Ding Guo-Hui

Charge Gap in One-Dimensional Extended Hubbard Model*

By using the bosonization and renormalization group methods, we have studied the low energy physical properties in one-dimensional extended Hubbard model. The formation of charge and spin gaps is investigated at the half-filled electron band. An analytical expression for the charge gap in terms of the Coulomb repulsive interaction strength U and the nearest-neighbour interaction parameter V is obtained.

Quantum Phase Transition and Ferromagnetic Spin Correlation in Parallel Double Quantum Dots

We investigate electronic transport through a parallel double quantum dot (DQD) system with strong on-site Coulomb interaction, as well as the interdot tunnelling. By applying numerical renormalization group method, the ground state of the system and the transmission probability at zero temperature are obtained. For a system of quantum dots with degenerate energy levels and small interdot tunnel coupling, the spin correlations between the DQDs is ferromagnetic, and the ground state of the system is a spin-1 triplet state. The linear conductance will reach the unitary limit (2e2/h) due to the Kondo effect at low temperature. As the interdot tunnel coupling increases, there is a quantum phase transition from ferromagnetic to anti-ferromagnetic spin correlation in DQDs and the linear conductance is strongly suppressed.

Ising Transition in Dimerized XY Quantum Spin Chain

In the present paper, we proposed a simple spin-1/2 model which provides a exactly solvable example to study the Ising criticality with central charge c=1/2. By mapping it onto the real Majorana fermions, the Ising critical behavior is explored explicitly, although its bosonized form is not the double frequency sine-Gordon model.We proposed a simple spin-1/2 model which provides an exactly solvable example to study the Ising criticality with central charge . By mapping it onto the real Majorana fermions, the Ising critical behavior is explored explicitly, although its bosonized form is not the double frequency sine-Gordon model.

Charge and spin gaps in the dimerized Hubbard model

By using the bosonization and renormalization group methods, we have studied the low energy physical properties in the one-dimensional dimerized Hubbard model. The formation of charge and spin gaps is investigated both for the half-filled electron band and away from the half-filled band. The scaling laws of the charge and spin gaps with the dimerization parameter Δ and the repulsive interaction strength U are obtained.

The Edge Magnetization and Strip Phase of Graphene Quantum Dots with Long-Range Coulomb Interaction

We investigate the magnetism and optical absorption properties of charge neutral hexagonal graphene quantum dots (GQDs) terminated with zigzag edges by using a tight-binding Hubbard type model for the π electrons. Within the Hartree—Fock approximation and taking into account the long-range Coulomb interaction, our calculation yields a ferromagnetic ground state with magnetic moments localized on the edges for GQDs, and also gives an antiferromagnetism state with the energy very close to the ferromagnetism ground state. We find that both the ferromagnetic and the antiferromagnetic states have stripe patterned charge density distributions as a result of the long-range Coulomb interaction. The optical conductivity for GQDs has an energy gap in the low frequency regime in contrast to the bulk neutral graphene sheet where a universal constant is approached.

Computing Ground State Solution of Bose?Einstein Condensates Trapped in One-Dimensional Harmonic Potential

For Bose–Einstein condensates trapped in a harmonic potential well, we present numerical results from solving the time-dependent nonlinear Schrodinger equation based on the Crank–Nicolson method. With this method we are able to find the ground state wave function and energy by evolving the trial initial wave function in real and imaginary time spaces, respectively. In real time space, the results are in agreement with [Phys. Rev. A 51 (1995) 4704], but the trial wave function is restricted in a very small range. On the contrary, in imaginary time space, the trial wave function can be chosen widely, moreover, the results are stable.

Renormalization Group Study of Ising Transition in Double-Frequency sine-Gordon Model*

We utilize the renormalization group (RG) technique to analyze the Ising critical behavior in the double frequency sine-Gordon model. The one-loop RG equations obtained show unambiguously that there exist two Ising critical points besides the trivial Gaussian fixed point. The topology of the RG flows is obtained as well.

Properties of Coherent State for Hydrogen Atom

We construct the coherent state for the two-dimensional hydrogen atom, for which the averaged motion of position describes a Kepler ellipse. The coherent state can be expanded with respect to the eigenstates of 2D hydrogen atom, from which we evaluate the binding energy of the wave packet for this state.

Liquid-Gas Transition in the Ionic System

The phase transition in the ionic system in dimension d = 3 is studied in the formulation of quantum sine-Gordon field theory. By a variational method the phase diagram is investigated, and the critical point terminating the coexistence of conducting liquid and conducting gas is obtained

Numerical Study of ϕ4 Model by Potential Importance Sampling Method

We investigate the phenomena of spontaneous symmetry breaking for 4 model on a square lattice in the parameter space by using the potential importance sampling method, which was proposed by Milchev, Heermann, and Binder [J. Stat. Phys. 44 (1986) 749]. The critical values of the parameters allow us to determine the phase diagram of the model. At the same time, some relevant quantities such as susceptibility and specific heat are also obtained.