Albert Liang Gengchiau

@article{ISI:000663272500001,
title = {Observation of the Out-of-Plane Polarized Spin Current from CVD Grown WTe_{2}},
author = {Shuyuan Shi and Jie Li and Chuang-Han Hsu and Kyusup Lee and Yi Wang and Li Yang and Junyong Wang and Qisheng Wang and Hao Wu and Wenfeng Zhang and Goki Eda and Gengchiau Liang and Haixin Chang and Hyunsoo Yang},
doi = {10.1002/qute.202100038},
times_cited = {35},
year = {2021},
date = {2021-06-19},
journal = {ADVANCED QUANTUM TECHNOLOGIES},
volume = {4},
number = {8},
publisher = {WILEY},
address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA},
abstract = {Weyl semimetal Td-phase WTe2 possesses the spin-resolved band structure with strong spin-orbit coupling, holding promises as a useful spin source material. The noncentrosymmetric crystalline structure of Td-WTe2 endows the generation of the out-of-plane polarized spin, which is of great interest in magnetic memory applications. Previously, WTe2 was explored in spin devices based on mechanically exfoliated single crystal flakes with a size of micrometers. For practical spintronics applications, it is highly desirable to implement wafer-scale thin films. In this work, centimeter-scale chemical vapor deposition (CVD) grown Td-WTe2 thin films are used and the spin current generation is studied by the spin torque ferromagnetic resonance (ST-FMR) technique. The in-plane and out-of-plane spin conductivities of 7.36 x 10(3) (PLANCK CONSTANT OVER TWO PI/2e) (ohm m)(-1) and 1.76 x 10(3) (PLANCK CONSTANT OVER TWO PI/2e) (ohm m)(-1), respectively, are found in CVD-growth 5 nm-WTe2. The current-induced magnetization switching in WTe2/NiFe is demonstrated at room temperature in the domain wall motion regime, which may invigorate potential spintronic device innovations based on Weyl semimetals.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{ISI:000611456700002,
title = {Room-temperature nonlinear Hall effect and wireless radiofrequency rectification in Weyl semimetal TaIrTe_{4}},
author = {Dushyant Kumar and Chuang-Han Hsu and Raghav Sharma and Tay-Rong Chang and Peng Yu and Junyong Wang and Goki Eda and Gengchiau Liang and Hyunsoo Yang},
doi = {10.1038/s41565-020-00839-3},
times_cited = {133},
issn = {1748-3387},
year = {2021},
date = {2021-01-25},
journal = {NATURE NANOTECHNOLOGY},
volume = {16},
number = {4},
pages = {421-+},
publisher = {NATURE RESEARCH},
address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY},
abstract = {The nonlinear Hall effect (NLHE), the phenomenon in which a transverse voltage can be produced without a magnetic field, provides a potential alternative for rectification or frequency doubling(1,2). However, the low-temperature detection of the NLHE limits its applications(3,4). Here, we report the room-temperature NLHE in a type-II Weyl semimetal TaIrTe4, which hosts a robust NLHE due to broken inversion symmetry and large band overlapping at the Fermi level. We also observe a temperature-induced sign inversion of the NLHE in TaIrTe4. Our theoretical calculations suggest that the observed sign inversion is a result of a temperature-induced shift in the chemical potential, indicating a direct correlation of the NLHE with the electronic structure at the Fermi surface. Finally, on the basis of the observed room-temperature NLHE in TaIrTe4 we demonstrate the wireless radiofrequency (RF) rectification with zero external bias and magnetic field. This work opens a door to realizing room-temperature applications based on the NLHE in Weyl semimetals.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{ISI:000545436900036,
title = {Voltage-Controlled Spintronic Stochastic Neuron for Restricted Boltzmann Machine With Weight Sparsity},
author = {Jiefang Deng and Venkata Pavan Kumar Miriyala and Zhifeng Zhu and Xuanyao Fong and Gengchiau Liang},
doi = {10.1109/LED.2020.2995874},
times_cited = {21},
issn = {0741-3106},
year = {2020},
date = {2020-07-01},
journal = {IEEE ELECTRON DEVICE LETTERS},
volume = {41},
number = {7},
pages = {1102-1105},
publisher = {IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC},
address = {445 HOES LANE, PISCATAWAY, NJ 08855-4141 USA},
abstract = {This work proposes a novel three-terminal magnetic tunnel junction (MTJ) as a stochastic neuron. The neuron is probabilistically switched based on the voltage-controlled magnetic anisotropy (VCMA) effect with the assistance of Rashba effective field. We find that a restricted Boltzmann machine (RBM) implemented using our proposed neuron for handwritten character recognition can achieve synaptic weight sparsity, without sacrificing the network classification accuracy. Moreover, the RBM implemented by this novel neuron performs even better in the presence of device variations, implying that our device is highly suitable for the hardware implementation of RBM.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{ISI:000488977100013,
