Besides equilibrium behavior,exploring the spin–phonon coupling in multiferroic materials under non-equilibrium conditions is crucial for a deep understanding of the mechanisms as well as their high-frequency applica...Besides equilibrium behavior,exploring the spin–phonon coupling in multiferroic materials under non-equilibrium conditions is crucial for a deep understanding of the mechanisms as well as their high-frequency applications.Here,by utilizing time-resolved refectance spectroscopy,we demonstrate ultrafast spin–phonon coupling dynamics in multiferroic 0.58BiFeO_(3)-0.42Bi_(0.5)K_(0.5)TiO_(3)(BF-BKT)single crystals.With ultrafast laser pumping,coherent acoustic phonons with low damping are created in BF-BKT.Temperature-dependent results indicate that both the frequency and amplitude of laser-induced coherent phonons are sensitive to the emergence of antiferromagnetic order.Moreover,the spin state change driven by external magnetic felds can enhance the oscillation amplitude of the coherent acoustic phonons even above the magnetic Néel temperature.These fndings experimentally confrm that spin–phonon coupling in multiferroic materials exists not only in the spin-ordered state but also in the spin-disordered state,and not only in the equilibrium state but also in the non-equilibrium state excited by ultrafast lasers,suggesting their promising applications in high-frequency devices.展开更多
Within the frame of the Pavlov–Firsov spin–phonon coupling model, we study the spin-flip assisted by the acoustical phonon scattering between the first-excited state and the ground state in quantum dots. We analyze ...Within the frame of the Pavlov–Firsov spin–phonon coupling model, we study the spin-flip assisted by the acoustical phonon scattering between the first-excited state and the ground state in quantum dots. We analyze the behaviors of the spin relaxation rates as a function of an external magnetic field and lateral radius of quantum dot. The different trends of the relaxation rates depending on the magnetic field and lateral radius are obtained, which may serve as a channel to distinguish the relaxation processes and thus control the spin state effectively.展开更多
High-performance infrared emitters hold substantial importance in modern engineering and physics.Here,we introduce graphene/PZT(lead zirconate titanate)heterostructure as a new platform for the development of infrared...High-performance infrared emitters hold substantial importance in modern engineering and physics.Here,we introduce graphene/PZT(lead zirconate titanate)heterostructure as a new platform for the development of infrared source structure based on an electron-phonon coupling and emitting mechanism.A series of electrical characterizations including carrier mobility[11,361.55 cm^(2)/(V.s)],pulse current(30 ms response time),and cycling stability(2000 cycles)modulated by polarized film was provided.展开更多
The time-dependent analysis of four-wave mixing(FWM) has been performed in four-level double semiconductor quantum wells(SQWs) considering the cross-coupling of the longitude-optical phonons(LOP) relaxation. It is sho...The time-dependent analysis of four-wave mixing(FWM) has been performed in four-level double semiconductor quantum wells(SQWs) considering the cross-coupling of the longitude-optical phonons(LOP) relaxation. It is shown that both the amplitude and the conversion efficiency of the FWM field enhance greatly with the increasing strength of cross-coupling of LOP relaxation. Interestingly, a double peak value of the conversion efficiency is obtained under a relatively weak single-photon detuning considering the LOP coupling. When the detuning becomes stronger,the double peaks turn into one peak appearing at the line respect to the about equality two control fields. The results can be interpreted by the effect of electromagnetically induced transparency and the indirect transition. Such controlled high efficiency FWM based on the cross-coupling LOP may have potential applications in quantum control and communications.展开更多
Blue-emission(~480 nm)CsPbBr_(3) nanoparticles with ultra-small size(~2.1 nm)are synthesized using the liquid nitrogen freezing with the ligand of dodecylbenzene sulfonic acid(DBSA).Asymmetric narrow emissions at the ...Blue-emission(~480 nm)CsPbBr_(3) nanoparticles with ultra-small size(~2.1 nm)are synthesized using the liquid nitrogen freezing with the ligand of dodecylbenzene sulfonic acid(DBSA).Asymmetric narrow emissions at the low energy side,with the full width at half-maximum of~20 nm,are observed in solution and film at room temperature.The spectral asymmetry is mainly ascribed to phonon vibronic replica with averaged phonon energy of~40 meV.Moreover,exciting this CsPbBr_(3) nanoparticles solution using linearly polarized 6 ns pulsed laser at 355 nm,we observe polarized emission with polarization degree(P_(PL))of~7%,and P_(PL) decreases more than 20%in the vibronic progression.However,the P_(PL) goes to zero in frozen solutions as well as in films.Thus we speculate the polarized emission is due to the photoinduced re-alignment of nanoparticles,and the diminished P_(PL) at the phonon side band may be due to the non-adiabatic electronic-to-vibronic transitions.The novel phenomena from the ultra-small CsPbBr_(3) nanoparticle demonstrated in this work may provide fundamental insights into its photophysics with direct implications for optoelectronics.展开更多
