Unconventional superconductivity of NpPd(5)Al(2)

Area of Science:

• Condensed Matter Physics
• Materials Science
• Superconductivity

Background:

• Heavy fermion systems exhibit unique electronic properties due to localized f-electrons interacting with conduction electrons.
• Neptunium (Np)-based intermetallic compounds are less explored compared to other actinide systems in superconductivity research.
• Understanding the interplay between magnetism and superconductivity in heavy fermion materials is crucial for fundamental physics.

Purpose of the Study:

• To synthesize and characterize novel neptunium-based heavy fermion superconductors.
• To investigate the superconducting properties of NpPd(5)Al(2), including critical temperature and upper critical field.
• To explore the relationship between the heavy electronic state, Pauli paramagnetic effects, and potential magnetic ordering in NpPd(5)Al(2).

Main Methods:

• Single crystal growth of NpPd(5)Al(2) using the lead (Pb) flux method.
• Measurement of superconducting properties, including critical temperature (T(sc)) and upper critical field (H(c2)).
• Analysis of the anisotropy and magnetic field dependence of H(c2) to probe electronic states and phase transitions.

Main Results:

• High-quality single crystals of NpPd(5)Al(2) with a body-centered tetragonal structure were successfully grown.
• NpPd(5)Al(2) was identified as the first neptunium-based heavy fermion superconductor with a critical temperature (T(sc)) of 4.9 K.
• A large and highly anisotropic upper critical field (H(c2)) was observed, exhibiting a strong Pauli paramagnetic effect and first-order transitions at H(c2).

Conclusions:

• NpPd(5)Al(2) represents a significant discovery in neptunium-based heavy fermion superconductivity.
• The observed properties suggest that NpPd(5)Al(2) is close to an antiferromagnetic phase, which may be suppressed by superconductivity.
• The superconductivity in NpPd(5)Al(2) is likely d-wave with a spin singlet state, influenced by strong Pauli paramagnetism.