Nanosecond Spin Lifetimes in Single- and Few-Layer Graphene–hBN Heterostructures at Room Temperature

Drögeler, Marc; Volmer, Frank; Wolter, Maik; Terrés, Bernat; Watanabe, Kenji; Taniguchi, Takashi; Güntherodt, G.; Stampfer, Christoph; Beschoten, Bernd

doi:10.1021/nl501278c

Cited by 166 publications

(226 citation statements)

References 39 publications

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“…Note that the obtained spin parameters for the encapsulated device should be considered lower bounds because they include the spin transport in the non-encapsulated contact regions. Our observation now allows us to speculate that the observed long spin lifetimes in the study by Drögeler et al 34 may be attributed mainly to the polymer-free fabrication of graphene spin valves rather than only the improvement in contacts. This is also consistent with the observation of a nearly threefold enhancement of an up to 2.7 ns spin-relaxation time in single-layer graphene upon plasma hydrogenation treatment, even when supported on SiO 2 , which may be partially attributed to the removal of such residues.…”

Section: Spin Transport In Bilayer Graphenesupporting

confidence: 55%

Electronic spin transport in dual-gated bilayer graphene

et al. 2016

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The elimination of extrinsic sources of spin relaxation is key to realizing the exceptional intrinsic spin transport performance of graphene. Toward this, we study charge and spin transport in bilayer graphene-based spin valve devices fabricated in a new device architecture that allows us to make a comparative study by separately investigating the roles of the substrate and polymer residues on spin relaxation. First, the comparison between spin valves fabricated on SiO 2 and BN substrates suggests that substrate-related charged impurities, phonons and roughness do not limit the spin transport in current devices. Next, the observation of a fivefold enhancement in the spin-relaxation time of the encapsulated device highlights the significance of polymer residues on spin relaxation. We observe a spin-relaxation length of~10 μm in the encapsulated bilayer, with a charge mobility of 24 000 cm 2 Vs − 1 . The carrier density dependence on the spin-relaxation time has two distinct regimes; no4 × 10 12 cm − 2 , where the spin-relaxation time decreases monotonically as the carrier concentration increases, and n ⩾ 4 × 10 12 cm − 2 , where the spin-relaxation time exhibits a sudden increase. The sudden increase in the spin-relaxation time with no corresponding signature in the charge transport suggests the presence of a magnetic resonance close to the charge neutrality point. We also demonstrate, for the first time, spin transport across bipolar p-n junctions in our dual-gated device architecture that fully integrates a sequence of encapsulated regions in its design. At low temperatures, strong suppression of the spin signal was observed while a transport gap was induced, which is interpreted as a novel manifestation of the impedance mismatch within the spin channel. INTRODUCTIONGraphene is considered to be a promising spin-channel material for future spintronics applications 1 because of its high-electronic mobility, 2 weak spin-orbit coupling 3,4 and a negligible hyperfine interaction. 5,6 The initial spin transport studies were mainly performed on single-layer 7-10 and bilayer exfoliated graphene, 9,11 and large-area graphene 12-15 deposited on conventional SiO 2 substrates. Although enhanced spin-relaxation times have been reported for bilayer graphene-based devices compared with those based on a single layer, the relatively low spin diffusion constants overall yield a lower spin-relaxation length of only 1-2 μm, 9,11 far below the theoretical predictions. 16 One approach suggested for achieving a longer distance spin communication is to increase the spin diffusion constants by fabricating higher mobility devices. 8,17 For charge transport, it has been shown that the carrier mobility of graphene devices on SiO 2 is mainly limited by interfacial charged impurities, surface roughness, and phonons. [18][19][20] The demonstration of an order-of-magnitude improvement in the mobility of graphene encapsulated between atomically flat, charge trap free boron nitride crystals 21,22 has triggered the recent spin transport studies...

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Section: Spin Transport In Bilayer Graphenesupporting

confidence: 55%

Electronic spin transport in dual-gated bilayer graphene

et al. 2016

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“…We observe phase-coherence lengths comparable with the sample size as well as phase-coherence times close to the values imposed by electron-electron interaction but limited by spin-flip scattering at low temperatures. Surprisingly, this spin-flip scattering time is more than an order of magnitude lower than observed in nonlocal spin-value measurements [44]. Moreover, we can unambiguously conclude that intra-valley scattering rather than inter-valley scattering is the limiting mechanism for electron transport in BLG, and we discuss strain fluctuations as the most probable source of mobility-limiting scattering processes.…”

