a Layered side view of TaS₂ material. b Structural diagram of the phase transition in TaS2 material. c The structure of Star-of-Daid. d Charge Transfer Analysis in 1T-TaS₂. e Optical image of a two-probe 1T-TaS₂ device. One electrode is grounded (GND) and the other was used to apply the voltage (V). f Temperature-electric field phase diagram of 1T-TaS₂ nanodevice, illustrating the resistance evolution across the NC-CDW to IC-CDW phase transition. g Temperature-dependent current-electric field characteristics of 1T-TaS₂ measured from 77 K to 300 K, revealing three distinct electronic phases: supercooled NC-CDW (sc-NC-CDW) at low fields, NC-CDW at intermediate fields, and IC-CDW at high fields. The threshold electric field for the NC-CDW to IC-CDW transition exhibits pronounced temperature dependence, increasing systematically with decreasing temperature, reflecting enhanced CDW phase stability at lower temperatures. h Triangular diagram illustrating the combined effect of environmental temperature T, electric field E, and light intensity U on the phase transition of 1T-TaS₂. The color gradient represents the electron temperature T_e, which is determined by T, E, and U as T_e = f(T,E,U). The free energy difference ΔG driving the phase transition is influenced by T_e. Below the threshold T_e < T_e−th, 1T-TaS₂ remains in the IC-CDW phase; above T_e > T_e−th, it transitions to the NC-CDW phase.

Figure 1e depicts the device configuration used for the experiments with the 1T-TaS₂ layer encapsulated by h-BN layers, where The encapsulation setup helps to isolate the 1T-TaS₂ layer from environmental effects and ensures a controlled environment for studying its electronic behavior. Notably, the NCCDW-CCDW phase transition typically observed in bulk crystals is absent in nanometer-thick 1T-TaS₂ devices, with no characteristic resistivity jump in temperature-dependent measurements, originates from thickness-dependent kinetic suppression of long-range lattice modulations³⁶ (Fig. 1f, g). The temperature-dependent resistance (Fig. 1f) reveals a single phase boundary between IC-CDW (high-E) and NC-CDW (low-E) states, with resistivity jump associated with commensurate ordering. The color gradient maps the sharp boundary between high-resistance (green) NC-CDW and low-resistance (blue) IC-CDW states, demonstrating the systematic increase in critical electric field required for phase transition as temperature decreases. The transition requires progressively higher threshold voltages at lower temperatures, with the resistance differential between phases becoming more significant—indicative of enhanced electron-lattice coupling and substantial electronic structure reorganization in the NC-CDW state. The voltage-temperature hysteresis in Fig. 1g arises from the enhanced electron-phonon coupling in the NC-CDW phase, where David-star domain pinning at discommensuration boundaries elevates the free-energy barrier for phase transitions. Notably, applying high in-plane electric fields (E > 0.23 V/μm) enables metastable state access by driving domain wall depinning. Figure 1h presents a thermodynamic phase space diagram illustrating the cooperative effects of temperature (1/T), electric field (E), and incident radiation intensity (U) on the NC-CDW to IC-CDW phase transition in 1T-TaS₂. The triangular representation depicts the free energy barrier (ΔG) separating these phases, where the non-linear coupling between the three stimuli (thermal, electrical, optical) through their cumulative effect on effective electronic temperature T_e. The colored gradient surface represents the effective electronic temperature distribution across this parameter space, with T_e-th marking the critical threshold value that determines the boundary between stable NC-CDW (T_e < T_e-th) and IC-CDW (T_e > T_e-th) phases. As ambient temperature decreases, the transition barrier increases substantially, necessitating stronger electric fields or higher radiation intensities to overcome the enhanced stability of the NC-CDW phase. The multi-parameter control of ΔG demonstrated in this phase diagram underpins the exceptional tunability of CDW-based optoelectronic devices, providing precise control over electronic transport properties through strategic combinations of thermal, electrical, and optical stimuli.

