X-Ray Observation of Crossover of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>2</mn><mrow><msub><mrow><mi>k</mi></mrow><mrow><mi mathvariant="normal">F</mi></mrow></msub></mrow></math> to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>4</mn><mrow><msub><mrow><mi>k</mi></mrow><mrow><mi mathvariant="normal">F</mi></mrow></msub></mrow></math> Scattering in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mo>(</mo><mi mathvariant="normal">N</mi><mo>−</mo><mi mathvariant="normal">M</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">t</mi><mi mathvariant="normal">h</mi><mi mathvariant="normal">y</mi><mi mathvariant="normal">l</mi><mi mathvariant="normal">p</mi><mi mathvariant="normal">h</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">n</mi><mi mathvariant="normal">a</mi><mi mathvariant="normal">z</mi><mi mathvariant="normal">i</mi><mi mathvariant="normal">n</mi><mi mathvariant="normal">i</mi><mi mathvariant="normal">u</mi><mi mathvariant="normal">m</mi><mo>)</mo></mrow><mrow><mi>x</mi></mrow></msub></mrow><mrow><msub><mrow><mo>(</mo><mi mathvariant="normal">Phenazine</mi><mo>)</mo></mrow><mrow><mn>1</mn><mo>−</mo><mi>x</mi></mrow></msub></mrow><mo>(</mo><mi mathvariant="normal">Tetracyanoquinodimethane</mi><mo>)</mo><mo>[</mo><mrow><msub><mrow><mo>(</mo><mi mathvariant="normal">NMP</mi><mo>)</mo></mrow><mrow><mi>x</mi></mrow></msub></mrow><mrow><msub><mrow><mo>(</mo><mi mathvariant="normal">Phen</mi><mo>)</mo></mrow><mrow><mn>1</mn><mo>−</mo><mi>x</mi></mrow></msub></mrow><mo>(</mo><mi mathvariant="normal">TCNQ</mi><mo>)</mo><mo>]</mo></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>0.5</mn><mo><~</mo><mi>x</mi><mo><~</mo><mn>1.0</mn></math>

A. J. Epstein; J. S. Miller; J. P. Pouget; R. Comès

doi:10.1103/PhysRevLett.47.741

X-Ray Observation of Crossover of $2 k_{F}$ to $4 k_{F}$ Scattering in ${(N - M e t h y l p h e n a z i n i u m)}_{x} {(Phenazine)}_{1 - x} (Tetracyanoquinodimethane) [{(NMP)}_{x} {(Phen)}_{1 - x} (TCNQ)]$ , $0.5 <~ x <~ 1.0$

A. J. Epstein, J. S. Miller, J. P. Pouget, and R. Comès

Phys. Rev. Lett. 47, 741 – Published 7 September 1981

Abstract

We report the temperature-dependent x-ray diffuse scattering of ${(NMP)}_{x} {(Phen)}_{1 - x}$ -(TCNQ) as a function of conduction-electron density ( $x$ ). With decreasing $x$ three different unique electronic instability regimes are successively observed on the TCNQ chains: (i) the $2 k_{F}$ instability for $\frac{2}{3} <~ x <~ 1$ , (ii) both $2 k_{F}$ and $4 k_{F}$ instabilities for $0.57 <~ x <~ \frac{2}{3}$ , and (iii) the $4 k_{F}$ instability alone for $x$ close to 0.5. These results provide direct evidence for the critical role of interchain screening in determining the magnitude of the effective Coulomb interaction.