Showing papers on "Bipolaron published in 2021"
TL;DR: In this article, a mean-field theory for heavy polarons in a one-dimensional Bose gas is presented, which is based on a nonperturbative theory and complemented with exact numerical simulations.
Abstract: Bose polarons, quasiparticles composed of mobile impurities surrounded by cold Bose gas, can experience strong interactions mediated by the many-body environment and form bipolaron bound states. Here we present a detailed study of heavy polarons in a one-dimensional Bose gas by formulating a nonperturbative theory and complementing it with exact numerical simulations. We develop an analytic approach for weak boson-boson interactions and arbitrarily strong impurity-boson couplings. Our approach is based on a mean-field theory that accounts for deformations of the superfluid by the impurities and in this way minimizes quantum fluctuations. The mean-field equations are solved exactly in the Born-Oppenheimer approximation, leading to an analytic expression for the interaction potential of heavy polarons, which is found to be in excellent agreement with quantum Monte Carlo (QMC) results. In the strong coupling limit, the potential substantially deviates from the exponential form valid for weak coupling and has a linear shape at short distances. Taking into account the leading-order Born-Huang corrections, we calculate bipolaron binding energies for impurity-boson mass ratios as low as 3 and find excellent agreement with QMC results.
21 citations
TL;DR: It is shown that for one particular push-pull material, the charge carriers created by doping are entirely non-conductive bipolarons and not single polarons, and that transient absorption spectroscopy following excitation in the infrared can readily distinguish the two types of charge carriers.
Abstract: Molecular dopants are often added to semiconducting polymers to improve electrical conductivity. However, the use of such dopants does not always produce mobile charge carriers. In this work, ultrafast spectroscopy is used to explore the nature of the carriers created following doping of conjugated push-pull polymers with both F4 TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) and FeCl3 . It is shown that for one particular push-pull material, the charge carriers created by doping are entirely non-conductive bipolarons and not single polarons, and that transient absorption spectroscopy following excitation in the infrared can readily distinguish the two types of charge carriers. Based on density functional theory calculations and experiments on multiple push-pull conjugated polymers, it is argued that the size of the donor push units determines the relative stabilities of polarons and bipolarons, with larger donor units stabilizing the bipolarons by providing more area for two charges to co-reside.
17 citations
TL;DR: In this article, the polaronic properties of impurities immersed in a correlated trapped one-dimensional Bose-Bose mixture were investigated, where the impurity residue peak and strength of induced interactions can be controlled by varying the coupling of the impurities to the individual bosonic components.
Abstract: We unravel the polaronic properties of impurities immersed in a correlated trapped one-dimensional Bose-Bose mixture. This setup allows the impurities to couple either attractively or repulsively to a specific host, thus offering a highly flexible platform for steering the emergent polaronic properties. Specifically, the impurity residue peak and strength of induced interactions can be controlled by varying the coupling of the impurities to the individual bosonic components. In particular, it is possible to maintain the quasiparticle character for larger interaction strengths as compared to the case of impurities immersed in a single bosonic species. We explicate a hierarchy of the polaron binding energies in terms of the impurity-medium interactions, thereby elucidating the identification of the polaronic resonances in recent experimental radio-frequency schemes. For strong attractive impurity-medium couplings, bipolaron formation is captured. Our findings pave the way for continuously changing the quasiparticle character, under the impact of trap effects, while exposing the role of correlations in triple-mixture settings.
13 citations
TL;DR: In this paper, the authors employ classical Monte Carlo simulations to study a semiclassical three-orbital model with off-diagonal $e$-ph interactions and demonstrate the existence of (bi)polaron correlations that persists in the model at high temperatures and for hole doping away from the bond-disproportionated insulating phase.