THz photocurrent generation mechanisms and optoelectronic response

We have developed a THz detection device on a high-resistance silicon substrate, where 1T-TaS₂ functions as the active charge transport channel due to its tunable CDW properties. The device architecture incorporates h-BN encapsulation to preserve the intrinsic material properties and mitigate environmental degradation, while Au/Cr electrodes ensure ohmic contacts with minimal interfacial resistance, as illustrated in Fig. 2a. Detailed experimental setup and measurement protocols are documented in Fig. S2 (Supporting Information). When the THz wave interacts with the metal antennas, it induces the collective oscillation of surface electrons, generating spoof surface plasmons^38,39, which effectively enhance the localized electric field near the channel, thereby amplifying the interaction between the THz radiation and the 1T-TaS₂ CDW. In Fig. 2b, we recorded the distinct phase transition behaviors under varying light intensities demonstrate a clear dependence of the phase transition on the incident light power, modulating the CDW states under external photoexcitation. The hysteresis phenomenon originates from the potential barriers between different phase states of materials, enabling it to maintain its state even when the intensity of the external electric field is reduced. Figure 2b elucidates the critical relationship between threshold voltage and incident power density, wherein subtle variations in illumination produce measurable shifts in the phase transition thresholds. The CDW state response to the dual stimulus of electrical bias and terahertz radiation demonstrates distinctive non-equilibrium dynamics. The different threshold voltages observed during forward and reverse bias sweeps (V_th-H and V_th-L, respectively) reflect the metastable states formed during the transition process. Notably, increasing light intensity reduces the critical bias voltage required to trigger transitions, indicating that photon energy reduces the free-energy barrier separating the NC-CDW and IC-CDW phases. The phenomenon stems from photo-induced modulation of electron-phonon coupling, which lowers the effective activation energy landscape and facilitates phase transitions at lower voltages. We observe a sharp current jump when the applied voltage exceeds V_th-H, marking the threshold switching from a low-conductivity state to a high-conductivity state. During the reverse sweep, the transition back to the low-conductivity state occurs at a lower voltage V_th-L, corresponding to a smaller critical electric field, thus forming a hysteresis window defined as V_th-H−V_th-L. The hysteresis can be attributed to the following mechanisms: (1) Field-Induced Depinning and Joule Heating: As reported in prior studies^40,41, the electric-field-driven phase transition in 1T-TaS₂ results from a combination of field-induced depinning of the CDW and Joule heating effects. The applied electric field overcomes the pinning potential, allowing the CDW to slide, while Joule heating (P = I²R) raises the local temperature, further facilitating the transition to the IC-CDW state. (2) THz-Induced Lattice Dynamics: The 0.12 THz field induces coherent vibrations of Ta atoms, modulating the Ta-Ta bond distances and perturbing the periodic lattice distortion associated with the CDW. This reduces the pinning potential, promoting localized CDW sliding or collapse, which manifests as a stepwise decrease in resistance. This THz-driven effect synergistically enhances the nonlinear response of the current to the applied bias, with the maximum amplification occurring near the threshold voltage V_th-H. During the reverse sweep, the recovery of the pinning potential and the cooling of the device lag behind, resulting in a lower V_th-L, thus contributing to the hysteresis. As shown in Fig. 2c, the device was irradiated with THz light of varying power densities ranging from 0.42 mW/cm² to 2.5 mW/cm² modulated at 1 Hz, with the dark current also indicated at the beginning. The device demonstrates a clear photocurrent response to different THz power levels, as evidenced by the periodic current modulation in response to the 1 Hz light pulses. The inset shows a linear relationship between the photocurrent (I_ph) and the input power (P_in), with a power-law fitting coefficient of approximately α = 0.94, confirming that the photocurrent scales almost linearly with THz power.

