We are the quantum nanoelectronic transport group in School of Physics at Peking University.

 

 

  Our current research is focused on quantum transport and optoelectronics in Dirac/Weyl semimetals, graphene, topological insulators, and semiconductor nanowires.

1. Dirac/Weyl semimetals

Dirac electronic materials beyond graphene and topological insulators have recently attracted considerable attention. Cd3As2 is a newly booming Dirac semimetal with linear dispersion along all three momentum directions and can be viewed as 3D analog of graphene. As breaking of either time reversal symmetry or spatial inversion symmetry, the Dirac semimetal is believed to transform into Weyl semimetal with exotic chiral anomaly effect. Topological surface states with Fermi arcs are predicted on the surface and have been observed by angle-resolved photoemission spectroscopy experiments. We have observed the large negative magnetoresistance with magnitude of -63% at 60 K and -11% at 300 K in individual Cd3As2 nanowires, giving evidence of the chiral anomaly effect [1]. Moreover, we observed the Aharonov-Bohm oscillations in individual single-crystal Cd3As2 nanowires with low carrier concentration and large surface-to-volume ratio, providing transport evidence of the surface state in three-dimensional Dirac semimetals [2]. The quantum transport can be modulated by tuning the Fermi level using a gate voltage, enabling a deeper understanding of rich physics residing in Dirac semimetals.

Referring to our previous works:

[1] C. Z. Li, et al., Nat. Commun. 6, 10137 (2015).

[2] L. X. Wang, et al., Nat. Commun. 7, 10769 (2016).

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).

 

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