Thermal entanglement and sharp specific-heat peak in an exactly solved spin-1/2 Ising-Heisenberg ladder with alternating Ising and Heisenberg inter–leg couplings

Abstract

The spin-1/2 Ising-Heisenberg two-leg ladder accounting for alternating Ising and Heisenberg inter-leg couplings in addition to the Ising intra-leg coupling is rigorously mapped onto to a mixed spin-(3/2,1/2) Ising-Heisenberg diamond chain with the nodal Ising spins S = 3/2 and the interstitial spin-1/2 Heisenberg dimers. The latter effective model with higher-order interactions between the nodal and interstitial spins is subsequently exactly solved within the transfer-matrix method. The model under investigation exhibits five different ground states: ferromagnetic, antiferromagnetic, superantiferromagnetic and two types of frustrated ground states with a non-zero residual entropy. A detailed study of thermodynamic properties reveals an anomalous specific-heat peak at low enough temperatures, which is strongly reminiscent because of its extraordinary height and sharpness to an anomaly accompanying a phase transition. It is convincingly evidenced, however, that the anomalous peak in the specific heat is finite and it comes from vigorous thermal excitations from a two-fold degenerate ground state towards a macroscopically degenerate excited state. Thermal entanglement between the nearest-neighbor Heisenberg spins is also comprehensively explored by taking advantage of the concurrence. The threshold temperature delimiting a boundary between the entangled and disentangled parameter space may show presence of a peculiar temperature reentrance.

Quasi-phases and pseudo-transitions in one-dimensional models with nearest neighbor interactions

“…While for specific heat and magnetic susceptibility it exhibits an extremely sharp peak indicating a "pseudo-transition" between the quasi-phases, this pseudo-transition closely resembles a typical second-order phase transition. Some evidence of quasi-phase and pseudo-transitions have already been manifested in recent previous works, such as Ising-XYZ diamond chain [16], tetrahedral chain [17], Ising-Heisenberg ladder model [18], Ising-Heisenberg triangular tube models [19]. However, here we present a general condition for appearing this quasi-phases and pseudo-transitions.…”

“…Indeed, some evidence of this behavior has already been observed in previous work [17][18][19][20], and spin-ice model with shortrange interaction in the Bethe-Peierls approach [20]. The entropy behavior reveals the similarity with the firstorder phase transition [21], so it is interesting to define the "latent heat" associated with the system in T p as…”

“…Near the pseudo-critical temperature, the specific heat becomes C 0 ≈ 2∆ T 2 e −2∆/T for T < T p and C 2 ≈ ǫ2 T 2 e −ǫ2/T 1 + e −ǫ2/T −2 for T p < T . Some evidence of this effect has already been observed in one-dimensional models such as those discussed in the literature [17][18][19].…”

“…However, there are some particular models [16][17][18][19] that satisfy the following condition w 0 ∼ w 2 ≫ w 1 and |w 0 − w 2 | ≫ 2w 1 . The free energy using the Taylor series expansion around…”

“…Lately, several one-dimensional models have been investigated in the framework of decorated structures, particularly Ising and Heisenberg models with a variety of structures, such as the Ising-Heisenberg models in diamond chain structure [15,16] as shown in fig.1a, one-dimensional double-tetrahedral chain (see fig.1b), in which the localized Ising spin regularly alternates with two mobile electrons delocalized over a triangular plaquette [17], alternating Ising-Heisenberg ladder model [18], Ising-Heisenberg triangular tube model [19]. * Electronic address: ors@dfi.ufla.br…”