Method and device for regulating the coherent process of perovskite nanocrystal excitons by magnetic field

Abstract

The present invention belongs to the field of perovskite nanocrystal technology, and particularly relates to a method and device for regulating the coherent process of perovskite nanocrystal excitons by magnetic field. The method comprises passing an incident light beam of pump light and a detection white light through a perovskite nanocrystal at a low temperature, applying a magnetic field in the direction of light propagation, and the magnetic field converting the linearly polarized eigenstate in the perovskite nanocrystal into an elliptically polarized eigenstate, which approaches a circularly polarized eigenstate as the magnetic field increases; the beat frequency dynamics of the perovskite nanocrystal under circularly polarized light pump-probe will gradually weaken; under linearly polarized light pump-probe, the beat frequency dynamics of the perovskite nanocrystal will gradually increase; and the eigenstates and beat frequency dynamics of the perovskite nanocrystal are regulated by adjusting the magnetic field intensity. The present invention regulates the band-edge exciton eigenstates of the perovskite nanocrystal by changing the magnetic field intensity. Since changes in the band-edge exciton eigenstates will cause changes in the coherent state dynamics process, the coherent state dynamics of the perovskite nanocrystal is regulated by adjusting the magnetic field intensity.

Description

Technical Field

[0001] The present invention belongs to the technical field of perovskite nanocrystals (NCs), and in particular relates to a method and device for regulating the exciton coherence process of perovskite nanocrystals by using a magnetic field. Background Art

[0002] Semiconductor quantum dots are important building blocks of modern quantum information technology. On the one hand, they can generate high-purity single photons for photon-based quantum information processing; on the other hand, they can also serve as carriers of qubits based on carrier or exciton spin. However, traditional epitaxially grown quantum dots often require expensive and complex high-temperature and vacuum environments to be prepared, and the morphology of the quantum dots themselves is difficult to precisely control. Colloidal semiconductor quantum dot materials in the field of chemistry can be prepared at low cost and on a large scale through a rich solution chemistry approach, and the morphology and size can be precisely controlled through reaction kinetics and thermodynamics. Therefore, they may serve as a low-cost solution for quantum information technology. Although the technical route based on traditional II-VI group (such as CdSe, ZnSe, etc.) colloidal quantum dots has been initially explored, their smaller size brings a larger (specific) surface area and a small transition dipole moment, which brings great difficulties to the lifetime of quantum coherence and the control of quantum states.

[0003] Compared to the traditional colloidal quantum dots mentioned above, the emerging perovskite colloidal quantum dots have advantages such as defect tolerance, large transition dipole maximum, and long optical coherence time. They have also achieved numerous advances in quantum information technology, such as superfluorescence, coherent single-photon emission, stable band-edge exciton coherence, and carrier spin manipulation at room temperature. These significant advances are closely related to the fine structure of the band-edge excitons in perovskite quantum dots. The valence band edge is a relatively pure spin-1 / 2 state, while the conduction band edge is a state with a total angular momentum of 1 / 2 split by spin-orbit coupling. Taking into account the electron-hole exchange effect, the band-edge structure of perovskite colloidal quantum dots consists of bright triplet states and dark singlet states. Reduced symmetry of either the crystal outline or the lattice structure will lead to changes in the transition (polarization) selection law of the bright state, making it possible to measure the coherent behavior between these bright states using polarization spectroscopy. In the current study, the single-particle fluorescence spectrum in the liquid helium temperature region clearly revealed that external fields (such as electric fields, magnetic fields, etc.) can effectively regulate the position of the fine structure of band-edge excitons, but the regulation of their coherent behavior by external fields remains unknown. Especially at high temperatures, due to the broadening of colloidal quantum dots, this frequency domain measurement method can hardly even provide information on the fine structure of band-edge excitons, further increasing the difficulty of revealing the regulation of these fine structures under external fields. Although previous magneto-optical spectroscopy measurements of II-VI and III-V epitaxially grown single quantum dots have demonstrated the possibility of external field regulation of the coherent behavior of band-edge excitons, the fine structure of the band-edge excitons of this type of quantum dots has only two bright states, which is significantly different from perovskite quantum dots (three). These differences need to be reconsidered and established when establishing the method. Summary of the Invention

