arXiv subjects

Yupeng Wang

Publications and source records attributed to Yupeng Wang.

At least 127 records · Page 7Linked to original sources

arXiv2009

Interaction-induced anomalous transport behavior in one dimensional optical lattice

The non-equilibrium dynamics of spin impurity atoms in a strongly interacting one-dimensional (1D) Bose gas under the gravity field is studied. We show that due to the non-equilibrium preparation of the initial state as well as the interaction between the impurity atoms and other bosons, a counterintuitive phenomenon may emerge: the impurity atoms could propagate upwards automatically in the gravity field . The effects of the strength of interaction, the gradient of the gravity field, as well as the different configurations of the initial state are investigated by studying the time-dependent evolution of the 1D strongly interacting bosonic system using time-evolving block decimation (TEBD) method. A profound connection between this counterintuitive phenomenon and the repulsive bound pair is also revealed.

cond-mat.quant-gas↗

arXiv2009

Magnetic impurities in the two-band $s_\pm$-wave superconductors

We investigate the effects of magnetic impurities in a superconducting state with $s_\pm$ pairing symmetry. Within a two-band model, we find that the intra-band magnetic scattering serves as a pair breaker while the inter-band magnetic scattering preserves pairing and hardly affects transition temperature in the Born limit. We also show that the same physics can persist beyond the weak scattering region. Our results coincide with recent experimental measurements in iron-based superconductors and thus provides an indirect evidence of the possible $s_\pm$ pairing symmetry in these materials.

cond-mat.supr-con↗

arXiv2009

Cooperative order and excitation spectra in the bicomponent spin networks

A ferrimagnetic spin model composed of $S=1/2$ spin-dimers and $S=5/2$ spin-chains is studied by combining the bond-operator representation (for $S=1/2$ spin-dimers) and Holstein-Primakoff transformation (for $S=5/2$ spins). A finite interaction $J_{\rm DF}$ between the spin-dimer and the spin chain makes the spin chains ordered antiferromagnetically and the spin dimers polarized. The effective interaction between the spin chains, mediated by the spin dimers, is calculated up to the third order. The staggered magnetization in the spin dimer is shown proportional to $J_{\rm DF}$. It presents an effective staggered field reacting on the spin chains. The degeneracy of the triplons is lifted due to the chain magnetization and a mode with longitudinal polarization is identified. Due to the triplon-magnon interaction, the hybridized triplon-like excitations show different behaviors near the vanishing $J_{\rm DF}$. On the other hand, the hybridized magnon-like excitations open a gap $Δ_A\sim J_{\rm DF}$. These results consist well with the experiments on Cu$_{2}$Fe$_{2}$Ge$_{4}$O$_{13}$.

cond-mat.str-el↗

arXiv2009

Bose-Fermi mixture in one-dimensional optical lattices with hard-core interactions

We study a mixture of $N_{b}$ bosons with point hard-core boson-boson interactions and $N_{f}$ noninteracting spinless fermions with point hard-core boson-fermion interactions in 1D optical lattice with external harmonic confine potential. Using an extended Jordan-Winger transformation (JWT) which maps the hard-core Bose-Fermi mixture into two component noninteracting spinless fermions with hard-core interactions between them, we get the ground states of the system. Then we determine in details the one particle density matrix, density profile, momentum distribution, the natural orbitals and their occupations based on the constructed ground state wavefunctions. We also discuss the ground state properties of the system with large but finite interactions which lead to the lift of ground degeneracy. Our results show that, although the total density profile is almost not affected, the distributions for bosons and fermions strongly depend on the relative strengthes of boson-boson interactions and boson-fermion interactions.

cond-mat.quant-gas↗

arXiv2009

Fractional topological excitations and quantum phase transition in a bilayer 2DEG adjacent to a superconductor film

