Nernst Effect of High-Mobility Weyl Electrons in NdAlSi Enhanced by a Fermi Surface Nesting Instability

The thermoelectric Nernst effect of solids converts heat flow to beneficial electronic voltages. Here, using a correlated topological semimetal with high carrier mobility <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>μ</a:mi></a:math> in the presence of magnetic fluctuations, we demonstrate an enhancement of the Nernst effect close to a magnetic phase transition. A magnetic instability in NdAlSi modifies the carrier relaxation time on “hot spots” in momentum space, causing a strong band filling dependence of <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>μ</c:mi></c:math>. We quantitatively derive electronic band parameters from a novel two-band analysis of the Nernst effect <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mrow><e:msub><e:mi>S</e:mi><e:mrow><e:mi>x</e:mi><e:mi>y</e:mi></e:mrow></e:msub></e:mrow></e:math>, in good agreement with quantum oscillation measurements and band calculations. While the Nernst response of NdAlSi behaves much like conventional semimetals at high temperatures, an additional contribution <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mrow><g:mi mathvariant="normal">Δ</g:mi><g:msub><g:mi>S</g:mi><g:mrow><g:mi>xy</g:mi></g:mrow></g:msub></g:mrow></g:math> from electronic correlations appears just above the magnetic transition. Our work demonstrates the engineering of the relaxation time, or the momentum-dependent self-energy, to generate a large Nernst response independent of a material’s carrier density, i.e., for metals, semimetals, and semiconductors with large <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"><j:mi>μ</j:mi></j:math>.