Stephan Roche

@article{ISI:000655306100001,
title = {Room-temperature tunnel magnetoresistance across biomolecular tunnel junctions based on ferritin},
author = {Senthil Kumar Karuppannan and Rupali Reddy Pasula and Tun Seng Herng and Jun Ding and Xiao Chi and Enrique del Barco and Stephan Roche and Xiaojiang Yu and Nikolai Yakovlev and Sierin Lim and Christian A Nijhuis},
doi = {10.1088/2515-7639/abfa79},
times_cited = {4},
year = {2021},
date = {2021-07-01},
journal = {JOURNAL OF PHYSICS-MATERIALS},
volume = {4},
number = {3},
publisher = {IOP Publishing Ltd},
address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND},
abstract = {We report exceptionally large tunnel magnetoresistance (TMR) for biomolecular tunnel junctions based on ferritins immobilized between Ni and EGaIn electrodes. Ferritin stores iron in the form of ferrihydrite nanoparticles (NPs) and fulfills the following roles: (a) it dictates the tunnel barrier, (b) it magnetically decouples the NPs from the ferromagnetic (FM) electrode, (c) it stabilizes the NPs, and (d) it acts as a spin filter reducing the complexity of the tunnel junctions since only one FM electrode is required. The mechanism of charge transport is long-range tunneling which results in TMR of 60 +/- 10% at 200 K and 25 +/- 5% at room temperature. We propose a magnon-assisted transmission to explain the substantially larger TMR switching fields (up to 1 Tesla) than the characteristic coercive fields (a few Gauss) of ferritin ferrihydrite particles at T < 20 K. These results highlight the genuine potential of biomolecular tunnel junctions in designing functional nanoscale spintronic devices.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{ISI:000600286000017,
title = {Canted Persistent Spin Texture and Quantum Spin Hall Effect in WTe_2},
author = {Jose H Garcia and Marc Vila and Chuang-Han Hsu and Xavier Waintal and Vitor M Pereira and Stephan Roche},
doi = {10.1103/PhysRevLett.125.256603},
times_cited = {47},
issn = {0031-9007},
year = {2020},
date = {2020-12-18},
journal = {PHYSICAL REVIEW LETTERS},
volume = {125},
number = {25},
publisher = {AMER PHYSICAL SOC},
address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},
abstract = {We report an unconventional quantum spin Hall phase in the monolayer WTe2, which exhibits hitherto unknown features in other topological materials. The low symmetry of the structure induces a canted spin texture in the yz plane, which dictates the spin polarization of topologically protected boundary states. Additionally, the spin Hall conductivity gets quantized (2e(2)/h) with a spin quantization axis parallel to the canting direction. These findings are based on large-scale quantum simulations of the spin Hall conductivity tensor and nonlocal resistances in multiprobe geometries using a realistic tight-binding model elaborated from first-principle methods. The observation of this canted quantum spin Hall effect, related to the formation of topological edge states with nontrivial spin polarization, demands for specific experimental design and suggests interesting alternatives for manipulating spin information in topological materials.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{ISI:000379651600002,
title = {Spin dynamics in bilayer graphene: Role of electron-hole puddles and Dyakonov-Perel mechanism},
author = {Dinh Van Tuan and Shaffique Adam and Stephan Roche},
doi = {10.1103/PhysRevB.94.041405},
times_cited = {2},
issn = {2469-9950},
year = {2016},
date = {2016-07-15},
journal = {PHYSICAL REVIEW B},
volume = {94},
number = {4},
publisher = {AMER PHYSICAL SOC},
address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},
abstract = {We report on spin transport features which are unique to high quality bilayer graphene, in the absence of magnetic contaminants and strong intervalley mixing. The time-dependent spin polarization of a propagating wave packet is computed using an efficient quantum transport method. In the limit of vanishing effects of substrate and disorder, the energy dependence of the spin lifetime is similar to monolayer graphene with an M-shaped profile and minimum value at the charge neutrality point, but with an electron-hole asymmetry fingerprint. In sharp contrast, the incorporation of substrate-induced electron-hole puddles (characteristics of supported graphene either on SiO2 or hBN) surprisingly results in a large enhancement of the low-energy spin lifetime and a lowering of its high-energy values. Such a feature, unique to the bilayer, is explained in terms of a reinforced Dyakonov-Perel mechanism at the Dirac point, whereas spin relaxation at higher energies is driven by pure dephasing effects. This suggests further electrostatic control of the spin transport length scales in graphene devices.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{ISI:000302957000011,
title = {Quenching of the Quantum Hall Effect in Graphene with Scrolled Edges},
author = {Alessandro Cresti and Michael M Fogler and Francisco Guinea and Castro A H Neto and Stephan Roche},
doi = {10.1103/PhysRevLett.108.166602},
times_cited = {17},
issn = {0031-9007},
year = {2012},
date = {2012-04-18},
journal = {PHYSICAL REVIEW LETTERS},
volume = {108},
number = {16},
publisher = {AMER PHYSICAL SOC},
address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},
abstract = {Edge nanoscrolls are shown to strongly influence transport properties of suspended graphene in the quantum Hall regime. The relatively long arclength of the scrolls in combination with their compact transverse size results in formation of many nonchiral transport channels in the scrolls. They short circuit the bulk current paths and inhibit the observation of the quantized two-terminal resistance. Unlike competing theoretical proposals, this mechanism of disrupting the Hall quantization in suspended graphene is not caused by ill-chosen placement of the contacts, singular elastic strains, or a small sample size.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}