Abstract: Bismuth perovskites $A{\mathrm{BiO}}_{3}$ ($A$ = Sr, Ba) host a variety of peculiar phenomena including bond-disproportionated insulating phases and high-temperature superconductivity upon hole doping. While the mechanisms underlying these phenomena are still debated, off-diagonal electron-phonon ($e$-ph) coupling originating from the modulation of the orbital overlaps has emerged as a promising candidate. Here, we employ classical Monte Carlo simulations to study a semiclassical three-orbital model with off-diagonal $e$-ph interactions. We demonstrate the existence of (bi)polaron correlations that persists in the model at high temperatures and for hole doping away from the bond-disproportionated insulating phase. Using a spatiotemporal regression analysis between various local quantities and the lattice degrees of freedom, we also identify the similarity between heating- and doping-induced melting of a bond-disproportionated insulator at a microscopic level. Our results imply that (bi)polaron physics can be a unifying concept that helps us understand the rich bismuth perovskite phase diagram.
11 citations
TL;DR: In this article, the authors investigate whether unusual properties of PSSH polarons depend on the type of the displacement-modulated hopping and to what degree they survive in higher dimensions.
Abstract: Polarons with different types of electron-phonon coupling have fundamentally different properties. When the dominant interaction is between the electron density and lattice displacement, the momentum of the ground state does not change and the polaron gets exponentially heavy at strong coupling. In contrast, one-dimensional Peierls/Su-Schrieffer-Heeger (PSSH) polarons with interaction originating from displacement-modulated hopping feature a shift of the ground-state momentum to finite values and moderate values of effective mass as coupling is increased [D. J. J. Marchand et al., Phys. Rev. Lett. 105, 266605 (2010)]. Based on Diagrammatic Monte Carlo method, we investigate whether unusual properties of PSSH polarons depend on the type of the displacement-modulated hopping and to what degree they survive in higher dimension. We study two different PSSH models: with bosonic degrees of freedom residing on sites (model A) and bonds (model B) of the two-dimensional square lattice. For model A, we find that in both adiabatic and intermediate regimes, the momentum of the ground state experiences a continuous transition from zero to a finite value as a function of coupling strength. The transition is driven by quadratic instability of the dispersion function, implying that effective mass diverges at the critical point, and then decreases in an anisotropic fashion with increasing coupling. Unexpectedly, for model B, the momentum of the ground state always stays at zero and the effective mass increases monotonously with coupling. The increase is far from exponential and tends to level off at strong interaction, resulting in relatively light polarons. Having light polarons in the strong coupling regime is crucial for the bipolaron mechanism of high-temperature superconductivity [J. Sous, M. Chakraborty, R. V. Krems, and M. Berciu, Phys. Rev. Lett. 121, 247001 (2018).]
9 citations
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TL;DR: In this paper, a weakly-interacting one-dimensional Bose gas with two impurities coupled locally to the boson density was studied and the quantum contribution to the induced interaction was analyzed.
Abstract: We study a weakly-interacting one-dimensional Bose gas with two impurities coupled locally to the boson density. We derive analytical results for the induced interaction between the impurities at arbitrary coupling and separation $r$. At $r\lesssim \xi$, where $\xi$ denotes the healing length of the Bose gas, the interaction is well described by the mean-field contribution. Its form changes as the coupling is increased, approaching a linear function of $r$ at short distances in the regime of strong coupling. The mean-field contribution decays exponentially at arbitrary coupling for $r\gg\xi$. At such long distances, however, the effect of quantum fluctuations becomes important, giving rise to a long-ranged quantum contribution to the induced interaction. At longest distances it behaves as $1/r^3$, while at strong coupling we find an intermediate distance regime with a slower decay, $1/r$. The quantum contribution in the crossover regime is also calculated. The induced interaction between impurities (i.e., polarons) is attractive and leads to the formation of their bound state, known as bipolaron. We discuss its binding energy.
8 citations
01 Jan 2021
TL;DR: In this paper, a theory of translation invariant polarons and bipolarons based on the theory of squeezed vacuum wave functions is presented, which explains a large number of experiments on the thermodynamic, spectroscopic and transport characteristics of high-temperature superconductors, Josephson tunneling, angle-resolved photoemission spectroscopy, neutron scattering, etc.
