Layer-controlled orbital-selective Mott transition in monolayer nickelate

Dimensionality and electronic correlations are crucial elements of many quantum material properties. An example is the change of the electronic structure accompanied by the loss of quasiparticles when a metal is reduced from three dimensions to a lower dimension, where the Coulomb interaction between carriers becomes poorly screened. Here, using angle-resolved photoemission spectroscopy, we report an orbital-selective decoherence of spectral density in the perovskite nickelate <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mi>LaNi</a:mi> <a:msub> <a:mi mathvariant="normal">O</a:mi> <a:mn>3</a:mn> </a:msub> </a:mrow> </a:math> toward the monolayer limit. The spectral weight of the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:msub> <c:mi>d</c:mi> <c:mrow> <c:mi>z</c:mi> <c:mn>2</c:mn> </c:mrow> </c:msub> </c:math> band vanishes much faster than that of the <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:msub> <d:mi>d</d:mi> <d:mrow> <d:mi>x</d:mi> <d:mn>2</d:mn> <d:mo>−</d:mo> <d:mi>y</d:mi> <d:mn>2</d:mn> </d:mrow> </d:msub> </d:math> band as the thickness of the <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mrow> <e:mi>LaNi</e:mi> <e:msub> <e:mi mathvariant="normal">O</e:mi> <e:mn>3</e:mn> </e:msub> </e:mrow> </e:math> layer is decreased to a single unit cell, indicating a stronger correlation effect for the former upon dimensional confinement. Dynamical mean-field theory calculations show an orbital-selective Mott transition largely due to the localization of <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"> <g:msub> <g:mi>d</g:mi> <g:mrow> <g:mi>z</g:mi> <g:mn>2</g:mn> </g:mrow> </g:msub> </g:math> electrons along the <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"> <h:mi>c</h:mi> </h:math> axis in the monolayer limit. This orbital-selective correlation effect underpins many macroscopic properties of nickelates, such as metal-to-insulator transition and superconductivity, where most theories are built upon a <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"> <i:mrow> <i:msub> <i:mi>d</i:mi> <i:mrow> <i:mi>x</i:mi> <i:mn>2</i:mn> <i:mo>−</i:mo> <i:mi>y</i:mi> <i:mn>2</i:mn> </i:mrow> </i:msub> <i:mtext>–</i:mtext> <i:msub> <i:mi>d</i:mi> <i:mrow> <i:mi>z</i:mi> <i:mn>2</i:mn> </i:mrow> </i:msub> </i:mrow> </i:math> two-band model.