Figure 1

Temperature-dependent Luttinger surface maps: (a),(b),(c) show the Luttinger surfaces of TTF-TCNQ as a function of temperature (200, 100, and 30 K), obtained from angle-resolved photoemission spectra. (a) shows the TTF (along slice 2, centered at $k_y\sim \pm 0.13b^{*}$) and TCNQ (along slice 1, centered at $k_y\sim \pm 0.17b^{*}$) main Luttinger surfaces are separated in momentum space [see also schematic (e)]. The TCNQ surface shows a $4k_F$ CDW superstructure at about $\pm 0.43b^{*}$ along slice 1 ($\Gamma \mathrm{\text{−}}Y$) in $k$ space. The $T=100\mathrm{K}$ map (b) shows features due to the $2k_F$ CDW order in addition to the $4k_F$ CDW vectors which evolve with reducing temperature. (c) shows that the low temperature ($T=30\mathrm{K}$) main TTF and TCNQ Luttinger surfaces are nearly one dimensional, in good agreement with a nesting picture of the $2k_F$ CDW vector. The main Luttinger surfaces occur at $k_y\sim \pm 0.15b^{*}$ and the $4k_F$ superstructures are at $\sim \pm 0.45b^{*}$ along slice 1 ($\Gamma \mathrm{\text{−}}Y$) in $k$ space [dark blue and green regions shown schematically in (f)]. (d) is a gray scale map of (c), showing the weaker backfolded structures (at $k_y\sim 0b^{*}$ and $\pm 0.3b^{*}$) more clearly. Along slice 2, the superstructures reflect deviations from perfect nesting due to small differences in peak positions and widths of the main Luttinger surfaces. (e) schematically shows the presence of the $4k_F$ CDW order (connecting red and brown regions), in the absence of $2k_F$ CDW order. Light blue and green regions in schematic (f) show the relation of the backfolded features with the $2k_F$ and $4k_F$ CDW order.Reuse & Permissions

Figure 2

Momentum distributuion curves of TTF-TCNQ: (a),(b) show the momentum distribution curves (MDCs) along slice 1 (TCNQ derived band) and slice 2 (TTF-derived band) at $T=30\mathrm{K}$ obtained using ARPES spectra. At $T=30\mathrm{K}$, the separation in their positions $(0.3\pm 0.01)b^{*}$ matches the CDW vector ($2k_F=0.295b^{*}$) known from structural studies. The peak widths imply a CDW coherence length of $\sim 120\AA$ for the TCNQ and $\sim 60\AA$ for the TTF-derived surfaces. Small gray arrow marks the weak superstructure also seen in the maps [Fig. 1d].Reuse & Permissions