title = {All-electric magnetization switching and Dzyaloshinskii-Moriya interaction in WTe_{2}/ferromagnet heterostructures},
author = {Shuyuan Shi and Shiheng Liang and Zhifeng Zhu and Kaiming Cai and Shawn D Pollard and Yi Wang and Junyong Wang and Qisheng Wang and Pan He and Jiawei Yu and Goki Eda and Gengchiau Liang and Hyunsoo Yang},
doi = {10.1038/s41565-019-0525-8},
times_cited = {211},
issn = {1748-3387},
year = {2019},
date = {2019-10-01},
journal = {NATURE NANOTECHNOLOGY},
volume = {14},
number = {10},
pages = {945-+},
publisher = {NATURE PUBLISHING GROUP},
address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND},
abstract = {All-electric magnetization manipulation at low power is a prerequisite for a wide adoption of spintronic devices. Materials such as heavy metals(1-3) or topological insulators(4,5) provide good charge-to-spin conversion efficiencies. They enable magnetization switching in heterostructures with either metallic ferromagnets or with magnetic insulators. Recent work suggests a pronounced Edelstein effect in Weyl semimetals due to their non-trivial band structure(6,7); the Edelstein effect can be one order of magnitude stronger than it is in topological insulators or Rashba systems. Furthermore, the strong intrinsic spin Hall effect from the bulk states in Weyl semimetals can contribute to the spin current generation(8). The Td phase of the Weyl semimetal WTe2 (WTe2 hereafter) possesses strong spin-orbit coupling(6,9) and non-trivial band structures(10) with a large spin polarization protected by time-reversal symmetry in both the surface and bulk states(9-11). Atomically flat surfaces, which can be produced with high quality(12), facilitate spintronic device applications. Here, we use WTe2 as a spin current source in WTe2/Ni81Fe19 (Py) heterostructures. We report field-free current-induced magnetization switching at room temperature. A charge current density of similar to 2.96 x 10(5) A cm(-2) suffices to switch the magnetization of the Py layer. With the charge current along the b axis of the WTe2 layer, the thickness-dependent charge-to-spin conversion efficiency reaches 0.51 at 6-7 GHz. At the WTe2/Py interface, a Dzyaloshinskii-Moriya interaction (DMI) with a DMI constant of -1.78 +/- 0.06 mJ m(-2) induces chiral domain wall tilting. Our study demonstrates the capability of WTe2 to efficiently manipulate magnetization and sheds light on the role of the interface in Weyl semimetal/magnet heterostructures.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{ISI:000435987400033,
title = {Electric-field-induced three-terminal pMTJ switching in the absence of an external magnetic field},
author = {Jiefang Deng and Xuanyao Fong and Gengchiau Liang},
doi = {10.1063/1.5027759},
times_cited = {6},
issn = {0003-6951},
year = {2018},
date = {2018-06-18},
journal = {APPLIED PHYSICS LETTERS},
volume = {112},
number = {25},
publisher = {AMER INST PHYSICS},
address = {1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA},
abstract = {Since it is undesirable to require an external magnetic field for on-chip memory applications, we investigate the use of a Rashba effective field alternatively for assisting the electric-field-induced switching operation of a three terminal perpendicular magnetic tunnel junction (pMTJ). By conducting macro-spin simulations, we show that a pMTJ with a thermal stability of 61 can be switched in 0.5 ns, consuming a switching energy of 6 fJ, and the voltage operation margin can be improved to 0.8 ns. Furthermore, the results also demonstrate that a heavy metal system that can provide a large field-like torque rather than the damping-like torque is favored for the switching. Published by AIP Publishing.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{ISI:000416409400004,
title = {Ultrafast and low-energy switching in voltage-controlled elliptical pMTJ},
author = {Jiefang Deng and Gengchiau Liang and Gaurav Gupta},
doi = {10.1038/s41598-017-16292-7},
times_cited = {13},
issn = {2045-2322},
year = {2017},
date = {2017-11-29},
journal = {SCIENTIFIC REPORTS},
volume = {7},
publisher = {NATURE PORTFOLIO},
address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY},
