Carrier-envelope Phase Control Achieves Photocurrent Modulation in Mono, Bi, and Tri-layer MoS

Controlling the flow of electrical current with light offers exciting possibilities for next-generation optoelectronics, and researchers are now extending this control to increasingly thin materials. Johannes Schmuck, Björn Sinz, and Nina Pettinger, alongside colleagues at the Walter Schottky Institute and Technical University of Munich, demonstrate precise control of electrical currents generated in layered molybdenum disulfide using tailored light pulses. The team achieves this control by manipulating the phase of the light’s electromagnetic field, a technique known as carrier-envelope phase control, and importantly, finds that the generated current responds predictably to changes in light intensity. This achievement extends light-sensitive current control from traditional materials to two-dimensional semiconductors, paving the way for novel optoelectronic devices with enhanced speed and efficiency.

Few-Cycle Laser Pulses Probe MoS2 Layers

Scientists engineered a sophisticated optical setup to investigate ultrafast electronic responses within layered molybdenum disulfide (MoS2). The study employed a train of few-cycle laser pulses, each lasting 5. 9 femtoseconds at a center wavelength of 826 nanometers, with pulse energies reaching 2. 2 nanojoules and a repetition frequency of 80 megahertz. Crucially, the laser’s phase was precisely controlled using a stabilization technique, ensuring accurate timing of the light pulses.

To compensate for pulse distortion, the team pre-compressed the pulses with specialized mirrors before attenuating them. They fabricated two-terminal devices from mechanically exfoliated mono-, bi-, and tri-layer MoS2, transferring these onto silicon substrates. Raman and photoluminescence spectroscopy confirmed the quality and layer number of the MoS2. Metal contacts were deposited using optical lithography and e-beam evaporation, resulting in devices that exhibited linear current-voltage characteristics. Experiments were conducted within a high-vacuum chamber, and a focused laser beam, approximately 5 micrometers in diameter, was aligned perpendicular to the MoS2 devices.

To modulate the laser pulse’s phase, scientists translated a calcium fluoride wedge, introducing a controlled optical path difference. This adjustment enabled precise control over the phase shift, allowing accurate measurement of the resulting photocurrent modulation. Measurements were performed at zero bias voltage and room temperature, and spatial maps of both time-integrated photocurrent and reflectance were acquired concurrently to correlate signal origin with device geometry.

CEP Control of Photocurrents in Molybdenum Disulfide

Scientists have demonstrated control of electrical current in mono-, bi-, and tri-layer molybdenum disulfide (MoS2) using few-cycle laser pulses, revealing a new pathway for manipulating charge carriers in two-dimensional materials. Experiments involved irradiating mechanically exfoliated MoS2 layers with 5. 9 femtosecond laser pulses centered at 826 nanometers, achieving pulse energies up to 2. 2 nanojoules with a repetition frequency of 80 megahertz. The laser’s phase was stabilized using a feedback loop, ensuring precise control over the optical waveform.

Measurements reveal a quadratic scaling between the photocurrent and the applied field strength, confirming that carrier dynamics occur in a perturbative regime, distinct from strong-field tunneling. This indicates that the photocurrent arises from field-driven separation and acceleration of charge carriers, rather than nonlinear tunneling processes. Researchers fabricated two-terminal devices with parallel contacts on the MoS2 layers, confirming linear current-voltage characteristics. The study extends light-field-sensitive current control from bulk materials to atomically thin semiconductors, opening opportunities for designing ultrafast, low-dimensional optoelectronic devices. By exploring devices with varying layer numbers, the team demonstrated how the 2D geometry and crystal symmetry govern the strength and polarity of the response. These findings establish a foundation for manipulating charge carriers on sub-cycle timescales in 2D materials, potentially enabling new advancements in high-speed electronics and optoelectronics.

Laser Waveform Controls Two-Dimensional Current Flow

This research demonstrates the generation and control of electrical current in molybdenum disulfide (MoS2) using precisely shaped laser pulses, extending this capability to two-dimensional materials. Scientists successfully induced photocurrents in single, double, and triple layers of MoS2, and importantly, controlled these currents by manipulating the phase of the laser pulses. The observed quadratic relationship between current and laser field strength indicates that the process relies on single-photon excitation, a different mechanism than previously observed in other materials. These findings reveal that the laser’s waveform directly influences the movement of photoexcited electrons within the MoS2, allowing for control of the generated current.

The strength of this control is greatest in single-layer MoS2, likely due to more efficient light absorption and direct electronic transitions. While the experiments demonstrate clear control, the magnitude of the current modulation is relatively small, on the order of one percent. The authors acknowledge that further investigation into the behaviour of charge carriers within the material is needed, and future research will likely focus on enhancing the magnitude of the effect and exploring the potential of this technique for developing new optoelectronic devices sensitive to light and electric fields.