arXiv subjects

Fu-Zhou Chen

Publications and source records attributed to Fu-Zhou Chen.

7 recordsLinked to original sources

arXiv2024

Identifying the ground state phases by spin-patterns in the Shastry-Sutherland model

Exploring the influence of frustration on the phases and related phase transitions in condensed matter physics is of fundamental importance in uncovering the role played by frustration. In the two-dimensional square lattice, a minimal frustration has been formulated in 1981 as the Shastry-Sutherland (SS) model described by competitions between the nearest-neighbor bond ($J_1$) and the next-nearest-neighbor one ($J_2$). In the two limits of $α=J_2/J_1$, i.e. $α\ll 1$ and $α\gg 1$, the corresponding phases are the N{é}el antiferromagnet (AFM) and the dimer-singlet(DS). Unfortunately, the intermediate regime remains controversial, and the nature of transition from the N{é}el AFM to the intermediate state is also unclear. Here we provide a pattern language to explore the SS model and take the lattice size $L=4 \times4$ with periodic boundary condition. We firstly diagonalize the Hamiltonian in an operator space to obtain all fundamental spin-patterns and then analyze their energy and occupancy evolutions with the frustration parameter $κ=α/ (1+α)$. Our results indicate that the intermediate regime is characterized by diagonal two-domain spin-pattern while the N{é}el AFM state has a diagonal single-domain and the DS has mixings of diagonal single- and four-domain. While the transition from the DS to the intermediate phase occurred around $α_c = 1.5$ is the first-order in nature, consistent with that in literature, the one from the intermediate phase to the AFM is clearly seen around $α_c = 1.277$, where it has a reversal of the contributions from the single- and two-domain patterns to the ground state. The result indicates that the pattern language is powerful in identifying the possible phases in frustrated models.

cond-mat.str-el↗

arXiv2023

An explicit evolution from Néel to striped antiferromagnetic states in the spin-1/2 $J_{1}$-$J_{2}$ Heisenberg model on the square lattice

The frustrated spin-$1/2$ $J_1-J_2$ Heisenberg model on the square lattice has been extensively studied since 1988 because of its close relationship to the high-temperature superconductivity in cuprates and more importantly involved novel phase of matter in its own right, namely, quantum spin liquid (QSL), one of hot topics in condensed matter physics in recent years. However, the phase diagram of the model, particularly in the maximally frustrated regime $J_2/J_1 \sim 0.5$, is quite controversial, and more seriously the nature of the QSL is not clear at all. Here we provide a pattern picture, on one hand, to show explicitly how the system evolves from the Néel antiferromagnetic (AFM) state at small $J_2$ to the striped AFM one at large $J_2$; on the other hand, to uncover the nature of the QSL if it exists in the intermediate $J_2$ coupling regime. For simplicity, we show our results by taking the square lattice $L=L_x \times L_y$ with size $L_x=L_y=4$ here and periodic boundary condition is considered, and furthermore, exact diagonalization is employed to confirm the correctness of our picture. Our results indicate that the highly frustration regime is characterized by diagonal two-domain, while the Néel AFM state has a diagonal single-domain and the striped AFM state shows itself as a diagonal four-domain, namely, completely diagonal antiferromagnetic order, in the present case. Increasing the system size, the number of the diagonal domains increases correspondingly, but the diagonal single-domain for the Néel AFM state and the diagonal $L_{x(y)}$-domain for the striped AFM state remain unchanged. Our results shed light on the understanding of the QSL.

cond-mat.str-el↗

arXiv2023

Ground state properties of the one-dimensional axial next-nearest-neighbor Ising model in a transverse field

Describing and understanding the consequences of competing interactions remains profoundly challenging in both classical and quantum systems, as it is difficult to identify suitable order parameters, thereby hindering the characterization of certain phases such as the floating phase found in the one-dimensional axial next-nearest-neighbor Ising (ANNNI) model in the presence of the frustration interactions between the nearest and next-nearest neighbor sites. In this work, we employ the pattern picture to explore the frustration physics in such a model. This picture has been comprehensively detailed in our previous article [Yang and Luo, Phys. Rev. E \textbf{112}, 044102 (2025)]. Here, we apply it to the ANNNI model with periodic boundary conditions, considering system sizes ranging from $L=16$ to $L=128$. Our results demonstrate that the ground state of the system comprises four phases: ferromagnetic, paramagnetic, floating, and $\langle 2,2 \rangle$ antiphase. The transition from the ferromagnetic to the paramagnetic phase is continuous, analogous to that in the transverse-field Ising model, while the transition from the floating phase to the antiphase is first order. Furthermore, the floating phase exhibits particularly intriguing characteristics: states with distinct domain structures emerge successively as the frustration parameter increases. As the system size grows, this succession becomes progressively denser, leading to the reasonable inference that it eventually approaches a continuous variation in the thermodynamic limit. To validate the effectiveness of our picture, we computed the second derivative of the ground-state energy, which exhibits multiple dips within the floating phase$-$consistent with the pattern language.