[0004] In response to the above problems, the purpose of the present invention is to provide a method and device for regulating the coherence process of perovskite nanocrystal excitons through a magnetic field, so as to solve the above-mentioned technical problem of regulating the coherence process between lead-based perovskite nanocrystal excitons.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] On one hand, the present invention provides a method for regulating the exciton coherence process of perovskite nanocrystals by magnetic field, which is characterized in that an incident light beam containing pump light and detection white light passes through the perovskite nanocrystal at low temperature, and a magnetic field of 0 to 7T is applied in the direction of light propagation. The magnetic field converts the linearly polarized eigenstate in the perovskite nanocrystal at low temperature into an elliptically polarized eigenstate, and approaches the circularly polarized eigenstate as the magnetic field increases; under circularly polarized light pump-probe, the beat frequency dynamics of the perovskite nanocrystal will gradually weaken; while under linearly polarized light pump-probe, the beat frequency dynamics of the perovskite nanocrystal will gradually increase; by adjusting the magnetic field intensity, the eigenstate and beat frequency dynamics of the perovskite nanocrystal can be regulated.

[0007] Femtosecond pulse lasers are used as pump light and probe light to improve the dynamic resolution in the time domain. The pump light is a resonant monochromatic femtosecond pulse that only excites the band-edge bright-state excitons of the perovskite nanocrystal. The probe light is a supercontinuum white light femtosecond pulse with a wavelength covering the band-edge energy levels of the perovskite nanocrystal and 515 to 1000 nm. The angle between the pump light and the probe light is less than 10°, and both are polarized light, including circularly polarized light and linearly polarized light.

[0008] Another aspect of the present invention provides a device for implementing the method of regulating the coherent process of perovskite nanocrystal excitons by a magnetic field as described above, the device comprising:

[0009] A femtosecond pulse generation system is used to obtain an incident light beam, wherein the incident light beam is a femtosecond pulse laser including pump light and detection white light;

[0010] The sample chamber is provided with an incident window and an exit window. The incident light beam generated by the femtosecond pulse generation system enters through the incident window and then passes through the perovskite nanocrystal and is emitted from the exit window.

[0011] A sample stage is provided in the sample chamber and is used to carry perovskite nanocrystals;

[0012] Cooling system, used to provide a low temperature environment for the sample chamber;

[0013] A superconducting magnet is arranged around the sample stage, and applies a magnetic field to the perovskite nanocrystal along the direction of light propagation;

[0014] The data acquisition system is used to receive the laser beam emitted from the exit window of the sample chamber and record the intensity according to the wavelength of the laser beam.

[0015] The femtosecond pulse generation system includes a laser, a beam splitter, a pump light generating optical component and a detection light generating optical component, wherein the laser is used to generate femtosecond pulse laser, which is divided into two laser beams by the beam splitter. The first laser beam is emitted into the pump light generating optical component to generate pump light; the second laser beam is emitted into the detection light generating optical component to generate detection light.

[0016] The pump light generating optical component includes an optical parametric amplifier, a chopper, an attenuator I, a wave plate group I and a telephoto lens I arranged in sequence along the optical path, wherein the optical parametric amplifier is used to obtain femtosecond light of a resonant excitation wavelength; the femtosecond light obtains the required polarization after passing through the chopper, attenuator I and wave plate group I, and is then focused into the sample chamber through the telephoto lens I.

[0017] The pump light generating optical component also includes a telescope group, a reflector I and a reflector II, wherein the telescope group is arranged between the optical parametric amplifier and the chopper for expanding the beam of femtosecond light; the telescope group includes two plano-convex lenses arranged in sequence along the optical path; the reflector I and the reflector II are respectively arranged on both sides of the attenuation plate I along the optical path for steering the optical path.

[0018] The detection light generation optical component includes a mechanical delay stage, an attenuation plate II, a short-focus lens, a YAG crystal, a wave plate group II and a long-focus lens II arranged in sequence along the optical path, wherein the mechanical delay stage is used to control the optical path difference between the pump light and the detection light; after the second laser beam is attenuated by the attenuation plate II, it is focused on the YAG crystal through the short-focus lens. The YAG crystal excites supercontinuum white light in the visible-near-infrared band, then obtains the required polarization through the wave plate group II, and is finally focused into the sample chamber through the long-focus lens II.

