Enhanced laser-induced single-cycle terahertz generation in a spintronic emitter with a gradient interface

Area of Science:

• Spintronics
• Terahertz (THz) Photonics
• Materials Science

Background:

• Efficient spintronic emitters are crucial for generating broadband terahertz (THz) pulses.
• The interface between ferromagnetic and nonmagnetic layers significantly impacts spin current generation and conversion efficiency.
• Optimizing heterostructures is key to advancing THz spintronic devices.

Purpose of the Study:

• To experimentally investigate the effect of a composition-gradient interface on THz pulse generation.
• To compare the performance of a Pt/Co emitter with a gradient interface against one with an abrupt interface.
• To understand the underlying mechanisms responsible for enhanced THz emission efficiency.

Main Methods:

• Fabrication of Pt/Co spintronic emitters with a 1.2-nm-thick composition-gradient interface.
• Experimental examination of single-cycle THz pulse generation using laser-pulse excitation.
• Comparative analysis of THz emission efficiency and optical-to-THz conversion across varying optical fluences.

Main Results:

• The gradient interface enhanced optics-to-THz conversion efficiency by a factor of two compared to the abrupt interface.
• This improvement is attributed to increased transmittance of laser-driven spin-polarized current across the gradient interface.
• Spin accumulation effects were observed to degrade spin current transmission at higher laser fluences.

Conclusions:

• Composition-gradient interfaces offer a promising route to significantly boost THz pulse generation in spintronic emitters.
• The enhanced spin-polarized current transmittance through gradient interfaces is the primary mechanism for improved efficiency.
• Understanding and mitigating spin accumulation effects is important for optimizing emitter performance at high laser fluences.