Liu Wei

@article{ISI:001205711600001,
title = {Upconversion electroluminescence in 2D semiconductors integrated with plasmonic tunnel junctions},
author = {Zhe Wang and Vijith Kalathingal and Maxim Trushin and Jiawei Liu and Junyong Wang and Yongxin Guo and Barbaros Ozyilmaz and Christian A Nijhuis and Goki Eda},
doi = {10.1038/s41565-024-01650-0},
times_cited = {4},
issn = {1748-3387},
year = {2024},
date = {2024-04-19},
journal = {NATURE NANOTECHNOLOGY},
volume = {19},
number = {7},
publisher = {NATURE PORTFOLIO},
address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY},
abstract = {Plasmonic tunnel junctions are a unique electroluminescent system in which light emission occurs via an interplay between tunnelling electrons and plasmonic fields instead of electron-hole recombination as in conventional light-emitting diodes. It was previously shown that placing luminescent molecules in the tunneling pathway of nanoscopic tunnel junctions results in peculiar upconversion electroluminescence where the energy of emitted photons exceeds that of excitation electrons. Here we report the observation of upconversion electroluminescence in macroscopic van der Waals plasmonic tunnel junctions comprising gold and few-layer graphene electrodes separated by a similar to 2-nm-thick hexagonal boron nitride tunnel barrier and a monolayer semiconductor. We find that the semiconductor ground exciton emission is triggered at excitation electron energies lower than the semiconductor optical gap. Interestingly, this upconversion is reached in devices operating at a low conductance (<10(-6) S) and low power density regime (<10(2) W cm(-2)), defying explanation through existing proposed mechanisms. By examining the scaling relationship between plasmonic and excitonic emission intensities, we elucidate the role of inelastic electron tunnelling dipoles that induce optically forbidden transitions in the few-layer graphene electrode and ultrafast hot carrier transfer across the van der Waals interface.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{ISI:001195156600001,
title = {Evolution of Graphene Dirac Fermions in Electric Double-Layer Transistors with a Soft Barrier},
author = {Fanrong Lin and Jiawei Liu and Huan Lu and Xin Liu and Ying Liu and Zhili Hu and Pin Lyu and Zhuhua Zhang and Jens Martin and Wanlin Guo and Yanpeng Liu},
doi = {10.1002/adfm.202400553},
times_cited = {0},
issn = {1616-301X},
year = {2024},
date = {2024-04-02},
journal = {ADVANCED FUNCTIONAL MATERIALS},
volume = {34},
number = {34},
publisher = {WILEY-V C H VERLAG GMBH},
address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY},
abstract = {The interface and dielectric environment of graphene transistors are of great importance to commercial circuit integrations. The tangling bond in oxide-based dielectric severely lagged the carrier mobility while the 2D dielectric layer (for instance, hexagonal boron nitride) unavoidably hastened complicated condensed physics even at room temperature. Herein, multilayer black phosphorus (BP) a versatile and widely-tunable dielectric candidate for manifesting graphene fermions is demonstrated. Because of hetero-interfacial charge redistributions, a vertical electric double-layer between the bottom BP layer and top graphene spontaneously forms with the central BP layer as a soft barrier. Under dual-gate modulation, abnormal step-like evolution of Dirac fermions and charge-transfer quantum Hall effect arises while the intrinsic Dirac behavior of graphene is preserved, ascribing to the gate-tunable charge redistributions of dielectric BP layer. Moreover, the electric double-layer transistors apply equally well to bilayer graphene with similar Dirac behavior but an enhanced interfacial charge interference. The findings not only create a new avenue to manipulate the fermions by assembling graphene with narrow-gapped 2D layered materials but also promote electric double-layer transistors as a new build block to design multifunctional devices.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{ISI:001142010100002,
title = {Highly anisotropic spin transport in ultrathin black phosphorus},
author = {Luke Cording and Jiawei Liu and Jun You Tan and Kenji Watanabe and Takashi Taniguchi and Ahmet Avsar and Barbaros Ozyilmaz},
doi = {10.1038/s41563-023-01779-8},
times_cited = {10},
issn = {1476-1122},
year = {2024},
date = {2024-01-12},
journal = {NATURE MATERIALS},
volume = {23},
number = {4},
publisher = {NATURE PORTFOLIO},
address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY},
abstract = {In anisotropic crystals, the direction-dependent effective mass of carriers can have a profound impact on spin transport dynamics. The puckered crystal structure of black phosphorus leads to direction-dependent charge transport and optical response, suggesting that it is an ideal system for studying anisotropic spin transport. To this end, we fabricate and characterize high-mobility encapsulated ultrathin black-phosphorus-based spin valves in a four-terminal geometry. Our measurements show that in-plane spin lifetimes are strongly gate tunable and exceed one nanosecond. Through high out-of-plane magnetic fields, we observe a fivefold enhancement in the out-of-plane spin signal case compared to in-plane and estimate a colossal spin-lifetime anisotropy of similar to 6. This finding is further confirmed by oblique Hanle measurements. Additionally, we estimate an in-plane spin-lifetime anisotropy ratio of up to 1.8. Our observation of strongly anisotropic spin transport along three orthogonal axes in this pristine material could be exploited to realize directionally tunable spin transport.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}