Exact treatment of magnetism-driven ferroelectricity in the one-dimensional compass model

We consider a class of one-dimensional compass models with antisymmetric Dzyaloshinskii-Moriya exchange interaction in an external magnetic field. Based on the exact solution derived by means of Jordan-Wigner transformation, we study the excitation gap, spin correlations, ground-state degeneracy, and critical properties at phase transitions. The phase diagram at finite electric and magnetic field consists of three phases: ferromagnetic, canted antiferromagnetic, and chiral. Dzyaloshinskii-Moriya interaction induces an electrical polarization in the ground state of the chiral phase, where the nonlocal string order and special features of entanglement spectra arise, while strong chiral correlations emerge at finite temperature in the other phases and are controlled by a gap between the nonchiral ground state and the chiral excitations. We further show that the magnetoelectric effects in all phases disappear above a typical temperature corresponding to the total bandwidth of the effective fermionic model. To this end we explore the entropy, specific heat, magnetization, electric polarization, and the magnetoelectric tensor at finite temperature. We identify rather peculiar specific-heat and polarization behavior of the compass model which follows from highly frustrated interactions.Comment: 15 pages, 15 figures, Slight change comparing with the published versio

6-Formyl-2-naphthyl cis-1,5,7-trimethyl-2,4-dioxo-3-aza­bicyclo­[3.3.1]nonane-7-carboxyl­ate

In the title compound, C23H23NO5, the C5N ring adopts an envelope conformation with a C atom as the flap, whilst the saturated C6 ring fused to it adopts a chair conformation. In the crystal, inversion dimers linked by pairs of N—H⋯O hydrogen bonds generate R 2 2(8) loops

2,5-Dibromo­terephthalic acid dihydrate

The asymmetric unit of the title compound, C8H4Br2O4·2H2O, contains one half-mol­ecule of 2,5-dibromo­terephthalic acid (DBTA) and one water mol­ecule. The DBTA mol­ecule is centrosymmetric. In the crystal structure, inter­molecular O—H⋯O hydrogen bonds link the mol­ecules, forming a three-dimensional framework

1-Diphenyl­phosphino-1′-(diphenyl­phosphinoyl)cobaltocenium hexa­fluorido­phosphate

The title compound, [Co(C17H14OP)(C17H14P)]PF6, was obtained unintentionally as the product of an attempted synthesis of [1,1′-bis­(oxodiphenyl­phospho­ranyl)cobaltocenium] hexa­fluorido­phosphate. The O atom of the oxo group is disordered over two positions with site occupancies of 0.65:0.35. The crystal structure contains weak inter­molecular C—H⋯F hydrogen bonds, connecting the components of the structure into chains parallel to [010]

(2′-Amino-4,4′-bi-1,3-thia­zol-2-aminium-κ2 N,N′)aqua­[citrato(4−)-κ3 O,O′,O′′)chromium(III) dihydrate

In the title compound, [Cr(C6H7N4S2)(C6H4O7)(H2O)]·2H2O, the CrIII atom is in a distorted octa­hedral environment, coordinated by one water mol­ecule, two N atoms from a protonated diamino­bithia­zole ligand and three O atoms from a citrate(4−) anion. The complex is zwitterionic, with the H atom from the uncoordinated carboxyl­ate group of the citrate anion transferred to one amino group of the diamino­bithia­zole ligand. O—H⋯O and N—H⋯O hydrogen bonds link the complexes into layers including the two uncoordinated water mol­ecules