Chern Insulators at Integer and Fractional Filling in Moiré Pentalayer Graphene

The advent of moiré platforms for engineered quantum matter has led to discoveries of integer and fractional quantum anomalous Hall effects, with predictions for correlation-driven topological states based on electron crystallization. Here, we report an array of trivial and topological insulators formed in a moiré lattice of rhomobohedral pentalayer graphene (R5G). At a doping of one electron per moiré unit cell (<a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>ν</a:mi><a:mo>=</a:mo><a:mn>1</a:mn></a:math>), we see a correlated insulator with a Chern number that can be tuned between <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>C</c:mi><c:mo>=</c:mo><c:mn>0</c:mn></c:math> and <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mo>+</e:mo><e:mn>1</e:mn></e:math> by an electric displacement field. This is accompanied by a series of additional Chern insulators with <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mi>C</g:mi><g:mo>=</g:mo><g:mo>+</g:mo><g:mn>1</g:mn></g:math> originating from fractional fillings of the moiré lattice—<i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mi>ν</i:mi><i:mo>=</i:mo><i:mn>1</i:mn><i:mo>/</i:mo><i:mn>4</i:mn></i:math>, <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:mn>1</k:mn><k:mo>/</k:mo><k:mn>3</k:mn></k:math>, and <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mn>2</m:mn><m:mo>/</m:mo><m:mn>3</m:mn></m:math>—associated with the formation of moiré-driven topological electronic crystals. At <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:mi>ν</o:mi><o:mo>=</o:mo><o:mn>2</o:mn><o:mo>/</o:mo><o:mn>3</o:mn></o:math> the system exhibits an integer quantum anomalous Hall effect at zero magnetic field, but further develops hints of an incipient <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"><q:mi>C</q:mi><q:mo>=</q:mo><q:mn>2</q:mn><q:mo>/</q:mo><q:mn>3</q:mn></q:math> fractional Chern insulator in a modest field. Our results establish moiré R5G as a fertile platform for studying the competition and potential intertwining of integer and fractional Chern insulators.