The Influence of Dimensionality on the Charge‐Density‐Wave Transition and its Application on Mid‐Infrared Photodetection

2D charge density wave (CDW) materials receive 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, a sharp CDW transition in quasi‐1D (TaSe4)2I is reported and applied for broadband photodetection. Especially at mid‐infrared region, the device shows both high photo responsivity of 1.18 ×103 A W−1 and large light on/off ratio of 80, which is superior to 2D CDW TaS2 and most reported low‐dimensional materials. Such high performance relies on two aspects. One is the much lower dark current density resulting 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 “Fröhlich superconductivity” state, manifested by an ultrasensitive switching, which can be only accessible in 1D CDW materials, in agreement with the authors’ density functional theory calculation. This work thus reveals the pivotal role of dimensionality in CDW phase transition and paves a way for implementing highly sensitive broadband photodetector. Sharp 1D charge density wave (CDW) transition in (TaSe4)2I is experimentally and theoretically investigated and applied for sensitive mid‐infrared photodetection; the achieved photo responsivity and on/off ratio are superior to 2D CDW TaS2 and most other low‐dimensional materials. This work not only reveals the important role of the dimensionality in CDW transition but also sheds light on the way for advanced mid‐infrared application.