In soft-lattice lead-halide perovskites,the polaronic effects involving stabilization of localized charge character by structural deformations and polarizations have an important effect on the properties of functional...In soft-lattice lead-halide perovskites,the polaronic effects involving stabilization of localized charge character by structural deformations and polarizations have an important effect on the properties of functional materials such as the band gap,which has attracted considerable investigations.However,the concept of polaron assisted nonlinear photonics remains largely unexplored,which has a wide range of applications from optoelectronics to telecommunications and quantum technologies.Here,we report the first observation of the polaronic state assisted saturable absorption through subbandgap excitation with a redshift exceeding 60 meV.By combining photoluminescence,transient absorption measurements and density functional theory calculations,we explicate that the anomalous nonlinear saturable absorption under sub-bandgap excitation is caused by the transient picosecond timescale polaronic state formed by strong carrier/excitonphonon coupling effect.The bandgap fluctuation caused by polaron formation can be further tuned through excitonphonon coupling of perovskites with different Young’s modulus.This suggests that we can design targeted soft lattice lead-halide perovskite with a specific structure to effectively manipulate exciton-phonon coupling and exciton-polaron formation.These findings profoundly expand our understanding of exciton-polaronic nonlinear optics physics and provide an ideal platform for developing actively tunable nonlinear photonics applications.展开更多
The effects of exciton-optical phonon interaction on the binding energy and the total and reduced effective masses of an exciton in a cylindrical quantum wire have been investigated. We adopt a perturbative-PLL [T.D. ...The effects of exciton-optical phonon interaction on the binding energy and the total and reduced effective masses of an exciton in a cylindrical quantum wire have been investigated. We adopt a perturbative-PLL [T.D. Lee,F. Low, and D. Pines, Phys. Rev. B90 (1953) 297] technique to construct an effective Hamiltonian and then use a variational solution to deal with the exciton-phonon system. The interactions of exciton with the longitudinal-optical phonon and the surface-optical phonon have been taken into consideration. The numerical calculations for GaAs show that the influences of phonon modes on the exciton in a quasi-one-dimensional quantum wire are considerable and should not be neglected. Moreover the numerical results for heavy- and light-hole exciton are obtained, which show that the polaronic effects on two types of excitons are very different but both depend heavily on the sizes of the wire.展开更多
The electronic structure of iron-pnictide compound superconductor Ba_2Ti_2Fe_2As_4O, which has metallic intermediate Ti_2O layers, is studied using angle-resolved photoemission spectroscopy. The Ti-related bands show ...The electronic structure of iron-pnictide compound superconductor Ba_2Ti_2Fe_2As_4O, which has metallic intermediate Ti_2O layers, is studied using angle-resolved photoemission spectroscopy. The Ti-related bands show a‘peak-dip-hump＇ line shape with two branches of dispersion associated with the polaronic states at temperatures below around 120 K. This change in the spectra occurs along with the resistivity anomaly that was not clearly understood in a previous study. Moreover, an energy gap induced by the superconducting proximity effect opens in the polaronic bands at temperatures below T_c（~21 K）. Our study provides the spectroscopic evidence that superconductivity coexists with polarons in the same bands near the Fermi level, which provides a suitable platform to study interactions between charge, lattice and spin freedoms in a correlated system.展开更多
Feynman variational path integral theory was used to obtain the ground state energy of a polaron in a quantum well in the presence of a Coulomb potential for arbitrary values of the electron phonon coupling constan...Feynman variational path integral theory was used to obtain the ground state energy of a polaron in a quantum well in the presence of a Coulomb potential for arbitrary values of the electron phonon coupling constant α . Numerical and analytical results showed that the energy shift was more sensitive to α than to the Coulomb binding parameter ( β ) and increased with the decrease of effective quantum well width l Z . It was interesting that due to the electronic confinement in the quasi 2D (quantum well) structures, the lower bound of the strong coupling regime was shifted to smaller values of α . Comparison of the polaron in the quantum well with that in the quantum wire or dot showed that the polaronic effect strengthened with decrease of the confinement dimension.展开更多
The planar oxygen isotope effect on Tc observed in copper oxide superconductors is remarkable in that it increases from near nil at optimal doping to a value twice that derived from BCS theory in the underdoped region...The planar oxygen isotope effect on Tc observed in copper oxide superconductors is remarkable in that it increases from near nil at optimal doping to a value twice that derived from BCS theory in the underdoped region. This behavior is quantitatively followed by a formula proposed by Kresin and Wolf in 1994 for polarons along the c-axis. Herein it is revisited in a more transparent way, and it is pointed out that the heterogeneity of pairing is relevant and has to be taken into account to explain the unusual planar isotope effects on Tc in underdoped cuprates.展开更多
