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Sung-Sik Lee

Publications and source records attributed to Sung-Sik Lee.

80 records · Page 5Linked to original sources
arXiv2000

Importance of Coupling between the Charge and Spin Degrees of Freedom in High Tc Superconductivity

Based on an improved SU(2) slave-boson approach showing coupling between the cha rge and spin degrees of freedom, we derive a phase diagram of high $T_c$ cuprate s which displays both the superconducting and pseudogap phases in the plane of t emperature vs. hole doping rate. It is shown that phase fluctuations in the order parameters results in a closer agreement with the observed phase diagram of an arch shape, by manifesting the p resence of an optimal doping rate.

cond-mat.supr-con↗
arXiv2000

Origin of the Quasiparticle Peaks of Spectral Functions in High $T_c$ Cuprates

Based on the SU(2) slave-boson approach to the t-J Hamiltonian, we examine the cause of the sharp peaks('quasiparticle' peaks) in the observed spectral functions in high $T_c$ cuprates. The computed results reveal that the spectral weight of the sharp peaks increases with hole doping rate in agreement with observation. It is shown that the observed sharp peaks are attributed to the enhancement of spinon pairing(spin singlet pair formation) by the presence of holon pair bosons in the superconducting state.

cond-mat.supr-con↗
arXiv2000

Holon Pairing Instability based on the Bethe-Salpeter Equation obtained from the t-J Hamiltonians of both U(1) and SU(2) Slave-boson Symmetries

We investigate a possibility of holon pairing for bose condensation based on the Bethe-Salpeter equation obtained from the use of the t-J Hamiltonians of both t he U(1) and SU(2) slave-boson symmetries. It is shown that the vertex function contributed from ladder diagram series involving holon-holon scattering channel in the Bethe-Salpeter equation leads to a singular behavior at a critical temperature at each hole doping concentration, showing the instability of the normal state against holon pairing. We find that the holon pairing instability occurs only in a limited range of hole doping, by showing an "arch" shaped bose condensation line in agreement with observation for high $T_c$ cuprates. It is revealed that this is in agreement with a functional integral approach of the slave-boson theories.

cond-mat.supr-con↗
arXiv2000

Holon Pair Bose Condensation in High $T_c$ Cuprates; Symmetry Breaking and Supersymmetry Conditions

Using the t-J Hamiltonian of U(1) slave-boson symmetry, bose condensation is discussed by showing the occurrence of symmetry breaking in the hole doped high $T_c$ cuprates. The symmetry breaking is shown to take place with the d-wave hole pairing, but not with the s-wave hole pairing. Based on a derived supersymmetry Hamiltonian we find that there exists a possibility of supersymmetry conditions in association with the pairing order parameters of both spinon and holon.

cond-mat.supr-con↗
arXiv2000

High $T_c$ Phase Diagram based on the SU(2) Slave-Boson Approach to the t-J Hamiltonian

Based on an improved SU(2) slave-boson approach to the t-J Hamiltonian, we derive a phase diagram of high $T_c$ cuprates which displays both the superconducting and pseudogap phases in the plane of temperature vs. hole doping rate. It is shown that the inclusion of phase fluctuations in the order parameters results in a closer agreement with the observed superconducting temperature(bose condensation line) of an arch shape as a function of hole doping rate.

cond-mat.supr-con↗
arXiv1999

Lanczos exact diagonalization study of field-induced phase transition for Ising and Heisenberg antiferromagnets

Using an exact diagonalization treatment of Ising and Heisenberg model Hamiltonians, we study field-induced phase transition for two-dimensional antiferromagnets. For the system of Ising antiferromagnet the predicted field-induced phase transition is of first order, while for the system of Heisenberg antiferromagnet it is the second-order transition. We find from the exact diagonalization calculations that the second-order phase transition (metamagnetism) occurs through a spin-flop process as an intermediate step.

cond-mat.str-el↗
arXiv1998

Study of Holon Pair Condensation Based on the U(1) Slave Boson Approach to a Modified t-J Hamiltonian

In order to obtain a reasonable phase diagram involving hole-pair condensation for hole-doped cuprate systems, we propose a modified t-J Hamiltonian in which a Coulomb repulsion term between nearest neighbor holes is considered. We show from the investigation of free energy that holon pair condensation can occur as a result of symmetry breaking. In addition, we introduce a possibility of supersymmetry condition at $T=0K$ in the intermediate region between the antiferromagnetic phase and the superconducting phase.

cond-mat.supr-con↗