Probing uniform and nonuniform charge ordering with polarized femtosecond optical pulses in geometrically frustrated <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>θ</mml:mi><mml:mtext>−</mml:mtext><mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:mi>BEDT</mml:mi><mml:mtext>−</mml:mtext><mml:mi>TTF</mml:mi><mml:mo>)</mml:mo></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:mi>M</mml:mi><mml:mi>Zn</mml:mi><mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:mi>SCN</mml:mi><mml:mo>)</mml:mo…

In this work, we investigated polarization-resolved photoinduced carrier relaxation dynamics associated with charge ordering (CO) in geometrically frustrated organic conductors $\ensuremath{\theta}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}M\mathrm{Zn}{(\mathrm{SCN})}_{4}$ (M = Rb, Cs) as a function of temperature. $\ensuremath{\theta}\text{\ensuremath{-}}\mathrm{Rb}$ Rb), polarization-dependent (anisotropic) and independent (isotropic) show similar temperature dependence. Moreover, discontinuous changes transient reflectivity amplitude an enhancement time are observed only upon heating near ${T}_{\mathrm{co}}=195\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. This is the first order phase transition due to long-range CO. However, $\ensuremath{\theta}\text{\ensuremath{-}}\mathrm{Cs}$ where frustration stronger than that $\ensuremath{\theta}\text{\ensuremath{-}}\mathrm{Rb}$, decreases below ${T}_{\mathrm{nco}}\phantom{\rule{4pt}{0ex}}\ensuremath{\approx}$ 150 K, anisotropic component slightly while isotropic one increases gradually without hysteresis. The behaviors indicate CO formed nonuniformly, is, multiple short-range domains appear distributed different orientations. found long-relaxation times suppress ${T}_{\mathrm{s}}\phantom{\rule{4pt}{0ex}}\ensuremath{\approx}$ 50 which lower glass ${T}_{\mathrm{g}}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}$ 100 whereas grows monotonically. distinct difference between them suggests occurrence structural lattice deforms randomly match glassy distribution charge-lattice coupling.