Regulation of Anabaena sp. strain PCC 7120 glutamine synthetase activity in a Synechocystis sp. strain PCC 6803 derivative strain bearing the Anabaena glnA gene and a mutated host glnA gene.

PubMed Central

Mérida, A; Flores, E; Florencio, F J

1992-01-01

The glnA gene from Synechocystis sp. strain PCC 6803 was cloned by hybridization with the glnA gene from Anabaena sp. strain PCC 7120, and a deletion-insertion mutation of the Synechocystis gene was generated in vitro. A strain derived from Synechocystis sp. strain PCC 6803 which contained integrated into the chromosome, in addition to its own glnA gene, the Anabaena glnA gene was constructed. From that strain, a Synechocystis sp. glnA mutant could be obtained by transformation with the inactivated Synechocystis glnA gene; this mutant grew by using Anabaena glutamine synthetase and was not a glutamine auxotroph. A Synechocystis sp. glnA mutant could not be obtained, however, from the wild-type Synechocystis sp. The Anabaena glutamine synthetase enzyme was subject to ammonium-promoted inactivation when expressed in the Synechocystis strain but not in the Anabaena strain itself. Images PMID:1345914

Direct Involvement of the Master Nitrogen Metabolism Regulator GlnR in Antibiotic Biosynthesis in Streptomyces.

PubMed

He, Juan-Mei; Zhu, Hong; Zheng, Guo-Song; Liu, Pan-Pan; Wang, Jin; Zhao, Guo-Ping; Zhu, Guo-Qiang; Jiang, Wei-Hong; Lu, Yin-Hua

2016-12-16

GlnR, an OmpR-like orphan two-component system response regulator, is a master regulator of nitrogen metabolism in the genus Streptomyces In this work, evidence that GlnR is also directly involved in the regulation of antibiotic biosynthesis is provided. In the model strain Streptomyces coelicolor M145, an in-frame deletion of glnR resulted in markedly increased actinorhodin (ACT) production but reduced undecylprodigiosin (RED) biosynthesis when exposed to R2YE culture medium. Transcriptional analysis coupled with DNA binding studies revealed that GlnR represses ACT but activates RED production directly via the pathway-specific activator genes actII-ORF4 and redZ, respectively. The precise GlnR-binding sites upstream of these two target genes were defined. In addition, the direct involvement of GlnR in antibiotic biosynthesis was further identified in Streptomyces avermitilis, which produces the important anthelmintic agent avermectin. We found that S. avermitilis GlnR (GlnRsav) could stimulate avermectin but repress oligomycin production directly through the respective pathway-specific activator genes, aveR and olmRI/RII To the best of our knowledge, this report describes the first experimental evidence demonstrating that GlnR regulates antibiotic biosynthesis directly through pathway-specific regulators in Streptomyces Our results suggest that GlnR-mediated regulation of antibiotic biosynthesis is likely to be universal in streptomycetes. These findings also indicate that GlnR is not only a master nitrogen regulator but also an important controller of secondary metabolism, which may help to balance nitrogen metabolism and antibiotic biosynthesis in streptomycetes. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

Synthetic approaches to peptides containing the L-Gln-L-Val-D(S)-Dmt motif.

PubMed

Suaifan, Ghadeer A R Y; Arafat, Tawfiq; Threadgill, Michael D

2007-05-15

The pseudoprolines S-Dmo (5,5-dimethyl-4-oxaproline) and R-Dmt (5,5-dimethyl-4-thiaproline) have been used to study the effects of forcing a fully cis conformation in peptides. Synthesis of peptides containing these (which have the same configuration as L-Pro) is straightforward. However, synthesis of peptides containing S-Dmt is difficult, owing to the rapid cyclisation of L-Aaa-S-Dmt amides and esters to form the corresponding diketopiperazines (DKP); thus the intermediacy of L-Aaa-S-Dmt amides and esters must be avoided in the synthetic sequence. Peptides containing the L-Gln-L-Val-D(S)-Dmt motif are particularly difficult, owing to the insolubility of coupling partners containing Gln. Introduction of Gln as N-Boc-pyroglutamate overcame the latter difficulty and the dipeptide active ester BocPygValOC(6)F(5) coupled in good yield with S-DmtOH. BocPygVal-S- DmtNH(CH(2))(2)C(6)H(4)NO(2) was converted quantitatively to BocGlnVal-S-DmtNH(CH(2))(2)C(6)H(4)NO(2) with ammonia, demonstrating the utility of this approach. Two peptide derivatives (CbzSerLysLeuGlnVal-S-DmtNH(CH(2))(2)C(6)H(4)NO(2) and CbzSerSerLysLeuGlnVal-S- DmtNH(CH(2))(2)C(6)H(4)NO(2)) were assembled, using these new methods of coupling a dipeptide acid active ester with S-DmtOH and introduction of Gln as Pyg, followed by conventional peptide couplings. The presence of the Val caused these peptides to be cleaved very slowly by prostate-specific antigen (PSA) at Leu Gln, rather than the expected Gln Val.

Neurovascular control during exercise in acute coronary syndrome patients with Gln27Glu polymorphism of β2-adrenergic receptor

PubMed Central

Ferreira-Santos, Larissa; Martinez, Daniel G.; Nicolau, José Carlos; Moreira, Humberto G.; Alves, Maria Janieire; Pereira, Alexandre C.; Trombetta, Ivani C.; Negrão, Carlos Eduardo

2017-01-01

Background Gln27Glu (rs1042714) polymorphism of the β2-adrenergic receptor (ADRB2) has been association with cardiovascular functionality in healthy subjects. However, it is unknown whether the presence of the ADRB2 Gln27Glu polymorphism influences neurovascular responses during exercise in patients with acute coronary syndromes (ACS). We tested the hypothesis that patients with ACS homozygous for the Gln allele would have increased muscle sympathetic nerve activity (MSNA) responses and decreased forearm vascular conductance (FVC) responses during exercise compared with patients carrying the Glu allele (Gln27Glu and Glu27Glu). In addition, exercise training would restore these responses in Gln27Gln patients. Methods and results Thirty-days after an ischemic event, 61 patients with ACS without ventricular dysfunction were divided into 2 groups: (1) Gln27Gln (n = 35, 53±1years) and (2) Gln27Glu+Glu27Glu (n = 26, 52±2years). MSNA was directly measured using the microneurography technique, blood pressure (BP) was measured with an automatic oscillometric device, and blood flow was measured using venous occlusion plethysmography. MSNA, mean BP, and FVC were evaluated at rest and during a 3-min handgrip exercise. The MSNA (P = 0.02) and mean BP (P = 0.04) responses during exercise were higher in the Gln27Gln patients compared with that in the Gln27Glu+Glu27Glu patients. No differences were found in FVC. Two months of exercise training significantly decreased the MSNA levels at baseline (P = 0.001) and in their response during exercise (P = 0.02) in Gln27Gln patients, but caused no changes in Gln27Glu+Glu27Glu patients. Exercise training increased FVC responses in Gln27Glu+Glu27Glu patients (P = 0.03), but not in Gln27Gln patients. Conclusion The exaggerated MSNA and mean BP responses during exercise suggest an increased cardiovascular risk in patients with ACS and Gln27Gln polymorphism. Exercise training emerges as an important strategy for restoring this reflex

Neurovascular control during exercise in acute coronary syndrome patients with Gln27Glu polymorphism of β2-adrenergic receptor.

PubMed

Ferreira-Santos, Larissa; Martinez, Daniel G; Nicolau, José Carlos; Moreira, Humberto G; Alves, Maria Janieire; Pereira, Alexandre C; Trombetta, Ivani C; Negrão, Carlos Eduardo; Rondon, Maria Urbana P B

2017-01-01

Gln27Glu (rs1042714) polymorphism of the β2-adrenergic receptor (ADRB2) has been association with cardiovascular functionality in healthy subjects. However, it is unknown whether the presence of the ADRB2 Gln27Glu polymorphism influences neurovascular responses during exercise in patients with acute coronary syndromes (ACS). We tested the hypothesis that patients with ACS homozygous for the Gln allele would have increased muscle sympathetic nerve activity (MSNA) responses and decreased forearm vascular conductance (FVC) responses during exercise compared with patients carrying the Glu allele (Gln27Glu and Glu27Glu). In addition, exercise training would restore these responses in Gln27Gln patients. Thirty-days after an ischemic event, 61 patients with ACS without ventricular dysfunction were divided into 2 groups: (1) Gln27Gln (n = 35, 53±1years) and (2) Gln27Glu+Glu27Glu (n = 26, 52±2years). MSNA was directly measured using the microneurography technique, blood pressure (BP) was measured with an automatic oscillometric device, and blood flow was measured using venous occlusion plethysmography. MSNA, mean BP, and FVC were evaluated at rest and during a 3-min handgrip exercise. The MSNA (P = 0.02) and mean BP (P = 0.04) responses during exercise were higher in the Gln27Gln patients compared with that in the Gln27Glu+Glu27Glu patients. No differences were found in FVC. Two months of exercise training significantly decreased the MSNA levels at baseline (P = 0.001) and in their response during exercise (P = 0.02) in Gln27Gln patients, but caused no changes in Gln27Glu+Glu27Glu patients. Exercise training increased FVC responses in Gln27Glu+Glu27Glu patients (P = 0.03), but not in Gln27Gln patients. The exaggerated MSNA and mean BP responses during exercise suggest an increased cardiovascular risk in patients with ACS and Gln27Gln polymorphism. Exercise training emerges as an important strategy for restoring this reflex control. Gln27Glu polymorphism of ADRB2

The complete nucleotide sequence of the glnALG operon of Escherichia coli K12.

PubMed Central

Miranda-Ríos, J; Sánchez-Pescador, R; Urdea, M; Covarrubias, A A

1987-01-01

The nucleotide sequence of the E. coli glnALG operon has been determined. The glnL (ntrB) and glnG (ntrC) genes present a high homology, at the nucleotide and aminoacid levels, with the corresponding genes of Klebsiella pneumoniae. The predicted aminoacid sequence for glutamine synthetase allowed us to locate some of the enzyme domains. The structure of this operon is discussed. PMID:2882477

Spin-adapted open-shell random phase approximation and time-dependent density functional theory. I. Theory.

PubMed

Li, Zhendong; Liu, Wenjian

2010-08-14

The spin-adaptation of single-reference quantum chemical methods for excited states of open-shell systems has been nontrivial. The primary reason is that the configuration space, generated by a truncated rank of excitations from only one component of a reference multiplet, is spin-incomplete. Those "missing" configurations are of higher ranks and can, in principle, be recaptured by a particular class of excitation operators. However, the resulting formalisms are then quite involved and there are situations [e.g., time-dependent density functional theory (TD-DFT) under the adiabatic approximation] that prevent one from doing so. To solve this issue, we propose here a tensor-coupling scheme that invokes all the components of a reference multiplet (i.e., a tensor reference) rather than increases the excitation ranks. A minimal spin-adapted n-tuply excited configuration space can readily be constructed by tensor products between the n-tuple tensor excitation operators and the chosen tensor reference. Further combined with the tensor equation-of-motion formalism, very compact expressions for excitation energies can be obtained. As a first application of this general idea, a spin-adapted open-shell random phase approximation is first developed. The so-called "translation rule" is then adopted to formulate a spin-adapted, restricted open-shell Kohn-Sham (ROKS)-based TD-DFT (ROKS-TD-DFT). Here, a particular symmetry structure has to be imposed on the exchange-correlation kernel. While the standard ROKS-TD-DFT can access only excited states due to singlet-coupled single excitations, i.e., only some of the singly excited states of the same spin (S(i)) as the reference, the new scheme can capture all the excited states of spin S(i)-1, S(i), or S(i)+1 due to both singlet- and triplet-coupled single excitations. The actual implementation and computation are very much like the (spin-contaminated) unrestricted Kohn-Sham-based TD-DFT. It is also shown that spin-contaminated spin

GlnR-mediated regulation of nitrogen metabolism in the actinomycete Saccharopolyspora erythraea.

PubMed

Yao, Li-Li; Liao, Cheng-Heng; Huang, Gang; Zhou, Ying; Rigali, Sebastien; Zhang, Buchang; Ye, Bang-Ce

2014-09-01

Nitrogen source sensing, uptake, and assimilation are central for growth and development of microorganisms which requires the participation of a global control of nitrogen metabolism-associated genes at the transcriptional level. In soil-dwelling antibiotic-producing actinomycetes, this role is played by GlnR, an OmpR family regulator. In this work, we demonstrate that SACE_7101 is the ortholog of actinomycetes' GlnR global regulators in the erythromycin producer Saccharopolyspora erythraea. Indeed, the chromosomal deletion of SACE_7101 severely affects the viability of S. erythraea when inoculated in minimal media supplemented with NaNO3, NaNO2, NH4Cl, glutamine, or glutamate as sole nitrogen source. Combination of in silico prediction of cis-acting elements, subsequent in vitro (through gel shift assays) and in vivo (real-time reverse transcription polymerase chain reaction) validations of the predicted target genes revealed a very large GlnR regulon aimed at adapting the nitrogen metabolism of S. erythraea. Indeed, enzymes/proteins involved in (i) uptake and assimilation of ammonium, (ii) transport and utilization of urea, (iii) nitrite/nitrate, (iv) glutamate/glutamine, (v) arginine metabolism, (vi) nitric oxide biosynthesis, and (vii) signal transduction associated with the nitrogen source supplied have at least one paralog gene which expression is controlled by GlnR. Our work highlights a GlnR-binding site consensus sequence (t/gna/cAC-n6-GaAAc) which is similar although not identical to the consensus sequences proposed for other actinomycetes. Finally, we discuss the distinct and common features of the GlnR-mediated transcriptional control of nitrogen metabolism between S. erythraea and the model organism Streptomyces coelicolor.

A meta-analysis of xeroderma pigmentosum gene D Ls751Gln polymorphism and susceptibility to hepatocellular carcinoma.

PubMed

Wang, Yu; Zhao, Yingren; Zhang, Aiyun; Ma, Juan; Wang, Zhenzhen; Zhang, Xu

2015-01-01

Hepatocellular carcinoma (HCC) is one of most common malignant tumors worldwide, but with unclear mechanisms. Xeroderma pigmentosum gene D (XPD) is one important DNA damage repair gene and can be involved in protein mutation. Currently little has been known about XPD polymorphism and HCC susceptibility in Chinese people. This study used a meta-analysis approach to comprehensively investigate the correlation between XPD polymorphism and HCC susceptibility in Chinese population, based on previously published literatures. A computer retrieval system was used to collect all case-control studies about XPD Lys751Gln polymorphism and HCC susceptibility. Data in literatures were extracted for meta-analysis. After the primary screening, four independent studies, which were published in 3 English articles and one Chinese article, were recruited in this study. There were 1,717 samples included in all studies. Using Gln/Gln + Lys/Gln, Lys/Lys + Lys/Gln and Lys allels as the reference, HCC disease alleles including Lys/Lys, Gln/Gln and Gln had OR values (95% CI, I(2)) of 1.007 (0.657~4.672, 91%), 3.516 (0.220~20.661, 48%) and 3.225 (0.278~12.326, 84%), respectively. The polymorphism of XPD751 loci is closely correlated with primary HCC. Lys751Gln polymorphism of XPD gene can be used as one susceptibility factor for HCC.

Spin-polarized electron current from carbon-doped open armchair boron nitride nanotubes: Implication for nano-spintronic devices

NASA Astrophysics Data System (ADS)

Zhou, Gang; Duan, Wenhui

2007-03-01

Spin-polarized density functional calculations show that the substitutional doping of carbon (C) atom at the mouth changes the atomic and spin configurations of open armchair boron nitride nanotubes (BNNTs). The occupied/unoccupied deep gap states are observed with the significant spin-splitting. The structures and spin-polarized properties are basically stable under the considerable electric field, which is important for practical applications. The magnetization mechanism is attributed to the interactions of s, p states between the C and its neighboring B or N atoms. Ultimately, advantageous geometrical and electronic effects mean that C-doped open armchair BNNTs would have promising applications in nano-spintronic devices.

Reciprocal Regulation of GlnR and PhoP in Response to Nitrogen and Phosphate Limitations in Saccharopolyspora erythraea

PubMed Central

Yao, Li-li

2015-01-01

Nitrogen and phosphate source sensing, uptake, and assimilation are essential for the growth and development of microorganisms. In this study, we demonstrated that SACE_6965 encodes the phosphate regulator PhoP, which controls the transcription of genes involved in phosphate metabolism in the erythromycin-producing Saccharopolyspora erythraea. We found that PhoP and the nitrogen regulator GlnR both regulate the transcription of glnR as well as other nitrogen metabolism-related genes. Interestingly, both GlnR- and PhoP-binding sites were identified in the phoP promoter region. Unlike the nonreciprocal regulation of GlnR and PhoP observed in Streptomyces coelicolor and Streptomyces lividans, GlnR negatively controls the transcription of the phoP gene in S. erythraea. This suggests that GlnR directly affects phosphate metabolism and demonstrates that the cross talk between GlnR and PhoP is reciprocal. Although GlnR and PhoP sites in the glnR and phoP promoter regions are located in close proximity to one another (separated by only 2 to 4 bp), the binding of both regulators to their respective region was independent and noninterfering. These results indicate that two regulators could separately bind to their respective binding sites and control nitrogen and phosphate metabolism in response to environmental changes. The reciprocal cross talk observed between GlnR and PhoP serves as a foundation for understanding the regulation of complex primary and secondary metabolism in antibiotic-producing actinomycetes. PMID:26519391

The crystal structure of human GlnRS provides basis for the development of neurological disorders

DOE PAGES

Ognjenovic, Jana; Wu, Jiang; Matthies, Doreen; ...

2016-02-10

Cytosolic glutaminyl-tRNA synthetase (GlnRS) is the singular enzyme responsible for translation of glutamine codons. Compound heterozygous mutations in GlnRS cause severe brain disorders by a poorly understood mechanism. Herein, we present crystal structures of the wild type and two pathological mutants of human GlnRS, which reveal, for the first time, the domain organization of the intact enzyme and the structure of the functionally important N-terminal domain (NTD). Pathological mutations mapping in the NTD alter the domain structure, and decrease catalytic activity and stability of GlnRS, whereas missense mutations in the catalytic domain induce misfolding of the enzyme. Our results suggestmore » that the reduced catalytic efficiency and a propensity of GlnRS mutants to misfold trigger the disease development. As a result, this report broadens the spectrum of brain pathologies elicited by protein misfolding and provides a paradigm for understanding the role of mutations in aminoacyl-tRNA synthetases in neurological diseases. Keywords« less

The crystal structure of human GlnRS provides basis for the development of neurological disorders

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ognjenovic, Jana; Wu, Jiang; Matthies, Doreen

Cytosolic glutaminyl-tRNA synthetase (GlnRS) is the singular enzyme responsible for translation of glutamine codons. Compound heterozygous mutations in GlnRS cause severe brain disorders by a poorly understood mechanism. Herein, we present crystal structures of the wild type and two pathological mutants of human GlnRS, which reveal, for the first time, the domain organization of the intact enzyme and the structure of the functionally important N-terminal domain (NTD). Pathological mutations mapping in the NTD alter the domain structure, and decrease catalytic activity and stability of GlnRS, whereas missense mutations in the catalytic domain induce misfolding of the enzyme. Our results suggestmore » that the reduced catalytic efficiency and a propensity of GlnRS mutants to misfold trigger the disease development. As a result, this report broadens the spectrum of brain pathologies elicited by protein misfolding and provides a paradigm for understanding the role of mutations in aminoacyl-tRNA synthetases in neurological diseases. Keywords« less

Mechanism of Disruption of the Amt-GlnK Complex by PII-Mediated Sensing of 2-Oxoglutarate

PubMed Central

Maier, Sarah; Schleberger, Paula; Lü, Wei; Wacker, Tobias; Pflüger, Tobias; Litz, Claudia; Andrade, Susana L. A.

2011-01-01

GlnK proteins regulate the active uptake of ammonium by Amt transport proteins by inserting their regulatory T-loops into the transport channels of the Amt trimer and physically blocking substrate passage. They sense the cellular nitrogen status through 2-oxoglutarate, and the energy level of the cell by binding both ATP and ADP with different affinities. The hyperthermophilic euryarchaeon Archaeoglobus fulgidus possesses three Amt proteins, each encoded in an operon with a GlnK ortholog. One of these proteins, GlnK2 was recently found to be incapable of binding 2-OG, and in order to understand the implications of this finding we conducted a detailed structural and functional analysis of a second GlnK protein from A. fulgidus, GlnK3. Contrary to Af-GlnK2 this protein was able to bind both ATP/2-OG and ADP to yield inactive and functional states, respectively. Due to the thermostable nature of the protein we could observe the exact positioning of the notoriously flexible T-loops and explain the binding behavior of GlnK proteins to their interaction partner, the Amt proteins. A thermodynamic analysis of these binding events using microcalorimetry evaluated by microstate modeling revealed significant differences in binding cooperativity compared to other characterized PII proteins, underlining the diversity and adaptability of this class of regulatory signaling proteins. PMID:22039461

Bacillus subtilis glutamine synthetase regulates its own synthesis by acting as a chaperone to stabilize GlnR-DNA complexes.

PubMed

Fisher, Susan H; Wray, Lewis V

2008-01-22

The Bacillus subtilis GlnR repressor controls gene expression in response to nitrogen availability. Because all GlnR-regulated genes are expressed constitutively in mutants lacking glutamine synthetase (GS), GS is required for repression by GlnR. Feedback-inhibited GS (FBI-GS) was shown to activate GlnR DNA binding with an in vitro electophoretic mobility shift assay (EMSA). The activation of GlnR DNA binding by GS in these experiments depended on the feedback inhibitor glutamine and did not occur with mutant GS proteins defective in regulating GlnR activity in vivo. Although stable GS-GlnR-DNA ternary complexes were not observed in the EMSA experiments, cross-linking experiments showed that a protein-protein interaction occurs between GlnR and FBI-GS. This interaction was reduced in the absence of the feedback inhibitor glutamine and with mutant GS proteins. Because FBI-GS significantly reduced the dissociation rate of the GlnR-DNA complexes, the stability of these complexes is enhanced by FBI-GS. These results argue that FBI-GS acts as a chaperone that activates GlnR DNA binding through a transient protein-protein interaction that stabilizes GlnR-DNA complexes. GS was shown to control the activity of the B. subtilis nitrogen transcription factor TnrA by forming a stable complex between FBI-GS and TnrA that inhibits TnrA DNA binding. Thus, B. subtilis GS is an enzyme with dual catalytic and regulatory functions that uses distinct mechanisms to control the activity of two different transcription factors.

Structure of an archaeal non-discriminating glutamyl-tRNA synthetase: a missing link in the evolution of Gln-tRNAGln formation.

PubMed

Nureki, Osamu; O'Donoghue, Patrick; Watanabe, Nobuhisa; Ohmori, Atsuhiko; Oshikane, Hiroyuki; Araiso, Yuhei; Sheppard, Kelly; Söll, Dieter; Ishitani, Ryuichiro

2010-11-01

The molecular basis of the genetic code relies on the specific ligation of amino acids to their cognate tRNA molecules. However, two pathways exist for the formation of Gln-tRNA(Gln). The evolutionarily older indirect route utilizes a non-discriminating glutamyl-tRNA synthetase (ND-GluRS) that can form both Glu-tRNA(Glu) and Glu-tRNA(Gln). The Glu-tRNA(Gln) is then converted to Gln-tRNA(Gln) by an amidotransferase. Since the well-characterized bacterial ND-GluRS enzymes recognize tRNA(Glu) and tRNA(Gln) with an unrelated α-helical cage domain in contrast to the β-barrel anticodon-binding domain in archaeal and eukaryotic GluRSs, the mode of tRNA(Glu)/tRNA(Gln) discrimination in archaea and eukaryotes was unknown. Here, we present the crystal structure of the Methanothermobacter thermautotrophicus ND-GluRS, which is the evolutionary predecessor of both the glutaminyl-tRNA synthetase (GlnRS) and the eukaryotic discriminating GluRS. Comparison with the previously solved structure of the Escherichia coli GlnRS-tRNA(Gln) complex reveals the structural determinants responsible for specific tRNA(Gln) recognition by GlnRS compared to promiscuous recognition of both tRNAs by the ND-GluRS. The structure also shows the amino acid recognition pocket of GluRS is more variable than that found in GlnRS. Phylogenetic analysis is used to reconstruct the key events in the evolution from indirect to direct genetic encoding of glutamine.

Charge and Spin Currents in Open-Shell Molecules:  A Unified Description of NMR and EPR Observables.

PubMed

Soncini, Alessandro

2007-11-01

The theory of EPR hyperfine coupling tensors and NMR nuclear magnetic shielding tensors of open-shell molecules in the limit of vanishing spin-orbit coupling (e.g., for organic radicals) is analyzed in terms of spin and charge current density vector fields. The ab initio calculation of the spin and charge current density response has been implemented at the Restricted Open-Shell Hartree-Fock, Unrestricted Hartree-Fock, and unrestricted GGA-DFT level of theory. On the basis of this formalism, we introduce the definition of nuclear hyperfine coupling density, a scalar function of position providing a partition of the EPR observable over the molecular domain. Ab initio maps of spin and charge current density and hyperfine coupling density for small radicals are presented and discussed in order to illustrate the interpretative advantages of the newly introduced approach. Recent NMR experiments providing evidence for the existence of diatropic ring currents in the open-shell singlet pancake-bonded dimer of the neutral phenalenyl radical are directly assessed via the visualization of the induced current density.

Open Systems with Error Bounds: Spin-Boson Model with Spectral Density Variations.

PubMed

Mascherpa, F; Smirne, A; Huelga, S F; Plenio, M B

2017-03-10

In the study of open quantum systems, one of the most common ways to describe environmental effects on the reduced dynamics is through the spectral density. However, in many models this object cannot be computed from first principles and needs to be inferred on phenomenological grounds or fitted to experimental data. Consequently, some uncertainty regarding its form and parameters is unavoidable; this in turn calls into question the accuracy of any theoretical predictions based on a given spectral density. Here, we focus on the spin-boson model as a prototypical open quantum system, find two error bounds on predicted expectation values in terms of the spectral density variation considered, and state a sufficient condition for the strongest one to apply. We further demonstrate an application of our result, by bounding the error brought about by the approximations involved in the hierarchical equations of motion resolution method for spin-boson dynamics.

Effect of T- and C-loop mutations on the Herbaspirillum seropedicae GlnB protein in nitrogen signalling.

PubMed

Bonatto, Ana C; Souza, Emanuel M; Pedrosa, Fábio O; Yates, M Geoffrey; Benelli, Elaine M

2005-01-01

Proteins of the PII family are found in species of all kingdoms. Although these proteins usually share high identity, their functions are specific to the different organisms. Comparison of structural data from Escherichia coli GlnB and GlnK and Herbaspirillum seropedicae GlnB showed that the T-loop and C-terminus were variable regions. To evaluate the role of these regions in signal transduction by the H. seropedicae GlnB protein, four mutants were constructed: Y51F, G108A/P109a, G108W and Q3R/T5A. The activities of the native and mutated proteins were assayed in an E. coli background constitutively expressing the Klebsiella pneumoniae nifLA operon. The results suggested that the T-loop and C-terminus regions of H. seropedicae GlnB are involved in nitrogen signal transduction.

Equation-of-motion coupled-cluster method for ionised states with spin-orbit coupling using open-shell reference wavefunction

NASA Astrophysics Data System (ADS)

Wang, Zhifan; Wang, Fan

2018-04-01

The equation-of-motion coupled-cluster method for ionised states at the singles and doubles level (EOM-IP-CCSD) with spin-orbit coupling (SOC) included in post-Hartree-Fock (HF) steps is extended to spatially non-degenerate open-shell systems such as high spin states of s1, p3, σ1 or π2 configuration in this work. Pseudopotentials are employed to treat relativistic effects and spin-unrestricted scalar relativistic HF determinant is adopted as reference in calculations. Symmetry is not exploited in the implementation since both time-reversal and spatial symmetry is broken due to SOC. IPs with the EOM-IP-CCSD approach are those from the 3Σ1- states for high spin state of π2 configuration, while the ground state is the 3Σ0- state. When removing an electron from the high spin state of p3 configuration, only the 3P2 state can be reached. The open-shell EOM-IP-CCSD approach with SOC was employed in calculating IPs of some open-shell atoms with s1 configuration, diatomic molecules with π2 configuration and SOC splitting of the ionised π1 state, as well as IPs of VA atoms with p3 configuration. Our results demonstrate that this approach can be applied to ionised states of spatially non-degenerate open-shell states containing heavy elements with reasonable accuracy.

Development of New Open-Shell Perturbation and Coupled-Cluster Theories Based on Symmetric Spin Orbitals

NASA Technical Reports Server (NTRS)

Lee, Timothy J.; Arnold, James O. (Technical Monitor)

1994-01-01

A new spin orbital basis is employed in the development of efficient open-shell coupled-cluster and perturbation theories that are based on a restricted Hartree-Fock (RHF) reference function. The spin orbital basis differs from the standard one in the spin functions that are associated with the singly occupied spatial orbital. The occupied orbital (in the spin orbital basis) is assigned the delta(+) = 1/square root of 2(alpha+Beta) spin function while the unoccupied orbital is assigned the delta(-) = 1/square root of 2(alpha-Beta) spin function. The doubly occupied and unoccupied orbitals (in the reference function) are assigned the standard alpha and Beta spin functions. The coupled-cluster and perturbation theory wave functions based on this set of "symmetric spin orbitals" exhibit much more symmetry than those based on the standard spin orbital basis. This, together with interacting space arguments, leads to a dramatic reduction in the computational cost for both coupled-cluster and perturbation theory. Additionally, perturbation theory based on "symmetric spin orbitals" obeys Brillouin's theorem provided that spin and spatial excitations are both considered. Other properties of the coupled-cluster and perturbation theory wave functions and models will be discussed.

The integrable quantum group invariant A2n-1(2) and Dn+1(2) open spin chains

NASA Astrophysics Data System (ADS)

Nepomechie, Rafael I.; Pimenta, Rodrigo A.; Retore, Ana L.

2017-11-01

A family of A2n(2) integrable open spin chains with Uq (Cn) symmetry was recently identified in arxiv:arXiv:1702.01482. We identify here in a similar way a family of A2n-1(2) integrable open spin chains with Uq (Dn) symmetry, and two families of Dn+1(2) integrable open spin chains with Uq (Bn) symmetry. We discuss the consequences of these symmetries for the degeneracies and multiplicities of the spectrum. We propose Bethe ansatz solutions for two of these models, whose completeness we check numerically for small values of n and chain length N. We find formulas for the Dynkin labels in terms of the numbers of Bethe roots of each type, which are useful for determining the corresponding degeneracies. In an appendix, we briefly consider Dn+1(2) chains with other integrable boundary conditions, which do not have quantum group symmetry.

The separation of Gln and Glu in STEAM: a comparison study using short and long TEs/TMs at 3 and 7 T.

PubMed

Dou, Weiqiang; Kaufmann, Jörn; Li, Meng; Zhong, Kai; Walter, Martin; Speck, Oliver

2015-08-01

This study aimed to determine the optimal echo time (TE) and mixing time (TM) for in vivo glutamine (Gln) and glutamate (Glu) separation in stimulated-echo acquisition mode at 3 and 7 T. We applied a short TE/TM (20/10 ms) for a high signal-to-noise-ratio and a field-specific long TE/TM (3 T: 72/6 ms; 7 T: 74/68 ms) for optimal Gln and Glu separation of the Carbon-4 proton resonances. Corresponding Gln and Glu spectra were simulated using VeSPA software, and measured in a phantom and human brains at 3 and 7 T. Higher spectral separation for Gln and Glu was achieved at 7 than 3 T. At 7 T, short TE/TM provided comparable spectral separation and in vitro Gln and Glu quantification compared to long TE/TM. Moreover, it showed greater reliability in in vivo Gln and Glu detection and separation than long TE/TM, with significantly lower Cramer-Rao lower bounds (Gln: 14.9 vs. 75.8; Glu: 3.8 vs. 6.5) and correlation between Gln and Glu (p = 0.004). Based on the optimal separation for Gln and Glu, a short TE/TM at 7 T is proposed for future in vivo Gln and Glu acquisition.

Dual-targeted tRNA-dependent amidotransferase ensures both mitochondrial and chloroplastic Gln-tRNAGln synthesis in plants

PubMed Central

Pujol, Claire; Bailly, Marc; Kern, Daniel; Maréchal-Drouard, Laurence; Becker, Hubert; Duchêne, Anne-Marie

2008-01-01

Aminoacyl-tRNAs are generally formed by direct attachment of an amino acid to tRNAs by aminoacyl-tRNA synthetases, but Gln-tRNA is an exception to this rule. Gln-tRNAGln is formed by this direct pathway in the eukaryotic cytosol and in protists or fungi mitochondria but is formed by an indirect transamidation pathway in most of bacteria, archaea, and chloroplasts. We show here that the formation of Gln-tRNAGln is also achieved by the indirect pathway in plant mitochondria. The mitochondrial-encoded tRNAGln, which is the only tRNAGln present in mitochondria, is first charged with glutamate by a nondiscriminating GluRS, then is converted into Gln-tRNAGln by a tRNA-dependent amidotransferase (AdT). The three subunits GatA, GatB, and GatC are imported into mitochondria and assemble into a functional GatCAB AdT. Moreover, the mitochondrial pathway of Gln-tRNAGln formation is shared with chloroplasts as both the GluRS, and the three AdT subunits are dual-imported into mitochondria and chloroplasts. PMID:18441100

Structure of GlnK1 with bound effectors indicates regulatory mechanism for ammonia uptake.

PubMed

Yildiz, Ozkan; Kalthoff, Christoph; Raunser, Stefan; Kühlbrandt, Werner

2007-01-24

A binary complex of the ammonia channel Amt1 from Methanococcus jannaschii and its cognate P(II) signalling protein GlnK1 has been produced and characterized. Complex formation is prevented specifically by the effector molecules Mg-ATP and 2-ketoglutarate. Single-particle electron microscopy of the complex shows that GlnK1 binds on the cytoplasmic side of Amt1. Three high-resolution X-ray structures of GlnK1 indicate that the functionally important T-loop has an extended, flexible conformation in the absence of Mg-ATP, but assumes a compact, tightly folded conformation upon Mg-ATP binding, which in turn creates a 2-ketoglutarate-binding site. We propose a regulatory mechanism by which nitrogen uptake is controlled by the binding of both effector molecules to GlnK1. At normal effector levels, a 2-ketoglutarate molecule binding at the apex of the compact T-loop would prevent complex formation, ensuring uninhibited ammonia uptake. At low levels of Mg-ATP, the extended loops would seal the ammonia channels in the complex. Binding of both effector molecules to P(II) signalling proteins may thus represent an effective feedback mechanism for regulating ammonium uptake through the membrane.

Effect of protein solution components in the adsorption of Herbaspirillum seropedicae GlnB protein on mica.

PubMed

Ferreira, Cecília F G; Benelli, Elaine M; Klein, Jorge J; Schreiner, Wido; Camargo, Paulo C

2009-10-15

The adsorption of proteins and its buffer solution on mica surfaces was investigated by atomic force microscopy (AFM). Different salt concentration of the Herbaspirillum seropedicae GlnB protein (GlnB-Hs) solution deposited on mica was investigated. This protein is a globular, soluble homotrimer (36kDa), member of PII-like proteins family involved in signal transducing in prokaryote. Supramolecular structures were formed when this protein was deposited onto bare mica surface. The topographic AFM images of the GlnB-Hs films showed that at high salt concentration the supramolecular structures are spherical-like, instead of the typical doughnut-like shape for low salt concentration. AFM images of NaCl and Tris from the buffer solution showed structures with the same pattern as those observed for high salt protein solution, misleading the image interpretation. XPS experiments showed that GlnB protein film covers the mica surface without chemical reaction.

Lactosylated Gramicidin-based lipid nanoparticles (Lac-GLN) for targeted delivery of anti-miR-155 to hepatocellular carcinoma

PubMed Central

Zhang, Mengzi; Zhou, Xiaoju; Wang, Bo; Yung, Bryant C.; Lee, Ly J.; Ghoshal, Kalpana; Lee, Robert J.

2013-01-01

Lactosylated gramicidin-containing lipid nanoparticles (Lac-GLN) were developed for delivery of anti-microRNA-155 (anti-miR-155) to hepatocellular carcinoma (HCC) cells. MiR-155 is an oncomiR frequently elevated in HCC. The Lac-GLN formulation contained N-lactobionyl-dioleoyl phosphatidylethanolamine (Lac-DOPE), a ligand for the asialoglycoprotein receptor (ASGR), and an antibiotic peptide gramicidin A. The nanoparticles exhibited a mean particle diameter of 73 nm, zeta potential of +3.5 mV, anti-miR encapsulation efficiency of 88%, and excellent colloidal stability at 4°C. Lac-GLN effectively delivered anti-miR-155 to HCC cells with a 16.1- and 4.1-fold up-regulation of miR-155 targets C/EBPβ and FOXP3 genes, respectively, and exhibited significant greater efficiency over Lipofectamine 2000. In mice, intravenous injection of Lac-GLN containing Cy3-anti-miR-155 led to preferential accumulation of the anti-miR-155 in hepatocytes. Intravenous administration of 1.5 mg/kg anti-miR-155 loaded Lac-GLN resulted in up-regulation of C/EBPβ and FOXP3 by 6.9- and 2.2- fold, respectively. These results suggest potential application of Lac-GLN as a liver-specific delivery vehicle for anti-miR therapy. PMID:23567045

Methionine sulfoximine-treatment and carbon starvation elicit Snf1-independent phosphorylation of the transcription activator Gln3 in Saccharomyces cerevisiae

PubMed Central

Tate, Jennifer J.; Rai, Rajendra; Cooper, Terrance G.

2008-01-01

SUMMARY Tor proteins are global regulators situated at the top of a signal transduction pathway conserved from yeast to humans. Specific inhibition of the two S. cerevisiae Tor proteins by rapamycin alters many cellular processes and the expression of hundreds of genes. Among the regulated genes are those whose expression is activated by the GATA-family transcription activator, Gln3. The extent of Gln3 phosphorylation has been thought to determine its intracellular localization, with phosphorylated and dephosphorylated forms accumulating in the cytoplasm and nucleus, respectively. Data presented here demonstrate that rapamycin and the glutamine synthetase inhibitor, methionine sulfoximine (MSX), although eliciting the same outcomes with respect to Gln3-Myc13 nuclear accumulation and NCR-sensitive transcription, generate diametrically opposite effects on Gln3-Myc13 phosphorylation. MSX increases Gln3-Myc13 phosphorylation while rapamycin decreases it. Gln3-Myc13 phosphorylation levels are regulated by at least three mechanisms: (i) one, observed during carbon starvation, depends on Snf1 kinase, (ii) another, observed during both carbon-starvation and MSX-treatment, is Snf1-independent, and (iii) the last is rapamycin-induced dephosphorylation. MSX and rapamycin act additively on Gln3-Myc13 phosphorylation, but MSX clearly predominates. These results suggest that MSX- and rapamycin-inhibited proteins are more likely to function in separate regulatory pathways than they are to function tandemly in a single pathway as previously thought. Further, Gln3 phosphorylation/dephosphorylation, that we and others have detected thus far, is not a demonstrably required step in achieving Gln3 nuclear localization and NCR-sensitive transcription in response to MSX- or rapamycin-treatment. PMID:15911613

Polymorphisms in XPD (Asp312Asn and Lys751Gln) genes, sunburn and arsenic-related skin lesions.

PubMed

McCarty, Kathleen M; Smith, Thomas J; Zhou, Wei; Gonzalez, Ernesto; Quamruzzaman, Quazzi; Rahman, Mahmuder; Mahiuddin, Golam; Ryan, Louise; Su, Li; Christiani, David C

2007-08-01

Single-nucleotide polymorphisms in genes related to DNA repair capacity and ultraviolet exposure have not been well investigated in relation to skin lesions associated with arsenic exposure. This population based case-control study, of 600 cases and 600 controls, frequency matched on age and gender in Pabna, Bangladesh, in 2001-2002, investigated the association and potential effect modification between polymorphisms in Xeroderma Pigmentosum complementation group D (XPD) (Lys751Gln and Asp312Asn) genes, tendency to sunburn and arsenic-related skin lesions. Unconditional logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs). No significant association was observed between skin lesions and the XPD 312 Asp/Asn (adjusted OR = 0.87, 95% CI = 0.65-1.15) Asn/Asn (adjusted OR = 0.76, 95% CI = 0.50-1.15) (referent Asp/Asp); XPD 751 Lys/Gln (adjusted OR = 0.92, 95% CI = 0.69-1.23) Gln/Gln (adjusted OR = 0.98, 95% CI = 0.66-1.45) (referent Lys/Lys). While we did not observe any evidence of effect modification of these polymorphisms on the association between well arsenic concentration and skin lesions, we did observe effect modification between these polymorphisms and sunburn tendency and arsenic-related skin lesions. Individuals with the heterozygote or homozygote variant forms (Asp/Asn or Asn/Asn) had half the risk of skin lesions (OR = 0.45, 95% CI = 0.29-0.68) compared with those with the wild-type XPDAsp312Asn genotype (Asp/Asp) and individuals with heterozygote or homozygote variant forms (Lys/Gln or Gln/Gln) had half the risk of skin lesions (OR = 0.47, 95% CI = 0.31-0.72) compared with those with the wild-type XPDLys751Gln genotype (Lys/Lys), within the least sensitive strata of sunburn severity. We observed effect modification on the multiplicative scale for XPD 751 and XPD 312. XPD polymorphisms modified the relationship between tendency to sunburn and skin lesions in an arsenic exposed population. Further study is necessary

Polymorphisms in XPD (Asp312Asn and Lys751Gln) genes, sunburn and arsenic-related skin lesions

PubMed Central

McCarty, Kathleen M.; Smith, Thomas J.; Zhou, Wei; Gonzalez, Ernesto; Quamruzzaman, Quazzi; Rahman, Mahmuder; Mahiuddin, Golam; Ryan, Louise; Su, Li; Christiani, David C.

2013-01-01

Background Single-nucleotide polymorphisms in genes related to DNA repair capacity and ultraviolet exposure have not been well investigated in relation to skin lesions associated with arsenic exposure. This population based case–control study, of 600 cases and 600 controls, frequency matched on age and gender in Pabna, Bangladesh, in 2001–2002, investigated the association and potential effect modification between polymorphisms in Xeroderma Pigmentosum complementation group D (XPD) (Lys751Gln and Asp312Asn) genes, tendency to sunburn and arsenic-related skin lesions. Methods Unconditional logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs). Result No significant association was observed between skin lesions and the XPD 312 Asp/Asn (adjusted OR = 0.87, 95% CI = 0.65–1.15) Asn/Asn (adjusted OR = 0.76, 95% CI = 0.50–1.15) (referent Asp/Asp); XPD 751 Lys/Gln (adjusted OR = 0.92, 95% CI = 0.69–1.23) Gln/Gln (adjusted OR = 0.98, 95% CI = 0.66–1.45) (referent Lys/Lys). While we did not observe any evidence of effect modification of these polymorphisms on the association between well arsenic concentration and skin lesions, we did observe effect modification between these polymorphisms and sunburn tendency and arsenic-related skin lesions. Individuals with the heterozygote or homozygote variant forms (Asp/Asn or Asn/Asn) had half the risk of skin lesions (OR = 0.45, 95% CI = 0.29–0.68) compared with those with the wild-type XPDAsp312Asn genotype (Asp/Asp) and individuals with heterozygote or homozygote variant forms (Lys/Gln or Gln/Gln) had half the risk of skin lesions (OR = 0.47, 95% CI = 0.31–0.72) compared with those with the wild-type XPDLys751Gln genotype (Lys/Lys), within the least sensitive strata of sunburn severity. We observed effect modification on the multiplicative scale for XPD 751 and XPD 312. Conclusion XPD polymorphisms modified the relationship between tendency to sunburn and skin lesions in an

Torque Enhancement, Spin Equilibrium, and Jet Power from Disk-Induced Opening of Pulsar Magnetic Fields

NASA Astrophysics Data System (ADS)

Parfrey, Kyle; Spitkovsky, Anatoly; Beloborodov, Andrei M.

2016-05-01

The interaction of a rotating star’s magnetic field with a surrounding plasma disk lies at the heart of many questions posed by neutron stars in X-ray binaries. We consider the opening of stellar magnetic flux due to differential rotation along field lines coupling the star and disk, using a simple model for the disk-opened flux, the torques exerted on the star by the magnetosphere, and the power extracted by the electromagnetic wind. We examine the conditions under which the system enters an equilibrium spin state, in which the accretion torque is instantaneously balanced by the pulsar wind torque alone. For magnetic moments, spin frequencies, and accretion rates relevant to accreting millisecond pulsars, the spin-down torque from this enhanced pulsar wind can be substantially larger than that predicted by existing models of the disk-magnetosphere interaction, and is in principle capable of maintaining spin equilibrium at frequencies less than 1 kHz. We speculate that this mechanism may account for the non-detection of frequency increases during outbursts of SAX J1808.4-3658 and XTE J1814-338, and may be generally responsible for preventing spin-up to sub-millisecond periods. If the pulsar wind is collimated by the surrounding environment, the resulting jet can satisfy the power requirements of the highly relativistic outflows from Cir X-1 and Sco X-1. In this framework, the jet power scales relatively weakly with accretion rate, {L}{{j}}\\propto {\\dot{M}}4/7, and would be suppressed at high accretion rates only if the stellar magnetic moment is sufficiently low.

Baryonic and mesonic 3-point functions with open spin indices

NASA Astrophysics Data System (ADS)

Bali, Gunnar S.; Collins, Sara; Gläßle, Benjamin; Heybrock, Simon; Korcyl, Piotr; Löffler, Marius; Rödl, Rudolf; Schäfer, Andreas

2018-03-01

We have implemented a new way of computing three-point correlation functions. It is based on a factorization of the entire correlation function into two parts which are evaluated with open spin-(and to some extent flavor-) indices. This allows us to estimate the two contributions simultaneously for many different initial and final states and momenta, with little computational overhead. We explain this factorization as well as its efficient implementation in a new library which has been written to provide the necessary functionality on modern parallel architectures and on CPUs, including Intel's Xeon Phi series.

XRCC1 Arg194Trp and Arg399Gln polymorphisms and arsenic methylation capacity are associated with urothelial carcinoma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chiang, Chien-I; Huang, Ya-Li; Chen, Wei-Jen

The association between DNA repair gene polymorphisms and bladder cancer has been widely studied. However, few studies have examined the correlation between urothelial carcinoma (UC) and arsenic or its metabolites. The aim of this study was to examine the association between polymorphisms of the DNA repair genes, XRCC1 Arg194Trp, XRCC1 Arg399Gln, XRCC3 Thr241Met, and XPD Lys751Gln, with urinary arsenic profiles and UC. To this end, we conducted a hospital-based case–control study with 324 UC patients and 647 age- and gender-matched non-cancer controls. Genomic DNA was used to examine the genotype of XRCC1 Arg194Trp, XRCC1 Arg399Gln, XRCC3 Thr241Met, and XPD Lys751Glnmore » by PCR-restriction fragment length polymorphism analysis (PCR-RFLP). Urinary arsenic profiles were measured by high performance liquid chromatography (HPLC) linked with hydride generator and atomic absorption spectrometry. The XRCC1 399 Gln/Gln and 194 Arg/Trp and Trp/Trp genotypes were significantly related to UC, and the odds ratio (OR) and 95% confidence interval (95%CI) were 1.68 (1.03–2.75) and 0.66 (0.48–0.90), respectively. Participants with higher total urinary arsenic levels, a higher percentage of inorganic arsenic (InAs%) and a lower percentage of dimethylarsinic acid (DMA%) had a higher OR of UC. Participants carrying XRCC1 risk diplotypes G-C/G-C, A-C/A-C, and A-T/G-T, and who had higher total arsenic levels, higher InAs%, or lower DMA% compared to those with other XRCC1 diplotypes had a higher OR of UC. Our results suggest that the XRCC1 399 Gln/Gln and 194 Arg/Arg DNA repair genes play an important role in poor arsenic methylation capacity, thereby increasing the risk of UC in non-obvious arsenic exposure areas. - Highlights: • The XRCC1 399Gln/Gln genotype was significantly associated with increased OR of UC. • The XRCC1 194 Arg/Trp and Trp/Trp genotype had a significantly decreased OR of UC. • Combined effect of the XRCC1 genotypes and poor arsenic methylation

Spin asymmetric band gap opening in graphene by Fe adsorption

NASA Astrophysics Data System (ADS)

del Castillo, E.; Cargnoni, F.; Achilli, S.; Tantardini, G. F.; Trioni, M. I.

2015-04-01

The adsorption of Fe atom on graphene is studied by first-principles Density Functional Theory. The structural, electronic, and magnetic properties are analyzed at different coverages, all preserving C6v symmetry for the Fe adatom. We observed that binding energies, magnetic moments, and adsorption distances rapidly converge as the size of the supercell increases. Among the considered supercells, those constituted by 3n graphene unit cells show a very peculiar behavior: the adsorption of a Fe atom induces the opening of a spin-dependent gap in the band structure. In particular, the gap amounts to tenths of eV in the majority spin component, while in the minority one it has a width of about 1 eV for the 3 × 3 supercell and remains significant even at very low coverages (0.25 eV for θ ≃ 2%). The charge redistribution upon Fe adsorption has also been analyzed according to state of the art formalisms indicating an appreciable charge transfer from Fe to the graphene layer.

Effects of Ala-Gln feeding strategies on growth, metabolism, and crowding stress resistance of juvenile Cyprinus carpio var. Jian.

PubMed

Chen, Xiu-Mei; Guo, Gui-Liang; Sun, Li; Yang, Qiu-Shi; Wang, Gui-Qin; Qin, Gui-Xin; Zhang, Dong-Ming

2016-04-01

The present study was conducted to evaluate the effects of different L-alanyl-l-glutamine (Ala-Gln) feeding strategies on the growth performance, metabolism and crowding stress resistance related parameters in juvenile Jian carp (Cyprinus carpio var. Jian) under crowded condition (80 g/L). Juvenile Jian carp (initial weight 26.1 ± 0.6 g) were distributed into five groups which fed with graded concentrations (0% or 1.0%) of Ala-Gln for eight weeks. Control group (I, 0/0) fed with control diet (0% Ala-Gln) throughout the feeding trial. The other four groups employed different control and experimental diet feeding strategies ranging from two weeks control diet fed and two weeks experimental diet (1% Ala-Gln) fed (II, 0/2) to eight weeks experimental diet fed (V, 4/4). Results revealed that Mean weight gain (MEG) under all different feeding strategies of Ala-Gln were significantly higher than that of the control group (p < 0.05), and MEG of group II (201.90%) was even higher than that of group IV (184.70%). Liver glycogen and blood total protein of groups II, III and V were significantly higher than that in groups I and IV (p < 0.05). The highest level of serum thyroxine (10.07 ng/ml), insulin-like growth factor-I (52.40 ng/ml) and insulin (9.73 μ IU/mL) were observed in group V. However, diet supplemented with Ala-Gln did not affect the levels of serum glucose, cortisol and catecholamine in fish. The mRNA expression of GR1a, GR1b and GR2 were also significantly changed in Ala-Gln supplementation groups compared with control group (p < 0.05). After fish intraperitoneally injected with virulent Aeromonas hydrophila, the fish survival rates were significantly increased in all Ala-Gln supplementation groups compared with control group (p < 0.05). Results from the present experiment showed the importance of dietary supplementation of Ala-Gln in benefaction of the growth performance, metabolism and crowding stress resistance in Jian carp breeding. The

Association of Gln223 Arg polymorphism of the leptin receptor gene with indicators of energy expenditure in obese children.

PubMed

Répásy, Judit; Bokor, Szilvia; Erhardt, Éva; Molnár, Dénes

2014-01-01

Gln223 Arg polymorphism of the leptin receptor (LEPR) gene is one of the most frequently examined polymorphisms of this gene and has been suggested to be associated with energy expenditure (EE). The aim of the present study was to investigate the association of this variant on indicators of EE-resting metabolic rate (RMR), postabsorptive and postprandial respiratory quotient (RQ), and food-induced thermogenesis (FIT)-in obese children. The study included 486 genotyped children (obese, n = 355). RMR was measured by indirect calorimetry for 45 min. Subsequent to test-food consumption, FIT was measured in a subsample of obese children (n = 121, body mass index 31.9 kg/m(2) (mean ± SD 5.1). Obese children with the Gln223 Gln genotype showed a significantly lower post-absorptive and postprandial RQ (P = 0.0055 versus P = 0.0002, adjusted for age, sex, and lean body mass) than did groups of children with Gln223 Arg and Arg223 Arg genotypes. No significant differences were observed in FIT and RMR among the carriers and non-carriers of the 223 Arg allele. The significantly lower post-absorptive and postprandial RQ in the group of Gln223 Gln genotype children indicates that the fat oxidation of these children maybe increased before and subsequent to food consumption, which can be important in the planning of diet of these children. Copyright © 2014 Elsevier Inc. All rights reserved.

Role of B13 Glu in insulin assembly. The hexamer structure of recombinant mutant (B13 Glu-->Gln) insulin.

PubMed

Bentley, G A; Brange, J; Derewenda, Z; Dodson, E J; Dodson, G G; Markussen, J; Wilkinson, A J; Wollmer, A; Xiao, B

1992-12-20

The assembly of the insulin hexamer brings the six B13 glutamate side-chains at the centre into close proximity. Their mutual repulsion is unfavourable and zinc co-ordination to B10 histidine is necessary to stabilize the well known zinc-containing hexamers. Since B13 is always a carboxylic acid in all known sequences of hexamer forming insulins, it is likely to be important in the hormone's biology. The mutation of B13 Glu-->Gln leads to a stable zinc-free hexamer with somewhat reduced potency. The structures of the zinc-free B13 Gln hexamer and the 2Zn B13 insulin hexamer have been determined by X-ray analysis and refined with 2.5 A and 2.0 A diffraction data, respectively. Comparisons show that in 2Zn B13 Gln insulin, the hexamer structure (T6) is very like that of the native hormone. On the other hand, the zinc-free hexamer assumes a quaternary structure (T3/R3) seen in the native 4Zn insulin hexamer, and normally associated only with high chloride ion concentrations in the medium. The crystal structures show the B13 Gln side-chains only contact water in contrast to the B13 glutamate in 2Zn insulin. The solvation of the B13 Gln may be associated with this residue favouring helix at B1 to B8. The low potency of the B13 Gln insulin also suggests the residue influences the hormone's conformation.

