Superconductivity in 3R-Ta(1-x)M(x)Se2 (M = W, Mo)

Area of Science:

• Materials Science
• Condensed Matter Physics
• Superconductivity

Background:

• The 3-layer rhombohedral (3R) polytype of tantalum diselenide (TaSe2-xTex) shows superconductivity 6-17 times higher than the 2-layer hexagonal (2H) polytype.
• The enhanced superconductivity in the 3R polytype was potentially attributed to electronic effects from Te-Se substitution.

Purpose of the Study:

• To investigate whether polytype structure or Te-Se substitution is responsible for the enhanced superconductivity in TaSe2.
• To determine the role of stacking sequence in superconductivity within the TaSe2 system.

Main Methods:

• Synthesizing Ta1-xMo x Se2 and Ta1-xW x Se2 via doping.
• Inducing a 2H to 3R polytype transition using molybdenum (Mo) or tungsten (W) doping.
• Measuring the superconducting transition temperature (Tc) of the resulting polytypes.

Main Results:

• Small amounts of Mo or W doping successfully induced the 3R polytype in TaSe2.
• The 3R polytype Ta1-xMo x Se2 and Ta1-xW x Se2 exhibited significantly higher Tc (~2 K) compared to the 2H polytype (0.15 K).
• These findings ruled out Te-Se substitution as the sole cause for the Tc difference.

Conclusions:

• The three-layer stacking sequence (3R) is strongly preferred for superconductivity over the two-layer sequence (2H) in the TaSe2 system.
• Polytype structure, not specific elemental substitution, is the primary driver for enhanced superconductivity in these materials.