Disorder Induced Phase Transitions In Double Weyl Semimetals

Double Weyl semimetal（DWSM）is a kind of three-dimensional topological ma-terial,which has a wide application prospect in the field of next generation low power quantum devices.This thesis utilizes the transfer matrix,noncommutative Kubo formula,nonequilibrium Green’s function and self-consistent Born approximation method to study the disorder-induced phase transitions and transport properties in DWSM.These results can provide theoretical guidance for the design and fabrication of novel devices.Firstly,this thesis studies the disorder-induced phase transitions in DWSM and gives the grobal phase diagrams.Firstly,for the on-site nonmagnetic disorder,with the increase of the disorder strength,the system can enter the diffusive metal（DM）phase from DWSM phase,and eventually evolves into the Anderson insulator（AI）phase.Or the system goes into the DM phase from the three-dimensional quantum anomalous Hall（3D QAH）phase,and enters the AI phase in the end.For theσ_xorbital disorder,increasing this disorder strength can generate a pair of double Weyl nodes at the boundary of the Brillouin zone and induce the 3D QAH–DWSM phase transition.Notably,theσ_xorbital disorder can induce a direct DWSM-NI phase transition.The results indicate that theσ₀andσ_xdisorders have a diverse impact on the transport properties of the system.Then the thesis investigates the influence of three orbital disorders on the system.At last,this thesis utilizes the SCBA to explain the disorder-induced phase transitions in DWSM.Next,this thesis studies the transport properties of DWSM in the presence of electric and magnetic field.This thesis investigates the effect of tilt parameter t₀/t_zon the band structure and transport properties.The results indicate that when the system goes into the type-II DWSM from type-I DWSM,the conductance changes from 0 to a finite value at E=0e V.When a magnetic field is applied,the chiral Landau levels appear and contribute to a quantized conductance G=40e²/h.When a electric field is applied,the results manifest that the electric field can break the double Weyl nodes and open a band gap.