Sucrose breakdown within guard cells provides substrates for glycolysis and glutamine biosynthesis during light-induced stomatal opening.

PubMed

Medeiros, David B; Perez Souza, Leonardo; Antunes, Werner C; Araújo, Wagner L; Daloso, Danilo M; Fernie, Alisdair R

2018-05-01

Sucrose has long been thought to play an osmolytic role in stomatal opening. However, recent evidence supports the idea that the role of sucrose in this process is primarily energetic. Here we used a combination of stomatal aperture assays and kinetic [U- 13 C]-sucrose isotope labelling experiments to confirm that sucrose is degraded during light-induced stomatal opening and to define the fate of the C released from sucrose breakdown. We additionally show that addition of sucrose to the medium did not enhance light-induced stomatal opening. The isotope experiment showed a consistent 13 C enrichment in fructose and glucose, indicating that during light-induced stomatal opening sucrose is indeed degraded. We also observed a clear 13 C enrichment in glutamate and glutamine (Gln), suggesting a concerted activation of sucrose degradation, glycolysis and the tricarboxylic acid cycle. This is in contrast to the situation for Gln biosynthesis in leaves under light, which has been demonstrated to rely on previously stored C. Our results thus collectively allow us to redraw current models concerning the influence of sucrose during light-induced stomatal opening, in which, instead of being accumulated, sucrose is degraded providing C skeletons for Gln biosynthesis. © 2018 The Authors The Plant Journal © 2018 John Wiley & Sons Ltd.

Co-Inactivation of GlnR and CodY Regulators Impacts Pneumococcal Cell Wall Physiology.

PubMed

Johnston, Calum; Bootsma, Hester J; Aldridge, Christine; Manuse, Sylvie; Gisch, Nicolas; Schwudke, Dominik; Hermans, Peter W M; Grangeasse, Christophe; Polard, Patrice; Vollmer, Waldemar; Claverys, Jean-Pierre

2015-01-01

CodY, a nutritional regulator highly conserved in low G+C Gram-positive bacteria, is essential in Streptococcus pneumoniae (the pneumococcus). A published codY mutant possessed suppressing mutations inactivating the fatC and amiC genes, respectively belonging to iron (Fat/Fec) and oligopeptide (Ami) ABC permease operons, which are directly repressed by CodY. Here we analyzed two additional published codY mutants to further explore the essentiality of CodY. We show that one, in which the regulator of glutamine/glutamate metabolism glnR had been inactivated by design, had only a suppressor in fecE (a gene in the fat/fec operon), while the other possessed both fecE and amiC mutations. Independent isolation of three different fat/fec suppressors thus establishes that reduction of iron import is crucial for survival without CodY. We refer to these as primary suppressors, while inactivation of ami, which is not essential for survival of codY mutants and acquired after initial fat/fec inactivation, can be regarded as a secondary suppressor. The availability of codY- ami+ cells allowed us to establish that CodY activates competence for genetic transformation indirectly, presumably by repressing ami which is known to antagonize competence. The glnR codY fecE mutant was then found to be only partially viable on solid medium and hypersensitive to peptidoglycan (PG) targeting agents such as the antibiotic cefotaxime and the muramidase lysozyme. While analysis of PG and teichoic acid composition uncovered no alteration in the glnR codY fecE mutant compared to wildtype, electron microscopy revealed altered ultrastructure of the cell wall in the mutant, establishing that co-inactivation of GlnR and CodY regulators impacts pneumococcal cell wall physiology. In light of rising levels of resistance to PG-targeting antibiotics of natural pneumococcal isolates, GlnR and CodY constitute potential alternative therapeutic targets to combat this debilitating pathogen, as co

Characterization of the orf1glnKamtB operon of Herbaspirillum seropedicae.

PubMed

Noindorf, Lilian; Rego, Fabiane G M; Baura, Valter A; Monteiro, Rose A; Wassem, Roseli; Cruz, Leonardo M; Rigo, Liu U; Souza, Emanuel M; Steffens, Maria B R; Pedrosa, Fabio O; Chubatsu, Leda S

2006-03-01

Herbaspirillum seropedicae is an endophytic nitrogen-fixing bacterium that colonizes economically important grasses. In this organism, the amtB gene is co-transcribed with two other genes: glnK that codes for a PII-like protein and orf1 that codes for a probable periplasmatic protein of unknown function. The expression of the orf1glnKamtB operon is increased under nitrogen-limiting conditions and is dependent on NtrC. An amtB mutant failed to transport methylammonium. Post-translational control of nitrogenase was also partially impaired in this mutant, since a complete switch-off of nitrogenase after ammonium addition was not observed. This result suggests that the AmtB protein is involved in the signaling pathway for the reversible inactivation of nitrogenase in H. seropedicae.

No association of the neuropeptide Y (Leu7Pro) and ghrelin gene (Arg51Gln, Leu72Met, Gln90Leu) single nucleotide polymorphisms with eating disorders.

PubMed

Kindler, Jochen; Bailer, Ursula; de Zwaan, Martina; Fuchs, Karoline; Leisch, Friedrich; Grün, Bettina; Strnad, Alexandra; Stojanovic, Mirjana; Windisch, Julia; Lennkh-Wolfsberg, Claudia; El-Giamal, Nadja; Sieghart, Werner; Kasper, Siegfried; Aschauer, Harald

2011-06-01

Genetic factors likely contribute to the biological vulnerability of eating disorders. Case-control association study on one neuropeptide Y gene (Leu7Pro) polymorphism and three ghrelin gene (Arg51Gln, Leu72Met and Gln90Leu) polymorphisms. 114 eating disorder patients (46 with anorexia nervosa, 30 with bulimia nervosa, 38 with binge eating disorder) and 164 healthy controls were genotyped. No differences were detected between patients and controls for any of the four polymorphisms in allele frequency and genotype distribution (P > 0.05). Allele frequencies and genotypes had no significant influence on body mass index (P > 0.05) in eating disorder patients. Positive findings of former case-control studies of associations between ghrelin gene polymorphisms and eating disorders could not be replicated. Neuropeptide Y gene polymorphisms have not been investigated in eating disorders before.

Spin temperature concept verified by optical magnetometry of nuclear spins

NASA Astrophysics Data System (ADS)

Vladimirova, M.; Cronenberger, S.; Scalbert, D.; Ryzhov, I. I.; Zapasskii, V. S.; Kozlov, G. G.; Lemaître, A.; Kavokin, K. V.

2018-01-01

We develop a method of nonperturbative optical control over adiabatic remagnetization of the nuclear spin system and apply it to verify the spin temperature concept in GaAs microcavities. The nuclear spin system is shown to exactly follow the predictions of the spin temperature theory, despite the quadrupole interaction that was earlier reported to disrupt nuclear spin thermalization. These findings open a way for the deep cooling of nuclear spins in semiconductor structures, with the prospect of realizing nuclear spin-ordered states for high-fidelity spin-photon interfaces.

Ehrlichia chaffeensis Proliferation Begins with NtrY/NtrX and PutA/GlnA Upregulation and CtrA Degradation Induced by Proline and Glutamine Uptake

PubMed Central

Cheng, Zhihui; Lin, Mingqun

2014-01-01

ABSTRACT How the obligatory intracellular bacterium Ehrlichia chaffeensis begins to replicate upon entry into human monocytes is poorly understood. Here, we examined the potential role of amino acids in initiating intracellular replication. PutA converts proline to glutamate, and GlnA converts glutamate to glutamine. E. chaffeensis PutA and GlnA complemented Escherichia coli putA and glnA mutants. Methionine sulfoximine, a glutamine synthetase inhibitor, inhibited E. chaffeensis GlnA activity and E. chaffeensis infection of human cells. Incubation of E. chaffeensis with human cells rapidly induced putA and glnA expression that peaked at 24 h postincubation. E. chaffeensis took up proline and glutamine but not glutamate. Pretreatment of E. chaffeensis with a proline transporter inhibitor (protamine), a glutamine transporter inhibitor (histidine), or proline analogs inhibited E. chaffeensis infection, whereas pretreatment with proline or glutamine enhanced infection and upregulated putA and glnA faster than no treatment or glutamate pretreatment. The temporal response of putA and glnA expression was similar to that of NtrY and NtrX, a two-component system, and electrophoretic mobility shift assays showed specific binding of recombinant E. chaffeensis NtrX (rNtrX) to the promoter regions of E. chaffeensis putA and glnA. Furthermore, rNtrX transactivated E. chaffeensis putA and glnA promoter-lacZ fusions in E. coli. Growth-promoting activities of proline and glutamine were also accompanied by rapid degradation of the DNA-binding protein CtrA. Our results suggest that proline and glutamine uptake regulates putA and glnA expression through NtrY/NtrX and facilitates degradation of CtrA to initiate a new cycle of E. chaffeensis growth. PMID:25425236

Leptin receptor expression and Gln223Arg polymorphism as prognostic markers in oral and oropharyngeal cancer.

PubMed

Rodrigues, P R S; Maia, L L; Santos, M; Peterle, G T; Alves, L U; Takamori, J T; Souza, R P; Barbosa, W M; Mercante, A M C; Nunes, F D; Carvalho, M B; Tajara, E H; Louro, I D; Silva-Conforti, A M A

2015-11-25

The leptin gene product is released into the blood stream, passes through the blood-brain barrier, and finds the leptin receptor (LEPR) in the central nervous system. This hormone regulates food intake, hematopoiesis, inflammation, immunity, differentiation, and cell proliferation. The LEPR Gln223Arg polymorphism has been reported to alter receptor function and expression, both of which have been related with prognostics in several tumor types. Furthermore, several studies have shown a relationship between the Gln223Arg polymorphism and tumor development, and its role in oral and oropharyngeal squamous cell carcinoma is now well understood. In this study, 315 DNA samples were used for LEPR Gln223Arg genotyping and 87 primary oral and oropharyngeal squamous cell carcinomas were used for immunohistochemical expression analysis, such that a relationship between these and tumor development and prognosis could be established. Homozygous LEPR Arg223 was found to be associated with a 2-fold reduction in oral and oropharyngeal cancer risk. In contrast, the presence of the Arg223 allele in tumors was associated with worse disease-free and disease-specific survival. Low LEPR expression was found to be an independent risk factor, increasing the risk for lymph node metastasis 4-fold. In conclusion, the Gln223Arg polymorphism and LEPR expression might be valuable markers for oral and oropharyngeal cancer, suggesting that LEPR might serve as a potential target for future therapies.

Gln27Glu polymorphism in the beta2 adrenergic receptor gene and lipid metabolism during exercise in obese women.

PubMed

Macho-Azcarate, T; Marti, A; González, A; Martinez, J A; Ibañez, J

2002-11-01

The Glu27Glu genotype in the beta-2-adrenergic receptor (ADRB2) is associated with fat mass, body mass index and obesity in females. In our population, we previously found an association of higher body mass index (BMI) among women who reported more physical activity and carried the Glu27 allele as compared to non carriers with the same level of activity. To examine the lipid metabolism differences, both at rest and during submaximal exercise in ADRB2 Glu27Glu vs Gln27Gln obese women. Eight obese women with the Glu27Glu genotype (age, 43+/-5 y; body mass index (BMI), 31.7+/-0.9 kg/m(2); percentage fat mass, 42.0+/-1.3; WHR, 0.83+/-0.02; and VO(2max), 21.6+/-0.9 ml/kg/min) were compared with seven obese women with the Gln27Gln genotype (age, 43+/-5 y; BMI, 33.9+/-1.3 kg/m(2); percentage fat mass, 41.6+/-1.2; WHR, 0.83+/-0.02; and VO(2max), 20.6+/-0.8 ml/kg/min). The ADRB2 polymorphism was identified by PCR-RFLP. Respiratory quotient was determined by indirect calorimetry at baseline, during 1 h of walking on a treadmill and 1 h after the exercise. Plasma triglycerides, glycerol, FFA, hydroxybutyrate, glucose and lactate were assayed by spectrophotometric methods. Insulin, leptin and progesterone were measured by radioimmunoassay. Adrenaline and noradrenaline were quantified by high performance liquid chromatography. The ADRB2 Glu27Glu subjects had lower plasma glycerol (P=0.047) and lower hydroxybutyrate (P=0.001) throughout the study than the Gln27Gln group. Plasma triglycerides (P=0.001), lactate (P<0.05) and serum insulin (P<0.05) remained higher in the Glu27Glu group vs the Gln27Gln group. The respiratory quotient (RQ) was higher in the Glu27Glu obese women along the study (P=0.046), and fat oxidation was significantly lower in this group during the recovery (P=0.048). The other variables did not differ statistically between groups. These data suggest that both lipolysis and fat oxidation promoted by an acute submaximal exercise intervention could be blunted in

Design of spin-Seebeck diode with spin semiconductors.

PubMed

Zhang, Zhao-Qian; Yang, Yu-Rong; Fu, Hua-Hua; Wu, Ruqian

2016-12-16

We report a new design of spin-Seebeck diode using two-dimensional spin semiconductors such as sawtooth-like (ST) silicence nanoribbons (SiNRs), to generate unidirectional spin currents with a temperature gradient. ST SiNRs have subbands with opposite spins across the Fermi level and hence the flow of thermally excited carriers may produce a net spin current but not charge current. Moreover, we found that even-width ST SiNRs display a remarkable negative differential thermoelectric resistance due to a charge-current compensation mechanism. In contrast, odd-width ST SiNRs manifest features of a thermoelectric diode and can be used to produce both charge and spin currents with temperature gradient. These findings can be extended to other spin semiconductors and open the door for designs of new materials and spin caloritronic devices.

A dual-specific Glu-tRNA(Gln) and Asp-tRNA(Asn) amidotransferase is involved in decoding glutamine and asparagine codons in Acidithiobacillus ferrooxidans.

PubMed

Salazar, J C; Zúñiga, R; Raczniak, G; Becker, H; Söll, D; Orellana, O

2001-07-06

The gatC, gatA and gatB genes encoding the three subunits of glutamyl-tRNA(Gln) amidotransferase from Acidithiobacillus ferrooxidans, an acidophilic bacterium used in bioleaching of minerals, have been cloned and expressed in Escherichia coli. As in Bacillus subtilis the three gat genes are organized in an operon-like structure in A. ferrooxidans. The heterologously overexpressed enzyme converts Glu-tRNA(Gln) to Gln-tRNA(Gln) and Asp-tRNA(Asn) to Asn-tRNA(Asn). Biochemical analysis revealed that neither glutaminyl-tRNA synthetase nor asparaginyl-tRNA synthetase is present in A. ferrooxidans, but that glutamyl-tRNA synthetase and aspartyl-tRNA synthetase enzymes are present in the organism. These data suggest that the transamidation pathway is responsible for the formation of Gln-tRNA and Asn-tRNA in A. ferrooxidans.

Gln3p and Nil1p regulation of invertase activity and SUC2 expression in Saccharomyces cerevisiae.

PubMed

Oliveira, Edna Maria Morais; Mansure, José João; Bon, Elba Pinto da Silva

2005-04-01

In Saccharomyces cerevisiae, sensing and signalling pathways regulate gene expression in response to quality of carbon and nitrogen sources. One such system, the target of rapamycin (Tor) proteins, senses nutrients and uses the GATA activators Gln3p and Nil1p to regulate translation in response to low-quality carbon and nitrogen. The signal transduction, triggered in response to nitrogen nutrition that is sensed by the Tor proteins, operates via a regulatory pathway involving the cytoplasmic factor Ure2p. When carbon and nitrogen are abundant, the phosphorylated Ure2p anchors the also phosphorylated Gln3p and Nil1p in the cytoplasm. Upon a shift from high- to low-quality nitrogen or treatment with rapamycin all three proteins are dephosphorylated, causing Gln3p and Nil1p to enter the nucleus and promote transcription. The genes that code for yeast periplasmic enzymes with nutritional roles would be obvious targets for regulation by the sensing and signalling pathways that respond to quality of carbon and nitrogen sources. Indeed, previous results from our laboratory had shown that the GATA factors Gln3p, Nil1p, Dal80p, Nil2p and also the protein Ure2 regulate the expression of asparaginase II, coded by ASP3. We also had observed that the activity levels of the also periplasmic invertase, coded by SUC2, were 6-fold lower in ure2 mutant cells in comparison to wild-type cells collected at stationary phase. These results suggested similarities between the signalling pathways regulating the expression of ASP3 and SUC2. In the present work we showed that invertase levels displayed by the single nil1 and gln3 and by the double gln3nil1 mutant cells, cultivated in a sucrose-ammonium medium and collected at the exponential phase, were 6-, 10- and 60-fold higher, respectively, in comparison to their wild-type counterparts. RT-PCR data of SUC2 expression in the double-mutant cells indicated a 10-fold increase in the mRNA(SUC2) levels.

Spin filter for arbitrary spins by substrate engineering

NASA Astrophysics Data System (ADS)

Pal, Biplab; Römer, Rudolf A.; Chakrabarti, Arunava

2016-08-01

We design spin filters for particles with potentially arbitrary spin S≤ft(=1/2,1,3/2,\\ldots \\right) using a one-dimensional periodic chain of magnetic atoms as a quantum device. Describing the system within a tight-binding formalism we present an analytical method to unravel the analogy between a one-dimensional magnetic chain and a multi-strand ladder network. This analogy is crucial, and is subsequently exploited to engineer gaps in the energy spectrum by an appropriate choice of the magnetic substrate. We obtain an exact correlation between the magnitude of the spin of the incoming beam of particles and the magnetic moment of the substrate atoms in the chain desired for opening up of a spectral gap. Results of spin polarized transport, calculated within a transfer matrix formalism, are presented for particles having half-integer as well as higher spin states. We find that the chain can be made to act as a quantum device which opens a transmission window only for selected spin components over certain ranges of the Fermi energy, blocking them in the remaining part of the spectrum. The results appear to be robust even when the choice of the substrate atoms deviates substantially from the ideal situation, as verified by extending the ideas to the case of a ‘spin spiral’. Interestingly, the spin spiral geometry, apart from exhibiting the filtering effect, is also seen to act as a device flipping spins—an effect that can be monitored by an interplay of the system size and the period of the spiral. Our scheme is applicable to ultracold quantum gases, and might inspire future experiments in this direction.

XRCC1 Arg399Gln was associated with repair capacity for DNA damage induced by occupational chromium exposure

PubMed Central

2012-01-01

Background Occupational chromium exposure may induce DNA damage and lead to lung cancer and other work-related diseases. DNA repair gene polymorphisms, which may alter the efficiency of DNA repair, thus may contribute to genetic susceptibility of DNA damage. The aim of this study was to test the hypothesis that the genetic variations of 9 major DNA repair genes could modulate the hexavalent chromium (Cr (VI))-induced DNA damage. Findings The median (P25-P75) of Olive tail moment was 0.93 (0.58–1.79) for individuals carrying GG genotype of XRCC1 Arg399Gln (G/A), 0.73 (0.46–1.35) for GA heterozygote and 0.50 (0.43–0.93) for AA genotype. Significant difference was found among the subjects with three different genotypes (P = 0.048) after adjusting the confounding factors. The median of Olive tail moment of the subjects carrying A allele (the genotypes of AA and GA) was 0.66 (0.44–1.31), which was significantly lower than that of subjects with GG genotype (P = 0.043). The A allele conferred a significantly reduced risk of DNA damage with the OR of 0.39 (95% CI: 0.15–0.99, P = 0.048). No significant association was found between the XRCC1Arg194Trp, ERCC1 C8092A, ERCC5 His1104Asp, ERCC6 Gly399Asp, GSTP1 Ile105Val, OGG1 Ser326Cys, XPC Lys939Gln, XPD Lys751Gln and DNA damage. Conclusion The polymorphism of Arg399Gln in XRCC1 was associated with the Cr (VI)- induced DNA damage. XRCC1 Arg399Gln may serve as a genetic biomarker of susceptibility for Cr (VI)- induced DNA damage. PMID:22642904

Spin-dependent optimized effective potential formalism for open and closed systems

NASA Astrophysics Data System (ADS)

Rigamonti, S.; Horowitz, C. M.; Proetto, C. R.

2015-12-01

Orbital-based exchange (x ) correlation (c ) energy functionals, leading to the optimized effective potential (OEP) formalism of density-functional theory (DFT), are gaining increasing importance in ground-state DFT, as applied to the calculation of the electronic structure of closed systems with a fixed number of particles, such as atoms and molecules. These types of functionals prove also to be extremely valuable for dealing with solid-state systems with reduced dimensionality, such as is the case of electrons trapped at the interface between two different semiconductors, or narrow metallic slabs. In both cases, electrons build a quasi-two-dimensional electron gas, or Q2DEG. We provide here a general DFT-OEP formal scheme valid both for Q2DEGs either isolated (closed) or in contact with a particle bath (open), and show that both possible representations are equivalent, being the choice of one or the other essentially a question of convenience. Based on this equivalence, a calculation scheme is proposed which avoids the noninvertibility problem of the density response function for closed systems. We also consider the case of spontaneously spin-polarized Q2DEGs, and find that far from the region where the Q2DEG is localized, the exact x -only exchange potential approaches two different, spin-dependent asymptotic limits. As an example, aside from these formal results, we also provide numerical results for a spin-polarized jellium slab, using the new OEP formalism for closed systems. The accuracy of the Krieger-Li-Iafrate approximation has been also tested for the same system, and found to be as good as it is for atoms and molecules.

The Dual Regulatory Role of Amino Acids Leu480 and Gln481 of Prothrombin*

PubMed Central

Wiencek, Joesph R.; Hirbawi, Jamila; Yee, Vivien C.; Kalafatis, Michael

2016-01-01

Prothrombin (FII) is activated to α-thrombin (IIa) by prothrombinase. Prothrombinase is composed of a catalytic subunit, factor Xa (fXa), and a regulatory subunit, factor Va (fVa), assembled on a membrane surface in the presence of divalent metal ions. We constructed, expressed, and purified several mutated recombinant FII (rFII) molecules within the previously determined fVa-dependent binding site for fXa (amino acid region 473–487 of FII). rFII molecules bearing overlapping deletions within this significant region first established the minimal stretch of amino acids required for the fVa-dependent recognition exosite for fXa in prothrombinase within the amino acid sequence Ser478–Val479–Leu480–Gln481–Val482. Single, double, and triple point mutations within this stretch of rFII allowed for the identification of Leu480 and Gln481 as the two essential amino acids responsible for the enhanced activation of FII by prothrombinase. Unanticipated results demonstrated that although recombinant wild type α-thrombin and rIIaS478A were able to induce clotting and activate factor V and factor VIII with rates similar to the plasma-derived molecule, rIIaSLQ→AAA with mutations S478A/L480A/Q481A was deficient in clotting activity and unable to efficiently activate the pro-cofactors. This molecule was also impaired in protein C activation. Similar results were obtained with rIIaΔSLQ (where rIIaΔSLQ is recombinant human α-thrombin with amino acids Ser478/Leu480/Gln481 deleted). These data provide new evidence demonstrating that amino acid sequence Leu480–Gln481: 1) is crucial for proper recognition of the fVa-dependent site(s) for fXa within prothrombinase on FII, required for efficient initial cleavage of FII at Arg320; and 2) is compulsory for appropriate tethering of fV, fVIII, and protein C required for their timely activation by IIa. PMID:26601957

Enteral Arg-Gln Dipeptide Administration Increases Retinal Docosahexaenoic Acid and Neuroprotectin D1 in a Murine Model of Retinopathy of Prematurity

PubMed Central

Shaw, Lynn Calvin; Li Calzi, Sergio; Li, Nan; Moldovan, Leni; Sengupta-Caballero, Nilanjana; Quigley, Judith Lindsey; Ivan, Mircea; Jun, Bokkyoo; Bazan, Nicolas G.; Boulton, Michael Edwin; Busik, Julia; Neu, Josef; Grant, Maria B.

2018-01-01

Purpose Low levels of the long chain polyunsaturated fatty acid (LCPUFA) docosahexaenoic acid (DHA) have been implicated in retinopathy of prematurity (ROP). However, oral DHA suffers from poor palatability and is associated with increased bleeding in premature infants. We asked whether oral administration of the neutraceutical arginine-glutamine (Arg-Glu) could increase retinal DHA and improve outcomes in a mouse model of oxygen-induced retinopathy (OIR). Methods Postnatal day 7 (P7) pups were maintained at 75% oxygen for 5 days and then returned to room air on P12. Pups were gavaged twice daily with Arg-Gln or vehicle from P12 to P17 and eyes were harvested for analysis on P17. Vaso-obliteration and vascular density were assessed on retinal flat mounts and preretinal neovascularization was assessed on retinal cross sections. Retinas were used for measurement of DHA and 10,17S-docosatriene (neuroprotectin D1, NPD1), a key DHA-derived lipid, and for analysis by reverse-phase protein array (RPPA). Results With Arg-Gln treatment, retinal DHA and NPD1 levels were increased in OIR pups. Arg-Gln reduced preretinal neovascularization by 39 ± 6% (P < 0.05) relative to vehicle control. This was accompanied by a restoration of vascular density of the retina in the pups treated with Arg-Gln (73.0 ± 3.0%) compared to vehicle (53.1 ± 3.4%; P < 0.05). Arg-Gln dipeptide restored OIR-induced signaling changes toward normoxia and was associated with normalization of insulin-like growth factor receptor 1 signaling and reduction of apoptosis and an increase in anti-apoptosis proteins. Conclusions Arg-Gln may serve as a safer and easily tolerated nutraceutical agent for prevention or treatment of ROP. PMID:29490339

Enteral Arg-Gln Dipeptide Administration Increases Retinal Docosahexaenoic Acid and Neuroprotectin D1 in a Murine Model of Retinopathy of Prematurity.

PubMed

Shaw, Lynn Calvin; Li Calzi, Sergio; Li, Nan; Moldovan, Leni; Sengupta-Caballero, Nilanjana; Quigley, Judith Lindsey; Ivan, Mircea; Jun, Bokkyoo; Bazan, Nicolas G; Boulton, Michael Edwin; Busik, Julia; Neu, Josef; Grant, Maria B

2018-02-01

Low levels of the long chain polyunsaturated fatty acid (LCPUFA) docosahexaenoic acid (DHA) have been implicated in retinopathy of prematurity (ROP). However, oral DHA suffers from poor palatability and is associated with increased bleeding in premature infants. We asked whether oral administration of the neutraceutical arginine-glutamine (Arg-Glu) could increase retinal DHA and improve outcomes in a mouse model of oxygen-induced retinopathy (OIR). Postnatal day 7 (P7) pups were maintained at 75% oxygen for 5 days and then returned to room air on P12. Pups were gavaged twice daily with Arg-Gln or vehicle from P12 to P17 and eyes were harvested for analysis on P17. Vaso-obliteration and vascular density were assessed on retinal flat mounts and preretinal neovascularization was assessed on retinal cross sections. Retinas were used for measurement of DHA and 10,17S-docosatriene (neuroprotectin D1, NPD1), a key DHA-derived lipid, and for analysis by reverse-phase protein array (RPPA). With Arg-Gln treatment, retinal DHA and NPD1 levels were increased in OIR pups. Arg-Gln reduced preretinal neovascularization by 39 ± 6% (P < 0.05) relative to vehicle control. This was accompanied by a restoration of vascular density of the retina in the pups treated with Arg-Gln (73.0 ± 3.0%) compared to vehicle (53.1 ± 3.4%; P < 0.05). Arg-Gln dipeptide restored OIR-induced signaling changes toward normoxia and was associated with normalization of insulin-like growth factor receptor 1 signaling and reduction of apoptosis and an increase in anti-apoptosis proteins. Arg-Gln may serve as a safer and easily tolerated nutraceutical agent for prevention or treatment of ROP.

Tomograms for open quantum systems: In(finite) dimensional optical and spin systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thapliyal, Kishore, E-mail: tkishore36@yahoo.com; Banerjee, Subhashish, E-mail: subhashish@iitj.ac.in; Pathak, Anirban, E-mail: anirban.pathak@gmail.com

Tomograms are obtained as probability distributions and are used to reconstruct a quantum state from experimentally measured values. We study the evolution of tomograms for different quantum systems, both finite and infinite dimensional. In realistic experimental conditions, quantum states are exposed to the ambient environment and hence subject to effects like decoherence and dissipation, which are dealt with here, consistently, using the formalism of open quantum systems. This is extremely relevant from the perspective of experimental implementation and issues related to state reconstruction in quantum computation and communication. These considerations are also expected to affect the quasiprobability distribution obtained frommore » experimentally generated tomograms and nonclassicality observed from them. -- Highlights: •Tomograms are constructed for open quantum systems. •Finite and infinite dimensional quantum systems are studied. •Finite dimensional systems (phase states, single & two qubit spin states) are studied. •A dissipative harmonic oscillator is considered as an infinite dimensional system. •Both pure dephasing as well as dissipation effects are studied.« less

Analytic first derivatives for a spin-adapted open-shell coupled cluster theory: Evaluation of first-order electrical properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Datta, Dipayan, E-mail: datta@uni-mainz.de; Gauss, Jürgen, E-mail: gauss@uni-mainz.de

2014-09-14

An analytic scheme is presented for the evaluation of first derivatives of the energy for a unitary group based spin-adapted coupled cluster (CC) theory, namely, the combinatoric open-shell CC (COSCC) approach within the singles and doubles approximation. The widely used Lagrange multiplier approach is employed for the derivation of an analytical expression for the first derivative of the energy, which in combination with the well-established density-matrix formulation, is used for the computation of first-order electrical properties. Derivations of the spin-adapted lambda equations for determining the Lagrange multipliers and the expressions for the spin-free effective density matrices for the COSCC approachmore » are presented. Orbital-relaxation effects due to the electric-field perturbation are treated via the Z-vector technique. We present calculations of the dipole moments for a number of doublet radicals in their ground states using restricted open-shell Hartree-Fock (ROHF) and quasi-restricted HF (QRHF) orbitals in order to demonstrate the applicability of our analytic scheme for computing energy derivatives. We also report calculations of the chlorine electric-field gradients and nuclear quadrupole-coupling constants for the CCl, CH{sub 2}Cl, ClO{sub 2}, and SiCl radicals.« less

Demonstration of the spin solar cell and spin photodiode effect

PubMed Central

Endres, B.; Ciorga, M.; Schmid, M.; Utz, M.; Bougeard, D.; Weiss, D.; Bayreuther, G.; Back, C.H.

2013-01-01

Spin injection and extraction are at the core of semiconductor spintronics. Electrical injection is one method of choice for the creation of a sizeable spin polarization in a semiconductor, requiring especially tailored tunnel or Schottky barriers. Alternatively, optical orientation can be used to generate spins in semiconductors with significant spin-orbit interaction, if optical selection rules are obeyed, typically by using circularly polarized light at a well-defined wavelength. Here we introduce a novel concept for spin injection/extraction that combines the principle of a solar cell with the creation of spin accumulation. We demonstrate that efficient optical spin injection can be achieved with unpolarized light by illuminating a p-n junction where the p-type region consists of a ferromagnet. The discovered mechanism opens the window for the optical generation of a sizeable spin accumulation also in semiconductors without direct band gap such as Si or Ge. PMID:23820766

Tuning spin-spin interactions in radical dendrimers.

PubMed

Vidal-Gancedo, José; Lloveras, Vega; Liko, Flonja; Pinto, Luiz F; Muñoz-Gómez, Jose L

2018-05-10

Two generations of phosphorous dendrimers were synthesized and fully functionalized with TEMPO radicals via acrylamido or imino group linkers to evaluate the impact of the linker substitution on the radical-radical interactions. A drastic change in the way that the radicals interacted among them was observed by EPR and CV studies: while radicals in Gn-imino-TEMPO dendrimers presented a strong spin-spin interaction, in the Gn-acrylamido-TEMPO ones they acted mainly as independent radicals. This shows that these interactions could be tuned by the solely substitution of the radical linker, opening the perspective of controlling and modulating the extension of these interactions depending on each application. The chemical properties of the linker strongly influence the spin-spin exchange between pendant radicals. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Structure and thermodynamics of effector molecule binding to the nitrogen signal transduction PII protein GlnZ from Azospirillum brasilense.

PubMed

Truan, Daphné; Bjelić, Saša; Li, Xiao-Dan; Winkler, Fritz K

2014-07-29

The trimeric PII signal transduction proteins regulate the function of a variety of target proteins predominantly involved in nitrogen metabolism. ATP, ADP and 2-oxoglutarate (2-OG) are key effector molecules influencing PII binding to targets. Studies of PII proteins have established that the 20-residue T-loop plays a central role in effector sensing and target binding. However, the specific effects of effector binding on T-loop conformation have remained poorly documented. We present eight crystal structures of the Azospirillum brasilense PII protein GlnZ, six of which are cocrystallized and liganded with ADP or ATP. We find that interaction with the diphosphate moiety of bound ADP constrains the N-terminal part of the T-loop in a characteristic way that is maintained in ADP-promoted complexes with target proteins. In contrast, the interactions with the triphosphate moiety in ATP complexes are much more variable and no single predominant interaction mode is apparent except for the ternary MgATP/2-OG complex. These conclusions can be extended to most investigated PII proteins of the GlnB/GlnK subfamily. Unlike reported for other PII proteins, microcalorimetry reveals no cooperativity between the three binding sites of GlnZ trimers for any of the three effectors under carefully controlled experimental conditions. Copyright © 2014 Elsevier Ltd. All rights reserved.

Arg753gln and Arg677 Trp Polymorphisms of Toll-Like Receptor 2 In Acute Apical Abscess.

PubMed

Miri-Moghaddam, Ebrahim; Farhad Mollashahi, Narges; Naghibi, Nava; Garme, Yasaman; Bazi, Ali

2018-06-01

Genetic polymorphisms can alter immunity response against pathogens, which in turn influence individuals' susceptibility to certain infections. Our aim was to determine the association of Arg753Gln (rs5743708) and Arg677Trp (rs12191786) polymorphisms of toll like receptor-2 gene with the two clinical forms of apical periodontitis: acute apical abscess (AAA) and asymptomatic apical periodontitis (AAP). There were 50 patients with AAA as case group and 50 with AAP as control group. Genotyping was done using Tetra-ARMS (amplification refractory mutation system) PCR. Heterozygous genotype of Arg677Trp polymorphism was associated with risk of AAA (OR=1.9, 95% CI: 0.7-5.5, p = 0.05). Although statistically insignificant, Arg677Trp polymorphism promoted the risk of AAA in dominant model (OR=2.1, 95% CI: 0.7-5.9, p > 0.05). The frequency of mutant allele (T) of Arg677Trp polymorphism was higher in AAA (14%) than AAP (7%) subjects (OR=1.7, 95% CI: 0.6-4.7). For Arg753Gln polymorphism, wild homozygous (GG) represented the dominant genotype in both cases (96%) and controls (100%). Variant allele (A) of Arg753Gln polymorphism was identified in 2% of AAA, while no individual represented with this allele in AAP subjects. Individuals with Arg753Gln; Arg677Trp (GG; TC) combination showed an elevated risk of AAA (OR=1.6, 95% CI: 0.5- 4.2, p > 0.05). Arg677Trp polymorphism of TLR-2 rendered a higher risk for the development of abscesses in apical periodontitis. It is recommended to explore role of this polymorphism in other populations.

DNA Repair Gene (XRCC1) Polymorphism (Arg399Gln) Associated with Schizophrenia in South Indian Population: A Genotypic and Molecular Dynamics Study

PubMed Central

Sujitha, S. P.; Kumar, D. Thirumal; Doss, C. George Priya; Aavula, K.; Ramesh, R.; Lakshmanan, S.; Gunasekaran, S.; Anilkumar, G.

2016-01-01

This paper depicts the first report from an Indian population on the association between the variant Arg399Gln of XRCC1 locus in the DNA repair system and schizophrenia, the debilitating disease that affects 1% of the world population. Genotypic analysis of a total of 523 subjects (260 patients and 263 controls) revealed an overwhelming presence of Gln399Gln in the case subjects against the controls (P < 0.0068), indicating significant level of association of this nsSNP with schizophrenia; the Gln399 allele frequency was also perceptibly more in cases than in controls (p < 0.003; OR = 1.448). The results of the genotypic studies were further validated using pathogenicity and stability prediction analysis employing computational tools [I-Mutant Suite, iStable, PolyPhen2, SNAP, and PROVEAN], with a view toassess the magnitude of deleteriousness of the mutation. The pathogenicity analysis reveals that the nsSNP could be deleterious inasmuch as it could affect the functionality of the gene, and interfere with protein function. Molecular dynamics simulation of 60ns was performed using GROMACS to analyse structural change due to a mutation (Arg399Gln) that was never examined before. RMSD, RMSF, hydrogen bonds, radius of gyration and SASA analysis showedthe existence of asignificant difference between the native and the mutant protein. The present study gives astrong indication that the XRCC1 locus deserves serious attention, as it could be a potential candidatecontributing to the etio-pathogenesis of the disease. PMID:26824244

DNA Repair Gene (XRCC1) Polymorphism (Arg399Gln) Associated with Schizophrenia in South Indian Population: A Genotypic and Molecular Dynamics Study.

PubMed

Sujitha, S P; Kumar, D Thirumal; Doss, C George Priya; Aavula, K; Ramesh, R; Lakshmanan, S; Gunasekaran, S; Anilkumar, G

2016-01-01

This paper depicts the first report from an Indian population on the association between the variant Arg399Gln of XRCC1 locus in the DNA repair system and schizophrenia, the debilitating disease that affects 1% of the world population. Genotypic analysis of a total of 523 subjects (260 patients and 263 controls) revealed an overwhelming presence of Gln399Gln in the case subjects against the controls (P < 0.0068), indicating significant level of association of this nsSNP with schizophrenia; the Gln399 allele frequency was also perceptibly more in cases than in controls (p < 0.003; OR = 1.448). The results of the genotypic studies were further validated using pathogenicity and stability prediction analysis employing computational tools [I-Mutant Suite, iStable, PolyPhen2, SNAP, and PROVEAN], with a view toassess the magnitude of deleteriousness of the mutation. The pathogenicity analysis reveals that the nsSNP could be deleterious inasmuch as it could affect the functionality of the gene, and interfere with protein function. Molecular dynamics simulation of 60ns was performed using GROMACS to analyse structural change due to a mutation (Arg399Gln) that was never examined before. RMSD, RMSF, hydrogen bonds, radius of gyration and SASA analysis showedthe existence of asignificant difference between the native and the mutant protein. The present study gives astrong indication that the XRCC1 locus deserves serious attention, as it could be a potential candidatecontributing to the etio-pathogenesis of the disease.

Perspective: Interface generation of spin-orbit torques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sklenar, Joseph; Zhang, Wei; Jungfleisch, Matthias B.

We present that most of the modern spintronics developments rely on the manipulation of magnetization states via electric currents, which started with the discovery of spin transfer torque effects 20 years ago. By now, it has been realized that spin-orbit coupling provides a particularly efficient pathway for generating spin torques from charge currents. At the same time, spin-orbit effects can be enhanced at interfaces, which opens up novel device concepts. Here, we discuss two examples of such interfacial spin-orbit torques, namely, systems with inherently two-dimensional materials and metallic bilayers with strong Rashba spin-orbit coupling at their interfaces. We show howmore » ferromagnetic resonance excited by spin-orbit torques can provide information about the underlying mechanisms. In addition, this article provides a brief overview of recent developments with respect to interfacial spin-orbit torques and an outlook of still open questions.« less

Perspective: Interface generation of spin-orbit torques

DOE PAGES

Sklenar, Joseph; Zhang, Wei; Jungfleisch, Matthias B.; ...

2016-11-14

We present that most of the modern spintronics developments rely on the manipulation of magnetization states via electric currents, which started with the discovery of spin transfer torque effects 20 years ago. By now, it has been realized that spin-orbit coupling provides a particularly efficient pathway for generating spin torques from charge currents. At the same time, spin-orbit effects can be enhanced at interfaces, which opens up novel device concepts. Here, we discuss two examples of such interfacial spin-orbit torques, namely, systems with inherently two-dimensional materials and metallic bilayers with strong Rashba spin-orbit coupling at their interfaces. We show howmore » ferromagnetic resonance excited by spin-orbit torques can provide information about the underlying mechanisms. In addition, this article provides a brief overview of recent developments with respect to interfacial spin-orbit torques and an outlook of still open questions.« less

Spin caloric effects in antiferromagnets assisted by an external spin current

NASA Astrophysics Data System (ADS)

Gomonay, O.; Yamamoto, Kei; Sinova, Jairo

2018-07-01

Searching for novel spin caloric effects in antiferromagnets, we study the properties of thermally activated magnons in the presence of an external spin current and temperature gradient. We predict the spin Peltier effect—generation of a heat flux by spin accumulation—in an antiferromagnetic insulator with cubic or uniaxial magnetic symmetry. This effect is related to the spin-current induced splitting of the relaxation times of the magnons with the opposite spin direction. We show that the Peltier effect can trigger antiferromagnetic domain wall motion with a force whose value grows with the temperature of a sample. At a temperature larger than the energy of the low-frequency magnons, this force is much larger than the force caused by direct spin transfer between the spin current and the domain wall. We also demonstrate that the external spin current can induce the magnon spin Seebeck effect. The corresponding Seebeck coefficient is controlled by the current density. These spin-current assisted caloric effects open new ways for the manipulation of the magnetic states in antiferromagnets.

Beneficial effects of (pGlu-Gln)-CCK-8 on energy intake and metabolism in high fat fed mice are associated with alterations of hypothalamic gene expression.

PubMed

Montgomery, I A; Irwin, N; Flatt, P R

2013-06-01

Cholecystokinin (CCK) is a gastrointestinal hormone with potential therapeutic promise for obesity-diabetes. The present study examined the effects of twice daily administration of the N-terminally modified stable CCK-8 analogue, (pGlu-Gln)-CCK-8, on metabolic control and hypothalamic gene expression in high fat fed mice. Sub-chronic twice daily injection of (pGlu-Gln)-CCK-8 for 16 days significantly decreased body weight (p<0.05), energy intake (p<0.01), circulating blood glucose (p<0.001), and plasma insulin (p<0.001) compared to high fat controls. Furthermore, (pGlu-Gln)-CCK-8 markedly improved glucose tolerance (p<0.05) and insulin sensitivity (p<0.05). Assessment of hypothalamic gene expression on day 16 revealed significantly elevated NPY (p<0.05) and reduced POMC (p<0.05) and MC4R (p<0.05) mRNA expression in (pGlu-Gln)-CCK-8 treated mice. High fat feeding or (pGlu-Gln)-CCK-8 treatment had no significant effects on hypothalamic gene expression of receptors for leptin, CCK₁ and GLP-1. These studies underscore the potential of (pGlu-Gln)-CCK-8 for the treatment of obesity-diabetes and suggest modulation of NPY and melanocortin related pathways may be involved in the observed beneficial effects. © Georg Thieme Verlag KG Stuttgart · New York.

Graphene-based half-metal and spin-semiconductor for spintronic applications.

PubMed

Qi, Jingshan; Chen, Xiaofang; Hu, Kaige; Feng, Ji

2016-03-31

In this letter we propose a strategy to make graphene become a half-metal or spin-semiconductor by combining the magnetic proximity effects and sublattice symmetry breaking in graphone/graphene and graphone/graphene/BN heterostructures. Exchange interactions lift the spin degeneracy and sublattice symmetry breaking opens a band gap in graphene. More interestingly, the gap opening depends on the spin direction and the competition between the sublattice asymmetry and exchange field determines the system is a half-metal or a spin-semiconductor. By first-principles calculations and a low-energy effective model analysis, we elucidate the underlying physical mechanism of spin-dependent gap opening and spin degeneracy splitting. This offers an alternative practical platform for graphene-based spintronics.

Nitrogen Starvation and TorC1 Inhibition Differentially Affect Nuclear Localization of the Gln3 and Gat1 Transcription Factors Through the Rare Glutamine tRNACUG in Saccharomyces cerevisiae

PubMed Central

Tate, Jennifer J.; Rai, Rajendra; Cooper, Terrance G.

2015-01-01

A leucine, leucyl-tRNA synthetase–dependent pathway activates TorC1 kinase and its downstream stimulation of protein synthesis, a major nitrogen consumer. We previously demonstrated, however, that control of Gln3, a transcription activator of catabolic genes whose products generate the nitrogenous precursors for protein synthesis, is not subject to leucine-dependent TorC1 activation. This led us to conclude that excess nitrogen-dependent down-regulation of Gln3 occurs via a second mechanism that is independent of leucine-dependent TorC1 activation. A major site of Gln3 and Gat1 (another GATA-binding transcription activator) control occurs at their access to the nucleus. In excess nitrogen, Gln3 and Gat1 are sequestered in the cytoplasm in a Ure2-dependent manner. They become nuclear and activate transcription when nitrogen becomes limiting. Long-term nitrogen starvation and treatment of cells with the glutamine synthetase inhibitor methionine sulfoximine (Msx) also elicit nuclear Gln3 localization. The sensitivity of Gln3 localization to glutamine and inhibition of glutamine synthesis prompted us to investigate the effects of a glutamine tRNA mutation (sup70-65) on nitrogen-responsive control of Gln3 and Gat1. We found that nuclear Gln3 localization elicited by short- and long-term nitrogen starvation; growth in a poor, derepressive medium; Msx or rapamycin treatment; or ure2Δ mutation is abolished in a sup70-65 mutant. However, nuclear Gat1 localization, which also exhibits a glutamine tRNACUG requirement for its response to short-term nitrogen starvation or growth in proline medium or a ure2Δ mutation, does not require tRNACUG for its response to rapamycin. Also, in contrast with Gln3, Gat1 localization does not respond to long-term nitrogen starvation. These observations demonstrate the existence of a specific nitrogen-responsive component participating in the control of Gln3 and Gat1 localization and their downstream production of nitrogenous precursors

Full four-component relativistic calculations of the one-bond 77Se-13C spin-spin coupling constants in the series of selenium heterocycles and their parent open-chain selenides.

PubMed

Rusakov, Yury Yu; Rusakova, Irina L; Krivdin, Leonid B

2014-05-01

Four-component relativistic calculations of (77)Se-(13)C spin-spin coupling constants have been performed in the series of selenium heterocycles and their parent open-chain selenides. It has been found that relativistic effects play an essential role in the selenium-carbon coupling mechanism and could result in a contribution of as much as 15-25% of the total values of the one-bond selenium-carbon spin-spin coupling constants. In the overall contribution of the relativistic effects to the total values of (1)J(Se,C), the scalar relativistic corrections (negative in sign) by far dominate over the spin-orbit ones (positive in sign), the latter being of less than 5%, as compared to the former (ca 20%). A combination of nonrelativistic second-order polarization propagator approach (CC2) with the four-component relativistic density functional theory scheme is recommended as a versatile tool for the calculation of (1)J(Se,C). Solvent effects in the values of (1)J(Se,C) calculated within the polarizable continuum model for the solvents with different dielectric constants (ε 2.2-78.4) are next to negligible decreasing negative (1)J(Se,C) in absolute value by only about 1 Hz. The use of the locally dense basis set approach applied herewith for the calculation of (77)Se-(13)C spin-spin coupling constants is fully justified resulting in a dramatic decrease in computational cost with only 0.1-0.2-Hz loss of accuracy. Copyright © 2014 John Wiley & Sons, Ltd.

Arg753gln and Arg677 Trp Polymorphisms of Toll-Like Receptor 2 In Acute Apical Abscess

PubMed Central

Miri-Moghaddam, Ebrahim; Farhad Mollashahi, Narges; Naghibi, Nava; Garme, Yasaman; Bazi, Ali

2018-01-01

Statement of the Problem: Genetic polymorphisms can alter immunity response against pathogens, which in turn influence individuals’ susceptibility to certain infections. Purpose: Our aim was to determine the association of Arg753Gln (rs5743708) and Arg677Trp (rs12191786) polymorphisms of toll like receptor-2 gene with the two clinical forms of apical periodontitis: acute apical abscess (AAA) and asymptomatic apical periodontitis (AAP). Materials and Method: There were 50 patients with AAA as case group and 50 with AAP as control group. Genotyping was done using Tetra-ARMS (amplification refractory mutation system) PCR. Results: Heterozygous genotype of Arg677Trp polymorphism was associated with risk of AAA (OR=1.9, 95% CI: 0.7-5.5, p= 0.05). Although statistically insignificant, Arg677Trp polymorphism promoted the risk of AAA in dominant model (OR=2.1, 95% CI: 0.7-5.9, p> 0.05). The frequency of mutant allele (T) of Arg677Trp polymorphism was higher in AAA (14%) than AAP (7%) subjects (OR=1.7, 95% CI: 0.6-4.7). For Arg753Gln polymorphism, wild homozygous (GG) represented the dominant genotype in both cases (96%) and controls (100%). Variant allele (A) of Arg753Gln polymorphism was identified in 2% of AAA, while no individual represented with this allele in AAP subjects. Individuals with Arg753Gln; Arg677Trp (GG; TC) combination showed an elevated risk of AAA (OR=1.6, 95% CI: 0.5- 4.2, p> 0.05). Conclusion: Arg677Trp polymorphism of TLR-2 rendered a higher risk for the development of abscesses in apical periodontitis. It is recommended to explore role of this polymorphism in other populations. PMID:29854884

Surveying the quantum group symmetries of integrable open spin chains

NASA Astrophysics Data System (ADS)

Nepomechie, Rafael I.; Retore, Ana L.

2018-05-01

Using anisotropic R-matrices associated with affine Lie algebras g ˆ (specifically, A2n(2), A2n-1 (2) , Bn(1), Cn(1), Dn(1)) and suitable corresponding K-matrices, we construct families of integrable open quantum spin chains of finite length, whose transfer matrices are invariant under the quantum group corresponding to removing one node from the Dynkin diagram of g ˆ . We show that these transfer matrices also have a duality symmetry (for the cases Cn(1) and Dn(1)) and additional Z2 symmetries that map complex representations to their conjugates (for the cases A2n-1 (2) , Bn(1) and Dn(1)). A key simplification is achieved by working in a certain "unitary" gauge, in which only the unbroken symmetry generators appear. The proofs of these symmetries rely on some new properties of the R-matrices. We use these symmetries to explain the degeneracies of the transfer matrices.

XPD Asp312Asn and Lys751Gln polymorphisms and breast cancer susceptibility: a meta-analysis.

PubMed

Yan, Yulan; Liang, Hongjie; Light, Morning; Li, Taijie; Deng, Yan; Li, Meng; Li, Shan; Qin, Xue

2014-03-01

The association between xeroderma pigmentosum complementation group D (XPD) Asp312Asn and Lys751Gln gene polymorphisms and breast cancer risk has been widely reported, but the results were inconsistent. In order to derive a more precise estimation of the relationship, a meta-analysis was performed. A comprehensive search strategy was conducted towards the electronic databases including Medline, PubMed, Web of Science, Embase, and Chinese Biomedical Literature Database (Chinese). The association between the XPD polymorphism and breast cancer risk was conducted by odds ratios (ORs) and 95% confidence intervals (95% CIs). A total of 22 studies with 18,136 cases and 18,351 controls were included in our meta-analysis. Among these, 12 studies with 7,667 cases and 7,480 controls for Asp312Asn polymorphism and 20 studies with 10,469 cases and 10,871 controls for Lys751Gln polymorphism. With regard to Asp312Asn polymorphism, no significantly associated was found with breast cancer risk. However, significant association was found between Lys751Gln polymorphism and breast cancer risk under all genetic models in overall populations (C vs. A-OR = 1.10, 95% CI = 1.04-1.17, P = 0.002; CC vs. AA-OR = 1.17, 95% CI = 1.06-1.30, P = 0.003; AC vs. AA-OR = 1.06, 95% CI = 1.01-1.12, P = 0.032; CC vs. AC/AA-OR = 1.17, 95% CI = 1.04-1.32, P = 0.009; CC/AC vs. AA-OR = 1.07, 95% CI = 1.02-1.12, P = 0.005). In subgroup analysis base on ethnicity, significance was found in Caucasians and mix. The results suggest that XPD Asp312Asn polymorphism was not associated with breast cancer. The XPD Lys751Gln polymorphism significantly increased breast cancer risk, especially for Caucasian and mix.

A phase II study of HMB/Arg/Gln against oral mucositis induced by chemoradiotherapy for patients with head and neck cancer.

PubMed

Yokota, Tomoya; Hamauchi, Satoshi; Yoshida, Yukio; Yurikusa, Takashi; Suzuki, Miho; Yamashita, Aiko; Ogawa, Hirofumi; Onoe, Tsuyoshi; Mori, Keita; Onitsuka, Tetsuro

2018-04-07

This phase II trial assessed the clinical benefit of beta-hydroxy-beta-methylbutyrate, arginine, and glutamine (HMB/Arg/Gln) for preventing chemoradiotherapy (CRT)-induced oral mucositis (OM) in patients with head and neck cancer (HNC). Patients with HNC receiving definitive or postoperative cisplatin-based CRT were enrolled. HMB/Arg/Gln was administered orally or per percutaneous endoscopic gastrostomy from the first day of CRT up to its completion. All patients received opioid-based pain control and oral care programs that we previously reported. The primary endpoint was the incidence of grade ≥ 3 OM (functional/symptomatic) according to the Common Terminology Criteria of Adverse Events version 3.0. Quality of life (EORTC QLQ-C30/PROMS) at baseline and upon radiotherapy at a dosage of 50 Gy were assessed. Thirty-five patients with HNC were enrolled. Sixteen of them (45.7%) developed grade ≥ 3 OM (i.e., functional/symptomatic). The incidence of grade ≤ 1 OM (functional/symptomatic) was 51.5% at 2 weeks and 82.9% at 4 weeks after radiotherapy completion. Clinical examination revealed that 10 patients (28.6%) developed grade ≥ 3 OM. The incidence of grade ≤ 1 OM (clinical exam) was 80.0% at 2 weeks and 100% at 4 weeks after radiotherapy completion. Adverse events related to HMB/Arg/Gln were an increase in blood urea nitrogen and diarrhea, but were easily managed. The addition of HMB/Arg/Gln to opioid-based pain control and oral care programs was feasible but still insufficient at reducing the incidence of CRT-induced severe OM. However, the benefit of HMB/Arg/Gln should not be neglected given the findings of clinical examinations and the rapid recovery from severe OM. UMIN000016453.