[0019] The detection light generating optical component also includes a reflector III, an off-axis parabolic mirror and a reflector IV, wherein the reflector III is arranged between the mechanical delay stage and the attenuation plate II, and the off-axis parabolic mirror and the reflector IV are arranged along the optical path between the YAG crystal and the wave plate group II for optical path steering.

[0020] A silver mirror is provided under the sample stage. The pump light and the probe light are incident on the silver mirror at an angle of less than 10°. The silver mirror is used to reflect the pump light and the probe light entering from the incident window onto the sample stage. The pump light passes through the perovskite nanocrystal along a direction with an angle of less than 10° to the direction of the magnetic field, and the probe light passes through the perovskite nanocrystal along a direction parallel to the magnetic field.

[0021] The cooling system includes a liquid storage tank, a liquid helium tank and a compressor, wherein the liquid storage tank and the liquid helium tank are arranged in the sample chamber, and the liquid storage tank is arranged below the sample stage. The liquid storage tank is connected to the sample stage via copper to cool the perovskite nanocrystals on the sample stage; the sample stage is made of non-magnetic metal; the liquid storage tank is connected to the sample stage and the superconducting magnet, and the compressor is arranged outside the sample chamber and connected to the liquid storage tank and the liquid helium tank via a circulation pipeline to form a circulating cooling pipeline.

[0022] The advantages and beneficial effects of the present invention are: the present invention provides a method for regulating the coherent process of perovskite nanocrystal excitons through a magnetic field, which can regulate the eigenstates of perovskite nanocrystals' band-edge excitons by changing the magnetic field intensity, and since the change of the band-edge exciton eigenstates will cause the coherent state dynamics process to change, the coherent state dynamics of perovskite nanocrystals (NCs) can be regulated by adjusting the magnetic field intensity.

[0023] This study uses steady-state magnetic field and ultrafast transient absorption spectroscopy (TA) to characterize the red-edge photoabsorption of CsPbI3 NCs (cesium lead iodide, a type of perovskite nanocrystal) at 250K under different magnetic fields. The results demonstrate that the energy gap of in-plane excitons with edge-polarization expands and transitions to a circularly polarized state due to the Zeeman energy contribution under magnetic fields, significantly shortening the beat frequency oscillation period of the NCs while maintaining no significant change in the apparent depolarization lifetime. This method of regulating the coherent exciton dynamics of perovskite NCs using magnetic fields provides a new approach for controlling excitons in future spintronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the working principle of the device for regulating the coherent process of perovskite nanocrystal excitons through a magnetic field;

[0025] Figure 2 This is a diagram showing the structure of a sample chamber of a device for regulating the coherent process of perovskite nanocrystal excitons through a magnetic field according to the present invention;

[0026] Figure 3 is a graph showing the reflectivity of the silver mirror in the sample chamber to incident light of different polarizations and wavelengths in an embodiment of the present invention;

[0027] Figure 4 is a morphology image of the CsPbI3NCs sample in an embodiment of the present invention;

[0028] Figure 5 is the steady-state absorption spectrum of the CSPbI3NCs sample in the embodiment of the present invention;

[0029] Figure 6 (a)-(b) are schematic diagrams of the dynamic measurement results of band-edge excitons at a wavelength of 684 nm under different magnetic fields and polarizations in an embodiment of the present invention;

[0030] Figure 7 It is a two-dimensional grayscale image of the signal under different magnetic fields and polarizations in an embodiment of the present invention.

[0031] In the figure: 1-laser, 2-beam splitter, 3-optical parametric amplifier, 4-chopper, 5-reflector I, 6-attenuator I, 7-reflector II, 8-wave plate group I, 9-telephoto lens I, 10-mechanical delay stage, 11-reflector III, 12-attenuator II, 13-short-focus lens, 14-YAG crystal, 15-off-axis parabolic mirror, 16-reflector IV, 17-wave plate group II, 18-telephoto lens II, 19-silver mirror, 20-superconducting magnet, 21-magnetic flux lines, 22-sample, 23-sample chamber, 24-liquid storage tank, 25-sample stage, 26-incident beam, 27-incident window, 28-exit window, 29-liquid helium tank, 30-compressor. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] On one hand, the present invention provides a method for regulating the exciton coherence process of perovskite nanocrystals through a magnetic field. A magnetic field of 0 to 7 T is applied in the direction of light propagation. The magnetic field converts the linearly polarized eigenstate (a state that can obtain a certain energy value under the action of an energy operator is an eigenstate; linear polarization or circular polarization is the polarization property of the state) in the perovskite nanocrystal at a low temperature into an elliptically polarized eigenstate, and approaches the circularly polarized eigenstate as the magnetic field increases. Under circularly polarized light pumping and probing, the beat frequency dynamics of the perovskite nanocrystal will gradually weaken; while under linearly polarized light pumping and probing, the beat frequency dynamics of the perovskite nanocrystal will gradually increase. By adjusting the magnetic field intensity, the eigenstate and beat frequency dynamics of the perovskite nanocrystal can be regulated.

