexes, such as trions and biexcitons whose binding energies scale accordingly. Here, we report on the existence of biexcitons in mechanically exfoliated WS2 flakes from 78 K up to room temperature. Performing temperature and power dependent PL measurements, we identify …
We present a study of free carrier photo-generation and multi-carrier bound states, such as biexcitons and trions (ionized excitons), in semiconducting single-walled carbon nanotubes. Pump-and-probe measurements performed with fs pulses reveal the effects of strong Coulomb interactions between carriers on their dynamics. Biexciton formation by optical transition from exciton population results in an induced absorption line (binding energy 130 meV). Exciton-exciton annihilation process is shown to evolve at high densities towards an Auger process that can expel carriers from nanotubes. The rema…
We present results of atomistic empirical pseudopotential calculations and configuration interaction for excitons, positive and negative trions (X\pm), positive and negative quartons (X2\pm) and biexcitons. The structure investigated are laterally aligned InGaAs quantum dot molecules embedded in GaAs under a lateral electric field. The rather simple energetic of excitons becomes more complex in the case of charged quasiparticles but remains tractable. The negative trion spectrum shows four anticrossings in the presently available range of fields while the positive trion shows two. The magnitud…
For many applications of semiconductor quantum dots in quantum technology a well controlled state preparation of the quantum dot states is mandatory. Since quantum dots are embedded in the semiconductor matrix, the interaction with phonons plays often a major role in the preparation process. In this review, we discuss the influence of phonons on three basically different optical excitation schemes which can be used for the preparation of exciton, biexciton, and superposition states: a resonant excitation leading to Rabi rotations in the excitonic system, an excitation with chirped pulses explo…
We consider quantum phase transitions in a system of bright dipolar excitons which can form bound pairs (dipolar biexcitons). We assume a narrow resonance in the interaction of excitons with opposite spins. At sufficiently large density a resonant exciton superfluid transforms into a superfluid of biexcitons. The transition may be either of the first or the second kind. The average relative momenta of excitons in the pairs being beyond the light cone, the transition should be accompanied by reduction of the photoluminescence intensity. Effective magnetic fields due to the long-range exchange s…
We study the coherent mixing between two-particle (single exciton) and four-particle (biexciton) states of a semiconductor nanocrystal resulting from the coulomb coupling between states with different numbers of electron-hole pairs. Using a simple model of the nanocrystal wave functions and an envelope function approach, we estimate the efficiency of the multiple exciton generation (MEG) process resulting from such coherent admixture mechanism, including all the relevant states in a very broad energy interval. We show that in a typical ensemble of nanocrystals with 3~nm average radius, the ons…
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…
We detect a novel radiative cascade from a neutral semiconductor quantum dot. The cascade initiates from a metastable biexciton state in which the holes form a spin-triplet configuration, Pauli-blockaded from relaxation to the spin-singlet ground state. The triplet biexciton has two photon-phonon-photon decay paths. Unlike in the singlet-ground state biexciton radiative cascade, in which the two photons are co-linearly polarized, in the triplet biexciton cascade they are crosslinearly polarized. We measured the two-photon polarization density matrix and show that the phonon emitted when the in…
We address the photoluminescence emission of individual germanium extrinsic centers in Al_0.3Ga0.7As epilayers grown on germanium substrates. Through a thorough analysis of micro-photoluminescence experiments we demonstrate the capability of high temperature emission (70 K) and multiexcitonic features (neutral exciton X, biexciton XX, positive X+ and negative X- charged exciton) of these quantum emitters. Finally, we investigate the renormalization of each energy level showing a large and systematic change of the binding energy of XX and X+ from positive to negative values (from ~+5 meV up to …
The quantum state of the emitted light from the cascade recombination of a biexciton in a quantum dot is theoretically investigated including exciton fine structure splitting (FSS) and electron-nuclear spin hyperfine interactions. In an ideal situation, the emitted photons are entangled in polarization making the biexciton recombination process a candidate source of entangled photons necessary for the growing field of quantum communication and computation. The coherence of the exciton states in real quantum dots is affected by a finite FSS and the hyperfine interactions via the effective magne…
The monolayers of semiconducting transition metal dichalcogenides host strongly bound excitonic complexes and are an excellent platform for exploring many-body physics. Here we demonstrate a controlled kinetic manipulation of the five-particle excitonic complex, the charged biexciton, through a systematic dependence of the biexciton peak on excitation power, gate voltage, and temperature using steady-state and time-resolved photoluminescence (PL). With the help of a combination of the experimental data and a rate equation model, we argue that the binding energy of the charged biexciton is less…
The optical properties of atomically thin transition metal dichalcogenides (TMDCs) are dominated by Coulomb bound quasi-particles, such as excitons, trions, and biexcitons. Due to the number and density of possible states, attributing different spectral peaks to the specific origin can be difficult. In particular, there has been much conjecture around the presence, binding energy and/or nature of biexcitons in these materials. In this work, we remove any ambiguity in identifying and separating the optically excited biexciton in monolayer WS2 using two-quantum multidimensional coherent spectros…