The experimental realization of observable phonon angular momentum(PAM)in feasible systems using relatively simple methods remains a critical challenge.Motivated by the chiral-induced spin selectivity effect,this stud...The experimental realization of observable phonon angular momentum(PAM)in feasible systems using relatively simple methods remains a critical challenge.Motivated by the chiral-induced spin selectivity effect,this study explores the generation of PAM during the transport of electrically driven polarons along a singlestranded helix structure.We demonstrate that the motion of a polaron under an applied electric field inherently induces a finite PAM,exhibiting drift-locked behavior between the PAM and the polaron.By analyzing the time evolution of PAM distribution at each site,we identify the observed PAM as a natural consequence of coherent superposition between lattice waves,in which the chiral structure selectively determines the direction of induced PAM.Furthermore,we examine the roles of two types of electron-phonon interactions and structural periodicity in modulating PAM.These findings highlight the potential of chiral molecules as platforms for PAM generation and offer new insights into developing phonon-spin-based devices for information processing and transmission.展开更多
Since the preliminary work of Anisimov and co-workers,the Hubbard corrected DFT+U functional has been used for predicting properties of correlated materials by applying on-site effective Coulomb interactions to specif...Since the preliminary work of Anisimov and co-workers,the Hubbard corrected DFT+U functional has been used for predicting properties of correlated materials by applying on-site effective Coulomb interactions to specific orbitals.However,the determination of the Hubbard U parameter has remained under intense discussion despite the multitude of approaches proposed.Here,we define a selection criterion based on the use of polaronic defect states for the enforcement of the piecewise linearity of the total energy upon electron occupation.A good agreement with results from piecewise linear hybrid functionals is found for the electronic and structural properties of polarons,including the formation energies.The values of U determined in this way are found to give a robust description of the polaron energetics upon variation of the considered state.In particular,we also address a polaron hopping pathway,finding that the determined value of U leads to accurate energetics without requiring a configurational-dependent U.It is emphasized that the selection of U should be based on physical properties directly associated with the orbitals to which U is applied,rather than on more global properties such as band gaps and band widths.For comparison,we also determine U through a well-established linear-response scheme finding noticeably different values of U and consequently different formation energies.Possible origins of these discrepancies are discussed.As case studies,we consider the self-trapped electron in BiVO_(4),the self-trapped hole in MgO,the Li-trapped hole in MgO,and the Al-trapped hole inα-SiO_(2).展开更多
Charge transport in organic molecular crystals (OMCs) is conventionally categorized into two limiting regimes − band transport,characterized by weak electron-phonon (e-ph) interactions,and charge hopping due to locali...Charge transport in organic molecular crystals (OMCs) is conventionally categorized into two limiting regimes − band transport,characterized by weak electron-phonon (e-ph) interactions,and charge hopping due to localized polarons formed by strong e-ph interactions.However,between these two limiting cases there is a less well understood intermediate regime where polarons are present but transport does not occur via hopping.Here we show a many-body first-principles approach that can accurately predict the carrier mobility in this intermediate regime and shed light on its microscopic origin.Our approach combines a finite-temperature cumulant method to describe strong e-ph interactions with Green-Kubo transport calculations.We apply this parameter-free framework to naphthalene crystal,demonstrating electron mobility predictions within a factor of 1.5−2 of experiment between 100 and 300 K.Our analysis reveals the formation of a broad polaron satellite peak in the electron spectral function and the failure of the Boltzmann equation in the intermediate regime.展开更多
We hereby report the room-temperature structural and optical characterization of RECr_(0.85)Mn_(0.15)O_(3)(RECMO,RE=Ho,Gd and Pr)compounds synthesized by the auto-combustion sol-gel route.Their low temperature dielect...We hereby report the room-temperature structural and optical characterization of RECr_(0.85)Mn_(0.15)O_(3)(RECMO,RE=Ho,Gd and Pr)compounds synthesized by the auto-combustion sol-gel route.Their low temperature dielectric properties are also presented.The RECMO compounds crystallize in an orthorhombic Pbnm symmetry with an average grain size range of 51-80 nm.Structural analysis reveals an increase in the structural distortion compared to that of the undoped bulk compounds.Optical measurements exhibit a significant reduction in bandgap values for RECMO nanoparticles when compared with their undoped bulk compounds.Further,from the absorbance measurements various optical parameters such as skin depth,extinction coefficient,refractive index and optical conductivity were also calculated.The dielectric analysis confirms the lower values of the dielectric permittivity and dielectric loss than those of their corresponding bulk compounds.AC conductivity versus frequency and temperature data are fitted according to the Jonscher's power law and Arrhenius law,respectively.The small polaron hopping is responsible for the electric conduction in these compounds.The tunability of the optical and dielectric properties as a result of substitution and particle size reduction makes these materials useful for various potential applications in photocatalysis,optoelectronics and low permittivity dielectrics.展开更多
