Bulk high-temperature superconductivity in pressurized tetragonal La₂PrNi₂O₇.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid State Chemistry

Background:

• Ruddlesden-Popper (R-P) bilayer nickelates, like La3Ni2O7, show potential for high-temperature superconductivity (HTSC) under pressure.
• Previous studies reported zero resistance in nickelates but lacked definitive diamagnetic signals, hindering confirmation of bulk superconductivity.
• Phase identification challenges, including competing R-P phases and polymorphs, complicated the understanding of HTSC in these materials.

Purpose of the Study:

• To achieve bulk HTSC in bilayer nickelates and identify the specific superconducting phase.
• To investigate the effect of Pr-doping on the structural and superconducting properties of La2Ni2O7.
• To resolve existing controversies regarding the nature and detection of HTSC in these materials.

Main Methods:

• Synthesis of praseodymium (Pr)-doped La2PrNi2O7 polycrystalline samples.
• Application of hydrostatic pressure and measurement of electrical resistance.
• Detection of diamagnetic signals to confirm bulk superconductivity.
• Structural analysis to identify phase transitions and purity.

Main Results:

• Pr-doping effectively suppresses competing R-P phases, yielding a nearly pure bilayer structure in La2PrNi2O7.
• A pressure-induced structural transition from orthorhombic to tetragonal occurs around 11 GPa, above which HTSC emerges.
• Superconducting transition temperatures reach record highs (up to ~XX K) at 18-20 GPa.
• Clear diamagnetic signals confirming bulk HTSC with significant shielding fractions are observed above 15 GPa, below ~75 K.

Conclusions:

• Bulk HTSC in bilayer nickelates is confirmed in Pr-doped La2PrNi2O7, resolving previous ambiguities.
• The study provides a pathway for achieving and identifying bulk HTSC in related materials.
• These findings offer crucial insights for the ongoing search for novel superconductors.