Acoustic wave exhibits inherently different characters of propagation, excitation and coupling in phonon band-gap materials in which its elastic, piezoelectric constants are modulated in order of acoustic wavelength. ...Acoustic wave exhibits inherently different characters of propagation, excitation and coupling in phonon band-gap materials in which its elastic, piezoelectric constants are modulated in order of acoustic wavelength. These kinds of novel materials were exampled by phononic crystals with elastic constants modulation, acoustic superlattice and ionic-type phononic crystals with piezoelectric constants modulation. In this talk, phonic crystals were constructed with steel rods embedded in air. Negative refraction of acoustic wave was both experimentally and theoretically established in the phononic crystals. The propagation of acoustic wave in the crystals show acoustic band structures because the waves are strong scattered at the Brillouin Zone Boundaries, analogy to electron band structure in real crystals and photonic band structure in photonic crystals. In the acoustic superlattice, ultrasonic waves could be excited by applied alternative electric fields by piezoelectric effect. The frequency, mode and amplitude of the excited wave are determined by the microstructured parameters of the acoustic superlattice at the condition of phase matching. Ionic-type phononic crystals describe the coupling between superlattice phonon and electromagnetic wave. The coupling process resulted in the polariton with a dispersion relation totally different from that of both superlattice phonon and E-M waves, analogy to the polariton of the ionic crystals but in microwave instead of infrared light. These microstructural dielectric materials show artificial abnormal properties and will find novel application in ultrasonic devices and microwave devices.展开更多
The high-pressure phase diagram of the Nb-Ti binary system at 0 K is explored by systematic crystal structure prediction.The results highlight a novel niobium-rich bcc phase,Nb_(7)Ti,which is the only dynamically stab...The high-pressure phase diagram of the Nb-Ti binary system at 0 K is explored by systematic crystal structure prediction.The results highlight a novel niobium-rich bcc phase,Nb_(7)Ti,which is the only dynamically stable ordered Nb-Ti compound under ambient pressure.Extensive first-principles calculations have provided insights into the electronic structure,bonding and superconducting properties of Nb_(7)Ti.The superconducting transition temperature(T_(c))for Nb_(7)Ti at ambient pressure is estimated within the framework of BCS theory to be about 17.5 K,which is significantly higher—nearly double—that of the widely utilized NbTi alloy.Furthermore,the results unveil that the high T_(c) is mainly attributed to the unique ordered lattice along with the strong electron-phonon coupling driven by interatomic interactions at mid-frequency and phonon softening induced by low-frequency Fermi surface nesting.Valuable insights are provided for the subsequent synthesis of application-oriented superconductors at low pressure.展开更多
The glasses of 59 5H 3BO 3 40XF n 0 5Eu 2O 3 (X=Ca, Mg, Y, Pb, n =2 or 3) were prepared. The measurement of phonon sideband was performed. The higher energy range of phonon sideband spectra was fitted ...The glasses of 59 5H 3BO 3 40XF n 0 5Eu 2O 3 (X=Ca, Mg, Y, Pb, n =2 or 3) were prepared. The measurement of phonon sideband was performed. The higher energy range of phonon sideband spectra was fitted by Gaussian function, and the electron phonon coupling constant was calculated. The decreasing order of electron phonon coupling constant is from CaF 2, YF 3, MgF 2 to PbF 2, and the phonon sideband spectra are coincide with Raman scattering spectra.展开更多
In the phase diagram of the nickel-based superconductor Ba_(1-x)Sr_(x)Ni_(2)As_(2),T_(C) has been found to be enhanced sixfold near the quantum critical point(QCP) x=0.71 compared with the parent compound.However,the ...In the phase diagram of the nickel-based superconductor Ba_(1-x)Sr_(x)Ni_(2)As_(2),T_(C) has been found to be enhanced sixfold near the quantum critical point(QCP) x=0.71 compared with the parent compound.However,the mechanism is still under debate.Here,we report a detailed investigation of the superconducting properties near the QCP(x≈0.7) by utilizing scanning tunneling microscopy and spectroscopy.The temperature-dependent superconducting gap and magnetic vortex state were obtained and analyzed in the framework of the Bardeen-Cooper-Schrieffer model.The ideal isotropic s-wave superconducting gap excludes the long-speculated nematic fluctuations while preferring strong electron-phonon coupling as the mechanism for T_(C) enhancement near the QCP.The lower than expected gap ratio of Δ/(k_(B) T_(C)) is rooted in the fact that Ba_(1-x)Sr_(x)Ni_(2)As_(2) falls into the dirty limit with a serious pair breaking effect similar to the parent compound.展开更多
The infrared absorption spectra of the CO monomer isolated in solid N2 have been recorded at various temperatures between 4.5 and 30 K. The absorption features of the fundamen- tal stretching mode show its linewidth a...The infrared absorption spectra of the CO monomer isolated in solid N2 have been recorded at various temperatures between 4.5 and 30 K. The absorption features of the fundamen- tal stretching mode show its linewidth and matrix-induced frequency shift to be weakly temperature-dependent. As the temperature of the matrix was raised, an increase in the linewidth together with a redshift in the central frequency was observed. These observations were explained in terms of the quenching of the CO rotational states by the N2 matrix into closely-lying librational states. A quantitative model was then used to calculate the energy difference between these librational states. Results show that they can be thermally populated through the absorption of matrix phonons.展开更多
