Nonlinear and Nonreciprocal Transport Effects in Untwinned Thin Films of Ferromagnetic Weyl Metal SrRuO3

The identification of distinct charge transport features, deriving from nontrivial bulk band and surface states, has been a challenging subject in the field of topological systems. In topological Dirac and Weyl semimetals, nontrivial conical bands with Fermi-arc surface states give rise to negative longitudinal magnetoresistance due to chiral anomaly effect and unusual thickness dependent quantum oscillation from Weyl-orbit effect, which were demonstrated recently in experiments. In this work, we report the experimental observations of large nonlinear and nonreciprocal transport effects for both longitudinal and transverse channels in an untwinned Weyl metal of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:msub><a:mrow><a:mi>SrRuO</a:mi></a:mrow><a:mrow><a:mn>3</a:mn></a:mrow></a:msub></a:mrow></a:math> thin film grown on a <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mrow><c:msub><c:mrow><c:mi>SrTiO</c:mi></c:mrow><c:mrow><c:mn>3</c:mn></c:mrow></c:msub></c:mrow></c:math> substrate. From rigorous measurements with bias current applied along various directions with respect to the crystalline principal axes, the magnitude of nonlinear Hall signals from the transverse channel exhibits a simple <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mrow><e:mi>sin</e:mi><e:mi>α</e:mi></e:mrow></e:math> dependence at low temperatures, where <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mi>α</g:mi></g:math> is the angle between bias current direction and orthorhombic <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mrow><i:mo stretchy="false">[</i:mo><i:mn>001</i:mn><i:msub><i:mrow><i:mo stretchy="false">]</i:mo></i:mrow><i:mrow><i:mi mathvariant="normal">o</i:mi></i:mrow></i:msub></i:mrow></i:math>, reaching a maximum when current is along orthorhombic <n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"><n:mrow><n:mo stretchy="false">[</n:mo><n:mn>1</n:mn><n:mover accent="true"><n:mrow><n:mn>1</n:mn></n:mrow><n:mrow><n:mo stretchy="false">¯</n:mo></n:mrow></n:mover><n:mn>0</n:mn><n:msub><n:mrow><n:mo stretchy="false">]</n:mo></n:mrow><n:mrow><n:mi mathvariant="normal">o</n:mi></n:mrow></n:msub></n:mrow></n:math>. On the contrary, the magnitude of nonlinear and nonreciprocal signals in the longitudinal channel attains a maximum for bias current along <u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline"><u:mrow><u:mo stretchy="false">[</u:mo><u:mn>001</u:mn><u:msub><u:mrow><u:mo stretchy="false">]</u:mo></u:mrow><u:mrow><u:mi mathvariant="normal">o</u:mi></u:mrow></u:msub></u:mrow></u:math>, and it vanishes for bias current along <z:math xmlns:z="http://www.w3.org/1998/Math/MathML" display="inline"><z:mrow><z:mo stretchy="false">[</z:mo><z:mn>1</z:mn><z:mover accent="true"><z:mrow><z:mn>1</z:mn></z:mrow><z:mrow><z:mo stretchy="false">¯</z:mo></z:mrow></z:mover><z:mn>0</z:mn><z:msub><z:mrow><z:mo stretchy="false">]</z:mo></z:mrow><z:mrow><z:mi mathvariant="normal">o</z:mi></z:mrow></z:msub></z:mrow></z:math>. The observed <gb:math xmlns:gb="http://www.w3.org/1998/Math/MathML" display="inline"><gb:mi>α</gb:mi></gb:math>-dependent nonlinear and nonreciprocal signals in longitudinal and transverse channels reveal a magnetic Weyl phase with an effective Berry curvature dipole along <ib:math xmlns:ib="http://www.w3.org/1998/Math/MathML" display="inline"><ib:mrow><ib:mo stretchy="false">[</ib:mo><ib:mn>1</ib:mn><ib:mover accent="true"><ib:mrow><ib:mn>1</ib:mn></ib:mrow><ib:mrow><ib:mo stretchy="false">¯</ib:mo></ib:mrow></ib:mover><ib:mn>0</ib:mn><ib:msub><ib:mrow><ib:mo stretchy="false">]</ib:mo></ib:mrow><ib:mrow><ib:mi mathvariant="normal">o</ib:mi></ib:mrow></ib:msub></ib:mrow></ib:math> from surface states, accompanied by 1D chiral edge modes along <pb:math xmlns:pb="http://www.w3.org/1998/Math/MathML" display="inline"><pb:mrow><pb:mo stretchy="false">[</pb:mo><pb:mn>001</pb:mn><pb:msub><pb:mrow><pb:mo stretchy="false">]</pb:mo></pb:mrow><pb:mrow><pb:mi mathvariant="normal">o</pb:mi></pb:mrow></pb:msub></pb:mrow></pb:math>. Published by the American Physical Society 2024