Abstract: The monograph presents the theory of translation-invariant polarons and bipolarons based on the theory of squeezed vacuum wave functions. It is shown that the Tulub ansatz, which establishes a connection between the generalized Bogolyubov transformation with the unitary squeezed operator gives a solution to the spectral problem for a bipolaron. The solutions obtained are used to construct a theory of superconductivity based on the Froehlich Hamiltonian with a strong electron-phonon interaction. The role of Cooper pairs in it is played by TI bipolarons of spatially delocalized electrons with a small correlation length. The theory developed explains a large number of experiments on the thermodynamic, spectroscopic and transport characteristics of high-temperature superconductors, Josephson tunneling, angle-resolved photoemission spectroscopy, neutron scattering, etc. The book is intended for physicists and mathematicians who work in the field of the theory of condensed matter, as well as graduate students and senior students of universities.
8 citations
TL;DR: In this paper, a comparative study of polyaniline (PANI) and poly(N-methylaniline) (PNMA) has been performed by means of Raman spectroelectrochemical technique at 633nm and 785nm laser line excitations.
6 citations
TL;DR: In this article, the ground and first excited states of the bipolaron were obtained using the variational method and it was shown that the optical absorption of a bipolaron in graphene depends strongly on the laser parameter.
Abstract: In this work, we are studying thermodynamics properties and optical absorption of bipolaron in graphene under a laser field using the variational method. We obtain the ground and first excited states of the bipolaron which strongly depend on laser parameter and graphene characteristics. It is seen that the optical absorption of a bipolaron in graphene depends strongly on the laser parameter. We observed that laser reduces the absorption of photons by laser. The latter also reinforces the electron–electron bound state in graphene leading to its strong energy storage capabilities. Our results show that the electron–electron interaction and laser parameters are important to control the disorder of the system. Due to its intensity and frequency, laser contribution is highest on the entropy, internal energy and specific heat, while the contribution of phonon modes is minimum on these thermodynamics properties suggesting the importance of laser on graphene structures. The results obtained are efficient because bipolaron is well formed and stable in graphene. This investigation may enlighten the understanding of the charge transport mechanism in graphene nanomaterials.
5 citations
5 citations
TL;DR: In this paper, morphological, topographical, magnetoresistance and thermoelectric properties of nanobulk assembly of sulfur doped Sb2Se3nanotubes synthesized by novel microwave assisted solvothermal process are investigated and reported.
TL;DR: In this paper, a one-pot, one-step methodology to synthesize isomeric polythiophene (IPTh) possessing 2,2, 2,4 and 5,4 linkages was reported.
Abstract: Herein we have reported for the first time a one-pot, one step methodology to synthesize isomeric polythiophene (IPTh) possessing 2,2, 2,4 and 5,4 linkages. The method of polymerization of thiophene to IPTh involved reacting thiophene with DDQ in the presence of concentrated H2SO4 at 40 °C and the polymerization is completed in 10 minutes. The synthesized IPTh was characterized by various spectroscopic and microscopic techniques. The formation of polaron and bipolaron in an iodine doped sample (IPTh-I2) has been confirmed by IR, Raman and UV-Vis spectra. The electrical conductivity of the synthesized IPTh and IPTh-I2 have been studied by impedance spectroscopy and found to be ∼10−5 and 10−3 S cm−1 respectively. IPTh exhibits an excellent thermal stability up to 150 °C, and low optical band gap of 3.49 eV suitable for photovoltaic applications. The weight average molecular weight of IPTh has been found to be 18.636 kDa, and it has a better post functionalization capability and hence wider scope than polythiophene (PTh).
TL;DR: In this article, a broad band impedance spectroscopy (BSIS) was used to detect single and bipolaron hopping in chalcogenide glasses and its interdependencies on thermal history of the glass samples.
