New Luttinger-Liquid Physics from Photoemission on ${\mathrm{Li}}_{0.9}{\mathrm{Mo}}_6{\mathrm{O}}_{17}$

Temperature dependent high resolution photoemission spectra of quasi-one-dimensional ${\mathrm{Li}}_{0.9}{\mathrm{Mo}}_6{\mathrm{O}}_{17}$ evince a strong renormalization of its Luttinger-liquid density-of-states anomalous exponent. We trace this new effect to interacting charge neutral critical modes that emerge naturally from the two-band nature of the material. ${\mathrm{Li}}_{0.9}{\mathrm{Mo}}_6{\mathrm{O}}_{17}$ is shown thereby to be a paradigm material that is capable of revealing new Luttinger physics.

Figure 1

ARPES spectra of ${\mathrm{Li}}_{0.9}{\mathrm{Mo}}_6{\mathrm{O}}_{17}$ measured at $T=200\mathrm{K}$, $h\nu =30\mathrm{eV}$. (a), (b) Energy vs momentum spectra taken along $\Gamma -Y$ and off-normal direction, respectively. (c) A schematic view of the 1D FS with the $k$ space paths of (a) and (b) indicated. (d) Stack view of (b), with dashed lines highlighting the band dispersions.

Figure 2

(a) $T$-dependent spectra angle integrated along path for Fig. 1a. Only selected temperatures are shown for clarity. Inset shows the wide energy range spectrum at 30 K. (b)–(d) Fitting with finite $T$ LL spectral function. Inset in (b) shows the details of the fitting between $-0.04\mathrm{eV}$ and $-0.07\mathrm{eV}$.

Figure 3

(a) $\alpha (T)$ extracted from fitting of the spectra in Fig. 2a (●) for a complete $T$ series and the same (▴) measured for the $k$ path of Fig. 1b on the same sample. Typical error bar from fitting $\approx \pm 0.03$. The line is a theory calculation with our model (see text). (b) Kosterlitz-Thouless flow for $V_2=0$, $g_{\sigma -}=0$; finite values give the same basic structure. (c) $\alpha (T)$ as $V_1$ increases, showing two different behaviors. (d) $\alpha (T)$ measured on 6 samples, with error bars (not shown) similar to (a). Shading highlights two different behaviors much like those in theory curves of panel (c) (see text).