Polaron Effective Mass Research Articles

Influence of spin–orbit interaction on the effective mass of bound polaron in a parabolic quantum well

Using Tokuda's linear combination operator method and variational technique, we derive the effective mass of strongly coupled bound polaron in a parabolic quantum well. Due to the spin–orbit interaction, the effective mass of bound polaron splits into two branches. In the present calculation, we discuss dependence of effective mass on vibration frequency, electron–phonon coupling strength, Coulomb-bound potential strength, spin–orbit and velocity. The theoretical results show that effective mass of polaron is an increasing function of vibration frequency, Coulomb-bound potential strength and electron–phonon coupling strength. The absolute value of the total spin-splitting effective mass increases with the increase of spin–orbit, but decreases with the increase of velocity. It is found that, due to the heavy hole characteristic of spin–orbit interaction, the total spin-splitting effective mass is negative.

Temperature effect and Rashba effect of polaron in a parabolic quantum well

Using Tokuda’s improved linear combination operator method and variational technique, the expression of the polaron effective mass in an parabolic quantum well is derived. Due to the spin-orbit interaction, the effective mass of polaron splits into two branches. The dependence of effective mass on temperature and mean number phonons is discussed by numerical calculation. The effective mass of polaron is an increasing function of temperature and mean number phonons. The absolute value of total spin splitting effective mass increases with the increase in temperature and spin-orbit coupling parameter, and decreases with the increase in velocity. Due to the heavy hole characteristic, the spin splitting effective mass is negative.

Influence of Temperature and Spin–Orbit Interaction on the Effective Mass of Polaron in an Anisotropic Quantum Dot

Influence of Temperature and Spin–Orbit Interaction on the Effective Mass of Polaron in an Anisotropic Quantum Dot

Effective mass and interaction energy of heavy Bose polarons at unitarity

Effective mass and interaction energy of heavy Bose polarons at unitarity

Subsonic and supersonic polaron dynamics in polyacetylene

The paper considers the dynamics of a polaron in an electric field on a polyacetylene lattice. The one-electron non-adiabatic approximation based on the Su–Schrieffer–Heeger model is used. In an electric field, a polaron gains one of two saturated velocities, — subsonic and supersonic. Velocity bifurcation occurs in a very narrow range of electric field strengths. In an electric field, the polaron’s internal dynamic and electronic structure changes in a complex way. The supersonic polaron transforms the energy received from the electric field into monochromatic lattice oscillations. The generation of these oscillations is due to the internal polaron dynamics. The effective polaron mass is determined and m* ≈ 1.3. The negative effective mass was also identified. An analysis of the wave function and its phases provides useful information about the polaron evolution. The polaron dynamics is also studied depending on the mode of switching on and off the electric field and in multiple electric fields.

Polarons in binary Bose–Einstein condensates

Bose polarons are quasiparticles formed through the interaction between impurities and Bose–Einstein condensates. In this paper, we derive an effective Fröhlich Hamiltonian using the generalized Bogoliubov transformation. The effective Fröhlich Hamiltonian encompasses two types of effective interactions: impurity-density (ID) coupling and impurity-spin (IS) coupling. Furthermore, we employ the Lee–Low–Pines variational approach to investigate the relevant properties of Bose polarons induced by the ID and IS coupling. These properties include the ground state energy, effective mass, and average number of virtual phonons. Our findings reveal that the contribution resulting from IS couplings to the ground energy decreases to zero near the miscible–immiscible boundary. Additionally, the increase of the IS coupling induces a greater number of virtual phonons, impeding the movement of impurities and leading to a significant increase in the effective mass of Bose polarons.