Abstract: We report direct evidence for the characteristic behavior of single and bipolarons in chalcogenide glasses by using broad band impedance spectroscopy. The measured ac conductivity, σ(f, T) of Te based glasses exhibit distinct behavior from those reported in amorphous tetrahedral semiconductors depending on the temperature and frequency. At low temperatures, the measured conductivity is exclusively due to the bipolarons between two charged defect centers. On the other hand, at high temperatures we find in addition to bipolaronic contribution, the single polaron hopping between a charged and neutral defect centers. The behavior of both types of charge carrier (single and bipolaron) shows the distinct relaxation characteristics within the measured frequency window. Remarkably, we observe existence of neutral defect centers with large concentration in tellurium-based chalcogenide glass under dark (normal) conditions revealed by the electron spin resonance (ESR) spectroscopy, which is an essential component for the single polaron hopping process. The estimated neutral defect centers from the dc conductivity measurements are in agreement with those derived from the ESR results. Further, we found that the effective correlation energy (Ueff) becomes less negative in glasses which exhibit single polaron hopping than the glasses found to exhibit typical bipolaronic conduction. The present work unequivocally demonstrates the characteristic behavior of single and bipolarons in chalcogenide glasses and its interdependence on thermal history of the glass samples.
TL;DR: In this article, the nuclear spin fluctuations lead to the electric current noise in mesoscopic samples of organic semiconductors, which show the pronounced magnetoresistance in weak magnetic fields.
Abstract: We demonstrate that the nuclear spin fluctuations lead to the electric current noise in mesoscopic samples of organic semiconductors, which show the pronounced magnetoresistance in weak magnetic fields. For the bipolaron and electron-hole mechanisms of organic magnetoresistance, the current noise spectrum consists of the high-frequency peak related to the nuclear spin precession in the Knight field of the charge carriers and the low-frequency peak related to the nuclear spin relaxation. The shape of the spectrum depends on the external magnetic and radio frequency fields, which allows one to prove the role of the nuclei in the magnetoresistance experimentally.
TL;DR: In this paper, the shape of redox peaks related to the W(VI)/W(V) couple in the CVs of WO3 and the composite PEDOT/WO3 films were analyzed with respect to changes of the shapes of the spectra and characteristic band positions.
Abstract: Cyclic voltammograms and optical absorption spectra of PEDOT/WO3 composite films were recorded in order to identify possible interactions and modes of improved performance of the composite as compared to the single materials. Changes in the shape of redox peaks related to the W(VI)/W(V) couple in the CVs of WO3 and the composite PEDOT/WO3 films indicate electrostatic interactions between the negatively charged tungsten oxide species and the positively charged conducting polymer. Smaller peak separation suggests a more reversible redox process due to the presence of the conducting polymer matrix, accelerating electron transfer between tungsten ions. Electronic absorption spectra of the materials were analyzed with respect to changes of the shapes of the spectra and characteristic band positions. There are no noticeable changes in the position of the electronic absorption bands of the main chromophores in the electronic spectra of the composite film. Obviously, the interactions accelerating the redox performance do not show up in the optical spectra. This suggests that the existing electrostatic interactions in the composite do not significantly change the opto-electronic properties of components of the composite but resulted in the redistribution of fractions of polaron and bipolaron forms in the polymer.
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TL;DR: In this article, the Born-Oppenheimer approximation was improved by accounting for boson-boson interactions already on the mean-field level, which can be found in weak coupling regime and for sufficiently large impurity separations.
Abstract: Impurities immersed into a surrounding ultra-cold Bose gas experience interactions mediated by the surrounding many-body environment. If one focuses on two impurities that are sufficiently close to each other, they can form a bipolaron pair. Here, we discuss how the standard methods based on linearizing the condensate field lead to results only valid in the weak coupling regime and for sufficiently large impurity separations. We show how those shortcomings can be remedied within the Born-Oppenheimer approximation by accounting for boson-boson interactions already on the mean-field level.
TL;DR: In this paper, the polaronic version of the generalized tight-binding method was used to investigate a multiband two-dimensional model taking into account both Holstein and Su-Schrieffer-Heeger types of electron-lattice contributions.
