arXiv subjects

D. S. Smirnov

Publications and source records attributed to D. S. Smirnov.

At least 19 recordsLinked to original sources

arXiv2026

Random fine structure and polarized luminescence of triplet excitons in semiconductor nanocrystals

We present a theory of polarized photoluminescence of triplet excitons in semiconductor nanocrystal ensembles with the random fine structure contributed by the electron-hole exchange and carrier-nuclear hyperfine interactions. The interaction parameters are assumed to be normally and isotropically distributed. In particular, the exchange interaction is described by the Gaussian orthogonal ensemble of random matrices. The intensity of luminescence as well as the optical orientation and alignment are calculated as functions of the fine structure splitting parameters and the exciton lifetime. We have also analyzed the suppression of optical alignment and enhancement of optical orientation in an external longitudinal magnetic field.

cond-mat.mes-hall↗

arXiv2026

Scaling laws of electron and hole spin relaxation in indirect band gap (In,Al)As/AlAs quantum dots

We investigate the electron and heavy hole spin dynamics as a function of magnetic field in ensembles of indirect band gap (In,Al)As/AlAs quantum dots (QDs) with type-I band alignment. Employing a comprehensive model that accounts for both the exciton level quartet and the magnetic-field-driven redistribution of excitons between these states via spin relaxation processes, we extract the electron ($τ_{se}$) and heavy hole ($τ_{sh}$) spin relaxation times as a function of magnetic field for QDs of varying sizes. Our analysis reveals that both $τ_{se}(B)$ and $τ_{sh}(B)$ exhibit power-law scaling behavior, yet the scaling exponents for electrons and heavy holes show markedly different evolution with QD size. For QDs with a diameter of about 9 nm, we find $τ_{se}(B)\propto B^{-5}$ and $τ_{sh}(B)\propto B^{-3}$. Remarkably, increasing the QD diameter to about 16 nm results in a drastic change of the scaling laws, with both $τ_{se}(B)$ and $τ_{sh}(B)$ following a $\propto B^{-9}$ dependence. We discuss the underlying mechanisms responsible for this size-dependent transformation of the magnetic field scaling behavior of carrier spin relaxation.

cond-mat.mes-hall↗

arXiv2026

Tunable linear polarization of interface excitons at lateral heterojunctions

We develop a theory of polarized photoluminescence of interface excitons localized at lateral heterojunctions between transition metal dichalcogenide monolayers. We show that the circular selection rules governing interband optical transitions exactly at the band extrema are modified at finite wave vectors. The corresponding wave-vector-dependent corrections to the optical matrix elements result in a net linear polarization of excitonic photoluminescence. We identify two microscopic mechanisms responsible for linear polarization$-$trigonal warping of the electron and hole dispersions and the energy dependence of the effective masses. Their interplay controls both the magnitude and the angle of the emitted light polarization, with distinct dependences on the crystallographic orientation of the interface. Using a microscopic variational approach, we demonstrate that the degree of linear polarization can reach values exceeding 10% in realistic heterostructures. Furthermore, due to the large built-in dipole moment of interface excitons, their optical response can be tuned by an external in-plane electric field, enabling control over the strength and direction of the polarization.

cond-mat.mes-hall↗

arXiv2025

Spin noise of localized electrons in CdTe/CdMgTe quantum well

The spin dynamics of localized electrons in bulk semiconductors is governed by the interplay of effective nuclear field fluctuations, spin exchange between electrons, and spin transitions into the conduction band. Using spin noise spectroscopy, we reveal this interplay for donor-bound electrons in a CdTe/CdMgTe quantum well and spectrally separate electron spin relaxation and dephasing in zero magnetic field. We identify a specific regime of the electron spin dynamics, where temperature-induced activation of spin-independent hopping leads to a monotonic acceleration of electron spin relaxation. This behavior contrasts with bulk CdTe crystals, where the motional narrowing effect is observed. We attribute this difference to the significantly larger inhomogeneous broadening of the donor-related trion resonance in our quantum well compared to bulk samples. The theoretical analysis of the spin noise power and the strength of the spin exchange interaction provides the estimation of the donor concentration in our unintentionally doped structure.