Polarons are widely considered to play a crucial role in the charge transport and photocatalytic performance of materials,but the mechanisms of their formation and the underlying driving factors remain a matter of con...Polarons are widely considered to play a crucial role in the charge transport and photocatalytic performance of materials,but the mechanisms of their formation and the underlying driving factors remain a matter of controversy.This study delves into the formation of polarons in different crystalline forms of TiO_(2) and their connection with the materials'structure.By employing density functional theory calculations with on-site Coulomb interaction correction(DFT+U),we provide a detailed analysis of the electronic polarization behavior in the anatase and rutile forms of TiO_(2).We focus on the polarization properties of defect-induced and photoexcited excess electrons on various TiO_(2) surfaces.The results reveal that the defect electrons can form small polarons on the anatase TiO_(2)(101)surface,while on the rutile TiO_(2)(110)surface,both small and large polarons(hybrid-state polarons)are formed.Photoexcited electrons are capable of forming both small and large polarons on the surfaces of both crystal types.The analysis indicates that the differences in polaron distribution are primarily determined by the intrinsic properties of the crystals;the structural and symmetry differences between anatase and rutile TiO_(2) lead to the distinct polaron behaviors.Further investigation suggests that the polarization behavior of defect electrons is also related to the arrangement of electron orbitals around the Ti atoms,while the polarization of photoexcited electrons is mainly facilitated by the lattice distortions.These findings elucidate the formation mechanisms of different types of polarons and may contribute to understanding the performance of TiO_(2)in different fields.展开更多
As typical strongly correlated electronic materials, manganites show rich magnetic phase diagrams and electronic structures depending on the doped carrier density. Most previous relevant studies of doped manganites re...As typical strongly correlated electronic materials, manganites show rich magnetic phase diagrams and electronic structures depending on the doped carrier density. Most previous relevant studies of doped manganites rely on the cubic/orthorhombic structures, while the hexagonal structure is much less studied. Here first-principles calculations are employed to investigate the magnetic and electronic structures of La-doped 4H-SrMnO_(3). By systematically analyzing the two kinds of La-doped positions, our calculations predict that the doped electron with lattice distortion would prefer to form polarons, which contribute to the local magnetic phase transition, nonzero net magnetization, and semiconducting behavior. In addition, the energy gap decreases gradually with increasing doping concentration, indicating a tendency of insulator–metal transition.展开更多
We conduct a theoretical study on the properties of a bound polaron in a quantum well under an electric field using linear combination operator and unitary transformation methods, which are valid in the whole range of...We conduct a theoretical study on the properties of a bound polaron in a quantum well under an electric field using linear combination operator and unitary transformation methods, which are valid in the whole range of electron-LO phonon coupling. The changing relations between the ground-state energy of the bound polaron in the quantum well and the Coulomb bound potential, the electric field strength, and the well width are derived. The numerical results show that the ground-state energy increases with the increase of the electric field strength and the Coulomb bound potential and decreases as the well width increases.展开更多
The properties of a bound polaron in a parabolic quantum dot with weak electron-LO-phonon coupling under a Coulomb field are studied. The ground state energy of the bound polaron is derived by using a linear combinati...The properties of a bound polaron in a parabolic quantum dot with weak electron-LO-phonon coupling under a Coulomb field are studied. The ground state energy of the bound polaron is derived by using a linear combination operator and the perturbation method. The influence of the interaction between phonons with different wave vectors in the recoil process on the ground state energy of the bound polaron is discussed. Numerical calculations are performed,and the results show that the ground state energy increases significantly as the effective confinement length of the quantum dot decreases,considering of the interaction between phonons. When l0〉1.0, the influence of the interaction between phonons on the ground state energy cannot be ignored.展开更多
The binding energy of a bound polaron in a finite parabolic quantum well is studied theoretically by a fractional- dimensional variational method. The numerical results for the binding energies of the bound polaron an...The binding energy of a bound polaron in a finite parabolic quantum well is studied theoretically by a fractional- dimensional variational method. The numerical results for the binding energies of the bound polaron and longitudinal-optical phonon contributions in GaAs/Al0.3 Ga0.7 AS parabolic quantum well structures are obtained as functions of the well width. It is shown that the binding energies of the bound polaron are obviously reduced by the electron-phonon interaction and the phonon contribution is observable and cannot be neglected.展开更多
The ground-state energy and the average number of virtual phonons around the electron of a hydrogenic impurity confined in a parabolic quantum dot are calculated using the squeezed-state variational approach,which is ...The ground-state energy and the average number of virtual phonons around the electron of a hydrogenic impurity confined in a parabolic quantum dot are calculated using the squeezed-state variational approach,which is based on two successive canonical transformations and uses a displaced-oscillator type unitary transformation to deal with the bilinear terms,which are usually neglected.Numerical calculations are carried out in order to study the relation between the ground-state energy and the average number of virtual phonons around the electron of a bound polaron in a parabolic quantum dot with the Coulomb binding parameter.The electron-phonon coupling constant and the confinement length are derived.展开更多