[Correlation of polymorphisms of adiponectin receptor 2 gene +33371Gln/Arg, cytochrome P4502E1 gene Rsa I and smoking with nonalcoholic fatty liver disease].

PubMed

Zhang, Chaoxian; Guo, Like

2014-10-01

To investigate the correlation of the polymorphisms of adiponectin receptor 2 (AdipoR2) gene +33371Gln/;Arg and cytochromes P4502E1 gene Rsa I (CYP2E1-Rsa I) as well as smoking with nonalcoholic fatty liver disease (NAFLD). The polymorphisms of AdipoR2 gene +33371Gln/Arg and CYP2E1-Rsa I were analyzed with PCR technique in peripheral blood leukocytes from 750 NAFLD cases and 750 healthy subjects. The frequencies of AdipoR2 gene +33371Gln/Arg (A/A) and CYP2E1-Rsa I (c2/c2 ) were 39.20% and 71.73% in NAFLD cases, respectively, significantly higher than those in healthy subjects (21.07% and 43.07%, respectively, P<0.01). The risk of NAFLD increased significantly in subjects carrying +33371Gln/Arg (A/A) (OR=2.4156, 95% CI=1.8164-4.0725) and CYP2E1-Rsa I (c2/c2) (OR=3.3547, 95% CI=1.9182-4.5057). Combined analysis of the polymorphisms showed that the percentage of +33371Gln/Arg (A/A)/CYP2E1-Rsa I (c2/c2) was 32. 67% in NAFLD cases, significantly higher than that in the healthy subjects (6.40%, P<0.01), and subjects carrying both +33371Gln/Arg (A/A) and CYP2E1-Rsa I (c2/c2) had a high risk of NAFLD (OR=9.9264, 95% CI=4.2928-12.4241). The smoking rate was significantly higher in the case group than in the control group (OR=2.5919, 95% CI=1.4194-4. 9527, P<0.01), and statistical analysis suggested an interaction between smoking and +33371Gln/Arg (A/A)/CYP2E1-Rsa I (c2/c2) to increase the risk of NAFLD (OR=34.6764, 95% CI=18.9076-61.5825). +33371Gln/Arg (A/A), CYP2E1-Rsa I (c2/c2 ) and smoking are risk factors for NAFLD and coordinately contribute to the occurrence of NAFLD.

Identification and functional characterization of NifA variants that are independent of GlnB activation in the photosynthetic bacterium Rhodospirillum rubrum.

PubMed

Zou, Xiaoxiao; Zhu, Yu; Pohlmann, Edward L; Li, Jilun; Zhang, Yaoping; Roberts, Gary P

2008-09-01

The activity of NifA, the transcriptional activator of the nitrogen fixation (nif) gene, is tightly regulated in response to ammonium and oxygen. However, the mechanisms for the regulation of NifA activity are quite different among various nitrogen-fixing bacteria. Unlike the well-studied NifL-NifA regulatory systems in Klebsiella pneumoniae and Azotobacter vinelandii, in Rhodospirillum rubrum NifA is activated by a direct protein-protein interaction with the uridylylated form of GlnB, which in turn causes a conformational change in NifA. We report the identification of several substitutions in the N-terminal GAF domain of R. rubrum NifA that allow NifA to be activated in the absence of GlnB. Presumably these substitutions cause conformational changes in NifA necessary for activation, without interaction with GlnB. We also found that wild-type NifA can be activated in a GlnB-independent manner under certain growth conditions, suggesting that some other effector(s) can also activate NifA. An attempt to use Tn5 mutagenesis to obtain mutants that altered the pool of these presumptive effector(s) failed, though much rarer spontaneous mutations in nifA were detected. This suggests that the necessary alteration of the pool of effector(s) for NifA activation cannot be obtained by knockout mutations.

Nitrogen-responsive Regulation of GATA Protein Family Activators Gln3 and Gat1 Occurs by Two Distinct Pathways, One Inhibited by Rapamycin and the Other by Methionine Sulfoximine*

PubMed Central

Georis, Isabelle; Tate, Jennifer J.; Cooper, Terrance G.; Dubois, Evelyne

2011-01-01

Nitrogen availability regulates the transcription of genes required to degrade non-preferentially utilized nitrogen sources by governing the localization and function of transcription activators, Gln3 and Gat1. TorC1 inhibitor, rapamycin (Rap), and glutamine synthetase inhibitor, methionine sulfoximine (Msx), elicit responses grossly similar to those of limiting nitrogen, implicating both glutamine synthesis and TorC1 in the regulation of Gln3 and Gat1. To better understand this regulation, we compared Msx- versus Rap-elicited Gln3 and Gat1 localization, their DNA binding, nitrogen catabolite repression-sensitive gene expression, and the TorC1 pathway phosphatase requirements for these responses. Using this information we queried whether Rap and Msx inhibit sequential steps in a single, linear cascade connecting glutamine availability to Gln3 and Gat1 control as currently accepted or alternatively inhibit steps in two distinct parallel pathways. We find that Rap most strongly elicits nuclear Gat1 localization and expression of genes whose transcription is most Gat1-dependent. Msx, on the other hand, elicits nuclear Gln3 but not Gat1 localization and expression of genes that are most Gln3-dependent. Importantly, Rap-elicited nuclear Gln3 localization is absolutely Sit4-dependent, but that elicited by Msx is not. PP2A, although not always required for nuclear GATA factor localization, is highly required for GATA factor binding to nitrogen-responsive promoters and subsequent transcription irrespective of the gene GATA factor specificities. Collectively, our data support the existence of two different nitrogen-responsive regulatory pathways, one inhibited by Msx and the other by rapamycin. PMID:22039046

Nitrogen-responsive regulation of GATA protein family activators Gln3 and Gat1 occurs by two distinct pathways, one inhibited by rapamycin and the other by methionine sulfoximine.

PubMed

Georis, Isabelle; Tate, Jennifer J; Cooper, Terrance G; Dubois, Evelyne

2011-12-30

Nitrogen availability regulates the transcription of genes required to degrade non-preferentially utilized nitrogen sources by governing the localization and function of transcription activators, Gln3 and Gat1. TorC1 inhibitor, rapamycin (Rap), and glutamine synthetase inhibitor, methionine sulfoximine (Msx), elicit responses grossly similar to those of limiting nitrogen, implicating both glutamine synthesis and TorC1 in the regulation of Gln3 and Gat1. To better understand this regulation, we compared Msx- versus Rap-elicited Gln3 and Gat1 localization, their DNA binding, nitrogen catabolite repression-sensitive gene expression, and the TorC1 pathway phosphatase requirements for these responses. Using this information we queried whether Rap and Msx inhibit sequential steps in a single, linear cascade connecting glutamine availability to Gln3 and Gat1 control as currently accepted or alternatively inhibit steps in two distinct parallel pathways. We find that Rap most strongly elicits nuclear Gat1 localization and expression of genes whose transcription is most Gat1-dependent. Msx, on the other hand, elicits nuclear Gln3 but not Gat1 localization and expression of genes that are most Gln3-dependent. Importantly, Rap-elicited nuclear Gln3 localization is absolutely Sit4-dependent, but that elicited by Msx is not. PP2A, although not always required for nuclear GATA factor localization, is highly required for GATA factor binding to nitrogen-responsive promoters and subsequent transcription irrespective of the gene GATA factor specificities. Collectively, our data support the existence of two different nitrogen-responsive regulatory pathways, one inhibited by Msx and the other by rapamycin.

Detection of Short-Waved Spin Waves in Individual Microscopic Spin-Wave Waveguides Using the Inverse Spin Hall Effect.

PubMed

Brächer, T; Fabre, M; Meyer, T; Fischer, T; Auffret, S; Boulle, O; Ebels, U; Pirro, P; Gaudin, G

2017-12-13

The miniaturization of complementary metal-oxide-semiconductor (CMOS) devices becomes increasingly difficult due to fundamental limitations and the increase of leakage currents. Large research efforts are devoted to find alternative concepts that allow for a larger data-density and lower power consumption than conventional semiconductor approaches. Spin waves have been identified as a potential technology that can complement and outperform CMOS in complex logic applications, profiting from the fact that these waves enable wave computing on the nanoscale. The practical application of spin waves, however, requires the demonstration of scalable, CMOS compatible spin-wave detection schemes in material systems compatible with standard spintronics as well as semiconductor circuitry. Here, we report on the wave-vector independent detection of short-waved spin waves with wavelengths down to 150 nm by the inverse spin Hall effect in spin-wave waveguides made from ultrathin Ta/Co 8 Fe 72 B 20 /MgO. These findings open up the path for miniaturized scalable interconnects between spin waves and CMOS and the use of ultrathin films made from standard spintronic materials in magnonics.

Excitation of propagating spin waves by pure spin current

NASA Astrophysics Data System (ADS)

Demokritov, Sergej

Recently it was demonstrated that pure spin currents can be utilized to excite coherent magnetization dynamics, which enables development of novel magnetic nano-oscillators. Such oscillators do not require electric current flow through the active magnetic layer, which can help to reduce the Joule power dissipation and electromigration. In addition, this allows one to use insulating magnetic materials and provides an unprecedented geometric flexibility. The pure spin currents can be produced by using the spin-Hall effect (SHE). However, SHE devices have a number of shortcomings. In particular, efficient spin Hall materials exhibit a high resistivity, resulting in the shunting of the driving current through the active magnetic layer and a significant Joule heating. These shortcomings can be eliminated in devices that utilize spin current generated by the nonlocal spin-injection (NLSI) mechanism. Here we review our recent studies of excitation of magnetization dynamics and propagating spin waves by using NLSI. We show that NLSI devices exhibit highly-coherent dynamics resulting in the oscillation linewidth of a few MHz at room temperature. Thanks to the geometrical flexibility of the NLSI oscillators, one can utilize dipolar fields in magnetic nano-patterns to convert current-induced localized oscillations into propagating spin waves. The demonstrated systems exhibit efficient and controllable excitation and directional propagation of coherent spin waves characterized by a large decay length. The obtained results open new perspectives for the future-generation electronics using electron spin degree of freedom for transmission and processing of information on the nanoscale.

Polymorphism of DNA repair gene XPD Lys751Gln and chromosome aberrations in lymphocytes of thyroid cancer patients exposed to ionizing radiation due to the Chornobyl accident.

PubMed

Shkarupa, V M; Mishcheniuk, O Y; Henyk-Berezovska, S O; Palamarchuk, V O; Klymenko, S V

2016-12-01

The aim of this work was to analyze the relationship between polymorphisms of DNA repair gene XPD Lys751Gln and frequency and spectrum of chromosome aberrations in the culture of peripheral blood lymphocytes of thyroid cancer (TC) patients having been exposed to ionizing radiation due to the Chornobyl accident. XPD Lys751Gln polymorphisms were detected by polymerase chain reaction in 102 TC patients including 38 patients exposed to ionizing radiation due to Chornobyl disaster (Chornobyl recovery workers, evacuees, and the residents of contaminated areas), 64 patients without history of ionizing radiation exposure and 45 healthy residents of Ukraine as control group. In homozygous carriers of the minor allele XPD Gln751Gln, exposed to ionizing radiation, the significantly increased risk of TC (odds ratio = 3.66; p = 0.03; 95% confidence interval 1.04-12.84) was found. Among evacuees and residents of contaminated areas, homozygous carriers of the minor allele variants of XPD gene were characterized by the high level of spontaneous chromosome aberrations. TC patients without history of ionizing radiation exposure, being homozygous carriers of the allele XPD Lys751Lys, had significantly reduced frequency of chromosome-type aberrations. The carriage of homozygous minor allele of DNA repair gene XPD Gln751Gln is a risk factor for TC in persons from Ukrainian population exposed to ionizing radiation and is associated with the increased levels of chromosomal instability. This article is a part of a Special Issue entitled "The Chornobyl Nuclear Accident: Thirty Years After".

Glutamyl-gamma-boronate inhibitors of bacterial Glu-tRNA(Gln) amidotransferase.

PubMed

Decicco, C P; Nelson, D J; Luo, Y; Shen, L; Horiuchi, K Y; Amsler, K M; Foster, L A; Spitz, S M; Merrill, J J; Sizemore, C F; Rogers, K C; Copeland, R A; Harpel, M R

2001-09-17

Analogues of glutamyl-gamma-boronate (1) were synthesized as mechanism-based inhibitors of bacterial Glu-tRNA(Gln) amidotransferase (Glu-AdT) and were designed to engage a putative catalytic serine nucleophile required for the glutaminase activity of the enzyme. Although 1 provides potent enzyme inhibition, structure-activity studies revealed a narrow range of tolerated chemical changes that maintained activity. Nonetheless, growth inhibition of organisms that require Glu-AdT by the most potent enzyme inhibitors appears to validate mechanism-based inhibitor design of Glu-AdT as an approach to antimicrobial development.

Ultrafast spintronics roadmap: from femtosecond spin current pulses to terahertz non-uniform spin dynamics via nano-confined spin transfer torques (Conference Presentation)

NASA Astrophysics Data System (ADS)

Melnikov, Alexey; Razdolski, Ilya; Alekhin, Alexandr; Ilin, Nikita; Meyburg, Jan; Diesing, Detlef; Roddatis, Vladimir; Rungger, Ivan; Stamenova, Maria; Sanvito, Stefano; Bovensiepen, Uwe

2016-10-01

Further development of spintronics requires miniaturization and reduction of characteristic timescales of spin dynamics combining the nanometer spatial and femtosecond temporal ranges. These demands shift the focus of interest towards the fundamental open question of the interaction of femtosecond spin current (SC) pulses with a ferromagnet (FM). The spatio-temporal properties of the spin transfer torque (STT) exerted by ultrashort SC pulses on the FM open the time domain for studying STT fingerprint on spatially non-uniform magnetization dynamics. Using the sensitivity of magneto-induced second harmonic generation to SC, we develop technique for SC monitoring. With 20 fs resolution, we demonstrate the generation of 250 fs-long SC pulses in Fe/Au/Fe/MgO(001) structures. Their temporal profile indicates (i) nearly-ballistic hot electron transport in Au and (ii) that the pulse duration is primarily determined by the thermalization time of laser-excited hot carriers in Fe. Together with strongly spin-dependent Fe/Au interface transmission calculated for these carriers, this suggests the non-thermal spin-dependent Seebeck effect dominating the generation of ultrashort SC pulses. The analysis of SC transmission/reflection at the Au/Fe interface shows that hot electron spins orthogonal to the Fe magnetization rotate gaining huge parallel (anti-parallel) projection in transmitted (reflected) SC. This is accompanied by a STT-induced perturbation of the magnetization localized at the interface, which excites the inhomogeneous high-frequency spin dynamics in the FM. Time-resolved magneto-optical studies reveal the excitation of several standing spin wave modes in the Fe film with their spectrum extending up to 0.6 THz and indicating the STT spatial confinement to 2 nm.

Nonlinear spin conductance of yttrium iron garnet thin films driven by large spin-orbit torque

NASA Astrophysics Data System (ADS)

Thiery, N.; Draveny, A.; Naletov, V. V.; Vila, L.; Attané, J. P.; Beigné, C.; de Loubens, G.; Viret, M.; Beaulieu, N.; Ben Youssef, J.; Demidov, V. E.; Demokritov, S. O.; Slavin, A. N.; Tiberkevich, V. S.; Anane, A.; Bortolotti, P.; Cros, V.; Klein, O.

2018-02-01

We report high power spin transfer studies in open magnetic geometries by measuring the spin conductance between two nearby Pt wires deposited on top of an epitaxial yttrium iron garnet thin film. Spin transport is provided by propagating spin waves that are generated and detected by direct and inverse spin Hall effects. We observe a crossover in spin conductance from a linear transport dominated by exchange magnons (low current regime) to a nonlinear transport dominated by magnetostatic magnons (high current regime). The latter are low-damping magnetic excitations, located near the spectral bottom of the magnon manifold, with a sensitivity to the applied magnetic field. This picture is supported by microfocus Brillouin light-scattering spectroscopy. Our findings could be used for the development of controllable spin conductors by variation of relatively weak magnetic fields.

The Impact of LEP G-2548A and LEPR Gln223Arg Polymorphisms on Adiposity, Leptin, and Leptin-Receptor Serum Levels in a Mexican Mestizo Population.

PubMed

Chavarria-Avila, Efraín; Vázquez-Del Mercado, Mónica; Gomez-Bañuelos, Eduardo; Ruiz-Quezada, Sandra-Luz; Castro-Albarran, Jorge; Sánchez-López, Lizeth; Martín-Marquez, Beatriz Teresita; Navarro-Hernández, Rosa-Elena

2015-01-01

The polymorphisms in leptin (LEP G-2548A) and leptin-receptor (LEPR Gln223Arg) seem to influence obesity and lipid metabolism among others. The aim of this study was to investigate the effect of these polymorphisms on adiposity, leptin (sLeptin), and leptin-receptor (sLeptin-receptor) serum concentrations as well as inflammation markers. We included 382 adults originally from Western Mexico. They were genotyped by PCR-RFLP. Obese individuals showed higher sLeptin (58.2 ± 31.35 ng/mL) but lower sLeptin-receptor (12.6 ± 3.74 ng/mL) levels than normal weight ones (17.6 ± 14.62 ng/mL, 17.4 ± 4.62 ng/mL, resp.), P < 0.001. Obese subjects carriers of Arg/Arg genotype had more (P = 0.016) sLeptin-receptor (14.7 ± 4.96 ng/mL) and less (P = 0.004) sLeptin (44.0 ± 28.12 ng/mL) levels than Gln/Gln genotype (11.0 ± 2.92 ng/mL, 80.3 ± 33.24 ng/mL, resp.). Body fat mass was lower (P from 0.003 to 0.045) for A/A (36.5% ± 6.80) or Arg/Arg (36.8% ± 6.82) genotypes with respect to G/G (41.3% ± 5.52) and G/A (41.6% ± 5.61) or Gln/Gln (43.7% ± 4.74) and Gln/Arg (41.0% ± 5.52) genotypes carriers. Our results suggest that LEP -2548A and LEPR 223Arg could be genetic markers of less body fat mass accumulation in obese subjects from Western Mexico.

Analysis of Gln223Agr polymorphism of Leptin Receptor Gene in type II diabetic mellitus subjects among Malaysians.

PubMed

Etemad, Ali; Ramachandran, Vasudevan; Pishva, Seyyed Reza; Heidari, Farzad; Aziz, Ahmad Fazli Abdul; Yusof, Ahmad Khairuddin Mohamed; Pei, Chong Pei; Ismail, Patimah

2013-09-18

Leptin is known as the adipose peptide hormone. It plays an important role in the regulation of body fat and inhibits food intake by its action. Moreover, it is believed that leptin level deductions might be the cause of obesity and may play an important role in the development of Type 2 Diabetes Mellitus (T2DM), as well as in cardiovascular diseases (CVD). The Leptin Receptor (LEPR) gene and its polymorphisms have not been extensively studied in relation to the T2DM and its complications in various populations. In this study, we have determined the association of Gln223Agr loci of LEPR gene in three ethnic groups of Malaysia, namely: Malays, Chinese and Indians. A total of 284 T2DM subjects and 281 healthy individuals were recruited based on International Diabetes Federation (IDF) criteria. Genomic DNA was extracted from the buccal specimens of the subjects. The commercial polymerase chain reaction (PCR) method was carried out by proper restriction enzyme MSP I to both amplify and digest the Gln223Agr polymorphism. The p-value among the three studied races was 0.057, 0.011 and 0.095, respectively. The values such as age, WHR, FPG, HbA1C, LDL, HDL, Chol and Family History were significantly different among the subjects with Gln223Agr polymorphism of LEPR (p < 0.05).

Probing the holographic principle using dynamical gauge effects from open spin-orbit coupling

NASA Astrophysics Data System (ADS)

Zhao, Jianshi; Price, Craig; Liu, Qi; Gemelke, Nathan

2016-05-01

Dynamical gauge fields result from locally defined symmetries and an effective over-labeling of quantum states. Coupling atoms weakly to a reservoir of laser modes can create an effective dynamical gauge field purely due to the disregard of information in the optical states. Here we report measurements revealing effects of open spin-orbit coupling in a system where an effective model can be formed from a non-abelian SU(2) × U(1) field theory following the Yang-Mills construct. Forming a close analogy to dynamical gauge effects in quantum chromodynamics, we extract a measure of atomic motion which reveals the analog of a closing mass gap for the relevant gauge boson, shedding insight on long standing open problems in gauge-fixing scale anomalies. Using arguments following the holographic principle, we measure scaling relations which can be understood by quantifying information present in the local potential. New prospects using these techniques for developing fractionalization of multi-particle and macroscopic systems using dissipative and non-abelian gauge fields will also be discussed. We acknowledge support from NSF Award No. 1068570, and the Charles E. Kaufman Foundation.

Effect of ATP and 2-oxoglutarate on the in vitro interaction between the NifA GAF domain and the GlnB protein of Azospirillum brasilense

PubMed Central

Sotomaior, P.; Araújo, L.M.; Nishikawa, C.Y.; Huergo, L.F.; Monteiro, R.A.; Pedrosa, F.O.; Chubatsu, L.S.; Souza, E.M.

2012-01-01

Azospirillum brasilense is a diazotroph that associates with important agricultural crops and thus has potential to be a nitrogen biofertilizer. The A. brasilense transcription regulator NifA, which seems to be constitutively expressed, activates the transcription of nitrogen fixation genes. It has been suggested that the nitrogen status-signaling protein GlnB regulates NifA activity by direct interaction with the NifA N-terminal GAF domain, preventing the inhibitory effect of this domain under conditions of nitrogen fixation. In the present study, we show that an N-terminal truncated form of NifA no longer required GlnB for activity and lost regulation by ammonium. On the other hand, in trans co-expression of the N-terminal GAF domain inhibited the N-truncated protein in response to fixed nitrogen levels. We also used pull-down assays to show in vitro interaction between the purified N-terminal GAF domain of NifA and the GlnB protein. The results showed that A. brasilense GlnB interacts directly with the NifA N-terminal domain and this interaction is dependent on the presence of ATP and 2-oxoglutarate. PMID:22983183

Effect of ATP and 2-oxoglutarate on the in vitro interaction between the NifA GAF domain and the GlnB protein of Azospirillum brasilense.

PubMed

Sotomaior, P; Araújo, L M; Nishikawa, C Y; Huergo, L F; Monteiro, R A; Pedrosa, F O; Chubatsu, L S; Souza, E M

2012-12-01

Azospirillum brasilense is a diazotroph that associates with important agricultural crops and thus has potential to be a nitrogen biofertilizer. The A. brasilense transcription regulator NifA, which seems to be constitutively expressed, activates the transcription of nitrogen fixation genes. It has been suggested that the nitrogen status-signaling protein GlnB regulates NifA activity by direct interaction with the NifA N-terminal GAF domain, preventing the inhibitory effect of this domain under conditions of nitrogen fixation. In the present study, we show that an N-terminal truncated form of NifA no longer required GlnB for activity and lost regulation by ammonium. On the other hand, in trans co-expression of the N-terminal GAF domain inhibited the N-truncated protein in response to fixed nitrogen levels. We also used pull-down assays to show in vitro interaction between the purified N-terminal GAF domain of NifA and the GlnB protein. The results showed that A. brasilense GlnB interacts directly with the NifA N-terminal domain and this interaction is dependent on the presence of ATP and 2-oxoglutarate.

Possible Release of an ArgGlyArgProGln Pentapeptide with Innate Immunity Properties from Acidic Proline-Rich Proteins by Proteolytic Activity in Commensal Streptococcus and Actinomyces Species

PubMed Central

Li, Tong; Bratt, Per; Jonsson, Andreas P.; Ryberg, Mats; Johansson, Ingegerd; Griffiths, William J.; Bergman, Tomas; Strömberg, Nicklas

2000-01-01

This study suggests degradation of salivary acidic proline-rich proteins (PRPs) into potential innate-immunity-like peptides by oral Streptococcus and Actinomyces species. PRP degradation paralleled cleavage of Pro-containing substrates. PRP degradation by S. gordonii strain SK12 instantly released a Pyr1-Pro104Pro105 and a Gly111-Pro149Gln150 peptide together with a presumed Arg106Gly107Arg108Pro109Gln110 pentapeptide. The synthetic Arg106Gly107Arg108Pro109Gln110 peptide desorbed bound bacteria and counteracted sucrose-induced decrease of dental plaque pH in vitro. PMID:10948176

Spin valve effect of the interfacial spin accumulation in yttrium iron garnet/platinum bilayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin, Lichuan; Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716; Zhang, Dainan

2014-09-29

We report the spin valve effect in yttrium iron garnet/platinum (YIG/Pt) bilayers. The spin Hall effect (SHE) generates spin accumulation at the YIG/Pt interface and can be opened/closed by magnetization switching in the electrical insulator YIG. The interfacial spin accumulation was measured in both YIG/Pt and YIG/Cu/Pt structures using a planar Hall configuration. The spin valve effect remained, even after a 2 nm thick Cu layer was inserted between the YIG and Pt layers, which aimed to exclude the induced magnetization at the YIG/Pt interface. The transverse Hall voltage and switching field were dependent on the applied charge current density. Themore » origin of this behavior can be explained by the SHE induced torque exerted on the domain wall, caused by the transfer of the spin angular momentum from the spin-polarized current to the YIG magnetic moment.« less

Spin-wave diode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lan, Jin; Yu, Weichao; Wu, Ruqian

A diode, a device allowing unidirectional signal transmission, is a fundamental element of logic structures, and it lies at the heart of modern information systems. The spin wave or magnon, representing a collective quasiparticle excitation of the magnetic order in magnetic materials, is a promising candidate for an information carrier for the next-generation energy-saving technologies. Here, we propose a scalable and reprogrammable pure spin-wave logic hardware architecture using domain walls and surface anisotropy stripes as waveguides on a single magnetic wafer. We demonstrate theoretically the design principle of the simplest logic component, a spin-wave diode, utilizing the chiral bound statesmore » in a magnetic domain wall with a Dzyaloshinskii-Moriya interaction, and confirm its performance through micromagnetic simulations. As a result, these findings open a new vista for realizing different types of pure spin-wave logic components and finally achieving an energy-efficient and hardware-reprogrammable spin-wave computer.« less

Spin-wave diode

DOE PAGES

Lan, Jin; Yu, Weichao; Wu, Ruqian; ...

2015-12-28

A diode, a device allowing unidirectional signal transmission, is a fundamental element of logic structures, and it lies at the heart of modern information systems. The spin wave or magnon, representing a collective quasiparticle excitation of the magnetic order in magnetic materials, is a promising candidate for an information carrier for the next-generation energy-saving technologies. Here, we propose a scalable and reprogrammable pure spin-wave logic hardware architecture using domain walls and surface anisotropy stripes as waveguides on a single magnetic wafer. We demonstrate theoretically the design principle of the simplest logic component, a spin-wave diode, utilizing the chiral bound statesmore » in a magnetic domain wall with a Dzyaloshinskii-Moriya interaction, and confirm its performance through micromagnetic simulations. As a result, these findings open a new vista for realizing different types of pure spin-wave logic components and finally achieving an energy-efficient and hardware-reprogrammable spin-wave computer.« less

Herbaspirillum seropedicae signal transduction protein PII is structurally similar to the enteric GlnK.

PubMed

Machado Benelli, Elaine; Buck, Martin; Polikarpov, Igor; Maltempi de Souza, Emanuel; Cruz, Leonardo M; Pedrosa, Fábio O

2002-07-01

PII-like proteins are signal transduction proteins found in bacteria, archaea and eukaryotes. They mediate a variety of cellular responses. A second PII-like protein, called GlnK, has been found in several organisms. In the diazotroph Herbaspirillum seropedicae, PII protein is involved in sensing nitrogen levels and controlling nitrogen fixation genes. In this work, the crystal structure of the unliganded H. seropedicae PII was solved by X-ray diffraction. H. seropedicae PII has a Gly residue, Gly108 preceding Pro109 and the main-chain forms a beta turn. The glycine at position 108 allows a bend in the C-terminal main-chain, thereby modifying the surface of the cleft between monomers and potentially changing function. The structure suggests that the C-terminal region of PII proteins may be involved in specificity of function, and nonenteric diazotrophs are found to have the C-terminal consensus XGXDAX(107-112). We are also proposing binding sites for ATP and 2-oxoglutarate based on the structural alignment of PII with PII-ATP/GlnK-ATP, 5-carboxymethyl-2-hydroxymuconate isomerase and 4-oxalocrotonate tautomerase bound to the inhibitor 2-oxo-3-pentynoate.

Spin-exchange-induced spin-orbit coupling in a superfluid mixture

NASA Astrophysics Data System (ADS)

Chen, Li; Zhu, Chuanzhou; Zhang, Yunbo; Pu, Han

2018-03-01

We investigate the ground-state properties of a dual-species spin-1/2 Bose-Einstein condensate. One of the species is subjected to a pair of Raman laser beams that induces spin-orbit (SO) coupling, whereas the other species is not coupled to the Raman laser. In certain limits, analytical results can be obtained. It is clearly shown that, through the interspecies spin-exchange interaction, the second species also exhibits SO coupling. This mixture system displays a very rich phase diagram, with many of the phases not present in an SO-coupled single-species condensate. Our work provides a way of creating SO coupling in atomic quantum gases, and opens up an avenue of research in SO-coupled superfluid mixtures. From a practical point of view, the spin-exchange-induced SO coupling may overcome the heating issue for certain atomic species when subjected to Raman beams.

Notes on integrable boundary interactions of open SU(4) alternating spin chains

NASA Astrophysics Data System (ADS)

Wu, JunBao

2018-07-01

Ref. [J. High Energy Phys. 1708, 001 (2017)] showed that the planar flavored Ahanory-Bergman-Jafferis-Maldacena (ABJM) theory is integrable in the scalar sector at two-loop order using coordinate Bethe ansatz. A salient feature of this case is that the boundary reflection matrices are anti-diagonal with respect to the chosen basis. In this paper, we relax the coefficients of the boundary terms to be general constants to search for integrable systems among this class. We found that the only integrable boundary interaction at each end of the spin chain aside from the one in ref. [J. High Energy Phys. 1708, 001 (2017)] is the one with vanishing boundary interactions leading to diagonal reflection matrices. We also construct non-supersymmetric planar flavored ABJM theory which leads to trivial boundary interactions at both ends of the open chain from the two-loop anomalous dimension matrix in the scalar sector.

Effects of symmetry and spin configuration on spin-dependent transport properties of iron-phthalocyanine-based devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cui, Li-Ling; School of Science, Hunan University of Technology, Zhuzhou 412007; Yang, Bing-Chu, E-mail: bingchuyang@csu.edu.cn

2014-07-21

Spin-dependent transport properties of nanodevices constructed by iron-phthalocyanine (FePc) molecule sandwiched between two zigzag graphene nanoribbon electrodes are studied using first-principles quantum transport calculations. The effects of the symmetry and spin configuration of electrodes have been taken into account. It is found that large magnetoresistance, large spin polarization, dual spin-filtering, and negative differential resistance (NDR) can coexist in these devices. Our results show that 5Z-FePc system presents well conductive ability in both parallel (P) and anti-parallel (AP) configurations. For 6Z-FePc-P system, spin filtering effect and large spin polarization can be found. A dual spin filtering and NDR can also bemore » shown in 6Z-FePc-AP. Our studies indicate that the dual spin filtering effect depends on the orbitals symmetry of the energy bands and spin mismatching of the electrodes. And all the effects would open up possibilities for their applications in spin-valve, spin-filter as well as effective spin diode devices.« less

Quantum group symmetries and completeness for \\boldsymbol {A}_{\\boldsymbol {2n}}^{\\boldsymbol{(2)}} open spin chains

NASA Astrophysics Data System (ADS)

Ahmed, Ibrahim; Nepomechie, Rafael I.; Wang, Chunguang

2017-07-01

We argue that the Hamiltonians for A(2)2n open quantum spin chains corresponding to two choices of integrable boundary conditions have the symmetries Uq(Bn) and Uq(Cn) , respectively. We find a formula for the Dynkin labels of the Bethe states (which determine the degeneracies of the corresponding eigenvalues) in terms of the numbers of Bethe roots of each type. With the help of this formula, we verify numerically (for a generic value of the anisotropy parameter) that the degeneracies and multiplicities of the spectra implied by the quantum group symmetries are completely described by the Bethe ansatz.

The spin-partitioned total position-spread tensor: An application to Heisenberg spin chains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fertitta, Edoardo; Paulus, Beate; El Khatib, Muammar

2015-12-28

The spin partition of the Total Position-Spread (TPS) tensor has been performed for one-dimensional Heisenberg chains with open boundary conditions. Both the cases of a ferromagnetic (high-spin) and an anti-ferromagnetic (low-spin) ground-state have been considered. In the case of a low-spin ground-state, the use of alternating magnetic couplings allowed to investigate the effect of spin-pairing. The behavior of the spin-partitioned TPS (SP-TPS) tensor as a function of the number of sites turned to be closely related to the presence of an energy gap between the ground-state and the first excited-state at the thermodynamic limit. Indeed, a gapped energy spectrum ismore » associated to a linear growth of the SP-TPS tensor with the number of sites. On the other hand, in gapless situations, the spread presents a faster-than-linear growth, resulting in the divergence of its per-site value. Finally, for the case of a high-spin wave function, an analytical expression of the dependence of the SP-TPS on the number of sites n and the total spin-projection S{sub z} has been derived.« less

Extracting current induced spins from topological insulator wires: gate control of extracted spin polarization

NASA Astrophysics Data System (ADS)

Adagideli, Inanc

Spin-momentum locking featured by the surface states of 3D topological insulators (TIs) allows electrical generation of spin accumulations and provides a new avenue for spintronics applications. In this work, we explore how to extract electrically induced spins from topological insulator surfaces, where they are generated into topologically trivial metallic leads that are commonly used in conventional electronic devices. We first focus on an effective surface theory of current induced spin accumulation in topological insulators. Then we focus on a particular geometry: a metallic pocket attached to top and side faces of a 3D topological insulator quantum wire with a rectangular cross section, and explore spin extraction into topologically non-trivial materials. We find surprisingly that the doping in and/or a gate voltage applied to the metallic side pocket can control the direction of the extracted spin polarization opening the possibility for a spin transistor operation of these device geometries. We also perform numerical simulations of nonequilibrium spin accumulations generated by an applied bias in the same geometry and demonstrate the spin polarization control via applied gate voltages. Work funded by TUBITAK Grant No 114F163.

Higher-order spin and charge dynamics in a quantum dot-lead hybrid system.

PubMed

Otsuka, Tomohiro; Nakajima, Takashi; Delbecq, Matthieu R; Amaha, Shinichi; Yoneda, Jun; Takeda, Kenta; Allison, Giles; Stano, Peter; Noiri, Akito; Ito, Takumi; Loss, Daniel; Ludwig, Arne; Wieck, Andreas D; Tarucha, Seigo

2017-09-22

Understanding the dynamics of open quantum systems is important and challenging in basic physics and applications for quantum devices and quantum computing. Semiconductor quantum dots offer a good platform to explore the physics of open quantum systems because we can tune parameters including the coupling to the environment or leads. Here, we apply the fast single-shot measurement techniques from spin qubit experiments to explore the spin and charge dynamics due to tunnel coupling to a lead in a quantum dot-lead hybrid system. We experimentally observe both spin and charge time evolution via first- and second-order tunneling processes, and reveal the dynamics of the spin-flip through the intermediate state. These results enable and stimulate the exploration of spin dynamics in dot-lead hybrid systems, and may offer useful resources for spin manipulation and simulation of open quantum systems.

Antiferromagnetic domain wall as spin wave polarizer

NASA Astrophysics Data System (ADS)

Lan, Jin; Yu, Weichao; Xiao, Jiang

Spin waves are collective excitations of local magnetizations that can effectively propagate information even in magnetic insulators. In antiferromagnet, spin waves are endowed with additional polarization freedom. Here we propose that the antiferromagnetic domain wall can act as a spin wave polarizer, which perfectly passes one linearly polarized spin wave while substantially reflects the perpendicular one. We show that the polarizing effect lies in the suppression of one linear polarization inside domain wall, in close analogy to the wire-grid optical polarizer. Our finding opens up new possibilities in magnonic processing by harnessing spin wave polarization in antiferromagnet.

Milder clinical and biochemical phenotypes associated with the c.482G>A (p.Arg161Gln) pathogenic variant in cobalamin C disease: Implications for management and screening.

PubMed

Almannai, Mohammed; Marom, Ronit; Divin, Kristian; Scaglia, Fernando; Sutton, V Reid; Craigen, William J; Lee, Brendan; Burrage, Lindsay C; Graham, Brett H

2017-09-01

Cobalamin C disease is a multisystemic disease with variable manifestations and age of onset. Genotype-phenotype correlations are well-recognized in this disorder. Here, we present a large cohort of individuals with cobalamin C disease, several of whom are heterozygous for the c.482G>A pathogenic variant (p.Arg161Gln). We compared clinical characteristics of individuals with this pathogenic variant to those who do not have this variant. To our knowledge, this study represents the largest single cohort of individuals with the c.482G>A (p.Arg161Gln) pathogenic variant. A retrospective chart review of 27 individuals from 21 families with cobalamin C disease who are followed at our facility was conducted. 13 individuals (48%) are compound heterozygous with the c.482G>A (p.Arg161Gln) on one allele and a second pathogenic variant on the other allele. Individuals with the c.482G>A (p.Arg161Gln) pathogenic variant had later onset of symptoms and easier metabolic control. Moreover, they had milder biochemical abnormalities at presentation which likely contributed to the observation that 4 individuals (31%) in this group were missed by newborn screening. The c.482G>A (p.Arg161Gln) pathogenic variant is associated with milder disease. These individuals may not receive a timely diagnosis as they may not be identified on newborn screening or because of unrecognized, late onset symptoms. Despite the milder presentation, significant complications can occur, especially if treatment is delayed. Copyright © 2017 Elsevier Inc. All rights reserved.

Strong spin-photon coupling in silicon

NASA Astrophysics Data System (ADS)

Samkharadze, N.; Zheng, G.; Kalhor, N.; Brousse, D.; Sammak, A.; Mendes, U. C.; Blais, A.; Scappucci, G.; Vandersypen, L. M. K.

2018-03-01

Long coherence times of single spins in silicon quantum dots make these systems highly attractive for quantum computation, but how to scale up spin qubit systems remains an open question. As a first step to address this issue, we demonstrate the strong coupling of a single electron spin and a single microwave photon. The electron spin is trapped in a silicon double quantum dot, and the microwave photon is stored in an on-chip high-impedance superconducting resonator. The electric field component of the cavity photon couples directly to the charge dipole of the electron in the double dot, and indirectly to the electron spin, through a strong local magnetic field gradient from a nearby micromagnet. Our results provide a route to realizing large networks of quantum dot–based spin qubit registers.

Spin-orbit proximity effect in graphene

NASA Astrophysics Data System (ADS)

Avsar, A.; Tan, J. Y.; Taychatanapat, T.; Balakrishnan, J.; Koon, G. K. W.; Yeo, Y.; Lahiri, J.; Carvalho, A.; Rodin, A. S.; O'Farrell, E. C. T.; Eda, G.; Castro Neto, A. H.; Özyilmaz, B.

2014-09-01

The development of spintronics devices relies on efficient generation of spin-polarized currents and their electric-field-controlled manipulation. While observation of exceptionally long spin relaxation lengths makes graphene an intriguing material for spintronics studies, electric field modulation of spin currents is almost impossible due to negligible intrinsic spin-orbit coupling of graphene. In this work, we create an artificial interface between monolayer graphene and few-layer semiconducting tungsten disulphide. In these devices, we observe that graphene acquires spin-orbit coupling up to 17 meV, three orders of magnitude higher than its intrinsic value, without modifying the structure of the graphene. The proximity spin-orbit coupling leads to the spin Hall effect even at room temperature, and opens the door to spin field effect transistors. We show that intrinsic defects in tungsten disulphide play an important role in this proximity effect and that graphene can act as a probe to detect defects in semiconducting surfaces.

The Gln223Arg polymorphism of the leptin receptor in Pima Indians: influence on energy expenditure, physical activity and lipid metabolism.

PubMed

Stefan, N; Vozarova, B; Del Parigi, A; Ossowski, V; Thompson, D B; Hanson, R L; Ravussin, E; Tataranni, P A

2002-12-01

Leptin regulates body weight by its receptor-mediated anorectic, thermogenic and antisteatotic effects. Recently, lower leptin binding to the soluble form of the leptin receptor (LEPR) was shown in carriers of the Arg223-encoding allele of the Gln223Arg polymorphism of the LEPR. To investigate whether this variant influences energy metabolism and adiposity in Pima Indians, we genotyped non-diabetic Pima Indians in whom we had measured body composition and 24 h energy expenditure (24 h EE), physical activity level (PAL) and 24 h respiratory quotient (24 h RQ) in a respiratory chamber (n=268) and who had undergone percutaneous fat biopsies from the periumbilical region (n=184). Genotype was not associated with percent body fat (P>0.39), but was associated with 24 h EE, PAL and mean subcutaneous abdominal adipocyte size (SAAS all P<0.05). Homozygotes for the Arg223-encoding allele had lower 24 h EE (P=0.04) and PAL (P=0.007), but larger SAAS (P=0.01) than Gln homozygotes. These findings are consistent with a role of the Gln223Arg polymorphism in reducing peripheral and central leptin binding to the LEPR in humans. However, these effects do not seem to have a major impact on adiposity in this population.

Gate-Driven Pure Spin Current in Graphene

NASA Astrophysics Data System (ADS)

Lin, Xiaoyang; Su, Li; Si, Zhizhong; Zhang, Youguang; Bournel, Arnaud; Zhang, Yue; Klein, Jacques-Olivier; Fert, Albert; Zhao, Weisheng

2017-09-01

The manipulation of spin current is a promising solution for low-power devices beyond CMOS. However, conventional methods, such as spin-transfer torque or spin-orbit torque for magnetic tunnel junctions, suffer from large power consumption due to frequent spin-charge conversions. An important challenge is, thus, to realize long-distance transport of pure spin current, together with efficient manipulation. Here, the mechanism of gate-driven pure spin current in graphene is presented. Such a mechanism relies on the electrical gating of carrier-density-dependent conductivity and spin-diffusion length in graphene. The gate-driven feature is adopted to realize the pure spin-current demultiplexing operation, which enables gate-controllable distribution of the pure spin current into graphene branches. Compared with the Elliott-Yafet spin-relaxation mechanism, the D'yakonov-Perel spin-relaxation mechanism results in more appreciable demultiplexing performance. The feature of the pure spin-current demultiplexing operation will allow a number of logic functions to be cascaded without spin-charge conversions and open a route for future ultra-low-power devices.

Spin-Caloritronic Batteries

NASA Astrophysics Data System (ADS)

Yu, Xiao-Qin; Zhu, Zhen-Gang; Su, Gang; Jauho, A.-P.

2017-11-01

The thermoelectric performance of a topological energy converter is analyzed. The H -shaped device is based on a combination of transverse topological effects involving the spin: the inverse spin Hall effect and the spin Nernst effect. The device can convert a temperature drop in one arm into an electric power output in the other arm. Analytical expressions for the output voltage, the figure of merit (Z T ), and energy-converting efficiency are reported. We show that the output voltage and the Z T can be tuned by the geometry of the device and the physical properties of the material. Importantly, contrary to a conventional thermoelectric device, here a low electric conductivity may, in fact, enhance the Z T value, thereby opening a path to strategies in optimizing the figure of merit.

Efficient and accurate local single reference correlation methods for high-spin open-shell molecules using pair natural orbitals

NASA Astrophysics Data System (ADS)

Hansen, Andreas; Liakos, Dimitrios G.; Neese, Frank

2011-12-01

A production level implementation of the high-spin open-shell (spin unrestricted) single reference coupled pair, quadratic configuration interaction and coupled cluster methods with up to doubly excited determinants in the framework of the local pair natural orbital (LPNO) concept is reported. This work is an extension of the closed-shell LPNO methods developed earlier [F. Neese, F. Wennmohs, and A. Hansen, J. Chem. Phys. 130, 114108 (2009), 10.1063/1.3086717; F. Neese, A. Hansen, and D. G. Liakos, J. Chem. Phys. 131, 064103 (2009), 10.1063/1.3173827]. The internal space is spanned by localized orbitals, while the external space for each electron pair is represented by a truncated PNO expansion. The laborious integral transformation associated with the large number of PNOs becomes feasible through the extensive use of density fitting (resolution of the identity (RI)) techniques. Technical complications arising for the open-shell case and the use of quasi-restricted orbitals for the construction of the reference determinant are discussed in detail. As in the closed-shell case, only three cutoff parameters control the average number of PNOs per electron pair, the size of the significant pair list, and the number of contributing auxiliary basis functions per PNO. The chosen threshold default values ensure robustness and the results of the parent canonical methods are reproduced to high accuracy. Comprehensive numerical tests on absolute and relative energies as well as timings consistently show that the outstanding performance of the LPNO methods carries over to the open-shell case with minor modifications. Finally, hyperfine couplings calculated with the variational LPNO-CEPA/1 method, for which a well-defined expectation value type density exists, indicate the great potential of the LPNO approach for the efficient calculation of molecular properties.

Interfacial spin-filter assisted spin transfer torque effect in Co/BeO/Co magnetic tunnel junction

NASA Astrophysics Data System (ADS)

Tang, Y.-H.; Chu, F.-C.

2015-03-01

The first-principles calculation is employed to demonstrate the spin-selective transport properties and the non-collinear spin-transfer torque (STT) effect in the newly proposed Co/BeO/Co magnetic tunnel junction. The subtle spin-polarized charge transfer solely at O/Co interface gives rise to the interfacial spin-filter (ISF) effect, which can be simulated within the tight binding model to verify the general expression of STT. This allows us to predict the asymmetric bias behavior of non-collinear STT directly via the interplay between the first-principles calculated spin current densities in collinear magnetic configurations. We believe that the ISF effect, introduced by the combination between wurtzite-BeO barrier and the fcc-Co electrode, may open a new and promising route in semiconductor-based spintronics applications.

An explicitly spin-free compact open-shell coupled cluster theory using a multireference combinatoric exponential ansatz: formal development and pilot applications.

PubMed

Datta, Dipayan; Mukherjee, Debashis

2009-07-28

In this paper, we present a comprehensive account of an explicitly spin-free compact state-universal multireference coupled cluster (CC) formalism for computing the state energies of simple open-shell systems, e.g., doublets and biradicals, where the target open-shell states can be described by a few configuration state functions spanning a model space. The cluster operators in this formalism are defined in terms of the spin-free unitary generators with respect to the common closed-shell component of all model functions (core) as vacuum. The spin-free cluster operators are either closed-shell-like n hole-n particle excitations (denoted by T(mu)) or involve excitations from the doubly occupied (nonvalence) orbitals to the singly occupied (valence) orbitals (denoted by S(e)(mu)). In addition, there are cluster operators with exchange spectator scatterings involving the valence orbitals (denoted by S(re)(mu)). We propose a new multireference cluster expansion ansatz for the wave operator with the above generally noncommuting cluster operators which essentially has the same physical content as the Jeziorski-Monkhorst ansatz with the commuting cluster operators defined in the spin-orbital basis. The T(mu) operators in our ansatz are taken to commute with all other operators, while the S(e)(mu) and S(re)(mu) operators are allowed to contract among themselves through the spectator valence orbitals. An important innovation of this ansatz is the choice of an appropriate automorphic factor accompanying each contracted composite of cluster operators in order to ensure that each distinct excitation generated by this composite appears only once in the wave operator. The resulting CC equations consist of two types of terms: a "direct" term and a "normalization" term containing the effective Hamiltonian operator. It is emphasized that the direct term is almost quartic in the cluster amplitudes, barring only a handful of terms and termination of the normalization term depends on

Field-Free Programmable Spin Logics via Chirality-Reversible Spin-Orbit Torque Switching.

PubMed

Wang, Xiao; Wan, Caihua; Kong, Wenjie; Zhang, Xuan; Xing, Yaowen; Fang, Chi; Tao, Bingshan; Yang, Wenlong; Huang, Li; Wu, Hao; Irfan, Muhammad; Han, Xiufeng

2018-06-21

Spin-orbit torque (SOT)-induced magnetization switching exhibits chirality (clockwise or counterclockwise), which offers the prospect of programmable spin-logic devices integrating nonvolatile spintronic memory cells with logic functions. Chirality is usually fixed by an applied or effective magnetic field in reported studies. Herein, utilizing an in-plane magnetic layer that is also switchable by SOT, the chirality of a perpendicular magnetic layer that is exchange-coupled with the in-plane layer can be reversed in a purely electrical way. In a single Hall bar device designed from this multilayer structure, three logic gates including AND, NAND, and NOT are reconfigured, which opens a gateway toward practical programmable spin-logic devices. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dynamic spin injection into a quantum well coupled to a spin-split bound state

NASA Astrophysics Data System (ADS)

Maslova, N. S.; Rozhansky, I. V.; Mantsevich, V. N.; Arseyev, P. I.; Averkiev, N. S.; Lähderanta, E.

2018-05-01

We present a theoretical analysis of dynamic spin injection due to spin-dependent tunneling between a quantum well (QW) and a bound state split in spin projection due to an exchange interaction or external magnetic field. We focus on the impact of Coulomb correlations at the bound state on spin polarization and sheet density kinetics of the charge carriers in the QW. The theoretical approach is based on kinetic equations for the electron occupation numbers taking into account high order correlation functions for the bound state electrons. It is shown that the on-site Coulomb repulsion leads to an enhanced dynamic spin polarization of the electrons in the QW and a delay in the carriers tunneling into the bound state. The interplay of these two effects leads to nontrivial dependence of the spin polarization degree, which can be probed experimentally using time-resolved photoluminescence experiments. It is demonstrated that the influence of the Coulomb interactions can be controlled by adjusting the relaxation rates. These findings open a new way of studying the Hubbard-like electron interactions experimentally.

Open quantum system approach to the modeling of spin recombination reactions.

PubMed

Tiersch, M; Steiner, U E; Popescu, S; Briegel, H J

2012-04-26

In theories of spin-dependent radical pair reactions, the time evolution of the radical pair, including the effect of the chemical kinetics, is described by a master equation in the Liouville formalism. For the description of the chemical kinetics, a number of possible reaction operators have been formulated in the literature. In this work, we present a framework that allows for a unified description of the various proposed mechanisms and the forms of reaction operators for the spin-selective recombination processes. On the basis of the concept that master equations can be derived from a microscopic description of the spin system interacting with external degrees of freedom, it is possible to gain insight into the underlying microscopic processes and develop a systematic approach toward determining the specific form of the reaction operator in concrete scenarios.

Direct detection of spin Nernst effect in platinum

NASA Astrophysics Data System (ADS)

Bose, A.; Bhuktare, S.; Singh, H.; Dutta, S.; Achanta, V. G.; Tulapurkar, A. A.

2018-04-01

Generation of spin current lies at the heart of spintronic research. The spin Hall effect and the spin Seebeck effect have drawn considerable attention in the last few years to create pure spin current by heavy metals and ferromagnets, respectively. In this work, we show the direct evidence of heat current to spin current conversion in non-magnetic Platinum by the spin Nernst effect (SNE) at room temperature. This is the thermal analogue of the spin Hall effect in non-magnets. We have shown that the 8 K/μm thermal gradient in Pt can lead to the generation of pure spin current density of the order of 108 A/m2 by virtue of SNE. This opens up an additional possibility to couple the relativistic spin-orbit interaction with the thermal gradient for spintronic applications.

Kinetic analysis of spin current contribution to spectrum of electromagnetic waves in spin-1/2 plasma. I. Dielectric permeability tensor for magnetized plasmas

NASA Astrophysics Data System (ADS)

Andreev, Pavel A.

2017-02-01

The dielectric permeability tensor for spin polarized plasmas is derived in terms of the spin-1/2 quantum kinetic model in six-dimensional phase space. Expressions for the distribution function and spin distribution function are derived in linear approximations on the path of dielectric permeability tensor derivation. The dielectric permeability tensor is derived for the spin-polarized degenerate electron gas. It is also discussed at the finite temperature regime, where the equilibrium distribution function is presented by the spin-polarized Fermi-Dirac distribution. Consideration of the spin-polarized equilibrium states opens possibilities for the kinetic modeling of the thermal spin current contribution in the plasma dynamics.

Frequencies of the Arg16Gly, Gln27Glu and Thr164Ile Adrenoceptor β2 Polymorphisms among Omanis

PubMed Central

Al-Balushi, Khalid; Zadjali, Fahad; Al-Sinani, Sawsan; Al-Zadjali, Al-Muatasim; Bayoumi, Riad

2015-01-01

Objectives: This study aimed to assess the distribution of missense mutations in the adrenoceptor β2 (ADRB2) gene in an Omani cohort. Methods: This study was carried out between May 2014 and March 2015 at the Sultan Qaboos University, Muscat, Oman. Blood samples were taken from 316 unrelated Omani subjects. Genotyping for rs1042713 (c.46A>G, p.Arg16Gly), rs1042714 (c.79C>G, p.Gln27Glu) and rs1800888 (c.491C>T, p.Thr164Ile) polymorphisms was performed by real-time polymerase chain reaction using single nucleotide polymorphism (SNP) genotyping assays. The allelic frequencies of these polymorphisms were estimated on the basis of the observed numbers of specific alleles from the genotype data for male and female subjects. The genotype frequencies for each polymorphism were tested for deviation from the Hardy-Weinberg equilibrium. Results: Gly16 and Glu27 were the most frequent variants found among the cohort (63% and 75%, respectively). The Ile164 variant was not detected in the study population. There was a significant linkage disequilibrium between the rs1042713 and rs1042714 SNPs (r2 = 0.209; P ≤0.001). The most observed haplotypes were Gly16-Gln27 and Arg16-Gln27 (0.37 and 0.38, respectively). The frequency of Gly16-Glu27 was 0.25, comprising all Glu27 carriers. Conclusion: The allelic distribution of variants in this Omani cohort was similar to distributions reported among Caucasian populations. PMID:26629374

No association of the Arg51Gln and Leu72Met polymorphisms of the ghrelin gene and polycystic ovary syndrome.

