Mapping multi-valley Lifshitz transitions induced by field-effect doping in strained MoS₂ nanolayers

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanoscience

Background:

• Gate-induced superconductivity in semiconducting transition metal dichalcogenides (TMDs) exhibits high transition temperatures and robustness against magnetic fields.
• Understanding the Fermi surface geometry, particularly valley filling at K/K and Q/Q points, is crucial for elucidating the microscopic origin of superconductivity.
• Field-effect doping controls the Fermi level, influencing the electronic band structure and potentially triggering Lifshitz transitions.

Purpose of the Study:

• To determine the Fermi surface geometry as a function of field-effect doping in semiconducting TMD nanolayers.
• To investigate the role of inequivalent valleys (K/K and Q/Q) in hosting Cooper pairs.
• To establish a method for mapping Fermi surface evolution and detecting Lifshitz transitions in real devices.

Main Methods:

• Combining density functional theory (DFT) calculations for bandstructure analysis.
• Performing transport measurements on ion-gated 2H-MoS2 nanolayers.
• Developing a 2D model to analyze experimental data and temperature-dependent effects.

Main Results:

• The Fermi level crosses the Q/Q valleys at experimentally detected doping levels, correlating with kinks in transconductance.
• A 2D model quantitatively describes the broadening of these kinks with increasing temperature.
• The study demonstrates a method to map Fermi surface dependence on doping and detect Lifshitz transitions.

Conclusions:

• The combined DFT and transport measurement approach accurately maps the Fermi surface evolution in TMD nanolayers.
• This method allows for the detection of Lifshitz transitions and the determination of strain and spin-orbit splitting.
• The findings provide critical insights into the unconventional superconductivity in TMDs.