Electronic structure of the quasi-one-dimensional organic conductors DCNQI (N,N′-dicyanoquinonediimine)-Cu salts

Akinori Tanaka, Ashish Chainani, Takayoshi Yokoya, Takashi Takahashi, Takafumi Miyazaki, Shinji Hasegawa, Takehiko Mori

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Abstract

A comparative study of the electronic structure of in situ synthesized quasi-one-dimensional organic conductors (DMe-DCNQI)2Cu and (MeBr-DCNQI)2Cu has been carried out using various techniques of electron spectroscopy, where DMe-DCNQI and MeBr-DCNQI are 2,5-dimethyl-N,N′-dicyanoquinonediimine and 2,5-methylbromine-N,N′-dicyanoquinonediimine, respectively. From the photon-energy dependence of the valence-band photoemission spectra obtained using synchrotron radiation, the origins of each observed feature are unambiguously characterized. While the feature at the Fermi level is primarily derived from π-bonded C and N 2p states, the contribution of Cu 3d states at the Fermi level is larger in the (MeBr-DCNQI)2Cu compared to the (DMe-DCNQI)2Cu. X-ray photoemission spectra of the valence band imply extensive hybridization of the Cu 3d states with C and N 2p states near the Fermi level. Line-shape analyses of the Cu 2p core-level spectra show that the ratio of Cu2+ to Cu+ is higher in (MeBr-DCNQI)2Cu compared to (DMe-DCNQI)2Cu, with the ratio being closer to 1:2 for (MeBr-DCNQI)2Cu. From a comparison of C KVV and Cu LVV Auger spectra with the self-convolution of the valence-band spectra, it is found that the effective on-site Coulomb correlation energies between the valence electrons are high on C sites as well as Cu sites in both salts, with U(pp)=6.5 eV and U(dd)=8.0 eV, respectively. In conjunction with core-level spectra, the spectra indicate that the on-site Coulomb correlation, the hybridization strength, and the charge-transfer energy between the Cu 3d and N 2p ligands are very similar in the two salts. The metal-insulator transition in (MeBr-DCNQI)2Cu at 160 K is then facilitated by the proximity of the Cu2+-to-Cu+ ratio to 1:2 supporting charge disproportion, while deviation from it stabilizes the metallic phase in (DMe-DCNQI)2Cu down to very low temperatures.

Original languageEnglish
Pages (from-to)7951-7959
Number of pages9
JournalPhysical Review B
Volume52
Issue number11
DOIs
Publication statusPublished - 1995
Externally publishedYes

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Organic conductors
Valence bands
Fermi level
Electronic structure
Core levels
conductors
Salts
Photoemission
electronic structure
salts
Metal insulator transition
Electron spectroscopy
valence
Synchrotron radiation
Convolution
Charge transfer
Photons
Ligands
photoelectric emission
X rays

ASJC Scopus subject areas

  • Condensed Matter Physics

Cite this

Electronic structure of the quasi-one-dimensional organic conductors DCNQI (N,N′-dicyanoquinonediimine)-Cu salts. / Tanaka, Akinori; Chainani, Ashish; Yokoya, Takayoshi; Takahashi, Takashi; Miyazaki, Takafumi; Hasegawa, Shinji; Mori, Takehiko.

In: Physical Review B, Vol. 52, No. 11, 1995, p. 7951-7959.

Research output: Contribution to journalArticle

Tanaka, Akinori ; Chainani, Ashish ; Yokoya, Takayoshi ; Takahashi, Takashi ; Miyazaki, Takafumi ; Hasegawa, Shinji ; Mori, Takehiko. / Electronic structure of the quasi-one-dimensional organic conductors DCNQI (N,N′-dicyanoquinonediimine)-Cu salts. In: Physical Review B. 1995 ; Vol. 52, No. 11. pp. 7951-7959.
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abstract = "A comparative study of the electronic structure of in situ synthesized quasi-one-dimensional organic conductors (DMe-DCNQI)2Cu and (MeBr-DCNQI)2Cu has been carried out using various techniques of electron spectroscopy, where DMe-DCNQI and MeBr-DCNQI are 2,5-dimethyl-N,N′-dicyanoquinonediimine and 2,5-methylbromine-N,N′-dicyanoquinonediimine, respectively. From the photon-energy dependence of the valence-band photoemission spectra obtained using synchrotron radiation, the origins of each observed feature are unambiguously characterized. While the feature at the Fermi level is primarily derived from π-bonded C and N 2p states, the contribution of Cu 3d states at the Fermi level is larger in the (MeBr-DCNQI)2Cu compared to the (DMe-DCNQI)2Cu. X-ray photoemission spectra of the valence band imply extensive hybridization of the Cu 3d states with C and N 2p states near the Fermi level. Line-shape analyses of the Cu 2p core-level spectra show that the ratio of Cu2+ to Cu+ is higher in (MeBr-DCNQI)2Cu compared to (DMe-DCNQI)2Cu, with the ratio being closer to 1:2 for (MeBr-DCNQI)2Cu. From a comparison of C KVV and Cu LVV Auger spectra with the self-convolution of the valence-band spectra, it is found that the effective on-site Coulomb correlation energies between the valence electrons are high on C sites as well as Cu sites in both salts, with U(pp)=6.5 eV and U(dd)=8.0 eV, respectively. In conjunction with core-level spectra, the spectra indicate that the on-site Coulomb correlation, the hybridization strength, and the charge-transfer energy between the Cu 3d and N 2p ligands are very similar in the two salts. The metal-insulator transition in (MeBr-DCNQI)2Cu at 160 K is then facilitated by the proximity of the Cu2+-to-Cu+ ratio to 1:2 supporting charge disproportion, while deviation from it stabilizes the metallic phase in (DMe-DCNQI)2Cu down to very low temperatures.",
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AU - Takahashi, Takashi