[0034] Furthermore, femtosecond pulse lasers are used as pump light and probe light to improve the dynamic resolution in the time domain; the pump light is a resonant monochromatic femtosecond pulse that only excites the band-edge bright-state excitons of the perovskite nanocrystal; the pump light passes through the sample at an angle of less than 10° to the direction of the magnetic field; the probe light is a supercontinuum white light femtosecond pulse, with a wavelength covering the band-edge energy level and higher energy levels of the perovskite nanocrystal (515-1000nm); the angle between the pump light and the probe light is less than 10°, and both are polarized light, including circularly polarized light and linearly polarized light.

[0035] The present invention provides a method for regulating the coherent process of perovskite nanocrystal excitons through a magnetic field. By changing the magnetic field intensity, the eigenstates of the band-edge excitons of the perovskite nanocrystals can be regulated. Since the change of the eigenstates of the band-edge excitons will cause the coherent state dynamics process to change, the coherent state dynamics of perovskite nanocrystals (NCs) can be regulated by adjusting the magnetic field intensity.

[0036] See also Figure 1 、 Figure 2As shown, another aspect of the present invention provides a device for regulating the coherent process of perovskite nanocrystal excitons by a magnetic field, the device comprising a femtosecond pulse generating system, a sample chamber 23, a sample stage 25, a cooling system, a superconducting magnet 20 and a data acquisition system, wherein the femtosecond pulse generating system is used to obtain an incident light beam 26, the incident light beam 26 is a femtosecond pulse laser containing pump light and detection white light; the sample chamber 23 is provided with an incident window 27 and an exit window 28, the incident light beam 26 generated by the femtosecond pulse generating system enters the incident window 27 through the incident window 28. The light enters the sample chamber 23, passes through the perovskite nanocrystal, and is then emitted from the exit window 28; the sample stage 25 is arranged in the sample chamber 23, and the sample stage 25 is used to carry the perovskite nanocrystal; the cooling system is used to provide a low-temperature environment for the sample chamber 23; the superconducting magnet 20 is arranged around the sample stage 25, and the magnetic flux lines 21 generated by the superconducting magnet 20 pass through the perovskite nanocrystal, and the magnetic flux lines near the sample are parallel to the direction of light propagation; the data acquisition system is used to receive the laser beam emitted from the exit window 28 of the sample chamber 23, and record the intensity according to the wavelength of the laser beam.

[0037] See also Figure 1 As shown, in an embodiment of the present invention, a femtosecond pulse generating system includes a laser 1, a beam splitter 2, a pump light generating optical component and a detection light generating optical component, wherein the laser 1 is used to generate a femtosecond pulse laser, and the femtosecond pulse laser is divided into two laser beams by the beam splitter 2, the first laser beam is incident on the pump light generating optical component to generate pump light; the second laser beam is incident on the detection light generating optical component to generate detection light.

[0038] In an embodiment of the present invention, the pump light generation optical assembly includes an optical parametric amplifier 3, a chopper 4, an attenuator I 6, a wave plate assembly I 8, and a telephoto lens I, arranged sequentially along the optical path. The optical parametric amplifier 3 is used to obtain femtosecond light of a resonant excitation wavelength. The pump light is generated by the optical parametric amplifier 3 (OPA) using a frequency-combining method, and only half of the pulses are allowed to pass through the chopper 4. The femtosecond light obtains the desired polarization after passing through the attenuator I 6 and the wave plate assembly I 8, and is then focused into the sample chamber 23 through the telephoto lens I. Specifically, the wave plate assembly I 8 includes a wire grid, a λ / 2 wave plate, and a λ / 4 wave plate, arranged sequentially along the optical path. Polarization conversion is achieved by adjusting the angles of the λ / 2 wave plate and the λ / 4 wave plate.

