[Paper Review] Attosecond-resolved petahertz carrier motion in semi-metallic TiS2

Bárbara Buades, Antonio Picón+15 more|arXiv (Cornell University)|Aug 20, 2018

Chalcogenide Semiconductor Thin Films12 citations

TL;DR

This study demonstrates attosecond-resolved control of petahertz carrier motion in semi-metallic TiS2 using weak-field infrared excitation and attosecond soft x-ray spectroscopy at the Ti L-edge. By injecting 0.2% of valence band carriers into the conduction band with high mobility, the work achieves ultrafast opto-electronic control at petahertz speeds, enabling prospects for optical field-effect devices and sensors in layered materials.

ABSTRACT

Knowledge about the real-time response of carriers to optical fields in solids is paramount to advance information processing towards optical frequencies or to understand the bottlenecks of light-matter interaction and energy harvesting. Of particular importance are semi-metals and transition metal dichalcogenides due to their small band gap and high carrier mobility. Here, we examine the opto-electronic response of TiS2 to optical excitation by means of attosecond soft x-ray spectroscopy at the L-edges of Ti at 460 eV. Using weak-field infrared single-photon excitation, we examine conditions that avoid excessive excitation, but still attain efficient injection of 0.2% of valence band carriers into the lowest lying conduction band. We demonstrate that the efficient injection and the high- carrier mobility of the conduction band permits leveraging the material to achieve petahertz-speed opto-electronic control of its carriers. Our results are an important step towards understanding the dynamics of carriers and their control under field conditions that are realistic for device implementation in semi-metallic layered materials, thus they may lead to ultrafast and optically controlled field-effect devices and sensors.

Motivation & Objective

• To understand real-time carrier dynamics in semi-metals under realistic optical excitation conditions.
• To investigate how high carrier mobility and small band gaps in transition metal dichalcogenides enable ultrafast opto-electronic control.
• To achieve efficient, low-excitation carrier injection into the conduction band without excessive excitation.
• To demonstrate the feasibility of petahertz-speed control in semi-metallic layered materials for device applications.

Proposed method

• Employed attosecond soft x-ray spectroscopy at the Ti L-edge (460 eV) to probe carrier dynamics in real time.
• Used weak-field infrared single-photon excitation to inject carriers without inducing excessive excitation.
• Focused on TiS2, a semi-metallic transition metal dichalcogenide with small band gap and high carrier mobility.
• Monitored the injection of 0.2% of valence band carriers into the lowest conduction band states.
• Analyzed the temporal evolution of electronic states with attosecond time resolution to resolve carrier motion.
• Leveraged the high mobility of conduction band carriers to assess the potential for petahertz-speed opto-electronic control.

Experimental results

Research questions

• RQ1 Can attosecond spectroscopy resolve real-time carrier motion in semi-metallic TiS2 under weak optical excitation?
• RQ2 What fraction of valence band carriers can be efficiently injected into the conduction band without excessive excitation?
• RQ3 How does the high carrier mobility in TiS2 enable petahertz-speed opto-electronic control?
• RQ4 What are the dynamics of carrier injection and motion in layered semi-metals under realistic field conditions?
• RQ5 Can TiS2 support ultrafast, optically controlled field-effect devices based on its intrinsic electronic properties?

Key findings

• Attosecond soft x-ray spectroscopy successfully resolved the real-time motion of carriers in TiS2 with sub-cycle time resolution.
• Weak-field infrared excitation enabled efficient injection of 0.2% of valence band carriers into the conduction band.
• The high mobility of conduction band carriers in TiS2 supports petahertz-speed opto-electronic control.
• The observed dynamics occur under conditions realistic for device implementation, minimizing non-linear effects.
• The results demonstrate a viable pathway toward ultrafast, optically controlled field-effect devices and sensors in layered semi-metals.
• The study establishes a foundation for understanding light-matter interactions in materials with small band gaps and high carrier mobility.