Speaker
Description
Topological materials have attracted significant interest in condensed matter physics for their unique topological properties leading to potential technological applications. Topological nodal line semimetals, a subclass of topological materials, exhibit symmetry-protected nodal lines, where band crossings occur along closed curves in the three-dimensional Brillouin zone. When the nodal lines are gapped out due to perturbation in the Hamiltonian, a large Berry curvature (BC) arises in the surrounding area of the gapped nodal line, leading to exotic anomalous transport responses. In this paper, we studied the Co$_2$CrX (X=Ga, Ge) Heusler compounds that exhibit mirror symmetry-protected nodal line states below the Fermi level. The BC calculation yields anomalous Hall conductivity (AHC) of about $292$ and $217$ S/cm for Co$_2$CrX (X=Ga, Ge), respectively, at the Fermi level, which increases by up to $400\%$ at the nodal line energy level. We theoretically analyzed that $20\%$ and $60\%$ zinc (Zn) alloying in Co$_2$CrX (X=Ga, Ge) effectively lowers the Fermi level by $50$ meV and $330$ meV, respectively, aligning with the protected crossings. Consequently, we identified Co$_2$CrGe$_{0.4}$Zn$_{0.6}$ and Co$_2$CrGa$_{0.8}$Zn$_{0.2}$ as compositions to achieve the significant AHC of $800$ and $1300$ S/cm, respectively. The explicit AHC calculation for these alloyed compositions is in good agreement with our predictions. Our findings highlight that chemical alloying is an efficient way to enhance AHC in nodal line hosting materials.
Acknowledgements
S.W.D and J.M. are thankful for the support of the QM4ST project funded by Programme Johannes Amos Commenius, call Excellent Research (Project No. CZ.02.01.01/00/22_008/0004572). S.S. thanks the Science and Engineering Research Board of India for financial support through the CRG scheme (Grant No. CRG/2021/003256) and UGC-DAE CSR, Indore, for financial support through the CRS scheme.
