arXiv subjects

Zhi-Gang Yu

Publications and source records attributed to Zhi-Gang Yu.

5 recordsLinked to original sources

arXiv2019

Ultrafast acoustic phonon scattering in CH$_3$NH$_3$PbI$_3$ revealed by femtosecond four-wave mixing

Carrier scattering processes are studied in CH$_3$NH$_3$PbI$_3$ using temperature-dependent four-wave mixing experiments. Our results indicate that scattering by ionized impurities limits the interband dephasing time (T$_2$) below 30~K, with strong electron-phonon scattering dominating at higher temperatures (with a timescale of 125 fs at 100 K). Our theoretical simulations provide quantitative agreement with the measured carrier scattering rate and show that the rate of acoustic phonon scattering is enhanced by strong spin-orbit coupling, which modifies the band-edge density of states. The Rashba coefficient extracted from fitting the experimental results ($γ_c=2$ eV angstrom) is in agreement with calculations of the surface Rashba effect and recent experiments using the photogalvanic effect on thin films.

cond-mat.mtrl-sci↗

arXiv2019

Controlling magnetoresistance by oxygen impurities in Mq3-based molecular spin valves

The understanding of magnetoresistance (MR) in organic spin valves (OSVs) based on molecular semiconductors is still incomplete after its demonstration more than a decade ago. While carrier concentration may play an essential role in spin transport in these devices, direct experimental evidence of its importance is lacking. We probed the role of charge carrier concentration by studying the interplay between MR and multilevel resistive switching in OSVs. The present work demonstrates that all salient features of these devices, particularly the intimate correlation between MR and resistance, can be accounted for by the impurity band model, based on oxygen migration. Finally, we highlight the critical importance of carrier concentration in determining spin transport and MR in OSVs and the role of interface-mediated oxygen migration in controlling the OSVs response.

physics.app-ph↗

arXiv2018

Detection of Rashba spin splitting in 2D organic-inorganic perovskite via precessional carrier spin relaxation

The strong spin-orbit interaction in the organic-inorganic perovskites tied to the incorporation of heavy elements (\textit{e.g.} Pb, I) makes these materials interesting for applications in spintronics. Due to a lack of inversion symmetry associated with distortions of the metal-halide octahedra, the Rashba effect (used \textit{e.g.} in spin field-effect transistors and spin filters) has been predicted to be much larger in these materials than in traditional III-V semiconductors such as GaAs, supported by the recent observation of a near record Rashba spin splitting in CH$_3$NH$_3$PbBr$_3$ using angle-resolved photoemission spectroscopy (ARPES). More experimental studies are needed to confirm and quantify the presence of Rashba effects in the organic-inorganic perovskite family of materials. Here we apply time-resolved circular dichroism techniques to the study of carrier spin dynamics in a 2D perovskite thin film [(BA)$_2$MAPb$_2$I$_7$; BA = CH$_3$(CH$_2$)$_3$NH$_3$, MA = CH$_3$NH$_3$]. Our findings confirm the presence of a Rashba spin splitting via the dominance of precessional spin relaxation induced by the Rashba effective magnetic field. The size of the Rashba spin splitting in our system was extracted from simulations of the measured spin dynamics incorporating LO-phonon and electron-electron scattering, yielding a value of 10 meV at an electron energy of 50 meV above the band gap, representing a 20 times larger value than in GaAs quantum wells.

cond-mat.mtrl-sci↗

arXiv2004

Spin Gunn Effect

We predict that the flow of unpolarized current in electron-doped GaAs and InP at room temperature is unstable at high electric fields to the dynamic formation of spin-polarized current pulses. Spin-polarized current is spontaneously generated because the conductivity of a spin-polarized electron gas differs from that of an unpolarized electron gas, even in the absence of spin-orbit interaction. Magnetic fields are not required for the generation of these spin-polarized current pulses, although they can help align the polarization of sequential pulses along the same axis.

cond-mat.mes-hall↗

arXiv1998

Signatures of Stripe Phases in Hole Doped $La_2NiO_4$

We study nickelate-centered and oxygen-centered stripe phases in doped La$_{2}$NiO$_{4}$ materials. We use an inhomogeneous Hartree-Fock and random-phase approximation approach including both electron-electron and electron-lattice(e-l) coupling for a layer of La$_{2}$NiO$_{4}$. We find that whether the ground state after commensurate hole doping comprises Ni-centered or O-centered charge-localized stripes depends sensitively on the e-l interaction. With increasing e-l interaction strength, a continuous transition from an O-centered stripe phase to a Ni-centered one is found. Various low- and high-energy signatures of these two kinds of stripe phases are predicted, which can clearly distinguish them. These signatures reflect the strongly correlated spin-charge-lattice features in the vicinity of Ni-centered or O-centered stripe domains. The importance of e-l interaction for recent experiments on stripe phases is discussed.

cond-mat.supr-con↗