Quantifying the U 5f covalence and degree of localization in U intermetallics

A procedure for quantifying the U <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mn>5</a:mn><a:mi>f</a:mi></a:mrow></a:math> electronic covalency and degree of localization in U intermetallic compounds is presented. To this end, bulk sensitive hard and soft x-ray photoelectron spectroscopy were utilized in combination with density-functional theory (DFT) plus dynamical mean-field theory (DMFT) calculations. The energy dependence of the photoionization cross sections allows the disentanglement of the U <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mrow><b:mn>5</b:mn><b:mi>f</b:mi></b:mrow></b:math> contribution to the valence band from the various other atomic subshells so the computational parameters in the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mi>DFT</c:mi><c:mo>+</c:mo><c:mi>DMFT</c:mi></c:mrow></c:math> can be reliably determined. Applying this method to <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:msub><d:mi>UGa</d:mi><d:mn>2</d:mn></d:msub></d:math> and <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:msub><e:mi>UB</e:mi><e:mn>2</e:mn></e:msub></e:math> as model compounds from opposite ends of the (de)localization range, we have achieved excellent simulations of the valence band and core-level spectra. The width in the distribution of atomic U <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:mrow><f:mn>5</f:mn><f:mi>f</f:mi></f:mrow></f:math> configurations contributing to the ground state, as obtained from the calculations, quantifies the correlated nature and degree of localization of the U <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:mn>5</g:mn><g:mi>f</g:mi></g:math>. The findings permit answering the longstanding question why different spectroscopic techniques give seemingly different numbers for the U <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"><h:mn>5</h:mn><h:mi>f</h:mi></h:math> valence in intermetallic U compounds. Published by the American Physical Society 2024