| Pressure can effectively compress the interatomic distance of the material and change the lattice and energy band structure,resulting in novel properties and effects in the materials.Diamond anvil cell(DAC)is an important device for generating static high pressure and many singular phenomena in the materials that cannot be achieved under ambient pressure are discovered by in-situ detection technology based on DAC,which greatly enrich people's understanding of the material world.Among them,the study of pressure-induced high-temperature superconductivity has always been a frontier subject in physics,and the research on metal-hydrogen superconductivity at room temperature is known as the"holy grail"of high-pressure physics.The study of pressure-induced superconductivity requires establish high pressure in-situ superconductivity detection method in DAC.However,conventional resistance measurement and diamagnetic measurement methods can't satisfy the accurate detection of superconductivity.It is because that the metal electrode is likely to react with the sample in an ultra-high pressure environment,resulting in a fundamental change in the properties of the sample.Meanwhile,the extremely small size of sample also reduces the sensitivity of diamagnetic detection,which brings inevitable difficulties for distinguishing the superconductivity.Therefore,it is crucial to carry out a new superconducting measurement technology in the DAC for the study of high pressure superconductivity.Diamond nitrogen-vacancy centers(NV~-centers)provide an opportunity for the measurement of Meissner effect on extremely small superconducting samples in DAC due to their high sensitivity and high spatial resolution for detecting the tiny change of magnetic field.In this paper,the finite element analysis method was used to simulate the variation of the magnetic field distribution around the sample as the superconducting transition occurs in different samples in DAC based on the Meissner effect measurement by NV~-center,and obtained the following conclusions:1.In view of the superiority and feasibility of NV~-center in detecting magnetic field,an effective experimental method and experimental model for in-situ Meissner effect measurement by NV~-center in DAC are established.Microwaves are introduced into the sample chamber of DAC to excite the electron spin resonance of NV~-center,and an excitation coil is placed around the anvil to generate a static magnetic field.The NV~-center is placed near the sample and the Meissner effect is detected by monitoring the electron spin resonance peak of the NV~-center to judge the occurrence of superconducting state.2.For the magnetic sample and the non-magnetic sample,the position where the magnetic flux density varied most after superconductivity is only inside the sample area,while the magnetic flux density almost unvaried in the area outside sample.3.The magnetic flux density vary most obviously on the center of sample sidewall after the superconductivity of magnetic sample and on the edge of sample sidewall which near coil after the superconductivity of non-magnetic sample,respectively.4.The influence of the exciting coil position on the magnetic field distribution of the DAC sample was studied.It was found that the closer the coil to sample,the larger magnetic flux density in sample,the more obvious variation of magnetic flux density after sample superconductivity.5.The results of finite element analysis show that magnetic flux density gets the largest change on the sidewall of sample where NV~-centers can detect the strongest signal variation of magnetic field.In addition,we also study the effect of magnetic coil placement on the magnetic field variation.It is found that the optimal position for the coil to generate the greatest change in magnetic field strength is at the place as close as possible to the sample.The experimental simulation in this paper provides the best experimental solution for the Meissner effect measurement by using NV~-center in DAC.It has guiding significance for the specific integration and arrangement of the NV~-center and the excitation coil,and provides the possibility of high-precision and space-resolvable superconductivity measurement of materials under high pressure,and also provide a new method for high-pressure superconductivity research.Furthermore,it will play an important role on the high-pressure superconductivity and other research in high-pressure physics. |
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