Anisotropic magnetoresistance and planar Hall effect in an antiferromagnetic insulator-topological insulator heterostructure

The coupling between magnetism and topological states at a topological insulator (TI)-magnetic insulator interface can induce exchange gap opening and spin texture change, resulting in many emergent transport phenomena, including anisotropic magnetoresistance (AMR) and planar Hall effect (PHE). While AMR/PHE have been reported in several ferromagnetic insulator-TI heterostructures so far, such effects in antiferromagnetic insulator-TI heterostructure remain elusive. Here, we observe unique features of AMR and PHE in an antiferromagnetic insulator-TI heterostructure <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mi>MnSe</a:mi><a:mtext>/</a:mtext><a:msub><a:mrow><a:mo>(</a:mo><a:mrow><a:mi>Bi</a:mi><a:mo>,</a:mo><a:mi>Sb</a:mi></a:mrow><a:mo>)</a:mo></a:mrow><a:mn>2</a:mn></a:msub><a:mi mathvariant="normal">T</a:mi><a:msub><a:mi mathvariant="normal">e</a:mi><a:mn>3</a:mn></a:msub></a:mrow></a:math>. Specifically, at low magnetic fields (<d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mi>H</d:mi></d:math>), the in-plane AMR exhibits dips under <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mi>H</e:mi></e:math> applied parallel to the current (<f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:mi>H</f:mi><f:mtext>//</f:mtext><f:mi>I</f:mi></f:math>) but peaks under the perpendicular geometry (<g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:mi>H</g:mi><g:mtext>⊥</g:mtext><g:mi>I</g:mi></g:math>), opposite to the zero AMR features in ferromagnetic insulator-TI heterostructures. The low-field PHE is most striking at <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"><h:mi>H</h:mi><h:mtext>//</h:mtext><h:mi>I</h:mi></h:math>, but gradually suppressed when <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"><i:mi>H</i:mi></i:math> deviates from parallel direction. At high magnetic fields, both AMR and PHE show prominent π-period oscillation. Gate-tuning and temperature-dependence measurements demonstrate that the observed AMR/PHE originate from the interplay between the topological surface state of TI with the spin canting and magnetic phase transition of MnSe. These results not only differentiate the AMR/PHE in TI-based magnetic heterostructure from the pristine TI, but also offer a feasible way to distinguish spin Hall effect and AMR in TI-based heterostructures.