We study spectroscopic signatures of a monochromatic boson mode interacting with a T-shape double quantum dot coupled between the metallic and superconducting leads. Focusing on a weak interdot coupling, we find that ...We study spectroscopic signatures of a monochromatic boson mode interacting with a T-shape double quantum dot coupled between the metallic and superconducting leads. Focusing on a weak interdot coupling, we find that the proximity effect together with the bosonic mode are responsible for the series of Fano-type resonances appearing simultaneously at negative and positive energies. We investigate these interferometric features and discuss their influence on the subgap Andreev conductance taking into account the correlation effects driven by the Coulomb repulsion.展开更多
In contrast to so-called Auger process resulting in electron ejection from oxygen atom of water molecule under X-ray absorption, the coupling of the opposite charges in liquid water leads to polaronic exciton formatio...In contrast to so-called Auger process resulting in electron ejection from oxygen atom of water molecule under X-ray absorption, the coupling of the opposite charges in liquid water leads to polaronic exciton formation. As a result, polaronic exciton stabilized by the structure of water tetrahedron can serve as the reaction center for deuterium creation under X-ray absorption. In this case, X-ray emission spectra of H：O and D20 give a clue for the deciphering of the events followed by X-ray photon absorption. It appears to be that spin-orbit interaction under proton sharing and the interaction between LO （longitudinal optical） phonon and bipolaron in the excited state are responsible for the energy levels determining neutrino energy. The energy gap between the levels with pATe andplle spin configurations of proton and electron is found to be 325.51 cm^-1 in the case of the spin-orbit interaction in polaronic exciton, while 1,556.054 cm^-1 under LO phonon interaction with the proton of the bipolaron producing the change of the nucleus spin direction to the opposite.展开更多
A 2D electron-longitudinal-acoustic-phonon interaction Hamiltonian is derived and used to calculate the groundstate energy of the acoustic polarons in two dimensions. The numerical results for the ground-state energy ...A 2D electron-longitudinal-acoustic-phonon interaction Hamiltonian is derived and used to calculate the groundstate energy of the acoustic polarons in two dimensions. The numerical results for the ground-state energy of the acoustic polarons in two and three dimensions are obtained. The 3D results agree with those obtained by using the Feynman path-integral approach. It is found that the critical coupling constant of the transition from the quasifree state to the self-trapped state in the 2D case is much smaller than in the 3D case for a given cutoff wave-vector. The theory has been used to judge the possibility of the self-trapping for several real materials. The results indicate that the self-trappings of the electrons in AlN and the holes in AlN and GaN are expected to be observed in 2D systems.展开更多
The expression of the ground-state energy of the electron coupled simultaneously with a Coulomb potential and a longitudinal-optical phonon field in parabolic quantum dots and wires is derived within the framework of ...The expression of the ground-state energy of the electron coupled simultaneously with a Coulomb potential and a longitudinal-optical phonon field in parabolic quantum dots and wires is derived within the framework of Feynman variational path integral theory.We obtain a general result with arbitrary electron-phonon coupling constant,Coulomb binding parameters,and confining potential strength,which could be used for further numerical calculation of polaron properties.Moreover,it is shown that all the previous path-integral formulae for free polarons,bound polarons,and polarons confined in parabolic quantum dots and wires can be recovered in the present formalism.展开更多
Opaque thermal barrier materials play a pivotal role in thermal radiation shielding of turbine blades,since the intensity of thermal radiation rapidly increases with the increase of operating temperature of gas turbin...Opaque thermal barrier materials play a pivotal role in thermal radiation shielding of turbine blades,since the intensity of thermal radiation rapidly increases with the increase of operating temperature of gas turbines and has become a new and major concern for the durability of metallic blades.The conventional thermal barrier coating(TBC)materials such as YSZ and Gd_(2)Zr_(2)O_(7),however,are almost translucent to thermal radiation and are unable to protect the blades at such harsh environment.Although searching for new thermal barrier materials is significant,it is still a challenge to make the current TBC materials opaque without significantly modifying the composition or other physical properties.To cope with this challenge,GdMnO_(3) is incorporated as an absorptive second phase into Gd_(2)Zr_(2)O_(7) in this work,which is originally translucent(absorption coefficient 10^(1)-10^(2) m^(-1))in the near-infrared wavelengths.Intriguingly,with less than 5 wt.%GdMnO_(3),the Gd_(2)Zr_(2)O_(7)/GdMnO_(3) becomes opaque to thermal radiation and successfully refrains the rise of thermal conductivity at high temperatures.Meanwhile,the lattice thermal conductivity and mechanical properties are almost unchanged.The small polaron mechanism is confirmed for GdMnO_(3),leading to a high absorption coefficient(>10^(6) m^(-1))for near-infrared radiation.To understand the underling mechanism,a theoretical model is built to estimate the absorption coefficient of the Gd_(2)Zr_(2)O_(7)/GdMnO_(3) composites(>10^(4) m^(-1)).This paper proposes a powerful strategy to design thermal-radiation-shielding TBCs through incorporating minor second-phase particles with high-absorption mechanism,such as polaron excitation.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.62275275,11904239,62422506,12474383,52273202)National Key R&D Program of China(2022YFA1604200)+2 种基金Natural Science Foundation of Hunan Province(Grant Nos.2021JJ40709,2022JJ20080,2024JJ6481)Postgraduate Innovative Project of Central South University(Grant No.CX20230246)supported in part by the High-Performance Computing Center of Central South University and Open Sharing Found for the Large-scale Instruments and Equipment of Central South University.