cond-mat.mes-hall↗

arXiv2025

Modification of Hanle and polarization recovery curves under interplay of hopping and quantum measurement back action

The measurements of Hanle and polarization recovery effects for localized charge carriers are the basic tools for determining parameters of the spin dynamics, such as strength of the hyperfine interaction, for example, in quantum dots. We describe the dependence of the spin polarization of localized electrons on transverse and longitudinal magnetic fields taking into account the interplay between electron hopping and measurement back action. We show that these two have a qualitatively similar effect in the Faraday geometry, but compete in the Voigt geometry. This allows one to describe a broad range of the experimental results and study the fundamental effects of quantum measurements.

cond-mat.mes-hall↗

arXiv2025

Ultimate photon entanglement in biexciton cascade

The polarization entanglement of photons emitted by semiconductor quantum dots is unavoidably limited by the spin fluctuations of the host lattice nuclei. To overcome this limitation, we develop a theory of entangled photon pair generation by a symmetric colloidal quantum dot mediated by a triplet exciton. We derive general analytical expressions for the concurrence as a function of the hyperfine interaction strength and show that it is intrinsically higher than that in conventional doublet-exciton systems such as self-assembled quantum dots. The concurrence sensitively depends on the shape anisotropy and the strain applied to a nanocrystal. In particular, we uncover a possibility of completely suppressing the detrimental effect of the hyperfine interaction due to the interplay between nanocrystal anisotropy and electron-hole exchange interaction. We argue that this represents the ultimate limit for the generation of entangled photon pairs by semiconductor quantum dots.

cond-mat.mes-hall↗

arXiv2025

Magnetic field induced exciton spin dynamics in indirect band gap (In,Al)As/AlAs quantum dots

The exciton recombination and spin dynamics are investigated both experimentally and theoretically in an ensemble of indirect band gap (In,Al)As/AlAs quantum dots (QDs) with type-I band alignment. The magnetic-field-induced circular polarization of the time-integrated photoluminescence changes sign across the emission spectrum with a width reflecting the QD size. It is negative on the low energy side, i.e. for emission from large QDs, but positive on the high energy side, i.e. for emission from small QDs. However, the exciton g factor, measured by spin-flip Raman scattering, is positive across the whole QD ensemble. The magnetic-field-induced circular polarization of the photoluminescence dynamics is studied as function of the magnetic field strength and direction. The dynamics are non-monotonic over a time range up to milliseconds. The time dependence of the photoluminescence circular polarization degree and sign strongly depends on the emission energy and changes with magnetic field orientation. The observed nonmonotonic behavior is provided by the interplay of bright and dark exciton states, contributing to the emission. The experiment is interpreted using a kinetic theory, which accounts for the dynamics of the spin states in the exciton level quartet in longitudinal and tilted magnetic fields, the radiative recombination processes, and the redistribution of the excitons between these states as result of spin relaxation. The model allows us to evaluate the electron and heavy hole spin relaxation times in QDs with different sizes.

cond-mat.mes-hall↗

arXiv2025

Spin noise reveals spin dynamics and recharging of lead halide perovskite nanocrystals

The lead halide perovskite nanocrystals embedded into a glass matrix exhibit strong interaction with light and demonstrate exceptional optical and spin related features along with long-term chemical and physical stability. We apply the spin noise spectroscopy technique which offers a number of specific opportunities to study the spin system of CsPbI$_3$ nanocrystals in a fluorophosphate glass matrix. A pronounced spin precession peak with an isotropic $g$-factor absolute value of 2.7 and record dephasing time of T$_{2\text{,e}}$ = 2.7 ns is ascribed to resident electrons in the perovskite nanocrystals. The experimentally observed Faraday rotation noise with no noise of ellipticity is explained by saturation of the inhomogeneously broadened optical transition. Increasing the probe intensity, we went beyond the non-perturbative regime and observed a number of light-induced effects. In particular, the illumination with shorter wavelength light gives rise to a persistent recharging of the quantum dots by holes ($|g|=0.17$ and T$^*_{2\text{,h}}$ = 1.4 ns, T$^*_{1\text{,h}}$ $\geq$ 30 ns), which remains stable over multiple cycles of heating to the room temperature and cooling. In addition, elliptically polarized light induced an "optical" magnetic field on the system due to the AC Stark effect. It is confirmed using a new modification of polarization noise spectroscopy with a small degree of circular polarization of the probe light added with different frequencies.