We study a bilayer two-dimension-electron-gas (2DEG) adjacent to a type-II superconductor thin film with a pinned vortex lattice. We find that with increasing interlayer tunneling, the system of half filling presents three phases: gapped phase-I (topological insulator), gapless critical phase-II (metal), and gapped phase-III (band insulator). The Hall conductance for phase-I/III is 2/0 $e^{2}/h$, and has non-quantized values in phase-II. The excitation (response to topological defect, a local vortex defect) in these three phases shows different behaviors due to the topological property of the system, including fractional charge $e/2$ for each layer in phase-I. While in the case of quarter filling, the system undergoes a quantum phase transition from metallic phase to topological insulator phase (with excitation of fractional charge $e/4$).

cond-mat.mes-hall↗

arXiv2009

Exact Solutions of a One-dimensional Quantum Spin Chain with SO(5)-Symmetry

A new exactly solvable one-dimensional spin-3/2 Heisenberg model with SO(5)-invariance is proposed. The eigenvalues and Bethe ansatz equations of the model are obtained by using the nested algebraic Bethe ansatz approach. Several exotic elementary excitations in the antiferromagnetic region such as neutral spinon with zero spin, heavy spinon with spin-3/2 and dressed spinon with spin-1/2 are found.

cond-mat.str-el↗

arXiv2009

Phase diagram of imbalanced fermions in optical lattices

The zero-temperature phase diagrams of imbalanced fermions in 3D optical lattices are investigated to evaluate the validity of the Fermi-Hubbard model. It is found that depending on the filling factor, s-wave scattering strength and lattice potential, the system may fall into the normal($N$) phase, magnetized superfluid(SF$_M$) or phase separation of $N$ and BCS state. By tuning these parameters, the superfluidity could be favorable by enhanced effective couplings or suppressed by the increased band gap. The phase profiles in the presence of a harmonic trap are also investigated under LDA, which show some exotic shell structures compared to those without the optical lattice.

cond-mat.quant-gas↗

arXiv2009

Exact solution for infinitely strongly interacting Fermi gases in tight waveguides

We present an exact analytical solution of the fundamental systems of quasi-one-dimensional spin-1/2 fermions with infinite repulsion for arbitrary confining potential. The eigenfunctions are constructed by the combination of Gireardeau's hard-core contacting boundary condition and group theoretical method which guarantees the obtained states to be simultaneously the eigenstates of $S$ and $S_z$ and fulfill the antisymmetry under odd permutation. We show that the total ground-state density profile behaves like the polarized noninteracting fermions, whereas the spin-dependent densities display different properties for different spin configurations. We also discuss the splitting of the ground states for large but finite repulsion.

cond-mat.str-el↗

arXiv2009

Exact solutions of an SO(5)-invariant spin-3/2 Fermi gas model

An exactly solvable model describing the dilute spin-3/2 fermion gas in one-dimensional optical trap is proposed. The diagonalization of the model Hamiltonian is derived by means of the Bethe ansatz method. Exotic spin excitations such as the heavy spinon with fractional spin 3/2, the neutral spinon with spin zero and the dressed spinon with spin 1/2 are found based on the exact solution.

cond-mat.str-el↗

arXiv2008

Topological edge states and quantum Hall effect in the Haldane model

We study the topological edge states of the Haldane's graphene model with zigzag/armchair lattice edges. The Harper equation for solving the energies of the edge states is derived. The results show that there are two edge states in the bulk energy gap, corresponding to the two zero points of the Bloch function on the complex-energy Riemann surface. The edge-state energy loops move around the hole of the Riemann surface in appropriate system parameter regimes. The quantized Hall conductance can be expressed by the winding numbers of the edge states, which reflects the topological feature of the Haldane model.

cond-mat.mes-hall↗

arXiv2008

Conservation laws of the Haldane-Shastry type spin chains

A systematic method to construct the complete set of conserved quantities of the Haldane-Shastry type spin chains is proposed. The hidden relationship between the Yang-Baxter relation and the conservation laws of the long-range interacting integrable models is exposed explicitly. An integrable anisotropic Haldane-Shastry model is also constructed.

