  Two-dimensional charge density wave (CDW) materials received much attention
for high responsivity and broadband photodetection in recent years, due to
their collective electron transport and narrow bandgap. However, the high dark
current density problem hinders their real application. Here we report a sharp
CDW transition in quasi-1D (TaSe4)2I, and apply it for broadband
photodetection. Especially at mid-infrared region, the device shows both high
photo responsivity of 1.18e3 A/W and large light on-off ratio of 80, which is
superior than 2D CDW TaS2 and most reported low-dimensional materials. The fact
for such high performance lies on two aspects. One is the much lower dark
current density resulted from the pseudo gap associated with 1D Luttinger
liquid state, which is supported by finite size scaling of nonlinear I-V at
variable temperatures and occurrence of 1D structural phase transition
consolidated by In-situ Raman spectroscopy. The other is the high photocurrent
associated with the Frohlich superconductivity state, manifested by an
ultrasensitive switching, which can be only accessible in 1D CDW materials, in
agreement with our density functional theory calculation. Our work thus reveals
the pivotal role of dimensionality in CDW phase transition, and paves a way for
implementing highly sensitive broadband photodetector.
