Pressure-Induced Superconductivity In Polycrystalline <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>La</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>Ni</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>7</mml:mn><mml:mo>−</mml:mo><mml:mi>δ</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>

We synthesized polycrystalline <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:msub><a:mi>La</a:mi><a:mn>3</a:mn></a:msub><a:msub><a:mi>Ni</a:mi><a:mn>2</a:mn></a:msub><a:msub><a:mi mathvariant="normal">O</a:mi><a:mrow><a:mn>7</a:mn><a:mo>−</a:mo><a:mi>δ</a:mi></a:mrow></a:msub></a:mrow></a:math> (<d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"><d:mrow><d:mi>δ</d:mi><d:mo>≈</d:mo><d:mn>0.0</d:mn><d:mn>7</d:mn></d:mrow></d:math>) samples by using the sol-gel method without postannealing under high oxygen pressure, and then measured temperature-dependent resistivity under various hydrostatic pressures up to 18 GPa by using the cubic anvil and two-stage multianvil apparatus. We find that the density-wave-like anomaly in resistivity is progressively suppressed with increasing pressure and the resistivity drop corresponding to the onset of superconductivity emerges at pressure as low as <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"><f:mrow><f:mo form="prefix">∼</f:mo><f:mn>6</f:mn><f:mtext> </f:mtext><f:mtext> </f:mtext><f:mi>GPa</f:mi></f:mrow></f:math>. Zero resistivity is achieved at 9 GPa below <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mrow><i:msubsup><i:mi>T</i:mi><i:mi mathvariant="normal">c</i:mi><i:mrow><i:mrow><i:mi>zero</i:mi></i:mrow></i:mrow></i:msubsup><i:mo>≈</i:mo><i:mn>6.6</i:mn><i:mtext> </i:mtext><i:mtext> </i:mtext><i:mi mathvariant="normal">K</i:mi></i:mrow></i:math>, which increases quickly with pressure to 41 K at 18 GPa. However, the diamagnetic response was not detected in the ac magnetic susceptibility measurements up to 15 GPa, indicating a filamentary nature of the observed superconductivity in the studied pressure range. The constructed <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mrow><m:mi>T</m:mi><m:mtext>−</m:mtext><m:mi>P</m:mi></m:mrow></m:math> phase diagram reveals an intimate relationship between superconductivity, density-wave-like order, and the strange-metal-like behaviors. The observation of zero-resistance state in the polycrystalline <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:mrow><o:msub><o:mi>La</o:mi><o:mn>3</o:mn></o:msub><o:msub><o:mi>Ni</o:mi><o:mn>2</o:mn></o:msub><o:msub><o:mi mathvariant="normal">O</o:mi><o:mrow><o:mn>7</o:mn><o:mo>−</o:mo><o:mi>δ</o:mi></o:mrow></o:msub></o:mrow></o:math> samples under high pressures not only corroborates the recent report of superconductivity in the pressurized <r:math xmlns:r="http://www.w3.org/1998/Math/MathML" display="inline"><r:mrow><r:msub><r:mi>La</r:mi><r:mn>3</r:mn></r:msub><r:msub><r:mi>Ni</r:mi><r:mn>2</r:mn></r:msub><r:msub><r:mi mathvariant="normal">O</r:mi><r:mn>7</r:mn></r:msub></r:mrow></r:math> crystals but also facilitates further studies on this emerging family of nickelate high-<u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline"><u:mrow><u:msub><u:mi>T</u:mi><u:mi mathvariant="normal">c</u:mi></u:msub></u:mrow></u:math> superconductors. Published by the American Physical Society 2024