Fig. 2: The schematic of TaS₂ device, THz detection mechanism and related performance.

a Schematic illustration of the THz photodetection setup showing the optical path from laser source through parabolic mirror to the device, with cross-sectional view of the 1T-TaS₂/h-BN heterostructure on Si/SiO? substrate and Au electrodes labeled as source (S) and drain (D). b Current-voltage characteristics of the device under varying THz illumination intensities (0–4.1 mW/cm²), showing distinct hysteresis loops and threshold voltage shifts. Inset: equivalent circuit diagram and magnified view of threshold voltage region. c Time-dependent photocurrent response showing power-law relationship (I_ph ∝ P^a) with exponent α = 0.94, as measured over increasing power densities from 0.42 to 2.5 mW/cm². d Schematic comparison of atomic arrangements in normal state versus CDW state, illustrating the periodic lattice distortion with wavelength π/k? in the CDW phase. e Energy-momentum diagram showing the potential energy landscape modification under applied voltage, demonstrating how CDW states are influenced by external electric fields. f The band structure undergoes changes during the I-CDW to N-CDW transition in TaS₂. g Detailed current-electric field characteristics under dark and THz illumination conditions, revealing parallel shifts in I-V curves with increasing THz intensity. h Three-dimensional mapping of photocurrent as a function of temperature and electric field. i Time-resolved photocurrent waveforms at different power densities (0.1–2.5 mW/cm²). j Expanded view of rise and fall edges in the temporal response with increasing power density. k Three-dimensional mapping of frequency and voltage-dependent responsivity across different bias voltages.

As depicted in Fig. 2d, e, the structural configuration undergoes a dramatic transformation from uniform atomic spacing in the normal state to a periodically modulated arrangement in the CDW state, where the lattice distortion with periodicity π/k? manifests as a result of strong electron-phonon coupling. The detected photocurrent cannot be attributed to conventional photoexcitation processes, as terahertz photons (on the order of millielectronvolts) possess energies significantly below the bandgap of 1T-TaS₂ (0.2–0.5 eV), precluding direct band-to-band transitions. The electronic structure of the 1T-TaS? changes depending on the CDW phase in Fig. 2f. In the I-CDW phase, 1T-TaS? exhibits metallic behavior with little to no band gap, allowing for easier charge carrier movement. In contrast, the N-CDW phase open of a band gap, limiting the flow of charge carriers²⁶.

Instead, our experimental evidence in Fig. 2h, i suggests a non-thermal collective excitation mechanism. The microsecond-scale response time observed in our measurements contradicts the millisecond timescales characteristic of thermal effects, effectively ruling out heat accumulation as the dominant mechanism. Figure 2g reveals the distinctive current-electric field characteristics under different terahertz illumination conditions, demonstrating clear photoresponse in illuminated states. The parallel shift in the I-V curves with increasing illumination intensity indicates that terahertz radiation couples resonantly with the collective phase modes of the CDW, which typically oscillate in the 0.1–1 THz frequency range⁴². The resonant coupling efficiently drives lattice vibrations through nonlinear phononic interactions, coherently displacing Ta atoms and transiently altering Ta-Ta distances. These perturbations destabilize the periodic distortions characteristic of the CDW state, weakening the pinning potential and liberating localized electrons from David-star clusters into mobile carriers. The three-dimensional photocurrent mapping shown in Fig. 2h further elucidates the temperature and electric field dependence of the photoresponse, revealing a pronounced enhancement near the phase transition boundary (indicated by V_th-H). The behavior confirms that the bias voltage predisposes the system toward a metastable state by weakening CDW electron localization. Near the resistance transition threshold, terahertz excitation reduces the energy barrier for phase transition, triggering localized CDW sliding or collapse that releases additional charge carriers and amplifies the photoresponse. Joule heating effects cannot be entirely ruled out, generated by the applied bias voltage⁴³, which could increase the lattice temperature and influence the phase transition. This would mean that some portion of the photocurrent could be due to thermal effects, where the heat assists in overcoming the energy barrier between different CDW phases.