Multi-exciton states such as biexcitons, albeit theoretically predicted, have remained challenging to identify in atomically thin transition metal dichalcogenides so far. Here, we use excitation-power, electric-field and magnetic-field dependence of photoluminescence to report direct experimental evidence of two biexciton complexes in monolayer tungsten diselenide: the neutral and the negatively charged biexciton. We demonstrate bias-controlled switching between these two states, we determine their internal structure and we resolve a fine-structure splitting of 2.5 meV for the neutral biexcito…
We developed a comprehensive theoretical framework focusing on many-body effects of exciton species in monolayer WS$_2$, including bright and dark excitons, and intra- and inter-valley biexcitons, to investigate valley dynamics in monolayer WS$_2$ subjected to a tilted magnetic field B. In particular, the evolution of the exciton population densities and the many-body particle scatterings are considered to calculate the valley polarization (V P ) as a function of the magnetic field. We found valley splittings for the dark exciton and biexciton energy levels that are larger than those of bright…
Mott insulators sometimes show dramatic changes in their electronic states after photoirradiation, as indicated by photoinduced Mott-insulator-to-metal transition. In the photoexcited states of Mott insulators, electron wavefunctions are more delocalized than in the ground state, and long-range Coulomb interactions play important roles in charge dynamics. However, their effects are difficult to discriminate experimentally. Here, we show that in a one-dimensional Mott insulator, bis(ethylenedithio)tetrathiafulvalene-difluorotetracyanoquinodimethane (ET-F2TCNQ), long-range Coulomb interactions s…
We propose a method for calculating Coulomb matrix elements between exciton and biexciton states in semiconductor nanocrystals based on the envelope function formalism. We show that such a calculation requires proper treatment of the Bloch parts of the carrier wave functions which, in the leading order, leads to spin selection rules identical to those holding for optical interband transitions. Compared to the usual (intraband) Coulomb couplings, the resulting matrix elements are additionally scaled by the ratio of the lattice constant to the nanocrystal radius. As a result, the Coulomb couplin…
We have observed photoinduced negative optical conductivity, or gain, in the terahertz frequency range in a GaAs multiple-quantum-well structure in a strong perpendicular magnetic field at low temperatures. The gain is narrow-band: it appears as a sharp peak (linewidth $<$0.45 meV) whose frequency shifts with applied magnetic field. The gain has a circular-polarization selection rule: a strong line is observed for hole-cyclotron-resonance-active polarization. Furthermore, the gain appears only when the exciton $1s$ state is populated, which rules out intraexcitonic transitions to be its origin…
We investigate the effect of Cooper pair injection in shifting biexciton energy level of low-symmetry (C2v) quantum dots (QDs) exhibiting nontrivial fine structure splitting. Coupling QDs to the superconducting coherent state forms extra fine structures by intermixing the ground and biexcitonic states where spectroscopic separation of neutral exciton and biexciton can be diminished, yielding a system to be utilized in time reordering scheme. The separability of exciton and biexciton energy levels is ascribed to the corresponding direct, exchange and correlation energies calculated here through…
In atomically thin transition metal dichalcogenides (TMDs), reduced dielectric screening of the Coulomb interaction leads to strongly correlated many-body states, including excitons and trions, that dominate the optical properties. Higher-order states, such as bound biexcitons, are possible but are difficult to identify unambiguously using linear optical spectroscopy methods alone. Here, we implement polarization-resolved two-dimensional coherent spectroscopy to unravel the complex optical response of monolayer MoSe$_2$ and identify multiple higher-order correlated states. Decisive signatures …
We investigate the magnetic-field-induced splitting of biexcitons in monolayer WS$_2$ using polarization-resolved photoluminescence spectroscopy in out-of-plane magnetic fields up to 30 T. The observed $g$ factor of the biexciton amounts to $-3.89$, closely matching the $g$ factor of the neutral exciton. The biexciton emission shows an inverted circular field-induced polarization upon linearly polarized excitation, i.e. it exhibits preferential emission from the high-energy peak in a magnetic field. This phenomenon is explained by taking into account the configuration of the biexciton constitu…
Recently in [Phys. Rev. B 99, 241301(R) (2019)] tensor networks build upon logical circuits were briefly introduced to retrieve exciton and biexciton states. Compared to a conventional approach the tensor network methods scales logarithmic instead of linear in the grid points of the Brioullin zone and linear instead of exponential in the number of electrons and holes. This enables calculations with higher precision on the full Brioullin zone than previously possible. In this paper extensive details for an efficient implementation and the corresponding mathematical background are presented. In …
Strong coupling of excitonic resonances with a cavity gives rise to exciton-polaritons which possess a modified energy landscape compared to the uncoupled emitter. However, due to the femtosecond lifetime of the so-called bright polariton states and transient changes of the cavity reflectivity under excitation, it is challenging to directly measure the polariton excited state dynamics. Here, near-infrared pump-probe spectroscopy is used to investigate the ultrafast dynamics of exciton-polaritons based on strongly-coupled (6,5) single-walled carbon nanotubes in metal-clad microcavities. We pres…
