arXiv subjects

Josep Ingla-Aynés

Publications and source records attributed to Josep Ingla-Aynés.

23 records · Page 2Linked to original sources

arXiv2018

Efficient spin injection into graphene through trilayer hBN tunnel barriers

We characterize the spin injection into bilayer graphene fully encapsulated in hBN using trilayer (3L) hexagonal boron nitride (hBN) tunnel barriers. As a function of the DC bias, the differential spin injection polarization is found to rise up to -60% at -250 mV DC bias voltage. We measure a DC spin polarization of $\sim$ 50%, a 30% increase compared to 2L-hBN. The large polarization is confirmed by local, two terminal spin transport measurements up to room temperature. We observe comparable differential spin injection efficiencies from Co/2L-hBN and Co/3L-hBN into graphene and conclude that possible exchange interaction between cobalt and graphene is likely not the origin of the bias dependence. Furthermore, our results show that local gating, arising from the applied DC bias is not responsible for the DC bias dependence. Carrier density dependent measurements of the spin injection efficiency are discussed, where we find no significant modulation of the differential spin injection polarization. We also address the bias dependence of the injection of in-plane and out-of-plane spins and conclude that the spin injection polarization is isotropic and does not depend on the applied bias.

cond-mat.mes-hall↗

arXiv2018

Observation of spin-valley coupling induced large spin lifetime anisotropy in bilayer graphene

We report the first observation of a large spin lifetime anisotropy in bilayer graphene (BLG) fully encapsulated between hexagonal boron nitride. We characterize the out-of-plane ($τ_\perp$) and in-plane ($τ_\parallel$) spin lifetimes by oblique Hanle spin precession. At 75~K and the charge neutrality point (CNP) we observe a strong anisotropy of $τ_\perp/τ_\parallel$ = 8 $\pm$ 2. This value is comparable to graphene/TMD heterostructures, whereas our high quality BLG provides with $τ_\perp$ up to 9~ns, a more than two orders of magnitude larger spin lifetime. The anisotropy decreases to 3.5 $\pm$ 1 at a carrier density of n = $6\times 10^{11}~$cm$^{-2}$. Temperature dependent measurements show above 75~K a decrease of $τ_\perp/τ_\parallel$ with increasing temperature, reaching the isotropic case close to room temperature. We explain our findings with electric field induced spin-valley coupling arising from the small intrinsic spin orbit fields in BLG of 12~$μ$eV at the CNP.

cond-mat.mes-hall↗

arXiv2017

Large Proximity-Induced Spin Lifetime Anisotropy in Transition Metal Dichalcogenide/Graphene Heterostructures

Van-der-Waals heterostructures have become a paradigm for designing new materials and devices, in which specific functionalities can be tailored by combining the properties of the individual 2D layers. A single layer of transition metal dichalcogenide (TMD) is an excellent complement to graphene (Gr), since the high quality of charge and spin transport in Gr is enriched with the large spin-orbit coupling of the TMD via proximity effect. The controllable spin-valley coupling makes these heterostructures particularly attractive for spintronic and opto-valleytronic applications. In this work, we study spin precession in a monolayer MoSe2/Gr heterostructure and observe an unconventional, dramatic modulation of the spin signal, showing one order of magnitude longer lifetime of out-of-plane spins (40 ps) compared with that of in-plane spins (3.5 ps). This demonstration of a large spin lifetime anisotropy in TMD/Gr heterostructures, is a direct evidence of induced spin-valley coupling in Gr and provides an accessible route for manipulation of spin dynamics in Gr, interfaced with TMDs.

cond-mat.mes-hall↗

arXiv2016

98% directional guiding of spin currents with 90 micrometer relaxation length in bilayer graphene using carrier drift

Electrical control of spin signals and long distance spin transport are major requirements in the field of spin electronics. Here we report the efficient guiding of spin currents at room temperature in high mobility hexagonal boron nitride encapsulated bilayer graphene using carrier drift. Our experiments, together with modelling, show that the spin relaxation length can be tuned from 2 to 88 micrometers when applying a DC current of $\mp$40 uA respectively. Our model predicts that, extending the range up to $\mathrm{I_{dc}}=\mp$150 uA, the spin relaxation length can be tuned from 0.6 to 320 um respectively, indicating that spin relaxation lengths in the millimeter range are within scope in near future with moderate current densities. Our results also show that we are able to direct spin currents on either side of a spin injection contact. 98% of the injected spins flow to the left when $\mathrm{I_{dc}}$= -40 uA and 65% flow to the right when the drift current is reversed. Our model shows that, for $\mathrm{I_{dc}}=\mp$150 uA the numbers reach 99.8% and 95% respectively showing the potential of carrier drift for spin-based logic operations and devices.

cond-mat.mes-hall↗

arXiv2015

24 \textmu m length spin relaxation length in boron nitride encapsulated bilayer graphene

We have performed spin and charge transport measurements in dual gated high mobility bilayer graphene encapsulated in hexagonal boron nitride. Our results show spin relaxation lengths $λ_s$ up to 13~\textmu m at room temperature with relaxation times $τ_s$ of 2.5~ns. At 4~K, the diffusion coefficient rises up to 0.52~m$^2$/s, a value 5 times higher than the best achieved for graphene spin valves up to date. As a consequence, $λ_s$ rises up to 24~\textmu m with $τ_s$ as high as 2.9~ns. We characterized 3 different samples and observed that the spin relaxation times increase with the device length. We explain our results using a model that accounts for the spin relaxation induced by the non-encapsulated outer regions.

cond-mat.mes-hall↗