The spin-polarized band structures of an ultrathinheterostructure are calculated via first-principles density functional theory.The electron–phonon interaction and the superconducting properties of the ultrathinheter...The spin-polarized band structures of an ultrathinheterostructure are calculated via first-principles density functional theory.The electron–phonon interaction and the superconducting properties of the ultrathinheterostructure are studied by using the fully anisotropic Migdal–Eliashberg theory powered by Wannier–Fourier interpolation.Due to the complex Fermi surface in this low-dimensional system,the electron–phonon interaction and the superconducting gap display significant anisotropy.The temperature dependence of the superconducting gap can be fitted by solving numerically the Bardeen–Cooper–Schrieffer(BCS)gap equation with an adjustable parameter α,suggesting that phonon-mediated mechanism as its superconducting origin.Large Rashba spin-splitting and superconductivity coexist in this heterostructure,suggesting that this hybrid low-dimensional system will have some specific applications.展开更多
This paper reports that La-doped BiFeO3 （Bil-xLaxFeO3, x = 0, 0.1, 0.2, 0.3, 0.6, 0.8 and 1.0） were studied by using micro-Raman spectroscopy and x-ray diffraction （XRD）. The XRD patterns indicate that the structu...This paper reports that La-doped BiFeO3 （Bil-xLaxFeO3, x = 0, 0.1, 0.2, 0.3, 0.6, 0.8 and 1.0） were studied by using micro-Raman spectroscopy and x-ray diffraction （XRD）. The XRD patterns indicate that the structure of Bi1-xLaxFeO3 changes from rhombohedral BiFeO3 to orthorhombic LaFeO3. The results of Raman spectroscopy show good agreement with the XRD results. Strikingly, the phonon peak at around 610 cm^-1 and the two-phonon peaks in the high frequency range exist in all compounds and enhance with increasing La substitution. The increasing intensity of the 610 cm-1 peak is attributed to the changes in the FeO6 octahedron during the rhombohedral-orthorhombic phase transition. The enhancements of the two-phonon peaks are associated with the breakdown of the cycloid spin configuration with the appearance of the orthorhombic structure. These results indicate the existence of strong spin phonon coupling in Bi1-xLaxFeO3, which may provide useful information for understanding the effects of La content on the structural and magnetic properties of Bi1 -xLaxFeO3.展开更多
The behavior of lattice distortion in spin 1/2 antiferromagnetic XY models with random magnetic modulation is investigated with the consideration of spin–phonon coupling in the adiabatic limit. It is found that latti...The behavior of lattice distortion in spin 1/2 antiferromagnetic XY models with random magnetic modulation is investigated with the consideration of spin–phonon coupling in the adiabatic limit. It is found that lattice distortion relies on the strength of the random modulation. For strong or weak enough spin–phonon couplings, the average lattice distortion may decrease or increase as the random modulation is strengthened. This may be the result of competition between the random magnetic modulation and the spin–phonon coupling.展开更多
Exploring the mechanism of interfacial thermal transport and reducing the interfacial thermal resistance are of great importance for thermal management and modulation.Herein,the interfacial thermal resistance between ...Exploring the mechanism of interfacial thermal transport and reducing the interfacial thermal resistance are of great importance for thermal management and modulation.Herein,the interfacial thermal resistance between overlapped graphene nanoribbons is largely reduced by adding bonded carbon chains as shown by molecular dynamics simulations.And the analytical model(phonon weak couplings model,PWCM)is utilized to analyze and explain the two-dimensional thermal transport mechanism at the cross-interface.An order of magnitude reduction of the interfacial thermal resistance is found as the graphene nanoribbons are bonded by just one carbon chain.Interestingly,the decreasing rate of the interfacial thermal resistance slows down gradually with the increasing number of carbon chains,which can be explained by the proposed theoretical relationship based on analytical model.Moreover,by the comparison of PWCM and the traditional simplified model,the accuracy of PWCM is demonstrated in the overlapped graphene nanoribbons.This work provides a new way to improve the interfacial thermal transport and reveal the essential mechanism for low-dimensional materials applied in thermal management.展开更多
The diameter and chiral angle of a single-walled carbon nanotube(SWCNT)jointly determine its chiral indices(n,m),which consequently dictate its properties.Theoretical predictions suggest that SWCNTs with extremely sma...The diameter and chiral angle of a single-walled carbon nanotube(SWCNT)jointly determine its chiral indices(n,m),which consequently dictate its properties.Theoretical predictions suggest that SWCNTs with extremely small diameters exhibit strong electron–phonon coupling[1],potentially leading to intriguing properties such as superconductivity and high fluorescence quantum yield.Early attempts synthesized 0.4 nm SWCNT arrays within zeolite AlPO4-5 channels by pyrolyzing tripropylamine molecules in a vacuum of 10−4 Torr[2].However,the significant curvature-strain energy renders these SWCNTs inherently unstable.Upon extraction from the channels,these unstable SWCNTs transform into graphite fragments,hindering the exploration of their intrinsic properties free from zeolite interference and potential applications[2].展开更多