[0039] Furthermore, the pump light generating optical component also includes a telescope group, a reflector I5 and a reflector II7, wherein the telescope group is arranged between the optical parametric amplifier 3 and the chopper 4 for expanding the beam of femtosecond light; the telescope group includes two plano-convex lenses arranged in sequence along the optical path; the reflector I5 and the reflector II7 are respectively arranged on both sides of the attenuation plate I6 along the optical path for steering the optical path.

[0040] In an embodiment of the present invention, the optical assembly for generating the probe light includes a mechanical delay stage 10, an attenuation plate II 12, a short-focus lens 13, a YAG crystal 14, a wave plate group II 17, and a long-focus lens II 18, which are sequentially arranged along the optical path. The mechanical delay stage 10 is used to control the optical path difference between the pump light and the probe light. After the second laser beam is attenuated by the attenuation plate II 12, it is focused on the YAG crystal 14 through the short-focus lens 13. The YAG crystal 14 (yttrium aluminum garnet) excites supercontinuum white light in the visible-near infrared band, which is then polarized by the wave plate group II 17 and focused into the sample chamber 23 by the long-focus lens II 18. The delay time between the two femtosecond pulses is controlled by controlling the optical path difference through the electric mechanical translation stage 10. Specifically, the wave plate group II 17 includes a wire grid and a λ / 4 wave plate, and the polarization transformation is achieved by adjusting the angle of the λ / 4 wave plate.

[0041] Furthermore, the detection light generating optical component also includes a reflector III 11, an off-axis parabolic mirror 15 and a reflector IV 16, wherein the reflector III 11 is arranged between the mechanical delay stage 10 and the attenuation plate II 12, and the off-axis parabolic mirror 15 and the reflector IV 16 are arranged along the optical path between the YAG crystal 14 and the wave plate group II 17 for optical path steering.

[0042] See also Figure 2 As shown, in an embodiment of the present invention, a silver mirror 19 is embedded below the sample stage 25. The pump light and the probe light are incident on the silver mirror 19 at an angle of less than 10°. The silver mirror 19 is used to deflect the pump light and the probe light entering through the incident window 27 by 90° and then reflect them onto the sample stage 25. Specifically, the pump light passes through the perovskite nanocrystal at an angle of less than 10° to the magnetic field direction, and the probe light passes through the perovskite nanocrystal parallel to the magnetic field.

[0043] Specifically, the sample chamber 23 is a hollow cylindrical structure with the superconducting magnet 20 on the periphery. An incident window 27 is provided on the side of the sample chamber 23 and an exit window 28 is provided on the top.

[0044] See also Figure 2 As shown, in an embodiment of the present invention, the cooling system includes a liquid storage tank 24, a liquid helium tank 29, and a compressor 30. The liquid storage tank 24 and the liquid helium tank 29 are disposed within the sample chamber 23. The liquid storage tank 24 is disposed below the sample stage 25. The liquid storage tank 24 is connected to the sample stage 25 via copper to cool the perovskite nanocrystals on the sample stage 25. The sample stage 25 is made of a non-magnetic metal, preferably copper. The liquid storage tank 24 is connected to the sample stage 25 and the superconducting magnet 20. The compressor 30 is disposed outside the sample chamber 23 and is connected to the liquid storage tank 24 and the liquid helium tank 29 via a circulation pipeline, forming a circulating cooling pipeline.

[0045] In one embodiment of the present invention, the data acquisition system includes a linear array CCD camera and a computer. After passing through an optical fiber, the probe light is split by a grating. Light of different wavelengths enters different pixels on the linear array CCD camera. Electrical signals are generated based on the intensity, converted into digital signals, and then input into the computer for recording and storage. Pump light is emitted from the sample chamber 23, focused by a lens, and then fed into the optical fiber and into the linear array CCD camera.

