The electronic conditions in the 5d<sup>1</sup>layer-metal LaI<sub>2</sub>making comparison with the iso-electronic tantalum dichalcogenides, with the other RE di-iodides, and with the RE monochalcogenides

Burrow, J H; Maule, C H; Strange, Paul; Tothill, J.N.; Wilson, J. A.

doi:10.1088/0022-3719/20/26/014

Cited by 35 publications

(14 citation statements)

References 49 publications

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“…Correspondingly both LaS and LaI 2 are La II compounds -in this case both metals; likewise GdS and GdI 2 are metallic Gd II compounds [160]. These two pairings, each divalent in our standard terminology, take approximate metal atom configurations of f 0 d 1 and f 7 d 1 respectively, and they are to be distinguished from trivalent La III and Gd III in say LaI 3 and GdI 3 , where we have outer configurations approximating to f 0 (d 0 ) and f 7 (d 0 ) respectively.…”

Section: Terminology and Treatment Of Valence And Electronic Configur...mentioning

confidence: 99%

Developments in the negative-Umodelling of the cuprate HTSC systems

Wilson

2001

J. Phys.: Condens. Matter

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This paper emphasizes once more the many strands which go into creating the unique and complex nature of the mixed-valent HTSC cuprates, above T c as below. Clearly it is not sensible to look in isolation to the lattice, magnetic or electronic aspects of the situation. Circumstances are too tightly coupled and interdependent. What one is in a position to do is to ascribe some preeminence in these matters. The line taken in this paper, as in its predecessors, is that charge constitutes the prime mover, but this taken within a chemical context, relating to bonding effects in the copper oxides and to a crucial shell-filling negative-U term of large magnitude. What dictates the uniqueness of copper in this is its particular position within the periodic table at the end of the 3dseries. This provides access to (i) three stable valencies, (ii) to the limited metallicity of tightbinding, mixed-valent YBa 2 Cu 3 O 7 , etc., (iii) to the p/d hybridized limitation of magnetic behaviour, and (iv) above all to the shell closure effects, with their dramatic energy adjustments of the relevant double-loading states when sited in high-valent local environment. This behaviour rests on the inhomogeneous electronic and structural conditions existing within these tight-binding mixed-valent systems. Normally such systems show strong positive-U behaviour and are magnetic. Here the shell-filling effects negate this U term to leave a net negative U eff of −3 eV per pair. That positions the bosonic electron pairs degenerate with E F . RVB spin coupling within the stripe phase geometry set up by the doped charge removes much spin-flip pair breaking, while the adopted 2D crystal structure with its saddle-point dominated F.S. provides the ideal k-space geometry from which to secure the negative-U driven pair formation. The Jahn-Teller effect associated with the d 9 electron count is crucial in upholding the two-subsystem nature of the HTSC materials.This paper looks at the support for this scenario that can be extracted from the recent work of Corson, Li, Mook, Valla, Norman, Varma, Gyorffy and many others. To the author it remains a mystery why other researchers have not examined the potential of this route for understanding the unique characteristics of the HTSC cuprates.3

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Section: Terminology and Treatment Of Valence And Electronic Configur...mentioning

confidence: 99%

Developments in the negative-Umodelling of the cuprate HTSC systems

Wilson

2001

J. Phys.: Condens. Matter

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“…Burrow et al [2] related this behavior to a contamination of their sample by semiconducting LaI 2.42 . Correction of the susceptibility values for a Curie impurity contribution resulted in the Pauli paramagnetism of the order of χ ≈ 100 × 10 −6 cm 3 /mol, a value, that exceeds the estimated value for a free-electron d 1 metal by approximately a factor of 3.…”

Section: Resultsmentioning

confidence: 97%

“…Each La atom is surrounded by a cube of I atoms slightly compressed along the c axis. Band structure calculations [2] revealed strong nesting characteristics at the Fermi surface of LaI 2 . However, no superconductivity or charge-density wave instability was found and their absence was attributed to insufficient electron-phonon interaction.…”

Section: Introductionmentioning

confidence: 96%

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The structural change of lanthanum diiodide upon hydrogenation

Ryazanov

Simon

Mattausch

et al. 2004

Journal of Alloys and Compounds

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“…The physical properties of these layered metallic iodides with 4 4 and 3 6 nets have been amply explored [26,[28][29][30][31]. The conduction band is of 5d character alone, no contribution of the 4f electrons or of iodine can be detected.…”

Section: Structures and Propertiesmentioning

confidence: 99%