Distinct orbital contributions to electronic and magnetic structures in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>La</mml:mi> <mml:mn>4</mml:mn> </mml:msub> <mml:msub> <mml:mi>Ni</mml:mi> <mml:mn>3</mml:m

High- <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:msub> <a:mi>T</a:mi> <a:mi>c</a:mi> </a:msub> </a:math> superconductivity has recently been discovered in Ruddlesden-Popper (RP)-phase nickelates under pressure, where the low-energy electronic structure is dominated by Ni <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:msub> <b:mi>d</b:mi> <b:mrow> <b:msup> <b:mi>x</b:mi> <b:mn>2</b:mn> </b:msup> <b:mo>−</b:mo> <b:msup> <b:mi>y</b:mi> <b:mn>2</b:mn> </b:msup> </b:mrow> </b:msub> </b:math> and <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:msub> <c:mi>d</c:mi> <c:msup> <c:mi>z</c:mi> <c:mn>2</c:mn> </c:msup> </c:msub> </c:math> orbitals. However, the respective roles of these orbitals in superconductivity remain unclear. Here, by combining x-ray absorption, electron energy loss spectroscopy, and density functional theory calculations on <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mrow> <d:msub> <d:mi>La</d:mi> <d:mn>4</d:mn> </d:msub> <d:msub> <d:mi>Ni</d:mi> <d:mn>3</d:mn> </d:msub> <d:msub> <d:mi mathvariant="normal">O</d:mi> <d:mn>10</d:mn> </d:msub> </d:mrow> </d:math> single crystals, we identify ligand holes in the <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"> <f:msub> <f:mi>p</f:mi> <f:mrow> <f:mi>x</f:mi> <f:mo>,</f:mo> <f:mi>y</f:mi> </f:mrow> </f:msub> </f:math> orbitals of planar oxygen and the <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"> <g:msub> <g:mi>p</g:mi> <g:mi>z</g:mi> </g:msub> </g:math> orbitals of apical oxygen, which hybridize with the Ni <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"> <h:msub> <h:mi>d</h:mi> <h:mrow> <h:msup> <h:mi>x</h:mi> <h:mn>2</h:mn> </h:msup> <h:mo>−</h:mo> <h:msup> <h:mi>y</h:mi> <h:mn>2</h:mn> </h:msup> </h:mrow> </h:msub> </h:math> and <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"> <i:msub> <i:mi>d</i:mi> <i:msup> <i:mi>z</i:mi> <i:mn>2</i:mn> </i:msup> </i:msub> </i:math> orbitals, respectively. These ligand holes enable orbital-selective O <j:math xmlns:j="http://www.w3.org/1998/Math/MathML"> <j:mi>K</j:mi> </j:math> -edge resonant inelastic x-ray scattering (RIXS) study, which reveals that <k:math xmlns:k="http://www.w3.org/1998/Math/MathML"> <k:msub> <k:mi>d</k:mi> <k:mrow> <k:msup> <k:mi>x</k:mi> <k:mn>2</k:mn> </k:msup> <k:mo>−</k:mo> <k:msup> <k:mi>y</k:mi> <k:mn>2</k:mn> </k:msup> </k:mrow> </k:msub> </k:math> states dominate the low-energy charge excitations and are more itinerant. We also observe an <l:math xmlns:l="http://www.w3.org/1998/Math/MathML"> <l:mrow> <l:mo>∼</l:mo> <l:mn>0.1</l:mn> <l:mspace width="0.16em"/> <l:mi>eV</l:mi> </l:mrow> </l:math> bimagnon through RIXS and Raman spectroscopy. Our results reveal distinct contributions of Ni <n:math xmlns:n="http://www.w3.org/1998/Math/MathML"> <n:msub> <n:mi>d</n:mi> <n:mrow> <n:msup> <n:mi>x</n:mi> <n:mn>2</n:mn> </n:msup> <n:mo>−</n:mo> <n:msup> <n:mi>y</n:mi> <n:mn>2</n:mn> </n:msup> </n:mrow> </n:msub> </n:math> and <o:math xmlns:o="http://www.w3.org/1998/Math/MathML"> <o:msub> <o:mi>d</o:mi> <o:msup> <o:mi>z</o:mi> <o:mn>2</o:mn> </o:msup> </o:msub> </o:math> orbitals to the electronic and magnetic structure and provide direct experimental insights to understand the RP-phase nickelate superconductors.