전자밀도함수론과 동적평균장 이론을 이용한 강상계 연구

Abstract

We have studied electronic structures of the heavy fermion compounds, CeIrIn5 and CeCoGe2, using the combined approach of the density function theory (DFT) and the dynamical mean field theory(DMFT). The DFT calculation has successfully explained many solid state phenomena. The DFT and its limitations will be reviewed in the introduction chapter. These explanation is connected to why the DFT+DMFT is needed in the heavy fermion compound. In the following chapters, we have provided one successful example of the DFT calculation, and two DFT+DMFT calculation for the heavy fermion compounds. Spinel ZnMn2O4 was reported to exhibit a rst order structural phase transition under high pressure. Using the DFT method, we have investigated the change of the electronic structure with varying both the volume and c/a ratio. Under high pressure, we have demonstrated the close relation between the structural change and the spin-state transition from a high-spin to a low-spin conguration of Mn3+. We have studied theoretically the evolution of the heavy fermion Fermi surface (FS) as a function of temperature (T) in heavy fermion compound, CeIrIn 5, using the DFT+DMFT method. Upon cooling, both the quantum oscillation frequencies and cyclotron masses show logarithmic scaling behavior (ln(T0=T)) with different characteristic temperaturesT0= 130 and 50 K, respectively. The resistivity coherence peak observed atT≃50 K is discussed with the scaling analysis of th FS with respect toT. The formation of the Kondo resonance (KR) band in the heavy fermion CeCoGe2 has been also studied using the DFT+DMFT method. The low T spectral function shows the dispersive KR states in momentum space. The size of the induced hyridization gap was also investigated as a function of T. During the evolution from the spd bands at highT to the dispersive KR bands at low T, we have found the existence of kinks in the spectral function near EF. The relation between the kink and hybridization gap has been discussed in comparison with the scaling analysis of the FS. In summary, we have explored the incoherent regime in heavy fermion compounds between high and low T. We have found the scaling properties in T-dependent FS evolution with the successful description of the electron transport. We have demonstrated how the Kondo resonance states are produced in comparison with the scaling analysis of the FS.