PubMed

Wang, Kehua; Wang, Leiguang; Zhao, Yueran; Shi, Yuhua; Wang, Laicheng; Chen, Zi-Jiang

2009-02-01

Ghrelin plays a role in regulating glucose metabolism and energy balance. Polymorphisms in preproghrelin and ghrelin gene could be responsible for obesity, insulin resistance and low ghrelin levels observed in some individuals. The objective of this study was to evaluate the influence of two single-nucleotide polymorphisms (SNPs) of ghrelin gene on the clinical, the hormonal and metabolic features in women with polycystic ovary syndrome (PCOS) in a Chinese population. A large sample of Chinese PCOS (n = 271) women and a control group (n = 296) of healthy women matched for age were studied. Hormone and metabolic profiles were measured and blood samples were collected for genotype and allelic frequency analysis. Non-synonymous SNPs in the coding region (exon 2) of the preproghrelin gene (Arg51Gln (346 G>A) and Leu72Met (408 C>A) were studied using PCR and restriction fragment length polymorphism analysis. The polymorphism Arg51Gln was not found in the cohorts studied. The distribution of Leu72Met was similar in PCOS group and in healthy controls. There was no significant difference in age, BMI, waist-hip-ratio and levels of FSH, LH, estradiol, testosterone and prolactin between PCOS patients with different genotypes, and the level of plasma glucose and insulin was also similar. No association was found between Leu72Met and Arg51Gln polymorphisms in the ghrelin gene and PCOS in Chinese population.

The IL23R A/Gln381 allele promotes IL-23 unresponsiveness in human memory T-helper 17 cells and impairs Th17 responses in psoriasis patients.

PubMed

Di Meglio, Paola; Villanova, Federica; Napolitano, Luca; Tosi, Isabella; Terranova Barberio, Manuela; Mak, Rose K; Nutland, Sarah; Smith, Catherine H; Barker, Jonathan N W N; Todd, John A; Nestle, Frank O

2013-10-01

We and others have shown that the minor, nonconserved allele Gln381 of the Arg381Gln single-nucleotide polymorphism (rs11209026G>A) of the IL-23 receptor gene (IL23R) protects against psoriasis. Moreover, we have recently shown impaired IL-23-induced IL-17A production and STAT-3 phosphorylation in Th17 cells generated in vitro from healthy individuals heterozygous for the protective A allele (GA). However, the biological effect of this variant has not been determined in homozygous carriers of the protective A allele (AA), nor in psoriatic patients. Here we expand our functional investigation of the IL23R Arg381Gln gene variant to include AA homozygous individuals. By using isolated memory CD4+ T cells, we found attenuated IL-23-induced Th17 response in heterozygous individuals. Moreover, we found that AA homozygous individuals were strikingly unresponsive to IL-23, with minimal or no IL-17A and IL-17F production and failure of human memory Th17 cell survival/expansion. Finally, IL-23-induced Th17 response was also attenuated in age- and sex-matched GA versus GG psoriatic patients undergoing systemic treatment. Taken together, our data provide evidence for an allele-dosage effect for IL-23R Gln381 and indicate that common gene alleles associated with complex diseases might have biological effects of considerable magnitude in homozygous carriers.

Modulation of pure spin currents with a ferromagnetic insulator

NASA Astrophysics Data System (ADS)

Villamor, Estitxu; Isasa, Miren; Vélez, Saül; Bedoya-Pinto, Amilcar; Vavassori, Paolo; Hueso, Luis E.; Bergeret, F. Sebastián; Casanova, Fèlix

2015-01-01

We propose and demonstrate spin manipulation by magnetically controlled modulation of pure spin currents in cobalt/copper lateral spin valves, fabricated on top of the magnetic insulator Y3F e5O12 (YIG). The direction of the YIG magnetization can be controlled by a small magnetic field. We observe a clear modulation of the nonlocal resistance as a function of the orientation of the YIG magnetization with respect to the polarization of the spin current. Such a modulation can only be explained by assuming a finite spin-mixing conductance at the Cu/YIG interface, as it follows from the solution of the spin-diffusion equation. These results open a path towards the development of spin logics.

Thickness dependence and the role of spin transfer torque in nonlinear giant magnetoresistance of permalloy dual spin valves

NASA Astrophysics Data System (ADS)

Banerjee, N.; Aziz, A.; Ali, M.; Robinson, J. W. A.; Hickey, B. J.; Blamire, M. G.

2010-12-01

The recent discovery of nonlinear current-dependent magnetoresistance in dual spin valve devices [A. Aziz, O. P. Wessely, M. Ali, D. M. Edwards, C. H. Marrows, B. J. Hickey, and M. G. Blamire, Phys. Rev. Lett. 103, 237203 (2009)10.1103/PhysRevLett.103.237203] opens up the possibility for distinct physics which extends the standard model of giant magnetoresistance. When the outer ferromagnetic layers of a dual spin valve are antiparallel, the resulting accumulation of spin in the middle ferromagnetic layer strongly modifies its bulk and interfacial spin asymmetry and resistance. Here, we report experimental evidence of the role of bulk spin accumulation in this nonlinear effect and show that interfacial spin accumulation alone cannot account for the observed dependence of the effect on the thickness of the middle ferromagnetic layer. It is also shown that spin torque acting on the middle ferromagnetic layer combined with the nonlinear effect might be useful in understanding the dynamical features associated with the nonlinear behavior.

Genetic polymorphisms of xeroderma pigmentosum group D gene Asp312Asn and Lys751Gln and susceptibility to prostate cancer: a systematic review and meta-analysis.

PubMed

Ma, Qingtong; Qi, Can; Tie, Chong; Guo, Zhanjun

2013-11-10

Many studies have reported the role of xeroderma pigmentosum group D (XPD) with prostate cancer risk, but the results remained controversial. To derive a more precise estimation of the relationship, a meta-analysis was performed. Odds ratios (ORs) with 95% confidence intervals (CIs) were estimated to assess the association between XPD Asp312Asn and Lys751Gln polymorphisms and prostate cancer risk. A total of 8 studies including 2620 cases and 3225 controls described Asp312Asn genotypes, among which 10 articles involving 3230 cases and 3582 controls described Lys751Gln genotypes and were also involved in this meta-analysis. When all the eligible studies were pooled into this meta-analysis, a significant association between prostate cancer risk and XPD Asp312Asn polymorphism was found. For Asp312Asn polymorphism, in the stratified analysis by ethnicity and source of controls, prostate cancer risk was observed in co-dominant, dominant and recessive models, while no evidence of any associations of XPD Lys751Gln polymorphism with prostate cancer was found in the overall or subgroup analyses. Our meta-analysis supports that the XPD Asp312Asn polymorphism contributed to the risk of prostate cancer from currently available evidence. However, a study with a larger sample size is needed to further evaluate gene-environment interaction on XPD Asp312Asn and Lys751Gln polymorphisms and prostate cancer risk. © 2013.

A two-dimensional spin field-effect switch

NASA Astrophysics Data System (ADS)

Yan, Wenjing; Txoperena, Oihana; Llopis, Roger; Dery, Hanan; Hueso, Luis E.; Casanova, Fèlix

2016-11-01

Future development in spintronic devices will require an advanced control of spin currents, for example by an electric field. Here we demonstrate an approach that differs from previous proposals such as the Datta and Das modulator, and that is based on a van de Waals heterostructure of atomically thin graphene and semiconducting MoS2. Our device combines the superior spin transport properties of graphene with the strong spin-orbit coupling of MoS2 and allows switching of the spin current in the graphene channel between ON and OFF states by tuning the spin absorption into the MoS2 with a gate electrode. Our proposal holds potential for technologically relevant applications such as search engines or pattern recognition circuits, and opens possibilities towards electrical injection of spins into transition metal dichalcogenides and alike materials.

Solution-processed organic spin-charge converter.

PubMed

Ando, Kazuya; Watanabe, Shun; Mooser, Sebastian; Saitoh, Eiji; Sirringhaus, Henning

2013-07-01

Conjugated polymers and small organic molecules are enabling new, flexible, large-area, low-cost optoelectronic devices, such as organic light-emitting diodes, transistors and solar cells. Owing to their exceptionally long spin lifetimes, these carbon-based materials could also have an important impact on spintronics, where carrier spins play a key role in transmitting, processing and storing information. However, to exploit this potential, a method for direct conversion of spin information into an electric signal is indispensable. Here we show that a pure spin current can be produced in a solution-processed conducting polymer by pumping spins through a ferromagnetic resonance in an adjacent magnetic insulator, and that this generates an electric voltage across the polymer film. We demonstrate that the experimental characteristics of the generated voltage are consistent with it being generated through an inverse spin Hall effect in the conducting polymer. In contrast with inorganic materials, the conducting polymer exhibits coexistence of high spin-current to charge-current conversion efficiency and long spin lifetimes. Our discovery opens a route for a new generation of molecular-structure-engineered spintronic devices, which could lead to important advances in plastic spintronics.

Designing spin-channel geometries for entanglement distribution

NASA Astrophysics Data System (ADS)

Levi, E. K.; Kirton, P. G.; Lovett, B. W.

2016-09-01

We investigate different geometries of spin-1/2 nitrogen impurity channels for distributing entanglement between pairs of remote nitrogen vacancy centers (NVs) in diamond. To go beyond the system size limits imposed by directly solving the master equation, we implement a matrix product operator method to describe the open system dynamics. In so doing, we provide an early demonstration of how the time-evolving block decimation algorithm can be used for answering a problem related to a real physical system that could not be accessed by other methods. For a fixed NV separation there is an interplay between incoherent impurity spin decay and coherent entanglement transfer: Long-transfer-time, few-spin systems experience strong dephasing that can be overcome by increasing the number of spins in the channel. We examine how missing spins and disorder in the coupling strengths affect the dynamics, finding that in some regimes a spin ladder is a more effective conduit for information than a single-spin chain.

Enhanced thermo-spin effects in iron-oxide/metal multilayers

NASA Astrophysics Data System (ADS)

Ramos, R.; Lucas, I.; Algarabel, P. A.; Morellón, L.; Uchida, K.; Saitoh, E.; Ibarra, M. R.

2018-06-01

Since the discovery of the spin Seebeck effect (SSE), much attention has been devoted to the study of the interaction between heat, spin, and charge in magnetic systems. The SSE refers to the generation of a spin current upon the application of a thermal gradient and detected by means of the inverse spin Hall effect. Conversely, the spin Peltier effect (SPE) refers to the generation of a heat current as a result of a spin current induced by the spin Hall effect. Here we report a strong enhancement of both the SSE and SPE in Fe3O4/Pt multilayered thin films at room temperature as a result of an increased thermo-spin conversion efficiency in the multilayers. These results open the possibility to design thin film heterostructures that may boost the application of thermal spin currents in spintronics.

Hierarchical spin-orbital polarization of a giant Rashba system

PubMed Central

Bawden, Lewis; Riley, Jonathan M.; Kim, Choong H.; Sankar, Raman; Monkman, Eric J.; Shai, Daniel E.; Wei, Haofei I.; Lochocki, Edward B.; Wells, Justin W.; Meevasana, Worawat; Kim, Timur K.; Hoesch, Moritz; Ohtsubo, Yoshiyuki; Le Fèvre, Patrick; Fennie, Craig J.; Shen, Kyle M.; Chou, Fangcheng; King, Phil D. C.

2015-01-01

The Rashba effect is one of the most striking manifestations of spin-orbit coupling in solids and provides a cornerstone for the burgeoning field of semiconductor spintronics. It is typically assumed to manifest as a momentum-dependent splitting of a single initially spin-degenerate band into two branches with opposite spin polarization. Combining polarization-dependent and resonant angle-resolved photoemission measurements with density functional theory calculations, we show that the two “spin-split” branches of the model giant Rashba system BiTeI additionally develop disparate orbital textures, each of which is coupled to a distinct spin configuration. This necessitates a reinterpretation of spin splitting in Rashba-like systems and opens new possibilities for controlling spin polarization through the orbital sector. PMID:26601268

Hierarchical spin-orbital polarization of a giant Rashba system.

PubMed

Bawden, Lewis; Riley, Jonathan M; Kim, Choong H; Sankar, Raman; Monkman, Eric J; Shai, Daniel E; Wei, Haofei I; Lochocki, Edward B; Wells, Justin W; Meevasana, Worawat; Kim, Timur K; Hoesch, Moritz; Ohtsubo, Yoshiyuki; Le Fèvre, Patrick; Fennie, Craig J; Shen, Kyle M; Chou, Fangcheng; King, Phil D C

2015-09-01

The Rashba effect is one of the most striking manifestations of spin-orbit coupling in solids and provides a cornerstone for the burgeoning field of semiconductor spintronics. It is typically assumed to manifest as a momentum-dependent splitting of a single initially spin-degenerate band into two branches with opposite spin polarization. Combining polarization-dependent and resonant angle-resolved photoemission measurements with density functional theory calculations, we show that the two "spin-split" branches of the model giant Rashba system BiTeI additionally develop disparate orbital textures, each of which is coupled to a distinct spin configuration. This necessitates a reinterpretation of spin splitting in Rashba-like systems and opens new possibilities for controlling spin polarization through the orbital sector.

Spin transport in epitaxial graphene

NASA Astrophysics Data System (ADS)

Tbd, -

2014-03-01

Spintronics is a paradigm focusing on spin as the information vector in fast and ultra-low-power non volatile devices such as the new STT-MRAM. Beyond its widely distributed application in data storage it aims at providing more complex architectures and a powerful beyond CMOS solution for information processing. The recent discovery of graphene has opened novel exciting opportunities in terms of functionalities and performances for spintronics devices. We will present experimental results allowing us to assess the potential of graphene for spintronics. We will show that unprecedented highly efficient spin information transport can occur in epitaxial graphene leading to large spin signals and macroscopic spin diffusion lengths (~ 100 microns), a key enabler for the advent of envisioned beyond-CMOS spin-based logic architectures. We will also show that how the device behavior is well explained within the framework of the Valet-Fert drift-diffusion equations. Furthermore, we will show that a thin graphene passivation layer can prevent the oxidation of a ferromagnet, enabling its use in novel humide/ambient low-cost processes for spintronics devices, while keeping its highly surface sensitive spin current polarizer/analyzer behavior and adding new enhanced spin filtering property. These different experiments unveil promising uses of graphene for spintronics.

Current induced multi-mode propagating spin waves in a spin transfer torque nano-contact with strong perpendicular magnetic anisotropy

NASA Astrophysics Data System (ADS)

Mohseni, S. Morteza; Yazdi, H. F.; Hamdi, M.; Brächer, T.; Mohseni, S. Majid

2018-03-01

Current induced spin wave excitations in spin transfer torque nano-contacts are known as a promising way to generate exchange-dominated spin waves at the nano-scale. It has been shown that when these systems are magnetized in the film plane, broken spatial symmetry of the field around the nano-contact induced by the Oersted field opens the possibility for spin wave mode co-existence including a non-linear self-localized spin-wave bullet and a propagating mode. By means of micromagnetic simulations, here we show that in systems with strong perpendicular magnetic anisotropy (PMA) in the free layer, two propagating spin wave modes with different frequency and spatial distribution can be excited simultaneously. Our results indicate that in-plane magnetized spin transfer nano-contacts in PMA materials do not host a solitonic self-localized spin-wave bullet, which is different from previous studies for systems with in plane magnetic anisotropy. This feature renders them interesting for nano-scale magnonic waveguides and crystals since magnon transport can be configured by tuning the applied current.

Antiferromagnetic Spin Wave Field-Effect Transistor

DOE PAGES

Cheng, Ran; Daniels, Matthew W.; Zhu, Jian-Gang; ...

2016-04-06

In a collinear antiferromagnet with easy-axis anisotropy, symmetry dictates that the spin wave modes must be doubly degenerate. Theses two modes, distinguished by their opposite polarization and available only in antiferromagnets, give rise to a novel degree of freedom to encode and process information. We show that the spin wave polarization can be manipulated by an electric field induced Dzyaloshinskii-Moriya interaction and magnetic anisotropy. We propose a prototype spin wave field effect transistor which realizes a gate-tunable magnonic analog of the Faraday effect, and demonstrate its application in THz signal modulation. In conclusion, our findings open up the exciting possibilitymore » of digital data processing utilizing antiferromagnetic spin waves and enable the direct projection of optical computing concepts onto the mesoscopic scale.« less

Spin-Dependent Transport through Chiral Molecules Studied by Spin-Dependent Electrochemistry

PubMed Central

2016-01-01

��dark” measurements, we also describe photoelectrochemical measurements in which light is used to affect the spin selective electron transport through the chiral molecules. We describe how the excitation of a chromophore (such as CdSe nanoparticles), which is attached to a chiral working electrode, can flip the preferred spin orientation of the photocurrent, when measured under the identical conditions. Thus, chirality-induced spin polarization, when combined with light and magnetic field effects, opens new avenues for the study of the spin transport properties of chiral molecules and biomolecules and for creating new types of spintronic devices in which light and molecular chirality provide new functions and properties. PMID:27797176

Full control of the spin-wave damping in a magnetic insulator using spin orbit torque

NASA Astrophysics Data System (ADS)

Klein, Olivier

2015-03-01

The spin-orbit interaction (SOI) has been an interesting and useful addition in the field of spintronics by opening it to non-metallic magnet. It capitalizes on adjoining a strong SOI normal metal next to a thin magnetic layer. The SOI converts a charge current, Jc, into a spin current, Js, with an efficiency parametrized by ΘSH, the spin Hall angle. An important benefit of the SOI is that Jc and Js are linked through a cross-product, allowing a charge current flowing in-plane to produce a spin current flowing out-of-plane. Hence it enables the transfer of spin angular momentum to non-metallic materials and in particular to insulating oxides, which offer improved performance compared to their metallic counterparts. Among all oxides, Yttrium Iron Garnet (YIG) holds a special place for having the lowest known spin-wave (SW) damping factor. Until recently the transmission of spin current through the YIG|Pt interface has been subject to debate. While numerous experiments have reported that Js produced by the excitation of ferromagnetic resonance (FMR) in YIG can cross efficiently the YIG|Pt interface and be converted into Jc in Pt through the inverse spin Hall effect (ISHE), most attempts to observe the reciprocal effect, where Js produced in Pt by the direct spin Hall effect (SHE) is transferred to YIG, resulting in damping compensation, have failed. This has been raising fundamental questions about the reciprocity of the spin transparency of the interface between a metal and a magnetic insulator. In this talk it will be demonstrated that the threshold current for damping compensation can be reached in a 5 μm diameter YIG(20nm)|Pt(7nm) disk. Reduction of both the thickness and lateral size of a YIG-structure were key to reach the microwave generation threshold current, Jc*. The experimental evidence rests upon the measurement of the ferromagnetic resonance linewidth as a function of Idc using a magnetic resonance force microscope (MRFM). It is shwon that the

A two-dimensional spin field-effect switch

DOE PAGES

Yan, Wenjing; Txoperena, Oihana; Llopis, Roger; ...

2016-11-11

Future development in spintronic devices will require an advanced control of spin currents, for example by an electric field. Here we demonstrate an approach that differs from previous proposals such as the Datta and Das modulator, and that is based on a van de Waals heterostructure of atomically thin graphene and semiconducting MoS 2. Our device combines the superior spin transport properties of graphene with the strong spin–orbit coupling of MoS 2 and allows switching of the spin current in the graphene channel between ON and OFF states by tuning the spin absorption into the MoS 2 with a gatemore » electrode. Lastly, our proposal holds potential for technologically relevant applications such as search engines or pattern recognition circuits, and opens possibilities towards electrical injection of spins into transition metal dichalcogenides and alike materials.« less

PREFACE: Spin Electronics

NASA Astrophysics Data System (ADS)

Dieny, B.; Sousa, R.; Prejbeanu, L.

2007-04-01

tunnel junctions were introduced as memory elements in new types of non-volatile magnetic memories (MRAM). A first 4Mbit product was launched by Freescale in July 2006. Future generations of memories are being developed by academic groups or companies. the combination of magnetic elements with CMOS components opens a whole new paradigm in hybrid electronic components which can change the common conception of the architecture of complex electronic components with a much tighter integration of logic and memory. the steady magnetic excitations stimulated by spin-transfer might be used in a variety of microwave components provided the output power can be increased. Intense research and development efforts are being aimed at increasing this power by the synchronization of oscillators. The articles compiled in this special issue of Journal of Physics: Condensed Matter, devoted to spin electronics, review these recent developments. All the contributors are greatly acknowledged.

Parity-Time Symmetry Breaking in Spin Chains.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galda, Alexey; Vinokur, Valerii M.

We investigate nonequilibrium phase transitions in classical Heisenberg spin chains associated with spontaneous breaking of parity-time (PT) symmetry of the system under the action of Slonczewski spin-transfer torque (STT) modeled by an applied imaginary magnetic field. We reveal the STT-driven PT symmetry-breaking phase transition between the regimes of precessional and exponentially damped spin dynamics and show that its several properties can be derived from the distribution of zeros of the system's partition function, the approach first introduced by Yang and Lee for studying equilibrium phase transitions in Ising spin chains. The physical interpretation of imaginary magnetic field as describing themore » action of nonconservative forces opens the possibility of direct observations of Lee-Yang zeros in nonequilibrium physical systems.« less

Parity-time symmetry breaking in spin chains

NASA Astrophysics Data System (ADS)

Galda, Alexey; Vinokur, Valerii M.

2018-05-01

We investigate nonequilibrium phase transitions in classical Heisenberg spin chains associated with spontaneous breaking of parity-time (PT ) symmetry of the system under the action of Slonczewski spin-transfer torque (STT) modeled by an applied imaginary magnetic field. We reveal the STT-driven PT symmetry-breaking phase transition between the regimes of precessional and exponentially damped spin dynamics and show that its several properties can be derived from the distribution of zeros of the system's partition function, the approach first introduced by Yang and Lee for studying equilibrium phase transitions in Ising spin chains. The physical interpretation of imaginary magnetic field as describing the action of nonconservative forces opens the possibility of direct observations of Lee-Yang zeros in nonequilibrium physical systems.

Spin-polarized confined states in Ag films on Fe(110)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moras, Paolo; Bihlmayer, G.; Vescovo, Elio

Spin- and angle-resolved photoemission spectroscopy of thin Ag(111) films on ferromagnetic Fe(110) shows a series of spin-polarized peaks. These features derive from Ag sp-bands, which form quantum well states and resonances due to confinement by a spin-dependent interface potential barrier. The spin-up states are broader and located at higher binding energy than the corresponding spin-down states at Gamma, although the differences attenuate near the Fermi level. The spin-down states display multiple gap openings, which interrupt their parabolic-like dispersion. As a result, first-principles calculations attribute these findings to the symmetry- and spin-selective hybridization of the Ag states with the exchange-split bandsmore » of the substrate.« less

Spin-polarized confined states in Ag films on Fe(110)

DOE PAGES

Moras, Paolo; Bihlmayer, G.; Vescovo, Elio; ...

2017-11-16

Spin- and angle-resolved photoemission spectroscopy of thin Ag(111) films on ferromagnetic Fe(110) shows a series of spin-polarized peaks. These features derive from Ag sp-bands, which form quantum well states and resonances due to confinement by a spin-dependent interface potential barrier. The spin-up states are broader and located at higher binding energy than the corresponding spin-down states at Gamma, although the differences attenuate near the Fermi level. The spin-down states display multiple gap openings, which interrupt their parabolic-like dispersion. As a result, first-principles calculations attribute these findings to the symmetry- and spin-selective hybridization of the Ag states with the exchange-split bandsmore » of the substrate.« less

A two-dimensional spin field-effect switch

NASA Astrophysics Data System (ADS)

Casanova, Felix

The integration of the spin degree of freedom in charge-based electronic devices has revolutionised both sensing and memory capability in microelectronics. Further development in spintronic devices requires electrical manipulation of spin current for logic operations. The mainstream approach followed so far, inspired by the seminal proposal of the Datta and Das spin modulator, has relied on the spin-orbit field as a medium for electrical control of the spin state. However, the still standing challenge is to find a material whose spin-orbit coupling (SOC) is weak enough to transport spins over long distances, while also being strong enough to allow their electrical manipulation. In our recent work, we demonstrate a radically different approach by engineering a van der Waals heterostructure from atomically thin crystals, and which combines the superior spin transport properties of graphene with the strong SOC of MoS2, a transition metal dichalcogenide with semiconducting properties. The spin transport in the graphene channel is modulated between ON and OFF states by tuning the spin absorption into the MoS2 layer with a gate electrode. Our demonstration of a spin field-effect switch using two-dimensional (2D) materials identifies a new route towards spin logic operations for beyond CMOS technology. Furthermore, the van der Waals heterostructure at the core of our experiments opens the path for fundamental research of exotic transport properties predicted for transition metal dichalcogenides, in which electrical spin injection has so far been elusive.

Terahertz spin current pulses controlled by magnetic heterostructures

NASA Astrophysics Data System (ADS)

Kampfrath, T.; Battiato, M.; Maldonado, P.; Eilers, G.; Nötzold, J.; Mährlein, S.; Zbarsky, V.; Freimuth, F.; Mokrousov, Y.; Blügel, S.; Wolf, M.; Radu, I.; Oppeneer, P. M.; Münzenberg, M.

2013-04-01

In spin-based electronics, information is encoded by the spin state of electron bunches. Processing this information requires the controlled transport of spin angular momentum through a solid, preferably at frequencies reaching the so far unexplored terahertz regime. Here, we demonstrate, by experiment and theory, that the temporal shape of femtosecond spin current bursts can be manipulated by using specifically designed magnetic heterostructures. A laser pulse is used to drive spins from a ferromagnetic iron thin film into a non-magnetic cap layer that has either low (ruthenium) or high (gold) electron mobility. The resulting transient spin current is detected by means of an ultrafast, contactless amperemeter based on the inverse spin Hall effect, which converts the spin flow into a terahertz electromagnetic pulse. We find that the ruthenium cap layer yields a considerably longer spin current pulse because electrons are injected into ruthenium d states, which have a much lower mobility than gold sp states. Thus, spin current pulses and the resulting terahertz transients can be shaped by tailoring magnetic heterostructures, which opens the door to engineering high-speed spintronic devices and, potentially, broadband terahertz emitters.

First example of a high-level correlated calculation of the indirect spin-spin coupling constants involving tellurium: tellurophene and divinyl telluride.

PubMed

Rusakov, Yury Yu; Krivdin, Leonid B; Østerstrøm, Freja F; Sauer, Stephan P A; Potapov, Vladimir A; Amosova, Svetlana V

2013-08-21

This paper documents the very first example of a high-level correlated calculation of spin-spin coupling constants involving tellurium taking into account relativistic effects, vibrational corrections and solvent effects for medium sized organotellurium molecules. The (125)Te-(1)H spin-spin coupling constants of tellurophene and divinyl telluride were calculated at the SOPPA and DFT levels, in good agreement with experimental data. A new full-electron basis set, av3z-J, for tellurium derived from the "relativistic" Dyall's basis set, dyall.av3z, and specifically optimized for the correlated calculations of spin-spin coupling constants involving tellurium was developed. The SOPPA method shows a much better performance compared to DFT, if relativistic effects calculated within the ZORA scheme are taken into account. Vibrational and solvent corrections are next to negligible, while conformational averaging is of prime importance in the calculation of (125)Te-(1)H spin-spin couplings. Based on the performed calculations at the SOPPA(CCSD) level, a marked stereospecificity of geminal and vicinal (125)Te-(1)H spin-spin coupling constants originating in the orientational lone pair effect of tellurium has been established, which opens a new guideline in organotellurium stereochemistry.

Cavity Mediated Manipulation of Distant Spin Currents Using a Cavity-Magnon-Polariton.

PubMed

Bai, Lihui; Harder, Michael; Hyde, Paul; Zhang, Zhaohui; Hu, Can-Ming; Chen, Y P; Xiao, John Q

2017-05-26

Using electrical detection of a strongly coupled spin-photon system comprised of a microwave cavity mode and two magnetic samples, we demonstrate the long distance manipulation of spin currents. This distant control is not limited by the spin diffusion length, instead depending on the interplay between the local and global properties of the coupled system, enabling systematic spin current control over large distance scales (several centimeters in this work). This flexibility opens the door to improved spin current generation and manipulation for cavity spintronic devices.

(3) He Spin Filter for Neutrons.

PubMed

Batz, M; Baeßler, S; Heil, W; Otten, E W; Rudersdorf, D; Schmiedeskamp, J; Sobolev, Y; Wolf, M

2005-01-01

The strongly spin-dependent absorption of neutrons in nuclear spin-polarized (3)He opens up the possibility of polarizing neutrons from reactors and spallation sources over the full kinematical range of cold, thermal and hot neutrons. This paper gives a report on the neutron spin filter (NSF) development program at Mainz. The polarization technique is based on direct optical pumping of metastable (3)He atoms combined with a polarization preserving mechanical compression of the gas up to a pressure of several bar, necessary to run a NSF. The concept of a remote type of operation using detachable NSF cells is presented which requires long nuclear spin relaxation times of order 100 hours. A short survey of their use under experimental conditions, e.g. large solid-angle polarization analysis, is given. In neutron particle physics NSFs are used in precision measurements to test fundamental symmetry concepts.

3He Spin Filter for Neutrons

PubMed Central

Batz, M.; Baeßler, S.; Heil, W.; Otten, E. W.; Rudersdorf, D.; Schmiedeskamp, J.; Sobolev, Y.; Wolf, M.

2005-01-01

The strongly spin-dependent absorption of neutrons in nuclear spin-polarized 3He opens up the possibility of polarizing neutrons from reactors and spallation sources over the full kinematical range of cold, thermal and hot neutrons. This paper gives a report on the neutron spin filter (NSF) development program at Mainz. The polarization technique is based on direct optical pumping of metastable 3He atoms combined with a polarization preserving mechanical compression of the gas up to a pressure of several bar, necessary to run a NSF. The concept of a remote type of operation using detachable NSF cells is presented which requires long nuclear spin relaxation times of order 100 hours. A short survey of their use under experimental conditions, e.g. large solid-angle polarization analysis, is given. In neutron particle physics NSFs are used in precision measurements to test fundamental symmetry concepts. PMID:27308139

Spin-filtering at COSY

NASA Astrophysics Data System (ADS)

Weidemann, Christian; PAX Collaboration

2011-05-01

The Spin Filtering experiments at COSY and AD at CERN within the framework of the Polarized Antiproton EXperiments (PAX) are proposed to determine the spin-dependent cross sections in bar pp scattering by observation of the buildup of polarization of an initially unpolarized stored antiproton beam after multiple passage through an internal polarized gas target. In order to commission the experimental setup for the AD and to understand the relevant machine parameters spin-filtering will first be done with protons at COSY. A first major step toward this goal has been achieved with the installation of the required mini-β section in summer 2009 and it's commissioning in January 2010. The target chamber together with the atomic beam source and the so-called Breit-Rabi polarimeter have been installed and commissioned in summer 2010. In addition an openable storage cell has been used. It provides a target thickness of 5·1013 atoms/cm2. We report on the status of spin-filtering experiments at COSY and the outcome of a recent beam time including studies on beam lifetime limitations like intra-beam scattering and the electron-cooling performance as well as machine acceptance studies.

Spin transport and spin torque in antiferromagnetic devices

DOE PAGES

Zelezny, J.; Wadley, P.; Olejnik, K.; ...

2018-03-02

Ferromagnets are key materials for sensing and memory applications. In contrast, antiferromagnets which represent the more common form of magnetically ordered materials, have found less practical application beyond their use for establishing reference magnetic orientations via exchange bias. This might change in the future due to the recent progress in materials research and discoveries of antiferromagnetic spintronic phenomena suitable for device applications. Experimental demonstration of the electrical switching and detection of the Néel order open a route towards memory devices based on antiferromagnets. Apart from the radiation and magnetic-field hardness, memory cells fabricated from antiferromagnets can be inherently multilevel, whichmore » could be used for neuromorphic computing. Switching speeds attainable in antiferromagnets far exceed those of ferromagnetic and semiconductor memory technologies. Here we review the recent progress in electronic spin-transport and spin-torque phenomena in antiferromagnets that are dominantly of the relativistic quantum mechanical origin. We discuss their utility in pure antiferromagnetic or hybrid ferromagnetic/antiferromagnetic memory devices.« less

Spin transport and spin torque in antiferromagnetic devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zelezny, J.; Wadley, P.; Olejnik, K.

Ferromagnets are key materials for sensing and memory applications. In contrast, antiferromagnets which represent the more common form of magnetically ordered materials, have found less practical application beyond their use for establishing reference magnetic orientations via exchange bias. This might change in the future due to the recent progress in materials research and discoveries of antiferromagnetic spintronic phenomena suitable for device applications. Experimental demonstration of the electrical switching and detection of the Néel order open a route towards memory devices based on antiferromagnets. Apart from the radiation and magnetic-field hardness, memory cells fabricated from antiferromagnets can be inherently multilevel, whichmore » could be used for neuromorphic computing. Switching speeds attainable in antiferromagnets far exceed those of ferromagnetic and semiconductor memory technologies. Here we review the recent progress in electronic spin-transport and spin-torque phenomena in antiferromagnets that are dominantly of the relativistic quantum mechanical origin. We discuss their utility in pure antiferromagnetic or hybrid ferromagnetic/antiferromagnetic memory devices.« less

Spin transport and spin torque in antiferromagnetic devices

NASA Astrophysics Data System (ADS)

Železný, J.; Wadley, P.; Olejník, K.; Hoffmann, A.; Ohno, H.

2018-03-01

Ferromagnets are key materials for sensing and memory applications. In contrast, antiferromagnets, which represent the more common form of magnetically ordered materials, have found less practical application beyond their use for establishing reference magnetic orientations via exchange bias. This might change in the future due to the recent progress in materials research and discoveries of antiferromagnetic spintronic phenomena suitable for device applications. Experimental demonstration of the electrical switching and detection of the Néel order open a route towards memory devices based on antiferromagnets. Apart from the radiation and magnetic-field hardness, memory cells fabricated from antiferromagnets can be inherently multilevel, which could be used for neuromorphic computing. Switching speeds attainable in antiferromagnets far exceed those of ferromagnetic and semiconductor memory technologies. Here, we review the recent progress in electronic spin-transport and spin-torque phenomena in antiferromagnets that are dominantly of the relativistic quantum-mechanical origin. We discuss their utility in pure antiferromagnetic or hybrid ferromagnetic/antiferromagnetic memory devices.

Hydrodynamics of Normal Atomic Gases with Spin-orbit Coupling

PubMed Central

Hou, Yan-Hua; Yu, Zhenhua

2015-01-01

Successful realization of spin-orbit coupling in atomic gases by the NIST scheme opens the prospect of studying the effects of spin-orbit coupling on many-body physics in an unprecedentedly controllable way. Here we derive the linearized hydrodynamic equations for the normal atomic gases of the spin-orbit coupling by the NIST scheme with zero detuning. We show that the hydrodynamics of the system crucially depends on the momentum susceptibilities which can be modified by the spin-orbit coupling. We reveal the effects of the spin-orbit coupling on the sound velocities and the dipole mode frequency of the gases by applying our formalism to the ideal Fermi gas. We also discuss the generalization of our results to other situations. PMID:26483090

Hydrodynamics of Normal Atomic Gases with Spin-orbit Coupling.

PubMed

Hou, Yan-Hua; Yu, Zhenhua

2015-10-20

Successful realization of spin-orbit coupling in atomic gases by the NIST scheme opens the prospect of studying the effects of spin-orbit coupling on many-body physics in an unprecedentedly controllable way. Here we derive the linearized hydrodynamic equations for the normal atomic gases of the spin-orbit coupling by the NIST scheme with zero detuning. We show that the hydrodynamics of the system crucially depends on the momentum susceptibilities which can be modified by the spin-orbit coupling. We reveal the effects of the spin-orbit coupling on the sound velocities and the dipole mode frequency of the gases by applying our formalism to the ideal Fermi gas. We also discuss the generalization of our results to other situations.

Generation of spin currents by surface plasmon resonance

PubMed Central

Uchida, K.; Adachi, H.; Kikuchi, D.; Ito, S.; Qiu, Z.; Maekawa, S.; Saitoh, E.

2015-01-01

Surface plasmons, free-electron collective oscillations in metallic nanostructures, provide abundant routes to manipulate light–electron interactions that can localize light energy and alter electromagnetic field distributions at subwavelength scales. The research field of plasmonics thus integrates nano-photonics with electronics. In contrast, electronics is also entering a new era of spintronics, where spin currents play a central role in driving devices. However, plasmonics and spin-current physics have so far been developed independently. Here we report the generation of spin currents by surface plasmon resonance. Using Au nanoparticles embedded in Pt/BiY2Fe5O12 bilayer films, we show that, when the Au nanoparticles fulfill the surface-plasmon-resonance conditions, spin currents are generated across the Pt/BiY2Fe5O12 interface. This spin-current generation cannot be explained by conventional heating effects, requiring us to introduce nonequilibrium magnons excited by surface-plasmon-induced evanescent electromagnetic fields in BiY2Fe5O12. This plasmonic spin pumping integrates surface plasmons with spin-current physics, opening the door to plasmonic spintronics. PMID:25569821

Control of single-spin magnetic anisotropy by exchange coupling

NASA Astrophysics Data System (ADS)

Oberg, Jenny C.; Calvo, M. Reyes; Delgado, Fernando; Moro-Lagares, María; Serrate, David; Jacob, David; Fernández-Rossier, Joaquín; Hirjibehedin, Cyrus F.

2014-01-01

The properties of quantum systems interacting with their environment, commonly called open quantum systems, can be affected strongly by this interaction. Although this can lead to unwanted consequences, such as causing decoherence in qubits used for quantum computation, it can also be exploited as a probe of the environment. For example, magnetic resonance imaging is based on the dependence of the spin relaxation times of protons in water molecules in a host's tissue. Here we show that the excitation energy of a single spin, which is determined by magnetocrystalline anisotropy and controls its stability and suitability for use in magnetic data-storage devices, can be modified by varying the exchange coupling of the spin to a nearby conductive electrode. Using scanning tunnelling microscopy and spectroscopy, we observe variations up to a factor of two of the spin excitation energies of individual atoms as the strength of the spin's coupling to the surrounding electronic bath changes. These observations, combined with calculations, show that exchange coupling can strongly modify the magnetic anisotropy. This system is thus one of the few open quantum systems in which the energy levels, and not just the excited-state lifetimes, can be renormalized controllably. Furthermore, we demonstrate that the magnetocrystalline anisotropy, a property normally determined by the local structure around a spin, can be tuned electronically. These effects may play a significant role in the development of spintronic devices in which an individual magnetic atom or molecule is coupled to conducting leads.

Rotatable spin-polarized electron source for inverse-photoemission experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stolwijk, S. D., E-mail: Sebastian.Stolwijk@wwu.de; Wortelen, H.; Schmidt, A. B.

2014-01-15

We present a ROtatable Spin-polarized Electron source (ROSE) for the use in spin- and angle-resolved inverse-photoemission (SR-IPE) experiments. A key feature of the ROSE is a variable direction of the transversal electron beam polarization. As a result, the inverse-photoemission experiment becomes sensitive to two orthogonal in-plane polarization directions, and, for nonnormal electron incidence, to the out-of-plane polarization component. We characterize the ROSE and test its performance on the basis of SR-IPE experiments. Measurements on magnetized Ni films on W(110) serve as a reference to demonstrate the variable spin sensitivity. Moreover, investigations of the unoccupied spin-dependent surface electronic structure of Tl/Si(111)more » highlight the capability to analyze complex phenomena like spin rotations in momentum space. Essentially, the ROSE opens the way to further studies on complex spin-dependent effects in the field of surface magnetism and spin-orbit interaction at surfaces.« less

Long distance spin communication in chemical vapour deposited graphene

NASA Astrophysics Data System (ADS)

Kamalakar, M. Venkata; Groenveld, Christiaan; Dankert, André; Dash, Saroj P.

2015-04-01

Graphene is an ideal medium for long-distance spin communication in future spintronic technologies. So far, the prospect is limited by the smaller sizes of exfoliated graphene flakes and lower spin transport properties of large-area chemical vapour-deposited (CVD) graphene. Here we demonstrate a high spintronic performance in CVD graphene on SiO2/Si substrate at room temperature. We show pure spin transport and precession over long channel lengths extending up to 16 μm with a spin lifetime of 1.2 ns and a spin diffusion length ~6 μm at room temperature. These spin parameters are up to six times higher than previous reports and highest at room temperature for any form of pristine graphene on industrial standard SiO2/Si substrates. Our detailed investigation reinforces the observed performance in CVD graphene over wafer scale and opens up new prospects for the development of lateral spin-based memory and logic applications.

Graphene-diamond interface: Gap opening and electronic spin injection

NASA Astrophysics Data System (ADS)

Ma, Yandong; Dai, Ying; Guo, Meng; Huang, Baibiao

2012-06-01

Creating a finite band gap, injecting electronic spin, and finding a suitable substrate are the three important challenges for building graphene-based devices. Here, first-principles calculations are performed to investigate the electronic and magnetic properties of graphene adsorbed on the (111) surface of diamond, which is synthesized experimentally [Nature10.1038/nature09979 472, 74 (2011); J. Appl. Phys.10.1063/1.3627370 110, 044324 (2011); Nano Lett.10.1021/nl204545q 12, 1603 (2012); ACS Nano10.1021/nn204362p 6, 1018 (2012)]. Our results reveal that the graphene adsorbed on the diamond surface is a semiconductor with a finite gap depending on the adsorption arrangements due to the variation of on-site energy induced by the diamond surface, with the extra advantage of maintaining main characters of the linear band dispersion of graphene. More interestingly, different from typical graphene/semiconductor hybrid systems, we find that electronic spin can arise ``intrinsically'' in graphene owing to the exchange proximity interaction between electrons in graphene and localized electrons in the diamond surface rather than the characteristic graphene states. These predications strongly revive this new synthesized system as a viable candidate to overcome all the aforementioned challenges, providing an ideal platform for future graphene-based electronics.

Nanopatterned reconfigurable spin-textures for magnonics

NASA Astrophysics Data System (ADS)

Albisetti, E.; Petti, D.; Pancaldi, M.; Madami, M.; Tacchi, S.; Curtis, J.; King, W. P.; Papp, A.; Csaba, G.; Porod, W.; Vavassori, P.; Riedo, E.; Bertacco, R.

The control of spin-waves holds the promise to enable energy-efficient information transport and wave-based computing. Conventionally, the engineering of spin-waves is achieved via physically patterning magnetic structures such as magnonic crystals and micro-nanowires. We demonstrate a new concept for creating reconfigurable magnonic nanostructures, by crafting at the nanoscale the magnetic anisotropy landscape of a ferromagnet exchange-coupled to an antiferromagnet. By performing a highly localized field cooling with the hot tip of a scanning probe microscope, magnetic structures, with arbitrarily oriented magnetization and tunable unidirectional anisotropy, are patterned without modifying the film chemistry and topography. We demonstrate that, in such structures, the spin-wave excitation and propagation can be spatially controlled at remanence, and can be tuned by external magnetic fields. This opens the way to the use of nanopatterned spin-textures, such as domains and domain walls, for exciting and manipulating magnons in reconfigurable nanocircuits. Partially funded by the EC through project SWING (no. 705326).

Recent trends in spin-resolved photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Okuda, Taichi

2017-12-01

Since the discovery of the Rashba effect on crystal surfaces and also the discovery of topological insulators, spin- and angle-resolved photoelectron spectroscopy (SARPES) has become more and more important, as the technique can measure directly the electronic band structure of materials with spin resolution. In the same way that the discovery of high-Tc superconductors promoted the development of high-resolution angle-resolved photoelectron spectroscopy, the discovery of this new class of materials has stimulated the development of new SARPES apparatus with new functions and higher resolution, such as spin vector analysis, ten times higher energy and angular resolution than conventional SARPES, multichannel spin detection, and so on. In addition, the utilization of vacuum ultra violet lasers also opens a pathway to the realization of novel SARPES measurements. In this review, such recent trends in SARPES techniques and measurements will be overviewed.

Inverse spin Hall effect in a closed loop circuit

DOE Office of Scientific and Technical Information (OSTI.GOV)

Omori, Y.; Auvray, F.; Wakamura, T.

We present measurements of inverse spin Hall effects (ISHEs), in which the conversion of a spin current into a charge current via the ISHE is detected not as a voltage in a standard open circuit but directly as the charge current generated in a closed loop. The method is applied to the ISHEs of Bi-doped Cu and Pt. The derived expression of ISHE for the loop structure can relate the charge current flowing into the loop to the spin Hall angle of the SHE material and the resistance of the loop.

Going "open" with mesoscopy: a new dimension on multi-view imaging.

PubMed

Gualda, Emilio; Moreno, Nuno; Tomancak, Pavel; Martins, Gabriel G

2014-03-01

OpenSPIM and OpenSpinMicroscopy emerged as open access platforms for Light Sheet and Optical Projection Imaging, often called as optical mesoscopy techniques. Both projects can be easily reproduced using comprehensive online instructions that should foster the implementation and further development of optical imaging techniques with sample rotation control. This additional dimension in an open system offers the possibility to make multi-view microscopy easily modified and will complement the emerging commercial solutions. Furthermore, it is deeply based on other open platforms such as MicroManager and Arduino, enabling development of tailored setups for very specific biological questions. In our perspective, the open access principle of OpenSPIM and OpenSpinMicroscopy is a game-changer, helping the concepts of light sheet and optical projection tomography (OPT) to enter the mainstream of biological imaging.

Coherent ultrafast spin-dynamics probed in three dimensional topological insulators

PubMed Central

Boschini, F.; Mansurova, M.; Mussler, G.; Kampmeier, J.; Grützmacher, D.; Braun, L.; Katmis, F.; Moodera, J. S.; Dallera, C.; Carpene, E.; Franz, C.; Czerner, M.; Heiliger, C.; Kampfrath, T.; Münzenberg, M.

2015-01-01

Topological insulators are candidates to open up a novel route in spin based electronics. Different to traditional ferromagnetic materials, where the carrier spin-polarization and magnetization are based on the exchange interaction, the spin properties in topological insulators are based on the coupling of spin- and orbit interaction connected to its momentum. Specific ways to control the spin-polarization with light have been demonstrated: the energy momentum landscape of the Dirac cone provides spin-momentum locking of the charge current and its spin. We investigate a spin-related signal present only during the laser excitation studying real and imaginary part of the complex Kerr angle by disentangling spin and lattice contributions. This coherent signal is only present at the time of the pump-pulses’ light field and can be described in terms of a Raman coherence time. The Raman transition involves states at the bottom edge of the conduction band. We demonstrate a coherent femtosecond control of spin-polarization for electronic states at around the Dirac cone. PMID:26510509

Entangled spins and ghost-spins

NASA Astrophysics Data System (ADS)

Jatkar, Dileep P.; Narayan, K.

2017-09-01

We study patterns of quantum entanglement in systems of spins and ghost-spins regarding them as simple quantum mechanical toy models for theories containing negative norm states. We define a single ghost-spin as in [20] as a 2-state spin variable with an indefinite inner product in the state space. We find that whenever the spin sector is disentangled from the ghost-spin sector (both of which could be entangled within themselves), the reduced density matrix obtained by tracing over all the ghost-spins gives rise to positive entanglement entropy for positive norm states, while negative norm states have an entanglement entropy with a negative real part and a constant imaginary part. However when the spins are entangled with the ghost-spins, there are new entanglement patterns in general. For systems where the number of ghost-spins is even, it is possible to find subsectors of the Hilbert space where positive norm states always lead to positive entanglement entropy after tracing over the ghost-spins. With an odd number of ghost-spins however, we find that there always exist positive norm states with negative real part for entanglement entropy after tracing over the ghost-spins.

Adiabatic quantum computing with spin qubits hosted by molecules.

PubMed

Yamamoto, Satoru; Nakazawa, Shigeaki; Sugisaki, Kenji; Sato, Kazunobu; Toyota, Kazuo; Shiomi, Daisuke; Takui, Takeji

2015-01-28

A molecular spin quantum computer (MSQC) requires electron spin qubits, which pulse-based electron spin/magnetic resonance (ESR/MR) techniques can afford to manipulate for implementing quantum gate operations in open shell molecular entities. Importantly, nuclear spins, which are topologically connected, particularly in organic molecular spin systems, are client qubits, while electron spins play a role of bus qubits. Here, we introduce the implementation for an adiabatic quantum algorithm, suggesting the possible utilization of molecular spins with optimized spin structures for MSQCs. We exemplify the utilization of an adiabatic factorization problem of 21, compared with the corresponding nuclear magnetic resonance (NMR) case. Two molecular spins are selected: one is a molecular spin composed of three exchange-coupled electrons as electron-only qubits and the other an electron-bus qubit with two client nuclear spin qubits. Their electronic spin structures are well characterized in terms of the quantum mechanical behaviour in the spin Hamiltonian. The implementation of adiabatic quantum computing/computation (AQC) has, for the first time, been achieved by establishing ESR/MR pulse sequences for effective spin Hamiltonians in a fully controlled manner of spin manipulation. The conquered pulse sequences have been compared with the NMR experiments and shown much faster CPU times corresponding to the interaction strength between the spins. Significant differences are shown in rotational operations and pulse intervals for ESR/MR operations. As a result, we suggest the advantages and possible utilization of the time-evolution based AQC approach for molecular spin quantum computers and molecular spin quantum simulators underlain by sophisticated ESR/MR pulsed spin technology.

Spin Current Noise of the Spin Seebeck Effect and Spin Pumping

NASA Astrophysics Data System (ADS)

Matsuo, M.; Ohnuma, Y.; Kato, T.; Maekawa, S.

2018-01-01

We theoretically investigate the fluctuation of a pure spin current induced by the spin Seebeck effect and spin pumping in a normal-metal-(NM-)ferromagnet(FM) bilayer system. Starting with a simple ferromagnet-insulator-(FI-)NM interface model with both spin-conserving and non-spin-conserving processes, we derive general expressions of the spin current and the spin-current noise at the interface within second-order perturbation of the FI-NM coupling strength, and estimate them for a yttrium-iron-garnet-platinum interface. We show that the spin-current noise can be used to determine the effective spin carried by a magnon modified by the non-spin-conserving process at the interface. In addition, we show that it provides information on the effective spin of a magnon, heating at the interface under spin pumping, and spin Hall angle of the NM.

How the extra methylene group affects the ligation properties of Glu vs. Asp and Gln vs. Asn amino acids: a DFT/PCM study.

PubMed

Dudev, Todor; Doudeva, Lyudmila

2017-02-01

The effect of the extra methylene group on the ligation properties of glutamic (Glu) vs. aspartic (Asp) acid, and glutamine (Gln) vs. asparagine (Asn) amino acids-two pairs of protein building blocks differing by the length of their side chains-has been studied by employing DFT calculations combined with polarizable continuum model (PCM) computations. Complexes of the nominal species with partner ligands of various structures, charge states, and degree of solvent exposure have been examined. The results obtained reveal that the difference in the alkyl chain length of these amino acid residues does not affect the mode of their binding. This, however, influences the thermodynamics of the ligand-ligand and ligand-metal recognition thus bestowing unique ligation characteristics on the competing entities. The calculations reveal that the competition between the longer-chain and shorter-chain analogs is entropy driven and that the differential electronic effects are of minor importance for the process. Thus, the outcome of the rivalry between Asp and Glu, and Asn and Gln is almost unaffected by the nature of the partner ligand, its charge state and, in most cases, the dielectric properties of the binding site. The longer-chain Glu, as opposed to its shorter-chain Asp counterpart, is the preferred partner ligand in various protein binding sites. Contrariwise, the shorter-chain Asn binds more favorably to the respective binding sites than its longer-chain Gln analog. The results obtained shed additional light on the intimate mechanism of the ligand-ligand and ligand-metal recognition in proteins and could be employed as guidelines in protein engineering and design.

Role of β/δ101Gln in Regulating the Effect of Temperature and Allosteric Effectors on Oxygen Affinity in Woolly Mammoth Hemoglobin†

PubMed Central

Yuan, Yue; Byrd, Catherine; Shen, Tong-Jian; Simplaceanu, Virgil; Tam, Tsuey Chyi S.; Ho, Chien

2013-01-01

The oxygen affinity of woolly mammoth hemoglobin (rHb WM) is less affected by temperature change than that of Asian elephant hemoglobin (rHb AE) or human adult hemoglobin (Hb A). We report here a biochemical-biophysical study of Hb A, rHb AE, rHb WM and three rHb WM mutants with amino acid substitutions at β/δ101 (β/δ101Gln→Glu, Lys, or Asp) plus a double and a triple mutant, designed to clarify the role of the β/δ101 residue. The β/δ101Gln residue is important for responding to allosteric effectors, such as phosphate, inositol hexaphosphate (IHP), and chloride. The rHb WM mutants studied generally have higher affinity for oxygen under various conditions of pH, temperature, and salt concentration, and in the presence or absence of organic phosphate, than do rHb WM, rHb AE and Hb A. Titrations for the O2 affinity of these mutant rHbs as a function of chloride concentration indicate a lower heterotopic effect of this anion due to the replacement of β/δ101Gln in rHb WM. The alkaline Bohr effect of rHb WM and its mutants is reduced by 20–50% compared to that of Hb A and is independent of changes in temperature, in contrast to what has been observed in the hemoglobins of most mammalian species, including human. The results of our study on the temperature dependence of the O2 affinity of rHb WM and its mutant rHbs illustrate the important role of β/δ101Gln in regulating the functional properties of these hemoglobins. PMID:24228693

A magnetic phase-transition graphene transistor with tunable spin polarization

NASA Astrophysics Data System (ADS)

Vancsó, Péter; Hagymási, Imre; Tapasztó, Levente

2017-06-01

Graphene nanoribbons (GNRs) have been proposed as potential building blocks for field effect transistor (FET) devices due to their quantum confinement bandgap. Here, we propose a novel GNR device concept, enabling the control of both charge and spin signals, integrated within the simplest three-terminal device configuration. In a conventional FET device, a gate electrode is employed to tune the Fermi level of the system in and out of a static bandgap. By contrast, in the switching mechanism proposed here, the applied gate voltage can dynamically open and close an interaction gap, with only a minor shift of the Fermi level. Furthermore, the strong interplay of the band structure and edge spin configuration in zigzag ribbons enables such transistors to carry spin polarized current without employing an external magnetic field or ferromagnetic contacts. Using an experimentally validated theoretical model, we show that such transistors can switch at low voltages and high speed, and the spin polarization of the current can be tuned from 0% to 50% by using the same back gate electrode. Furthermore, such devices are expected to be robust against edge irregularities and can operate at room temperature. Controlling both charge and spin signal within the simplest FET device configuration could open up new routes in data processing with graphene based devices.