Abstract: We consider how electron-phonon interaction influences the insulator-metal transitions driven by doping in the strongly correlated system. Using the polaronic version of the generalized tight-binding method, we investigate a multiband two-dimensional model taking into account both Holstein and Su-Schrieffer-Heeger types of electron-lattice contributions. For adiabatic ratio of the hopping parameter and the phonon field energy, different types of band structure evolution are observed in a wide electron-phonon parameter range. We demonstrate the relationship between transition features and such properties of the system as the polaron and bipolaron crossovers, pseudogap behavior of various origin, orbital selectivity, and the redistribution of the spectral weight due to the electron-phonon interaction.
TL;DR: In this paper, a theory of a pseudogap phase of high-temperature superconductors where current carriers are translation invariant bipolarons is developed, and a temperature T * of a transition from a pseudo-ogap to a normal one is calculated.
Abstract: A theory of a pseudogap phase of high-temperature superconductors where current carriers are translation invariant bipolarons is developed. A temperature T* of a transition from a pseudogap phase to a normal one is calculated. For the temperature of a transition to the pseudogap phase, the isotope coefficient is found. It is shown that the results obtained, in particular, the possibility of negative values of the isotope coefficient, are consistent with the experiment. New experiments on the influence of the magnetic field on the isotope coefficient are proposed.
TL;DR: In this article, the Lee-Low-Pines-Huybrechts method and the Tokuda linear combination operator method were used to investigate the optical bipolaron properties in the symmetric quantum dot.
TL;DR: In this article, a theory of a pseudogap phase of high-temperature superconductors where current carriers are translation invariant bipolarons is developed, and a temperature T * of a transition from a pseudo-ogap to a normal one is calculated.
Abstract: A theory of a pseudogap phase of high-temperature superconductors where current carriers are translation invariant bipolarons is developed. A temperature T* of a transition from a pseudogap phase to a normal one is calculated. For the temperature of a transition to the pseudogap phase, the isotope coefficient is found. It is shown that the results obtained, in particular, the possibility of negative values of the isotope coefficient are consistent with the experiment. New experiments on the influence of the magnetic field on the isotope coefficient are proposed.
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TL;DR: In this paper, a variational calculation was performed to probe the existence of Fr{´o´hlich bipolarons in polar semiconductors. But they were only able to interpolate between the weak and strong coupling limits of the electron-phonon interaction and were not aware of any existing materials at these parameter values.
Abstract: Following a resurgence of interest in dilute superconductivity in polar semiconductors, we perform a variational calculation to probe the existence of Fr{\"o}hlich bipolarons in these materials. Our solution is capable of interpolating between the weak- and strong-coupling limits of the electron-phonon interaction. We predict bipolaron formation in solely the strong-coupling regime, and we are not aware of any existing materials at these parameter values. However, imposing an extrinsic electron size constraint to mimic confinement on the sub-micron scale produces binding in new parts of the phase diagram, including at weak coupling, within reach of the near-ferroelectric perovskites.
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TL;DR: A correlation between the theories of superconductivity based on the concept of charge density waves (CDW) and the translation invariant (TI) bipolaron theory is established in this paper, where it is shown that CDW are originated from TI-bipolaron states in the pseudogap phase due to Kohn anomaly and form a pair density wave (PDW) for wave vectors corresponding to nesting.
Abstract: A correlation is established between the theories of superconductivity based on the concept of charge density waves (CDW) and the translation invariant (TI) bipolaron theory. It is shown that CDW are originated from TI-bipolaron states in the pseudogap phase due to Kohn anomaly and form a pair density wave (PDW) for wave vectors corresponding to nesting. Emerging in the pseudogap phase, CDW coexist with superconductivity at temperatures below that of superconducting transition while their wave amplitudes decrease as a Bose condensate is formed from TI-bipolarons, vanishing at zero temperature.
TL;DR: In this paper, the authors studied the optical signature of bipolaron and its effects on the bandgap modulation in the single-layer Transition Metal Dichalcogenides (TMDs) under magnetic field.