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confidence: 40%

Limitations to Carrier Mobility and Phase-Coherent Transport in Bilayer Graphene

et al. 2014

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We present transport measurements on high-mobility bilayer graphene fully encapsulated in hexagonal boron nitride. We show two terminal quantum Hall effect measurements which exhibit full symmetry broken Landau levels at low magnetic fields. From weak localization measurements, we extract gate-tunable phase coherence times τ φ as well as the inter-and intra-valley scattering times τi and τ * . While τ φ is in qualitative agreement with an electron-electron interaction mediated dephasing mechanism, electron spin-flip scattering processes are limiting τ φ at low temperatures. The analysis of τi and τ * points to local strain fluctuation as the most probable mechanism for limiting the mobility in high-quality bilayer graphene.PACS numbers: 72.15.Rn, 73.43.Qt Bilayer graphene (BLG) is an interesting material system to explore phase-coherent mesoscopic transport with unique electronic properties [1]. In contrast to singlelayer graphene, in BLG a band gap can be opened by an external electric field [2,3] making local depletion of the two-dimensional electron gas (2DEG) possible similar to III/V heterostructures. This is an important prerequisite for implementing state-of-the-art phase-coherent quantum device concepts [4,5]. In contrast to conventional 2DEGs, the massive Dirac fermion nature of the quasiparticles in BLG results in an unconventional quantum Hall effect [6,7] and promises unique quantum interference properties [8]. So far, the observable transport phenomena in BLG devices suffer from the limited device quality which is most likely a consequence of the high sensitivity of BLG on the surrounding environment. Recent developments in device fabrication have shown that a significant improvement in sample quality can be obtained by replacing conventional SiO 2 with hexagonal boron nitride (hBN) [9]. This material provides an ultraflat substrate for graphene [9,10] and enables the realization of the high-mobility samples that are required to study, e.g. quantum phase transitions in the lowest quantum Hall state [11] or superlattice effects such as the Hofstadter butterfly [12][13][14]. However, despite these improvements, it remains difficult to experimentally address the microscopic mechanisms that limits carrier mobility and phase-coherence in high-quality BLG. To address these important questions, we present diffusive transport measurements on BLG fully encapsulated in hBN. Our fabrication technique allows to obtain highmobility samples, which show a well-developed quantum Hall effect and a full degeneracy breaking of the zero Landau level around B = 6 T. To investigate the limits of phase-coherent transport and to gain insights on the limitations to carrier mobility in these devices, we perform weak localization measurements [15]. From these measurements, we extract the inter-and intra-valley scattering times, as well as the phase-coherence time. Our results indicate (i) that the main sources of dephasing in high-quality BLG are the electron-electron interaction as well as electron spin-flip scattering, ...

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“…Carbon-based spintronic devices may have a distinct advantage over many other materials in that carbon has a very low spin-orbit coupling together with an absence of hyperfine interaction in the predominant 12 C isotope. This results in long spin lifetimes [2][3][4] , as well as large spin relaxation lengths, which have been found to be on the order of several microns at room temperature [2][3][4][5] and make graphene ideal for ballistic spin transport 6 . Pristine graphene is non-magnetic, but several suggestions on how to give graphene magnetic properties have been put forward.…”

Section: Introductionmentioning

confidence: 99%

Stability and magnetization of free-standing and graphene-embedded iron membranes

2015

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Inspired by recent experimental realizations of monolayer Fe membranes in graphene perforations, we perform ab initio calculations of Fe monolayers and membranes embedded in graphene in order to assess their structural stability and magnetization. We demonstrate that monolayer Fe has a larger spin magnetization per atom than bulk Fe and that Fe membranes embedded in graphene exhibit spin magnetization comparable to monolayer Fe. We find that free-standing monolayer Fe is structurally more stable in a triangular lattice compared to both square and honeycomb lattices. This is contradictory to the experimental observation that the embedded Fe membranes form a square lattice. However, we find that embedded Fe membranes in graphene perforations can be more stable in the square lattice configuration compared to the triangular. In addition, we find that the square lattice has a lower edge formation energy, which means that the square Fe lattice may be favored during formation of the membrane.

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Nanosecond Spin Lifetimes in Single- and Few-Layer Graphene–hBN Heterostructures at Room Temperature

Cited by 166 publications

References 39 publications

Electronic spin transport in dual-gated bilayer graphene

Electronic spin transport in dual-gated bilayer graphene

Limitations to Carrier Mobility and Phase-Coherent Transport in Bilayer Graphene

Stability and magnetization of free-standing and graphene-embedded iron membranes

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