The spin Hall angle (SHA) is a measure of the efficiency with which a transverse spin current is generated from a charge current by the spin-orbit coupling and disorder in the spin Hall effect (SHE). In a study of the SHE for a Pt|Py (Py=Ni_{80}Fe_{20}) bilayer using a first-principles scattering approach, we find a SHA that increases monotonically with temperature and is proportional to the resistivity for bulk Pt. By decomposing the room temperature SHE and inverse SHE currents into bulk and interface terms, we discover a giant interface SHA that dominates the total inverse SHE current with potentially major consequences for applications.

Extremely large non-saturating magnetoresistance has recently been reported for a large number of both topologically trivial and non-trivial materials. Different mechanisms have been proposed to explain the observed magnetotransport properties, yet without arriving to definitive conclusions or portraying a global picture. In this work, we investigate the transverse magnetoresistance of materials by combining the Fermi surfaces calculated from first principles with the Boltzmann transport theory approach relying on the semiclassical model and the relaxation time approximation. We first consider a series of simple model Fermi surfaces to provide a didactic introduction into the chargecarrier compensation and open-orbit mechanisms leading to non-saturating magnetoresistance. We then address in detail magnetotransport in three representative materials: (i) copper, a prototypical nearly free-electron metal characterized by the open Fermi surface that results in an intricate angular magnetoresistance, (ii) bismuth, a topologically trivial semimetal in which very large magnetoresistance is known to result from charge-carrier compensation, and (iii) tungsten diphosphide WP2, a recently discovered type-II Weyl semimetal that holds the record of magnetoresistance in compounds. In all three cases our calculations show excellent agreement with both the field dependence of magnetoresistance and its anisotropy measured at low temperatures. Furthermore, the calculations allow for a full interpretation of the observed features in terms of the Fermi surface topology. Our study thus establishes guidelines to clarifying the physical mechanisms underlying the magnetoransport properties in a broad range of materials. These results will help addressing a number of outstanding questions, such as the role of the topological phase in the pronounced large non-saturating magnetoresistance observed in topological materials. arXiv:1808.08178v1 [cond-mat.mtrl-sci]

We combine the theoretical method of calculating spin wave excitation with the finite-temperature modeling and calculate the magnon-phonon relaxation time in the technologically important material Yttrium iron garnet (YIG) from first principles. The finite lifetime of magnon excitation is found to arise from the fluctuation of the exchange interaction of magnetic atoms in YIG. At room temperature, the magnon spectra have significant broadening that is used to extract the magnonphonon relaxation time quantitatively. The latter is a phenomenological parameter of great importance in YIG-based spintronics research. We find that the magnon-phonon relaxation time for the optical magnon is a constant while that for the acoustic magnon is proportional to 1/k 2 in the long-wavelength regime.Yttrium iron garnet (Y 3 Fe 5 O 12 , YIG), a ferrimagnetic insulator, has been extensively applied in the spintronics experiments, such as the investigations of the spin Seebeck effect, 1 spin Hall magnetoresistance 2 and cavity magnon polariton.3 In particular, YIG is an ideal magnetic material for transport study of a pure spin current because electronic transport can be completely eliminated. For example, a spin wave is allowed to propagate in YIG over a long distance 4,5 due to its ultralow Gilbert damping 6 of YIG. Unlike the ferromagnetic metals, where the Gilbert damping is dominated by the conduction electrons near the Fermi level, 7,8 spin-lattice interaction is the main mechanism of dissipating angular momentum and magnetic energy during the magnetization dynamics of YIG. Fundamental research on the spin-lattice interaction can be traced back to the early works in 1950s, when Abrahams and Kittel developed a phenomenological theory of the magnetoelastic effects in magnetic metals.9-11 They introduced a phenomenological relaxation time to characterized the spin-lattice interaction. Later Sanders and Walton performed an experimental measurement investigating the magnon-phonon relaxation time τ mp in magnetic insulators.12 Recently, τ mp is found to be crucially important to describe many YIG-based spin transport phenomena.13-15 Nevertheless, a quantitative estimation of the phenomenological relaxation time in a complex magnetic material like YIG is essentially nontrivial; τ mp can be expressed in terms of the magnetoelastic coupling constants, which are, however, still short of reliable evaluation experimentally or theoretically.The present work aims at a quantitative evaluation of the magnon-phonon relaxation time in YIG using a physically transparent and numerically reliable method. More specifically, we combine the first-principles method of calculating magnon spectrum 16 and a finite-temperature modeling by displacing atoms from their equilibrium positions, 17,18 so as to obtain the fluctuation of the exchange interaction induced by lattice vibration. Such a computational scheme allows us to determine the magnon excitation mediated by phonons without imposing any phenomenological parameters. As a consequence, the fluctuatio...