abstract = {Switching magnetization in a perpendicular magnetic tunnel junction (pMTJ) via voltage controlled magnetic anisotropy (VCMA) has shown the potential to markedly reduce switching energy. However, the requirement of an external magnetic field poses a critical bottleneck for its practical applications. In this work, we propose an elliptical-shaped pMTJ to eliminate the requirement of providing an external field by an additional circuit. We demonstrate that a 10 nm thick in-plane magnetized bias layer (BL) separated by a metallic spacer of 3 nm from the free layer (FL) can be engineered within the MTJ stack to provide the 50 mT bias magnetic field for switching. By conducting macrospin simulation, we find that a fast switching in 0.38 ns with energy consumption as low as 0.3 fJ at a voltage of 1.6 V can be achieved. Furthermore, we study the phase diagram of switching probability, showing that a pulse duration margin of 0.15 ns is obtained and low-voltage operation (similar to 1V) is favored. Finally, the MTJ scalability is considered, and it is found that scaling down may not be appealing in terms of both the energy consumption and the switching time for precession based VCMA switching.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{ISI:000394691600035,
title = {Effects of Contact Placement and Intra/Interlayer Interaction in Current Distribution of Black Phosphorus Sub-10-nm FET},
author = {Sheng Luo and Kai-Tak Lam and Baokai Wang and Chuang-Han Hsu and Wen Huang and Liang-Zi Yao and Arun Bansil and Hsin Lin and Gengchiau Liang},
doi = {10.1109/TED.2016.2635690},
times_cited = {6},
issn = {0018-9383},
year = {2017},
date = {2017-02-01},
journal = {IEEE TRANSACTIONS ON ELECTRON DEVICES},
volume = {64},
number = {2},
pages = {579-586},
publisher = {IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC},
address = {445 HOES LANE, PISCATAWAY, NJ 08855-4141 USA},
abstract = {Black phosphorus (BP) has been proposed as the channel material in the next generation ultrascaled CMOS devices. In order to gain insight into the current characteristics in 2-D layered materials, the current distribution of a few-layer BP Schottky barrier FET is investigated via state-of-the-art quantum device simulations. Approximately 40% of the total currentwas foundto be concentrated in the top layer when the device was switched on, with the remaining current distributed among the other layers. In comparison, similar to 80% of the current concentrated belowthe surface in a Si device with the same structure. These features are related to the strength of the intra/interlayer interaction in few-layer BP and are unique to 2-D layered materials. Moreover, the current distribution and the device performance were different for the top-and side-contacted devices, with the side-contacted devices yielding lower resistance compared with the top-contacted devices.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{ISI:000361952400002,
title = {Carrier transport in Bi_{2}Se_{3} topological insulator slab},
author = {Gaurav Gupta and Hsin Lin and Arun Bansil and Mansoor Bin Abdul Jalil and Gengchiau Liang},
doi = {10.1016/j.physe.2015.06.003},
times_cited = {1},
issn = {1386-9477},
year = {2015},
date = {2015-11-01},
journal = {PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES},
volume = {74},
pages = {10-19},
publisher = {ELSEVIER SCIENCE BV},
address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS},
abstract = {Electron transport in Bi2Se3 topological insulator slabs is investigated in the thermal activation regime (>50 K) both in the absence (ballistic) and presence of weak and strong acoustic phonon scattering using the non-equilibrium Green function approach. Resistance of the slab is simulated as a function of temperature for a range of slab thicknesses and effective doping in order to gain a handle on how various factors interact and compete to determine the overall resistance of the slab, If the Bi2Se3 slab is biased at the Dirac point, resistance is found to display an insulating trend even for strong electron-phonon coupling strength. However, when the Fermi-level lies close to the bulk conduction band (heavy electron doping), phonon scattering can dominate and result in a metallic behavior, although the insulating trend is retained in the limit of ballistic transport. Depending on values of the operating parameters, the temperature dependence of the slab is found to exhibit a remarkably complex behavior, which ranges from insulating to metallic, and includes cases where the resistance exhibits a local maximum, much like the contradictory behaviors seen experimentally in various experiments. (C) 2015 Elsevier B.V. All rights reserved},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{ISI:000337341700004,
title = {Role of acoustic phonons in Bi_{2}Se_{3} topological insulator slabs: A quantum transport investigation},
