Study On The Detection Of Pressure-induced Superconductivity With Diamond NV Center

Pressure can induce superconducting transition of materials.Besides,the fact that pressure can greatly enhance the critical temperature of superconductors has been proved by several experiments.For instance,under the pressure of 153 GPa and 188GPa,H₂S and LaH₁₀ superconduct at 203 K and 260 K,respectively.These findings make it possible to achieve the goal of superconducting at room temperature,which is the final pursuit of human.It usually needs around 200 GPa or even higher pressure that can induce a critical temperature of a superconductor near to room temperature,thus,diamond anvil cell?DAC?is a must.However,carrying out in-situ ultrahigh pressure superconducting phenomena or measurements in DACs faces many technical difficulties.First of all,as for traditional methods of resistivity measurements,electrodes may react with samples preparing to be measured under ultrahigh pressure,which may destroy the intrinsic properties of samples.Secondly,the Meissner effect?flux exclusion?measurement usually needs introducing magnetic coils in DACs,but the sample under ultrahigh pressure is quite small?usually only a few microns?,so the signal of flux exclusion is correspondingly weak,which is not strong enough to be detected by the coil.Considering these technical difficulties described above,we based on the characteristic that ODMR spectrum of diamond NV center is extremely sensitive to changes of weak magnetic fields,and later,set up a new method for flux exclusion measurement in a DAC,which provides a new detecting method for in-situ superconducting phenomena and research under high pressure.In view of this,we carried out a series of preliminary preparation with the following results:?1?We observed the fluorescence of diamond NV center of two kinds.The size of them are around 60?m and 10?m,respectively.We found fluorescent peaks at a wavelength of 637 nm can be detected in both of two different sizes of NV centers.Meantime,both can be used for later experiments and measurements.?2?We used a continuous 532 nm laser to irradiate the NV center.A copper line with diameter of 20?m was straightly connected with SMA port line,which was used for the transmission of microwave.The end of copper line was at earth potential.Meantime,the NV center was placed near to the copper line as closely as possible,so that the ODMR spectra of NV center were obtained.?3?Through further improving experimental techniques,we brought this whole microwave transmission equipment into DAC,so that an experimental equipment that can achieve in-situ ODMR spectra of NV center under high pressure was set up.Considering the special structure of DAC,we used Pt line as the transmission line on the culet of DAC,copper line was used for lead wire,also,the end of copper line was at earth potential.By this,ODMR spectra of NV center under high pressure were obtained.By using one-dimensional Helmholtz coil,we obtained the changes of absorption peaks of ODMR spectra in different direct magnetic fields.?4?We investigated ODMR spectra of NV center under the condition of different design of microwave antenna,power of microwave generator and intensity of magnetic fields and further improved the programming language of LabVIEW,that is,introduce Butterworth filter to realize an effective collection of fluorescence of NV center.In addition,we theoretically studied the relationship between the band gap of indium oxide and pressure,and then,explained the mechanism the resistivity of it increases with pressure increasing.Theoretical calculation results showed that in the pressure range above 15.1 GPa,the rate of band broadening with pressure increasing was about 0.0217 eV/GPa,slightly lower than that before 15.1 GPa,that was 0.0296eV/GPa.At the same time,we found that the changing tendency at around 15.1 GPa was basically consistent with the pressure point of phase transition of indium oxide,which showed that the energy band dependence of pressure can also be used to reflect the occurrence of pressure-induced phase transition.The total and partial density of states of indium oxide were also calculated.The results showed that the element indium plays a leading role in the broadening of energy band caused by pressure.