Journal
PHYSICAL REVIEW B
Volume 99, Issue 11, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.99.115138
Keywords
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Funding
- National Natural Science Foundation of China [11574391, 11774424, 11874422]
- Fundamental Research Funds for the Central Universities
- Research Funds of Renmin University of China [18XNLG14, 19XNLG18]
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We report the magnetotransport properties of CaAl4 single crystals with C2/m structure at low temperature. CaAl4 exhibits large unsaturated magnetoresistance similar to 3000% at 2.5 K and 14 T. The nonlinear Hall resistivity is observed, which indicates the multi-band feature. The first-principles calculations show the electron-hole compensation and the complex Fermi surface in CaAl4, to which the two-band model with over-simplified carrier mobility can't completely apply. Evident quantum oscillations have been observed with B perpendicular to ab and B//ab configurations, from which the nontrivial Berry phase is extracted by the multi-band Lifshitz-Kosevich formula fitting and Landau level index fan diagram. The calculations also elucidate that CaAl4 possesses a Dirac nodal line type band structure around the Gamma point in the Z-Gamma-L plane, which is protected by the mirror symmetry as well as the space inversion and time reversal symmetries. Once the spin-orbit coupling is included, the crossed nodal line opens a negligible gap (less than 3 meV). The Z(2) invariant of CaAl4 equals 1, indicating its nontrivial topological properties. The open-orbit topology is also found in the electron-type Fermi surfaces by the first-principles calculations, which is believed to help enhance the magnetoresistance observed.
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