Peculiarities in pseudo-transitions of a mixed spin-$(1/2,1)$ Ising-Heisenberg double-tetrahedral chain in an external magnetic field

Spin dynamics of a tetrahedral cluster magnet

We study the magnetism of a lattice of coupled tetrahedral spin-1/2 clusters which might be of relevance to the tellurate compounds Cu2Te2O5X2, with X=Cl, Br. Using the flow equation method we perform a series expansion in terms of the inter-tetrahedral exchange couplings starting from the quadrumer limit. Results will be given for the magnetic instabilities of the quadrumer phase and the dispersion of elementary triplet excitations. In limiting cases of our model of one- or two dimensional character we show our results to be consistent with findings on previously investigated decoupled tetrah…

Interplay between spin frustration and thermal entanglement in the exactly solved Ising-Heisenberg tetrahedral chain

The spin-1/2 Ising-Heisenberg tetrahedral chain is exactly solved using its local gauge symmetry, which enables one to establish a rigorous mapping with the corresponding chain of composite Ising spins tractable within the transfer-matrix approach. Exact results derived for spin-spin correlation functions are employed to obtain the frustration temperature, at which a product of correlation functions along an elementary triangular plaquette becomes negative and the relevant spins experience a spin frustration. In addition, we have exactly calculated a concurrence quantifying thermal entanglemen…

Phase diagram of truncated tetrahedral model

Phase diagram of a discrete counterpart of the classical Heisenberg model, the truncated tetrahedral model, is analyzed on the square lattice, when the interaction is ferromagnetic. Each spin is represented by a unit vector that can point to one of the 12 vertices of the truncated tetrahedron, which is a continuous interpolation between the tetrahedron and the octahedron. Phase diagram of the model is determined by means of the statistical analogue of the entanglement entropy, which is numerically calculated by the corner transfer matrix renormalization group method. The obtained phase diagram…

Quantum internal modes of solitons in 1d easy-plane antiferromagnet in strong magnetic field

In presence of a strong external magnetic field the dynamics of solitons in a one-dimensional easy-plane Heisenberg antiferromagnet exhibits a number of peculiarities. Dynamics of internal soliton degrees of freedom is essentially quantum, and they are strongly coupled to the "translational" mode of soliton movement. These peculiarities lead to considerable changes in the response functions of the system which can be detected experimentally.

Ground state properties of a fully frustrated quantum spin system

We find that ground states of the quantum Heisenberg antiferromagnet on the geometrically frustrated pyrochlore checkerboard lattice are singlets and can be expressed in terms of positive matrices. The magnetization at zero external field vanishes for each frustrated tetrahedral unit separately and there is an upper bound of 1/8 in natural units on the susceptibility both for the ground state and at finite temperature. These results are the first exact ones in this field and generalize to some other lattices; the approach is also of interest for other spin systems.

Finite size induced phenomena in 2D classical spin models

We make a short overview of the recent analytic and numerical studies of the classical two-dimensional XY and Heisenberg models at low temperatures. Special attention is being paid to an influence of finite system size L on the peculiarities of the low-temperature phase. In accordance with the Mermin-Wagner-Hohenberg theorem, spontaneous magnetisation does not appear in the above models at infinite L. However it emerges for the finite system sizes and leads to new features of the low-temperature behaviour.

关于临界残余熵与一维模型有限温度伪相变之间关系的猜想

A conjecture on the relationship between critical residual entropy and finite temperature pseudo-transitions of one-dimensional models

本文提出猜想：若一维模型零温度临界点的残余熵单侧连续，则有限温度下将出现伪相变，并经 Ising-Heisenberg 模型验证。

Real-space renormalization group method for quantum 1/2 spins on the pyrochlore lattice

A simple phenomenological real-space renormalization group method for quantum Heisenberg spins with nearest and next nearest neighbour interactions on a pyrochlore lattice is presented. Assuming a scaling law for the order parameter of two clusters of different sizes a set of coupled equations that gives the fixed points of the renormalization group transformation and, thus, the critical temperatures and ordered phases of the system is found. The particular case of spins $\frac{1}{2}$ is studied in detail. Furthermore, to simplify the mathematical details, from all the possible phases arising …

Finite size effects around pseudo-transition in one-dimensional models with nearest neighbor interaction

Recently gigantic peaks in thermodynamic response functions have been observed at finite temperature for one-dimensional models with short-range coupling, closely resembling a second-order phase transition. Thus, we will analyze the finite temperature pseudo-transition property observed in some one-dimensional models and its relationship with finite size effect. In particular, we consider two chain models to study the finite size effects; these are the Ising-Heisenberg tetrahedral chain and an Ising-Heisenberg-type ladder model. Although the anomalous peaks of these one-dimensional models have…

Study of spin models with polyhedral symmetry on square lattice

Anisotropy is important for the existence of true long range order in two dimensional (2D) systems. This is firmly exemplified by the $q$-state clock models in which discreteness drives the quasi-long range order into a true long range order at low temperature for $q> 4$. Previously we studied 2D edge-cubic spin model, which is one of the discrete counterpart of the continuous Heisenberg model, and observed two finite temperature phase transitions, each corresponds to the breakdown of octahedral ($O_h$) symmetry and $C_{3h}$ symmetry, which finally freezes into ground state configuration. The …