Chisa Hotta

Multiferroicity in an organic charge-transfer salt that is suggestive of electric-dipole-driven magnetism

Multiferroics, showing simultaneous ordering of electrical and magnetic degrees of freedom, are remarkable materials as seen from both the academic and technological points of view. A prominent mechanism of multiferroicity is the spin-driven ferroelectricity, often found in frustrated antiferromagnets with helical spin order. There, as for conventional ferroelectrics, the electrical dipoles arise from an off-centre displacement of ions. However, recently a different mechanism, namely purely electronic ferroelectricity, where charge order breaks inversion symmetry, has attracted considerable interest. Here we provide evidence for ferroelectricity, accompanied by antiferromagnetic spin order, in a two-dimensional organic charge-transfer salt, thus representing a new class of multiferroics. We propose a charge-order-driven mechanism leading to electronic ferroelectricity in this material. Quite unexpectedly for electronic ferroelectrics, dipolar and spin order arise nearly simultaneously. This can be ascribed to the loss of spin frustration induced by the ferroelectric ordering. Hence, here the spin order is driven by the ferroelectricity, in marked contrast to the spin-driven ferroelectricity in helical magnets.

Anomalous dielectric response in the dimer Mott insulatorκ−(BEDT-TTF)2Cu2(CN)3

We have measured and analyzed the dielectric constant of the dimer Mott insulator

Classification of Quasi-Two Dimensional Organic Conductors Based on a New Minimal Model

\kappa-

Effects of localized spins in quasi-two dimensional organic conductors

(BEDT-TTF)

Controlling frustrated liquids and solids with an applied field in a kagome Heisenberg antiferromagnet

_2

Field-induced Tomonaga-Luttinger liquid phase of a two-leg spin-1/2 ladder with strong leg interactions

Cu

Wilson ratio of a Tomonaga-Luttinger liquid in a spin-1/2 Heisenberg ladder

_2

Interaction of the ground state of quarter-filled one-dimensional strongly correlated electronic system with localized spins.

(CN)

Large surface relaxation in the organic semiconductor tetracene

_3

Universal temperature dependence of the magnetization of gapped spin chains.

, which is known as a playground for a spin-liquid state. Most unexpectedly, this particular organic salt has nontrivial charge degrees of freedom, being characterized by a dipole-glass-like dielectric relaxation below around 60 K. This is ascribed to the charge disproportionation within the dimer due to the intersite Coulomb repulsion. In this respect, the dipole observed here is purely quantum mechanical, and thereby exhibits unexpected responses.