arXiv subjects

Yong-Jun Liu

Publications and source records attributed to Yong-Jun Liu.

8 recordsLinked to original sources

arXiv2016

Phase diagram of a frustrated asymmetric ferromagnetic spin ladder

We perform a systematic investigation on the ground state of an asymmetric two-leg spin ladder (where exchange couplings of the legs are unequal) with ferromagnetic (FM) nearest-neighbor interaction and diagonal anti-ferromagnetic frustration using the Density Matrix Renormalization Group (DMRG) method. When the ladder is strongly asymmetric with moderate frustration, a magnetic canted state is observed between a FM state and a singlet dimerized state. The phase boundaries are dependent on the asymmetric strength $α_{a}$. On the other hand, when the asymmetric strength is intermediate, a so-called spin-stripe state (spins align parallel on same legs, but antiparallel on rungs) is discovered, and the system experiences a first-order phase transition from the FM state to the spin-stripe state upon increasing frustration. We present numerical evidence to interpret the phase diagram in terms of frustration and the asymmetric strength.

cond-mat.str-el↗

arXiv2015

Coupled Cluster Treatment of the Alternating Bond Diamond Chain

By the analytical coupled cluster method (CCM), we study both the ground state and lowest-lying excited-state properties of the alternating bond diamond chain. The numerical exact diagonalization (ED) method is also applied to the chain to verify the accuracy of CCM results. The ED results show that the ground-state phase diagram contains two exact spin cluster solid ground states, namely, the tetramer-dimer (TD) state and dimer state, and the ferrimagnetic long-range-ordered state. We prove that the two exact spin cluster solid ground states can both be formed by CCM. Moreover, the exact spin gap in the TD state can be obtained by CCM. In the ferrimagnetic region, we find that the CCM results for some physical quantities, such as the ground-state energy, the sublattice magnetizations, and the antiferromagnetic gap, are comparable to the results obtained by numerical methods. The critical line dividing the TD state from the ferrimagnetic state is also given by CCM and is in perfect agreement with that determined by the ED method.

cond-mat.str-el↗

arXiv2015

Coupled cluster treatment of one quasi-one-dimensional coupled spin triangles

By using the coupled cluster method (CCM) and the numerical exact diagonalization (ED) method, we investigated the properties of the one quasi-one-dimensional coupled spin triangles. The results of ED disclose that the system is in the exact tetramer-dimer (TD) state if a ac1, we find that CCM results for some physical quantities, such as the ground state energy, the magnetization and the antiferromagnetic gap are in excellent agreement with the results obtained by ED. Thus, CCM can be used to accurately analyze the properties of the quasi-one-dimensional coupled spin triangles in the whole parameter region. We believe that it can also be applied to investigating the properties of other quasi-one spin systems reliably.

cond-mat.str-el↗

arXiv2015

Analytical and numerical studies of the one-dimensional sawtooth chain

By using the analytical coupled cluster method, the numerical exact diagonalization method, and the numerical density matrix renormalization group method, we investigated the properties of the one-dimensional sawtooth chain. The results of the coupled cluster method based on Neel state demonstrate that the ground state is in the quasi-Neel-long-range order state when a ac2. The results of the coupled cluster method and the density matrix renormalization group method both disclose that the type of the quantum phase transition occurring at ac2 belongs to the first-order transition.

cond-mat.str-el↗

arXiv2013

Noncollinear magnetism and half-metallicity in biased bilayer zigzag graphene nanoribbons

We study in this paper the edge polarizations and their consequences for a biased Bernal stacked bilayer graphene nanoribbon with zigzag termination. The magnetic states are classified according to the interlayer and intralayer couplings between the edge polarizations, and the magnetic phase diagram of doping versus bias voltage is given. Coplanar magnetic phase is found and the variation of its magnetic structure with the bias voltage is investigated. For all the magnetic states, we also discuss the possibility of the half-metallicity, and for a ribbon with perfect zigzag edges we predict seven kinds of the half-metallic states, which are characterized by their distinct magnetic structures and quantized electrical conductances along the ribbon.

cond-mat.mes-hall↗

arXiv2011

Zigzag graphene nanoribbons without inversion symmetry

Graphene on a substrate will suffer an inversion-symmetry-breaking (ISB) lattice potential. Taking electron-electron interaction into account, we study in this paper the possibility of half-metallicity and noncollinear (NC) magnetic phase for graphene zigzag nanoribbons without inversion symmetry. At half-filling it is found that half-metallic(HM) state can be achieved at an intermediate value of the ISB potential due to its competition with the electron-electron interaction. Away from half-filling, the phase diagrams of doping versus ISB potential for different ribbon width are given, where the regimes for the HM states and NC magnetic state are clearly indicated and discussed. For ribbons with perfect edges, we predict a topological transition between two HM states with different magnetic structures, which is accompanied by an abrupt transition of electrical conductance along the ribbon from $2e^2/h$ to $e^2/h$.

cond-mat.mes-hall↗

arXiv2001

The study of spin-spin correlations in quasi-one-dimensional Heisenberg antiferromagnetic clusters

For a class of quasi-one-dimensional clusters, by using exact diagonalization, we study the effect of side spins on the spin-spin correlations on chain. Our calculations show that the side spins added in the same sublattice can effectively strengthen the spin-spin correlations in large distance region and make the change tend to flat. It is exactly proved that periodically adding side spins can set up magnetic long-range orders in the ground state. Also we investigate the effect of the density of side spins on correlation strength. The case that two sublattices have different localized spins is discussed.

cond-mat.str-el↗

arXiv2001

Quantum Phase Transitions in Spin-1/2 Frustrated Molecular Cluster: the Numerical Evidence

By exact diagonalization, we investigate several spin-$\frac 12$ $J_1-J_2$ real clusters of molecular scale with different shapes. Our calculations show that when the ratio, $η$, of next nearest neighbor to nearest neighbor bonds is equal to 1, even the cluster of only 25 sites exhibits the bulk behaviors and has the quantum phase transitions. Two effective critical points are around $J_2/J_1=0.3762$ and 0.612 respectively. They are very close to those of the infinite $J_1-J_2$ square lattice. But, when $η\leq 0.85$, the quantum phase transition around $J_2/J_1=0.3762$ disappears. By calculating the distributions of the average values of $S_i^z$, the bulk behaviors are demonstrated graphically. In the intermediate phase, the sites on the corners have distinctly different character from the other sites. The distribution is obviously centralized on the corner sites.

cond-mat.str-el↗