Absence of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mtext>Ni</mml:mtext><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup><mml:mo>/</mml:mo><mml:msup><mml:mtext>Ni</mml:mtext><mml:mrow><mml:mn>3</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math> charge disproportionation and possible roles of O <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>2</mml:mn><mml:mi>p</mml:mi></mml:mrow></mml:math> holes in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mtext>La</mml:mtext><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mtext>Ni</mml:mtext><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mtext>O</mml:mtext><mml:mrow><mml:mn>7</mml:mn><mml:mo>−</mml:mo><mml:mi>δ</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math> revealed by hard x-ray photoemission spectroscopy

Abstract

We have investigated the electronic structure of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><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> <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mo>(</c:mo><c:mi>δ</c:mi><c:mo>≈</c:mo><c:mn>0.07</c:mn><c:mo>)</c:mo></c:mrow></c:math> by means of hard x-ray photoemission spectroscopy (HAXPES). Although the nominal Ni valence is close to <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mrow><d:mo>+</d:mo><d:mn>2.5</d:mn></d:mrow></d:math>, the Ni <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mrow><e:mn>2</e:mn><e:mi>p</e:mi></e:mrow></e:math> HAXPES spectra show an absence of <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:mrow><f:msup><f:mrow><f:mi>Ni</f:mi></f:mrow><f:mrow><f:mn>2</f:mn><f:mo>+</f:mo></f:mrow></f:msup><f:mo>/</f:mo><f:msup><f:mrow><f:mi>Ni</f:mi></f:mrow><f:mrow><f:mn>3</f:mn><f:mo>+</f:mo></f:mrow></f:msup></f:mrow></f:math> charge disproportionation. The Ni <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:mrow><g:mn>2</g:mn><g:mi>p</g:mi></g:mrow></g:math> spectral shape including the main peak and the charge-transfer satellite indicate that oxygen <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"><h:mrow><h:mn>2</h:mn><h:mi>p</h:mi></h:mrow></h:math> holes are heavily involved in the transport properties. The spectral weight suppression at the Fermi level indicates that the carriers of O <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"><i:mrow><i:mn>2</i:mn><i:mi>p</i:mi></i:mrow></i:math> character (mixed with Ni <j:math xmlns:j="http://www.w3.org/1998/Math/MathML"><j:mrow><j:mn>3</j:mn><j:mi>d</j:mi></j:mrow></j:math>) are affected by electronic correlation which would be associated with the density wave transition and the superconductivity controlled by pressure. Published by the American Physical Society 2024

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