Laser-induced melting plays a crucial role in advanced manufacturing technology and ultrafast science;however,its atomic processes and microscopic mechanisms,especially in a wide-gap ceramic,remain elusive due to comp...Laser-induced melting plays a crucial role in advanced manufacturing technology and ultrafast science;however,its atomic processes and microscopic mechanisms,especially in a wide-gap ceramic,remain elusive due to complex interplays between many degrees of freedom within a timescale of~100 fs.We report here that laser melting is greatly accelerated by intense laser-induced tunnel ionization,instead of a priori multiphoton absorption,in the archetypal ceramic magnesium oxide(MgO).The tunneling processes generate a large number of photocarriers and results in intense energy absorption,instantaneously altering the potential energy surface of lattice configuration.The strong electron–phonon couplings and fast carrier relaxation enable efficient energy transfer between electrons and the lattice.These results account well for the latest ultrafast melting experiments and provide atomistic details and nonequilibrium mechanism of photoinduced ultrafast phase transitions in wide-gap materials.The laser modulation of melting thresholds and phase boundary demonstrate the possibility of manipulating phase transition on demand.A shock wave curve is also obtained at moderate conditions(P=2 GPa),extending Hugoniot curve to new regimes.展开更多
Organic-inorganic layered perovskites are two-dimensional quantum well layers in which the layers of lead halide octahedra are stacked between the organic cation layers.The packing geometry of the soft organic molecul...Organic-inorganic layered perovskites are two-dimensional quantum well layers in which the layers of lead halide octahedra are stacked between the organic cation layers.The packing geometry of the soft organic molecules and the stiff ionic crystals induce structural deformation of the inorganic octahedra,generating complex lattice dynamics.Especially,the dielectric confinement and ionic sublattice lead to strong coupling between the photogenerated excitons and the phonons from the polar lattice which intensively affects the properties for device applications.The anharmonicity and dynamic disorder from the organic cations participate in the relaxation dynamics coupled with excitations.However,a detailed understanding of this underlying mechanism remains obscure.This work investigates the electron–optical phonon coupling dynamics by employing ultrafast pump-probe transient absorption spectroscopy.The activated different optical phonon modes are observed via systematic studies of(PEA)_(2)PbBr_(4) perovskite films on the ultrafast lattice vibrational dynamics.The experimental results indicate that solvent engineering has a significant influence on lattice vibrational modes and coherent phonon dynamics.This work provides fresh insights into electron-optical phonon coupling for emergent optoelectronics development based on layered perovskites.展开更多
Copper–carbon(Cu–C)composites have achieved great success in various fields owing to the greatly improved electrical properties compared to pure Cu,for example,a two-order-of-magnitude increase in current-carrying c...Copper–carbon(Cu–C)composites have achieved great success in various fields owing to the greatly improved electrical properties compared to pure Cu,for example,a two-order-of-magnitude increase in current-carrying capacity(ampacity).However,the frequent fuse failure caused by the poor thermal transport at the Cu–C heterointerface is still the main factor affecting the ampacity.In this study,we unconventionally leverage atomic distortion at Cu grain boundaries to alter the local atomic environments,thereby placing a premium on noticeable enhancement of phonon coupling at the Cu–C heterointerface.Without introducing any additional materials,interfacial thermal transport can be regulated solely through rational microstructural design.This new strategy effectively improves the interfacial thermal conductance by three-fold,reaching the state-of-the-art level in van der Waals(vdW)interface regulation.It can be an innovative strategy for interfacial thermal management by turning the detrimental grain boundaries into a beneficial thermal transport accelerator.展开更多
We demonstrate an ultra-low-threshold phonon laser using a coupled-microtoroid-cavity system by introducing a novel coupling approach.The scheme exhibits both high optical quality factors and high mechanical quality f...We demonstrate an ultra-low-threshold phonon laser using a coupled-microtoroid-cavity system by introducing a novel coupling approach.The scheme exhibits both high optical quality factors and high mechanical quality factors.We have experimentally obtained the mechanical quality factor up to 18,000 in vacuum for a radialbreathing mode of 59.2 MHz.The measured phonon lasing threshold is as low as 1.2μW,which is～5 times lower than the previous result.展开更多
基金supported by the National Key R&D Program of China(Grant No.2021YFA1600200)the National Natural Science Foundation of China(Grant Nos.U2032218 and 12111530283)。
文摘Besides equilibrium behavior,exploring the spin–phonon coupling in multiferroic materials under non-equilibrium conditions is crucial for a deep understanding of the mechanisms as well as their high-frequency applications.Here,by utilizing time-resolved refectance spectroscopy,we demonstrate ultrafast spin–phonon coupling dynamics in multiferroic 0.58BiFeO_(3)-0.42Bi_(0.5)K_(0.5)TiO_(3)(BF-BKT)single crystals.With ultrafast laser pumping,coherent acoustic phonons with low damping are created in BF-BKT.Temperature-dependent results indicate that both the frequency and amplitude of laser-induced coherent phonons are sensitive to the emergence of antiferromagnetic order.Moreover,the spin state change driven by external magnetic felds can enhance the oscillation amplitude of the coherent acoustic phonons even above the magnetic Néel temperature.These fndings experimentally confrm that spin–phonon coupling in multiferroic materials exists not only in the spin-ordered state but also in the spin-disordered state,and not only in the equilibrium state but also in the non-equilibrium state excited by ultrafast lasers,suggesting their promising applications in high-frequency devices.