Figure 2i illustrates the time-resolved photocurrent response at various incident power densities (0.1–2.5 mW/cm²), demonstrating well-defined square waveforms with exceptional signal-to-noise ratios even at 0.1 mW/cm². The rise time (τ_rise ≈ 1.7 μs) remains remarkably consistent across various incident power densities in Fig. 2j, whereas the fall time (τ_rall) exhibits pronounced power dependence, increasing from approximately 3.2 μs at 0.1 mW/cm² to 11.6 μs at 2.5 mW/cm², revealing the asymmetric dynamics between CDW excitation and relaxation. The power-independent τ_rise indicates that the initial phase transformation proceeds via a threshold-activated coherent excitation of CDW collective modes rather than thermal accumulation. The microsecond-scale response substantially outperforms conventional bolometric detectors, confirming direct coupling between THz radiation and the CDW order parameter through resonant excitation of amplitude and phase modes that destabilize the commensurate David-star clusters across coherently coupled domains^44,45. The relaxation dynamics involve complex reorganization of the perturbed CDW state, wherein higher excitation powers populate metastable configurations characterized by topological defects such as phase slips and discommensurations. These defects effectively function as pinning centers that introduce significant energy barriers against recovery to the ground state. Figure 2k shows the frequency-dependent responsivity landscape across multiple bias voltages, revealing a broadband photoresponse from 240 to 300 GHz with a peak value of 5.49 A/W. The pronounced bias-voltage dependence indicates that the detector operates in a regime where the external field tunes the energy barrier between competing CDW phases, effectively modulating the coupling efficiency between THz photons and lattice distortions. However, the butterfly-shaped antenna geometry introduces its own frequency-selective coupling, where the antenna dimensions determine resonant enhancement of the local electric field. The observed responsivity profile thus represents the combined effect of material-specific CDW dynamics and antenna-mediated field enhancement. The noise current density spectrum data and performance comparison are shown in the Fig. S3 (Supporting Information). Additionally, Our device achieves THz imaging and microwave heterodyne detection experiments. In Fig. S4 (Supporting Information), the paper clip was used as the test object, with dimensions measuring 15 × 30 millimeters. The resulting image comprised 150 × 300 pixels, with an integration time of 20 milliseconds per pixel. The varying shades in the 2D scanned image corresponded to the magnitude of the photocurrent, enabling differentiation of the object shape based on the variations in photocurrent. The imaging of a small-sized object validates the potential of our device for THz imaging. In Fig. S5 (Supporting Information), We illuminated the device with two microwave beams at 21 and 24 GHz. By using a low-noise power amplifier and spectrum analyzer, we extracted the IF signal. As an important step in optical communication, our device demonstrates the potential for nonlinear mixing.

Multi-state logic implementation via photoresponsive CDW transitions

The 1T-TaS? device leverages its CDW-driven resistive phase transition—a hysteretic switching between the IC-CDW (low-resistance state, LRS) and NC-CDW (high-resistance state, HRS) phases—to enable reconfigurable photonic logic. These transitions occur under specific conditions of bias voltage and temperature, modulated by incident THz radiation, which further extends the functionality of the device. In comparison to microwave and wireless optical communication, the application of this technology in THz communication exhibits several advantageous characteristics, including strong penetration, high efficiency, large capacity, high confidentiality, and favourable cost performance. The logic functionality is rooted in THz-induced phase reconfiguration: under controlled bias conditions (Fig. 3a), incident THz radiation drives non-thermal CDW phase transitions by resonantly exciting collective lattice modes. The dynamic modulation of the CDW order parameter allows the system to achieve resistance tuning within a 50% range at optimized bias voltages, with the LRS–HRS transition governed by the interplay between THz photon energy and applied electric field. The device can be programmed to implement logic gates (e.g., AND, OR), with phase transitions serving as the signal transduction mechanism and the logic state.

Fig. 3: Reconfigurable photoelectric logic characteristic of the 1T-TaS₂ device.

a The 1T-TaS₂ device functions as a logic device, considering both bias voltage and THz input as two inputs to achieve logical functionality. b IV characteristics driven by a current source at low temperature (77 K) with five sequential scanning times. c The effect of different power THz light on the phase transition bias point at low temperature (77 K). d–f Truth table of the logic functions implemented by the device under different bias waveforms. Truth tables for the 1T-TaS₂ device in three operational modes (C→F, D→F, and B→E). “Light density” denotes THz radiation intensity (00, 01, 10 correspond to 0, 2.1, and 4.1 mW/cm² in Fig. 4c). Vds represents the bias voltage (0 for lower voltage points C, D, B; 1 for higher voltage points F, E). “Last” indicates the initial resistance state (0 for HRS, NC-CDW phase; 1 for LRS, IC-CDW phase). “Out” is the resulting state based on the logic operations. g–i Schematic diagram of the logic function implemented by the device under different bias conditions. g illustrates the C→F logic operation with THz input and voltage control V_ds, incorporating “and” and “or” gates with a state transition mechanism. h shows the simplified D→F configuration where the device implements a different logical pathway with “and” and “or” gates. i depicts the B→E operation with THz input and V_ds control.