Full-gap superconductivity in spin-polarised surface states of topological semimetal β-PdBi2.

PubMed

Iwaya, K; Kohsaka, Y; Okawa, K; Machida, T; Bahramy, M S; Hanaguri, T; Sasagawa, T

2017-10-17

A bulk superconductor possessing a topological surface state at the Fermi level is a promising system to realise long-sought topological superconductivity. Although several candidate materials have been proposed, experimental demonstrations concurrently exploring spin textures and superconductivity at the surface have remained elusive. Here we perform spectroscopic-imaging scanning tunnelling microscopy on the centrosymmetric superconductor β-PdBi 2 that hosts a topological surface state. By combining first-principles electronic-structure calculations and quasiparticle interference experiments, we determine the spin textures at the surface, and show not only the topological surface state but also all other surface bands exhibit spin polarisations parallel to the surface. We find that the superconducting gap fully opens in all the spin-polarised surface states. This behaviour is consistent with a possible spin-triplet order parameter expected for such in-plane spin textures, but the observed superconducting gap amplitude is comparable to that of the bulk, suggesting that the spin-singlet component is predominant in β-PdBi 2 .Although several materials have been proposed as topological superconductors, spin textures and superconductivity at the surface remain elusive. Here, Iwaya et al. determine the spin textures at the surface of a superconductor β-PdBi 2 and find the superconducting gap opening in all spin-polarised surface states.

The determination of the in situ structure by nuclear spin contrast variation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stuhrmann, H.B.; Nierhaus, K.H.

1994-12-31

Polarized neutron scattering from polarized nuclear spins in hydrogenous substances opens a new way of contrast variation. The enhanced contrast due to proton spin polarization was used for the in situ structure determination of tRNA of the functional complex of the E.coli ribosome.

All electrical propagating spin wave spectroscopy with broadband wavevector capability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ciubotaru, F., E-mail: Florin.Ciubotaru@imec.be; KU Leuven, Departement Electrotechniek; Devolder, T.

2016-07-04

We developed an all electrical experiment to perform the broadband phase-resolved spectroscopy of propagating spin waves in micrometer sized thin magnetic stripes. The magnetostatic surface spin waves are excited and detected by scaled down to 125 nm wide inductive antennas, which award ultra broadband wavevector capability. The wavevector selection can be done by applying an excitation frequency above the ferromagnetic resonance. Wavevector demultiplexing is done at the spin wave detector thanks to the rotation of the spin wave phase upon propagation. A simple model accounts for the main features of the apparatus transfer functions. Our approach opens an avenue for themore » all electrical study of wavevector-dependent spin wave properties including dispersion spectra or non-reciprocal propagation.« less

Thermally driven magnetic precession in spin valves

NASA Astrophysics Data System (ADS)

Luc, David; Waintal, Xavier

2014-10-01

We investigate the angular dependence of the spin torque generated when applying a temperature difference across a spin valve. Our study shows the presence of a nontrivial fixed point in this angular dependence. This fixed point opens the possibility for a temperature gradient to stabilize radio frequency oscillations without the need for an external magnetic field. This so-called "wavy" behavior can already be found upon applying a voltage difference across a spin valve but we find that this effect is much more pronounced with a temperature difference. We find that a spin asymmetry of the Seebeck coefficient of the order of 20 μ VK -1 should be large enough for a temperature gradient of a few degrees to trigger the radio-frequency oscillations. Our semiclassical theory is fully parametrized with experimentally measured(able) parameters and allows one to quantitatively predict the amplitude of the torque.

Quantum communication through an unmodulated spin chain.

PubMed

Bose, Sougato

2003-11-14

We propose a scheme for using an unmodulated and unmeasured spin chain as a channel for short distance quantum communications. The state to be transmitted is placed on one spin of the chain and received later on a distant spin with some fidelity. We first obtain simple expressions for the fidelity of quantum state transfer and the amount of entanglement sharable between any two sites of an arbitrary Heisenberg ferromagnet using our scheme. We then apply this to the realizable case of an open ended chain with nearest neighbor interactions. The fidelity of quantum state transfer is obtained as an inverse discrete cosine transform and as a Bessel function series. We find that in a reasonable time, a qubit can be directly transmitted with better than classical fidelity across the full length of chains of up to 80 spins. Moreover, our channel allows distillable entanglement to be shared over arbitrary distances.

SPIN EVOLUTION OF ACCRETING YOUNG STARS. I. EFFECT OF MAGNETIC STAR-DISK COUPLING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matt, Sean P.; Greene, Thomas P.; Pinzon, Giovanni

2010-05-10

We present a model for the rotational evolution of a young, solar mass star interacting with an accretion disk. The model incorporates a description of the angular momentum transfer between the star and the disk due to a magnetic connection, and includes changes in the star's mass and radius and a decreasing accretion rate. The model also includes, for the first time in a spin evolution model, the opening of the stellar magnetic field lines, as expected to arise from twisting via star-disk differential rotation. In order to isolate the effect that this has on the star-disk interaction torques, wemore » neglect the influence of torques that may arise from open field regions connected to the star or disk. For a range of magnetic field strengths, accretion rates, and initial spin rates, we compute the stellar spin rates of pre-main-sequence stars as they evolve on the Hayashi track to an age of 3 Myr. How much the field opening affects the spin depends on the strength of the coupling of the magnetic field to the disk. For the relatively strong coupling (i.e., high magnetic Reynolds number) expected in real systems, all models predict spin periods of less than {approx}3 days, in the age range of 1-3 Myr. Furthermore, these systems typically do not reach an equilibrium spin rate within 3 Myr, so that the spin at any given time depends upon the choice of initial spin rate. This corroborates earlier suggestions that, in order to explain the full range of observed rotation periods of approximately 1-10 days, additional processes, such as the angular momentum loss from powerful stellar winds, are necessary.« less

Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

DOE PAGES

Ma, X.; Fang, F.; Li, Q.; ...

2015-10-28

In this study, optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recoverymore » time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.« less

Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

NASA Astrophysics Data System (ADS)

Ma, X.; Fang, F.; Li, Q.; Zhu, J.; Yang, Y.; Wu, Y. Z.; Zhao, H. B.; Lüpke, G.

2015-10-01

Optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.

Controlling nonlinear optical response in an open four-level molecular system using quantum control of spin-orbit interaction

NASA Astrophysics Data System (ADS)

Jamshidi-Ghaleh, Kazem; Ebrahimi-hamed, Zahra; Sahrai, Mostafa

2017-10-01

This paper investigates the behavior of linear and nonlinear optical susceptibility of an open four-level molecular system, under two-step excitation based on electromagnetically induced transparency (EIT). The system was irradiated with a weak probe field and strong coupling field. It is shown that the use of a strong coupling field in the triplet states of an alkali-metal dimer can change the spin-orbit interaction (SOI). The optical response of the system can then be modified in a controllable way. The electromagnetically induced transparency transforms into electromagnetically induced absorption (EIA) in the presence of a coupling field. Changing the sign of the dispersion, this region is associated with switching subluminal and superluminal propagation. Furthermore, for the proper value of the coupling field, the controllable parameters, enhanced Kerr nonlinearity with reduced linear absorption, can be obtained under a weak probe field. With this approach, SOI can be controlled by changing only one of the controllable parameters, using triplet-triplet strong coupling with different spin state. Therefore, the desired region of the spectra can be obtained, in contrast to the other four-level system, in which at least two strong fields are used to change optical properties. This mechanism can be suitable in molecular systems or semiconductors to be used in optical bistability and fast all-optical switching devices.

Spin-Dependent Processes Measured without a Permanent Magnet.

PubMed

Fontanesi, Claudio; Capua, Eyal; Paltiel, Yossi; Waldeck, David H; Naaman, Ron

2018-05-07

A novel Hall circuit design that can be incorporated into a working electrode, which is used to probe spin-selective charge transfer and charge displacement processes, is reviewed herein. The general design of a Hall circuit based on a semiconductor heterostructure, which forms a shallow 2D electron gas and is used as an electrode, is described. Three different types of spin-selective processes have been studied with this device in the past: i) photoinduced charge exchange between quantum dots and the working electrode through chiral molecules is associated with spin polarization that creates a local magnetization and generates a Hall voltage; ii) charge polarization of chiral molecules by an applied voltage is accompanied by a spin polarization that generates a Hall voltage; and iii) cyclic voltammetry (current-voltage) measurements of electrochemical redox reactions that can be spin-analyzed by the Hall circuit to provide a third dimension (spin) in addition to the well-known current and voltage dimensions. The three studies reviewed open new doors into understanding both the spin current and the charge current in electronic materials and electrochemical processes. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Magnetic nano-oscillator driven by pure spin current.

PubMed

Demidov, Vladislav E; Urazhdin, Sergei; Ulrichs, Henning; Tiberkevich, Vasyl; Slavin, Andrei; Baither, Dietmar; Schmitz, Guido; Demokritov, Sergej O

2012-12-01

With the advent of pure-spin-current sources, spin-based electronic (spintronic) devices no longer require electrical charge transfer, opening new possibilities for both conducting and insulating spintronic systems. Pure spin currents have been used to suppress noise caused by thermal fluctuations in magnetic nanodevices, amplify propagating magnetization waves, and to reduce the dynamic damping in magnetic films. However, generation of coherent auto-oscillations by pure spin currents has not been achieved so far. Here we demonstrate the generation of single-mode coherent auto-oscillations in a device that combines local injection of a pure spin current with enhanced spin-wave radiation losses. Counterintuitively, radiation losses enable excitation of auto-oscillation, suppressing the nonlinear processes that prevent auto-oscillation by redistributing the energy between different modes. Our devices exhibit auto-oscillations at moderate current densities, at a microwave frequency tunable over a wide range. These findings suggest a new route for the implementation of nanoscale microwave sources for next-generation integrated electronics.

Quantum spin dynamics with pairwise-tunable, long-range interactions

PubMed Central

Hung, C.-L.; González-Tudela, Alejandro; Cirac, J. Ignacio; Kimble, H. J.

2016-01-01

We present a platform for the simulation of quantum magnetism with full control of interactions between pairs of spins at arbitrary distances in 1D and 2D lattices. In our scheme, two internal atomic states represent a pseudospin for atoms trapped within a photonic crystal waveguide (PCW). With the atomic transition frequency aligned inside a band gap of the PCW, virtual photons mediate coherent spin–spin interactions between lattice sites. To obtain full control of interaction coefficients at arbitrary atom–atom separations, ground-state energy shifts are introduced as a function of distance across the PCW. In conjunction with auxiliary pump fields, spin-exchange versus atom–atom separation can be engineered with arbitrary magnitude and phase, and arranged to introduce nontrivial Berry phases in the spin lattice, thus opening new avenues for realizing topological spin models. We illustrate the broad applicability of our scheme by explicit construction for several well-known spin models. PMID:27496329

Spin Qubits in Germanium Structures with Phononic Gap

NASA Technical Reports Server (NTRS)

Smelyanskiy, V. N.; Vasko, F. T.; Hafiychuk, V. V.; Dykman, M. I.; Petukhov, A. G.

2014-01-01

We propose qubits based on shallow donor electron spins in germanium structures with phononic gap. We consider a phononic crystal formed by periodic holes in Ge plate or a rigid cover / Ge layer / rigid substrate structure with gaps approximately a few GHz. The spin relaxation is suppressed dramatically, if the Zeeman frequency omegaZ is in the phononic gap, but an effective coupling between the spins of remote donors via exchange of virtual phonons remains essential. If omegaZ approaches to a gap edge in these structures, a long-range (limited by detuning of omegaZ) resonant exchange interaction takes place. We estimate that ratio of the exchange integral to the longitudinal relaxation rate exceeds 10(exp 5) and lateral scale of resonant exchange 0.1 mm. The exchange contribution can be verified under microwave pumping through oscillations of spin echo signal or through the differential absorption measurements. Efficient manipulation of spins due to the Rabi oscillations opens a new way for quantum information applications.

Synchronization of spin-transfer torque oscillators by spin pumping, inverse spin Hall, and spin Hall effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elyasi, Mehrdad; Bhatia, Charanjit S.; Yang, Hyunsoo, E-mail: eleyang@nus.edu.sg

2015-02-14

We have proposed a method to synchronize multiple spin-transfer torque oscillators based on spin pumping, inverse spin Hall, and spin Hall effects. The proposed oscillator system consists of a series of nano-magnets in junction with a normal metal with high spin-orbit coupling, and an accumulative feedback loop. We conduct simulations to demonstrate the effect of modulated charge currents in the normal metal due to spin pumping from each nano-magnet. We show that the interplay between the spin Hall effect and inverse spin Hall effect results in synchronization of the nano-magnets.

Spin polarized semimagnetic exciton-polariton condensate in magnetic field.

PubMed

Król, Mateusz; Mirek, Rafał; Lekenta, Katarzyna; Rousset, Jean-Guy; Stephan, Daniel; Nawrocki, Michał; Matuszewski, Michał; Szczytko, Jacek; Pacuski, Wojciech; Piętka, Barbara

2018-04-27

Owing to their integer spin, exciton-polaritons in microcavities can be used for observation of non-equilibrium Bose-Einstein condensation in solid state. However, spin-related phenomena of such condensates are difficult to explore due to the relatively small Zeeman effect of standard semiconductor microcavity systems and the strong tendency to sustain an equal population of two spin components, which precludes the observation of condensates with a well defined spin projection along the axis of the system. The enhancement of the Zeeman splitting can be achieved by introducing magnetic ions to the quantum wells, and consequently forming semimagnetic polaritons. In this system, increasing magnetic field can induce polariton condensation at constant excitation power. Here we evidence the spin polarization of a semimagnetic polaritons condensate exhibiting a circularly polarized emission over 95% even in a moderate magnetic field of about 3 T. Furthermore, we show that unlike nonmagnetic polaritons, an increase on excitation power results in an increase of the semimagnetic polaritons condensate spin polarization. These properties open new possibilities for testing theoretically predicted phenomena of spin polarized condensate.

Structural insight into the role of Gln293Met mutation on the Peloruside A/Laulimalide association with αβ-tubulin from molecular dynamics simulations, binding free energy calculations and weak interactions analysis.

PubMed

Zúñiga, Matías A; Alderete, Joel B; Jaña, Gonzalo A; Jiménez, Verónica A

2017-07-01

Peloruside A (PLA) and Laulimalide (LAU) are novel microtubule-stabilizing agents with promising properties against different cancer types. These ligands share a non-taxoid binding site at the outer surface of β-tubulin and promote microtubule stabilization by bridging two adjacent αβ-tubulin dimers from parallel protofilaments. Recent site-directed mutagenesis experiments confirmed the existence of a unique β-tubulin site mutation (Gln293Met) that specifically increased the activity of PLA and caused resistance to LAU, without affecting the stability of microtubules in the absence of the ligands. In this work, fully atomistic molecular dynamics simulations were carried out to examine the PLA and LAU association with native and mutated αβ-tubulin in the search for structural and energetic evidence to explain the role of Gln293Met mutation on determining the activity of these ligands. Our results revealed that Gln293Met mutation induced the loss of relevant LAU-tubulin contacts but exerted negligible changes in the interaction networks responsible for PLA-tubulin association. Binding free energy calculations (MM/GBSA and MM/PBSA), and weak interaction analysis (aNCI) predicted an increased affinity for PLA, and a weakened association for LAU after mutation, thus suggesting that Gln293Met mutation exerts its action by a modulation of drug-tubulin interactions. These results are valuable to increase understanding about PLA and LAU activity and to assist the future design of novel agents targeting the PLA/LAU binding pocket.

Structural insight into the role of Gln293Met mutation on the Peloruside A/Laulimalide association with αβ-tubulin from molecular dynamics simulations, binding free energy calculations and weak interactions analysis

NASA Astrophysics Data System (ADS)

Zúñiga, Matías A.; Alderete, Joel B.; Jaña, Gonzalo A.; Jiménez, Verónica A.

2017-07-01

Peloruside A (PLA) and Laulimalide (LAU) are novel microtubule-stabilizing agents with promising properties against different cancer types. These ligands share a non-taxoid binding site at the outer surface of β-tubulin and promote microtubule stabilization by bridging two adjacent αβ-tubulin dimers from parallel protofilaments. Recent site-directed mutagenesis experiments confirmed the existence of a unique β-tubulin site mutation (Gln293Met) that specifically increased the activity of PLA and caused resistance to LAU, without affecting the stability of microtubules in the absence of the ligands. In this work, fully atomistic molecular dynamics simulations were carried out to examine the PLA and LAU association with native and mutated αβ-tubulin in the search for structural and energetic evidence to explain the role of Gln293Met mutation on determining the activity of these ligands. Our results revealed that Gln293Met mutation induced the loss of relevant LAU-tubulin contacts but exerted negligible changes in the interaction networks responsible for PLA-tubulin association. Binding free energy calculations (MM/GBSA and MM/PBSA), and weak interaction analysis (aNCI) predicted an increased affinity for PLA, and a weakened association for LAU after mutation, thus suggesting that Gln293Met mutation exerts its action by a modulation of drug-tubulin interactions. These results are valuable to increase understanding about PLA and LAU activity and to assist the future design of novel agents targeting the PLA/LAU binding pocket.

Effect of electron spin-spin interaction on level crossings and spin flips in a spin-triplet system

NASA Astrophysics Data System (ADS)

Jia, Wei; Hu, Fang-Qi; Wu, Ning; Zhao, Qing

2017-12-01

We study level crossings and spin flips in a system consisting of a spin-1 (an electron spin triplet) coupled to a nuclear spin of arbitrary size K , in the presence of a uniform magnetic field and the electron spin-spin interaction within the triplet. Through an analytical diagonalization based on the SU (3 ) Lie algebra, we find that the electron spin-spin interaction not only removes the curious degeneracy which appears in the absence of the interaction, but also produces some level anticrossings (LACs) for strong interactions. The real-time dynamics of the system shows that periodic spin flips occur at the LACs for arbitrary K , which might provide an option for nuclear or electron spin polarization.

Epidemic Dynamics in Open Quantum Spin Systems

NASA Astrophysics Data System (ADS)

Pérez-Espigares, Carlos; Marcuzzi, Matteo; Gutiérrez, Ricardo; Lesanovsky, Igor

2017-10-01

We explore the nonequilibrium evolution and stationary states of an open many-body system that displays epidemic spreading dynamics in a classical and a quantum regime. Our study is motivated by recent experiments conducted in strongly interacting gases of highly excited Rydberg atoms where the facilitated excitation of Rydberg states competes with radiative decay. These systems approximately implement open quantum versions of models for population dynamics or disease spreading where species can be in a healthy, infected or immune state. We show that in a two-dimensional lattice, depending on the dominance of either classical or quantum effects, the system may display a different kind of nonequilibrium phase transition. We moreover discuss the observability of our findings in laser driven Rydberg gases with particular focus on the role of long-range interactions.

Spin doping using transition metal phthalocyanine molecules

PubMed Central

Atxabal, A.; Ribeiro, M.; Parui, S.; Urreta, L.; Sagasta, E.; Sun, X.; Llopis, R.; Casanova, F.; Hueso, L. E.

2016-01-01

Molecular spins have become key enablers for exploring magnetic interactions, quantum information processes and many-body effects in metals. Metal-organic molecules, in particular, let the spin state of the core metal ion to be modified according to its organic environment, allowing localized magnetic moments to emerge as functional entities with radically different properties from its simple atomic counterparts. Here, using and preserving the integrity of transition metal phthalocyanine high-spin complexes, we demonstrate the magnetic doping of gold thin films, effectively creating a new ground state. We demonstrate it by electrical transport measurements that are sensitive to the scattering of itinerant electrons with magnetic impurities, such as Kondo effect and weak antilocalization. Our work expands in a simple and powerful way the classes of materials that can be used as magnetic dopants, opening a new channel to couple the wide range of molecular properties with spin phenomena at a functional scale. PMID:27941810

Estimating the spin diffusion length and the spin Hall angle from spin pumping induced inverse spin Hall voltages

NASA Astrophysics Data System (ADS)

Roy, Kuntal

2017-11-01

There exists considerable confusion in estimating the spin diffusion length of materials with high spin-orbit coupling from spin pumping experiments. For designing functional devices, it is important to determine the spin diffusion length with sufficient accuracy from experimental results. An inaccurate estimation of spin diffusion length also affects the estimation of other parameters (e.g., spin mixing conductance, spin Hall angle) concomitantly. The spin diffusion length for platinum (Pt) has been reported in the literature in a wide range of 0.5-14 nm, and in particular it is a constant value independent of Pt's thickness. Here, the key reasonings behind such a wide range of reported values of spin diffusion length have been identified comprehensively. In particular, it is shown here that a thickness-dependent conductivity and spin diffusion length is necessary to simultaneously match the experimental results of effective spin mixing conductance and inverse spin Hall voltage due to spin pumping. Such a thickness-dependent spin diffusion length is tantamount to the Elliott-Yafet spin relaxation mechanism, which bodes well for transitional metals. This conclusion is not altered even when there is significant interfacial spin memory loss. Furthermore, the variations in the estimated parameters are also studied, which is important for technological applications.

Plaquette order in a dimerized frustrated spin ladder

NASA Astrophysics Data System (ADS)

Shlagman, Ofer; Shimshoni, Efrat

2014-11-01

We study the effect of dimerization (due to, e.g., spin-Peierls instability) on the phase diagram of a frustrated antiferromagnetic spin-1/2 ladder, with weak transverse and diagonal rung coupling. Our analysis focuses on a one-dimensional version of the model (i.e., a single two-leg ladder) where we consider two forms of dimerization on the legs: columnar dimers (CDs) and staggered dimers (SDs). We examine in particular the regime of parameters (corresponding to an intermediate X X Z anisotropy) in which the leg dimerization and the rung coupling terms are equally relevant. In both the CD and SD cases, we find that the effective field theory describing the system is a self-dual sine-Gordon model, which favors ordering and the opening of a gap to excitations. The order parameter, which reflects the interplay between the leg and rung dimerization interactions, represents a crystal of 4-spin plaquettes on which longitudinal and transverse dimers are in a coherent superposition. Depending on the leg dimerization mode, these plaquettes are closed or open, however both types spontaneously break reflection symmetry across the ladder. The closed plaquettes are stable, while the open plaquette order is relatively fragile and the corresponding gap may be tuned to zero under extreme conditions. We further find that a first-order transition occurs from the plaquette order to a valence bond crystal (VBC) of dimers on the legs. This suggests that in a higher-dimensional version of this system, this variety of distinct VBC states with comparable energies leads to the formation of domains. Effectively one-dimensional gapless spinon modes on domain boundaries may account for the experimental observation of spin-liquid behavior in a physical realization of the model.

Spin current and spin transfer torque in ferromagnet/superconductor spin valves

NASA Astrophysics Data System (ADS)

Moen, Evan; Valls, Oriol T.

2018-05-01

Using fully self-consistent methods, we study spin transport in fabricable spin valve systems consisting of two magnetic layers, a superconducting layer, and a spacer normal layer between the ferromagnets. Our methods ensure that the proper relations between spin current gradients and spin transfer torques are satisfied. We present results as a function of geometrical parameters, interfacial barrier values, misalignment angle between the ferromagnets, and bias voltage. Our main results are for the spin current and spin accumulation as functions of position within the spin valve structure. We see precession of the spin current about the exchange fields within the ferromagnets, and penetration of the spin current into the superconductor for biases greater than the critical bias, defined in the text. The spin accumulation exhibits oscillating behavior in the normal metal, with a strong dependence on the physical parameters both as to the structure and formation of the peaks. We also study the bias dependence of the spatially averaged spin transfer torque and spin accumulation. We examine the critical-bias effect of these quantities, and their dependence on the physical parameters. Our results are predictive of the outcome of future experiments, as they take into account imperfect interfaces and a realistic geometry.

Development of a spinning wave heat engine

NASA Technical Reports Server (NTRS)

Zinn, B. T.; Powell, E. A.; Hubbartt, J. E.

1982-01-01

A theoretical analysis and an experimental investigation were conducted to assess the feasibility of developing a spinning wave heat engine. Such as engine would utilize a large amplitude traveling acoustic wave rotating around a cylindrica chamber, and it should not suffer from the inefficiency, noise, and intermittent thrust which characterizes pulse jet engines. The objective of this investigation was to determine whether an artificially driven large amplitude spinning transverse wave could induce a steady flow of air through the combustion chamber under cold flow conditions. In the theoretical analysis the Maslen and Moore perturbation technique was extended to study flat cylinders (pancake geometry) with completely open side walls and a central opening. In the parallel experimental study, a test moel was used to determine resonant frequencies and radial pressure distributions, as well as oscillatory and steady flow velocities at the inner and outer peripheries. The experimental frequency was nearly the same as the theoretical acoustic value for a model of the same outer diameter but without a central hole. Although the theoretical analysis did not predict a steady velocity component, simulaneous measurements of hotwire and microphone responses have shown that the spinning wave pumps a mean flow radially outward through the cavity.

Topological Phase Transitions in the Photonic Spin Hall Effect

DOE PAGES

Kort-Kamp, Wilton Junior de Melo

2017-10-04

The recent synthesis of two-dimensional staggered materials opens up burgeoning opportunities to study optical spin-orbit interactions in semiconducting Dirac-like systems. In this work, we unveil topological phase transitions in the photonic spin Hall effect in the graphene family materials. It is shown that an external static electric field and a high frequency circularly polarized laser allow for active on-demand manipulation of electromagnetic beam shifts. The spin Hall effect of light presents a rich dependence with radiation degrees of freedom, and material properties, and features nontrivial topological properties. Finally, we discover that photonic Hall shifts are sensitive to spin and valleymore » properties of the charge carriers, providing an unprecedented pathway to investigate spintronics and valleytronics in staggered 2D semiconductors.« less

Locking of electron spin coherence above 20 ms in natural silicon carbide

NASA Astrophysics Data System (ADS)

Simin, D.; Kraus, H.; Sperlich, A.; Ohshima, T.; Astakhov, G. V.; Dyakonov, V.

2017-04-01

We demonstrate that silicon carbide (SiC) with a natural isotope abundance can preserve a coherent spin superposition in silicon vacancies over an unexpectedly long time exceeding 20 ms. The spin-locked subspace with a drastically reduced decoherence rate is attained through the suppression of heteronuclear spin crosstalking by applying a moderate magnetic field in combination with dynamic decoupling from the nuclear spin baths. Furthermore, we identify several phonon-assisted mechanisms of spin-lattice relaxation and find that it can be extremely long at cryogenic temperatures, equal to or even longer than 10 s. Our approach may be extended to other polyatomic compounds and opens a path towards improved qubit memory for wafer-scale quantum technologies.

Roles of Residues Arg-61 and Gln-38 of Human DNA Polymerase η in Bypass of Deoxyguanosine and 7,8-Dihydro-8-oxo-2′-deoxyguanosine*

PubMed Central

Su, Yan; Patra, Amritraj; Harp, Joel M.; Egli, Martin; Guengerich, F. Peter

2015-01-01

Like the other Y-family DNA polymerases, human DNA polymerase η (hpol η) has relatively low fidelity and is able to tolerate damage during DNA synthesis, including 7,8-dihydro-8-oxo-2′-deoxyguanosine (8-oxoG), one of the most abundant DNA lesions in the genome. Crystal structures show that Arg-61 and Gln-38 are located near the active site and may play important roles in the fidelity and efficiency of hpol η. Site-directed mutagenesis was used to replace these side chains either alone or together, and the wild type or mutant proteins were purified and tested by replicating DNA past deoxyguanosine (G) or 8-oxoG. The catalytic activity of hpol η was dramatically disrupted by the R61M and Q38A/R61A mutations, as opposed to the R61A and Q38A single mutants. Crystal structures of hpol η mutant ternary complexes reveal that polarized water molecules can mimic and partially compensate for the missing side chains of Arg-61 and Gln-38 in the Q38A/R61A mutant. The combined data indicate that the positioning and positive charge of Arg-61 synergistically contribute to the nucleotidyl transfer reaction, with additional influence exerted by Gln-38. In addition, gel filtration chromatography separated multimeric and monomeric forms of wild type and mutant hpol η, indicating the possibility that hpol η forms multimers in vivo. PMID:25947374

Hybrid spin and valley quantum computing with singlet-triplet qubits.

PubMed

Rohling, Niklas; Russ, Maximilian; Burkard, Guido

2014-10-24

The valley degree of freedom in the electronic band structure of silicon, graphene, and other materials is often considered to be an obstacle for quantum computing (QC) based on electron spins in quantum dots. Here we show that control over the valley state opens new possibilities for quantum information processing. Combining qubits encoded in the singlet-triplet subspace of spin and valley states allows for universal QC using a universal two-qubit gate directly provided by the exchange interaction. We show how spin and valley qubits can be separated in order to allow for single-qubit rotations.

Nonequilibrium Phase Transition in a Periodically Driven XY Spin Chain

NASA Astrophysics Data System (ADS)

Prosen, Tomaž; Ilievski, Enej

2011-08-01

We present a general formulation of Floquet states of periodically time-dependent open Markovian quasifree fermionic many-body systems in terms of a discrete Lyapunov equation. Illustrating the technique, we analyze periodically kicked XY spin-(1)/(2) chain which is coupled to a pair of Lindblad reservoirs at its ends. A complex phase diagram is reported with reentrant phases of long range and exponentially decaying spin-spin correlations as some of the system’s parameters are varied. The structure of phase diagram is reproduced in terms of counting nontrivial stationary points of Floquet quasiparticle dispersion relation.

Electrical spin injection and detection in molybdenum disulfide multilayer channel

PubMed Central

Liang, Shiheng; Yang, Huaiwen; Renucci, Pierre; Tao, Bingshan; Laczkowski, Piotr; Mc-Murtry, Stefan; Wang, Gang; Marie, Xavier; George, Jean-Marie; Petit-Watelot, Sébastien; Djeffal, Abdelhak; Mangin, Stéphane; Jaffrès, Henri; Lu, Yuan

2017-01-01

Molybdenum disulfide has recently emerged as a promising two-dimensional semiconducting material for nano-electronic, opto-electronic and spintronic applications. However, the demonstration of an electron spin transport through a semiconducting MoS2 channel remains challenging. Here we show the evidence of the electrical spin injection and detection in the conduction band of a multilayer MoS2 semiconducting channel using a two-terminal spin-valve configuration geometry. A magnetoresistance around 1% has been observed through a 450 nm long, 6 monolayer thick MoS2 channel with a Co/MgO tunnelling spin injector and detector. It is found that keeping a good balance between the interface resistance and channel resistance is mandatory for the observation of the two-terminal magnetoresistance. Moreover, the electron spin-relaxation is found to be greatly suppressed in the multilayer MoS2 channel with an in-plane spin polarization. The long spin diffusion length (approximately ∼235 nm) could open a new avenue for spintronic applications using multilayer transition metal dichalcogenides. PMID:28387252

Structure and Dynamics of End-to-End Loop Formation of the Penta-Peptide Cys-Ala-Gly-Gln-Trp in Implicit Solvents

DTIC Science & Technology

2009-01-01

implicit solvents on peptide structure and dynamics , we performed extensive molecular dynamics simulations on the penta-peptide Cys-Ala-Gly-Gln-Trp. Two...end-to-end distances and dihedral angles obtained from molecular dynamics simulations with implicit solvent models were in a good agreement with those...to maintain the temperature of the systems. Introduction Molecular dynamics (MD) simulation techniques are widely used to study structure and

Exploring Closed-Shell Cationic Phenalenyl: From Catalysis to Spin Electronics.

PubMed

Mukherjee, Arup; Sau, Samaresh Chandra; Mandal, Swadhin K

2017-07-18

The odd alternant hydrocarbon phenalenyl (PLY) can exist in three different forms, a closed-shell cation, an open-shell radical, and a closed-shell anion, using its nonbonding molecular orbital (NBMO). The chemistry of PLY-based molecules began more than five decades ago, and so far, the progress has mainly involved the open-shell neutral radical state. Over the last two decades, we have witnessed the evolution of a range of PLY-based radicals generating an array of multifunctional materials. However, it has been admitted that the practical applications of PLY radicals are greatly challenged by the low stability of the open-shell (radical) state. Recently, we took a different route to establish the utility of these PLY molecules using the closed-shell cationic state. In such a design, the closed-shell unit of PLY can readily accept free electrons, stabilizing in its NBMO upon generation of the open-shell state of the molecule. Thus, one can synthetically avoid the unstable open-shell state but still take advantage of this state by in situ generating the radical through external electron transfer or spin injection into the empty NBMO. It is worth noting that such approaches using closed-shell phenalenyl have been missing in the literature. This Account focuses on our recent developments using the closed-shell cationic state of the PLY molecule and its application in broad multidisciplinary areas spanning from catalysis to spin electronics. We describe how this concept has been utilized to develop a variety of homogeneous catalysts. For example, this concept was used in designing an iron(III) PLY-based electrocatalyst for a single-compartment H 2 O 2 fuel cell, which delivered the best electrocatalytic activity among previously reported iron complexes, organometallic catalysts for various homogeneous organic transformations (hydroamination and polymerization), an organic Lewis acid catalyst for the ring opening of epoxides, and transition-metal-free C

Electrical controllable spin pump based on a zigzag silicene nanoribbon junction.

PubMed

Zhang, Lin; Tong, Peiqing

2017-12-13

We propose a possible electrical controllable spin pump based on a zigzag silicene nanoribbon ferromagnetic junction by applying two time-dependent perpendicular electric fields. By using the Keldysh Green's function method, we derive the analytic expression of the spin-resolved current at the adiabatic approximation and demonstrate that two asymmetric spin up and spin down currents can be pumped out in the device without an external bias. The pumped currents mainly come from the interplay between the photon-assisted spin pump effect and the electrically-modulated energy band structure of the tunneling junction. The spin valve phenomena are not only related to the energy gap opened by two perpendicular staggered potentials, but also dependent on the system parameters such as the pumping frequency, the pumping phase difference, the spin-orbit coupling and the Fermi level, which can be tuned by the electrical methods. The proposed device can also be used to produce a pure spin current and a 100% polarized spin current through the photon-assisted pumping process. Our investigations may provide an electrical manipulation of spin-polarized electrons in graphene-like pumping devices.

Roles of Residues Arg-61 and Gln-38 of Human DNA Polymerase η in Bypass of Deoxyguanosine and 7,8-Dihydro-8-oxo-2'-deoxyguanosine.

PubMed

Su, Yan; Patra, Amritraj; Harp, Joel M; Egli, Martin; Guengerich, F Peter

2015-06-26

Like the other Y-family DNA polymerases, human DNA polymerase η (hpol η) has relatively low fidelity and is able to tolerate damage during DNA synthesis, including 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxoG), one of the most abundant DNA lesions in the genome. Crystal structures show that Arg-61 and Gln-38 are located near the active site and may play important roles in the fidelity and efficiency of hpol η. Site-directed mutagenesis was used to replace these side chains either alone or together, and the wild type or mutant proteins were purified and tested by replicating DNA past deoxyguanosine (G) or 8-oxoG. The catalytic activity of hpol η was dramatically disrupted by the R61M and Q38A/R61A mutations, as opposed to the R61A and Q38A single mutants. Crystal structures of hpol η mutant ternary complexes reveal that polarized water molecules can mimic and partially compensate for the missing side chains of Arg-61 and Gln-38 in the Q38A/R61A mutant. The combined data indicate that the positioning and positive charge of Arg-61 synergistically contribute to the nucleotidyl transfer reaction, with additional influence exerted by Gln-38. In addition, gel filtration chromatography separated multimeric and monomeric forms of wild type and mutant hpol η, indicating the possibility that hpol η forms multimers in vivo. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

Spin pumping and inverse spin Hall effects—Insights for future spin-orbitronics (invited)

DOE PAGES

Zhang, Wei; Jungfleisch, Matthias B.; Jiang, Wanjun; ...

2015-03-13

Quantification of spin-charge interconversion has become increasingly important in the fast-developing field of spin-orbitronics. Pure spin current generated by spin pumping acts a sensitive probe for many bulk and interface spin-orbit effects, which has been indispensable for the discovery of many promising new spin-orbit materials. Here, we apply spin pumping and inverse spin Hall effect experiments, as a useful metrology, and study spin-orbit effects in a variety of metals and metal interfaces. We also quantify the spin Hall effects in Ir and W using the conventional bilayer structures, and discuss the self-induced voltage in a single layer of ferromagnetic permalloy.more » Finally, we extend our discussions to multilayer structures and quantitatively reveal the spin current flow in two consecutive normal metal layers.« less

The Enhancement of spin Hall torque efficiency and Reduction of Gilbert damping in spin Hall metal/normal metal/ferromagnetic trilayers

NASA Astrophysics Data System (ADS)

Nguyen, Minh-Hai; Pai, Chi-Feng; Ralph, Daniel C.; Buhrman, Robert A.

2015-03-01

The spin Hall effect (SHE) in ferromagnet/heavy metal bilayer structures has been demonstrated to be a powerful means for producing pure spin currents and for exerting spin-orbit damping-like and field-like torques on the ferromagnetic layer. Large spin Hall (SH) angles have been reported for Pt, beta-Ta and beta-W films and have been utilized to achieve magnetic switching of in-plane and out-of-plane magnetized nanomagnets, spin torque auto-oscillators, and the control of high velocity domain wall motion. For many of the proposed applications of the SHE it is also important to achieve an effective Gilbert damping parameter that is as low as possible. In general the spin orbit torques and the effective damping are predicted to depend directly on the spin-mixing conductance of the SH metal/ferromagnet interface. This opens up the possibility of tuning these properties with the insertion of a very thin layer of another metal between the SH metal and the ferromagnet. Here we will report on experiments with such trilayer structures in which we have observed both a large enhancement of the spin Hall torque efficiency and a significant reduction in the effective Gilbert damping. Our results indicate that there is considerable opportunity to optimize the effectiveness and energy efficiency of the damping-like torque through engineering of such trilayer structures. Supported in part by NSF and Samsung Electronics Corporation.

Interaction of GlnK with the GAF domain of Herbaspirillum seropedicae NifA mediates NH₄⁺-regulation.

PubMed

Oliveira, Marco A S; Aquino, Bruno; Bonatto, Ana Claudia; Huergo, Luciano F; Chubatsu, Leda S; Pedrosa, Fábio O; Souza, Emanuel M; Dixon, Ray; Monteiro, Rose A

2012-04-01

Nitrogen fixation in Herbaspirillum seropedicae is transcriptionally regulated by NifA, a σ(54) transcriptional activator with three structural domains: an N-terminal GAF domain, a catalytic AAA+ domain and a C-terminal DNA-binding domain. NifA is only active in H. seropedicae when cultures are grown in the absence of fixed nitrogen and at low oxygen tensions. There is evidence that the inactivation of NifA in response to fixed nitrogen is mediated by the regulatory GAF domain. However, the mechanism of NifA repression by the GAF domain, as well as the transduction of nitrogen status to NifA, is not understood. In order to study the regulation of NifA activity by fixed nitrogen independently of oxygen regulation, we constructed a chimeric protein containing the GAF domain of H. seropedicae NifA fused to the AAA+ and C-terminal domains of Azotobacter vinelandii NifA. This chimeric protein (NifAQ1) lacks the cysteine motif found in oxygen sensitive NifA proteins and is not oxygen responsive in vivo. Our results demonstrate that NifAQ1 responds to fixed nitrogen and requires GlnK protein for activity, a behavior similar to H. seropedicae NifA. In addition, protein footprinting analysis indicates that this response probably involves a protein-protein contact between the GAF domain and the GlnK protein. Copyright © 2012 Elsevier Masson SAS. All rights reserved.

Electrical control of a confined electron spin in a silicene quantum dot

NASA Astrophysics Data System (ADS)

Szafran, Bartłomiej; Mreńca-Kolasińska, Alina; Rzeszotarski, Bartłomiej; Żebrowski, Dariusz

2018-04-01

We study spin control for an electron confined in a flake of silicene. We find that the lowest-energy conduction-band levels are split by the diagonal intrinsic spin-orbit coupling into Kramers doublets with a definite projection of the spin on the orbital magnetic moment. We study the spin control by AC electric fields using the nondiagonal Rashba component of the spin-orbit interactions with the time-dependent atomistic tight-binding approach. The Rashba interactions in AC electric fields produce Rabi spin-flip times of the order of a nanosecond. These times can be reduced to tens of picoseconds provided that the vertical electric field is tuned to an avoided crossing opened by the Rashba spin-orbit interaction. We demonstrate that the speedup of the spin transitions is possible due to the intervalley coupling induced by the armchair edge of the flake. The study is confronted with the results for circular quantum dots decoupled from the edge with well defined angular momentum and valley index.

Spin-polarized electron emitter: Mn-doped GaN nanotubes and their arrays

NASA Astrophysics Data System (ADS)

Hao, Shaogang; Zhou, Gang; Wu, Jian; Duan, Wenhui; Gu, Bing-Lin

2004-03-01

The influences from the doping magnetic atom, Mn, on the geometry, electronic properties, and spin-polarization characteristics are demonstrated for open armchair gallium nitrogen (GaN) nanotubes and arrays by use of the first-principles calculations. The interaction between dangling bonds of Ga (Mn) and N atoms at the open-end promotes the self-close of the tube mouth and formation of a more stable open semicone top. Primarily owing to hybridization of Mn 3d and N 2p orbitals, one Mn atom introduces several impurity energy levels into the original energy gap, and the calculated magnetic moment is 4μB. The electron spin polarizations in the field emission are theoretically evaluated. We suggest that armchair open GaN nanotube arrays doped with a finite number of magnetic atoms may have application potential as the electron source of spintronic devices in the future.

Spin-orbit-coupled Fermi gases of two-electron ytterbium atoms

NASA Astrophysics Data System (ADS)

He, Chengdong; Song, Bo; Haciyev, Elnur; Ren, Zejian; Seo, Bojeong; Zhang, Shanchao; Liu, Xiong-Jun; Jo, Gyu-Boong

2017-04-01

Spin-orbit coupling (SOC) has been realized in bosonic and fermionic atomic gases opening an avenue to novel physics associated with spin-momentum locking. In this talk, we will demonstrate all-optical method coupling two hyperfine ground states of 173Yb fermions through a narrow optical transition 1S0 -> 3P1. An optical AC Stark shift is applied to split the ground hyperfine levels and separate out an effective spin-1/2 subspace from other spin states for the realization of SOC. The spin dephasing dynamics and the asymmetric momentum distribution of the spin-orbit coupled Fermi gas are observed as a hallmark of SOC. The implementation of all-optical SOC for ytterbium fermions should offer a new route to a long-lived spin-orbit coupled Fermi gas and greatly expand our capability in studying novel spin-orbit physics with alkaline-earth-like atoms. Other ongoing experimental works related to SOC will be also discussed. Funded by Croucher Foundation and Research Grants Council (RGC) of Hong Kong (Project ECS26300014, GRF16300215, GRF16311516, and Croucher Innovation Grants); MOST (Grant No. 2016YFA0301604) and NSFC (No. 11574008).

Versatile microwave-driven trapped ion spin system for quantum information processing

PubMed Central

Piltz, Christian; Sriarunothai, Theeraphot; Ivanov, Svetoslav S.; Wölk, Sabine; Wunderlich, Christof

2016-01-01

Using trapped atomic ions, we demonstrate a tailored and versatile effective spin system suitable for quantum simulations and universal quantum computation. By simply applying microwave pulses, selected spins can be decoupled from the remaining system and, thus, can serve as a quantum memory, while simultaneously, other coupled spins perform conditional quantum dynamics. Also, microwave pulses can change the sign of spin-spin couplings, as well as their effective strength, even during the course of a quantum algorithm. Taking advantage of the simultaneous long-range coupling between three spins, a coherent quantum Fourier transform—an essential building block for many quantum algorithms—is efficiently realized. This approach, which is based on microwave-driven trapped ions and is complementary to laser-based methods, opens a new route to overcoming technical and physical challenges in the quest for a quantum simulator and a quantum computer. PMID:27419233

Input-output theory for spin-photon coupling in Si double quantum dots

NASA Astrophysics Data System (ADS)

Benito, M.; Mi, X.; Taylor, J. M.; Petta, J. R.; Burkard, Guido

2017-12-01

The interaction of qubits via microwave frequency photons enables long-distance qubit-qubit coupling and facilitates the realization of a large-scale quantum processor. However, qubits based on electron spins in semiconductor quantum dots have proven challenging to couple to microwave photons. In this theoretical work we show that a sizable coupling for a single electron spin is possible via spin-charge hybridization using a magnetic field gradient in a silicon double quantum dot. Based on parameters already shown in recent experiments, we predict optimal working points to achieve a coherent spin-photon coupling, an essential ingredient for the generation of long-range entanglement. Furthermore, we employ input-output theory to identify observable signatures of spin-photon coupling in the cavity output field, which may provide guidance to the experimental search for strong coupling in such spin-photon systems and opens the way to cavity-based readout of the spin qubit.

Detection of Hb Constant Spring [α142, Term→Gln, TAA>CAA (α2)] in heterozygotes combined with β-thalassemia.

PubMed

Li, You-Qiong; Li, Ru; Li, Dong-Zhi

2013-01-01

Hb Constant Spring [Hb CS, α142, Term→Gln, TAA>CAA (α2)] is a nondeletional form of α-thalassemia (α-thal) that is most prevalent in Southern Chinese and Southeast Asian populations. We previously found that Hb CS trait could efficiently be screened using Sebia Capillarys2. In this study, we report that Hb CS heterozygotes combined with β-thal could not be detected by the Sebia Capillarys2 method due to the very small amount of Hb CS.

Radiation reaction for spinning bodies in effective field theory. II. Spin-spin effects

NASA Astrophysics Data System (ADS)

Maia, Natália T.; Galley, Chad R.; Leibovich, Adam K.; Porto, Rafael A.

2017-10-01

We compute the leading post-Newtonian (PN) contributions at quadratic order in the spins to the radiation-reaction acceleration and spin evolution for binary systems, entering at four-and-a-half PN order. Our calculation includes the backreaction from finite-size spin effects, which is presented for the first time. The computation is carried out, from first principles, using the effective field theory framework for spinning extended objects. At this order, nonconservative effects in the spin-spin sector are independent of the spin supplementary conditions. A nontrivial consistency check is performed by showing that the energy loss induced by the resulting radiation-reaction force is equivalent to the total emitted power in the far zone. We find that, in contrast to the spin-orbit contributions (reported in a companion paper), the radiation reaction affects the evolution of the spin vectors once spin-spin effects are incorporated.

Active control of magnetoresistance of organic spin valves using ferroelectricity

PubMed Central

Sun, Dali; Fang, Mei; Xu, Xiaoshan; Jiang, Lu; Guo, Hangwen; Wang, Yanmei; Yang, Wenting; Yin, Lifeng; Snijders, Paul C.; Ward, T. Z.; Gai, Zheng; Zhang, X.-G.; Lee, Ho Nyung; Shen, Jian

2014-01-01

Organic spintronic devices have been appealing because of the long spin lifetime of the charge carriers in the organic materials and their low cost, flexibility and chemical diversity. In previous studies, the control of resistance of organic spin valves is generally achieved by the alignment of the magnetization directions of the two ferromagnetic electrodes, generating magnetoresistance. Here we employ a new knob to tune the resistance of organic spin valves by adding a thin ferroelectric interfacial layer between the ferromagnetic electrode and the organic spacer: the magnetoresistance of the spin valve depends strongly on the history of the bias voltage, which is correlated with the polarization of the ferroelectric layer; the magnetoresistance even changes sign when the electric polarization of the ferroelectric layer is reversed. These findings enable active control of resistance using both electric and magnetic fields, opening up possibility for multi-state organic spin valves. PMID:25008155

All-optical control of long-lived nuclear spins in rare-earth doped nanoparticles.

PubMed

Serrano, D; Karlsson, J; Fossati, A; Ferrier, A; Goldner, P

2018-05-29

Nanoscale systems that coherently couple to light and possess spins offer key capabilities for quantum technologies. However, an outstanding challenge is to preserve properties, and especially optical and spin coherence lifetimes, at the nanoscale. Here, we report optically controlled nuclear spins with long coherence lifetimes (T 2 ) in rare-earth-doped nanoparticles. We detect spins echoes and measure a spin coherence lifetime of 2.9 ± 0.3 ms at 5 K under an external magnetic field of 9 mT, a T 2 value comparable to those obtained in bulk rare-earth crystals. Moreover, we achieve spin T 2 extension using all-optical spin dynamical decoupling and observe high fidelity between excitation and echo phases. Rare-earth-doped nanoparticles are thus the only nano-material in which optically controlled spins with millisecond coherence lifetimes have been reported. These results open the way to providing quantum light-atom-spin interfaces with long storage time within hybrid architectures.

Temperature evolution of the charge and spin transport in Cu/Nb interface

NASA Astrophysics Data System (ADS)

Ishitaki, Masayuki; Ohnishi, Kohei; Kimura, Takashi

2018-06-01

The transport properties for the charge and spin currents in a normal-metal/superconductor interface have been investigated by using a nano-pillar based lateral spin valve. Owing to the efficient reduction of the Joule heating, we were able to observe the temperature and bias-current dependences of the spin transport in the Cu/Nb bilayer system. From the temperature dependence of the spin signal, the superconducting gap of the Nb in contact with Cu was found to open gradually with decreasing the temperature. We also found that the inhomogeneous superconducting property produces the significant temperature and field dependences of the background signal in the nonlocal measurement around the transition temperature.

Caprine PrP variants harboring Asp-146, His-154 and Gln-211 alleles display reduced convertibility upon interaction with pathogenic murine prion protein in scrapie infected cells.

PubMed

Kanata, Eirini; Arsenakis, Minas; Sklaviadis, Theodoros

2016-09-02

Scrapie, the prion disease of sheep and goats, is a devastating malady of small ruminants. Due to its infectious nature, epidemic outbreaks may occur in flocks/herds consisting of highly susceptible animals. Field studies identified scrapie-protective caprine PrP variants, harboring specific single amino acid changes (Met-142, Arg-143, Asp-146, Ser-146, His-154, Gln-211 and Lys-222). Their effects are under further evaluation, and aim to determine the most protective allele. We assessed some of these variants (Asp-146, His-154, Gln-211 and Lys-222), after their exogenous expression as murine-caprine chimeras in a scrapie- infected murine cell line. We report that exogenously expressed PrPs undergo conformational conversion upon interaction with the endogenous pathological murine prion protein (PrP SC ), which results in the detection of goat-specific and partially PK-resistant moieties. These moieties display a PK-resistance pattern distinct from the one detected in natural goat scrapie cases. Within this cellular model, distinct conformational conversion potentials were assigned to the tested variants. Molecules carrying the Asp-146, His-154 and Gln-211 alleles showed significantly lower conversion levels compared to wild type, confirming their protective effects against scrapie. Although we utilized a heterologous conversion system, this is to our knowledge, the first study of caprine PrP variants in a cellular context of scrapie, that confirms the protective effects of some of the studied alleles.

Energy efficient hybrid computing systems using spin devices

NASA Astrophysics Data System (ADS)

Sharad, Mrigank

Emerging spin-devices like magnetic tunnel junctions (MTJ's), spin-valves and domain wall magnets (DWM) have opened new avenues for spin-based logic design. This work explored potential computing applications which can exploit such devices for higher energy-efficiency and performance. The proposed applications involve hybrid design schemes, where charge-based devices supplement the spin-devices, to gain large benefits at the system level. As an example, lateral spin valves (LSV) involve switching of nanomagnets using spin-polarized current injection through a metallic channel such as Cu. Such spin-torque based devices possess several interesting properties that can be exploited for ultra-low power computation. Analog characteristic of spin current facilitate non-Boolean computation like majority evaluation that can be used to model a neuron. The magneto-metallic neurons can operate at ultra-low terminal voltage of ˜20mV, thereby resulting in small computation power. Moreover, since nano-magnets inherently act as memory elements, these devices can facilitate integration of logic and memory in interesting ways. The spin based neurons can be integrated with CMOS and other emerging devices leading to different classes of neuromorphic/non-Von-Neumann architectures. The spin-based designs involve `mixed-mode' processing and hence can provide very compact and ultra-low energy solutions for complex computation blocks, both digital as well as analog. Such low-power, hybrid designs can be suitable for various data processing applications like cognitive computing, associative memory, and currentmode on-chip global interconnects. Simulation results for these applications based on device-circuit co-simulation framework predict more than ˜100x improvement in computation energy as compared to state of the art CMOS design, for optimal spin-device parameters.