[0046] Another aspect of the present invention provides a device for regulating the coherence process of perovskite nanocrystal excitons through a magnetic field, the working principle of which is:

[0047] The band edge structure of perovskite crystals is relatively simple. The energy band at the bottom of the conduction band is primarily a vacant band resulting from the spin-orbital coupling splitting of the lead 6p orbital and the halogen p orbital. This band edge consists solely of this vacant band, and the energy difference between this band edge and the other conduction bands can reach hundreds of millielectronvolts. The top of the valence band is primarily a filled band contributed by the lead 6s orbital, and the energy difference between the band edge and the other valence bands is also large. Perovskite nanocrystals incorporate quantum confinement on a crystalline basis, resulting in discontinuous band edge energy levels. Consequently, the band edge exciton structure of perovskite nanocrystals is very simple, requiring only four exciton states derived from linear combinations of two spin states each for electrons and holes. Of these four exciton states, only three are bright states permitted by the optical transition selection laws; the remaining dark state can have an energy difference of several millielectronvolts from the bright state. Due to the loss of lattice and morphological symmetry, the three bright states exhibit splitting linearly in energy levels. In the Faraday configuration, two linear excitons in the plane normal to the direction of light propagation couple, and the resulting exciton state is a linear superposition of the two. The resulting quantum state is not an eigenstate and evolves over time. The evolutionary path is related to the Hamiltonian, and therefore the eigenstates of the nanocrystal. An applied magnetic field can couple the two linear excitons in the plane into two circular excitons. The more circular the state, the closer the dynamical behavior is to population relaxation.

[0048] Before starting the measurement, the perovskite nanocrystal sample solution is concentrated and then spin-coated on the cut glass slide. The glass slide used is cleaned in advance with isopropyl alcohol in an ultrasonic cleaning machine for 20 minutes, then irradiated with a UV irradiator for 20 minutes, and then naturally cooled. The nanocrystalline film sample obtained by spin coating is transferred to a sample chamber 23 with a superconducting magnet 20. The sample chamber 23 is sealed, and nitrogen is introduced after the air is evacuated. The chamber is repeatedly evacuated to vacuum. Helium is compressed to obtain superfluid helium, which is then circulated in the pipeline. A part of the superconducting coil is used to keep the superconducting magnet 20 at a low temperature, and a part of the liquid storage tank 24 in the sample chamber 23 is filled. The liquid storage tank 24 is directly connected to the sample stage 25 by red copper to cool the sample 22 on the sample stage 25. Specifically, an external compressor 30 is used to compress helium into liquid helium and feed it into a liquid helium tank 29. This tank is connected to a liquid storage tank 24 within the sample chamber 23 and then cooled to a set temperature (250K in this embodiment) through heat transfer through copper fittings. The heated, vaporized helium is partially condensed through an internal gas path, and the remaining portion is compressed back into liquid helium by compressor 30. Sample 22 (perovskite nanocrystals) is in direct contact with sample stage 25 for heat transfer. After sample stage 25 reaches the set temperature, thermal equilibrium is continued for two hours to ensure that sample 22 reaches the set temperature.

[0049] A femtosecond laser with a wavelength of 1030 nanometers is extracted from laser 1. 75% of the laser light is fed into an optical parametric amplifier 3 via a beam splitter 2. The optical parametric amplifier 3 is adjusted to produce femtosecond light at the resonant excitation wavelength. The beam is then expanded by a telescope system consisting of two plano-convex lenses, and then the desired polarization is achieved by a chopper 4, attenuator I 6, and wave plate assembly I 8. The remaining 25% of the femtosecond light passes through a mechanical delay stage 10 (with a time range of 0 to 8 nanoseconds) and is attenuated by attenuator II 12. It is then focused onto a YAG crystal 14 via a short-focus lens 13, generating a supercontinuum white light in the visible-to-near-infrared band. This light is then parallelized by an off-axis parabolic mirror 15 and passed through wave plate assembly II 17 to achieve the desired polarization. The two beams of light each pass through a telephoto lens in a nearly collinear form (the angle between the two beams of light is less than 10°) through the window plate of the incident window 27 of the sample chamber 23 and intersect on the sample stage 25. The optical beam waists of the two beams of light (the position with the smallest optical radius in the direction of beam propagation) are also in the plane of the sample stage 25, and the pump light spot is larger than the detection light spot.

[0050] After cooling the sample, a circularly polarized pump beam passes through sample 22 at a small angle, preferably at an angle less than 10° to the magnetic field direction M, to excite the sample 22 within the beam waist. After a specified time, the probe beam, passing through the mechanical delay stage 10, probes the sample near the center of the pump beam waist with a smaller optical waist to avoid detecting samples at the edge of the beam waist that are unexcited or have weak excitation intensity. The two beams will experience a loss in polarization after passing through the silver mirror 19. The reflectivity of different polarizations at different wavelengths can be found in [1]. Figure 3 shown.