cond-mat.mes-hall↗

arXiv2025

Magnetic quadrupole dichroism in isotropic medium

For isotropic media, the magnetic field applied across the light propagation direction affects their optical properties only in the second order, and its effect proves to be much weaker than in the longitudinal field. In this work, we show that, under resonant excitation well beyond the linear regime, the situation changes drastically: A small magnetic linear anisotropy considerably increases, and an even stronger new quadrupole dichroism emerges. The latter manifests itself as the 90$^\circ$-periodic azimuthal dependence of the transmission and anisotropic rotation of the probe polarization plane. These effects are described microscopically in a toy model, and their symmetry analysis is presented. Both are observed experimentally on the D2 resonance of cesium vapor and agree with the theoretical predictions. The large magnitude of the quadrupole dichroism makes it promising for magnetometric applications and for studying the effects of anisotropic bleaching.

physics.optics↗

arXiv2024

Intervalley mixing of interface excitons at lateral heterojunctions

$\require{mediawiki-texvc}$ We demonstrate that the low symmetry of armchair lateral heterojunction between transition metal dichalcogenide monolayers allows for the mixing of $\mathbf{K}_+$ and $\mathbf{K}_-$ valleys. From the tight binding model we estimate the strength of the valley coupling to be of the order of $0.2$ eV$\cdotÅ$ for typical heteropairs. We show that the valley mixing gives rise to the in-plane $g$-factor of localized electrons leading to the spin precession in the in-plane magnetic field. We further study the effects of the valley mixing on the fine structure and dynamics of excitons at type-II lateral heterojunctions. We find that the interplay of the valley mixing and long-range exchange interaction leads to the linear polarization of exciton photoluminescence along the armchair heterojunction with the degree of polarization up to $1/3$ under unpolarized excitation. Application of the in-plane magnetic field of the order of 10$-$100 mT in any direction leads to the depolarization of the photoluminescence.

cond-mat.mes-hall↗

arXiv2024

Cooling and heating nuclear spins by strongly localized electrons

The concept of nuclear spin temperature has been a cornerstone of the theory of dynamic nuclear spin polarization by electrons in various semiconductor structures for decades. Still, it is not always applicable to strongly localized electrons due to their long spin correlation times. This motivated the use of the oversimplified central spin model for the description of the nuclear spin dynamics in quantum dots. Here, we present a microscopic theory that bridges the gap between these two approaches by describing the nuclear spin thermodynamics for systems with long electron spin correlation times. Importantly, our theory predicts that efficient nuclear spin cooling by strongly localized electrons requires an external magnetic field by far exceeding the local field of nuclear spin-spin interaction, and that the time of the nuclear spin heating by unpolarized electrons may change by several orders of magnitude depending on the magnetic field.

cond-mat.mes-hall↗

arXiv2024

Tunneling spin Nernst effect for a single quantum dot

We describe theoretically the spin Nernst effect for electrons tunneling to a quantum dot from a quantum wire with the heat flowing along it. Such a tunneling spin Nernst effect is shown to take place due to the spin-dependent electron tunneling produced by the spin-orbit coupling. The Coulomb interaction of electrons in the quantum dot is taken into account using nonequilibrium Green's functions and is shown to increase significantly the accumulated spin in a single quantum dot. The largest possible degree of spin polarization is discussed.

cond-mat.mes-hall↗

arXiv2024

Interplay between hyperfine and anisotropic exchange interactions in exciton luminescence of quantum dots

The optical orientation and alignment of excitons in semiconductor indirect gap quantum dots have been studied theoretically. A special regime is analyzed in which the energy of the hyperfine interaction of an electron with lattice nuclei is small compared to the exchange splitting between bright and dark excitonic levels, but is comparable to the anisotropic exchange splitting of the radiative doublet. The dependencies of degrees of circular and linear polarization on the external magnetic field under resonant excitation of excitons by polarized light are calculated.