基金supported by the National Natural Science Foundation of China(Grant No.11264001)the Natural Science Foundation of Inner Mongolia,China(Grant No.2012MS0116)
文摘Within the frame of the Pavlov–Firsov spin–phonon coupling model, we study the spin-flip assisted by the acoustical phonon scattering between the first-excited state and the ground state in quantum dots. We analyze the behaviors of the spin relaxation rates as a function of an external magnetic field and lateral radius of quantum dot. The different trends of the relaxation rates depending on the magnetic field and lateral radius are obtained, which may serve as a channel to distinguish the relaxation processes and thus control the spin state effectively.
基金Natural Science Foundation of Shanxi Province(20210302123056)Shanxi Provincial Key Research and Development Project(202102040201007,202203021223005)National Natural Science Foundation of China(52275577,52205609).
文摘High-performance infrared emitters hold substantial importance in modern engineering and physics.Here,we introduce graphene/PZT(lead zirconate titanate)heterostructure as a new platform for the development of infrared source structure based on an electron-phonon coupling and emitting mechanism.A series of electrical characterizations including carrier mobility[11,361.55 cm^(2)/(V.s)],pulse current(30 ms response time),and cycling stability(2000 cycles)modulated by polarized film was provided.
基金Supported by Program for Changjiang Scholars and Innovative Research Team in University under Grant(IRT1080)National Natural Science Foundation of China under Grant Nos.51272158,11374252,and 51372214+2 种基金Changjiang Scholar Incentive Program under Grant No.[2009]17Scientific Research Fund of Hunan Provincial Education Department of China under Grant No.12A140the Science and Technology Foundation of Guizhou Province of China under Grant No.J20122314
文摘The time-dependent analysis of four-wave mixing(FWM) has been performed in four-level double semiconductor quantum wells(SQWs) considering the cross-coupling of the longitude-optical phonons(LOP) relaxation. It is shown that both the amplitude and the conversion efficiency of the FWM field enhance greatly with the increasing strength of cross-coupling of LOP relaxation. Interestingly, a double peak value of the conversion efficiency is obtained under a relatively weak single-photon detuning considering the LOP coupling. When the detuning becomes stronger,the double peaks turn into one peak appearing at the line respect to the about equality two control fields. The results can be interpreted by the effect of electromagnetically induced transparency and the indirect transition. Such controlled high efficiency FWM based on the cross-coupling LOP may have potential applications in quantum control and communications.
基金supported by startup funding at Fudan University,National Natural Science Foundation of China (Nos.62074079,61774039)large instrument equipment open fund of Nanjing University of Science and Technology.
文摘Blue-emission(~480 nm)CsPbBr_(3) nanoparticles with ultra-small size(~2.1 nm)are synthesized using the liquid nitrogen freezing with the ligand of dodecylbenzene sulfonic acid(DBSA).Asymmetric narrow emissions at the low energy side,with the full width at half-maximum of~20 nm,are observed in solution and film at room temperature.The spectral asymmetry is mainly ascribed to phonon vibronic replica with averaged phonon energy of~40 meV.Moreover,exciting this CsPbBr_(3) nanoparticles solution using linearly polarized 6 ns pulsed laser at 355 nm,we observe polarized emission with polarization degree(P_(PL))of~7%,and P_(PL) decreases more than 20%in the vibronic progression.However,the P_(PL) goes to zero in frozen solutions as well as in films.Thus we speculate the polarized emission is due to the photoinduced re-alignment of nanoparticles,and the diminished P_(PL) at the phonon side band may be due to the non-adiabatic electronic-to-vibronic transitions.The novel phenomena from the ultra-small CsPbBr_(3) nanoparticle demonstrated in this work may provide fundamental insights into its photophysics with direct implications for optoelectronics.