Optical conductivity of an anharmonic large polaron gas at weak coupling

In a polar solid, electrons or other charge carriers can interact with the phonons of the ionic lattice, leading to the formation of polaron quasiparticles. The optical conductivity and optical absorption spectrum of a material are affected by this electron-phonon coupling, most notably leading to an absorption peak in the midinfrared region. Recently, a model Hamiltonian for anharmonic electron-phonon coupling was derived [M. Houtput and J. Tempere, Phys. Rev. B 103, 184306 (2021)] that includes both the conventional Fr\"ohlich interaction as well as an interaction in which an electron interacts with two phonons simultaneously. In this article, we calculate and investigate the optical conductivity of the anharmonic large polaron gas, and we show that an additional characteristic absorption peak appears due to this one-electron--two-phonon interaction. We calculate a semianalytical expression for the optical conductivity $\ensuremath{\sigma}(\ensuremath{\omega})$ at finite temperatures and weak coupling using the Kubo formula. The electronic and phononic contributions can be split and treated separately, such that the many-body effects of the electron gas may be taken into account through the well-known dynamical structure factor $S(\mathbf{k},\ensuremath{\omega})$. From the resulting optical conductivity, we calculate the polaron effective mass, an estimate for the electron-phonon scattering times, and the optical absorption spectrum of the anharmonic polaron gas. It is shown that the effects are negligible for four common III-V semiconductors (BN, AlN, BP, AlP) in the zinc-blende structure, which justifies the commonly used harmonic approximation in these materials. We show that alongside the well-known polaron absorption peak at the phonon energy $\ensuremath{\hbar}{\ensuremath{\omega}}_{\text{LO}}$, the one-electron--two-phonon interaction leads to an additional absorption peak at $2\ensuremath{\hbar}{\ensuremath{\omega}}_{\text{LO}}$. We propose this absorption peak as an experimentally measurable indicator for non-negligible one-electron--two-phonon interaction in a material, since the height of this peak is proportional to the strength of this anharmonic interaction.

Acceleration of polaron induced by site effective mass increment in organic ferromagnets

The polaron dynamics in organic ferromagnets (OFs) is investigated theoretically by considering the increment of site effective mass originating from the attachment of spin radicals. In spite of the increase of polaron effective mass, the results reveal two opposite effects on the polaron velocity caused by the increment of site effective mass. One is the normal decrease of the polaron velocity with the increment of site effective mass. The other is the abrupt acceleration of the polaron from below the sound velocity to the supersonic velocity upon a critical value of the site effective mass increment. Mechanism analysis shows that the acceleration of the polaron is attributed to the reduction of critical decoupling field for optical and acoustic deformations caused by the site effective mass increment. The second effect further depends on the polaron spin due to the existence of spin-dependent intrinsic dipole of the polarons. This work indicates the potential of high polaron mobility and efficient spin filtering effect under low electric fields in OFs.

Properties of acoustic polaron in free-standing slab

We investigated the ground state energy (GSE), ground state mobility (GSM), ground state lifetime (GSL), effective mass of acoustic polaron in free -standing slab using Pekar variational method. The influence of the electron and longitudinal acoustic phonon interaction, the slab thickness on the dynamics of acoustic polaron is highlighted. We showed that the slab thickness affects the dynamics of acoustic polaron. Although the standing slab is free, its thickness confines acoustic polaron and self-trapping state arrived. We first found that the GSE and effective mass of polaron increase with decreasing the thickness of the slab. Secondly, the wave function exhibits the threshold value where mobility and life time vanish.

Flexural deformations and collapse of bilayer two-dimensional crystals by interlayer excitons

We develop a consistent theory of the interlayer exciton-polaron formed in atomically-thin bilayers. Coulomb attraction between an electron and a hole situated in the different layers results in their flexural deformation and provides an efficient mechanism of the exciton coupling with flexural phonons. We study the effect of layers tension on the polaron binding energy and effective mass leading to suppression of polaron formation by the tension both in the weak and strong coupling regimes. We also consider the role of the nonlinearity related to the interaction between the out- and in-plane lattice displacements and obtain the criterion of the layer sticking, where the exciton collapses, due to the Coulomb attraction between the charge carriers.