The current-voltage (I-V) characteristics of the 1T-TaS? device (Fig. 3b) demonstrate repeatable resistive switching under THz illumination, with five sequential scans confirming the reproducibility of logic states. The switching behavior is governed by non-volatile resistive transitions between the LRS (~200 Ω) and HRS (~500 Ω), yielding a resistance ratio of 2.5—sufficient for unambiguous state differentiation in logic operations. The transitions are triggered by THz-induced CDW phase reconfiguration, with the critical switching voltage V_th-dark (1.98 V) and V_th-light (1.96 V) determined by the interplay between incident THz photon energy and applied bias voltage. The voltage-dependent hysteresis (Fig. 3c) arises from the metastable nature of the NC-CDW phase, which persists even after removal of the THz stimulus, endowing the device with non-volatile memory characteristics. At temperatures as low as 77 K, this interaction between THz photons and lattice is especially pronounced, with the increased stability of the NC-CDW phase making the phase transition highly sensitive to external stimuli, such as THz radiation and applied bias voltage. The increased phase transition barrier at lower temperatures results in the need for higher voltage or photon energy to induce the phase transition, a feature that is advantageous for controlled switching in logic circuits. The hysteretic IV curves at 77 K, as seen in Fig. 3c, demonstrate how the applied bias voltage under varying light intensities results in different voltage regions labeled A, B, C, D, E, F, G with each zone corresponding to a specific phase transition behavior. These zones are instrumental in defining the operational ranges for logic switching, where the device’s resistance can be reprogrammed and reset by adjusting the bias voltage. The data to be transmitted is initially transformed into a one-dimensional ASCII array and subsequently encrypted using a logical truth table. Subsequently, the laser transmits the encrypted information to a detector, which applies the corresponding modulation voltage. In the event that an eavesdropper were to intercept the information during this process with a conventional sensor, they would be provided with a one-dimensional array comprising a single intensity type, which would serve to significantly secure the optical communication process.

The truth tables in Fig. 3d–f systematically map the relationship between input conditions and the TaS₂ device response across three operational modes (C→F, D→F, and B→E). We define the light intensities corresponding to 0, 2.1, and 4.1 mW/cm² as “00”, “01”, and “10”, respectively. The CDW phase state postulates that, subsequent to the implementation of electrical or optical modulation, the device is in a state of being “Out” of the corresponding output. The pre-modulation state is designated as “Last”. When the bias voltage of the device works between C→F, once the bias voltage rises to the F area, the device can enter the LRS under the THz light of “01” and “10”. The resistance can be reset by change the bias voltage to the C zone. When the bias voltage waveform of the device works between D→F, once the bias voltage rises to the F area, the device can enter the LRS under the THz light of “01” and “10”. At this time, the resistance state of the device cannot be changed by the voltage conversion of the D/F zone. The resistance of the device can only be reset by changing the bias voltage zone. When the bias voltage waveform of the device works between B→E, it has a function similar to the C→F mode. But the light intensity of “01” in the E zone is not enough to cause resistance state transition of the device. By programming the working zone of light bias voltage, the device has the ability to recognize different light intensities, and this can be reflected in the dimension of resistance phase transition. Figure 3g–i is the photoelectric logic diagram corresponding to the C→F, D→F, B→E zone of the device. As demonstrated in Fig. S6 (Supporting Information), the device demonstrates non-volatile optoelectronic logic functions, including AND gate, OR gate, voltage follower, and state follower. This capability enables the realization of diverse coded logic circuits and follower configurations, thereby increasing functional complexity and supporting integrated terahertz memory logic functions. In this device, the bias current is preset 1 ms prior to the optical signal. The implementation of optical and electrical set/reset functions at the component level enables the realization of reconfigurable logic operations, facilitates algorithmic switching, reduces circuit complexity, and enhances chip integration. The potential applications of this single-device-level timing logic are numerous, spanning reconfigurable logic circuits, intelligent remote communication, and identification.