We use inelastic neutron scattering to study acoustic phonons and spin excitations in single crystals of NaFeAs, a parent compound of iron-pnictide superconductors. NaFeAs exhibits a tetragonalto-orthorhombic structural transition at T s ≈ 58 K and a collinear antiferromagnetic order at T N ≈ 45 K. While longitudinal and out-of-plane transverse acoustic phonons behave as expected, the in-plane transverse acoustic phonons reveal considerable softening on cooling to T s and then harden on approaching T N before saturating below T N . In addition, we find that spin-spin correlation lengths of low-energy magnetic excitations within the FeAs layer and along the c axis increase dramatically below T s and show a weak anomaly across T N . These results suggest that the electronic nematic phase present in the paramagnetic tetragonal phase is closely associated with dynamic spin-lattice coupling, possibly arising from the one-phonon-two-magnon mechanism.

PafA, the prokaryotic ubiquitin-like protein (Pup) ligase, catalyzes the Pup modification of bacterial proteins and targets the substrates for proteasomal degradation. It has been reported that that M. smegmatis PafA can be poly-pupylated. In this study, the mechanism of PafA self-pupylation is explored. We found that K320 is the major target residue for the pupylation of PafA. During the self-pupylation of PafA, the attachment of the first Pup to PafA is catalyzed by the other PafA molecule through an intermolecular reaction, while the formation of the polymeric Pup chain is carried out in an intramolecular manner through the internal ligase activity of the already pupylated PafA. Among the three lysine residues, K7, K31 and K61, in M. smegmatis Pup, K7 and K31 are involved in the formation of the poly-Pup chain in PafA poly-pupylation. Poly-pupylation of PafA can be reversibly regulated by depupylase Dop. The polymeric Pup chain formed through K7/K31 linkage is much more sensitive to Dop than the mono-Pup directly attached to PafA. Moreover, self-pupylation of PafA is involved in the regulation of its stability in vivo in a proteasome-dependent manner, suggesting that PafA self-pupylation functions as a mechanism in the auto-regulation of the Pup-proteasome system.

Visual word recognition, at a minimum, involves the processing of word form and lexical information. Opinions diverge on the spatiotemporal distribution of and interaction between the two types of information. Feedforward theory argues that they are processed sequentially, whereas interactive theory advocates that lexical information is processed fast and modulates early word form processing. To distinguish between the two theories, we applied stereoelectroencephalography (SEEG) to 33 human adults with epilepsy (25 males and eight females) during visual lexical decisions. The stimuli included real words (RWs), pseudowords (PWs) with legal radical positions, nonwords (NWs) with illegal radical positions, and stroked-changed words (SWs) in Chinese. Word form and lexical processing were measured by the word form effect (PW versus NW) and lexical effect (RW versus PW), respectively. Gamma-band (60 ; 140 Hz) SEEG activity was treated as an electrophysiological measure. A word form effect was found in eight left brain regions (i.e., the inferior parietal lobe, insula, fusiform, inferior temporal, middle temporal, middle occipital, precentral and postcentral gyri) from 50 ms poststimulus onset, whereas a lexical effect was observed in five left brain regions (i.e., the calcarine, middle temporal, superior temporal, precentral, and postcentral gyri) from 100 ms poststimulus onset. The two effects overlapped in the precentral (300 ; 500 ms) and postcentral (100 ; 200 ms and 250 ; 600 ms) gyri. Moreover, high-level regions provide early feedback to word form regions. These results demonstrate that lexical processing occurs early and modulates word form recognition, providing vital supportive evidence for interactive theory.

The phenylalanine ammonia-lyase (AvPAL) from Anabaena variabilis catalyzes the amination of substituent trans-cinnamic acid (t-CA) to produce racemic D,L-enantiomer arylalanine mixture owing to its low stereoselectivity. To produce high optically pure D-arylalanine, a modified AvPAL with high D-selectivity is expected. Based on the analyses of catalytic mechanism and structure, the Asn347 residue in the active site was proposed to control stereoselectivity. Therefore, Asn347 was mutated to construct mutant AvPAL-N347A, the stereoselectivity of AvPAL-N347A for D-enantiomer arylalanine was 2.3-fold higher than that of wild-type AvPAL (WtPAL). Furthermore, the residual L-enantiomer product in reaction solution could be converted into the D-enantiomer product through stereoselective oxidation by PmLAAD and nonselective reduction by reducing agent NHBH. At optimal conditions, the conversion rate of t-CA and optical purity (enantiomeric excess (ee)) of D-phenylalanine reached 82% and exceeded 99%, respectively. The two enzymes displayed activity toward a broad range of substrate and could be used to efficiently synthesize D-arylalanine with different groups on the phenyl ring. Among these D-arylalanines, the yield of m-nitro-D-phenylalanine was highest and reached 96%, and the ee exceeded 99%. This one-pot synthesis using AvPAL and PmLAAD has prospects for industrial application.

In the conventional paradigm of the spin Hall effect, the side-jump conductivity due to electronphonon scattering is regarded to be temperature independent. To the contrary, we draw the distinction that, while this side-jump conductivity is temperature independent in the classical equipartition regime where the longitudinal resistivity is linear in temperature, it is temperature dependent below the equipartition regime. The mechanism resulting in this temperature dependence differs from the familiar one of the longitudinal resistivity. In the concrete example of Pt, we show that the change of the spin Hall conductivity with temperature can be as high as 50%. Experimentally accessible high-purity Pt is proposed to be suitable for observing this prominent variation below 80 K.