文摘Acoustic wave exhibits inherently different characters of propagation, excitation and coupling in phonon band-gap materials in which its elastic, piezoelectric constants are modulated in order of acoustic wavelength. These kinds of novel materials were exampled by phononic crystals with elastic constants modulation, acoustic superlattice and ionic-type phononic crystals with piezoelectric constants modulation. In this talk, phonic crystals were constructed with steel rods embedded in air. Negative refraction of acoustic wave was both experimentally and theoretically established in the phononic crystals. The propagation of acoustic wave in the crystals show acoustic band structures because the waves are strong scattered at the Brillouin Zone Boundaries, analogy to electron band structure in real crystals and photonic band structure in photonic crystals. In the acoustic superlattice, ultrasonic waves could be excited by applied alternative electric fields by piezoelectric effect. The frequency, mode and amplitude of the excited wave are determined by the microstructured parameters of the acoustic superlattice at the condition of phase matching. Ionic-type phononic crystals describe the coupling between superlattice phonon and electromagnetic wave. The coupling process resulted in the polariton with a dispersion relation totally different from that of both superlattice phonon and E-M waves, analogy to the polariton of the ionic crystals but in microwave instead of infrared light. These microstructural dielectric materials show artificial abnormal properties and will find novel application in ultrasonic devices and microwave devices.
基金supported by the National Natural Science Foundation of China(Grant Nos.12122405,12274169,and 11574109)the Fundamental Research Funds for the Central Universities。
文摘The high-pressure phase diagram of the Nb-Ti binary system at 0 K is explored by systematic crystal structure prediction.The results highlight a novel niobium-rich bcc phase,Nb_(7)Ti,which is the only dynamically stable ordered Nb-Ti compound under ambient pressure.Extensive first-principles calculations have provided insights into the electronic structure,bonding and superconducting properties of Nb_(7)Ti.The superconducting transition temperature(T_(c))for Nb_(7)Ti at ambient pressure is estimated within the framework of BCS theory to be about 17.5 K,which is significantly higher—nearly double—that of the widely utilized NbTi alloy.Furthermore,the results unveil that the high T_(c) is mainly attributed to the unique ordered lattice along with the strong electron-phonon coupling driven by interatomic interactions at mid-frequency and phonon softening induced by low-frequency Fermi surface nesting.Valuable insights are provided for the subsequent synthesis of application-oriented superconductors at low pressure.
文摘The glasses of 59 5H 3BO 3 40XF n 0 5Eu 2O 3 (X=Ca, Mg, Y, Pb, n =2 or 3) were prepared. The measurement of phonon sideband was performed. The higher energy range of phonon sideband spectra was fitted by Gaussian function, and the electron phonon coupling constant was calculated. The decreasing order of electron phonon coupling constant is from CaF 2, YF 3, MgF 2 to PbF 2, and the phonon sideband spectra are coincide with Raman scattering spectra.
基金Project supported by the National Key R&D Program of China (Grant Nos. 2022YFA1403203, 2022YFA1403400, and 2021YFA1400400)the Innovation Program for Quantum Science and Technology (Grant No. 2021ZD0302802)+2 种基金the National Natural Science Foundation of China (Grant Nos. 12074002, 12104004, 12204008, and 12374133)the Chinese Academy of Sciences (Grant Nos. XDB33000000 and GJTD-2020-01)the Major Basic Program of Natural Science Foundation of Shandong Province (Grant No. ZR2021ZD01)。
文摘In the phase diagram of the nickel-based superconductor Ba_(1-x)Sr_(x)Ni_(2)As_(2),T_(C) has been found to be enhanced sixfold near the quantum critical point(QCP) x=0.71 compared with the parent compound.However,the mechanism is still under debate.Here,we report a detailed investigation of the superconducting properties near the QCP(x≈0.7) by utilizing scanning tunneling microscopy and spectroscopy.The temperature-dependent superconducting gap and magnetic vortex state were obtained and analyzed in the framework of the Bardeen-Cooper-Schrieffer model.The ideal isotropic s-wave superconducting gap excludes the long-speculated nematic fluctuations while preferring strong electron-phonon coupling as the mechanism for T_(C) enhancement near the QCP.The lower than expected gap ratio of Δ/(k_(B) T_(C)) is rooted in the fact that Ba_(1-x)Sr_(x)Ni_(2)As_(2) falls into the dirty limit with a serious pair breaking effect similar to the parent compound.
基金ACKNOWLEDGMENTS This work was supported by the Young International Scientist Fellowship from the Chinese Academy of Sciences, the National Natural Science Foundation （No.21225314 and No.11150110457）, the National Basic Research Program of China （No.2010CB923300）, and the Fundamental Research Funds for the Central Universities .
