Absence of E2g Nematic Instability and Dominant A1g …

Ever since the discovery of the charge density wave (CDW) transition in the kagome metal <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:msub><a:mrow><a:mi>CsV</a:mi></a:mrow><a:mrow><a:mn>3</a:mn></a:mrow></a:msub></a:mrow><a:mrow><a:msub><a:mrow><a:mi>Sb</a:mi></a:mrow><a:mrow><a:mn>5</a:mn></a:mrow></a:msub></a:mrow></a:math>, the nature of its symmetry breaking has been under intense debate. While evidence suggests that the rotational symmetry is already broken at the CDW transition temperature (<c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:msub><c:mi>T</c:mi><c:mrow><c:mi>CDW</c:mi></c:mrow></c:msub></c:math>), an additional electronic nematic instability well below <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:msub><e:mi>T</e:mi><e:mrow><e:mi>CDW</e:mi></e:mrow></e:msub></e:math> has been reported based on the diverging elastoresistivity coefficient in the anisotropic channel (<g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:msub><g:mi>m</g:mi><g:msub><g:mi>E</g:mi><g:mrow><g:mn>2</g:mn><g:mi>g</g:mi></g:mrow></g:msub></g:msub></g:math>). Verifying the existence of a nematic transition below <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:msub><i:mi>T</i:mi><i:mrow><i:mi>CDW</i:mi></i:mrow></i:msub></i:math> is not only critical for establishing the correct description of the CDW order parameter, but also important for understanding low-temperature superconductivity. Here, we report elastoresistivity measurements of <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:mrow><k:msub><k:mrow><k:mi>CsV</k:mi></k:mrow><k:mrow><k:mn>3</k:mn></k:mrow></k:msub></k:mrow><k:mrow><k:msub><k:mrow><k:mi>Sb</k:mi></k:mrow><k:mrow><k:mn>5</k:mn></k:mrow></k:msub></k:mrow></k:math> using three different techniques probing both isotropic and anisotropic symmetry channels. Contrary to previous reports, we find the anisotropic elastoresistivity coefficient <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:msub><m:mi>m</m:mi><m:msub><m:mi>E</m:mi><m:mrow><m:mn>2</m:mn><m:mi>g</m:mi></m:mrow></m:msub></m:msub></m:math> is temperature independent, except for a step jump at <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:msub><o:mi>T</o:mi><o:mrow><o:mi>CDW</o:mi></o:mrow></o:msub></o:math>. The absence of nematic fluctuations is further substantiated by measurements of the elastocaloric effect, which show no enhancement associated with nematic susceptibility. On the other hand, the symmetric elastoresistivity coefficient <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"><q:msub><q:mi>m</q:mi><q:msub><q:mi>A</q:mi><q:mrow><q:mn>1</q:mn><q:mi>g</q:mi></q:mrow></q:msub></q:msub></q:math> increases below <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"><s:msub><s:mi>T</s:mi><s:mrow><s:mi>CDW</s:mi></s:mrow></s:msub></s:math>, reaching a peak value of 90 at <u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline"><u:msup><u:mi>T</u:mi><u:mo>*</u:mo></u:msup><u:mo>=</u:mo><u:mn>20</u:mn><u:mtext> </u:mtext><u:mtext> </u:mtext><u:mi mathvariant="normal">K</u:mi></u:math>. Our results strongly indicate that the phase transition at <x:math xmlns:x="http://www.w3.org/1998/Math/MathML" display="inline"><x:msup><x:mi>T</x:mi><x:mo>*</x:mo></x:msup></x:math> is not nematic in nature and the previously reported diverging elastoresistivity is due to the contamination from the <z:math xmlns:z="http://www.w3.org/1998/Math/MathML" display="inline"><z:msub><z:mi>A</z:mi><z:mrow><z:mn>1</z:mn><z:mi>g</z:mi></z:mrow></z:msub></z:math> channel. Published by the American Physical Society 2024