The total position-spread tensor: Spin partition

DOE Office of Scientific and Technical Information (OSTI.GOV)

El Khatib, Muammar, E-mail: elkhatib@irsamc.ups-tlse.fr; Evangelisti, Stefano, E-mail: stefano@irsamc.ups-tlse.fr; Leininger, Thierry, E-mail: Thierry.Leininger@irsamc.ups-tlse.fr

2015-03-07

The Total Position Spread (TPS) tensor, defined as the second moment cumulant of the position operator, is a key quantity to describe the mobility of electrons in a molecule or an extended system. In the present investigation, the partition of the TPS tensor according to spin variables is derived and discussed. It is shown that, while the spin-summed TPS gives information on charge mobility, the spin-partitioned TPS tensor becomes a powerful tool that provides information about spin fluctuations. The case of the hydrogen molecule is treated, both analytically, by using a 1s Slater-type orbital, and numerically, at Full Configuration Interactionmore » (FCI) level with a V6Z basis set. It is found that, for very large inter-nuclear distances, the partitioned tensor growths quadratically with the distance in some of the low-lying electronic states. This fact is related to the presence of entanglement in the wave function. Non-dimerized open chains described by a model Hubbard Hamiltonian and linear hydrogen chains H{sub n} (n ≥ 2), composed of equally spaced atoms, are also studied at FCI level. The hydrogen systems show the presence of marked maxima for the spin-summed TPS (corresponding to a high charge mobility) when the inter-nuclear distance is about 2 bohrs. This fact can be associated to the presence of a Mott transition occurring in this region. The spin-partitioned TPS tensor, on the other hand, has a quadratical growth at long distances, a fact that corresponds to the high spin mobility in a magnetic system.« less

Calculation method of spin accumulations and spin signals in nanostructures using spin resistors

NASA Astrophysics Data System (ADS)

Torres, Williams Savero; Marty, Alain; Laczkowski, Piotr; Jamet, Matthieu; Vila, Laurent; Attané, Jean-Philippe

2018-02-01

Determination of spin accumulations and spin currents is essential for a deep understanding of spin transport in nanostructures and further optimization of spintronic devices. So far, they are easily obtained using different approaches in nanostructures composed of few elements; however their calculation becomes complicated as the number of elements increases. Here, we propose a 1-D spin resistor approach to calculate analytically spin accumulations, spin currents and magneto-resistances in heterostructures. Our method, particularly applied to multi-terminal metallic nanostructures, provides a fast and systematic mean to determine such spin properties in structures where conventional methods remain complex.

Spin-polarized scanning tunneling microscopy with quantitative insights into magnetic probes

NASA Astrophysics Data System (ADS)

Phark, Soo-hyon; Sander, Dirk

2017-04-01

Spin-polarized scanning tunneling microscopy and spectroscopy (spin-STM/S) have been successfully applied to magnetic characterizations of individual nanostructures. Spin-STM/S is often performed in magnetic fields of up to some Tesla, which may strongly influence the tip state. In spite of the pivotal role of the tip in spin-STM/S, the contribution of the tip to the differential conductance d I/d V signal in an external field has rarely been investigated in detail. In this review, an advanced analysis of spin-STM/S data measured on magnetic nanoislands, which relies on a quantitative magnetic characterization of tips, is discussed. Taking advantage of the uniaxial out-of-plane magnetic anisotropy of Co bilayer nanoisland on Cu(111), in-field spin-STM on this system has enabled a quantitative determination, and thereby, a categorization of the magnetic states of the tips. The resulting in-depth and conclusive analysis of magnetic characterization of the tip opens new venues for a clear-cut sub-nanometer scale spin ordering and spin-dependent electronic structure of the non-collinear magnetic state in bilayer high Fe nanoislands on Cu(111).

Robust spin-valley polarization in commensurate Mo S2 /graphene heterostructures

NASA Astrophysics Data System (ADS)

Du, Luojun; Zhang, Qian; Gong, Benchao; Liao, Mengzhou; Zhu, Jianqi; Yu, Hua; He, Rui; Liu, Kai; Yang, Rong; Shi, Dongxia; Gu, Lin; Yan, Feng; Zhang, Guangyu; Zhang, Qingming

2018-03-01

The investigation and control of quantum degrees of freedom (DoFs) of carriers lie at the heart of condensed-matter physics and next-generation electronics/optoelectronics. van der Waals heterostructures stacked from distinct two-dimensional (2D) crystals offer an unprecedented platform for combining the superior properties of individual 2D materials and manipulating spin, layer, and valley DoFs. Mo S2 /graphene heterostructures, harboring prominent spin-transport properties of graphene, giant spin-orbit coupling, and spin-valley polarization of Mo S2 , are predicted as a perfect venue for optospintronics. Here, we report the epitaxial growth of commensurate Mo S2 on graphene with high quality by chemical vapor deposition, and demonstrate robust temperature-independent spin-valley polarization at off-resonant excitation. We further show that the helicity of B exciton is larger than that of A exciton, allowing the manipulation of spin bits in the commensurate heterostructures by both optical helicity and wavelength. Our results open a window for controlling spin DoF by light and pave a way for taking spin qubits as information carriers in the next-generation valley-controlled optospintronics.

Dynamic spin polarization by orientation-dependent separation in a ferromagnet-semiconductor hybrid

NASA Astrophysics Data System (ADS)

Korenev, V. L.; Akimov, I. A.; Zaitsev, S. V.; Sapega, V. F.; Langer, L.; Yakovlev, D. R.; Danilov, Yu. A.; Bayer, M.

2012-07-01

Integration of magnetism into semiconductor electronics would facilitate an all-in-one-chip computer. Ferromagnet/bulk semiconductor hybrids have been, so far, mainly considered as key devices to read out the ferromagnetism by means of spin injection. Here we demonstrate that a Mn-based ferromagnetic layer acts as an orientation-dependent separator for carrier spins confined in a semiconductor quantum well that is set apart from the ferromagnet by a barrier only a few nanometers thick. By this spin-separation effect, a non-equilibrium electron-spin polarization is accumulated in the quantum well due to spin-dependent electron transfer to the ferromagnet. The significant advance of this hybrid design is that the excellent optical properties of the quantum well are maintained. This opens up the possibility of optical readout of the ferromagnet's magnetization and control of the non-equilibrium spin polarization in non-magnetic quantum wells.

Dynamic spin polarization by orientation-dependent separation in a ferromagnet-semiconductor hybrid.

PubMed

Korenev, V L; Akimov, I A; Zaitsev, S V; Sapega, V F; Langer, L; Yakovlev, D R; Danilov, Yu A; Bayer, M

2012-07-17

Integration of magnetism into semiconductor electronics would facilitate an all-in-one-chip computer. Ferromagnet/bulk semiconductor hybrids have been, so far, mainly considered as key devices to read out the ferromagnetism by means of spin injection. Here we demonstrate that a Mn-based ferromagnetic layer acts as an orientation-dependent separator for carrier spins confined in a semiconductor quantum well that is set apart from the ferromagnet by a barrier only a few nanometers thick. By this spin-separation effect, a non-equilibrium electron-spin polarization is accumulated in the quantum well due to spin-dependent electron transfer to the ferromagnet. The significant advance of this hybrid design is that the excellent optical properties of the quantum well are maintained. This opens up the possibility of optical readout of the ferromagnet's magnetization and control of the non-equilibrium spin polarization in non-magnetic quantum wells.

Quantum Spin Ice under a [111] Magnetic Field: From Pyrochlore to Kagome

NASA Astrophysics Data System (ADS)

Bojesen, Troels Arnfred; Onoda, Shigeki

2017-12-01

Quantum spin ice, modeled for magnetic rare-earth pyrochlores, has attracted great interest for hosting a U(1) quantum spin liquid, which involves spin-ice monopoles as gapped deconfined spinons, as well as gapless excitations analogous to photons. However, the global phase diagram under a [111] magnetic field remains open. Here we uncover by means of unbiased quantum Monte Carlo simulations that a supersolid of monopoles, showing both a superfluidity and a partial ionization, intervenes the kagome spin ice and a fully ionized monopole insulator, in contrast to classical spin ice where a direct discontinuous phase transition takes place. We also show that on cooling, kagome spin ice evolves towards a valence-bond solid similar to what appears in the associated kagome lattice model [S. V. Isakov et al., Phys. Rev. Lett. 97, 147202 (2006), 10.1103/PhysRevLett.97.147202]. Possible relevance to experiments is discussed.

Tunable spin-orbit coupling for ultracold atoms in two-dimensional optical lattices

NASA Astrophysics Data System (ADS)

Grusdt, Fabian; Li, Tracy; Bloch, Immanuel; Demler, Eugene

2017-06-01

Spin-orbit coupling (SOC) is at the heart of many exotic band structures and can give rise to many-body states with topological order. Here we present a general scheme based on a combination of microwave driving and lattice shaking for the realization of two-dimensional SOC with ultracold atoms in systems with inversion symmetry. We show that the strengths of Rashba and Dresselhaus SOC can be independently tuned in a spin-dependent square lattice. More generally, our method can be used to open gaps between different spin states without breaking time-reversal symmetry. We demonstrate that this allows for the realization of topological insulators with nontrivial spin textures closely related to the Kane-Mele model.

Crossover to the anomalous quantum regime in the extrinsic spin Hall effect of graphene

NASA Astrophysics Data System (ADS)

Ferreira, Aires; Milletari, Mirco

Recent reports of spin-orbit coupling enhancement in chemically modified graphene have opened doors to studies of the spin Hall effect with massless chiral fermions. Here, we theoretically investigate the interaction and impurity density dependence of the extrinsic spin Hall effect in spin-orbit coupled graphene. We present a nonperturbative quantum diagrammatic calculation of the spin Hall response function in the strong-coupling regime that incorporates skew scattering and anomalous impurity density-independent contributions on equal footing. The spin Hall conductivity dependence on Fermi energy and electron-impurity interaction strength reveals the existence of experimentally accessible regions where anomalous quantum processes dominate. Our findings suggest that spin-orbit-coupled graphene is an ideal model system for probing the competition between semiclassical and bona fide quantum scattering mechanisms underlying the spin Hall effect. A.F. gratefully acknowledges the financial support of the Royal Society (U.K.).

Tunable short-wavelength spin wave excitation from pinned magnetic domain walls

PubMed Central

Van de Wiele, Ben; Hämäläinen, Sampo J.; Baláž, Pavel; Montoncello, Federico; van Dijken, Sebastiaan

2016-01-01

Miniaturization of magnonic devices for wave-like computing requires emission of short-wavelength spin waves, a key feature that cannot be achieved with microwave antennas. In this paper, we propose a tunable source of short-wavelength spin waves based on highly localized and strongly pinned magnetic domain walls in ferroelectric-ferromagnetic bilayers. When driven into oscillation by a microwave spin-polarized current, the magnetic domain walls emit spin waves with the same frequency as the excitation current. The amplitude of the emitted spin waves and the range of attainable excitation frequencies depend on the availability of domain wall resonance modes. In this respect, pinned domain walls in magnetic nanowires are particularly attractive. In this geometry, spin wave confinement perpendicular to the nanowire axis produces a multitude of domain wall resonances enabling efficient spin wave emission at frequencies up to 100 GHz and wavelengths down to 20 nm. At high frequency, the emission of spin waves in magnetic nanowires becomes monochromatic. Moreover, pinning of magnetic domain wall oscillators onto the same ferroelectric domain boundary in parallel nanowires guarantees good coherency between spin wave sources, which opens perspectives towards the realization of Mach-Zehnder type logic devices and sensors. PMID:26883893

Local conservation laws in spin-\\frac{1}{2} XY chains with open boundary conditions

NASA Astrophysics Data System (ADS)

Fagotti, Maurizio

2016-06-01

We revisit the conserved quantities of the spin-\\frac{1}{2} XY model with open boundary conditions. In the absence of a transverse field, we find new families of local charges and show that half of the seeming conservation laws are conserved only if the number of sites is odd. In even chains the set of noninteracting charges is abelian, like in the periodic case when the number of sites is odd. In odd chains the set is doubled and becomes non-abelian, like in even periodic chains. The dependence of the charges on the parity of the chain’s size undermines the common belief that the thermodynamic limit of diagonal ensembles exists. We consider also the transverse-field Ising chain, where the situation is more ordinary. The generalization to the XY model in a transverse field is not straightforward and we propose a general framework to carry out similar calculations. We conjecture the form of the bulk part of the local charges and discuss the emergence of quasilocal conserved quantities. We provide evidence that in a region of the parameter space there is a reduction of the number of quasilocal conservation laws invariant under chain inversion. As a by-product, we study a class of block-Toeplitz-plus-Hankel operators and identify the conditions that their symbols satisfy in order to commute with a given block-Toeplitz.

Velocity barrier-controlled of spin-valley polarized transport in monolayer WSe2 junction

NASA Astrophysics Data System (ADS)

Qiu, Xuejun; Lv, Qiang; Cao, Zhenzhou

2018-05-01

In this work, we have theoretically investigated the influence of velocity barrier on the spin-valley polarized transport in monolayer (ML) WSe2 junction with a large spin-orbit coupling (SOC). Both the spin-valley resolved transmission probabilities and conductance are strong dependent on the velocity barrier, as the velocity barrier decreases to 0.06, a spin-valley polarization of exceeding 90% is observed, which is distinct from the ML MoS2 owing to incommensurable SOC. In addition, the spin-valley polarization is further increased above 95% in a ML WSe2 superlattice, in particular, it's found many extraordinary velocity barrier-dependent transport gaps for multiple barrier due to evanescent tunneling. Our results may open an avenue for the velocity barrier-controlled high-efficiency spin and valley polarizations in ML WSe2-based electronic devices.

Distinguishing spin-aligned and isotropic black hole populations with gravitational waves.

PubMed

Farr, Will M; Stevenson, Simon; Miller, M Coleman; Mandel, Ilya; Farr, Ben; Vecchio, Alberto

2017-08-23

The direct detection of gravitational waves from merging binary black holes opens up a window into the environments in which binary black holes form. One signature of such environments is the angular distribution of the black hole spins. Binary systems that formed through dynamical interactions between already-compact objects are expected to have isotropic spin orientations (that is, the spins of the black holes are randomly oriented with respect to the orbit of the binary system), whereas those that formed from pairs of stars born together are more likely to have spins that are preferentially aligned with the orbit. The best-measured combination of spin parameters for each of the four likely binary black hole detections GW150914, LVT151012, GW151226 and GW170104 is the 'effective' spin. Here we report that, if the magnitudes of the black hole spins are allowed to extend to high values, the effective spins for these systems indicate a 0.015 odds ratio against an aligned angular distribution compared to an isotropic one. When considering the effect of ten additional detections, this odds ratio decreases to 2.9 × 10 -7 against alignment. The existing preference for either an isotropic spin distribution or low spin magnitudes for the observed systems will be confirmed (or overturned) confidently in the near future.

Association of Arg194Trp, Arg280His and Arg399Gln Polymorphisms in X-ray Repair Cross-Complementing Group 1 Gene and Risk of Differentiated Thyroid Carcinoma in Iran

PubMed Central

Fard-Esfahani, Pezhman; Fard-Esfahani, Armaghan; Fayaz, Shima; Ghanbarzadeh, Bahareh; Saidi, Parinaz; Mohabati, Reyhaneh; Bidoki, Seyed Kazem; Majdi, Mina

2011-01-01

Background: X-ray repair cross-complementing group 1 (XRCC1) gene is a DNA repair gene and its non-synonymous single nucleotide polymorphisms (SNP) may influence DNA repair capacity which has been considered as a modifying risk factor for cancer development. Methods: A case-control study was conducted to investigate impact of three frequently studied polymorphisms (Arg194Trp, Arg280His and Arg399Gln) on developing differentiated thyroid carcinoma (DTC). Results: Increased risks for DTC were shown in homozygous (odds ratio [OR]: 3.66, 95% confidence interval [CI]: 0.38-35.60) and in dominant trait (OR: 1.22, 95% CI: 1.64-2.32) of Arg194Trp genotype. Also, for Arg280His genotype, an increased risk for DTC was shown in dominant trait (OR: 1.42, 95% confidence interval [CI]: 0.76-2.68), while a mildly reduction of risk for DTC (OR: 0.77, 95% [CI]: 0.50-1.17) was estimated in dominant Gln genotype of Arg399Gln. Considering combinatory effects of Arg194Trp and Arg280His genotypes on DTC, the calculated OR and 95% CI for being heterozygous for one of Arg194Trp or Arg280His genotypes were 1.57 and 0.90-2.74, respectively. Conclusion: Genotyping of codons 194, 280 and 399 in XRCC1 gene may use in risk assessment of DTC. PMID:21987112

Spin fluctations and heavy fermions in the Kondo lattice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khaliullin, G.G.

1994-09-01

This paper studies the spectrum of the spin and electronic excitations of the Kondo lattice at low temperatures. To avoid unphysical states, the Mattis {open_quotes}drone{close_quotes}-fermion representation for localized spins is employed. First, the known Fermi liquid properties of a single impurity are examined. The behavior of the correlator between a localized spin and the electron spin density at large distances shows that the effective interaction between electrons on the Fermi level and low-energy localized spin fluctuations scales as {rho}{sup {minus}1}, where {rho} is the band-state density. This fact is developed into a renormalization of the band spectrum in a periodicmore » lattice. If the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between localized spins is much smaller than the Kondo fluctuation frequency {omega}{sub k}, the temperature of the crossover to the single-parameter Fermi liquid mode is determined by {omega}{sub k}. When the RKKY interaction becomes of order {omega}{sub k}, there is a new scale {omega}{sub sf}, the energy of the (antiferromagnetic) paramagnon mode, with {omega}{sub sf}{much_lt}{omega}{sub k}. Here the coherent Fermi liquid regime is realized only below a temperature T{sub coh} of order {omega}{sub sf}, while above T{sub coh} quasiparticle damping exhibits a linear temperature dependence. Finally, the nuclear-spin relaxation rate is calculated. 42 refs.« less

Nonlocal spin-confinement of electrons in graphene with proximity exchange interaction

NASA Astrophysics Data System (ADS)

Ang, Yee Sin; Liang, Shi-Jun; Ooi, Kelvin J. A.; Zhang, Chao; Ma, Zhongshui; Ang, Lay Kee

In graphene-magnetic-insulator hybrid structure such as graphene-Europium-oxide (EuO-G), proximity induced exchange interaction opens up a spin-dependent bandgap and spin splitting in the Dirac band. We study the bound state formation in a hetero-interface composed of EuO-G. We theoretically predict a remarkable nonlocal spin-confinement effect in EuO-G and show that spin-polarized quasi-1D electron interface state can be generated in a magnetic-field-free channel. Quasiparticle transport mediated by the interface state can be efficiently controlled by the channel width and electrostatic gating. Our results suggest a pathway to further reduce the dimensionality of graphene quasiparticles from 2D to 1D, thus offering an exciting graphene-based platform for the search of exotic 1D physics and spintronic applications.

Spin Hall and Spin Swapping Torques in Diffusive Ferromagnets

NASA Astrophysics Data System (ADS)

Pauyac, Christian Ortiz; Chshiev, Mairbek; Manchon, Aurelien; Nikolaev, Sergey A.

2018-04-01

A complete set of the generalized drift-diffusion equations for a coupled charge and spin dynamics in ferromagnets in the presence of extrinsic spin-orbit coupling is derived from the quantum kinetic approach, covering major transport phenomena, such as the spin and anomalous Hall effects, spin swapping, spin precession, and relaxation processes. We argue that the spin swapping effect in ferromagnets is enhanced due to spin polarization, while the overall spin texture induced by the interplay of spin-orbital and spin precession effects displays a complex spatial dependence that can be exploited to generate torques and nucleate or propagate domain walls in centrosymmetric geometries without the use of external polarizers, as opposed to the conventional understanding of spin-orbit mediated torques.

Topological Phases in Graphene Nanoribbons: Junction States, Spin Centers, and Quantum Spin Chains

NASA Astrophysics Data System (ADS)

Cao, Ting; Zhao, Fangzhou; Louie, Steven G.

2017-08-01

We show that semiconducting graphene nanoribbons (GNRs) of different width, edge, and end termination (synthesizable from molecular precursors with atomic precision) belong to different electronic topological classes. The topological phase of GNRs is protected by spatial symmetries and dictated by the terminating unit cell. We have derived explicit formulas for their topological invariants and shown that localized junction states developed between two GNRs of distinct topology may be tuned by lateral junction geometry. The topology of a GNR can be further modified by dopants, such as a periodic array of boron atoms. In a superlattice consisting of segments of doped and pristine GNRs, the junction states are stable spin centers, forming a Heisenberg antiferromagnetic spin 1 /2 chain with tunable exchange interaction. The discoveries here not only are of scientific interest for studies of quasi-one-dimensional systems, but also open a new path for design principles of future GNR-based devices through their topological characters.

Topological Phases in Graphene Nanoribbons: Junction States, Spin Centers, and Quantum Spin Chains.

PubMed

Cao, Ting; Zhao, Fangzhou; Louie, Steven G

2017-08-18

We show that semiconducting graphene nanoribbons (GNRs) of different width, edge, and end termination (synthesizable from molecular precursors with atomic precision) belong to different electronic topological classes. The topological phase of GNRs is protected by spatial symmetries and dictated by the terminating unit cell. We have derived explicit formulas for their topological invariants and shown that localized junction states developed between two GNRs of distinct topology may be tuned by lateral junction geometry. The topology of a GNR can be further modified by dopants, such as a periodic array of boron atoms. In a superlattice consisting of segments of doped and pristine GNRs, the junction states are stable spin centers, forming a Heisenberg antiferromagnetic spin 1/2 chain with tunable exchange interaction. The discoveries here not only are of scientific interest for studies of quasi-one-dimensional systems, but also open a new path for design principles of future GNR-based devices through their topological characters.

Observation of spinon spin currents in one-dimensional spin liquid

NASA Astrophysics Data System (ADS)

Hirobe, Daichi; Sato, Masahiro; Kawamata, Takayuki; Shiomi, Yuki; Uchida, Ken-Ichi; Iguchi, Ryo; Koike, Yoji; Maekawa, Sadamichi; Saitoh, Eiji

To date, two types of spin current have been explored experimentally: conduction-electron spin current and spin-wave spin current. Here, we newly present spinon spin current in quantum spin liquid. An archetype of quantum spin liquid is realized in one-dimensional spin-1/2 chains with the spins coupled via antiferromagnetic interaction. Elementary excitation in such a system is known as a spinon. Theories have predicted that the correlation of spinons reaches over a long distance. This suggests that spin current may propagate via one-dimensional spinons even in spin liquid states. In this talk, we report the experimental observation that a spin liquid in a spin-1/2 quantum chain generates and conveys spin current, which is attributed to spinon spin current. This is demonstrated by observing an anisotropic negative spin Seebeck effect along the spin chains in Sr2CuO3. The results show that spin current can flow via quantum fluctuation in spite of the absence of magnetic order, suggesting that a variety of quantum spin systems can be applied to spintronics. Spin Quantum Rectification Project, ERATO, JST, Japan; PRESTO, JST, Japan.

Kitaev exchange and field-induced quantum spin-liquid states in honeycomb α-RuCl3

NASA Astrophysics Data System (ADS)

Yadav, Ravi; Bogdanov, Nikolay A.; Katukuri, Vamshi M.; Nishimoto, Satoshi; van den Brink, Jeroen; Hozoi, Liviu

2016-11-01

Large anisotropic exchange in 5d and 4d oxides and halides open the door to new types of magnetic ground states and excitations, inconceivable a decade ago. A prominent case is the Kitaev spin liquid, host of remarkable properties such as protection of quantum information and the emergence of Majorana fermions. Here we discuss the promise for spin-liquid behavior in the 4d5 honeycomb halide α-RuCl3. From advanced electronic-structure calculations, we find that the Kitaev interaction is ferromagnetic, as in 5d5 iridium honeycomb oxides, and indeed defines the largest superexchange energy scale. A ferromagnetic Kitaev coupling is also supported by a detailed analysis of the field-dependent magnetization. Using exact diagonalization and density-matrix renormalization group techniques for extended Kitaev-Heisenberg spin Hamiltonians, we find indications for a transition from zigzag order to a gapped spin liquid when applying magnetic field. Our results offer a unified picture on recent magnetic and spectroscopic measurements on this material and open new perspectives on the prospect of realizing quantum spin liquids in d5 halides and oxides in general.

Kitaev exchange and field-induced quantum spin-liquid states in honeycomb α-RuCl3.

PubMed

Yadav, Ravi; Bogdanov, Nikolay A; Katukuri, Vamshi M; Nishimoto, Satoshi; van den Brink, Jeroen; Hozoi, Liviu

2016-11-30

Large anisotropic exchange in 5d and 4d oxides and halides open the door to new types of magnetic ground states and excitations, inconceivable a decade ago. A prominent case is the Kitaev spin liquid, host of remarkable properties such as protection of quantum information and the emergence of Majorana fermions. Here we discuss the promise for spin-liquid behavior in the 4d 5 honeycomb halide α-RuCl 3 . From advanced electronic-structure calculations, we find that the Kitaev interaction is ferromagnetic, as in 5d 5 iridium honeycomb oxides, and indeed defines the largest superexchange energy scale. A ferromagnetic Kitaev coupling is also supported by a detailed analysis of the field-dependent magnetization. Using exact diagonalization and density-matrix renormalization group techniques for extended Kitaev-Heisenberg spin Hamiltonians, we find indications for a transition from zigzag order to a gapped spin liquid when applying magnetic field. Our results offer a unified picture on recent magnetic and spectroscopic measurements on this material and open new perspectives on the prospect of realizing quantum spin liquids in d 5 halides and oxides in general.

Kitaev exchange and field-induced quantum spin-liquid states in honeycomb α-RuCl3

PubMed Central

Yadav, Ravi; Bogdanov, Nikolay A.; Katukuri, Vamshi M.; Nishimoto, Satoshi; van den Brink, Jeroen; Hozoi, Liviu

2016-01-01

Large anisotropic exchange in 5d and 4d oxides and halides open the door to new types of magnetic ground states and excitations, inconceivable a decade ago. A prominent case is the Kitaev spin liquid, host of remarkable properties such as protection of quantum information and the emergence of Majorana fermions. Here we discuss the promise for spin-liquid behavior in the 4d5 honeycomb halide α-RuCl3. From advanced electronic-structure calculations, we find that the Kitaev interaction is ferromagnetic, as in 5d5 iridium honeycomb oxides, and indeed defines the largest superexchange energy scale. A ferromagnetic Kitaev coupling is also supported by a detailed analysis of the field-dependent magnetization. Using exact diagonalization and density-matrix renormalization group techniques for extended Kitaev-Heisenberg spin Hamiltonians, we find indications for a transition from zigzag order to a gapped spin liquid when applying magnetic field. Our results offer a unified picture on recent magnetic and spectroscopic measurements on this material and open new perspectives on the prospect of realizing quantum spin liquids in d5 halides and oxides in general. PMID:27901091

Nonlinear Metasurface for Simultaneous Control of Spin and Orbital Angular Momentum in Second Harmonic Generation.

PubMed

Li, Guixin; Wu, Lin; Li, King F; Chen, Shumei; Schlickriede, Christian; Xu, Zhengji; Huang, Siya; Li, Wendi; Liu, Yanjun; Pun, Edwin Y B; Zentgraf, Thomas; Cheah, Kok W; Luo, Yu; Zhang, Shuang

2017-12-13

The spin and orbital angular momentum (SAM and OAM) of light is providing a new gateway toward high capacity and robust optical communications. While the generation of light with angular momentum is well studied in linear optics, its further integration into nonlinear optical devices will open new avenues for increasing the capacity of optical communications through additional information channels at new frequencies. However, it has been challenging to manipulate the both SAM and OAM of nonlinear signals in harmonic generation processes with conventional nonlinear materials. Here, we report the generation of spin-controlled OAM of light in harmonic generations by using ultrathin photonic metasurfaces. The spin manipulation of OAM mode of harmonic waves is experimentally verified by using second harmonic generation (SHG) from gold meta-atom with 3-fold rotational symmetry. By introducing nonlinear phase singularity into the metasurface devices, we successfully generate and measure the topological charges of spin-controlled OAM mode of SHG through an on-chip metasurface interferometer. The nonlinear photonic metasurface proposed in this work not only opens new avenues for manipulating the OAM of nonlinear optical signals but also benefits the understanding of the nonlinear spin-orbit interaction of light in nanoscale devices.

Magnetic field tunability of spin polarized excitations in a high temperature magnet

NASA Astrophysics Data System (ADS)

Holinsworth, Brian; Sims, Hunter; Cherian, Judy; Mazumdar, Dipanjan; Harms, Nathan; Chapman, Brandon; Gupta, Arun; McGill, Steve; Musfeldt, Janice

Magnetic semiconductors are at the heart of modern device physics because they naturally provide a non-zero magnetic moment below the ordering temperature, spin-dependent band gap, and spin polarization that originates from exchange-coupled magnetization or an applied field creating a spin-split band structure. Strongly correlated spinel ferrites are amongst the most noteworthy contenders for semiconductor spintronics. NiFe2O4, in particular, displays spin-filtering, linear magnetoresistance, and wide application in the microwave regime. To unravel the spin-charge interaction in NiFe2O4, we bring together magnetic circular dichroism, photoconductivity, and prior optical absorption with complementary first principles calculations. Analysis uncovers a metamagnetic transition modifying electronic structure in the minority channel below the majority channel gap, exchange splittings emerging from spin-split bands, anisotropy of excitons surrounding the indirect gap, and magnetic-field dependent photoconductivity. These findings open the door for the creation and control of spin-polarized excitations from minority channel charge charge transfer in NiFe2O4 and other members of the spinel ferrite family.

Control of electron spin decoherence in nuclear spin baths

NASA Astrophysics Data System (ADS)

Liu, Ren-Bao

2011-03-01

Nuclear spin baths are a main mechanism of decoherence of spin qubits in solid-state systems, such as quantum dots and nitrogen-vacancy (NV) centers of diamond. The decoherence results from entanglement between the electron and nuclear spins, established by quantum evolution of the bath conditioned on the electron spin state. When the electron spin is flipped, the conditional bath evolution is manipulated. Such manipulation of bath through control of the electron spin not only leads to preservation of the center spin coherence but also demonstrates quantum nature of the bath. In an NV center system, the electron spin effectively interacts with hundreds of 13 C nuclear spins. Under repeated flip control (dynamical decoupling), the electron spin coherence can be preserved for a long time (> 1 ms) . Thereforesomecharacteristicoscillations , duetocouplingtoabonded 13 C nuclear spin pair (a dimer), are imprinted on the electron spin coherence profile, which are very sensitive to the position and orientation of the dimer. With such finger-print oscillations, a dimer can be uniquely identified. Thus, we propose magnetometry with single-nucleus sensitivity and atomic resolution, using NV center spin coherence to identify single molecules. Through the center spin coherence, we could also explore the many-body physics in an interacting spin bath. The information of elementary excitations and many-body correlations can be extracted from the center spin coherence under many-pulse dynamical decoupling control. Another application of the preserved spin coherence is identifying quantumness of a spin bath through the back-action of the electron spin to the bath. We show that the multiple transition of an NV center in a nuclear spin bath can have longer coherence time than the single transition does, when the classical noises due to inhomogeneous broadening is removed by spin echo. This counter-intuitive result unambiguously demonstrates the quantumness of the nuclear spin bath

Determinant representations of spin-operator matrix elements in the XX spin chain and their applications

NASA Astrophysics Data System (ADS)

Wu, Ning

2018-01-01

For the one-dimensional spin-1/2 XX model with either periodic or open boundary conditions, it is shown by using a fermionic approach that the matrix element of the spin operator Sj- (Sj-Sj'+ ) between two eigenstates with numbers of excitations n and n +1 (n and n ) can be expressed as the determinant of an appropriate (n +1 )×(n +1 ) matrix whose entries involve the coefficients of the canonical transformations diagonalizing the model. In the special case of a homogeneous periodic XX chain, the matrix element of Sj- reduces to a variant of the Cauchy determinant that can be evaluated analytically to yield a factorized expression. The obtained compact representations of these matrix elements are then applied to two physical scenarios: (i) Nonlinear optical response of molecular aggregates, for which the determinant representation of the transition dipole matrix elements between eigenstates provides a convenient way to calculate the third-order nonlinear responses for aggregates from small to large sizes compared with the optical wavelength; and (ii) real-time dynamics of an interacting Dicke model consisting of a single bosonic mode coupled to a one-dimensional XX spin bath. In this setup, full quantum calculation up to N ≤16 spins for vanishing intrabath coupling shows that the decay of the reduced bosonic occupation number approaches a finite plateau value (in the long-time limit) that depends on the ratio between the number of excitations and the total number of spins. Our results can find useful applications in various "system-bath" systems, with the system part inhomogeneously coupled to an interacting XX chain.

Aging, memory, and nonhierarchical energy landscape of spin jam

NASA Astrophysics Data System (ADS)

Samarakoon, Anjana; Sato, Taku J.; Chen, Tianran; Chern, Gai-Wei; Yang, Junjie; Klich, Israel; Sinclair, Ryan; Zhou, Haidong; Lee, Seung-Hun

2016-10-01

The notion of complex energy landscape underpins the intriguing dynamical behaviors in many complex systems ranging from polymers, to brain activity, to social networks and glass transitions. The spin glass state found in dilute magnetic alloys has been an exceptionally convenient laboratory frame for studying complex dynamics resulting from a hierarchical energy landscape with rugged funnels. Here, we show, by a bulk susceptibility and Monte Carlo simulation study, that densely populated frustrated magnets in a spin jam state exhibit much weaker memory effects than spin glasses, and the characteristic properties can be reproduced by a nonhierarchical landscape with a wide and nearly flat but rough bottom. Our results illustrate that the memory effects can be used to probe different slow dynamics of glassy materials, hence opening a window to explore their distinct energy landscapes.

Direct Identification of Dilute Surface Spins on Al2 O3 : Origin of Flux Noise in Quantum Circuits

NASA Astrophysics Data System (ADS)

de Graaf, S. E.; Adamyan, A. A.; Lindström, T.; Erts, D.; Kubatkin, S. E.; Tzalenchuk, A. Ya.; Danilov, A. V.

2017-02-01

An on-chip electron spin resonance technique is applied to reveal the nature and origin of surface spins on Al2 O3 . We measure a spin density of 2.2 ×1 017 spins/m2 , attributed to physisorbed atomic hydrogen and S =1 /2 electron spin states on the surface. This is direct evidence for the nature of spins responsible for flux noise in quantum circuits, which has been an issue of interest for several decades. Our findings open up a new approach to the identification and controlled reduction of paramagnetic sources of noise and decoherence in superconducting quantum devices.

Topological Triply Degenerate Points Induced by Spin-Tensor-Momentum Couplings

NASA Astrophysics Data System (ADS)

Hu, Haiping; Hou, Junpeng; Zhang, Fan; Zhang, Chuanwei

2018-06-01

The recent discovery of triply degenerate points (TDPs) in topological materials has opened a new perspective toward the realization of novel quasiparticles without counterparts in quantum field theory. The emergence of such protected nodes is often attributed to spin-vector-momentum couplings. We show that the interplay between spin-tensor- and spin-vector-momentum couplings can induce three types of TDPs, classified by different monopole charges (C =±2 , ±1 , 0). A Zeeman field can lift them into Weyl points with distinct numbers and charges. Different TDPs of the same type are connected by intriguing Fermi arcs at surfaces, and transitions between different types are accompanied by level crossings along high-symmetry lines. We further propose an experimental scheme to realize such TDPs in cold-atom optical lattices. Our results provide a framework for studying spin-tensor-momentum coupling-induced TDPs and other exotic quasiparticles.

Dynamical time-reversal symmetry breaking and photo-induced chiral spin liquids in frustrated Mott insulators

DOE PAGES

Claassen, Martin; Jiang, Hong -Chen; Moritz, Brian; ...

2017-10-30

The search for quantum spin liquids in frustrated quantum magnets recently has enjoyed a surge of interest, with various candidate materials under intense scrutiny. However, an experimental confirmation of a gapped topological spin liquid remains an open question. Here, we show that circularly polarized light can provide a knob to drive frustrated Mott insulators into a chiral spin liquid, realizing an elusive quantum spin liquid with topological order. We find that the dynamics of a driven Kagome Mott insulator is well-captured by an effective Floquet spin model, with heating strongly suppressed, inducing a scalar spin chirality S i · (Smore » j × S k) term which dynamically breaks time-reversal while preserving SU(2) spin symmetry. We fingerprint the transient phase diagram and find a stable photo-induced chiral spin liquid near the equilibrium state. Furthermore, the results presented suggest employing dynamical symmetry breaking to engineer quantum spin liquids and access elusive phase transitions that are not readily accessible in equilibrium.« less

Robust techniques for polarization and detection of nuclear spin ensembles

NASA Astrophysics Data System (ADS)

Scheuer, Jochen; Schwartz, Ilai; Müller, Samuel; Chen, Qiong; Dhand, Ish; Plenio, Martin B.; Naydenov, Boris; Jelezko, Fedor

2017-11-01

Highly sensitive nuclear spin detection is crucial in many scientific areas including nuclear magnetic resonance spectroscopy, magnetic resonance imaging (MRI), and quantum computing. The tiny thermal nuclear spin polarization represents a major obstacle towards this goal which may be overcome by dynamic nuclear spin polarization (DNP) methods. The latter often rely on the transfer of the thermally polarized electron spins to nearby nuclear spins, which is limited by the Boltzmann distribution of the former. Here we utilize microwave dressed states to transfer the high (>92 % ) nonequilibrium electron spin polarization of a single nitrogen-vacancy center (NV) induced by short laser pulses to the surrounding 13C carbon nuclear spins. The NV is repeatedly repolarized optically, thus providing an effectively infinite polarization reservoir. A saturation of the polarization of the nearby nuclear spins is achieved, which is confirmed by the decay of the polarization transfer signal and shows an excellent agreement with theoretical simulations. Hereby we introduce the polarization readout by polarization inversion method as a quantitative magnetization measure of the nuclear spin bath, which allows us to observe by ensemble averaging macroscopically hidden polarization dynamics like Landau-Zener-Stückelberg oscillations. Moreover, we show that using the integrated solid effect both for single- and double-quantum transitions nuclear spin polarization can be achieved even when the static magnetic field is not aligned along the NV's crystal axis. This opens a path for the application of our DNP technique to spins in and outside of nanodiamonds, enabling their application as MRI tracers. Furthermore, the methods reported here can be applied to other solid state systems where a central electron spin is coupled to a nuclear spin bath, e.g., phosphor donors in silicon and color centers in silicon carbide.

Molecular dynamics characterization of the SAMHD1 Aicardi-Goutières Arg145Gln mutant: structural determinants for the impaired tetramerization

NASA Astrophysics Data System (ADS)

Cardamone, Francesca; Falconi, Mattia; Desideri, Alessandro

2018-03-01

Aicardi-Goutières syndrome, a rare genetic disorder characterized by calcification of basal ganglia, results in psychomotor delays and epilepsy states from the early months of children life. This disease is caused by mutations in seven different genes encoding proteins implicated in the metabolism of nucleic acids, including SAMHD1. Twenty SAMHD1 gene variants have been discovered and in this work, a structural characterization of the SAMHD1 Aicardi-Goutières Arg145Gln mutant is reported by classical molecular dynamics simulation. Four simulations have been carried out and compared. Two concerning the wild-type SAMHD1 form in presence and absence of cofactors, in order to explain the role of cofactors in the SAMHD1 assembly/disassembly process and, two concerning the Arg145Gln mutant, also in presence and absence of cofactors, in order to have an accurate comparison with the corresponding native forms. Results show the importance of native residue Arg145 in maintaining the tetramer, interacting with GTP cofactor inside allosteric sites. Replacement of arginine in glutamine gives rise to a loosening of GTP-protein interactions, when cofactors are present in allosteric sites, whilst in absence of cofactors, the occurrence of intra and inter-chain interactions is observed in the mutant, not seen in the native enzyme, making energetically unfavourable the tetramerization process.

Molecular dynamics characterization of the SAMHD1 Aicardi-Goutières Arg145Gln mutant: structural determinants for the impaired tetramerization.

PubMed

Cardamone, Francesca; Falconi, Mattia; Desideri, Alessandro

2018-05-01

Aicardi-Goutières syndrome, a rare genetic disorder characterized by calcification of basal ganglia, results in psychomotor delays and epilepsy states from the early months of children life. This disease is caused by mutations in seven different genes encoding proteins implicated in the metabolism of nucleic acids, including SAMHD1. Twenty SAMHD1 gene variants have been discovered and in this work, a structural characterization of the SAMHD1 Aicardi-Goutières Arg145Gln mutant is reported by classical molecular dynamics simulation. Four simulations have been carried out and compared. Two concerning the wild-type SAMHD1 form in presence and absence of cofactors, in order to explain the role of cofactors in the SAMHD1 assembly/disassembly process and, two concerning the Arg145Gln mutant, also in presence and absence of cofactors, in order to have an accurate comparison with the corresponding native forms. Results show the importance of native residue Arg145 in maintaining the tetramer, interacting with GTP cofactor inside allosteric sites. Replacement of arginine in glutamine gives rise to a loosening of GTP-protein interactions, when cofactors are present in allosteric sites, whilst in absence of cofactors, the occurrence of intra and inter-chain interactions is observed in the mutant, not seen in the native enzyme, making energetically unfavourable the tetramerization process.

Molecular dynamics characterization of the SAMHD1 Aicardi-Goutières Arg145Gln mutant: structural determinants for the impaired tetramerization

NASA Astrophysics Data System (ADS)

Cardamone, Francesca; Falconi, Mattia; Desideri, Alessandro

2018-05-01

Aicardi-Goutières syndrome, a rare genetic disorder characterized by calcification of basal ganglia, results in psychomotor delays and epilepsy states from the early months of children life. This disease is caused by mutations in seven different genes encoding proteins implicated in the metabolism of nucleic acids, including SAMHD1. Twenty SAMHD1 gene variants have been discovered and in this work, a structural characterization of the SAMHD1 Aicardi-Goutières Arg145Gln mutant is reported by classical molecular dynamics simulation. Four simulations have been carried out and compared. Two concerning the wild-type SAMHD1 form in presence and absence of cofactors, in order to explain the role of cofactors in the SAMHD1 assembly/disassembly process and, two concerning the Arg145Gln mutant, also in presence and absence of cofactors, in order to have an accurate comparison with the corresponding native forms. Results show the importance of native residue Arg145 in maintaining the tetramer, interacting with GTP cofactor inside allosteric sites. Replacement of arginine in glutamine gives rise to a loosening of GTP-protein interactions, when cofactors are present in allosteric sites, whilst in absence of cofactors, the occurrence of intra and inter-chain interactions is observed in the mutant, not seen in the native enzyme, making energetically unfavourable the tetramerization process.

Spin-current emission governed by nonlinear spin dynamics.

PubMed

Tashiro, Takaharu; Matsuura, Saki; Nomura, Akiyo; Watanabe, Shun; Kang, Keehoon; Sirringhaus, Henning; Ando, Kazuya

2015-10-16

Coupling between conduction electrons and localized magnetization is responsible for a variety of phenomena in spintronic devices. This coupling enables to generate spin currents from dynamical magnetization. Due to the nonlinearity of magnetization dynamics, the spin-current emission through the dynamical spin-exchange coupling offers a route for nonlinear generation of spin currents. Here, we demonstrate spin-current emission governed by nonlinear magnetization dynamics in a metal/magnetic insulator bilayer. The spin-current emission from the magnetic insulator is probed by the inverse spin Hall effect, which demonstrates nontrivial temperature and excitation power dependences of the voltage generation. The experimental results reveal that nonlinear magnetization dynamics and enhanced spin-current emission due to magnon scatterings are triggered by decreasing temperature. This result illustrates the crucial role of the nonlinear magnon interactions in the spin-current emission driven by dynamical magnetization, or nonequilibrium magnons, from magnetic insulators.

Spin-current emission governed by nonlinear spin dynamics

PubMed Central

Tashiro, Takaharu; Matsuura, Saki; Nomura, Akiyo; Watanabe, Shun; Kang, Keehoon; Sirringhaus, Henning; Ando, Kazuya

2015-01-01

Coupling between conduction electrons and localized magnetization is responsible for a variety of phenomena in spintronic devices. This coupling enables to generate spin currents from dynamical magnetization. Due to the nonlinearity of magnetization dynamics, the spin-current emission through the dynamical spin-exchange coupling offers a route for nonlinear generation of spin currents. Here, we demonstrate spin-current emission governed by nonlinear magnetization dynamics in a metal/magnetic insulator bilayer. The spin-current emission from the magnetic insulator is probed by the inverse spin Hall effect, which demonstrates nontrivial temperature and excitation power dependences of the voltage generation. The experimental results reveal that nonlinear magnetization dynamics and enhanced spin-current emission due to magnon scatterings are triggered by decreasing temperature. This result illustrates the crucial role of the nonlinear magnon interactions in the spin-current emission driven by dynamical magnetization, or nonequilibrium magnons, from magnetic insulators. PMID:26472712

Spin Funneling for Enhanced Spin Injection into Ferromagnets

PubMed Central

Sayed, Shehrin; Diep, Vinh Q.; Camsari, Kerem Yunus; Datta, Supriyo

2016-01-01

It is well-established that high spin-orbit coupling (SOC) materials convert a charge current density into a spin current density which can be used to switch a magnet efficiently and there is increasing interest in identifying materials with large spin Hall angle for lower switching current. Using experimentally benchmarked models, we show that composite structures can be designed using existing spin Hall materials such that the effective spin Hall angle is larger by an order of magnitude. The basic idea is to funnel spins from a large area of spin Hall material into a small area of ferromagnet using a normal metal with large spin diffusion length and low resistivity like Cu or Al. We show that this approach is increasingly effective as magnets get smaller. We avoid unwanted charge current shunting by the low resistive NM layer utilizing the newly discovered phenomenon of pure spin conduction in ferromagnetic insulators via magnon diffusion. We provide a spin circuit model for magnon diffusion in FMI that is benchmarked against recent experiments and theory. PMID:27374496

Spin Funneling for Enhanced Spin Injection into Ferromagnets

NASA Astrophysics Data System (ADS)

Sayed, Shehrin; Diep, Vinh Q.; Camsari, Kerem Yunus; Datta, Supriyo

2016-07-01

It is well-established that high spin-orbit coupling (SOC) materials convert a charge current density into a spin current density which can be used to switch a magnet efficiently and there is increasing interest in identifying materials with large spin Hall angle for lower switching current. Using experimentally benchmarked models, we show that composite structures can be designed using existing spin Hall materials such that the effective spin Hall angle is larger by an order of magnitude. The basic idea is to funnel spins from a large area of spin Hall material into a small area of ferromagnet using a normal metal with large spin diffusion length and low resistivity like Cu or Al. We show that this approach is increasingly effective as magnets get smaller. We avoid unwanted charge current shunting by the low resistive NM layer utilizing the newly discovered phenomenon of pure spin conduction in ferromagnetic insulators via magnon diffusion. We provide a spin circuit model for magnon diffusion in FMI that is benchmarked against recent experiments and theory.

APEX/SPIN: a free test platform to measure speech intelligibility.

PubMed

Francart, Tom; Hofmann, Michael; Vanthornhout, Jonas; Van Deun, Lieselot; van Wieringen, Astrid; Wouters, Jan

2017-02-01

Measuring speech intelligibility in quiet and noise is important in clinical practice and research. An easy-to-use free software platform for conducting speech tests is presented, called APEX/SPIN. The APEX/SPIN platform allows the use of any speech material in combination with any noise. A graphical user interface provides control over a large range of parameters, such as number of loudspeakers, signal-to-noise ratio and parameters of the procedure. An easy-to-use graphical interface is provided for calibration and storage of calibration values. To validate the platform, perception of words in quiet and sentences in noise were measured both with APEX/SPIN and with an audiometer and CD player, which is a conventional setup in current clinical practice. Five normal-hearing listeners participated in the experimental evaluation. Speech perception results were similar for the APEX/SPIN platform and conventional procedures. APEX/SPIN is a freely available and open source platform that allows the administration of all kinds of custom speech perception tests and procedures.

Magnetic and metal-insulator transitions in coupled spin-fermion systems

DOE PAGES

Mondaini, R.; Paiva, T.; Scalettar, R. T.

2014-10-14

We use quantum Monte Carlo to determine the magnetic and transport properties of coupled square lattice spin and fermionic planes as a model for a metal-insulator interface. Specifically, layers of Ising spins with an intra-layer exchange constant J interact with the electronic spins of several adjoining metallic sheets via a coupling JH. When the chemical potential cuts across the band center, that is, at half-filling, the Neel temperature of antiferromagnetic (J > 0) Ising spins is enhanced by the coupling to the metal, while in the ferromagnetic case (J < 0) the metallic degrees of freedom reduce the ordering temperature.more » In the former case, a gap opens in the fermionic spectrum, driving insulating behavior, and the electron spins also order. This induced antiferromagnetism penetrates more weakly as the distance from the interface increases, and also exhibits a non-monotonic dependence on JH. For doped lattices an interesting charge disproportionation occurs where electrons move to the interface layer to maintain half-filling there.« less

Separated spin-up and spin-down quantum hydrodynamics of degenerated electrons: Spin-electron acoustic wave appearance.

PubMed

Andreev, Pavel A

2015-03-01

The quantum hydrodynamic (QHD) model of charged spin-1/2 particles contains physical quantities defined for all particles of a species including particles with spin-up and with spin-down. Different populations of states with different spin directions are included in the spin density (the magnetization). In this paper I derive a QHD model, which separately describes spin-up electrons and spin-down electrons. Hence electrons with different projections of spins on the preferable direction are considered as two different species of particles. It is shown that the numbers of particles with different spin directions do not conserve. Hence the continuity equations contain sources of particles. These sources are caused by the interactions of the spins with the magnetic field. Terms of similar nature arise in the Euler equation. The z projection of the spin density is no longer an independent variable. It is proportional to the difference between the concentrations of the electrons with spin-up and the electrons with spin-down. The propagation of waves in the magnetized plasmas of degenerate electrons is considered. Two regimes for the ion dynamics, the motionless ions and the motion of the degenerate ions as the single species with no account of the spin dynamics, are considered. It is shown that this form of the QHD equations gives all solutions obtained from the traditional form of QHD equations with no distinction of spin-up and spin-down states. But it also reveals a soundlike solution called the spin-electron acoustic wave. Coincidence of most solutions is expected since this derivation was started with the same basic equation: the Pauli equation. Solutions arise due to the different Fermi pressures for the spin-up electrons and the spin-down electrons in the magnetic field. The results are applied to degenerate electron gas of paramagnetic and ferromagnetic metals in the external magnetic field. The dispersion of the spin-electron acoustic waves in the partially spin

Spin nematics next to spin singlets

NASA Astrophysics Data System (ADS)

Yokoyama, Yuto; Hotta, Chisa

2018-05-01

We provide a route to generate nematic order in a spin-1/2 system. Unlike the well-known magnon-binding mechanism, our spin nematics requires neither the frustration effect nor spin polarization in a high field or in the vicinity of a ferromagnet, but instead appears next to the spin singlet phase. We start from a state consisting of a quantum spin-1/2 singlet dimer placed on each site of a triangular lattice, and show that interdimer ring exchange interactions efficiently dope the SU(2) triplets that itinerate and interact, easily driving a stable singlet state to either Bose-Einstein condensates or a triplet crystal, some hosting a spin nematic order. A variety of roles the ring exchange serves includes the generation of a bilinear-biquadratic interaction between nearby triplets, which is responsible for the emergent nematic order separated from the singlet phase by a first-order transition.

Dynamics of quantum tomography in an open system

NASA Astrophysics Data System (ADS)

Uchiyama, Chikako

2015-06-01

In this study, we provide a way to describe the dynamics of quantum tomography in an open system with a generalized master equation, considering a case where the relevant system under tomographic measurement is influenced by the environment. We apply this to spin tomography because such situations typically occur in μSR (muon spin rotation/relaxation/resonance) experiments where microscopic features of the material are investigated by injecting muons as probes. As a typical example to describe the interaction between muons and a sample material, we use a spin-boson model where the relevant spin interacts with a bosonic environment. We describe the dynamics of a spin tomogram using a time-convolutionless type of generalized master equation that enables us to describe short time scales and/or low-temperature regions. Through numerical evaluation for the case of Ohmic spectral density with an exponential cutoff, a clear interdependency is found between the time evolution of elements of the density operator and a spin tomogram. The formulation in this paper may provide important fundamental information for the analysis of results from, for example, μSR experiments on short time scales and/or in low-temperature regions using spin tomography.

How to fold a spin chain: Integrable boundaries of the Heisenberg XXX and Inozemtsev hyperbolic models

NASA Astrophysics Data System (ADS)

De La Rosa Gomez, Alejandro; MacKay, Niall; Regelskis, Vidas

2017-04-01

We present a general method of folding an integrable spin chain, defined on a line, to obtain an integrable open spin chain, defined on a half-line. We illustrate our method through two fundamental models with sl2 Lie algebra symmetry: the Heisenberg XXX and the Inozemtsev hyperbolic spin chains. We obtain new long-range boundary Hamiltonians and demonstrate that they exhibit Yangian symmetries, thus ensuring integrability of the models we obtain. The method presented provides a ;bottom-up; approach for constructing integrable boundaries and can be applied to any spin chain model.

Spin-orbit coupling manipulating composite topological spin textures in atomic-molecular Bose-Einstein condensates

NASA Astrophysics Data System (ADS)

Liu, Chao-Fei; Juzeliūnas, Gediminas; Liu, W. M.

2017-02-01

Atomic-molecular Bose-Einstein condensates (BECs) offer brand new opportunities to revolutionize quantum gases and probe the variation of fundamental constants with unprecedented sensitivity. The recent realization of spin-orbit coupling (SOC) in BECs provides a new platform for exploring completely new phenomena unrealizable elsewhere. In this study, we find a way of creating a Rashba-Dresselhaus SOC in atomic-molecular BECs by combining the spin-dependent photoassociation and Raman coupling, which can control the formation and distribution of a different type of topological excitation—carbon-dioxide-like skyrmion. This skyrmion is formed by two half-skyrmions of molecular BECs coupling with one skyrmion of atomic BECs, where the two half-skyrmions locate at both sides of one skyrmion. Carbon-dioxide-like skyrmion can be detected by measuring the vortices structures using the time-of-flight absorption imaging technique in real experiments. Furthermore, we find that SOC can effectively change the occurrence of the Chern number in k space, which causes the creation of topological spin textures from some separated carbon-dioxide-like monomers each with topological charge -2 to a polymer chain of the skyrmions. This work helps in creating dual SOC atomic-molecular BECs and opens avenues to manipulate topological excitations.

Structure and function in rhodopsin: Rhodopsin mutants with a neutral amino acid at E134 have a partially activated conformation in the dark state*

PubMed Central

Kim, Jong-Myoung; Altenbach, Christian; Thurmond, Robin L.; Khorana, H. Gobind; Hubbell, Wayne L.