文摘In soft-lattice lead-halide perovskites,the polaronic effects involving stabilization of localized charge character by structural deformations and polarizations have an important effect on the properties of functional materials such as the band gap,which has attracted considerable investigations.However,the concept of polaron assisted nonlinear photonics remains largely unexplored,which has a wide range of applications from optoelectronics to telecommunications and quantum technologies.Here,we report the first observation of the polaronic state assisted saturable absorption through subbandgap excitation with a redshift exceeding 60 meV.By combining photoluminescence,transient absorption measurements and density functional theory calculations,we explicate that the anomalous nonlinear saturable absorption under sub-bandgap excitation is caused by the transient picosecond timescale polaronic state formed by strong carrier/excitonphonon coupling effect.The bandgap fluctuation caused by polaron formation can be further tuned through excitonphonon coupling of perovskites with different Young’s modulus.This suggests that we can design targeted soft lattice lead-halide perovskite with a specific structure to effectively manipulate exciton-phonon coupling and exciton-polaron formation.These findings profoundly expand our understanding of exciton-polaronic nonlinear optics physics and provide an ideal platform for developing actively tunable nonlinear photonics applications.
文摘The effects of exciton-optical phonon interaction on the binding energy and the total and reduced effective masses of an exciton in a cylindrical quantum wire have been investigated. We adopt a perturbative-PLL [T.D. Lee,F. Low, and D. Pines, Phys. Rev. B90 (1953) 297] technique to construct an effective Hamiltonian and then use a variational solution to deal with the exciton-phonon system. The interactions of exciton with the longitudinal-optical phonon and the surface-optical phonon have been taken into consideration. The numerical calculations for GaAs show that the influences of phonon modes on the exciton in a quasi-one-dimensional quantum wire are considerable and should not be neglected. Moreover the numerical results for heavy- and light-hole exciton are obtained, which show that the polaronic effects on two types of excitons are very different but both depend heavily on the sizes of the wire.
基金Supported by the National Basic Research Program of China under Grant Nos 2013CB921700,2015CB921300 and2015CB921301the National Natural Science Foundation of China under Grant Nos 11234014,11622435,11274362,11674371 and11474340+1 种基金the National Key Research and Development Program of China under Grant Nos 2016YFA0300300,2016YFA0300600,2016YFA0401000 and 2016YFA0400902the Open Large Infrastructure Research of Chinese Academy of Sciences,and the Pioneer Hundred Talents Program(Type C)of Chinese Academy of Sciences
文摘The electronic structure of iron-pnictide compound superconductor Ba_2Ti_2Fe_2As_4O, which has metallic intermediate Ti_2O layers, is studied using angle-resolved photoemission spectroscopy. The Ti-related bands show a‘peak-dip-hump＇ line shape with two branches of dispersion associated with the polaronic states at temperatures below around 120 K. This change in the spectra occurs along with the resistivity anomaly that was not clearly understood in a previous study. Moreover, an energy gap induced by the superconducting proximity effect opens in the polaronic bands at temperatures below T_c（~21 K）. Our study provides the spectroscopic evidence that superconductivity coexists with polarons in the same bands near the Fermi level, which provides a suitable platform to study interactions between charge, lattice and spin freedoms in a correlated system.
文摘Feynman variational path integral theory was used to obtain the ground state energy of a polaron in a quantum well in the presence of a Coulomb potential for arbitrary values of the electron phonon coupling constant α . Numerical and analytical results showed that the energy shift was more sensitive to α than to the Coulomb binding parameter ( β ) and increased with the decrease of effective quantum well width l Z . It was interesting that due to the electronic confinement in the quasi 2D (quantum well) structures, the lower bound of the strong coupling regime was shifted to smaller values of α . Comparison of the polaron in the quantum well with that in the quantum wire or dot showed that the polaronic effect strengthened with decrease of the confinement dimension.
