Magnetic and Electric Properties of Organic Conductors Probed by 13C-NMR Using Selective-Site Substituted Molecules

Abstract

Quasi-One and quasi-two dimensional organic conductors consisting of TTF derivatives such as BEDT-TTF (bis-(ethylene-dithio)-tetra-thia-fulvalene) and TMTCF (C = S; TMTTF: tetra-methyl-tetra-thia-fulvalene, C = Se; TMTSF: tetra-methyl-tetraselena-fulvalene) have been well investigated in condensed matter physics because of interest in the emerging electric and magnetic properties, such as the spin density wave, charge order, superconductivity, anti-ferromagnetism, and so on. To probe the electronic state, nuclear magnetic resonance (NMR) is one of the most powerful tools as the microscopic magnetometer. A number of 13 C-NMR studies have been performed of the double-site central 13 C= 13C bond substituted molecules. However, problems with the coupled spin system of 13 C= 13 C complicated the interpretation for observations on NMR.Therefore, single-site 13 C-enriched molecules are desired. We summarize the problem of Pake doublet and the preparation of the single-site 13 C-susbstituted BEDT-TTF and TMTCF molecules. We also demonstrate the superiority of 13 C-NMR of the single-site 13 C-susbstituted molecule utilizing the hyperfine coupling tensor.

Evidence of antiferromagnetic fluctuation in the unconventional superconductor λ -(BETS) 2GaCl4 by CKobayashi1, Kawamoto2 2017Phys. Rev. B265260View full textAdd to dashboardCite

“…In consequence, A I for peak I is 2.61 kOe/μ B , A II for peak II is 8.55 kOe/μ B , and σ is 149 ppm. The σ of 149 ppm is comparable to that of ET molecules [14].…”

“…The contradictions arise from experimental difficulties with low sensitivity and broad linewidths in the 77 Se NMR signal and the additional relaxation mechanism from molecular motions due to weak coupling of the 1 H nuclei with the π conducting electrons. Therefore, measurements from the well-established 13 C nuclei are desirable [14]. In this paper, we performed these 13 C NMR measurements by synthesizing 13 C-enriched BETS molecules in which one side of the central C=C bond is replaced by 13 C. By using the 13 C-enriched sample, we can overcome the difficulties of previous NMR studies because the 13 C sites exhibit a sharp spectral response, high sensitivity, and large electron density at the nucleus.…”

Charge ordering and antiferromagnetism in (TMTTF)2SbF6

“…1, a single site of the central carbon 13 C-enriched TMTTF molecule has been prepared by the method of Sn complex 18 and single crystals of (TMTTF) 2 SbF 6 have been synthesized by the standard electrochemical method. This single site 13 C-enriched TMTTF prevents the split of the NMR spectra caused by the Pake doublet mechanism and simplifies the quantitative analysis of the NMR spectra and the site assignment.…”

13C NMR study of commensurate antiferromagnetism in (TMTTF)2Br

“…1(b)] was synthesized by coupling the dibutyltin complexes and was prepared as described. 18,19 The advantages of this method include the availability of 13 C-dichloroacetic acid methyl ester and the establishment of the precursors of butyltin and ester complexes. 18,20 One-sided 13 C-enriched TMTTF eliminates spectral splitting by Pake doublets and enables easy analysis of NMR spectra.…”

“…However, conventional 13 C NMR with double-sided 13 C-enriched molecules involves the Pake doublet problem or restriction of the field direction setting. 18 Therefore, we performed 13 C NMR with a one-sided 13 C-enriched molecule to determinate the commensurate antiferromagnetic structure of (TMTTF) 2 Br and to verify the CO state above the antiferromagnetic phase.…”