[0051] Subsequently, the pump light is emitted from the rear window of the exit window 28, converged at the optical fiber port through a short-focus lens, and enters the linear array CCD camera to be collected.

[0052] Specifically, the mechanical delay table 10, the laser 1, the chopper 4 and the linear array CCD camera are connected through a timing card. The laser 1 sends an electrical pulse to the timing card, and then the timing card sends the pulse signal to the chopper 4 and the linear array CCD camera. The computer controls the above components through the timing card.

[0053] The size distribution and room temperature absorption spectra of the CsPbI3NCs samples used are shown in Figure 4 、 Figure 5 As shown. Different magnetic fields are applied by the superconducting magnet 20, and then the different polarization signals are subtracted (σ + σ - -σ + σ + , VV-VH) obtained by dynamic detection results and two-dimensional grayscale images of the signal, see Figure 6 and Figure 7 As shown. It can be seen that at 0T, the results of circularly polarized excitation-probe show a weak beat signal, which comes from the circularly polarized pump light exciting a superposition state of linearly polarized eigenstates. The evolution of the state between eigenstates leads to projection in the initialization direction; the results of linearly polarized excitation-probe also have a beat signal, which is partly due to the uncertainty of the dipole orientation of the linearly polarized eigenstate, which allows the linearly polarized pump light to also excite a superposition state of eigenstates. At 7T, because the Zeeman energy dominates the energy gap between bright states, the angular momentum direction of the eigenstate is very close to the direction of light propagation. Therefore, one of the circularly polarized eigenstates in the excited states under circularly polarized excitation-probe occupies a dominant position, and the dynamic behavior can be fitted with a single exponential decay; and because the linearly polarized pump excites a superposition state of circularly polarized eigenstates, a beat signal can be observed.

[0054] In the examples of this invention, using a lead-based perovskite quantum dot ensemble as a model, magnetic fields were used to successfully achieve on-demand control of the coherence between these band-edge fine structures. Polarization-resolved transient absorption spectroscopy clearly demonstrated that the coherent signal of the band-edge fine structures changes from circular polarization to linear polarization under modulation by the longitudinal magnetic field. This control method not only modulates the band-edge exciton states but also provides a method for constructing a variety of novel quantum bits.

[0055] The present invention can regulate the band-edge exciton eigenstates of perovskite nanocrystals by changing the magnetic field intensity. Changes in the band-edge exciton eigenstates lead to changes in the coherent state dynamics. Using a steady-state magnetic field and ultrafast transient absorption spectroscopy (TA), the red-edge photoabsorption of CsPbI3 NCs at 250K and different magnetic fields was characterized. This demonstrates that the band-edge linearly polarized in-plane exciton energy gap expands and transitions to a circularly polarized state due to the Zeeman energy contribution under the magnetic field, significantly shortening the beat frequency oscillation period of the NCs while maintaining no significant change in the apparent depolarization lifetime. This method and device for regulating the coherent exciton process of perovskite nanocrystals via a magnetic field utilizes a steady-state magnetic field to achieve carrier dynamics regulation in perovskite nanocrystals, enabling non-destructive regulation of the exciton coherence dynamics of perovskite nanocrystals. This method has significant guiding value and significance for dynamic regulation in future spintronic devices.

[0056] The above description is only an embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modification, equivalent replacement, improvement, expansion, etc. made within the spirit and principle of the present invention are included in the scope of protection of the present invention.

