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Nano Lett. 2017 Apr 12;17(4):2211-2219. doi: 10.1021/acs.nanolett.6b04778. Epub 2017 Mar 2.

Direct Observation of Landau Level Resonance and Mass Generation in Dirac Semimetal Cd3As2 Thin Films.

Yuan X1,2, Cheng P1,2, Zhang L3,4, Zhang C1,2, Wang J5, Liu Y1,2, Sun Q6, Zhou P6, Zhang DW6, Hu Z5, Wan X3,4, Yan H1,2, Li Z7, Xiu F1,2.

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State Key Laboratory of Surface Physics and Department of Physics, Fudan University , Shanghai 200433, China.
Collaborative Innovation Center of Advanced Microstructures, Fudan University , Shanghai 200433, China.
National Laboratory of Solid State Microstructures, School of Physics, Nanjing University , Nanjing 210093, China.
Collaborative Innovation Center of Advanced Microstructures, Nanjing University , Nanjing 210093, China.
Key Laboratory of Polar Materials and Devices, Ministry of Education, Department of Electronic Engineering, East China Normal University , Shanghai 200241, China.
State Key Laboratory of ASIC and System, Department of Microelectronics, Fudan University , Shanghai 200433, China.
College of Physical Science and Technology, Sichuan University , Chengdu, Sichuan 610064, China.


Three-dimensional topological Dirac semimetals have hitherto stimulated unprecedented research interests as a new class of quantum materials. Breaking certain types of symmetries has been proposed to enable the manipulation of Dirac fermions, and that was soon realized by external modulations such as magnetic fields. However, an intrinsic manipulation of Dirac states, which is more efficient and desirable, remains a significant challenge. Here, we report a systematic study of quasi-particle dynamics and band evolution in Cd3As2 thin films with controlled chromium (Cr) doping by both magneto-infrared spectroscopy and electrical transport. We observe the √B relation of inter-Landau-level resonance in Cd3As2, an important signature of ultrarelativistic massless state inaccessible in previous optical experiments. A crossover from quantum to quasi-classical behavior makes it possible to directly probe the mass of Dirac fermions. Importantly, Cr doping allows for a Dirac mass acquisition and topological phase transition enabling a desired dynamic control of Dirac fermions. Corroborating with the density-functional theory calculations, we show that the mass generation can be explained by the explicit C4 rotation symmetry breaking and the resultant Dirac gap engineering through Cr substitution for Cd atoms. The manipulation of the system symmetry and Dirac mass in Cd3As2 thin films provides a tuning knob to explore the exotic states stemming from the parent phase of Dirac semimetals.


Cd3As2; Dirac semimetal; mass generation; topological phase transition

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