Abstract: We studied the optical signature of bipolaron and its effects on the bandgap modulation in the single-layer Transition Metal Dichalcogenides (TMDs) under magnetic field. Using the Huybrecht method, we derived the ground state energies in the modified zero Landau levels for all Frohlich coupling constants. We take into account both intrinsic longitudinal optical phonon modes and surface optical phonon modes induced by the polar substrate. We observed that the higher the coupling strength, the stronger is the magnetic field effect. The highest amplitude of the bandgap modulation is obtained for the MoS2 monolayer and the lowest with the WSe2 monolayer. We also found that the bipolaron is stable in TMDs. It is seen that the optical absorption presents the threshold values and respectively increases for WSe2, MoSe2, WS2 and MoS2.
TL;DR: In this article, the authors performed an investigation concerning bipolaron dynamics in armchair graphene nanoribbons (AGNRs) under the influence of different electric fields and electron-phonon coupling regimes.
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TL;DR: In this article, a sign-free Monte Carlo method based on the pathintegral formulation of the particle sector in combination with either the diagrammatic or Fock-path-integral representation of the phonon sector is proposed.
Abstract: Polarons originating from phonon displacement modulated hopping have relatively light masses and, thus, are of significant current interest as candidates for bipolaron mechanism of high-temperature superconductivity [Phys. Rev. Lett. {\bf 121}, 247001 (2018)]. We observe that the bond model, when the dominant coupling comes from atomic vibrations on lattice bonds, can be solved by efficient sign-free Monte Carlo methods based on the path-integral formulation of the particle sector in combination with either the (real-space) diagrammatic or Fock-path-integral representation of the phonon sector. We introduce the corresponding algorithms and provide illustrative results for bipolarons in two dimensions. The results suggest that the route towards high-temperature superconductivity (if any) in the multiparametric space of the model lies between the Scylla of large size of moderately light bipolarons and Charybdis of large mass of compact bipolarons. As a result, on-site repulsion is helping $s$-wave superconductivity in sharp contrast with existing expectations.
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TL;DR: In this article, it was shown that Ni vacancy generation results in the formation of hole polarons localised at the two oxygens next to the vacancy, and the hole bipolaron is converted into a hole polaron well-localized at one O atom.
Abstract: The development of new electrochromic materials and devices, like smart windows, has an enormous impact on the energy efficiency of modern society. One of the crucial materials in this technology is nickel-oxide. Ni-deficient NiO shows anodic electrochromism whose mechanism is still under debate. Using DFT+U calculations, we show that Ni vacancy generation results in the formation of hole polarons localised at the two oxygens next to the vacancy. Upon Li insertion or injection of an extra electron into Ni-deficient NiO, one hole gets filled, and the hole bipolaron is converted into a hole polaron well-localized at one O atom. Furthermore, the calculated absorption coefficients demonstrate that Li insertion/extraction or rather the addition/removal of an extra electron into Ni-deficient NiO can lead to switching between the oxidized (colored) and the reduced (bleached) states. Hence, our results suggest a new mechanism of Ni-deficient NiO electrochromism not related to the Ni2+/Ni3+ transition but based on the formation and annihilation of hole polarons in oxygen p-states.
TL;DR: In this article, the probability of the presence of two electrons at any point in space in a parabolic potential quantum dot under the effect of an external magnetic and electric fields was investigated.
Abstract: In this article, we study the probability of the presence of electrons at any point in space in a parabolic potential quantum dot under the effect of an external magnetic and electric fields. The ground state and the first excited state energies were evaluated using the Pekar-type variational method. Numerical calculations indicate that the application of electric and magnetic fields have effects on the properties of the bipolaron. We also observed that when the system is in the presence of both fields electric and magnetic, the probability of the appearance of the two electrons near the center of the quantum point is greater. In addition, we found that for some values of both fields in the system, we can better control the bipolaron and we can also be able to obtain some polaronic behavior.