文摘The planar oxygen isotope effect on Tc observed in copper oxide superconductors is remarkable in that it increases from near nil at optimal doping to a value twice that derived from BCS theory in the underdoped region. This behavior is quantitatively followed by a formula proposed by Kresin and Wolf in 1994 for polarons along the c-axis. Herein it is revisited in a more transparent way, and it is pointed out that the heterogeneity of pairing is relevant and has to be taken into account to explain the unusual planar isotope effects on Tc in underdoped cuprates.
基金supported by the National Key R&D Project from Ministry of Science and Technology of China(Grant No.2022YFA1203100)the National Natural Science Foundation of China(Grant No.52350088)+1 种基金the Department of Science and Technology of Jiangsu Province(Grant No.BK20220032)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX241797)。
文摘The experimental realization of observable phonon angular momentum(PAM)in feasible systems using relatively simple methods remains a critical challenge.Motivated by the chiral-induced spin selectivity effect,this study explores the generation of PAM during the transport of electrically driven polarons along a singlestranded helix structure.We demonstrate that the motion of a polaron under an applied electric field inherently induces a finite PAM,exhibiting drift-locked behavior between the PAM and the polaron.By analyzing the time evolution of PAM distribution at each site,we identify the observed PAM as a natural consequence of coherent superposition between lattice waves,in which the chiral structure selectively determines the direction of induced PAM.Furthermore,we examine the roles of two types of electron-phonon interactions and structural periodicity in modulating PAM.These findings highlight the potential of chiral molecules as platforms for PAM generation and offer new insights into developing phonon-spin-based devices for information processing and transmission.
文摘Since the preliminary work of Anisimov and co-workers,the Hubbard corrected DFT+U functional has been used for predicting properties of correlated materials by applying on-site effective Coulomb interactions to specific orbitals.However,the determination of the Hubbard U parameter has remained under intense discussion despite the multitude of approaches proposed.Here,we define a selection criterion based on the use of polaronic defect states for the enforcement of the piecewise linearity of the total energy upon electron occupation.A good agreement with results from piecewise linear hybrid functionals is found for the electronic and structural properties of polarons,including the formation energies.The values of U determined in this way are found to give a robust description of the polaron energetics upon variation of the considered state.In particular,we also address a polaron hopping pathway,finding that the determined value of U leads to accurate energetics without requiring a configurational-dependent U.It is emphasized that the selection of U should be based on physical properties directly associated with the orbitals to which U is applied,rather than on more global properties such as band gaps and band widths.For comparison,we also determine U through a well-established linear-response scheme finding noticeably different values of U and consequently different formation energies.Possible origins of these discrepancies are discussed.As case studies,we consider the self-trapped electron in BiVO_(4),the self-trapped hole in MgO,the Li-trapped hole in MgO,and the Al-trapped hole inα-SiO_(2).
基金This work was supported by the National Science Foundation under Grant No.DMR-1750613J.-J.Z.acknowledges support from the Joint Center for Artificial Photosynthesis,a DOE Energy Innovation Hub,as follows:the development of some computational methods employed in this work was supported through the Office of Science of the US Department of Energy under Award No.DE-SC0004993+1 种基金N.-E.L.was supported by the Air Force Office of Scientific Research through the Young Investigator Program,Grant FA9550-18-1-0280This research used resources of the National Energy Research Scientific Computing Center(NERSC),a U.S.Department of Energy Office of Science User Facility located at Lawrence Berkeley National Laboratory,operated under Contract No.DE-AC02-05CH11231.
文摘Charge transport in organic molecular crystals (OMCs) is conventionally categorized into two limiting regimes − band transport,characterized by weak electron-phonon (e-ph) interactions,and charge hopping due to localized polarons formed by strong e-ph interactions.However,between these two limiting cases there is a less well understood intermediate regime where polarons are present but transport does not occur via hopping.Here we show a many-body first-principles approach that can accurately predict the carrier mobility in this intermediate regime and shed light on its microscopic origin.Our approach combines a finite-temperature cumulant method to describe strong e-ph interactions with Green-Kubo transport calculations.We apply this parameter-free framework to naphthalene crystal,demonstrating electron mobility predictions within a factor of 1.5−2 of experiment between 100 and 300 K.Our analysis reveals the formation of a broad polaron satellite peak in the electron spectral function and the failure of the Boltzmann equation in the intermediate regime.