Crossover polarons in a strongly interacting Fermi superfluid

We investigate the zero-temperature quasiparticle properties of a mobile impurity immersed in a strongly interacting Fermi superfluid at the crossover from a Bose-Einstein condensate (BEC) to a Bardeen--Cooper--Schrieffer (BCS) superfluid, by using a many-body $T$-matrix approach that excludes Efimov trimer bound states. Termed BEC-BCS crossover polaron, or crossover polaron in short, this quasiparticle couples to elementary excitations of a many-body background and therefore could provide a useful probe of the underlying strongly interacting Fermi superfluid. Due to the existence of a significant pairing gap $\Delta$, we find that the repulsive polaron branch becomes less well-defined. In contrast, the attractive polaron branch is protected by the pairing gap and becomes more robust at finite momentum. It remains as a delta-function peak in the impurity spectral function below a threshold $2\Delta$. Above the threshold, the attractive polaron enters the particle-hole continuum and starts to get damped. We predict the polaron energy, residue and effective mass for realistic Bose-Fermi mixtures, where the minority bosonic atoms play the role of impurity. These results are practically useful for future cold-atom experiments on crossover polarons.

Bose polaron in a quantum fluid of light

We study the Bose polaron problem in a nonequilibrium setting, by considering an impurity embedded in a quantum fluid of light realized by exciton-polaritons in a microcavity, subject to a coherent drive and dissipation on account of pump and cavity losses. We obtain the polaron effective mass, the drag force acting on the impurity, and determine polaron trajectories at a semiclassical level. We find different dynamical regimes, originating from the unique features of the excitation spectrum of driven-dissipative polariton fluids, in particular a non-trivial regime of acceleration against the flow. Our work promotes the study of impurity dynamics as an alternative testbed for probing superfluidity in quantum fluids of light.

Fröhlich polaron effective mass and localization length in cubic materials: Degenerate and anisotropic electronic bands

Polarons, that is, charge carriers correlated with lattice deformations, are ubiquitous quasiparticles in semiconductors, and play an important role in electrical conductivity. To date most theoretical studies of so-called large polarons, in which the lattice can be considered as a continuum, have focused on the original Fr\"ohlich model: a simple (non-degenerate) parabolic isotropic electronic band coupled to one dispersionless longitudinal optical phonon branch. The Fr\"ohlich model allows one to understand characteristics such as polaron formation energy, radius, effective mass and mobility. Real cubic materials, instead, have electronic band extrema that are often degenerate or anisotropic and present several phonon modes. In the present work, we address such issues. We keep the continuum hypothesis inherent to the large polaron Fr\"ohlich model, but waive the isotropic and non-degeneracy hypotheses, and also include multiple phonon branches. For polaron effective masses, working at the lowest order of perturbation theory, we provide analytical results for the case of anisotropic electronic energy dispersion, with two distinct effective masses (uniaxial) and numerical simulations for the degenerate 3-band case, typical of III-V and II-VI semiconductor valence bands. We also deal with the strong-coupling limit, using a variational treatment: we propose trial wavefunctions for the above-mentioned cases, providing polaron radii and energies. Then, we evaluate the polaron formation energies, effective masses and localisation lengths using parameters representative of a dozen II-VI, III-V and oxide semiconductors, for both electron and hole polarons...In the non-degenerate case, we compare the perturbative approach with the Feynman path integral approach in characterisizing polarons in the weak coupling limit...

Finite-range effects in the unitary Fermi polaron

Quantum Monte Carlo techniques are employed to study the properties of polarons in an ultracold Fermi gas, at $T=0$, and in the unitary regime using both a zero-range model and a square-well potential. For a fixed density, the potential range is varied and results are extrapolated and compared against a zero-range model. A discussion regarding the choice of an interacting potential with a finite range is presented. We compute the polaron effective mass, the polaron binding energy, and the effective coupling between them. The latter is obtained using the Landau-Pomeranchuk's weakly interacting quasiparticle model. The contact parameter is estimated by fitting the pair distribution function of atoms in different spin states.

