The Study Of Spin Caloritronics Based On Black Phosphorus

In recent years,scientific researchers have explored some low-dimensional materials that have the good thermoelectric effect and the thermal spin current effect.It makes the low-dimensional materials have important application in spin caloritronics devices.Meanwhile it also promotes the development of spin caloritronics.An increasingly high-profiled new material-black phosphorus has been successfully synthesized in experiment.In order to realize its application in quantum devices,this thesis bases on the black phosphorus nanoribbons,we design the related spintronics devices and use the research method,which the density functional theory of the first-principles is combined with non-equilibrium Green's function theory,to study the thermal spin transport properties of this nanoribbons.As we well know that there is still few work to fabricate and study the spintronics devices based on black phosphorus nanoribbons.In our work,we construct the homogeneous junction device of the zigzag black phosphorus nanoribbons(ZBPNRs).First of all,we study the antiferromagnetic(AFM)state and ferromagnetic(FM)state energy band structure of black phosphorus nanoribbons in different width.It is shown that with the increase of the width of the ferromagnetic state black phosphorus nanoribbon,the energy bands of the spin up and the spin down will gradually separate,and appear band gap.Then setting width N = 15,we study the thermal spin transport properties.The results show that the thermal spinning currents have better the Spin-Seebeck effect(SSE).It points out that the homogeneous junction device of the ZBPNRs can generate the pure thermal spin currents.In addition,considering the low dimension materials can use defect and doping to change its electronic structure,we remove phosphorus atoms in individual lattice of the ZBPNRs to form defect.Because the black phosphorus has good ductility,we stretch the defect black phosphorus nanoribbons,and at the same time we use hydrogen passivationin edge.By calculating its band structure,we find when the defect is close to the nanoribbons edge,the spin-up energy band and the spin-down one of black phosphorus nanoribbons will gradually open the band gap.Based on this feature,we build the zigzag black phosphorus nanoribbons homogeneous junction device,which not only have defects in the edge but are stretched as well.When we take width N=8,with the increase of tensile strength,the spin-up and the spin-down band gap of this structure will increase slightly.By regulating the temperature of the source and the drain,we can get the spin-up and the spin-down currents to flow in the opposite direction,respectively.It is shown that the thermal excitation spin currents of this device present better Spin-Seebeck effect.And the pure charge currents are much smaller than the pure spin currents.Then increasing the width of black phosphorus nanoribbons,we study its thermal spin transport properties.When tensile strength reaches 1%,with the increase of the width,both the charge currents and the spin currents gradually decrease.When width is N = 10,the charge currents turn into zero,but the spin currents are very small.However,when tensile strength reaches 8%,the device presents better Spin-Seebeck effect,and the pure spin currents increase with the increase of the width.When width increases to N=10,the charge currents appear negative differential resistance(NDR)effect.As a result,the structure of the black phosphorus in this work is meaningful for designing and developing the thermal spin caloritronics devices.Finally,we discuss thermal spin transport properties of the zigzag black phosphorus nanoribbons device suspended sulfur atom.It is found the band structure will appear the spin splitting phenomenon in the ferromagnetic state,and it will become stable as the increase of the width.But it does not change properties of the black phosphorus passivated by the sulfur atoms when stretching this structure.And the thermal spin currents induced by this device have the very good spin filtering effect,because only the spin up currents will change when we adjust the temperature in the process,whereas the spin downcurrents is always keep zero.It is shown such a structure can be applied to the temperature control switch and other devices,which are dependent on spin.