基金Project supported by the Science and Engineering Research Board(SERB)New Delhi,India(ECR/2017/002681)Inter University Accelerator Centre,New Delhi,India(UFR-62317)。
文摘We hereby report the room-temperature structural and optical characterization of RECr_(0.85)Mn_(0.15)O_(3)(RECMO,RE=Ho,Gd and Pr)compounds synthesized by the auto-combustion sol-gel route.Their low temperature dielectric properties are also presented.The RECMO compounds crystallize in an orthorhombic Pbnm symmetry with an average grain size range of 51-80 nm.Structural analysis reveals an increase in the structural distortion compared to that of the undoped bulk compounds.Optical measurements exhibit a significant reduction in bandgap values for RECMO nanoparticles when compared with their undoped bulk compounds.Further,from the absorbance measurements various optical parameters such as skin depth,extinction coefficient,refractive index and optical conductivity were also calculated.The dielectric analysis confirms the lower values of the dielectric permittivity and dielectric loss than those of their corresponding bulk compounds.AC conductivity versus frequency and temperature data are fitted according to the Jonscher's power law and Arrhenius law,respectively.The small polaron hopping is responsible for the electric conduction in these compounds.The tunability of the optical and dielectric properties as a result of substitution and particle size reduction makes these materials useful for various potential applications in photocatalysis,optoelectronics and low permittivity dielectrics.
文摘Polarons are widely considered to play a crucial role in the charge transport and photocatalytic performance of materials,but the mechanisms of their formation and the underlying driving factors remain a matter of controversy.This study delves into the formation of polarons in different crystalline forms of TiO_(2) and their connection with the materials'structure.By employing density functional theory calculations with on-site Coulomb interaction correction(DFT+U),we provide a detailed analysis of the electronic polarization behavior in the anatase and rutile forms of TiO_(2).We focus on the polarization properties of defect-induced and photoexcited excess electrons on various TiO_(2) surfaces.The results reveal that the defect electrons can form small polarons on the anatase TiO_(2)(101)surface,while on the rutile TiO_(2)(110)surface,both small and large polarons(hybrid-state polarons)are formed.Photoexcited electrons are capable of forming both small and large polarons on the surfaces of both crystal types.The analysis indicates that the differences in polaron distribution are primarily determined by the intrinsic properties of the crystals;the structural and symmetry differences between anatase and rutile TiO_(2) lead to the distinct polaron behaviors.Further investigation suggests that the polarization behavior of defect electrons is also related to the arrangement of electron orbitals around the Ti atoms,while the polarization of photoexcited electrons is mainly facilitated by the lattice distortions.These findings elucidate the formation mechanisms of different types of polarons and may contribute to understanding the performance of TiO_(2)in different fields.
基金supported by the Natural Science Foundation of Nanjing University of Posts and Telecommunications (Grant Nos.NY222167 and NY220005)。
文摘As typical strongly correlated electronic materials, manganites show rich magnetic phase diagrams and electronic structures depending on the doped carrier density. Most previous relevant studies of doped manganites rely on the cubic/orthorhombic structures, while the hexagonal structure is much less studied. Here first-principles calculations are employed to investigate the magnetic and electronic structures of La-doped 4H-SrMnO_(3). By systematically analyzing the two kinds of La-doped positions, our calculations predict that the doped electron with lattice distortion would prefer to form polarons, which contribute to the local magnetic phase transition, nonzero net magnetization, and semiconducting behavior. In addition, the energy gap decreases gradually with increasing doping concentration, indicating a tendency of insulator–metal transition.
文摘We conduct a theoretical study on the properties of a bound polaron in a quantum well under an electric field using linear combination operator and unitary transformation methods, which are valid in the whole range of electron-LO phonon coupling. The changing relations between the ground-state energy of the bound polaron in the quantum well and the Coulomb bound potential, the electric field strength, and the well width are derived. The numerical results show that the ground-state energy increases with the increase of the electric field strength and the Coulomb bound potential and decreases as the well width increases.
文摘The properties of a bound polaron in a parabolic quantum dot with weak electron-LO-phonon coupling under a Coulomb field are studied. The ground state energy of the bound polaron is derived by using a linear combination operator and the perturbation method. The influence of the interaction between phonons with different wave vectors in the recoil process on the ground state energy of the bound polaron is discussed. Numerical calculations are performed,and the results show that the ground state energy increases significantly as the effective confinement length of the quantum dot decreases,considering of the interaction between phonons. When l0〉1.0, the influence of the interaction between phonons on the ground state energy cannot be ignored.
文摘The binding energy of a bound polaron in a finite parabolic quantum well is studied theoretically by a fractional- dimensional variational method. The numerical results for the binding energies of the bound polaron and longitudinal-optical phonon contributions in GaAs/Al0.3 Ga0.7 AS parabolic quantum well structures are obtained as functions of the well width. It is shown that the binding energies of the bound polaron are obviously reduced by the electron-phonon interaction and the phonon contribution is observable and cannot be neglected.
文摘The ground-state energy and the average number of virtual phonons around the electron of a hydrogenic impurity confined in a parabolic quantum dot are calculated using the squeezed-state variational approach,which is based on two successive canonical transformations and uses a displaced-oscillator type unitary transformation to deal with the bilinear terms,which are usually neglected.Numerical calculations are carried out in order to study the relation between the ground-state energy and the average number of virtual phonons around the electron of a bound polaron in a parabolic quantum dot with the Coulomb binding parameter.The electron-phonon coupling constant and the confinement length are derived.