1997-01-01

The Glu-134–Arg-135 residues in rhodopsin, located near the cytoplasmic end of the C helix, are involved in G protein binding, or activation, or both. Furthermore, the charge-neutralizing mutation Glu-134 to Gln-134 produces hyperactivity in the activated state and produces constitutive activity in opsin. The Glu/Asp-Arg charge pair is highly conserved in equivalent positions in other G protein-coupled receptors. To investigate the structural consequences of charge-neutralizing mutations at Glu-134 and Arg-135 in rhodopsin, single spin-labeled side chains were introduced at sites in the cytoplasmic domains of helices C (140), E (227), F (250), or G (316) to serve as “molecular sensors” of the local helix bundle conformation. In each of the spin-labeled rhodopsins, a Gln substitution was introduced at either Glu-134 or Arg-135, and the electron paramagnetic resonance spectrum of the spin label was used to monitor the structural response of the helix bundle. The results indicate that a Gln substitution at Glu-134 induces a photoactivated conformation around helices C and G even in the dark state, an observation of potential relevance to the hyperactivity and constitutive activity of the mutant. In contrast, little change is induced in helix F, which has been shown to undergo a dominant motion upon photoactivation. This result implies that the multiple helix motions accompanying photoactivation are not strongly coupled and can be induced to take place independently. Gln substitution at Arg-135 produces only minor structural changes in the dark- or light-activated conformation, suggesting that this residue is not a determinant of structure in the regions investigated, although it may be functionally important. PMID:9405602

Spin-transfer torque induced spin waves in antiferromagnetic insulators

DOE PAGES

Daniels, Matthew W.; Guo, Wei; Stocks, George Malcolm; ...

2015-01-01

We explore the possibility of exciting spin waves in insulating antiferromagnetic films by injecting spin current at the surface. We analyze both magnetically compensated and uncompensated interfaces. We find that the spin current induced spin-transfer torque can excite spin waves in insulating antiferromagnetic materials and that the chirality of the excited spin wave is determined by the polarization of the injected spin current. Furthermore, the presence of magnetic surface anisotropy can greatly increase the accessibility of these excitations.

Topological Magnonics: A Paradigm for Spin-Wave Manipulation and Device Design

NASA Astrophysics Data System (ADS)

Wang, X. S.; Zhang, H. W.; Wang, X. R.

2018-02-01

Conventional magnonic devices use magnetostatic waves whose properties are sensitive to device geometry and the details of magnetization structure, so the design and the scalability of the device or circuitry are difficult. We propose topological magnonics, in which topological exchange spin waves are used as information carriers, that do not suffer from conventional problems of magnonic devices with additional nice features of nanoscale wavelength and high frequency. We show that a perpendicularly magnetized ferromagnet on a honeycomb lattice is generically a topological magnetic material in the sense that topologically protected chiral edge spin waves exist in the band gap as long as a spin-orbit-induced nearest-neighbor pseudodipolar interaction (and/or a next-nearest-neighbor Dzyaloshinskii-Moriya interaction) is present. The edge spin waves propagate unidirectionally along sample edges and domain walls regardless of the system geometry and defects. As a proof of concept, spin-wave diodes, spin-wave beam splitters, and spin-wave interferometers are designed by using sample edges and domain walls to manipulate the propagation of topologically protected chiral spin waves. Since magnetic domain walls can be controlled by magnetic fields or electric current or fields, one can essentially draw, erase, and redraw different spin-wave devices and circuitry on the same magnetic plate so that the proposed devices are reconfigurable and tunable. The topological magnonics opens up an alternative direction towards a robust, reconfigurable and scalable spin-wave circuitry.

Quantum nonunital dynamics of spin-bath-assisted Fisher information

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hao, Xiang, E-mail: haoxiang-edu198126@163.com; Wu, Yinzhong

2016-04-15

The nonunital non-Markovian dynamics of qubits immersed in a spin bath is studied without any Markovian approximation. The environmental effects on the precisions of quantum parameter estimation are taken into account. The time-dependent transfer matrix and inhomogeneity vector are obtained for the description of the open dynamical process. The dynamical behaviour of one qubit coupled to a spin bath is geometrically described by the Bloch vector. It is found out that the nonunital non-Markovian effects can engender the improvement of the precision of quantum parameter estimation. This result contributes to the environment-assisted quantum information theory.

Quantum phase transition in dimerised spin-1/2 chains

NASA Astrophysics Data System (ADS)

Das, Aparajita; Bhadra, Sreeparna; Saha, Sonali

2015-11-01

Quantum phase transition in dimerised antiferromagnetic Heisenberg spin chain has been studied. A staircase structure in the variation of concurrence within strongly coupled pairs with that of external magnetic field has been observed indicating multiple critical (or critical like) points. Emergence of entanglement due to external magnetic field or magnetic entanglement is observed for weakly coupled spin pairs too in the same dimer chain. Though closed dimerised isotropic XXX Heisenberg chains with different dimer strengths were mainly explored, analogous studies on open chains as well as closed anisotropic (XX interaction) chains with tilted external magnetic field have also been studied.

Proca fields interpretation of spin 1 equation in Robertson-Walker space-time

NASA Astrophysics Data System (ADS)

Zecca, Antonio

2006-05-01

The general scheme for massive spin 1 equation in curved space-time is specialized to describe the Proca fields. The expressions of the Proca tensor fields are detailed in the Robertson-Walker space-time by means of the solutions of the spin 1 equation in a given tetrad and by the components of the tetrad itself. Asymptotic behaviours of the fields are discussed in the flat, closed and open space-time cases.

Surface Plasmon-Mediated Nanoscale Localization of Laser-Driven sub-Terahertz Spin Dynamics in Magnetic Dielectrics

NASA Astrophysics Data System (ADS)

Chekhov, Alexander L.; Stognij, Alexander I.; Satoh, Takuya; Murzina, Tatiana V.; Razdolski, Ilya; Stupakiewicz, Andrzej

2018-05-01

Ultrafast all-optical control of spins with femtosecond laser pulses is one of the hot topics at the crossroads of photonics and magnetism with a direct impact on future magnetic recording. Unveiling light-assisted recording mechanisms for an increase of the bit density beyond the diffraction limit without excessive heating of the recording medium is an open challenge. Here we show that surface plasmon-polaritons in hybrid metal-dielectric structures can provide spatial confinement of the inverse Faraday effect, mediating the excitation of localized coherent spin precession with 0.41 THz frequency. We demonstrate a two orders of magnitude enhancement of the excitation efficiency at the surface plasmon resonance within the 100 nm layer in dielectric garnet. Our findings broaden the horizons of ultrafast spin-plasmonics and open pathways towards non-thermal opto-magnetic recording at the nano-scale.

Gapped Spin-1/2 Spinon Excitations in a New Kagome Quantum Spin Liquid Compound Cu3Zn(OH)6FBr

NASA Astrophysics Data System (ADS)

Feng, Zili; Li, Zheng; Meng, Xin; Yi, Wei; Wei, Yuan; Zhang, Jun; Wang, Yan-Cheng; Jiang, Wei; Liu, Zheng; Li, Shiyan; Liu, Feng; Luo, Jianlin; Li, Shiliang; Zheng, Guo-qing; Meng, Zi Yang; Mei, Jia-Wei; Shi, Youguo

2017-06-01

We report a new kagome quantum spin liquid candidate Cu3Zn(OH)6FBr, which does not experience any phase transition down to 50 mK, more than three orders lower than the antiferromagnetic Curie-Weiss temperature (∼200 K). A clear gap opening at low temperature is observed in the uniform spin susceptibility obtained from 19F nuclear magnetic resonance measurements. We observe the characteristic magnetic field dependence of the gap as expected for fractionalized spin-1/2 spinon excitations. Our experimental results provide firm evidence for spin fractionalization in a topologically ordered spin system, resembling charge fractionalization in the fractional quantum Hall state. Supported by the National Key Research and Development Program of China under Grant Nos 2016YFA0300502, 2016YFA0300503, 2016YFA0300604, 2016YF0300300 and 2016YFA0300802, the National Natural Science Foundation of China under Grant Nos 11421092, 11474330, 11574359, 11674406, 11374346 and 11674375, the National Basic Research Program of China (973 Program) under Grant No 2015CB921304, the National Thousand-Young-Talents Program of China, the Strategic Priority Research Program (B) of the Chinese Academy of Sciences under Grant Nos XDB07020000, XDB07020200 and XDB07020300. The work in Utah is supported by DOE-BES under Grant No DE-FG02-04ER46148.

Observation of two-orbital spin-exchange interactions with ultracold SU(N)-symmetric fermions

NASA Astrophysics Data System (ADS)

Scazza, F.; Hofrichter, C.; Höfer, M.; de Groot, P. C.; Bloch, I.; Fölling, S.

2014-10-01

Spin-exchanging interactions govern the properties of strongly correlated electron systems such as many magnetic materials. When orbital degrees of freedom are present, spin exchange between different orbitals often dominates, leading to the Kondo effect, heavy fermion behaviour or magnetic ordering. Ultracold ytterbium or alkaline-earth ensembles have attracted much recent interest as model systems for these effects, with two (meta-) stable electronic configurations representing independent orbitals. We report the observation of spin-exchanging contact interactions in a two-orbital SU(N)-symmetric quantum gas realized with fermionic 173Yb. We find strong inter-orbital spin exchange by spectroscopic characterization of all interaction channels and demonstrate SU(N = 6) symmetry within our measurement precision. The spin-exchange process is also directly observed through the dynamic equilibration of spin imbalances between ensembles in separate orbitals. The realization of an SU(N)-symmetric two-orbital Hubbard Hamiltonian opens the route to quantum simulations with extended symmetries and with orbital magnetic interactions, such as the Kondo lattice model.

Quantum spin transistor with a Heisenberg spin chain.

PubMed

Marchukov, O V; Volosniev, A G; Valiente, M; Petrosyan, D; Zinner, N T

2016-10-10

Spin chains are paradigmatic systems for the studies of quantum phases and phase transitions, and for quantum information applications, including quantum computation and short-distance quantum communication. Here we propose and analyse a scheme for conditional state transfer in a Heisenberg XXZ spin chain which realizes a quantum spin transistor. In our scheme, the absence or presence of a control spin excitation in the central gate part of the spin chain results in either perfect transfer of an arbitrary state of a target spin between the weakly coupled input and output ports, or its complete blockade at the input port. We also discuss a possible proof-of-concept realization of the corresponding spin chain with a one-dimensional ensemble of cold atoms with strong contact interactions. Our scheme is generally applicable to various implementations of tunable spin chains, and it paves the way for the realization of integrated quantum logic elements.

Gate-tunable black phosphorus spin valve with nanosecond spin lifetimes

NASA Astrophysics Data System (ADS)

Avsar, Ahmet; Tan, Jun Y.; Kurpas, Marcin; Gmitra, Martin; Watanabe, Kenji; Taniguchi, Takashi; Fabian, Jaroslav; Özyilmaz, Barbaros

2017-09-01

Two-dimensional materials offer new opportunities for both fundamental science and technological applications, by exploiting the electron's spin. Although graphene is very promising for spin communication due to its extraordinary electron mobility, the lack of a bandgap restricts its prospects for semiconducting spin devices such as spin diodes and bipolar spin transistors. The recent emergence of two-dimensional semiconductors could help overcome this basic challenge. In this letter we report an important step towards making two-dimensional semiconductor spin devices. We have fabricated a spin valve based on ultrathin (~5 nm) semiconducting black phosphorus (bP), and established fundamental spin properties of this spin channel material, which supports all electrical spin injection, transport, precession and detection up to room temperature. In the non-local spin valve geometry we measure Hanle spin precession and observe spin relaxation times as high as 4 ns, with spin relaxation lengths exceeding 6 μm. Our experimental results are in a very good agreement with first-principles calculations and demonstrate that the Elliott-Yafet spin relaxation mechanism is dominant. We also show that spin transport in ultrathin bP depends strongly on the charge carrier concentration, and can be manipulated by the electric field effect.

Masses of constituent quarks confined in open bottom hadrons

NASA Astrophysics Data System (ADS)

Borka Jovanović, V.; Borka, D.; Jovanović, P.; Milošević, J.; Ignjatović, S. R.

2014-12-01

We apply color-spin and flavor-spin quark-quark interactions to the meson and baryon constituent quarks, and calculate constituent quark masses, as well as the coupling constants of these interactions. The main goal of this paper was to determine constituent quark masses from light and open bottom hadron masses, using the fitting method we have developed and clustering of hadron groups. We use color-spin Fermi-Breit (FB) and flavor-spin Glozman-Riska (GR) hyperfine interaction (HFI) to determine constituent quark masses (especially b quark mass). Another aim was to discern between the FB and GR HFI because our previous findings had indicated that both interactions were satisfactory. Our improved fitting procedure of constituent quark masses showed that on average color-spin (FB) HFI yields better fits. The method also shows the way how the constituent quark masses and the strength of the interaction constants appear in different hadron environments.

Spin filter and spin valve in ferromagnetic graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, Yu, E-mail: kwungyusung@gmail.com; Dai, Gang; Research Center for Microsystems and Terahertz, China Academy of Engineering Physics, Mianyang 621999

2015-06-01

We propose and demonstrate that a EuO-induced and top-gated graphene ferromagnetic junction can be simultaneously operated as a spin filter and a spin valve. We attribute such a remarkable result to a coexistence of a half-metal band and a common energy gap for opposite spins in ferromagnetic graphene. We show that both the spin filter and the spin valve can be effectively controlled by a back gate voltage, and they survive for practical metal contacts and finite temperature. Specifically, larger single spin currents and on-state currents can be reached with contacts with work functions similar to graphene, and the spinmore » filter can operate at higher temperature than the spin valve.« less

Aging, memory, and nonhierarchical energy landscape of spin jam

PubMed Central

Samarakoon, Anjana; Sato, Taku J.; Chen, Tianran; Chern, Gai-Wei; Yang, Junjie; Klich, Israel; Sinclair, Ryan; Zhou, Haidong; Lee, Seung-Hun

2016-01-01

The notion of complex energy landscape underpins the intriguing dynamical behaviors in many complex systems ranging from polymers, to brain activity, to social networks and glass transitions. The spin glass state found in dilute magnetic alloys has been an exceptionally convenient laboratory frame for studying complex dynamics resulting from a hierarchical energy landscape with rugged funnels. Here, we show, by a bulk susceptibility and Monte Carlo simulation study, that densely populated frustrated magnets in a spin jam state exhibit much weaker memory effects than spin glasses, and the characteristic properties can be reproduced by a nonhierarchical landscape with a wide and nearly flat but rough bottom. Our results illustrate that the memory effects can be used to probe different slow dynamics of glassy materials, hence opening a window to explore their distinct energy landscapes. PMID:27698141

Spin splitting generated in a Y-shaped semiconductor nanostructure with a quantum point contact

NASA Astrophysics Data System (ADS)

Wójcik, P.; Adamowski, J.; Wołoszyn, M.; Spisak, B. J.

2015-07-01

We have studied the spin splitting of the current in the Y-shaped semiconductor nanostructure with a quantum point contact (QPC) in a perpendicular magnetic field. Our calculations show that the appropriate tuning of the QPC potential and the external magnetic field leads to an almost perfect separation of the spin-polarized currents: electrons with opposite spins flow out through different output branches. The spin splitting results from the joint effect of the QPC, the spin Zeeman splitting, and the electron transport through the edge states formed in the nanowire at the sufficiently high magnetic field. The Y-shaped nanostructure can be used to split the unpolarized current into two spin currents with opposite spins as well as to detect the flow of the spin current. We have found that the separation of the spin currents is only slightly affected by the Rashba spin-orbit coupling. The spin-splitter device is an analogue of the optical device—the birefractive crystal that splits the unpolarized light into two beams with perpendicular polarizations. In the magnetic-field range, in which the current is carried through the edges states, the spin splitting is robust against the spin-independent scattering. This feature opens up a possibility of the application of the Y-shaped nanostructure as a non-ballistic spin-splitter device in spintronics.

Spin splitting generated in a Y-shaped semiconductor nanostructure with a quantum point contact

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wójcik, P., E-mail: pawel.wojcik@fis.agh.edu.pl; Adamowski, J., E-mail: janusz.adamowski@fis.agh.edu.pl; Wołoszyn, M.

2015-07-07

We have studied the spin splitting of the current in the Y-shaped semiconductor nanostructure with a quantum point contact (QPC) in a perpendicular magnetic field. Our calculations show that the appropriate tuning of the QPC potential and the external magnetic field leads to an almost perfect separation of the spin-polarized currents: electrons with opposite spins flow out through different output branches. The spin splitting results from the joint effect of the QPC, the spin Zeeman splitting, and the electron transport through the edge states formed in the nanowire at the sufficiently high magnetic field. The Y-shaped nanostructure can be usedmore » to split the unpolarized current into two spin currents with opposite spins as well as to detect the flow of the spin current. We have found that the separation of the spin currents is only slightly affected by the Rashba spin-orbit coupling. The spin-splitter device is an analogue of the optical device—the birefractive crystal that splits the unpolarized light into two beams with perpendicular polarizations. In the magnetic-field range, in which the current is carried through the edges states, the spin splitting is robust against the spin-independent scattering. This feature opens up a possibility of the application of the Y-shaped nanostructure as a non-ballistic spin-splitter device in spintronics.« less

Robust spin-current injection in lateral spin valves with two-terminal Co2FeSi spin injectors

NASA Astrophysics Data System (ADS)

Oki, S.; Kurokawa, T.; Honda, S.; Yamada, S.; Kanashima, T.; Itoh, H.; Hamaya, K.

2017-05-01

We demonstrate generation and detection of pure spin currents by combining a two-terminal spin-injection technique and Co2FeSi (CFS) spin injectors in lateral spin valves (LSVs). We find that the two-terminal spin injection with CFS has the robust dependence of the nonlocal spin signals on the applied bias currents, markedly superior to the four-terminal spin injection with permalloy reported previously. In our LSVs, since the spin transfer torque from one CFS injector to another CFS one is large, the nonlocal magnetoresistance with respect to applied magnetic fields shows large asymmetry in high bias-current conditions. For utilizing multi-terminal spin injection with CFS as a method for magnetization reversals, the terminal arrangement of CFS spin injectors should be taken into account.

Valley photonic crystals for control of spin and topology

NASA Astrophysics Data System (ADS)

Dong, Jian-Wen; Chen, Xiao-Dong; Zhu, Hanyu; Wang, Yuan; Zhang, Xiang

2017-03-01

Photonic crystals offer unprecedented opportunity for light manipulation and applications in optical communication and sensing. Exploration of topology in photonic crystals and metamaterials with non-zero gauge field has inspired a number of intriguing optical phenomena such as one-way transport and Weyl points. Recently, a new degree of freedom, valley, has been demonstrated in two-dimensional materials. Here, we propose a concept of valley photonic crystals with electromagnetic duality symmetry but broken inversion symmetry. We observe photonic valley Hall effect originating from valley-dependent spin-split bulk bands, even in topologically trivial photonic crystals. Valley-spin locking behaviour results in selective net spin flow inside bulk valley photonic crystals. We also show the independent control of valley and topology in a single system that has been long pursued in electronic systems, resulting in topologically-protected flat edge states. Valley photonic crystals not only offer a route towards the observation of non-trivial states, but also open the way for device applications in integrated photonics and information processing using spin-dependent transportation.

Angular dependence of spin-orbit spin-transfer torques

NASA Astrophysics Data System (ADS)

Lee, Ki-Seung; Go, Dongwook; Manchon, Aurélien; Haney, Paul M.; Stiles, M. D.; Lee, Hyun-Woo; Lee, Kyung-Jin

2015-04-01

In ferromagnet/heavy-metal bilayers, an in-plane current gives rise to spin-orbit spin-transfer torque, which is usually decomposed into fieldlike and dampinglike torques. For two-dimensional free-electron and tight-binding models with Rashba spin-orbit coupling, the fieldlike torque acquires nontrivial dependence on the magnetization direction when the Rashba spin-orbit coupling becomes comparable to the exchange interaction. This nontrivial angular dependence of the fieldlike torque is related to the Fermi surface distortion, determined by the ratio of the Rashba spin-orbit coupling to the exchange interaction. On the other hand, the dampinglike torque acquires nontrivial angular dependence when the Rashba spin-orbit coupling is comparable to or stronger than the exchange interaction. It is related to the combined effects of the Fermi surface distortion and the Fermi sea contribution. The angular dependence is consistent with experimental observations and can be important to understand magnetization dynamics induced by spin-orbit spin-transfer torques.

Quantum spin transistor with a Heisenberg spin chain

PubMed Central

Marchukov, O. V.; Volosniev, A. G.; Valiente, M.; Petrosyan, D.; Zinner, N. T.

2016-01-01

Spin chains are paradigmatic systems for the studies of quantum phases and phase transitions, and for quantum information applications, including quantum computation and short-distance quantum communication. Here we propose and analyse a scheme for conditional state transfer in a Heisenberg XXZ spin chain which realizes a quantum spin transistor. In our scheme, the absence or presence of a control spin excitation in the central gate part of the spin chain results in either perfect transfer of an arbitrary state of a target spin between the weakly coupled input and output ports, or its complete blockade at the input port. We also discuss a possible proof-of-concept realization of the corresponding spin chain with a one-dimensional ensemble of cold atoms with strong contact interactions. Our scheme is generally applicable to various implementations of tunable spin chains, and it paves the way for the realization of integrated quantum logic elements. PMID:27721438

Toward nonlinear magnonics: Intensity-dependent spin-wave switching in insulating side-coupled magnetic stripes

NASA Astrophysics Data System (ADS)

Sadovnikov, A. V.; Odintsov, S. A.; Beginin, E. N.; Sheshukova, S. E.; Sharaevskii, Yu. P.; Nikitov, S. A.

2017-10-01

We demonstrate that the nonlinear spin-wave transport in two laterally parallel magnetic stripes exhibit the intensity-dependent power exchange between the adjacent spin-wave channels. By the means of Brillouin light scattering technique, we investigate collective nonlinear spin-wave dynamics in the presence of magnetodipolar coupling. The nonlinear intensity-dependent effect reveals itself in the spin-wave mode transformation and differential nonlinear spin-wave phase shift in each adjacent magnetic stripe. The proposed analytical theory, based on the coupled Ginzburg-Landau equations, predicts the geometry design involving the reduction of power requirement to the all-magnonic switching. A very good agreement between calculation and experiment was found. In addition, a micromagnetic and finite-element approach has been independently used to study the nonlinear behavior of spin waves in adjacent stripes and the nonlinear transformation of spatial profiles of spin-wave modes. Our results show that the proposed spin-wave coupling mechanism provides the basis for nonlinear magnonic circuits and opens the perspectives for all-magnonic computing architecture.

Thermally Generated Spin Signals in a Nondegenerate Silicon Spin Valve

NASA Astrophysics Data System (ADS)

Yamashita, Naoto; Ando, Yuichiro; Koike, Hayato; Miwa, Shinji; Suzuki, Yoshishige; Shiraishi, Masashi

2018-05-01

Thermally generated spin signals are observed in a nondegenerate Si spin valve. The spin-dependent Seebeck effect is used for thermal spin-signal generation. A thermal gradient of about 200 mK at the interface of Fe and Si enables the generation of a spin voltage of 8 μ V at room temperature. A simple expansion of the conventional spin-drift-diffusion model that takes into account the spin-dependent Seebeck effect shows that semiconductor materials are more promising for thermal spin-signal generation comparing than metallic materials, and thus enable efficient heat recycling in semiconductor spin devices.

Microscopic studies of nonlocal spin dynamics and spin transport (invited)

NASA Astrophysics Data System (ADS)

Adur, Rohan; Du, Chunhui; Cardellino, Jeremy; Scozzaro, Nicolas; Wolfe, Christopher S.; Wang, Hailong; Herman, Michael; Bhallamudi, Vidya P.; Pelekhov, Denis V.; Yang, Fengyuan; Hammel, P. Chris

2015-05-01

Understanding the behavior of spins coupling across interfaces in the study of spin current generation and transport is a fundamental challenge that is important for spintronics applications. The transfer of spin angular momentum from a ferromagnet into an adjacent normal material as a consequence of the precession of the magnetization of the ferromagnet is a process known as spin pumping. We find that, in certain circumstances, the insertion of an intervening normal metal can enhance spin pumping between an excited ferromagnetic magnetization and a normal metal layer as a consequence of improved spin conductance matching. We have studied this using inverse spin Hall effect and enhanced damping measurements. Scanned probe magnetic resonance techniques are a complementary tool in this context offering high resolution magnetic resonance imaging, localized spin excitation, and direct measurement of spin lifetimes or damping. Localized magnetic resonance studies of size-dependent spin dynamics in the absence of lithographic confinement in both ferromagnets and paramagnets reveal the close relationship between spin transport and spin lifetime at microscopic length scales. Finally, detection of ferromagnetic resonance of a ferromagnetic film using the photoluminescence of nitrogen vacancy spins in neighboring nanodiamonds demonstrates long-range spin transport between insulating materials, indicating the complexity and generality of spin transport in diverse, spatially separated, material systems.

Spin resonance and spin fluctuations in a quantum wire

NASA Astrophysics Data System (ADS)

Pokrovsky, V. L.

2017-02-01

This is a review of theoretical works on spin resonance in a quantum wire associated with the spin-orbit interaction. We demonstrate that the spin-orbit induced internal "magnetic field" leads to a narrow spin-flip resonance at low temperatures in the absence of an applied magnetic field. An applied dc magnetic field perpendicular to and small compared with the spin-orbit field enhances the resonance absorption by several orders of magnitude. The component of applied field parallel to the spin-orbit field separates the resonance frequencies of right and left movers and enables a linearly polarized ac electric field to produce a dynamic magnetization as well as electric and spin currents. We start with a simple model of noninteracting electrons and then consider the interaction that is not weak in 1d electron system. We show that electron spin resonance in the spin-orbit field persists in the Luttinger liquid. The interaction produces an additional singularity (cusp) in the spin-flip channel associated with the plasma oscillation. As it was shown earlier by Starykh and his coworkers, the interacting 1d electron system in the external field with sufficiently large parallel component becomes unstable with respect to the appearance of a spin-density wave. This instability suppresses the spin resonance. The observation of the electron spin resonance in a thin wires requires low temperature and high intensity of electromagnetic field in the terahertz diapason. The experiment satisfying these two requirements is possible but rather difficult. An alternative approach that does not require strong ac field is to study two-time correlations of the total spin of the wire with an optical method developed by Crooker and coworkers. We developed theory of such correlations. We prove that the correlation of the total spin component parallel to the internal magnetic field is dominant in systems with the developed spin-density waves but it vanishes in Luttinger liquid. Thus, the

High-order moments of spin-orbit energy in a multielectron configuration

NASA Astrophysics Data System (ADS)

Na, Xieyu; Poirier, M.

2016-07-01

In order to analyze the energy-level distribution in complex ions such as those found in warm dense plasmas, this paper provides values for high-order moments of the spin-orbit energy in a multielectron configuration. Using second-quantization results and standard angular algebra or fully analytical expressions, explicit values are given for moments up to 10th order for the spin-orbit energy. Two analytical methods are proposed, using the uncoupled or coupled orbital and spin angular momenta. The case of multiple open subshells is considered with the help of cumulants. The proposed expressions for spin-orbit energy moments are compared to numerical computations from Cowan's code and agree with them. The convergence of the Gram-Charlier expansion involving these spin-orbit moments is analyzed. While a spectrum with infinitely thin components cannot be adequately represented by such an expansion, a suitable convolution procedure ensures the convergence of the Gram-Charlier series provided high-order terms are accounted for. A corrected analytical formula for the third-order moment involving both spin-orbit and electron-electron interactions turns out to be in fair agreement with Cowan's numerical computations.

Self-current induced spin-orbit torque in FeMn/Pt multilayers

NASA Astrophysics Data System (ADS)

Xu, Yanjun; Yang, Yumeng; Yao, Kui; Xu, Baoxi; Wu, Yihong

2016-05-01

Extensive efforts have been devoted to the study of spin-orbit torque in ferromagnetic metal/heavy metal bilayers and exploitation of it for magnetization switching using an in-plane current. As the spin-orbit torque is inversely proportional to the thickness of the ferromagnetic layer, sizable effect has only been realized in bilayers with an ultrathin ferromagnetic layer. Here we demonstrate that, by stacking ultrathin Pt and FeMn alternately, both ferromagnetic properties and current induced spin-orbit torque can be achieved in FeMn/Pt multilayers without any constraint on its total thickness. The critical behavior of these multilayers follows closely three-dimensional Heisenberg model with a finite Curie temperature distribution. The spin torque effective field is about 4 times larger than that of NiFe/Pt bilayer with a same equivalent NiFe thickness. The self-current generated spin torque is able to switch the magnetization reversibly without the need for an external field or a thick heavy metal layer. The removal of both thickness constraint and necessity of using an adjacent heavy metal layer opens new possibilities for exploiting spin-orbit torque for practical applications.

Self-current induced spin-orbit torque in FeMn/Pt multilayers

PubMed Central

Xu, Yanjun; Yang, Yumeng; Yao, Kui; Xu, Baoxi; Wu, Yihong

2016-01-01

Extensive efforts have been devoted to the study of spin-orbit torque in ferromagnetic metal/heavy metal bilayers and exploitation of it for magnetization switching using an in-plane current. As the spin-orbit torque is inversely proportional to the thickness of the ferromagnetic layer, sizable effect has only been realized in bilayers with an ultrathin ferromagnetic layer. Here we demonstrate that, by stacking ultrathin Pt and FeMn alternately, both ferromagnetic properties and current induced spin-orbit torque can be achieved in FeMn/Pt multilayers without any constraint on its total thickness. The critical behavior of these multilayers follows closely three-dimensional Heisenberg model with a finite Curie temperature distribution. The spin torque effective field is about 4 times larger than that of NiFe/Pt bilayer with a same equivalent NiFe thickness. The self-current generated spin torque is able to switch the magnetization reversibly without the need for an external field or a thick heavy metal layer. The removal of both thickness constraint and necessity of using an adjacent heavy metal layer opens new possibilities for exploiting spin-orbit torque for practical applications. PMID:27185656

Spin-Ice Thin Films: Large-N Theory and Monte Carlo Simulations

NASA Astrophysics Data System (ADS)

Lantagne-Hurtubise, Étienne; Rau, Jeffrey G.; Gingras, Michel J. P.

2018-04-01

We explore the physics of highly frustrated magnets in confined geometries, focusing on the Coulomb phase of pyrochlore spin ices. As a specific example, we investigate thin films of nearest-neighbor spin ice, using a combination of analytic large-N techniques and Monte Carlo simulations. In the simplest film geometry, with surfaces perpendicular to the [001] crystallographic direction, we observe pinch points in the spin-spin correlations characteristic of a two-dimensional Coulomb phase. We then consider the consequences of crystal symmetry breaking on the surfaces of the film through the inclusion of orphan bonds. We find that when these bonds are ferromagnetic, the Coulomb phase is destroyed by the presence of fluctuating surface magnetic charges, leading to a classical Z2 spin liquid. Building on this understanding, we discuss other film geometries with surfaces perpendicular to the [110] or the [111] direction. We generically predict the appearance of surface magnetic charges and discuss their implications for the physics of such films, including the possibility of an unusual Z3 classical spin liquid. Finally, we comment on open questions and promising avenues for future research.

Spin-orbit coupling and the static polarizability of single-wall carbon nanotubes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Diniz, Ginetom S., E-mail: ginetom@gmail.com; Ulloa, Sergio E.

2014-07-14

We calculate the static longitudinal polarizability of single-wall carbon tubes in the long wavelength limit taking into account spin-orbit effects. We use a four-orbital orthogonal tight-binding formalism to describe the electronic states and the random phase approximation to calculate the dielectric function. We study the role of both the Rashba as well as the intrinsic spin-orbit interactions on the longitudinal dielectric response, i.e., when the probing electric field is parallel to the nanotube axis. The spin-orbit interaction modifies the nanotube electronic band dispersions, which may especially result in a small gap opening in otherwise metallic tubes. The bandgap size andmore » state features, the result of competition between Rashba and intrinsic spin-orbit interactions, result in drastic changes in the longitudinal static polarizability of the system. We discuss results for different nanotube types and the dependence on nanotube radius and spin-orbit couplings.« less

Noise in tunneling spin current across coupled quantum spin chains

NASA Astrophysics Data System (ADS)

Aftergood, Joshua; Takei, So

2018-01-01

We theoretically study the spin current and its dc noise generated between two spin-1 /2 spin chains weakly coupled at a single site in the presence of an over-population of spin excitations and a temperature elevation in one subsystem relative to the other, and we compare the corresponding transport quantities across two weakly coupled magnetic insulators hosting magnons. In the spin chain scenario, we find that applying a temperature bias exclusively leads to a vanishing spin current and a concomitant divergence in the spin Fano factor, defined as the spin current noise-to-signal ratio. This divergence is shown to have an exact analogy to the physics of electron scattering between fractional quantum Hall edge states and not to arise in the magnon scenario. We also reveal a suppression in the spin current noise that exclusively arises in the spin chain scenario due to the fermion nature of the spin-1/2 operators. We discuss how the spin Fano factor may be extracted experimentally via the inverse spin Hall effect used extensively in spintronics.

The open XXX spin chain in the SoV framework: scalar product of separate states

NASA Astrophysics Data System (ADS)

Kitanine, N.; Maillet, J. M.; Niccoli, G.; Terras, V.

2017-06-01

We consider the XXX open spin-1/2 chain with the most general non-diagonal boundary terms, that we solve by means of the quantum separation of variables (SoV) approach. We compute the scalar products of separate states, a class of states which notably contains all the eigenstates of the model. As usual for models solved by SoV, these scalar products can be expressed as some determinants with a non-trivial dependance in terms of the inhomogeneity parameters that have to be introduced for the method to be applicable. We show that these determinants can be transformed into alternative ones in which the homogeneous limit can easily be taken. These new representations can be considered as generalizations of the well-known determinant representation for the scalar products of the Bethe states of the periodic chain. In the particular case where a constraint is applied on the boundary parameters, such that the transfer matrix spectrum and eigenstates can be characterized in terms of polynomial solutions of a usual T-Q equation, the scalar product that we compute here corresponds to the scalar product between two off-shell Bethe-type states. If in addition one of the states is an eigenstate, the determinant representation can be simplified, hence leading in this boundary case to direct analogues of algebraic Bethe ansatz determinant representations of the scalar products for the periodic chain.

When measured spin polarization is not spin polarization

NASA Astrophysics Data System (ADS)

Dowben, P. A.; Wu, Ning; Binek, Christian

2011-05-01

Spin polarization is an unusually ambiguous scientific idiom and, as such, is rarely well defined. A given experimental methodology may allow one to quantify a spin polarization but only in its particular context. As one might expect, these ambiguities sometimes give rise to inappropriate interpretations when comparing the spin polarizations determined through different methods. The spin polarization of CrO2 and Cr2O3 illustrate some of the complications which hinders comparisons of spin polarization values.

Linear dynamics of classical spin as Mobius transformation

DOE PAGES

Galda, Alexey; Vinokur, Valerii М.

2017-04-26

Though the overwhelming majority of natural processes occur far from the equilibrium, general theoretical approaches to non-equilibrium phase transitions remain scarce. Recent breakthroughs introduced a description of open dissipative systems in terms of non-Hermitian quantum mechanics enabling the identification of a class of non-equilibrium phase transitions associated with the loss of combined parity (reflection) and time-reversal symmetries. Here we report that the time evolution of a single classical spin (e.g. monodomain ferromagnet) governed by the Landau-Lifshitz-Gilbert-Slonczewski equation in the absence of magnetic anisotropy terms is described by a Mobius transformation in complex stereographic coordinates. We identify the parity-time symmetry-breaking phasemore » transition occurring in spin-transfer torque-driven linear spin systems as a transition between hyperbolic and loxodromic classes of Mobius transformations, with the critical point of the transition corresponding to the parabolic transformation. However, this establishes the understanding of non-equilibrium phase transitions as topological transitions in configuration space.« less

Spin currents and magnon dynamics in insulating magnets

NASA Astrophysics Data System (ADS)

Nakata, Kouki; Simon, Pascal; Loss, Daniel

2017-03-01

Nambu-Goldstone theorem provides gapless modes to both relativistic and nonrelativistic systems. The Nambu-Goldstone bosons in insulating magnets are called magnons or spin-waves and play a key role in magnetization transport. We review here our past works on magnetization transport in insulating magnets and also add new insights, with a particular focus on magnon transport. We summarize in detail the magnon counterparts of electron transport, such as the Wiedemann-Franz law, the Onsager reciprocal relation between the Seebeck and Peltier coefficients, the Hall effects, the superconducting state, the Josephson effects, and the persistent quantized current in a ring to list a few. Focusing on the electromagnetism of moving magnons, i.e. magnetic dipoles, we theoretically propose a way to directly measure magnon currents. As a consequence of the Mermin-Wagner-Hohenberg theorem, spin transport is drastically altered in one-dimensional antiferromagnetic (AF) spin-1/2 chains; where the Néel order is destroyed by quantum fluctuations and a quasiparticle magnon-like picture breaks down. Instead, the low-energy collective excitations of the AF spin chain are described by a Tomonaga-Luttinger liquid (TLL) which provides the spin transport properties in such antiferromagnets some universal features at low enough temperature. Finally, we enumerate open issues and provide a platform to discuss the future directions of magnonics.

Combining the spin-separated exact two-component relativistic Hamiltonian with the equation-of-motion coupled-cluster method for the treatment of spin-orbit splittings of light and heavy elements.

PubMed

Cao, Zhanli; Li, Zhendong; Wang, Fan; Liu, Wenjian

2017-02-01

The spin-separated exact two-component (X2C) relativistic Hamiltonian [sf-X2C+so-DKHn, J. Chem. Phys., 2012, 137, 154114] is combined with the equation-of-motion coupled-cluster method with singles and doubles (EOM-CCSD) for the treatment of spin-orbit splittings of open-shell molecular systems. Scalar relativistic effects are treated to infinite order from the outset via the spin-free part of the X2C Hamiltonian (sf-X2C), whereas the spin-orbit couplings (SOC) are handled at the CC level via the first-order Douglas-Kroll-Hess (DKH) type of spin-orbit operator (so-DKH1). Since the exponential of single excitations, i.e., exp(T 1 ), introduces sufficient spin orbital relaxations, the inclusion of SOC at the CC level is essentially the same in accuracy as the inclusion of SOC from the outset in terms of the two-component spinors determined variationally by the sf-X2C+so-DKH1 Hamiltonian, but is computationally more efficient. Therefore, such an approach (denoted as sf-X2C-EOM-CCSD(SOC)) can achieve uniform accuracy for the spin-orbit splittings of both light and heavy elements. For light elements, the treatment of SOC can even be postponed until the EOM step (denoted as sf-X2C-EOM(SOC)-CCSD), so as to further reduce the computational cost. To reveal the efficacy of sf-X2C-EOM-CCSD(SOC) and sf-X2C-EOM(SOC)-CCSD, the spin-orbit splittings of the 2 Π states of monohydrides up to the sixth row of the periodic table are investigated. The results show that sf-X2C-EOM-CCSD(SOC) predicts very accurate results (within 5%) for elements up to the fifth row, whereas sf-X2C-EOM(SOC)-CCSD is useful only for light elements (up to the third row but with some exceptions). For comparison, the sf-X2C-S-TD-DFT-SOC approach [spin-adapted open-shell time-dependent density functional theory, Mol. Phys., 2013, 111, 3741] is applied to the same systems. The overall accuracy (1-10%) is satisfactory.

Spin Relaxation and Manipulation in Spin-orbit Qubits

NASA Astrophysics Data System (ADS)

Borhani, Massoud; Hu, Xuedong

2012-02-01

We derive a generalized form of the Electric Dipole Spin Resonance (EDSR) Hamiltonian in the presence of the spin-orbit interaction for single spins in an elliptic quantum dot (QD) subject to an arbitrary (in both direction and magnitude) applied magnetic field. We predict a nonlinear behavior of the Rabi frequency as a function of the magnetic field for sufficiently large Zeeman energies, and present a microscopic expression for the anisotropic electron g-tensor. Similarly, an EDSR Hamiltonian is devised for two spins confined in a double quantum dot (DQD). Finally, we calculate two-electron-spin relaxation rates due to phonon emission, for both in-plane and perpendicular magnetic fields. Our results have immediate applications to current EDSR experiments on nanowire QDs, g-factor optimization of confined carriers, and spin decay measurements in DQD spin-orbit qubits.

Nonlinear spin current generation in noncentrosymmetric spin-orbit coupled systems

NASA Astrophysics Data System (ADS)

Hamamoto, Keita; Ezawa, Motohiko; Kim, Kun Woo; Morimoto, Takahiro; Nagaosa, Naoto

2017-06-01

Spin current plays a central role in spintronics. In particular, finding more efficient ways to generate spin current has been an important issue and has been studied actively. For example, representative methods of spin-current generation include spin-polarized current injections from ferromagnetic metals, the spin Hall effect, and the spin battery. Here, we theoretically propose a mechanism of spin-current generation based on nonlinear phenomena. By using Boltzmann transport theory, we show that a simple application of the electric field E induces spin current proportional to E2 in noncentrosymmetric spin-orbit coupled systems. We demonstrate that the nonlinear spin current of the proposed mechanism is supported in the surface state of three-dimensional topological insulators and two-dimensional semiconductors with the Rashba and/or Dresselhaus interaction. In the latter case, the angular dependence of the nonlinear spin current can be manipulated by the direction of the electric field and by the ratio of the Rashba and Dresselhaus interactions. We find that the magnitude of the spin current largely exceeds those in the previous methods for a reasonable magnitude of the electric field. Furthermore, we show that application of ac electric fields (e.g., terahertz light) leads to the rectifying effect of the spin current, where dc spin current is generated. These findings will pave a route to manipulate the spin current in noncentrosymmetric crystals.

Microscopic studies of nonlocal spin dynamics and spin transport (invited)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adur, Rohan; Du, Chunhui; Cardellino, Jeremy

2015-05-07

Understanding the behavior of spins coupling across interfaces in the study of spin current generation and transport is a fundamental challenge that is important for spintronics applications. The transfer of spin angular momentum from a ferromagnet into an adjacent normal material as a consequence of the precession of the magnetization of the ferromagnet is a process known as spin pumping. We find that, in certain circumstances, the insertion of an intervening normal metal can enhance spin pumping between an excited ferromagnetic magnetization and a normal metal layer as a consequence of improved spin conductance matching. We have studied this usingmore » inverse spin Hall effect and enhanced damping measurements. Scanned probe magnetic resonance techniques are a complementary tool in this context offering high resolution magnetic resonance imaging, localized spin excitation, and direct measurement of spin lifetimes or damping. Localized magnetic resonance studies of size-dependent spin dynamics in the absence of lithographic confinement in both ferromagnets and paramagnets reveal the close relationship between spin transport and spin lifetime at microscopic length scales. Finally, detection of ferromagnetic resonance of a ferromagnetic film using the photoluminescence of nitrogen vacancy spins in neighboring nanodiamonds demonstrates long-range spin transport between insulating materials, indicating the complexity and generality of spin transport in diverse, spatially separated, material systems.« less

Electric control of emergent magnonic spin current and dynamic multiferroicity in magnetic insulators at finite temperatures

NASA Astrophysics Data System (ADS)

Wang, Xi-guang; Chotorlishvili, L.; Guo, Guang-hua; Berakdar, J.

2018-04-01

Conversion of thermal energy into magnonic spin currents and/or effective electric polarization promises new device functionalities. A versatile approach is presented here for generating and controlling open circuit magnonic spin currents and an effective multiferroicity at a uniform temperature with the aid of spatially inhomogeneous, external, static electric fields. This field applied to a ferromagnetic insulator with a Dzyaloshinskii-Moriya type coupling changes locally the magnon dispersion and modifies the density of thermally excited magnons in a region of the scale of the field inhomogeneity. The resulting gradient in the magnon density can be viewed as a gradient in the effective magnon temperature. This effective thermal gradient together with local magnon dispersion result in an open-circuit, electric field controlled magnonic spin current. In fact, for a moderate variation in the external electric field the predicted magnonic spin current is on the scale of the spin (Seebeck) current generated by a comparable external temperature gradient. Analytical methods supported by full-fledge numerics confirm that both, a finite temperature and an inhomogeneous electric field are necessary for this emergent non-equilibrium phenomena. The proposal can be integrated in magnonic and multiferroic circuits, for instance to convert heat into electrically controlled pure spin current using for example nanopatterning, without the need to generate large thermal gradients on the nanoscale.

Spin-phase-space-entropy production

NASA Astrophysics Data System (ADS)

Santos, Jader P.; Céleri, Lucas C.; Brito, Frederico; Landi, Gabriel T.; Paternostro, Mauro

2018-05-01

Quantifying the degree of irreversibility of an open system dynamics represents a problem of both fundamental and applied relevance. Even though a well-known framework exists for thermal baths, the results give diverging results in the limit of zero temperature and are also not readily extended to nonequilibrium reservoirs, such as dephasing baths. Aimed at filling this gap, in this paper we introduce a phase-space-entropy production framework for quantifying the irreversibility of spin systems undergoing Lindblad dynamics. The theory is based on the spin Husimi-Q function and its corresponding phase-space entropy, known as Wehrl entropy. Unlike the von Neumann entropy production rate, we show that in our framework, the Wehrl entropy production rate remains valid at any temperature and is also readily extended to arbitrary nonequilibrium baths. As an application, we discuss the irreversibility associated with the interaction of a two-level system with a single-photon pulse, a problem which cannot be treated using the conventional approach.

PREFACE: SPIN2010 - Preface for Conference Proceedings

NASA Astrophysics Data System (ADS)

Ströher, Hans; Rathmann, Frank

2011-03-01

SPIN2010, the 19th International Spin Physics Symposium, took place between 27 September and 2 October, 2010 on the campus of Forschungszentrum Jülich GmbH (FZJ) in Jülich, Germany. The scientific program of this Symposium included many topics related to spin phenomena in particle and nuclear physics as well as those in related fields. The International Spin Physics Symposium series has combined the High Energy Spin Symposia and the Nuclear Polarization Conferences since 2000. The most recent two Symposia were held in Virginia, USA (October 2008) and in Kyoto, Japan (October 2006). The meeting was opened by the chairman of the Board of Management of Jülich Forschungszentrum, Professor Achim Bachem, who cordially welcomed the participants from all over the world and gave a brief introduction to the Center and the research conducted there. The scientific program consisted of plenary sessions and parallel sessions and included the following topics: Fundamental symmetries and spin Spin structure of hadrons Spin physics beyond the Standard Model Spin in hadronic reactions Spin physics with photons and leptons Spin physics in nuclear reactions and nuclei Acceleration, storage, and polarimetry of polarized beams Polarized ion and lepton sources and targets Future facilities and experiments Medical and technological applications of spin physics The 6-day symposium had about 300 participants. In total 35 plenary talks (including 3 summaries of other spin physics meetings) and 163 contributed talks were given. The contents of many of these can be found in the present contributions, arranged according to the above topics and the time sequence. In addition, a public lecture on "Drall in der Quantenwelt", presented by H O Meyer (Bloomington) was received very well. Participants had the option to visit the Cooler synchrotron COSY at the Nuclear Physics Institute (IKP) and the 9.4 T MRT-PET hybrid scanner at the Institute of Neuroscience and Medicine (INM), two unique

Electronic spin transport in gate-tunable black phosphorus spin valves

NASA Astrophysics Data System (ADS)

Liu, Jiawei; Avsar, Ahmet; Tan, Jun You; Oezyilmaz, Barbaros

High charge mobility, the electric field effect and small spin-orbit coupling make semiconducting black phosphorus (BP) a promising material for spintronics device applications requiring long spin distance spin communication with all rectification and amplification actions. Towards this, we study the all electrical spin injection, transport and detection under non-local spin valve geometry in fully encapsulated ultra-thin BP devices. We observe spin relaxation times as high as 4 ns, with spin relaxation lengths exceeding 6 μm. These values are an order of magnitude higher than what have been measured in typical graphene spin valve devices. Moreover, the spin transport depends strongly on charge carrier concentration and can be manipulated in a spin transistor-like manner by controlling electric field. This behaviour persists even at room temperature. Finally, we will show that similar to its electrical and optical properties, spin transport property is also strongly anisotropic.

Spin-Mechatronics

NASA Astrophysics Data System (ADS)

Matsuo, Mamoru; Saitoh, Eiji; Maekawa, Sadamichi

2017-01-01

We investigate the interconversion phenomena between spin and mechanical angular momentum in moving objects. In particular, the recent results on spin manipulation and spin-current generation by mechanical motion are examined. In accelerating systems, spin-dependent gauge fields emerge, which enable the conversion from mechanical angular momentum into spins. Such a spin-mechanical effect is predicted by quantum theory in a non-inertial frame. Experiments which confirm the effect, i.e., the resonance frequency shift in nuclear magnetic resonance, the stray field measurement of rotating metals, and electric voltage generation in liquid metals, are discussed.

Bulk electron spin polarization generated by the spin Hall current

NASA Astrophysics Data System (ADS)

Korenev, V. L.

2006-07-01

It is shown that the spin Hall current generates a nonequilibrium spin polarization in the interior of crystals with reduced symmetry in a way that is drastically different from the previously well-known “equilibrium” polarization during the spin relaxation process. The steady state spin polarization value does not depend on the strength of spin-orbit interaction offering possibility to generate relatively high spin polarization even in the case of weak spin-orbit coupling.

LADEE Spin Test

NASA Image and Video Library

2017-12-08

During preparations for NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) observatory launch on Sept. 6, 2013, the spacecraft went through final preparations and close-outs, which included checking alignment after its cross-country shipment, checking the propulsion system for leaks, inspecting and repairing solar panels, and final electrical tests. After these activities were completed, more challenging portions of the launch preparations began: spin testing and fueling. To make sure that the spacecraft is perfectly balanced for flight, engineers mounted it onto a spin table and rotate it at high speeds, approximately one revolution per second. The team measured any offsets during the spinning, and then added small weights to the spacecraft to balance it. Once the spacecraft was balanced dry, the team loaded the propulsion tanks with fuel, oxidizer, and pressurant. The spin testing was performed again "wet," or with fuel, in order to see if the balance changed with the full fuel tanks. Engineers from NASA's Ames Research Center in Moffett Field, Calif., have now successfully completed launch preparation activities for LADEE, which has been encapsulated into the nose-cone of the Minotaur V rocket at NASA's Wallops Flight Facility in Virginia. LADEE is ready to launch when the window opens on Friday. Image Credit: NASA ----- What is LADEE? The Lunar Atmosphere and Dust Environment Explorer (LADEE) is designed to study the Moon's thin exosphere and the lunar dust environment. An "exosphere" is an atmosphere that is so thin and tenuous that molecules don't collide with each other. Studying the Moon's exosphere will help scientists understand other planetary bodies with exospheres too, like Mercury and some of Jupiter's bigger moons. The orbiter will determine the density, composition and temporal and spatial variability of the Moon's exosphere to help us understand where the species in the exosphere come from and the role of the solar wind, lunar surface

Enhanced spin Seebeck effect signal due to spin-momentum locked topological surface states

DOE PAGES

Jiang, Zilong; Chang, Cui -Zu; Masir, Massoud Ramezani; ...

2016-05-04

Spin-momentum locking in protected surface states enables efficient electrical detection of magnon decay at a magnetic-insulator/topological-insulator heterojunction. Here we demonstrate this property using the spin Seebeck effect (SSE), that is, measuring the transverse thermoelectric response to a temperature gradient across a thin film of yttrium iron garnet, an insulating ferrimagnet, and forming a heterojunction with (Bi xSb 1–x) 2Te 3, a topological insulator. The non-equilibrium magnon population established at the interface can decay in part by interactions of magnons with electrons near the Fermi energy of the topological insulator. When this decay channel is made active by tuning (Bi xSbmore » 1–x) 2Te 3 into a bulk insulator, a large electromotive force emerges in the direction perpendicular to the in-plane magnetization of yttrium iron garnet. Lastly, the enhanced, tunable SSE which occurs when the Fermi level lies in the bulk gap offers unique advantages over the usual SSE in metals and therefore opens up exciting possibilities in spintronics.« less

Resolving quanta of collective spin excitations in a millimeter-sized ferromagnet

PubMed Central

Lachance-Quirion, Dany; Tabuchi, Yutaka; Ishino, Seiichiro; Noguchi, Atsushi; Ishikawa, Toyofumi; Yamazaki, Rekishu; Nakamura, Yasunobu

2017-01-01

Combining different physical systems in hybrid quantum circuits opens up novel possibilities for quantum technologies. In quantum magnonics, quanta of collective excitation modes in a ferromagnet, called magnons, interact coherently with qubits to access quantum phenomena of magnonics. We use this architecture to probe the quanta of collective spin excitations in a millimeter-sized ferromagnetic crystal. More specifically, we resolve magnon number states through spectroscopic measurements of a superconducting qubit with the hybrid system in the strong dispersive regime. This enables us to detect a change in the magnetic moment of the ferromagnet equivalent to a single spin flipped among more than 1019 spins. Our demonstration highlights the strength of hybrid quantum systems to provide powerful tools for quantum sensing and quantum information processing. PMID:28695204

High-Frequency Dynamics Modulated by Collective Magnetization Reversal in Artificial Spin Ice

NASA Astrophysics Data System (ADS)

Jungfleisch, Matthias B.; Sklenar, Joseph; Ding, Junjia; Park, Jungsik; Pearson, John E.; Novosad, Valentine; Schiffer, Peter; Hoffmann, Axel

2017-12-01

Spin-torque ferromagnetic resonance arises in heavy metal-ferromagnet heterostructures when an alternating charge current is passed through the bilayer stack. The methodology to detect the resonance is based on the anisotropic magnetoresistance, which is the change in the electrical resistance due to different orientations of the magnetization. In connected networks of ferromagnetic nanowires, known as artificial spin ice, the magnetoresistance is rather complex owing to the underlying collective behavior of the geometrically frustrated magnetic domain structure. Here, we demonstrate spin-torque ferromagnetic resonance investigations in a square artificial spin-ice system and correlate our observations to magnetotransport measurements. The experimental findings are described using a simulation approach that highlights the importance of the correlated dynamics response of the magnetic system. Our results open the possibility of designing reconfigurable microwave oscillators and magnetoresistive devices based on connected networks of nanomagnets.

