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- ItemGrowth of all-carbon horizontally aligned single-walled carbon nanotubes nucleated from fullerene-based structures(London : BioMed Central, 2013) Ibrahim, Imad; Zhang, Yang; Popov, Alexey; Dunsch, Lothar; Büchner, Bernd; Cuniberti, Gianaurelio; Rümmeli, Mark H.All-carbon single-walled carbon nanotubes (SWCNTs) were successfully synthesized, nucleated using a fullerene derivative. A systematic investigation into the initial preparation of C60 fullerenes as growth nucleators for the SWCNTs was conducted. Enhancement in the yield of the produced SWCNT has been achieved with exploring different dispersing media for the fullerenes, the period, and environment of the initial thermal treatment of the fullerenes in addition to the use of different fullerene-based structures. The systematic studies significantly advance our understanding of the growth of the all-carbon catalyst-free single-walled carbon nanotubes. Field-effect transistors were fabricated using the catalyst-free SWCNT and then electrically characterized, showing current capacity as high as the well-studied catalyst-assisted nanotubes.
- ItemWavelength-tunable entangled photons from silicon-integrated III–V quantum dots(London : Nature Publishing Group, 2016) Chen, Yan; Zhang, Jiaxiang; Zopf, Michael; Jung, Kyubong; Zhang, Yang; Keil, Robert; Ding, Fei; Schmidt, Oliver G.Many of the quantum information applications rely on indistinguishable sources of polarization-entangled photons. Semiconductor quantum dots are among the leading candidates for a deterministic entangled photon source; however, due to their random growth nature, it is impossible to find different quantum dots emitting entangled photons with identical wavelengths. The wavelength tunability has therefore become a fundamental requirement for a number of envisioned applications, for example, nesting different dots via the entanglement swapping and interfacing dots with cavities/atoms. Here we report the generation of wavelength-tunable entangled photons from on-chip integrated InAs/GaAs quantum dots. With a novel anisotropic strain engineering technique based on PMN-PT/silicon micro-electromechanical system, we can recover the quantum dot electronic symmetry at different exciton emission wavelengths. Together with a footprint of several hundred microns, our device facilitates the scalable integration of indistinguishable entangled photon sources on-chip, and therefore removes a major stumbling block to the quantum-dot-based solid-state quantum information platforms.
- ItemSpin Nernst effect in a p-band semimetal InBi(Bristol : IOP Publishing, 2020) Zhang, Yang; Xu, Qiunan; Koepernik, Klaus; Fu, Chenguang; Gooth, Johannes; van den Brink, Jeroen; Felser, Claudia; Sun, YanSince spin currents can be generated, detected, and manipulated via the spin Hall effect (SHE), the design of strong SHE materials has become a focus in the field of spintronics. Because of the recent experimental progress also the spin Nernst effect (SNE), the thermoelectrical counterpart of the SHE, has attracted much interest. Empirically strong SHEs and SNEs are associated with d-band compounds, such as transition metals and their alloys—the largest spin Hall conductivity (SHC) in a p-band material is $\sim 450\left(\hslash /e\right){\left({\Omega}\enspace \mathrm{c}\mathrm{m}\right)}^{-1}$ for a Bi–Sb alloy, which is only about a fifth of platinum. This raises the question whether either the SHE and SNE are naturally suppressed in p-bands compounds, or favourable p-band systems were just not identified yet. Here we consider the p-band semimetal InBi, and predict it has a record SHC ${\sigma }_{xy}^{z}\approx 1100\enspace \left(\hslash /e\right){\left({\Omega}\enspace \mathrm{c}\mathrm{m}\right)}^{-1}$ which is due to the presence of nodal lines in its band structure. Also the spin-Nernst conductivity ${\alpha }_{zx}^{y}\approx 1.2\enspace \left(\hslash /e\right)\left(A/m\cdot K\right)$ is very large, but our analysis shows its origin is different as the maximum appears in a different tensor element compared to that in SHC. This insight gained on InBi provides guiding principles to obtain a strong SHE and SNE in p-band materials and establishes a more comprehensive understanding of the relationship between the SHE and SNE.
- ItemDifferent types of spin currents in the comprehensive materials database of nonmagnetic spin Hall effect(London : Nature Publ. Group, 2021) Zhang, Yang; Xu, Qiunan; Koepernik, Klaus; Rezaev, Roman; Janson, Oleg; Železný, Jakub; Jungwirth, Tomáš; Felser, Claudia; van den Brink, Jeroen; Sun, YanSpin Hall effect (SHE) has its special position in spintronics. To gain new insight into SHE and to identify materials with substantial spin Hall conductivity (SHC), we performed high-precision high-throughput ab initio calculations of the intrinsic SHC for over 20,000 nonmagnetic crystals. The calculations revealed a strong relationship between the magnitude of the SHC and the crystalline symmetry, where a large SHC is typically associated with mirror symmetry-protected nodal line band structures. This database includes 11 materials with an SHC comparable to or even larger than that of Pt. Materials with different types of spin currents were additionally identified. Furthermore, we found that different types of spin current can be obtained by rotating applied electrical fields. This improves our understanding and is expected to facilitate the design of new types of spin-orbitronic devices.
- ItemTopological Weyl semimetals in the chiral antiferromagnetic materials Mn3Ge and Mn3Sn(Milton Park : Taylor & Francis, 2017) Yang, Hao; Sun, Yan; Zhang, Yang; Shi, Wu-Jun; Parkin, Stuart S.P.; Yan, BinghaiRecent experiments revealed that Mn3Sn and Mn3Ge exhibit a strong anomalous Hall effect at room temperature, provoking us to explore their electronic structures for topological properties. By ab initio band structure calculations, we have observed the existence of multiple Weyl points in the bulk and corresponding Fermi arcs on the surface, predicting antiferromagnetic Weyl semimetals in Mn3Ge and Mn3Sn. Here the chiral antiferromagnetism in the Kagome-type lattice structure is essential to determine the positions and numbers of Weyl points. Our work further reveals a new guiding principle to search for magnetic Weyl semimetals among materials that exhibit a strong anomalous Hall effect.