基金Project supported by the National Center of Science(Grant No.NN202 263138)
文摘We study spectroscopic signatures of a monochromatic boson mode interacting with a T-shape double quantum dot coupled between the metallic and superconducting leads. Focusing on a weak interdot coupling, we find that the proximity effect together with the bosonic mode are responsible for the series of Fano-type resonances appearing simultaneously at negative and positive energies. We investigate these interferometric features and discuss their influence on the subgap Andreev conductance taking into account the correlation effects driven by the Coulomb repulsion.
文摘In contrast to so-called Auger process resulting in electron ejection from oxygen atom of water molecule under X-ray absorption, the coupling of the opposite charges in liquid water leads to polaronic exciton formation. As a result, polaronic exciton stabilized by the structure of water tetrahedron can serve as the reaction center for deuterium creation under X-ray absorption. In this case, X-ray emission spectra of H：O and D20 give a clue for the deciphering of the events followed by X-ray photon absorption. It appears to be that spin-orbit interaction under proton sharing and the interaction between LO （longitudinal optical） phonon and bipolaron in the excited state are responsible for the energy levels determining neutrino energy. The energy gap between the levels with pATe andplle spin configurations of proton and electron is found to be 325.51 cm^-1 in the case of the spin-orbit interaction in polaronic exciton, while 1,556.054 cm^-1 under LO phonon interaction with the proton of the bipolaron producing the change of the nucleus spin direction to the opposite.
基金Project supported by the Doctoral Program Foundation of Institutions of Higher Education China （Grant No 20040126003） and the Natural Science Foundation of Inner Mongol of China （Grant No 200408020101）.
文摘A 2D electron-longitudinal-acoustic-phonon interaction Hamiltonian is derived and used to calculate the groundstate energy of the acoustic polarons in two dimensions. The numerical results for the ground-state energy of the acoustic polarons in two and three dimensions are obtained. The 3D results agree with those obtained by using the Feynman path-integral approach. It is found that the critical coupling constant of the transition from the quasifree state to the self-trapped state in the 2D case is much smaller than in the 3D case for a given cutoff wave-vector. The theory has been used to judge the possibility of the self-trapping for several real materials. The results indicate that the self-trappings of the electrons in AlN and the holes in AlN and GaN are expected to be observed in 2D systems.
基金Supported by the National Natural Science Foundation of China under Grant No.19804009.
文摘The expression of the ground-state energy of the electron coupled simultaneously with a Coulomb potential and a longitudinal-optical phonon field in parabolic quantum dots and wires is derived within the framework of Feynman variational path integral theory.We obtain a general result with arbitrary electron-phonon coupling constant,Coulomb binding parameters,and confining potential strength,which could be used for further numerical calculation of polaron properties.Moreover,it is shown that all the previous path-integral formulae for free polarons,bound polarons,and polarons confined in parabolic quantum dots and wires can be recovered in the present formalism.
基金financially supported by the National Natural Science Foundation of China(Nos.52022042 and 51590893)National Science and Technology Major Project(J2019-VII-00080148)。
文摘Opaque thermal barrier materials play a pivotal role in thermal radiation shielding of turbine blades,since the intensity of thermal radiation rapidly increases with the increase of operating temperature of gas turbines and has become a new and major concern for the durability of metallic blades.The conventional thermal barrier coating(TBC)materials such as YSZ and Gd_(2)Zr_(2)O_(7),however,are almost translucent to thermal radiation and are unable to protect the blades at such harsh environment.Although searching for new thermal barrier materials is significant,it is still a challenge to make the current TBC materials opaque without significantly modifying the composition or other physical properties.To cope with this challenge,GdMnO_(3) is incorporated as an absorptive second phase into Gd_(2)Zr_(2)O_(7) in this work,which is originally translucent(absorption coefficient 10^(1)-10^(2) m^(-1))in the near-infrared wavelengths.Intriguingly,with less than 5 wt.%GdMnO_(3),the Gd_(2)Zr_(2)O_(7)/GdMnO_(3) becomes opaque to thermal radiation and successfully refrains the rise of thermal conductivity at high temperatures.Meanwhile,the lattice thermal conductivity and mechanical properties are almost unchanged.The small polaron mechanism is confirmed for GdMnO_(3),leading to a high absorption coefficient(>10^(6) m^(-1))for near-infrared radiation.To understand the underling mechanism,a theoretical model is built to estimate the absorption coefficient of the Gd_(2)Zr_(2)O_(7)/GdMnO_(3) composites(>10^(4) m^(-1)).This paper proposes a powerful strategy to design thermal-radiation-shielding TBCs through incorporating minor second-phase particles with high-absorption mechanism,such as polaron excitation.