External electric and magnetic field effects on the polaron in a wurtzite nitride nanowire embedded in a nonpolar matrix

We examine the Frohlich polaron problem in wurtzite nitride cylindrical nanowire embedded in a nonpolar matrix within the framework of the Lee–Low–Pines variational approach. The effects of the external electric and magnetic fields and quantum-size confinement on polaron self-energy and effective mass due to electron interactions with both quasiconfined and interface optical phonons are investigated. The numerical results obtained for wurtzite GaN material are discussed in comparison with the zinc-blende structure cylindrical nanowires. The estimation of contributions of different phonon modes reveal that interface optical phonons are much more important in narrow wires. It is found that the electric field has a relatively pronounced influence on the polaron self-energy and effective mass, while the effect of the magnetic field is small. The obtained results will be of importance in further study of the phonon-assisted electro-optical properties in wurtzite semiconductor low-dimensional structures.

Cooperative origin of proton pair diffusivity in yttrium substituted barium zirconate

Proton conduction is an important property for fuel cell electrolytes. The search for molecular details on proton transport is an ongoing quest. Here, we show that in hydrated yttrium doped barium zirconate using X-ray and neutron diffraction that protons tend to localize near the dopant yttrium as a conjugated superstructure. The proton jump time measured using quasi-elastic neutron scattering follows the Holstein-Samgin polaron model, revealing that proton hopping is weakly coupled to the high-frequency O-H stretching motion, but strongly coupled to low-frequency lattice phonons. The ratio of the proton polaron effective mass, m*, and the proton mass is m*/m = 2, when coupled to the Zr-O stretching mode, giving experimental evidence of proton pairing in perovskites, as a result of proton-phonon coupling. Possible pathways of a proton pair are provided through Nudge Elastic Band calculations. The pairing of protons, when jumping, is discussed in context of a cooperative protonic charge transport process.

The effective mass of the polaron considering the Rashba effect in a weak triangular polar slab

Taking into account the interaction of the electron with bulk longitudinal-optical and the Rashba effect brought by the spin–orbit interaction, we have studied the effective mass ( $$ m^{*} $$ ) of the strong coupling polaron in semiconductor weak triangular polar slab. Using the method of Green’s function, $$ m^{*} $$ has been derived as a function of slab thickness $$ L_{z} $$ , the velocity $$ u $$ and the coupling constant $$ \alpha $$ . Numerical results showed that the interactions between the orbit and the spin directions will affect $$ m^{*} $$ .

The polaron at strong coupling

We review old and new results on the Fröhlich polaron model. The discussion includes the validity of the (classical) Pekar approximation in the strong coupling limit, quantum corrections to this limit, as well as the divergence of the effective polaron mass.

Lifetime and dynamics of polaron and bipolaron in graphene nanoribbon under laser

In this paper, we have investigated the lifetime, mobility and effective mass of polaron and bipolaron in graphene under laser field by using the well-known Lee–Low–Pines transformations. In this study, it is seen that the laser affects mostly the dynamics parameters of polaron and bipolaron in graphene. We found that the laser reduces the lifetime of the polaron in the fundamental state and increases it in its excited state. The excited polaron survives to the effects of laser more than the excited bipolaron. However, the polaron and bipolaron in the fundamental state have about the same laser sensitivity. The polaron and bipolaron in graphene become less heavy; under laser, they get massless. Polaron and bipolaron present a good mobility as charge carriers in the presence of laser effect.

Effective mass of strong-coupling polaron in polar slab considering the Rashba effect induced by LLP method

On the basis of Huybrechts’ strong-coupling polaron model, the Tokuda modified linear-combination operator method and the unitary transformation method were used to study the properties of the strong-coupling polaron in a polar slab considering the influence of the Rashba effect, which is caused by the spin–orbit interaction, with the triangular quantum well. Numerical calculation on the KCl, as an example, is performed. The expression for the effective mass(m±*) of the polaron as a function of the slab thickness (d), the velocity (u), and the coupling constant (α) was derived. Numerical results show that the interactions between the orbit and the spin with different directions have different effects on the m±* of the polaron.