Negatively enhanced thermopower near a Van Hove singularity in electron-doped Sr2RuO4

The layered perovskite <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:msub><a:mi>Sr</a:mi><a:mn>2</a:mn></a:msub><a:msub><a:mi>RuO</a:mi><a:mn>4</a:mn></a:msub></a:mrow></a:math> serves as a model material of the two-dimensional (2D) Fermi liquid but also exhibits various emergent phenomena including the non-Fermi-liquid (NFL) behavior under external perturbations such as uniaxial pressure and chemical substitutions. Here we present the thermoelectric transport of electron-doped system <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mrow><b:msub><b:mi>Sr</b:mi><b:mrow><b:mn>2</b:mn><b:mo>−</b:mo><b:mi>y</b:mi></b:mrow></b:msub><b:msub><b:mi>La</b:mi><b:mi>y</b:mi></b:msub><b:msub><b:mi>RuO</b:mi><b:mn>4</b:mn></b:msub></b:mrow></b:math>, in which a filling-induced Lifshitz transition occurs at the Van Hove singularity (VHS) point of <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mi>y</c:mi><c:mo>≈</c:mo><c:mn>0.2</c:mn></c:mrow></c:math>. We find that the sign of the low-temperature thermopower becomes negative only near the VHS point, where the NFL behavior has been observed in the earlier study. This observation is incompatible with either a numerical calculation within a constant relaxation-time approximation or a toy-model calculation for the 2D Lifshitz transition adopting an elastic carrier scattering. As a promising origin of the observed negatively enhanced thermopower, we propose a skewed NFL state, in which an inelastic scattering with a considerable odd-frequency term plays a crucial role to negatively enhance the thermopower. Published by the American Physical Society 2024