author = {Gaurav Gupta and Hsin Lin and Arun Bansil and Mansoor Bin Abdul Jalil and Gengchiau Liang},
doi = {10.1103/PhysRevB.89.245419},
times_cited = {13},
issn = {2469-9950},
year = {2014},
date = {2014-06-13},
journal = {PHYSICAL REVIEW B},
volume = {89},
number = {24},
publisher = {AMER PHYSICAL SOC},
address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},
abstract = {We present a model for quantum transport in a Bi2Se3 slab, which is based on using a nonequilibrium Green's function approach in which bulk and surface states are modeled realistically, and the effects of phonon scatterings are included. Resistivity is computed for different temperatures and strengths of the electron-phonon coupling at various doping levels. Temperature dependence of resistivity is found to display an insulating trend when the slab is biased at the Dirac point even in the presence of strong electron-phonon coupling. In sharp contrast, for carrier doping, the material displays a metallic behavior induced by acoustic scattering effects, even though purely ballistic transport yields an insulating trend, explaining contradictory trends reported in transport experiments on Bi2Se3. Our analysis, furthermore, suggests an experimental strategy for obtaining a handle on the strength of electron-phonon coupling in topological insulators via temperature-dependent transport measurements.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{ISI:000330839700055,
title = {Y-shape spin-separator for two-dimensional group-IV nanoribbons based on quantum spin hall effect},
author = {Gaurav Gupta and Hsin Lin and Arun Bansil and Mansoor Bin Abdul Jalil and Cheng-Yi Huang and Wei-Feng Tsai and Gengchiau Liang},
doi = {10.1063/1.4863088},
times_cited = {15},
issn = {0003-6951},
year = {2014},
date = {2014-01-20},
journal = {APPLIED PHYSICS LETTERS},
volume = {104},
number = {3},
publisher = {AMER INST PHYSICS},
address = {1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA},
abstract = {An efficient spin-separator that operates in quantum spin hall phase has been investigated for two-dimensional group-IV materials. A three-terminal Y-shaped device has been simulated via nonequilibrium Green Function to demonstrate the separation of unpolarized current at source terminal into spin-polarized current of opposite polarity at the two drain terminals. Device controls, i.e., tunable buckling and perpendicular magnetic field have been modeled comprehensively to evaluate the device feasibility and performance. It is shown that these controls can preferentially steer current between the two drains to create a differential charge current with complementary spin polarization, thus enabling a convenient regulation of output signal. (C) 2014 AIP Publishing LLC.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{ISI:000336781500069,
title = {Theoretical study of thermoelectric properties of few-layer MoS_{2} and WSe_{2}},
author = {Wen Huang and Xin Luo and Chee Kwan Gan and Su Ying Quek and Gengchiau Liang},
doi = {10.1039/c4cp00487f},
times_cited = {189},
issn = {1463-9076},
year = {2014},
date = {2014-01-01},
journal = {PHYSICAL CHEMISTRY CHEMICAL PHYSICS},
volume = {16},
number = {22},
pages = {10866-10874},
publisher = {ROYAL SOC CHEMISTRY},
address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND},
abstract = {Molybdenum disulfide (MoS2) and tungsten diselenide (WSe2) are prototypical layered two-dimensional transition metal dichalcogenide materials, with each layer consisting of three atomic planes. We refer to each layer as a trilayer (TL). We study the thermoelectric properties of 1-4TL MoS2 and WSe2 using a ballistic transport approach based on the electronic band structures and phonon dispersions obtained from first-principles calculations. Our results show that the thickness dependence of the thermoelectric properties is different under n-type and p-type doping conditions. Defining ZT(1st peak) as the first peak in the thermoelectric figure of merit ZT as doping levels increase from zero at 300 K, we found that ZT(1st peak) decreases as the number of layers increases for MoS2, with the exception of 2TL in n-type doping, which has a slightly higher value than 1TL. However, for WSe2, 2TL has the largest ZT(1st peak) in both n-type and p-type doping, with a ZT(1st peak) value larger than 1 for n-type WSe2. At high temperatures (T 4 300 K), ZT(1st peak) dramatically increases when the temperature increases, especially for n-type doping. The ZT(1st peak) of n-type 1TL-MoS2 and 2TL-WSe2 can reach 1.6 and 2.1, respectively.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}