cond-mat.str-el↗

arXiv2008

Quantum-Fluctuation-Driven Coherent Spin Dynamics in Small Condensates

We have studied quantum spin dynamics of small condensates of cold sodium atoms. For a condensate initially prepared in a mean field ground state, we show that coherent spin dynamics are {\em purely} driven by quantum fluctuations of collective spin coordinates and can be tuned by quadratic Zeeman coupling and magnetization. These dynamics in small condensates can be probed in a high-finesse optical cavity where temporal behaviors of excitation spectra of a coupled condensate-photon system reveal the time evolution of populations of atoms at different hyperfine spin states.

cond-mat.other↗

arXiv2008

Properties of A Class of Topological Phase Transition

The properties of a class of topological quantum phase transition (TQPT) are analyzed based on a model proposed by Haldane. We study the effect of finite temperature on this phase transition. We have found that finite temperature would drive this TQPT to be a crossover, while it is stable against the weak short range interaction. When the interaction is strong enough, however, this TQPT is unstable and other states would emerge. Then we investigate the effect of the on-site energy in the original haldane model. The critical difference between our TQPT and the topological phase transition in conventional quantum Hall system is discussed. Finally, we discuss the potential application of our analysis to a topological phase transition proposed in a realistic system.

cond-mat.mes-hall↗

arXiv2008

The minimum model for the iron-based superconductors

A single band $t$-$U$-$J_1$-$J_2$ model is proposed as the minimum model to describe the superconductivity of the newly discovered iron-based superconductors $R(O_{1-x}F_x)FeAs$ and $RO_{1-x}FeAs$ ($R=La, Ce, Sm, Pr, Nd,Gd$). With the mean-field approach, it is found that the pairing occurs in the d-wave channel. In the likely parameter region of the real materials, by lowering temperature, the system enters firstly the $d_{xy}$ superconducting phase with $D_{4h}$-symmetry and then enters the time-reversal-symmetry-broken $d_{xy}+id_{x^2-y^2}$ superconducting phase with $C_{4h}$-symmetry.

cond-mat.supr-con↗

arXiv2008

Intrinsic relation between ground-state fidelity and the characterization of a quantum phase transition

The notion of fidelity in quantum information science has been recently applied to analyze quantum phase transitions from the viewpoint of the ground state (GS) overlap for various many-body systems. In this work, we unveil the intrinsic relation between the GS fidelity and the derivatives of GS energy and find that they play equivalent role in identifying the quantum phase transition. The general connection between the two approaches enables us to understand the different singularity and scaling behaviors of fidelity exhibited in various systems on general grounds. Our general conclusions are illustrated via several quantum spin models which exhibit different kinds of QPTs.

cond-mat.other↗

arXiv2007

Fidelity and Quantum phase transition for the Heisenberg chain with the next-nearest-neighbor interaction

In this paper, we investigate the fidelity for the Heisenberg chain with the next-nearest-neighbor interaction (or the $J_1-J_2$ model) and analyze its connections with quantum phase transition. We compute the fidelity between the ground states and find that the phase transition point of the $J_1-J_2$ model can not be well characterized by the ground state fidelity for finite-size systems. Instead, we introduce and calculate the fidelity between the first excited states. Our results show that the quantum transition can be well characterized by the fidelity of the first excited state even for a small-size system.

cond-mat.other↗

arXiv2007

Partial entropy in finite-temperature phase transitions

It is shown that the von Neumann entropy, a measure of quantum entanglement, does have its classical counterpart in thermodynamic systems, which we call partial entropy. Close to the critical temperature the partial entropy shows perfect finite-size scaling behavior even for quite small system sizes. This provides a powerful tool to quantify finite-temperature phase transitions as demonstrated on the classical Ising model on a square lattice and the ferromagnetic Heisenberg model on a cubic lattice.

cond-mat.str-el↗

arXiv2007

Paired state in an integrable spin-1 boson model

An exactly solvable model describing the low density limit of the spin-1 bosons in a one-dimensional optical lattice is proposed. The exact Bethe ansatz solution shows that the low energy physics of this system is described by a quantum liquid of spin singlet bound pairs. Motivated by the exact results, a mean-field approach to the corresponding three-dimensional system is carried out. Condensation of singlet pairs and coexistence with ordinary Bose-Einstein condensation are predicted.

cond-mat.str-el↗