cond-mat.stat-mech↗

arXiv2022

Dissecting Quantum Phase Transition in the Transverse Ising Model

Despite the fact that a complete theoretical description of critical phenomena in connection with phase transitions has been well-established through the renormalization group theory, the microscopic nature of the phase transitions remains to be understood in a satisfactory way. For example, how does the interaction between individuals drive a system from one phase to another as a specific parameter varies, and how do the individuals respond to changes in this parameter during the process? Here we take the well-studied quantum phase transition (QPT) in the one-dimensional transverse Ising model (TIM) as an example to exhibit such a microscopic process. We first introduce $2L$ collective structures,referred to as patterns, for the TIM with $L$ ferromagnetically interacting spins, and then analyze the contributions of these patterns to the system's states, e.g., the ground state, the first excited state, and so on, from which the analogue of the QPT process between the disordered phase in the weakly coupling regime and the ferromagnetic phase in the strongly coupling regime is clearly identified around the interaction strength $J_c =1$. We systematically explore this process for small lattice sizes of $L=6, 8, 10, 12$, whose ground state energies are identical to those obtained by direct numerical exact diagonalization. Increasing the system size up to $L=128$, the actual QPT point located at $J_c = 1$ in the thermodynamical limit is gradually approached. Our results show that the pattern picture is not only able to provide a microscopic process of phase transitions, but also of practical interest in analyzing analogues of QPT in diverse quantum simulation platforms.

cond-mat.stat-mech↗

arXiv2017

Magnetization jump in one dimensional $J-Q_{2}$ model with anisotropic exchange

We investigate the adiabatic magnetization process of the one-dimensional $J-Q_{2}$ model with XXZ anisotropy $g$ in an external magnetic field $h$ by using density matrix renormalization group (DMRG) method. According to the characteristic of the magnetization curves, we draw a magnetization phase diagram consisting of four phases. For a fixed nonzero pair coupling $Q$, i) when $g<-1$, the ground state is always ferromagnetic in spite of $h$; ii) when $g>-1$ but still small, the whole magnetization curve is continuous and smooth; iii) if further increasing $g$, there is a macroscopic magnetization jump from partially- to fully-polarized state; iv) for a sufficiently large $g$, the magnetization jump is from non- to fully-polarized state. By examining the energy per magnon and the correlation function, we find that the origin of the magnetization jump is the condensation of magnons and the formation of magnetic domains. We also demonstrate that while the experienced states are Heisenberg-like without long-range order, all the \textit{jumped-over} states have antiferromagnetic or Néel long-range orders, or their mixing.

cond-mat.str-el↗

arXiv2014

Exotic phase separation in one-dimensional hard-core boson system with two- and three-body interactions

We investigate the ground state phase diagram of hard-core boson system with repulsive two-body and attractive three-body interactions in one-dimensional optic lattice. When these two interactions are comparable and increasing the hopping rate, physically intuitive analysis indicates that there exists an exotic phase separation regime between the solid phase with charge density wave order and superfluid phase. We identify these phases and phase transitions by numerically analyzing the density distribution, structure factor of density-density correlation function, three-body correlation function and von Neumann entropy estimator obtained by density matrix renormalization group method. These exotic phases and phase transitions are expected to be observed in the ultra-cold polar molecule experiments by properly tuning interaction parameters, which is constructive to understand the physics of ubiquitous insulating-superconducting phase transitions in condensed matter systems.

cond-mat.stat-mech↗

arXiv2013

Non-monotonic field dependence of Kondo conductance in a single-electron transistor driven by microwave field

The interplay between magnetic field and microwave applied in a single-electron transistor(SET) has a profound influence on the Kondo effect, as shown in a recent experiment[B. Hemingway, S. Herbert, M. Melloch and A. Kogan, arXiv:1304.0037(2013)]. For a given microwave frequency, the Kondo differential conductance shows a non-monotonic magnetic field dependence, and a very sharp peak is observed for certain field applied. Additionally, the microwave frequency is found to be larger of about one order than the corresponding Zeeman energy. These two features are not understood in the current theory. Here we propose a phenomenological mechanism to explain these observations. When both magnetic field and microwave are applied in the SET, if the frequency matches the (renormalized) Zeeman energy, it is assumed that the microwave is able to induce spin-flip in the SET, which leads to two consequences. One is the dot level shifts down and the other is the renormalization of the Zeeman energy. This picture can not only explain qualitatively the main findings in the experiment but also further stimulate the related experimental study of the dynamic response of the Kondo effect in out-of-equilibrium devices.

cond-mat.str-el↗