AU - Miyazaki, Takafumi

AU - Hasegawa, Shinji

AU - Mori, Takehiko

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N2 - A comparative study of the electronic structure of in situ synthesized quasi-one-dimensional organic conductors (DMe-DCNQI)2Cu and (MeBr-DCNQI)2Cu has been carried out using various techniques of electron spectroscopy, where DMe-DCNQI and MeBr-DCNQI are 2,5-dimethyl-N,N′-dicyanoquinonediimine and 2,5-methylbromine-N,N′-dicyanoquinonediimine, respectively. From the photon-energy dependence of the valence-band photoemission spectra obtained using synchrotron radiation, the origins of each observed feature are unambiguously characterized. While the feature at the Fermi level is primarily derived from π-bonded C and N 2p states, the contribution of Cu 3d states at the Fermi level is larger in the (MeBr-DCNQI)2Cu compared to the (DMe-DCNQI)2Cu. X-ray photoemission spectra of the valence band imply extensive hybridization of the Cu 3d states with C and N 2p states near the Fermi level. Line-shape analyses of the Cu 2p core-level spectra show that the ratio of Cu2+ to Cu+ is higher in (MeBr-DCNQI)2Cu compared to (DMe-DCNQI)2Cu, with the ratio being closer to 1:2 for (MeBr-DCNQI)2Cu. From a comparison of C KVV and Cu LVV Auger spectra with the self-convolution of the valence-band spectra, it is found that the effective on-site Coulomb correlation energies between the valence electrons are high on C sites as well as Cu sites in both salts, with U(pp)=6.5 eV and U(dd)=8.0 eV, respectively. In conjunction with core-level spectra, the spectra indicate that the on-site Coulomb correlation, the hybridization strength, and the charge-transfer energy between the Cu 3d and N 2p ligands are very similar in the two salts. The metal-insulator transition in (MeBr-DCNQI)2Cu at 160 K is then facilitated by the proximity of the Cu2+-to-Cu+ ratio to 1:2 supporting charge disproportion, while deviation from it stabilizes the metallic phase in (DMe-DCNQI)2Cu down to very low temperatures.

AB - A comparative study of the electronic structure of in situ synthesized quasi-one-dimensional organic conductors (DMe-DCNQI)2Cu and (MeBr-DCNQI)2Cu has been carried out using various techniques of electron spectroscopy, where DMe-DCNQI and MeBr-DCNQI are 2,5-dimethyl-N,N′-dicyanoquinonediimine and 2,5-methylbromine-N,N′-dicyanoquinonediimine, respectively. From the photon-energy dependence of the valence-band photoemission spectra obtained using synchrotron radiation, the origins of each observed feature are unambiguously characterized. While the feature at the Fermi level is primarily derived from π-bonded C and N 2p states, the contribution of Cu 3d states at the Fermi level is larger in the (MeBr-DCNQI)2Cu compared to the (DMe-DCNQI)2Cu. X-ray photoemission spectra of the valence band imply extensive hybridization of the Cu 3d states with C and N 2p states near the Fermi level. Line-shape analyses of the Cu 2p core-level spectra show that the ratio of Cu2+ to Cu+ is higher in (MeBr-DCNQI)2Cu compared to (DMe-DCNQI)2Cu, with the ratio being closer to 1:2 for (MeBr-DCNQI)2Cu. From a comparison of C KVV and Cu LVV Auger spectra with the self-convolution of the valence-band spectra, it is found that the effective on-site Coulomb correlation energies between the valence electrons are high on C sites as well as Cu sites in both salts, with U(pp)=6.5 eV and U(dd)=8.0 eV, respectively. In conjunction with core-level spectra, the spectra indicate that the on-site Coulomb correlation, the hybridization strength, and the charge-transfer energy between the Cu 3d and N 2p ligands are very similar in the two salts. The metal-insulator transition in (MeBr-DCNQI)2Cu at 160 K is then facilitated by the proximity of the Cu2+-to-Cu+ ratio to 1:2 supporting charge disproportion, while deviation from it stabilizes the metallic phase in (DMe-DCNQI)2Cu down to very low temperatures.

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