Claims

1. A device for regulating the coherent process of perovskite nanocrystal excitons by magnetic field, characterized in that: The device comprises: A femtosecond pulse generation system is used to obtain an incident light beam, wherein the incident light beam is a femtosecond pulse laser including pump light and detection white light; The sample chamber is provided with an incident window and an exit window. The incident light beam generated by the femtosecond pulse generation system enters through the incident window and then passes through the perovskite nanocrystal and is emitted from the exit window. A sample stage is provided in the sample chamber and is used to carry perovskite nanocrystals; Cooling system, used to provide a low temperature environment for the sample chamber; A superconducting magnet is arranged around the sample stage, and applies a magnetic field to the perovskite nanocrystal along the direction of light propagation; a data acquisition system for receiving the laser beam emitted from the exit window of the sample chamber and recording the intensity according to the wavelength of the laser beam; The femtosecond pulse generation system includes a laser, a beam splitter, a pump light generating optical component, and a probe light generating optical component. The laser is used to generate femtosecond pulse laser light. The femtosecond pulse laser light is divided into two laser beams by the beam splitter. The first laser beam is injected into the pump light generating optical component to generate pump light; the second laser beam is injected into the probe light generating optical component to generate probe light. The pump light generating optical component includes an optical parametric amplifier, a chopper, an attenuator I, a wave plate group I, and a telephoto lens I arranged in sequence along the optical path, wherein the optical parametric amplifier is used to obtain femtosecond light of a resonant excitation wavelength; the femtosecond light obtains the required polarization after passing through the chopper, the attenuator I, and the wave plate group I, and is then focused into the sample chamber through the telephoto lens I; The detection light generation optical assembly includes a mechanical delay stage, an attenuation plate II, a short-focus lens, a YAG crystal, a wave plate set II, and a long-focus lens II, which are sequentially arranged along the optical path. The mechanical delay stage is used to control the optical path difference between the pump light and the detection light. After the second laser beam is attenuated by the attenuation plate II, it is focused on the YAG crystal through the short-focus lens. The YAG crystal excites supercontinuum white light in the visible-near-infrared band, then obtains the desired polarization through the wave plate set II, and is finally focused into the sample chamber by the long-focus lens II. An incident beam consisting of pump light and probe white light passes through a low-temperature perovskite nanocrystal. A magnetic field of 0 to 7 T is applied in the direction of light propagation. The magnetic field transforms the linearly polarized eigenstates in the low-temperature perovskite nanocrystal into elliptically polarized eigenstates, which then approach circularly polarized eigenstates as the magnetic field increases. Under circularly polarized pump-probe conditions, the beat-frequency dynamics of the perovskite nanocrystal gradually weaken, while under linearly polarized pump-probe conditions, the beat-frequency dynamics gradually increase. By adjusting the magnetic field strength, the eigenstates and beat-frequency dynamics of the perovskite nanocrystal can be controlled. Femtosecond pulsed lasers are used as both pump and probe light to improve the dynamic resolution in the time domain. The pump light is a resonant monochromatic femtosecond pulse that excites only the bright-state excitons at the band edge of the perovskite nanocrystal. The probe light is a supercontinuum white light femtosecond pulse with a wavelength covering the band edge energy levels of the perovskite nanocrystal and 515 to 1000 nm. The angle between the pump and probe light is less than 10°, and both are polarized, including circularly polarized and linearly polarized light. The pump light passes through the perovskite nanocrystal at an angle less than 10° to the magnetic field direction, and the probe light passes through the perovskite nanocrystal parallel to the magnetic field direction.

2. The device according to claim 1, characterized in that The pump light generating optical component also includes a telescope group, a reflector I and a reflector II, wherein the telescope group is arranged between the optical parametric amplifier and the chopper for expanding the beam of femtosecond light; the telescope group includes two plano-convex lenses arranged in sequence along the optical path; the reflector I and the reflector II are respectively arranged on both sides of the attenuation plate I along the optical path for steering the optical path.

3. The device according to claim 1, characterized in that The detection light generating optical component also includes a reflector III, an off-axis parabolic mirror and a reflector IV, wherein the reflector III is arranged between the mechanical delay stage and the attenuation plate II, and the off-axis parabolic mirror and the reflector IV are arranged along the optical path between the YAG crystal and the wave plate group II for optical path steering.

4. The device according to claim 1, characterized in that A silver mirror is provided below the sample stage. The pump light and the detection light are incident on the silver mirror at an angle less than 10°. The silver mirror is used to reflect the pump light and the detection light entering from the incident window onto the sample stage.

5. The device according to claim 1, characterized in that The cooling system includes a liquid storage tank, a liquid helium tank and a compressor, wherein the liquid storage tank and the liquid helium tank are arranged in the sample chamber, and the liquid storage tank is arranged below the sample stage. The liquid storage tank is connected to the sample stage via copper to cool the perovskite nanocrystals on the sample stage; the sample stage is made of non-magnetic metal; the liquid storage tank is connected to the sample stage and the superconducting magnet, and the compressor is arranged outside the sample chamber and connected to the liquid storage tank and the liquid helium tank via a circulation pipeline to form a circulating cooling pipeline.

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