Electron spin relaxation in bilayer graphene

Abstract

Electron spin relaxation due to the D'yakonov-Perel' mechanism is investigated in bilayer graphene with only the lowest conduction band being relevant. The spin-orbit coupling is constructed from the symmetry group analysis with the parameters obtained by fitting to the numerical calculation according to the latest report by Konschuh et al. [Phys. Rev. B 85, 115423 (2012)] from first principles. In contrast to single-layer graphene, the leading term of the out-of-plane component of the spin-orbit coupling in bilayer graphene shows a Zeeman-like term with opposite effective magnetic fields in the two valleys. This Zeeman-like term opens a spin relaxation channel in the presence of intervalley scattering. It is shown that the intervalley electron-phonon scattering, which has not been reported in the previous literature, strongly suppresses the in-plane spin relaxation time at high temperature whereas the intervalley short-range scattering plays an important role in the in-plane spin relaxation especially at low temperature. A marked nonmonotonic dependence of the in-plane spin relaxation time on temperature with a minimum of several hundred picoseconds is predicted in the absence of the short-range scatterers. This minimum is comparable to the experimental data. Moreover, a peak in the electron density dependence of the in-plane spin relaxation time at low temperature, which is very different from the one in semiconductors, is predicted. We also find a rapid decrease in the in-plane spin relaxation time with increasing initial spin polarization at low temperature, which is opposite to the situation in both semiconductors and single-layer graphene. A strong anisotropy between the out-of-and in-plane spin relaxations at high temperature is also revealed with the out-of-plane spin relaxation time being about two orders of magnitude larger than the in-plane one. Detailed comparisons of the temperature and electron density dependences of the spin relaxation with the existing experiments [Phys. Rev. Lett. 107, 047206 (2011), Phys. Rev. Lett. 107, 047207 (2011) and Nano Lett. 11, 2363] are reported.

Structures of quasi-freestanding ultra-thin silicon films deposited on chemically inert surfaces

“…Actually it was reported that band structure of silicene deposited on Ag(111) drastically modified by the hybridization between the silicon and silver atoms, and the silicene loses its Dirac fermion characteristics due to substrate-induced symmetry breaking [37]. The effect of the hybridization between silicene and metals was supported by the theoretical calculations [38,39].…”

Resonant Scattering by Magnetic Impurities as a Model for Spin Relaxation in Bilayer Graphene

“…Unfortunately, spin relaxation in graphene structures has been a baffling problem [3]. While experiments in both single layer graphene (SLG) [4][5][6][7][8][9][10][11] and bilayer graphene (BLG) [7,8] yield spin lifetimes on the 100-1000 ps time scale (the highest values achieved in graphene/h-BN structures [12,13]), theories based on realistic spin-orbit coupling and transport parameters predict lifetimes on the order of microseconds [14][15][16][17][18][19][20][21][22][23][24].While the magnitudes of the spin-relaxation rates of SLG and BLG are similar, the dependence of the rates on the electron density is opposite in the two systems. In SLG the spin-relaxation rate decreases with increasing the carrier density [5][6][7][8], in BLG the spin-relaxation rate increases [7,8].…”

A statistical correlation investigation for the role of surface spins to the spin relaxation of nitrogen vacancy centers

“…Contribution from spins inside diamond have been studied intensely and understood clearly. 21,33 In the following, we simply assumed that the contribution from spins inside is the same as that in bulk diamond with the same density of N as in the NDs used in this work and designated the corresponding transverse relaxation time of the NV center in bulk diamonds as T 2, bulk , According to the Redfield theory, 28,29 and taking into account of the influence of all the surface spins, in the limit of very short correlation time τ c T 2 , the transverse spin relaxation time T 2 of the NV center in NDs can be expressed as…”

“…As reported previously, the transverse relaxation time is sensitive to the distribution or configuration of the P1 centers and 13 C nuclear spins. 33,34 To reach a more precise simulation results, the third term in Eq. (4) need be modified.…”

“…It has been reported that the variation in the distribution configuration of the surrounding spins played an important role on the spin relaxation of NV center. 33 Taking into account of this factors we recalculated the range of (T 1 , T 2 ) by setting T 2, bulk = 0.3 ∼ 3μs. With thus expanded range of the T 2, bulk value, the calculated (T 1 , T 2 ) range was shown by the orange area in Fig.…”