文摘The infrared absorption spectra of the CO monomer isolated in solid N2 have been recorded at various temperatures between 4.5 and 30 K. The absorption features of the fundamen- tal stretching mode show its linewidth and matrix-induced frequency shift to be weakly temperature-dependent. As the temperature of the matrix was raised, an increase in the linewidth together with a redshift in the central frequency was observed. These observations were explained in terms of the quenching of the CO rotational states by the N2 matrix into closely-lying librational states. A quantitative model was then used to calculate the energy difference between these librational states. Results show that they can be thermally populated through the absorption of matrix phonons.
基金Project supported by the Natural Science Foundation of Jiangsu Province,China(Grant No.BK20141441)
文摘The spin-polarized band structures of an ultrathinheterostructure are calculated via first-principles density functional theory.The electron–phonon interaction and the superconducting properties of the ultrathinheterostructure are studied by using the fully anisotropic Migdal–Eliashberg theory powered by Wannier–Fourier interpolation.Due to the complex Fermi surface in this low-dimensional system,the electron–phonon interaction and the superconducting gap display significant anisotropy.The temperature dependence of the superconducting gap can be fitted by solving numerically the Bardeen–Cooper–Schrieffer(BCS)gap equation with an adjustable parameter α,suggesting that phonon-mediated mechanism as its superconducting origin.Large Rashba spin-splitting and superconductivity coexist in this heterostructure,suggesting that this hybrid low-dimensional system will have some specific applications.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10674171 and 10874236)
文摘This paper reports that La-doped BiFeO3 （Bil-xLaxFeO3, x = 0, 0.1, 0.2, 0.3, 0.6, 0.8 and 1.0） were studied by using micro-Raman spectroscopy and x-ray diffraction （XRD）. The XRD patterns indicate that the structure of Bi1-xLaxFeO3 changes from rhombohedral BiFeO3 to orthorhombic LaFeO3. The results of Raman spectroscopy show good agreement with the XRD results. Strikingly, the phonon peak at around 610 cm^-1 and the two-phonon peaks in the high frequency range exist in all compounds and enhance with increasing La substitution. The increasing intensity of the 610 cm-1 peak is attributed to the changes in the FeO6 octahedron during the rhombohedral-orthorhombic phase transition. The enhancements of the two-phonon peaks are associated with the breakdown of the cycloid spin configuration with the appearance of the orthorhombic structure. These results indicate the existence of strong spin phonon coupling in Bi1-xLaxFeO3, which may provide useful information for understanding the effects of La content on the structural and magnetic properties of Bi1 -xLaxFeO3.
文摘The behavior of lattice distortion in spin 1/2 antiferromagnetic XY models with random magnetic modulation is investigated with the consideration of spin–phonon coupling in the adiabatic limit. It is found that lattice distortion relies on the strength of the random modulation. For strong or weak enough spin–phonon couplings, the average lattice distortion may decrease or increase as the random modulation is strengthened. This may be the result of competition between the random magnetic modulation and the spin–phonon coupling.
基金Project supported by the National Natural Science Foundation of China(Grant No.51606072)the Fundamental Research Funds for the Central Universities,HUST,China(Grant No.2019kfyRCPY045)。
文摘Exploring the mechanism of interfacial thermal transport and reducing the interfacial thermal resistance are of great importance for thermal management and modulation.Herein,the interfacial thermal resistance between overlapped graphene nanoribbons is largely reduced by adding bonded carbon chains as shown by molecular dynamics simulations.And the analytical model(phonon weak couplings model,PWCM)is utilized to analyze and explain the two-dimensional thermal transport mechanism at the cross-interface.An order of magnitude reduction of the interfacial thermal resistance is found as the graphene nanoribbons are bonded by just one carbon chain.Interestingly,the decreasing rate of the interfacial thermal resistance slows down gradually with the increasing number of carbon chains,which can be explained by the proposed theoretical relationship based on analytical model.Moreover,by the comparison of PWCM and the traditional simplified model,the accuracy of PWCM is demonstrated in the overlapped graphene nanoribbons.This work provides a new way to improve the interfacial thermal transport and reveal the essential mechanism for low-dimensional materials applied in thermal management.
基金supported by the Taishan Scholar Foundation of Shandong Province(tstp20230627)the Key Basic Research Project of Shandong Province(ZR2019ZD49).
文摘The diameter and chiral angle of a single-walled carbon nanotube(SWCNT)jointly determine its chiral indices(n,m),which consequently dictate its properties.Theoretical predictions suggest that SWCNTs with extremely small diameters exhibit strong electron–phonon coupling[1],potentially leading to intriguing properties such as superconductivity and high fluorescence quantum yield.Early attempts synthesized 0.4 nm SWCNT arrays within zeolite AlPO4-5 channels by pyrolyzing tripropylamine molecules in a vacuum of 10−4 Torr[2].However,the significant curvature-strain energy renders these SWCNTs inherently unstable.Upon extraction from the channels,these unstable SWCNTs transform into graphite fragments,hindering the exploration of their intrinsic properties free from zeolite interference and potential applications[2].