cond-mat.mes-hall↗

arXiv2023

Spin noise of a halide perovskite

We report on first observation of spin noise in a strongly birefringent semiconductor -- halide perovskite single crystal MAPbI$_3$. The observed spin noise resonance is ascribed to free holes with a record spin dephasing time of 4 ns. The spin dynamics is found to be affected by the residual light absorption of the crystal providing renormalization of the Larmor frequency. Extended spin noise spectroscopy with rotating magnetic field allowed us not only to evaluate the $g$-factor anisotropy, but also to distinguish two different spin subsystems tentatively associated to twinning of the crystal.

cond-mat.mes-hall↗

arXiv2023

Theory of polarized photoluminescence of indirect band gap excitons in type-I quantum dots

In this work, we theoretically investigate the optical orientation and alignment of excitons in quantum dots with weak electron-hole exchange interaction and long exciton radiative lifetimes. This particular regime is realized in semiconductor heterosystems where excitons are indirect in the $\boldsymbol r$ or $\boldsymbol k$ space. The main role in the fine structure of excitonic levels in these systems is played by the hyperfine interaction of the electron in the confined exciton and fluctuations of the Overhauser field. Along with it, the effects of nonradiative recombination and exchange interaction are considered. We start with the model of vanishing exchange interaction and nonradiative exciton recombination and then include them into consideration in addition to the strong Overhauser field. In the nanoobjects under study, the polarization properties of the resonant photoluminescence are shown to vary with the external magnetic filed in completely different way as compared with the behaviour of the conventional quantum dot structures.

cond-mat.mes-hall↗

arXiv2023

Spin light emitting diode based on exciton fine structure tuning in quantum dots

We propose a concept of quantum dot based light emitting diode that produces circularly polarized light due to the tuning of the exciton fine structure by magnetic field and electron nuclear hyperfine interaction. The device operates under injection of electrons and holes from nonmagnetic contacts in a small field of the order of milliteslas. Its size can be parametrically smaller than the light wavelength, and circular polarization degree of electroluminescence can reach 100%. The proposed concept is compatible with the micropillar cavities, which allows for the deterministic electrical generation of single circularly polarized photons.

cond-mat.mes-hall↗

arXiv2023

Kondo enhancement of current induced spin accumulation in a quantum dot

Weak spin-orbit coupling produces very limited current induced spin accumulation in semiconductor nanostructures. We demonstrate a possibility to increase parametrically the spin polarization using the Kondo effect. As a model object we consider a quantum dot side coupled to a quantum wire taking into account the spin dependent electron tunneling from the wire to the dot. Using the nonequilibrium Green's functions, we show that the many body correlations between the quantum dot and the quantum wire can increase the current induced spin accumulation at low temperatures by almost two orders of magnitude for the moderate system parameters. The enhancement is related to the Kondo peak formation in the density of states and the spin instability due to the strong Coulomb interaction. This effect may be useful to electrically manipulate the localized electron spins in quantum dots for their quantum applications.

cond-mat.mes-hall↗

arXiv2023

Optical orientation of excitons in a longitudinal magnetic field in indirect band gap (In,Al)As/AlAs quantum dots with type-I band alignment

The exciton recombination and spin dynamics in (In,Al)As/AlAs quantum dots (QDs) with indirect band gap and type-I band alignment are studied. The negligible (less than $0.2~μ$eV) value of the anisotropic exchange interaction in these QDs prevents a mixing of the excitonic basis states with pure spin and allows for the formation of spin polarized bright excitons for quasi-resonant circularly polarized excitation. In a longitudinal magnetic field, the recombination and spin dynamics of the excitons are controlled by the hyperfine interaction between the electron and nuclear spins. A QD blockade by dark excitons is observed in magnetic field eliminating the impact of the nuclear spin fluctuations. A kinetic equation model, which accounts for the population dynamics of the bright and dark exciton states as well as for the spin dynamics, has been developed, which allows for a quantitative description of the experimental data.

cond-mat.mes-hall↗