Abstract
Charge order affects most of the electronic properties but is believed not to alter the spin arrangement since the magnetic susceptibility remains unchanged. We present electron-spin-resonance experiments on quasi-one-dimensional(TMTTF)2Xsalts (X=PF6, AsF6, and SbF6), which reveal that the magnetic properties are modified belowTCOwhen electronic ferroelectricity sets in. The coupling of anions and organic molecules rotates the g-tensor out of the molecular plane creating magnetically nonequivalent sites on neighboring chains at domain walls. Due to anisotropic Zeeman interaction a novel magnetic interaction mechanism in the charge-ordered state is observed as a doubling of the rotational periodicity ofΔH.
Highlights
Charge disproportionation is a common ordering mechanism in correlated electron systems that is intensively investigated in transition-metal oxides as well as organic compounds [1, 2] because it is recognized to influence charge, lattice, and magnetic degrees of freedom
Report comprehensive electron spin resonance (ESR) investigations that reveal a novel magnetic interaction mechanism caused by charge disproportionation; we observe first evidence that charge order breaks the symmetry of the magnetic degree of freedom in these quantum spin chains
Our findings are in accord with the suggestion by Riera and Poilblanc [52] that charge order in TMTTF salts is a cooperative effect between the Coulomb interaction and the electronic coupling of the TMTTF stacks to the anions The charge disproportionation causes an imbalance in the Coulomb attraction on the anions, which become slightly distorted in bc plane in accord with thermal expansion results by de Souza et al [53]
Summary
Charge disproportionation is a common ordering mechanism in correlated electron systems that is intensively investigated in transition-metal oxides as well as organic compounds [1, 2] because it is recognized to influence charge, lattice, and magnetic degrees of freedom. Xray investigations could not identify any superstructure, on this account it is known as a “structureless” transition [27] In these strongly correlated electron systems, nearestneighbor Coulomb repulsion causes CO upon cooling below TCO characterized by a charge gap in the transport properties [28]. Report comprehensive electron spin resonance (ESR) investigations that reveal a novel magnetic interaction mechanism caused by charge disproportionation; we observe first evidence that charge order breaks the symmetry of the magnetic degree of freedom in these quantum spin chains
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