Incommensurate charge density wave order in U2Ti

Density functional theory predicted that the ground state of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:msub><a:mi mathvariant="normal">U</a:mi><a:mn>2</a:mn></a:msub><a:mi>Ti</a:mi></a:mrow></a:math> should undergo a Peierls-like doubling of its unit cell along the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mi>c</c:mi></c:math> axis on cooling from high temperature [G. Kaur , ]. We report x-ray diffraction, heat capacity, and resistivity measurements showing that with decreasing temperature the transition from the parent hexagonal structure occurs in two steps, via an incommensurate state below <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mrow><d:msub><d:mi>T</d:mi><d:mi>ICDW</d:mi></d:msub><d:mo>=</d:mo><d:mn>71</d:mn><d:mrow><d:mo>(</d:mo><d:mn>1</d:mn><d:mo>)</d:mo></d:mrow></d:mrow></d:math> K which then undergoes a lock-in transition to the predicted commensurate Peierls-like state at <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mrow><e:msub><e:mi>T</e:mi><e:mi>CCDW</e:mi></e:msub><e:mo>=</e:mo><e:mn>46</e:mn><e:mrow><e:mo>(</e:mo><e:mn>3</e:mn><e:mo>)</e:mo></e:mrow></e:mrow></e:math> K. The signatures of the upper transition in thermodynamic and transport measurements are weak, meaning that similar incommensurate charge density waves (ICDWs) preceding CDWs might occur more widely in other systems but elude detection. The collinear nature of both the ICDW and Peierls-like states we report is much simpler than more complex incommensurate states seen in <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:mi>α</f:mi><f:mtext>−</f:mtext><f:mi mathvariant="normal">U</f:mi></f:math>, which may in time provide greater insight into the mechanism for ICDW formation. Published by the American Physical Society 2024