Recently, we are working on new topological materials, novel physical properties, and new concept devices. Most of our recent progresses and the contents that we are going to study can be found in our Review Article “Topological Semimetal Nanostructures: From Properties to Topotronics”.

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1. Dirac/Weyl semimetals

There are several our recent works on the quantum transport properties of Dirac semimetal Cd₃As₂ nanostructures: the chiral anomaly induced negative magnetoresistance [1]; the Aharonov-Bohm oscillations originating from the topological surface states of the Dirac semimetal nanowires [2]; the Fano effect caused by the interference between the discrete surface state and the continuous bulk state of the Dirac semimetal Cd₃As₂ nanowires [3]; the quantum Hall effect from the topological surface states of a Dirac semimetal nanoplate [4]; the Fabry-Perot oscillations of critical supercurrent and the Majorana bound state evidenced by 4π-periodic supercurrent in a Dirac semimetal/superconductor heterojunction [5,6].
       
Referring to our previous works:

[1] Cai-Zhen Li, et al. Nature Communications 6, 10137 (2015).

[2] Li-Xian Wang, et al. Nature Communications 7, 10769 (2016).

[3] Shuo Wang, et al. Physical Review Letters 120, 257701 (2018).

[4] Ben-Chuan Lin, et al. Physical Review Letters 122, 036602 (2019).

[5] Cai-Zhen Li, et al. Physical Review B 97, 115446 (2018).

[6] An-Qi Wang, et al. Physical Review Letters 121, 237701 (2018).
               
2. Graphene

Graphene has potential applications due to its unique electronic, optical, mechanical, and chemical properties, which are primarily based on its two-dimensional nature. Graphene based vertical devices can extend the investigations and potential applications of graphene to three-dimension [1-6]. The interface properties are crucial for the function and performance of the graphene vertical devices. We developed a method to construct graphene based vertical structures by site-specifical transfer-printing individual graphene microsheets to arbitrary targets [2]. Layer-by-layer assembly of graphene has been proved to be an effective way to improve its mechanical properties [4,5]. We constructed graphene vertical devices with controllable functions via choosing different interfaces between graphene and other materials, for examples, graphene stacks sandwiched between two Au micro-strips, and between two Co layers. For the Au|graphene|Au junctions, an magnetoresistance (MR) up to 400% at 300 K at 14 T was obtained [1]. The Co|graphene|Co junctions display a robust spin valve effect at room temperature [1]. We also demonstrated that the vertical metal-graphene-metal structure can generate photocurrent over a broad light bandwidth with a large scalable junction area [6]. The devices showed evidence of the carrier multiplication effect and may open up new vistas of high-performance optoelectronic devices.
       
Referring to our previous works:

[1] Jing-Jing Chen, et al. Nature Communications 4, 1921 (2013).

[2] Ya-Qing Bie, et al. Advanced Materials 23, 3938 (2011).

[3] Zhi-Min Liao, et al. Advanced Materials 24, 1862 (2012).

[4] Qing-Yuan Lin, et al. ACS Nano 7, 1171 (2013).

[5] Qing-Yuan Lin, et al. ACS Nano 8, 10246 (2014).

[6] Jing-Jing Chen, et al. ACS Nano 9, 8851 (2015).
       
3. Topological Insulators

Topological insulators have exotic surface states that are massless Dirac fermions, manifesting special magnetotransport properties. In the surface Dirac cone, the band structures are typically closely related to the p-orbitals and possess a helical orbital texture. Like most layered materials, Bi₂Se₃, one typical kind of 3D topological insulators, can be grown by MBE method and mechanical exfoliation. In our lab, we synthesized Bi₂Se₃ nanostructures by catalyst-assisted PVD method. The synthesized nanostructures have high crystal quality and robust surface states with Hall mobility ~10,000 cm²/V∙s and prominent Shubnikov de Haas oscillations. The large positive magneto-resistance approaching to 400% is observed in Bi₂Se₃, consistent with the rather high mobility. Benefiting from the high-quality sample, we observed enhanced photo-thermoelectical effect in devices based on Bi₂Se₃ due to helical spin texture on the topological surface state.
       
Referring to our previous works:

[1] Yuan Yan, et al. Nano Letters 14, 4389 (2014).

[2] Yuan Yan, et al. ACS Nano 9, 10244 (2015).

[3] Liang Zhang, et al. ACS Nano 10, 3816 (2016).

[4] Yuan Yan, et al. Scientific Reports 3, 1264 (2013).

[5] Yuan Yan, et al. Scientific Reports 4, 3817 (2014).

[6] Li-Xian Wang, et al. Nanoscale 7, 16687 (2015).        
       
4. Semiconductor Nanowoires

Semiconductor nanowires have attracted a great deal of attention because of their potential applications in electronic and photonic devices. We have done works about single n-ZnO nanowire/p-GaN heterojunctions. This heterojunctions display excellent photovoltaic characters, UV electroluminescence, and self-powered photodetection. We also achieved the controlled alternation between memory and threshold Resistance Switching (RS) in single Ni/NiO core-shell nanowires by setting the compliance current (ICC) at room temperature. Recently, strain modulated physical properties of individual nanowires are under investigation.

Referring to our previous works:

[1] Li He, et al. Nano Letters 11, 4601 (2011).

[2] Zhi-Min Liao, et al. Nano Letters 6, 1087 (2006).

[3] Ya-Qing Bie, et al. Advanced Materials 23, 649 (2011).

[4] Ya-Qing Bie, et al. Advanced Materials 23, 3938 (2011).

[5] Xue-Wen Fu, et al. ACS Nano 7, 8891 (2013).

[6] Xue-Wen Fu, et al. ACS Nano 9, 11960 (2015).