Discovery of <math xmlns="http://www.w3.org/1998/Math/MathML"> <msub> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mover> <mi mathvariant="bold-italic">C</mi> <mo stretchy="false">^</mo> </mover> </mrow> </mrow> <mn>2</mn> </msub> </math> rotation anomaly in topological crystalline insulator SrPb.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 33824343.
- Also identified by DOI 10.1038/s41467-021-22350-6 and PMC identifier 8024327.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Topological crystalline insulators (TCIs) are insulating electronic states with nontrivial topology protected by crystalline symmetries. Recently, theory has proposed new classes of TCIs protected by rotation symmetries <math xmlns="http://www.w3.org/1998/Math/MathML"> <msub> <mrow class="MJX-TeXAtom-ORD"> <mover> <mi>C</mi> <mo stretchy="false">^</mo> </mover> </mrow> <mi>n</mi> </msub> </math>, which have surface rotation anomaly evading the fermion doubling theorem, i.e., n instead of 2n Dirac cones on the surface preserving the rotation symmetry. Here, we report the first realization of the <math xmlns="http://www.w3.org/1998/Math/MathML"> <msub> <mrow class="MJX-TeXAtom-ORD"> <mover> <mi>C</mi> <mo stretchy="false">^</mo> </mover> </mrow> <mn>2</mn> </msub> </math> rotation anomaly in a binary compound SrPb. Our first-principles calculations reveal two massless Dirac fermions protected by the combination of time-reversal symmetry <math xmlns="http://www.w3.org/1998/Math/MathML"> <mrow class="MJX-TeXAtom-ORD"> <mover> <mi>T</mi> <mo stretchy="false">^</mo> </mover> </mrow> </math> and <math xmlns="http://www.w3.org/1998/Math/MathML"> <msub> <mrow class="MJX-TeXAtom-ORD"> <mover> <mi>C</mi> <mo stretchy="false">^</mo> </mover> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> <mi>y</mi> </mrow> </msub> </math> on the (010) surface. Using angle-resolved photoemission spectroscopy, we identify two Dirac surface states inside the bulk band gap of SrPb, confirming the <math xmlns="http://www.w3.org/1998/Math/MathML"> <msub> <mrow class="MJX-TeXAtom-ORD"> <mover> <mi>C</mi> <mo stretchy="false">^</mo> </mover> </mrow> <mn>2</mn> </msub> </math> rotation anomaly in the new classes of TCIs. The findings enrich the classification of topological phases, which pave the way for exploring exotic behavior of the new classes of TCIs.