Electrically Pumped Valley Emitter in Transition Metal Dichalcogenides with Magnetic Manipulation.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Optical pumping is common for studying 2D transition metal dichalcogenides (TMDCs) but faces challenges with resonant excitation.
• Achieving consistent comparative studies across different TMDCs is difficult due to excitation limitations.

Purpose of the Study:

• To utilize electrical pumping for investigating excitonic effects in TMDCs under controlled conditions.
• To explore valley-polarized electroluminescence (VP-EL) and its magnetic field dependence in TMDCs.
• To compare VP-EL across different TMDC structures (monolayer, homobilayer, heterobilayer) and elucidate underlying mechanisms.

Main Methods:

• Employing electrical pumping on TMDC quantum well structures for equivalent carrier injection.
• Systematically investigating valley-polarized electroluminescence (VP-EL) under varying magnetic fields.
• Conducting comparative analysis of VP-EL in monolayer WS2, WS2/WS2 homobilayers, and WS2/WSe2 heterobilayers.

Main Results:

• Demonstrated reversal of EL valley polarization by reversing magnetic field direction without specialized electrodes.
• Observed tunable polarization reversal in WS2-based structures influenced by interlayer charge transfer and spin-matched interlayer hopping.
• Identified significant roles of large spin-orbit coupling (SOC) and dark exciton ground states in WS2.

Conclusions:

• Electrical pumping is a viable and effective technique for studying optical properties of 2D semiconductors.
• Spin-orbit coupling and excitonic states play crucial roles in magneto-electroluminescence phenomena in TMDCs.
• Interlayer interactions significantly influence and tune valley polarization reversal in TMDC heterostructures.