W. Żdanowicz

Bio: W. Żdanowicz is an academic researcher from Polish Academy of Sciences. The author has contributed to research in topics: Hall effect & Cadmium arsenide. The author has an hindex of 2, co-authored 3 publications receiving 23 citations.

Gate-tunable quantum oscillations in ambipolar Cd 3 As 2 thin films

Abstract: Electrostatic doping in materials can lead to various exciting electronic properties, such as metal–insulator transition and superconductivity, by altering the Fermi level position or introducing exotic phases. Cd3As2, a three-dimensional (3D) analog of graphene with extraordinary carrier mobility, was predicted to be a 3D Dirac semimetal, a feature confirmed by recent experiments. However, most research so far has been focused on metallic bulk materials that are known to possess ultra-high mobility and giant magneto-resistance but limited carrier transport tunability. Here we report on the first observation of a gate-induced transition from band conduction to hopping conduction in single-crystalline Cd3As2 thin films via electrostatic doping by solid electrolyte gating. The extreme charge doping enables the unexpected observation of p-type conductivity in a ∼50-nm-thick Cd3As2 thin film grown by molecular beam epitaxy. More importantly, the gate-tunable Shubnikov–de Haas oscillations and the temperature-dependent resistance reveal a unique band structure and bandgap opening when the dimensionality of Cd3As2 is reduced. This is also confirmed by our first-principle calculations. The present results offer new insights toward nanoelectronic and optoelectronic applications of Dirac semimetals in general and provide new routes in the search for the intriguing quantum spin Hall effect in low-dimension Dirac semimetals, an effect that is theoretically predicted but not yet experimentally realized. The tunable quantum transport capabilities of cadmium arsenide thin films may unlock new applications for graphene-like semiconductors. Cadmium arsenide has similar electronic properties to graphene, but is easier to work with thanks to its three-dimensional crystal structure. Faxian Xiu of Fudan University in Shanghai and co-workers have now mapped out this material's band structure in confined 50-nanometre-thin film structures. By using a source-drain layout with an unconventional gate electrode — a droplet of ionic electrolyte that electrostatically dopes cadmium arsenide and changes its Fermi level — they saw remarkable conductivity switching behaviour, which is useful for ambipolar field effect transistors. Applying magnetic fields during device operation also revealed the possibility of generating quantum spin Hall effects — the team observed intriguing quantum oscillation conductivity when the Fermi level was pushed into the high-mobility conduction band. Cd3As2, which is known as a topological Dirac semimetal, has been grown on mica substrates by molecular beam epitaxy with high mobility. The temperature-dependent resistance of as-grown Cd3As2 thin films showed semiconducting behavior, indicating the band gap opening as opposed to the bulk counterpart. By solid electrolyte gating, the ambipolar effect and gate-tunable quantum oscillations were clearly demonstrated. These features make the Cd3As2 thin film system a promising platform to observe various exotic phenomena and realize new electronic applications.

Thickness-dependent quantum oscillations in Cd3As2 thin films

Abstract: Cd3As2 is a new kind of three-dimensional (3D) Dirac semimetal with extraordinary carrier mobility, which can be viewed as '3D graphene'. Theory predicts that Cd3As2 can be driven into a quantum spin Hall insulator with a sizeable band gap by reducing dimensionality. In this letter, we report the systematic growth of undoped Cd3As2 thin films with the thickness of 50 ~ 900 nm by molecular beam epitaxy. The magneto-transport study on these single-crystalline films shows a high mobility in the range of 3.8 ~ 9.1 × 103 cm2 V−1 s−1 and a relative low electron concentration of 1 ~ 8 × 1017 cm−3. Significantly, a thickness-induced semimetal-to-semiconductor transition was observed. In contrast with what is expected in the bulk counterpart, the 50 nm-thick Cd3As2 film exhibits semiconducting characteristics, witnessing an emerged bandgap opening when the dimensionality is reduced. Finally, the analyses on the temperature- and angular-dependence of magneto-resistance and Shubnikov-de Hass oscillations reveal a non-trivial to trivial Berry's phase transition that is in connection with the reduced dimensionality. Our results demonstrate that the Cd3As2 thin films with unique electronic structure and high mobility hold promise for Dirac semimetal device applications.