Secure multicolor recognition and encrypted communication

Leveraging the reconfigurable logic function, our integrated device enables monochromatic light recognition through various combinations of laser intensity and modulation voltage. Although different coloured lights have similar outputs, the three laser intensity profiles as well as the modulation voltage profiles do not overlap completely, which prevents spectral crosstalk between the three colour units during the colour recognition process, and achieves optical encrypted information transmission. As shown in Fig. 4a, the experimental configuration for optical encrypted information transmission leverages the reconfigurable logic function. We developed a THz image sensor that is not only capable of recognizing RGB primary colors but also allows for the customization of individual pixels, which enhances the speed of color detection without the need for traditional color filters. By applying distinct bias voltage zones to the 1T-TaS? device, different pieces of information were extracted from the same optical input. Specifically, three sets of THz light beams with varying intensities, as demonstrated in Fig. 3c, were assigned unique keys (i.e., different modulation voltages corresponding to an output of “1”) that encoded the R, G, and B color information in the input image. The bias voltages for regions A→F were used as keys for V?→V?, respectively. The Fig. 4b shows the encrypted photoelectric logic communication experiment. We placed a lens and a chopper between the 1T-TaS₂ photodetector (PD) and the THz source, converting a 25 × 25 pixel image into the corresponding THz light encoding. By modulating the light through the chopper and the THz source, the image information was encoded into THz light of varying power levels, which the 1T-TaS? PD then interpreted in two dimensions: the THz response current and the state change in its resistance. As shown in Fig. 4c, d, bias voltage and light intensity were designated as inputs, whereas the resistance state transition was used as the output. In regions C→F and B→E, distinct resistance state transitions were observed under identical light intensity conditions, underscoring the critical importance of possessing the correct key for accurate information retrieval, thereby adding a significant layer of security to the system.

Fig. 4: Reconfigurable photoelectric logic experiment of the 1T-TaS₂ device.

a The setup with three types of bias waveforms and three power levels of THz light as logical inputs to the 1T-TaS₂ device. b The encrypted photoelectric logic communication experiment. c Under C-F bias, the output resistance state under different power levels of THz input. d Under B-E bias, the output resistance state under different power levels of THz input. e The transmission effect and final results under different bias waveforms and power levels.

In our cryptographic demonstration, it is imperative that the receiver has access to the correct key, in the form of a specific voltage pulse sequence, to successfully decrypt the transmitted message. In this case, assuming the correct information being transmitted involves an RGB color shift, only the alternating voltage pulses between C (1.755 V) and F (1.975 V) are capable of functioning as the correct key, which in turn yields accurate decryption, as shown in Fig. 3c. As shown in Fig. 4e, we can see the single THz light response output image and the output images under different photoelectric logic functions (numbered from left to right as i, ii, iii, iv). In traditional methods, a simple threshold is set to discretize the optical signal into binary states (either 1 or 0), where any light surpassing the detection threshold generates a photocurrent. However, such methods lack the capability to differentiate between light intensities, as can be seen in Fig. 4e–i. By integrating the photoelectric logic of resistance state transitions, our approach enables direct differentiation of varying light intensities. As demonstrated in Fig. 4e–ii and iii, we successfully achieved the distinction between light intensities “01” and “10” by applying different bias voltage zones. Moreover, by combining the transmitted information with a hierarchy of priority levels, we were able to recover the original transmitted information, as shown in Fig. 4e–iv. Furthermore, the unique hysteresis behavior exhibited by our device introduces an additional dynamic, wherein increasing or decreasing the frequency of the bias voltage leads to further modulation of its photoelectric logic, thus enhancing the device ability to recognize different light intensities.