基金National Key Research and Development Program of China(no.2021YFA1400200)National Natural Science Foundation of China(nos.12025407,11934003,and 12204513)“Strategic Priority Research Program(B)”of Chinese Academy of Sciences(grant nos.XDB330301 and YSBR047).
文摘Laser-induced melting plays a crucial role in advanced manufacturing technology and ultrafast science;however,its atomic processes and microscopic mechanisms,especially in a wide-gap ceramic,remain elusive due to complex interplays between many degrees of freedom within a timescale of~100 fs.We report here that laser melting is greatly accelerated by intense laser-induced tunnel ionization,instead of a priori multiphoton absorption,in the archetypal ceramic magnesium oxide(MgO).The tunneling processes generate a large number of photocarriers and results in intense energy absorption,instantaneously altering the potential energy surface of lattice configuration.The strong electron–phonon couplings and fast carrier relaxation enable efficient energy transfer between electrons and the lattice.These results account well for the latest ultrafast melting experiments and provide atomistic details and nonequilibrium mechanism of photoinduced ultrafast phase transitions in wide-gap materials.The laser modulation of melting thresholds and phase boundary demonstrate the possibility of manipulating phase transition on demand.A shock wave curve is also obtained at moderate conditions(P=2 GPa),extending Hugoniot curve to new regimes.
基金supported by the National Natural Science Foundation of China(Nos.U1804261,61627818,12074104,11804084,62075058,and 11827806)Natural Science Foundation of Henan Province(No.222300420057)+1 种基金the Outstanding Youth Foundation of Henan Normal University(No.20200171)the Young Backbone Teacher Training Program in Higher Education of Henan Province(No.2019GGJS065).
文摘Organic-inorganic layered perovskites are two-dimensional quantum well layers in which the layers of lead halide octahedra are stacked between the organic cation layers.The packing geometry of the soft organic molecules and the stiff ionic crystals induce structural deformation of the inorganic octahedra,generating complex lattice dynamics.Especially,the dielectric confinement and ionic sublattice lead to strong coupling between the photogenerated excitons and the phonons from the polar lattice which intensively affects the properties for device applications.The anharmonicity and dynamic disorder from the organic cations participate in the relaxation dynamics coupled with excitations.However,a detailed understanding of this underlying mechanism remains obscure.This work investigates the electron–optical phonon coupling dynamics by employing ultrafast pump-probe transient absorption spectroscopy.The activated different optical phonon modes are observed via systematic studies of(PEA)_(2)PbBr_(4) perovskite films on the ultrafast lattice vibrational dynamics.The experimental results indicate that solvent engineering has a significant influence on lattice vibrational modes and coherent phonon dynamics.This work provides fresh insights into electron-optical phonon coupling for emergent optoelectronics development based on layered perovskites.
基金financial support from the National Natural Science Foundation of China(Nos.52222602 and 52476052)Fundamental Research Funds for the Central Universities(FRF-TP-22-001C1 and FRF-EYIT-23-05).
文摘Copper–carbon(Cu–C)composites have achieved great success in various fields owing to the greatly improved electrical properties compared to pure Cu,for example,a two-order-of-magnitude increase in current-carrying capacity(ampacity).However,the frequent fuse failure caused by the poor thermal transport at the Cu–C heterointerface is still the main factor affecting the ampacity.In this study,we unconventionally leverage atomic distortion at Cu grain boundaries to alter the local atomic environments,thereby placing a premium on noticeable enhancement of phonon coupling at the Cu–C heterointerface.Without introducing any additional materials,interfacial thermal transport can be regulated solely through rational microstructural design.This new strategy effectively improves the interfacial thermal conductance by three-fold,reaching the state-of-the-art level in van der Waals(vdW)interface regulation.It can be an innovative strategy for interfacial thermal management by turning the detrimental grain boundaries into a beneficial thermal transport accelerator.
基金National Key Research and Development Program(2016YFA0302500)National Natural Science Foundation of China(NSFC)(61435007,11574144)+1 种基金Natural Science Foundation of Jiangsu Province(BK20150015)Fundamental Research Funds for the Central Universities
文摘We demonstrate an ultra-low-threshold phonon laser using a coupled-microtoroid-cavity system by introducing a novel coupling approach.The scheme exhibits both high optical quality factors and high mechanical quality factors.We have experimentally obtained the mechanical quality factor up to 18,000 in vacuum for a radialbreathing mode of 59.2 MHz.The measured phonon lasing threshold is as low as 1.2μW,which is～5 times lower than the previous result.