Atomic-Scale Engineering of Abrupt Interface for Direct Spin Contact of Ferromagnetic Semiconductor with Silicon

PubMed Central

Averyanov, Dmitry V.; Karateeva, Christina G.; Karateev, Igor A.; Tokmachev, Andrey M.; Vasiliev, Alexander L.; Zolotarev, Sergey I.; Likhachev, Igor A.; Storchak, Vyacheslav G.

2016-01-01

Control and manipulation of the spin of conduction electrons in industrial semiconductors such as silicon are suggested as an operating principle for a new generation of spintronic devices. Coherent injection of spin-polarized carriers into Si is a key to this novel technology. It is contingent on our ability to engineer flawless interfaces of Si with a spin injector to prevent spin-flip scattering. The unique properties of the ferromagnetic semiconductor EuO make it a prospective spin injector into silicon. Recent advances in the epitaxial integration of EuO with Si bring the manufacturing of a direct spin contact within reach. Here we employ transmission electron microscopy to study the interface EuO/Si with atomic-scale resolution. We report techniques for interface control on a submonolayer scale through surface reconstruction. Thus we prevent formation of alien phases and imperfections detrimental to spin injection. This development opens a new avenue for semiconductor spintronics. PMID:26957146

All-Electrical Spin Field Effect Transistor in van der Waals Heterostructures at Room Temperature

NASA Astrophysics Data System (ADS)

Dankert, André; Dash, Saroj

Spintronics aims to exploit the spin degree of freedom in solid state devices for data storage and information processing. Its fundamental concepts (creation, manipulation and detection of spin polarization) have been demonstrated in semiconductors and spin transistor structures using electrical and optical methods. However, an unsolved challenge is the realization of all-electrical methods to control the spin polarization in a transistor manner at ambient temperatures. Here we combine graphene and molybdenum disulfide (MoS2) in a van der Waals heterostructure to realize a spin field-effect transistor (spin-FET) at room temperature. These two-dimensional crystals offer a unique platform due to their contrasting properties, such as weak spin-orbit coupling (SOC) in graphene and strong SOC in MoS2. The gate-tuning of the Schottky barrier at the MoS2/graphene interface and MoS2 channel yields spins to interact with high SOC material and allows us to control the spin polarization and lifetime. This all-electrical spin-FET at room temperature is a substantial step in the field of spintronics and opens a new platform for testing a plethora of exotic physical phenomena, which can be key building blocks in future device architectures.

A spin-orbital-entangled quantum liquid on a honeycomb lattice

NASA Astrophysics Data System (ADS)

Kitagawa, K.; Takayama, T.; Matsumoto, Y.; Kato, A.; Takano, R.; Kishimoto, Y.; Bette, S.; Dinnebier, R.; Jackeli, G.; Takagi, H.

2018-02-01

The honeycomb lattice is one of the simplest lattice structures. Electrons and spins on this simple lattice, however, often form exotic phases with non-trivial excitations. Massless Dirac fermions can emerge out of itinerant electrons, as demonstrated experimentally in graphene, and a topological quantum spin liquid with exotic quasiparticles can be realized in spin-1/2 magnets, as proposed theoretically in the Kitaev model. The quantum spin liquid is a long-sought exotic state of matter, in which interacting spins remain quantum-disordered without spontaneous symmetry breaking. The Kitaev model describes one example of a quantum spin liquid, and can be solved exactly by introducing two types of Majorana fermion. Realizing a Kitaev model in the laboratory, however, remains a challenge in materials science. Mott insulators with a honeycomb lattice of spin-orbital-entangled pseudospin-1/2 moments have been proposed, including the 5d-electron systems α-Na2IrO3 (ref. 5) and α-Li2IrO3 (ref. 6) and the 4d-electron system α-RuCl3 (ref. 7). However, these candidates were found to magnetically order rather than form a liquid at sufficiently low temperatures, owing to non-Kitaev interactions. Here we report a quantum-liquid state of pseudospin-1/2 moments in the 5d-electron honeycomb compound H3LiIr2O6. This iridate does not display magnetic ordering down to 0.05 kelvin, despite an interaction energy of about 100 kelvin. We observe signatures of low-energy fermionic excitations that originate from a small number of spin defects in the nuclear-magnetic-resonance relaxation and the specific heat. We therefore conclude that H3LiIr2O6 is a quantum spin liquid. This result opens the door to finding exotic quasiparticles in a strongly spin-orbit-coupled 5d-electron transition-metal oxide.

Spin manipulation and relaxation in spin-orbit qubits

NASA Astrophysics Data System (ADS)

Borhani, Massoud; Hu, Xuedong

2012-03-01

We derive a generalized form of the electric dipole spin resonance (EDSR) Hamiltonian in the presence of the spin-orbit interaction for single spins in an elliptic quantum dot (QD) subject to an arbitrary (in both direction and magnitude) applied magnetic field. We predict a nonlinear behavior of the Rabi frequency as a function of the magnetic field for sufficiently large Zeeman energies, and present a microscopic expression for the anisotropic electron g tensor. Similarly, an EDSR Hamiltonian is devised for two spins confined in a double quantum dot (DQD), where coherent Rabi oscillations between the singlet and triplet states are induced by jittering the inter-dot distance at the resonance frequency. Finally, we calculate two-electron-spin relaxation rates due to phonon emission, for both in-plane and perpendicular magnetic fields. Our results have immediate applications to current EDSR experiments on nanowire QDs, g-factor optimization of confined carriers, and spin decay measurements in DQD spin-orbit qubits.

Second derivatives for approximate spin projection methods

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thompson, Lee M.; Hratchian, Hrant P., E-mail: hhratchian@ucmerced.edu

2015-02-07

The use of broken-symmetry electronic structure methods is required in order to obtain correct behavior of electronically strained open-shell systems, such as transition states, biradicals, and transition metals. This approach often has issues with spin contamination, which can lead to significant errors in predicted energies, geometries, and properties. Approximate projection schemes are able to correct for spin contamination and can often yield improved results. To fully make use of these methods and to carry out exploration of the potential energy surface, it is desirable to develop an efficient second energy derivative theory. In this paper, we formulate the analytical secondmore » derivatives for the Yamaguchi approximate projection scheme, building on recent work that has yielded an efficient implementation of the analytical first derivatives.« less

Wurtzite spin lasers

NASA Astrophysics Data System (ADS)

Faria Junior, Paulo E.; Xu, Gaofeng; Chen, Yang-Fang; Sipahi, Guilherme M.; Žutić, Igor

2017-03-01

Semiconductor lasers are strongly altered by adding spin-polarized carriers. Such spin lasers could overcome many limitations of their conventional (spin-unpolarized) counterparts. While the vast majority of experiments in spin lasers employed zinc-blende semiconductors, the room-temperature electrical manipulation was first demonstrated in wurtzite GaN-based lasers. However, the underlying theoretical description of wurtzite spin lasers is still missing. To address this situation, focusing on (In,Ga)N-based wurtzite quantum wells, we develop a theoretical framework in which the calculated microscopic spin-dependent gain is combined with a simple rate equation model. A small spin-orbit coupling in these wurtzites supports simultaneous spin polarizations of electrons and holes, providing unexplored opportunities to control spin lasers. For example, the gain asymmetry, as one of the key figures of merit related to spin amplification, can change the sign by simply increasing the carrier density. The lasing threshold reduction has a nonmonotonic dependence on electron-spin polarization, even for a nonvanishing hole spin polarization.

Squeezed spin states: Squeezing the spin uncertainty relations

NASA Technical Reports Server (NTRS)

Kitagawa, Masahiro; Ueda, Masahito

1993-01-01

The notion of squeezing in spin systems is clarified, and the principle for spin squeezing is shown. Two twisting schemes are proposed as building blocks for spin squeezing and are shown to reduce the standard quantum noise, s/2, of the coherent S-spin state down to the order of S(sup 1/3) and 1/2. Applications to partition noise suppression are briefly discussed.

Epitaxy of spin injectors and their application toward spin-polarized lasers

NASA Astrophysics Data System (ADS)

Holub, Michael A.

Spintronics is an emerging; multidisciplinary field which examines the role of electron and nuclear spin in solid-state physics. Recent experiments suggest that the spin degree of freedom may be exploited to enhance the functionality of conventional semi conductor devices. Such endeavors require methods for efficient spin injection; spin transport, and spin detection in semiconductor heterostructures. This dissertation investigates the molecular-beam epitaxial growth and properties of ferromagnetic materials for electrical spin injection. Spin-injecting contacts are incorporated into prototype spintronic devices and their performance is examined. Two classes of materials may be used for spin injection into semiconductors: dilute magnetic semiconductor and ferromagnetic metals. The low-temperature growth and properties of (Al)Gal4nAs and In(Ga)MnAs epilayers and nanostructures are investigated, and a technique for the self-organized growth of Mn-doped InAs quantum dots is developed. The epitaxial growth of (Fe,MnAs)/(Al)GaAs Schottky tunnel barriers for electron spin injection is also investigated. The spin-injection efficiency of these contacts is assessed using a spin-valve or spin-polarized light-emitting diode. Lateral MnAs/GaAs spin-valves where Schottky tunnel barriers enable all-electrical spin injection and detection are grown, fabricated, and characterized. The Rowell criteria confirm that tunneling is the dominant, transport mechanism for the Schottky tunnel contacts. A peak magnetoresistance of 3.6% at 10 K and 1.1% at 125 K are observed for a 0.5 pin channel length spin-valve. Measurements using non-local spin-valves and other control devices verify that spurious contributions from anisotropic magnetoresistance and local Hall effects are negligible. Spin-polarized lasers offer inherent polarization control, reduced chirp, and lower threshold currents and are expected to outperform their charge-based counterparts. Initial efforts to realize a spin

Spin-orbit coupling in ultracold Fermi gases of 173Yb atoms

NASA Astrophysics Data System (ADS)

Song, Bo; He, Chengdong; Hajiyev, Elnur; Ren, Zejian; Seo, Bojeong; Cai, Geyue; Amanov, Dovran; Zhang, Shanchao; Jo, Gyu-Boong

2017-04-01

Synthetic spin-orbit coupling (SOC) in cold atoms opens an intriguing new way to probe nontrivial topological orders beyond natural conditions. Here, we report the realization of the SOC physics both in a bulk system and in an optical lattice. First, we demonstrate two hallmarks induced from SOC in a bulk system, spin dephasing in the Rabi oscillation and asymmetric atomic distribution in the momentum space respectively. Then we describe the observation of non-trivial spin textures and the determination of the topological phase transition in a spin-dependent optical lattice dressed by the periodic Raman field. Furthermore, we discuss the quench dynamics between topological and trivial states by suddenly changing the band topology. Our work paves a new way to study non-equilibrium topological states in a controlled manner. Funded by Croucher Foundation and Research Grants Council (RGC) of Hong Kong (Project ECS26300014, GRF16300215, GRF16311516, and Croucher Innovation Grants).

Slotted rotatable target assembly and systematic error analysis for a search for long range spin dependent interactions from exotic vector boson exchange using neutron spin rotation

NASA Astrophysics Data System (ADS)

Haddock, C.; Crawford, B.; Fox, W.; Francis, I.; Holley, A.; Magers, S.; Sarsour, M.; Snow, W. M.; Vanderwerp, J.

2018-03-01

We discuss the design and construction of a novel target array of nonmagnetic test masses used in a neutron polarimetry measurement made in search for new possible exotic spin dependent neutron-atominteractions of Nature at sub-mm length scales. This target was designed to accept and efficiently transmit a transversely polarized slow neutron beam through a series of long open parallel slots bounded by flat rectangular plates. These openings possessed equal atom density gradients normal to the slots from the flat test masses with dimensions optimized to achieve maximum sensitivity to an exotic spin-dependent interaction from vector boson exchanges with ranges in the mm - μm regime. The parallel slots were oriented differently in four quadrants that can be rotated about the neutron beam axis in discrete 90°increments using a Geneva drive. The spin rotation signals from the 4 quadrants were measured using a segmented neutron ion chamber to suppress possible systematic errors from stray magnetic fields in the target region. We discuss the per-neutron sensitivity of the target to the exotic interaction, the design constraints, the potential sources of systematic errors which could be present in this design, and our estimate of the achievable sensitivity using this method.

Lattice spin models for non-Abelian chiral spin liquids

DOE PAGES

Lecheminant, P.; Tsvelik, A. M.

2017-04-26

Here, we suggest a class of two-dimensional lattice spin Hamiltonians describing non-Abelian SU(2) chiral spin liquids—spin analogs of fractional non-Abelian quantum Hall states—with gapped bulk and gapless chiral edge excitations described by the SU(2) n Wess-Zumino-Novikov-Witten conformal field theory. The models are constructed from an array of generalized spin-n/2 ladders with multi-spin-exchange interactions which are coupled by isolated spins. Such models allow a controllable analytic treatment starting from the one-dimensional limit and are characterized by a bulk gap and non-Abelian SU(2) n gapless edge excitations.

Effect of hyperfine-induced spin mixing on the defect-enabled spin blockade and spin filtering in GaNAs

NASA Astrophysics Data System (ADS)

Puttisong, Y.; Wang, X. J.; Buyanova, I. A.; Chen, W. M.

2013-03-01

The effect of hyperfine interaction (HFI) on the recently discovered room-temperature defect-enabled spin-filtering effect in GaNAs alloys is investigated both experimentally and theoretically based on a spin Hamiltonian analysis. We provide direct experimental evidence that the HFI between the electron and nuclear spin of the central Ga atom of the spin-filtering defect, namely, the Gai interstitials, causes strong mixing of the electron spin states of the defect, thereby degrading the efficiency of the spin-filtering effect. We also show that the HFI-induced spin mixing can be suppressed by an application of a longitudinal magnetic field such that the electronic Zeeman interaction overcomes the HFI, leading to well-defined electron spin states beneficial to the spin-filtering effect. The results provide a guideline for further optimization of the defect-engineered spin-filtering effect.

Pure spin current injection in hydrogenated graphene structures

NASA Astrophysics Data System (ADS)

Zapata-Peña, Reinaldo; Mendoza, Bernardo S.; Shkrebtii, Anatoli I.

2017-11-01

We present a theoretical study of spin-velocity injection (SVI) of a pure spin current (PSC) induced by linearly polarized light that impinges normally on the surface of two 50% hydrogenated noncentrosymmetric two-dimensional (2D) graphene structures. The first structure, labeled Up and also known as graphone, is hydrogenated only on one side, and the second, labeled Alt, is 25% hydrogenated at both sides. The hydrogenation opens an energy gap on both structures. The PSC formalism has been developed in the length gauge perturbing Hamiltonian, and includes, through the single-particle density matrix, the excited coherent superposition of the spin-split conduction bands inherent to the noncentrosymmetric nature of the structures considered in this work. We analyze two possibilities: in the first, the spin is fixed along a chosen direction, and the resulting SVI is calculated; in the second, we choose the SVI direction along the surface plane, and calculate the resulting spin orientation. This is done by changing the energy ℏ ω and polarization angle α of the incoming light. The results are calculated within a full electronic band structure scheme using the density functional theory (DFT) in the local density approximation (LDA). The maxima of the spin velocities are reached when ℏ ω =0.084 eV and α =35∘ for the Up structure, and ℏ ω =0.720 eV and α =150∘ for the Alt geometry. We find a speed of 668 and 645 km/s for the Up and the Alt structures, respectively, when the spin points perpendicularly to the surface. Also, the response is maximized by fixing the spin-velocity direction along a high-symmetry axis, obtaining a speed of 688 km/s with the spin pointing at 13∘ from the surface normal, for the Up, and 906 km/s and the spin pointing at 60∘ from the surface normal, for the Alt system. These speed values are orders of magnitude larger than those of bulk semiconductors, such as CdSe and GaAs, thus making the hydrogenated graphene structures

Spin transfer and spin pumping in disordered normal metal-antiferromagnetic insulator systems

NASA Astrophysics Data System (ADS)

Gulbrandsen, Sverre A.; Brataas, Arne

2018-02-01

We consider an antiferromagnetic insulator that is in contact with a metal. Spin accumulation in the metal can induce spin-transfer torques on the staggered field and on the magnetization in the antiferromagnet. These torques relate to spin pumping: the emission of spin currents into the metal by a precessing antiferromagnet. We investigate how the various components of the spin-transfer torque are affected by spin-independent disorder and spin-flip scattering in the metal. Spin-conserving disorder reduces the coupling between the spins in the antiferromagnet and the itinerant spins in the metal in a manner similar to Ohm's law. Spin-flip scattering leads to spin-memory loss with a reduced spin-transfer torque. We discuss the concept of a staggered spin current and argue that it is not a conserved quantity. Away from the interface, the staggered spin current varies around a 0 mean in an irregular manner. A network model explains the rapid decay of the staggered spin current.

High temperature spin dynamics in linear magnetic chains, molecular rings, and segments by nuclear magnetic resonance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adelnia, Fatemeh; Lascialfari, Alessandro; Dipartimento di Fisica, Università degli Studi di Pavia and INSTM, Pavia

2015-05-07

We present the room temperature proton nuclear magnetic resonance (NMR) nuclear spin-lattice relaxation rate (NSLR) results in two 1D spin chains: the Heisenberg antiferromagnetic (AFM) Eu(hfac){sub 3}NITEt and the magnetically frustrated Gd(hfac){sub 3}NITEt. The NSLR as a function of external magnetic field can be interpreted very well in terms of high temperature spin dynamics dominated by a long time persistence of the decay of the two-spin correlation function due to the conservation of the total spin value for isotropic Heisenberg chains. The high temperature spin dynamics are also investigated in Heisenberg AFM molecular rings. In both Cr{sub 8} closed ringmore » and in Cr{sub 7}Cd and Cr{sub 8}Zn open rings, i.e., model systems for a finite spin segment, an enhancement of the low frequency spectral density is found consistent with spin diffusion but the high cut-off frequency due to intermolecular anisotropic interactions prevents a detailed analysis of the spin diffusion regime.« less

Spin precession and spin Hall effect in monolayer graphene/Pt nanostructures

NASA Astrophysics Data System (ADS)

Savero Torres, W.; Sierra, J. F.; Benítez, L. A.; Bonell, F.; Costache, M. V.; Valenzuela, S. O.

2017-12-01

Spin Hall effects have surged as promising phenomena for spin logics operations without ferromagnets. However, the magnitude of the detected electric signals at room temperature in metallic systems has been so far underwhelming. Here, we demonstrate a two-order of magnitude enhancement of the signal in monolayer graphene/Pt devices when compared to their fully metallic counterparts. The enhancement stems in part from efficient spin injection and the large spin resistance of graphene but we also observe 100% spin absorption in Pt and find an unusually large effective spin Hall angle of up to 0.15. The large spin-to-charge conversion allows us to characterise spin precession in graphene under the presence of a magnetic field. Furthermore, by developing an analytical model based on the 1D diffusive spin-transport, we demonstrate that the effective spin-relaxation time in graphene can be accurately determined using the (inverse) spin Hall effect as a means of detection. This is a necessary step to gather full understanding of the consequences of spin absorption in spin Hall devices, which is known to suppress effective spin lifetimes in both metallic and graphene systems.

Evidence for a Field-Induced Quantum Spin Liquid in α -RuCl3

NASA Astrophysics Data System (ADS)

Baek, S.-H.; Do, S.-H.; Choi, K.-Y.; Kwon, Y. S.; Wolter, A. U. B.; Nishimoto, S.; van den Brink, Jeroen; Büchner, B.

2017-07-01

We report a 35Cl nuclear magnetic resonance study in the honeycomb lattice α -RuCl3 , a material that has been suggested to potentially realize a Kitaev quantum spin liquid (QSL) ground state. Our results provide direct evidence that α -RuCl3 exhibits a magnetic-field-induced QSL. For fields larger than ˜10 T , a spin gap opens up while resonance lines remain sharp, evidencing that spins are quantum disordered and locally fluctuating. The spin gap increases linearly with an increasing magnetic field, reaching ˜50 K at 15 T, and is nearly isotropic with respect to the field direction. The unusual rapid increase of the spin gap with increasing field and its isotropic nature are incompatible with conventional magnetic ordering and, in particular, exclude that the ground state is a fully polarized ferromagnet. The presence of such a field-induced gapped QSL phase has indeed been predicted in the Kitaev model.

Penrose limits and spin chains in the GJV/CS-SYM duality

NASA Astrophysics Data System (ADS)

Araujo, Thiago; Itsios, Georgios; Nastase, Horatiu; Colgáin, Eoin Ó.

2017-12-01

We examine Penrose limits of the duality proposed by Guarino, Jafferis and Varela between a type IIA massive background of the type of a warped, squashed AdS 4 × S 6, and a 2+1 dimensional IR fixed point of N=8 super Yang-Mills deformed by Chern-Simons terms to N=2 supersymmetry. One type of Penrose limit for closed strings corresponds to a large charge closed spin chain, and another, for open strings on giant graviton D-branes, corresponds to an open spin chain on sub-determinant operators. For the first limit, we find that like in the ABJM case, there are functions f a ( λ) that interpolate between the perturbative and nonperturbative (string) regions for the magnon energy. For the second, we are unable to match the gravity result with the expected field theory result, making this model more interesting than ones with more supersymmetry.

Ordered alternating binary polymer nanodroplet array by sequential spin dewetting.

PubMed

Bhandaru, Nandini; Das, Anuja; Salunke, Namrata; Mukherjee, Rabibrata

2014-12-10

We report a facile technique for fabricating an ordered array of nearly equal-sized mesoscale polymer droplets of two constituent polymers (polystyrene, PS and poly(methyl methacrylate), PMMA) arranged in an alternating manner on a topographically patterned substrate. The self-organized array of binary polymers is realized by sequential spin dewetting. First, a dilute solution of PMMA is spin-dewetted on a patterned substrate, resulting in an array of isolated PMMA droplets arranged along the substrate grooves due to self-organization during spin coating itself. The sample is then silanized with octadecyltrichlorosilane (OTS), and subsequently, a dilute solution of PS is spin-coated on to it, which also undergoes spin dewetting. The spin-dewetted PS drops having a size nearly equal to the pre-existing PMMA droplets position themselves between two adjacent PMMA drops under appropriate conditions, forming an alternating binary polymer droplet array. The alternating array formation takes place for a narrow range of solution concentration for both the polymers and depends on the geometry of the substrate. The size of the droplets depends on the extent of confinement, and droplets as small as 100 nm can be obtained by this method, on a suitable template. The findings open up the possibility of creating novel surfaces having ordered multimaterial domains with a potential multifunctional capability.

Spin-Selective Transmission and Devisable Chirality in Two-Layer Metasurfaces.

PubMed

Li, Zhancheng; Liu, Wenwei; Cheng, Hua; Chen, Shuqi; Tian, Jianguo

2017-08-15

Chirality is a nearly ubiquitous natural phenomenon. Its minute presence in most naturally occurring materials makes it incredibly difficult to detect. Recent advances in metasurfaces indicate that they exhibit devisable chirality in novel forms; this finding offers an effective opening for studying chirality and its features in such nanostructures. These metasurfaces display vast possibilities for highly sensitive chirality discrimination in biological and chemical systems. Here, we show that two-layer metasurfaces based on twisted nanorods can generate giant spin-selective transmission and support engineered chirality in the near-infrared region. Two designed metasurfaces with opposite spin-selective transmission are proposed for treatment as enantiomers and can be used widely for spin selection and enhanced chiral sensing. Specifically, we demonstrate that the chirality in these proposed metasurfaces can be adjusted effectively by simply changing the orientation angle between the twisted nanorods. Our results offer simple and straightforward rules for chirality engineering in metasurfaces and suggest intriguing possibilities for the applications of such metasurfaces in spin optics and chiral sensing.

Valley photonic crystals for control of spin and topology.

PubMed

Dong, Jian-Wen; Chen, Xiao-Dong; Zhu, Hanyu; Wang, Yuan; Zhang, Xiang

2017-03-01

Photonic crystals offer unprecedented opportunity for light manipulation and applications in optical communication and sensing. Exploration of topology in photonic crystals and metamaterials with non-zero gauge field has inspired a number of intriguing optical phenomena such as one-way transport and Weyl points. Recently, a new degree of freedom, valley, has been demonstrated in two-dimensional materials. Here, we propose a concept of valley photonic crystals with electromagnetic duality symmetry but broken inversion symmetry. We observe photonic valley Hall effect originating from valley-dependent spin-split bulk bands, even in topologically trivial photonic crystals. Valley-spin locking behaviour results in selective net spin flow inside bulk valley photonic crystals. We also show the independent control of valley and topology in a single system that has been long pursued in electronic systems, resulting in topologically-protected flat edge states. Valley photonic crystals not only offer a route towards the observation of non-trivial states, but also open the way for device applications in integrated photonics and information processing using spin-dependent transportation.

Current-limiting challenges for all-spin logic devices

PubMed Central

Su, Li; Zhang, Youguang; Klein, Jacques-Olivier; Zhang, Yue; Bournel, Arnaud; Fert, Albert; Zhao, Weisheng

2015-01-01

All-spin logic device (ASLD) has attracted increasing interests as one of the most promising post-CMOS device candidates, thanks to its low power, non-volatility and logic-in-memory structure. Here we investigate the key current-limiting factors and develop a physics-based model of ASLD through nano-magnet switching, the spin transport properties and the breakdown characteristic of channel. First, ASLD with perpendicular magnetic anisotropy (PMA) nano-magnet is proposed to reduce the critical current (Ic0). Most important, the spin transport efficiency can be enhanced by analyzing the device structure, dimension, contact resistance as well as material parameters. Furthermore, breakdown current density (JBR) of spin channel is studied for the upper current limitation. As a result, we can deduce current-limiting conditions and estimate energy dissipation. Based on the model, we demonstrate ASLD with different structures and channel materials (graphene and copper). Asymmetric structure is found to be the optimal option for current limitations. Copper channel outperforms graphene in term of energy but seriously suffers from breakdown current limit. By exploring the current limit and performance tradeoffs, the optimization of ASLD is also discussed. This benchmarking model of ASLD opens up new prospects for design and implementation of future spintronics applications. PMID:26449410

Tunable spin splitting and spin lifetime in polar WSTe monolayer

NASA Astrophysics Data System (ADS)

Adhib Ulil Absor, Moh.; Kotaka, Hiroki; Ishii, Fumiyuki; Saito, Mineo

2018-04-01

The established spin splitting with out-of-plane Zeeman spin polarizations in the monolayer (ML) of transition metal dichalcogenides (TMDs) is dictated by inversion symmetry breaking together with mirror symmetry in the surface plane. Here, by density functional theory calculations, we find that mirror symmetry breaking in the polar WSTe ML leads to large spin splitting exhibiting in-plane Rashba spin polarizations. We also find that the interplay between the out-of-plane Zeeman- and in-plane Rashba spin-polarized states sensitively affects the spin lifetime, which can be effectively controlled by in-plane strain. In addition, the tunability of spin splitting using an external electric field is also demonstrated. Our study clarifies that the use of in-plane strain and an external electric field is effective for tuning the spin splitting and spin lifetime of the polar WSTe ML; thus, it is useful for designing spintronic devices.

Nuclear spin noise in the central spin model

NASA Astrophysics Data System (ADS)

Fröhling, Nina; Anders, Frithjof B.; Glazov, Mikhail

2018-05-01

We study theoretically the fluctuations of the nuclear spins in quantum dots employing the central spin model which accounts for the hyperfine interaction of the nuclei with the electron spin. These fluctuations are calculated both with an analytical approach using homogeneous hyperfine couplings (box model) and with a numerical simulation using a distribution of hyperfine coupling constants. The approaches are in good agreement. The box model serves as a benchmark with low computational cost that explains the basic features of the nuclear spin noise well. We also demonstrate that the nuclear spin noise spectra comprise a two-peak structure centered at the nuclear Zeeman frequency in high magnetic fields with the shape of the spectrum controlled by the distribution of the hyperfine constants. This allows for direct access to this distribution function through nuclear spin noise spectroscopy.

High-Frequency Dynamics Modulated by Collective Magnetization Reversal in Artificial Spin Ice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jungfleisch, Matthias B.; Sklenar, Joseph; Ding, Junjia

Spin-torque ferromagnetic resonance arises in heavy metal-ferromagnet heterostructures when an alternating charge current is passed through the bilayer stack. The methodology to detect the resonance is based on the anisotropic magnetoresistance, which is the change in the electrical resistance due to different orientations of the magnetization. In connected networks of ferromagnetic nanowires, known as artificial spin ice, the magnetoresistance is rather complex owing to the underlying collective behavior of the geometrically frustrated magnetic domain structure. Here, we demonstrate spin-torque ferromagnetic resonance investigations in a square artificial spin-ice system and correlate our observations to magneto-transport measurements. The experimental findings are describedmore » using a simulation approach that highlights the importance of the correlated dynamics response of the magnetic system. Our results open the possibility of designing reconfigurable microwave oscillators and magnetoresistive devices based on connected networks of nanomagnets.« less

Competing Spin Liquids and Hidden Spin-Nematic Order in Spin Ice with Frustrated Transverse Exchange

NASA Astrophysics Data System (ADS)

Taillefumier, Mathieu; Benton, Owen; Yan, Han; Jaubert, L. D. C.; Shannon, Nic

2017-10-01

Frustration in magnetic interactions can give rise to disordered ground states with subtle and beautiful properties. The spin ices Ho2 Ti2 O7 and Dy2 Ti2 O7 exemplify this phenomenon, displaying a classical spin-liquid state, with fractionalized magnetic-monopole excitations. Recently, there has been great interest in closely related "quantum spin-ice" materials, following the realization that anisotropic exchange interactions could convert spin ice into a massively entangled, quantum spin liquid, where magnetic monopoles become the charges of an emergent quantum electrodynamics. Here we show that even the simplest model of a quantum spin ice, the XXZ model on the pyrochlore lattice, can realize a still-richer scenario. Using a combination of classical Monte Carlo simulation, semiclassical molecular-dynamics simulation, and analytic field theory, we explore the properties of this model for frustrated transverse exchange. We find not one, but three competing forms of spin liquid, as well as a phase with hidden, spin-nematic order. We explore the experimental signatures of each of these different states, making explicit predictions for inelastic neutron scattering. These results show an intriguing similarity to experiments on a range of pyrochlore oxides.

Spin transport study in a Rashba spin-orbit coupling system

PubMed Central

Mei, Fuhong; Zhang, Shan; Tang, Ning; Duan, Junxi; Xu, Fujun; Chen, Yonghai; Ge, Weikun; Shen, Bo

2014-01-01

One of the most important topics in spintronics is spin transport. In this work, spin transport properties of two-dimensional electron gas in AlxGa1-xN/GaN heterostructure were studied by helicity-dependent photocurrent measurements at room temperature. Spin-related photocurrent was detected under normal incidence of a circularly polarized laser with a Gaussian distribution. On one hand, spin polarized electrons excited by the laser generate a diffusive spin polarization current, which leads to a vortex charge current as a result of anomalous circular photogalvanic effect. On the other hand, photo-induced spin polarized electrons driven by a longitudinal electric field give rise to a transverse current via anomalous Hall Effect. Both of these effects originated from the Rashba spin-orbit coupling. By analyzing spin-related photocurrent varied with laser position, the contributions of the two effects were differentiated and the ratio of the spin diffusion coefficient to photo-induced anomalous spin Hall mobility Ds/μs = 0.08 V was extracted at room temperature. PMID:24504193

Separating inverse spin Hall voltage and spin rectification voltage by inverting spin injection direction

NASA Astrophysics Data System (ADS)

Zhang, Wenxu; Peng, Bin; Han, Fangbin; Wang, Qiuru; Soh, Wee Tee; Ong, Chong Kim; Zhang, Wanli

2016-03-01

We develop a method for universally resolving the important issue of separating the inverse spin Hall effect (ISHE) from the spin rectification effect (SRE) signal. This method is based on the consideration that the two effects depend on the spin injection direction: The ISHE is an odd function of the spin injection direction while the SRE is independent on it. Thus, the inversion of the spin injection direction changes the ISHE voltage signal, while the SRE voltage remains. It applies generally to analyzing the different voltage contributions without fitting them to special line shapes. This fast and simple method can be used in a wide frequency range and has the flexibility of sample preparation.

Quantum dynamics of nuclear spins and spin relaxation in organic semiconductors

NASA Astrophysics Data System (ADS)

Mkhitaryan, V. V.; Dobrovitski, V. V.

2017-06-01

We investigate the role of the nuclear-spin quantum dynamics in hyperfine-induced spin relaxation of hopping carriers in organic semiconductors. The fast-hopping regime, when the carrier spin does not rotate much between subsequent hops, is typical for organic semiconductors possessing long spin coherence times. We consider this regime and focus on a carrier random-walk diffusion in one dimension, where the effect of the nuclear-spin dynamics is expected to be the strongest. Exact numerical simulations of spin systems with up to 25 nuclear spins are performed using the Suzuki-Trotter decomposition of the evolution operator. Larger nuclear-spin systems are modeled utilizing the spin-coherent state P -representation approach developed earlier. We find that the nuclear-spin dynamics strongly influences the carrier spin relaxation at long times. If the random walk is restricted to a small area, it leads to the quenching of carrier spin polarization at a nonzero value at long times. If the random walk is unrestricted, the carrier spin polarization acquires a long-time tail, decaying as 1 /√{t } . Based on the numerical results, we devise a simple formula describing the effect quantitatively.

Manipulating topological states by imprinting non-collinear spin textures

DOE PAGES

Streubel, Robert; Han, Luyang; Im, Mi -Young; ...

2015-03-05

Topological magnetic states, such as chiral skyrmions, are of great scientific interest and show huge potential for novel spintronics applications, provided their topological charges can be fully controlled. So far skyrmionic textures have been observed in noncentrosymmetric crystalline materials with low symmetry and at low temperatures. We propose theoretically and demonstrate experimentally the design of spin textures with topological charge densities that can be tailored at ambient temperatures. Tuning the interlayer coupling in vertically stacked nanopatterned magnetic heterostructures, such as a model system of a Co/Pd multilayer coupled to Permalloy, the in-plane non-collinear spin texture of one layer can bemore » imprinted into the out-of-plane magnetised material. We observe distinct spin textures, e.g. vortices, magnetic swirls with tunable opening angle, donut states and skyrmion core configurations. We show that applying a small magnetic field, a reliable switching between topologically distinct textures can be achieved at remanence« less

Hysteresis, nucleation and growth phenomena in spin-crossover solids

NASA Astrophysics Data System (ADS)

Ridier, Karl; Molnár, Gábor; Salmon, Lionel; Nicolazzi, William; Bousseksou, Azzedine

2017-12-01

The observation and the study of first-order phase transitions in cooperative spin-crossover (SCO) solids exhibiting hysteresis behaviours are of particular interest and currently constitute a burgeoning area in the field of bistable molecular materials. The understanding and the control of the transition mechanisms (nucleation and growth processes) and their dynamics within the hysteresis region appear to be a general and appealing problem from a fundamental point of view and for technological applications as well. This review reports on the recent progresses and most important findings made on the spatiotemporal dynamics of the spin transition in SCO solids, particularly through the universal nucleation and growth process. Both thermally induced and light-induced spin transitions are discussed. We open up this review to the central question of the evolution of the transition mechanisms and dynamics in SCO nano-objects, which constitute promising systems to reach ultra-fast switching, and the experimental issues inherent to such studies at the micro- and nanometric scale.

Generalized Elliott-Yafet spin-relaxation time for arbitrary spin mixing

NASA Astrophysics Data System (ADS)

Vollmar, Svenja; Hilton, David J.; Schneider, Hans Christian

2017-08-01

We extend our recent result for the spin-relaxation time due to acoustic electron-phonon scattering in degenerate bands with spin mixing [New J. Phys. 18, 023012 (2016), 10.1088/1367-2630/18/2/023012] to include interactions with optical phonons, and present a numerical evaluation of the spin-relaxation time for intraband hole-phonon scattering in the heavy-hole (HH) bands of bulk GaAs. Comparing our computed spin-relaxation times to the conventional Elliott-Yafet result quantitatively demonstrates that the latter underestimates the spin-relaxation time because it does not correctly describe how electron-phonon interactions change the (vector) spin expectation value of the single-particle states. We show that the conventional Elliott-Yafet spin relaxation time is a special case of our result for weak spin mixing.

Magnetic domain walls as reconfigurable spin-wave nano-channels

NASA Astrophysics Data System (ADS)

Wagner, Kai

Research efforts to utilize spin waves as information carriers for wave based logic in micro- and nano-structured ferromagnetic materials have increased tremendously over the recent years. However, finding efficient means of tailoring and downscaling guided spin-wave propagation in two dimensions, while maintaining energy efficiency and reconfigurability, still remains a delicate challenge. Here we target these challenges by spin-wave transport inside nanometer-scaled potential wells formed along magnetic domain walls. For this, we investigate the magnetization dynamics of a rectangular-like element in a Landau state exhibiting a so called 180° Néel wall along its center. By microwave antennae the rf-excitation is constricted to one end of the domain wall and the spin-wave intensities are recorded by means of Brillouin-Light Scattering microscopy revealing channeled transport. Additional micromagnetic simulations with pulsed as well as cw-excitation are performed to yield further insight into this class of modes. We find several spin-wave modes quantized along the width of the domain wall yet with well defined wave vectors along the wall, exhibiting positive dispersion. In a final step, we demonstrate the flexibility of these spin-wave nano-channels based on domain walls. In contrast to wave guides realised by fixed geometries, domain walls can be easily manipulated. Here we utilize small external fields to control its position with nanometer precision over a micrometer range, while still enabling transport. Domain walls thus, open the perspective for reprogrammable and yet non-volatile spin-wave waveguides of nanometer width. Financial support by the Deutsche Forschungsgemeinschaft within project SCHU2922/1-1 is gratefully acknowledged.

Suppression of the impurity-induced local magnetism by the opening of a spin pseudogap in Ni-doped Sr2CuO3

NASA Astrophysics Data System (ADS)

Utz, Yannic; Hammerath, Franziska; Nishimoto, Satoshi; Hess, Christian; Beesetty, Neela Sekhar; Saint-Martin, Romuald; Revcolevschi, Alexandre; Büchner, Bernd; Grafe, Hans-Joachim

2015-08-01

The S =1 /2 antiferromagnetic Heisenberg spin chain compound Sr2CuO3 doped with 1 % and 2 % of Ni impurities has been studied by means of 63Cu nuclear magnetic resonance. A strong decrease of the spin-lattice relaxation rate T1-1 at low temperatures points toward a spin gap, while a stretching exponent λ <1 and a frequency dependence of T1-1 indicate that this spin gap varies spatially and should rather be characterized as a spin pseudogap. The magnitude of the spin pseudogap scales with doping level. Our results therefore evidence the finite-size character of this phenomenon. Moreover, an unusual narrowing of the low-temperature NMR lines reveals the suppression of the impurity-induced staggered paramagnetic response with increasing doping level.

Cross-correlation spin noise spectroscopy of heterogeneous interacting spin systems

DOE PAGES

Roy, Dibyendu; Yang, Luyi; Crooker, Scott A.; ...

2015-04-30

Interacting multi-component spin systems are ubiquitous in nature and in the laboratory. As such, investigations of inter-species spin interactions are of vital importance. Traditionally, they are studied by experimental methods that are necessarily perturbative: e.g., by intentionally polarizing or depolarizing one spin species while detecting the response of the other(s). Here, we describe and demonstrate an alternative approach based on multi-probe spin noise spectroscopy, which can reveal inter-species spin interactions - under conditions of strict thermal equilibrium - by detecting and cross-correlating the stochastic fluctuation signals exhibited by each of the constituent spin species. Specifically, we consider a two-component spinmore » ensemble that interacts via exchange coupling, and we determine cross-correlations between their intrinsic spin fluctuations. The model is experimentally confirmed using “two-color” optical spin noise spectroscopy on a mixture of interacting Rb and Cs vapors. Noise correlations directly reveal the presence of inter-species spin exchange, without ever perturbing the system away from thermal equilibrium. These non-invasive and noise-based techniques should be generally applicable to any heterogeneous spin system in which the fluctuations of the constituent components are detectable.« less

Spin-dependent dwell times of electron tunneling through double- and triple-barrier structures

NASA Astrophysics Data System (ADS)

Erić, Marko; Radovanović, Jelena; Milanović, Vitomir; Ikonić, Zoran; Indjin, Dragan

2008-04-01

We have analyzed the influence of Dresselhaus and Rashba spin-orbit couplings (caused by the bulk inversion asymmetry and the structural asymmetry, respectively) on electron tunneling through a double- and triple-barrier structures, with and without an externally applied electric field. The results indicate that the degree of structural asymmetry and external electric field can greatly affect the dwell times of electrons with opposite spin orientation. This opens up the possibilities of obtaining efficient spin separation in the time domain. The material system of choice is AlxGa1-xSb, and the presented model takes into account the position dependence of material parameters, as well as the effects of band nonparabolicity.

Probing Nuclear Spin Effects on Electronic Spin Coherence via EPR Measurements of Vanadium(IV) Complexes.

PubMed

Graham, Michael J; Krzyaniak, Matthew D; Wasielewski, Michael R; Freedman, Danna E

2017-07-17

Quantum information processing (QIP) has the potential to transform numerous fields from cryptography, to finance, to the simulation of quantum systems. A promising implementation of QIP employs unpaired electronic spins as qubits, the fundamental units of information. Though molecular electronic spins offer many advantages, including chemical tunability and facile addressability, the development of design principles for the synthesis of complexes that exhibit long qubit superposition lifetimes (also known as coherence times, or T 2 ) remains a challenge. As nuclear spins in the local qubit environment are a primary cause of shortened superposition lifetimes, we recently conducted a study which employed a modular spin-free ligand scaffold to place a spin-laden propyl moiety at a series of fixed distances from an S = 1 / 2 vanadium(IV) ion in a series of vanadyl complexes. We found that, within a radius of 4.0(4)-6.6(6) Å from the metal center, nuclei did not contribute to decoherence. To assess the generality of this important design principle and test its efficacy in a different coordination geometry, we synthesized and investigated three vanadium tris(dithiolene) complexes with the same ligand set employed in our previous study: K 2 [V(C 5 H 6 S 4 ) 3 ] (1), K 2 [V(C 7 H 6 S 6 ) 3 ] (2), and K 2 [V(C 9 H 6 S 8 ) 3 ] (3). We specifically interrogated solutions of these complexes in DMF-d 7 /toluene-d 8 with pulsed electron paramagnetic resonance spectroscopy and electron nuclear double resonance spectroscopy and found that the distance dependence present in the previously synthesized vanadyl complexes holds true in this series. We further examined the coherence properties of the series in a different solvent, MeCN-d 3 /toluene-d 8 , and found that an additional property, the charge density of the complex, also affects decoherence across the series. These results highlight a previously unknown design principle for augmenting T 2 and open new pathways for the

A Probabilistic Model of Spin and Spin Measurements

NASA Astrophysics Data System (ADS)

Niehaus, Arend

2016-01-01

Several theoretical publications on the Dirac equation published during the last decades have shown that, an interpretation is possible, which ascribes the origin of electron spin and magnetic moment to an autonomous circular motion of the point-like charged particle around a fixed centre. In more recent publications an extension of the original so called "Zitterbewegung Interpretation" of quantum mechanics was suggested, in which the spin results from an average of instantaneous spin vectors over a Zitterbewegung period. We argue that, the corresponding autonomous motion of the electron should, if it is real, determine non-relativistic spin measurements. Such a direct connection with the established formal quantum mechanical description of spin measurements, into which spin is introduced as a "non-classical" quantity has, to our knowledge, not been reported. In the present work we show that, under certain "model assumptions" concerning the proposed autonomous motion, results of spin measurements, including measurements of angular correlations in singlet systems, can indeed be correctly described using classical probabilities. The success of the model is evidence for the "reality" of the assumed autonomous motion. The resulting model violates the Bell—inequalities to the same extent as quantum mechanics.

SU (N ) spin-wave theory: Application to spin-orbital Mott insulators

NASA Astrophysics Data System (ADS)

Dong, Zhao-Yang; Wang, Wei; Li, Jian-Xin

2018-05-01

We present the application of the SU (N ) spin-wave theory to spin-orbital Mott insulators whose ground states exhibit magnetic orders. When taking both spin and orbital degrees of freedom into account rather than projecting Hilbert space onto the Kramers doublet, which is the lowest spin-orbital locked energy levels, the SU (N ) spin-wave theory should take the place of the SU (2 ) one due to the inevitable spin-orbital multipole exchange interactions. To implement the application, we introduce an efficient general local mean-field method, which involves all local fluctuations, and develop the SU (N ) linear spin-wave theory. Our approach is tested firstly by calculating the multipolar spin-wave spectra of the SU (4 ) antiferromagnetic model. Then, we apply it to spin-orbital Mott insulators. It is revealed that the Hund's coupling would influence the effectiveness of the isospin-1 /2 picture when the spin-orbital coupling is not large enough. We further carry out the SU (N ) spin-wave calculations of two materials, α -RuCl3 and Sr2IrO4 , and find that the magnonic and spin-orbital excitations are consistent with experiments.

Plasminogen activator inhibitor-1 4G/5G promoter polymorphism and coagulation factor VII Arg353-->Gln polymorphism in Korean patients with coronary artery disease.

PubMed Central

Song, J.; Yoon, Y. M.; Jung, H. J.; Hong, S. H.; Park, H.; Kim, J. Q.

2000-01-01

An increased risk for arterial thrombosis is associated with high plasma levels of coagulation and fibrinolytic factors such as PAI-1 and FVII. In this study, the 4G/5G polymorphism in the promoter of PAI-1 gene and Arg353-->Gln polymorphism in the FVII gene were analysed in 139 normal adults and 158 patients with coronary artery disease (CAD), and their association with plasma lipid traits was investigated. There were no significant differences in the allele frequencies of PAI-1 and FVII polymorphisms between control and patient groups. The allelic distributions of both polymorphisms in Koreans were similar to those in Japanese but significantly different from those in Caucasians. In the CAD group, the 4G homozygotes of PAI-1 polymorphism showed significantly higher levels of total (p=0.0250) and LDL cholesterol (p=0.0335) with individuals having other genotypes. However, FVII polymorphism showed no association with lipid levels. In conclusion, the 4G/5G PAI-1 promoter polymorphism and Arg353-->Gln FVII polymorphism are not major genetic risk factors for CAD in Koreans. However, 4G allele of PAI-1 polymorphism revealed to be associated with the levels of cholesterol, especially LDL cholesterol levels in CAD patients. PMID:10803689

Spin-Triplet Pairing Induced by Spin-Singlet Interactions in Noncentrosymmetric Superconductors

NASA Astrophysics Data System (ADS)

Matsuzaki, Tomoaki; Shimahara, Hiroshi

2017-02-01

In noncentrosymmetric superconductors, we examine the effect of the difference between the intraband and interband interactions, which becomes more important when the band splitting increases. We define the difference ΔVμ between their coupling constants, i.e., that between the intraband and interband hopping energies of intraband Cooper pairs. Here, the subscript μ of ΔVμ indicates that the interactions scatter the spin-singlet and spin-triplet pairs when μ = 0 and μ = 1,2,3, respectively. It is shown that the strong antisymmetric spin-orbit interaction reverses the target spin parity of the interaction: it converts the spin-singlet and spin-triplet interactions represented by ΔV0 and ΔVμ>0 into effective spin-triplet and spin-singlet pairing interactions, respectively. Hence, for example, triplet pairing can be induced solely by the singlet interaction ΔV0. We name the pairing symmetry of the system after that of the intraband Cooper pair wave function, but with an odd-parity phase factor excluded. The pairing symmetry must then be even, even for the triplet component, and the following results are obtained. When ΔVμ is small, the spin-triplet p-wave interactions induce spin-triplet s-wave and spin-triplet d-wave pairings in the regions where the repulsive singlet s-wave interaction is weak and strong, respectively. When ΔV0 is large, a repulsive interband spin-singlet interaction can stabilize spin-triplet pairing. When the Rashba interaction is adopted for the spin-orbit interaction, the spin-triplet pairing interactions mediated by transverse magnetic fluctuations do not contribute to triplet pairing.

Dynamical spin accumulation in large-spin magnetic molecules

NASA Astrophysics Data System (ADS)

Płomińska, Anna; Weymann, Ireneusz; Misiorny, Maciej

2018-01-01

The frequency-dependent transport through a nanodevice containing a large-spin magnetic molecule is studied theoretically in the Kondo regime. Specifically, the effect of magnetic anisotropy on dynamical spin accumulation is of primary interest. Such accumulation arises due to finite components of frequency-dependent conductance that are off diagonal in spin. Here, employing the Kubo formalism and the numerical renormalization group method, we demonstrate that the dynamical transport properties strongly depend on the relative orientation of spin moments in electrodes of the device, as well as on intrinsic parameters of the molecule. In particular, the effect of dynamical spin accumulation is found to be greatly affected by the type of magnetic anisotropy exhibited by the molecule, and it develops for frequencies corresponding to the Kondo temperature. For the parallel magnetic configuration of the device, the presence of dynamical spin accumulation is conditioned by the interplay of ferromagnetic-lead-induced exchange field and the Kondo correlations.

Hardy's argument and successive spin-s measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahanj, Ali

2010-07-15

We consider a hidden-variable theoretic description of successive measurements of noncommuting spin observables on an input spin-s state. In this scenario, the hidden-variable theory leads to a Hardy-type argument that quantum predictions violate it. We show that the maximum probability of success of Hardy's argument in quantum theory is ((1/2)){sup 4s}, which is more than in the spatial case.

Large spin current injection in nano-pillar-based lateral spin valve

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nomura, Tatsuya; Ohnishi, Kohei; Kimura, Takashi, E-mail: t-kimu@phys.kyushu-u.ac.jp

We have investigated the influence of the injection of a large pure spin current on a magnetization process of a non-locally located ferromagnetic dot in nano-pillar-based lateral spin valves. Here, we prepared two kinds of the nano-pillar-type lateral spin valve based on Py nanodots and CoFeAl nanodots fabricated on a Cu film. In the Py/Cu lateral spin valve, although any significant change of the magnetization process of the Py nanodot has not been observed at room temperature. The magnetization reversal process is found to be modified by injecting a large pure spin current at 77 K. Switching the magnetization bymore » the nonlocal spin injection has also been demonstrated at 77 K. In the CoFeAl/Cu lateral spin valve, a room temperature spin valve signal was strongly enhanced from the Py/Cu lateral spin valve because of the highly spin-polarized CoFeAl electrodes. The room temperature nonlocal switching has been demonstrated in the CoFeAl/Cu lateral spin valve.« less

Spin Hall effects

NASA Astrophysics Data System (ADS)

Sinova, Jairo; Valenzuela, Sergio O.; Wunderlich, J.; Back, C. H.; Jungwirth, T.

2015-10-01

Spin Hall effects are a collection of relativistic spin-orbit coupling phenomena in which electrical currents can generate transverse spin currents and vice versa. Despite being observed only a decade ago, these effects are already ubiquitous within spintronics, as standard spin-current generators and detectors. Here the theoretical and experimental results that have established this subfield of spintronics are reviewed. The focus is on the results that have converged to give us the current understanding of the phenomena, which has evolved from a qualitative to a more quantitative measurement of spin currents and their associated spin accumulation. Within the experimental framework, optical-, transport-, and magnetization-dynamics-based measurements are reviewed and linked to both phenomenological and microscopic theories of the effect. Within the theoretical framework, the basic mechanisms in both the extrinsic and intrinsic regimes are reviewed, which are linked to the mechanisms present in their closely related phenomenon in ferromagnets, the anomalous Hall effect. Also reviewed is the connection to the phenomenological treatment based on spin-diffusion equations applicable to certain regimes, as well as the spin-pumping theory of spin generation used in many measurements of the spin Hall angle. A further connection to the spin-current-generating spin Hall effect to the inverse spin galvanic effect is given, in which an electrical current induces a nonequilibrium spin polarization. This effect often accompanies the spin Hall effect since they share common microscopic origins. Both can exhibit the same symmetries when present in structures comprising ferromagnetic and nonmagnetic layers through their induced current-driven spin torques or induced voltages. Although a short chronological overview of the evolution of the spin Hall effect field and the resolution of some early controversies is given, the main body of this review is structured from a pedagogical

Spin-dependent thermoelectric effect and spin battery mechanism in triple quantum dots with Rashba spin-orbital interaction

NASA Astrophysics Data System (ADS)

Xu, Wei-Ping; Zhang, Yu-Ying; Wang, Qiang; Nie, Yi-Hang

2016-11-01

We have studied spin-dependent thermoelectric transport through parallel triple quantum dots with Rashba spin-orbital interaction (RSOI) embedded in an Aharonov-Bohm interferometer connected symmetrically to leads using nonequilibrium Green’s function method in the linear response regime. Under the appropriate configuration of magnetic flux phase and RSOI phase, the spin figure of merit can be enhanced and is even larger than the charge figure of merit. In particular, the charge and spin thermopowers as functions of both the magnetic flux phase and the RSOI phase present quadruple-peak structures in the contour graphs. For some specific configuration of the two phases, the device can provide a mechanism that converts heat into a spin voltage when the charge thermopower vanishes while the spin thermopower is not zero, which is useful in realizing the thermal spin battery and inducing a pure spin current in the device. Project supported by the National Natural Science Foundation of China (Grant Nos. 11274208 and 11447170).

Spin transport across antiferromagnets induced by the spin Seebeck effect

NASA Astrophysics Data System (ADS)

Cramer, Joel; Ritzmann, Ulrike; Dong, Bo-Wen; Jaiswal, Samridh; Qiu, Zhiyong; Saitoh, Eiji; Nowak, Ulrich; Kläui, Mathias

2018-04-01

For prospective spintronics devices based on the propagation of pure spin currents, antiferromagnets are an interesting class of materials that potentially entail a number of advantages as compared to ferromagnets. Here, we present a detailed theoretical study of magnonic spin current transport in ferromagnetic-antiferromagnetic multilayers by using atomistic spin dynamics simulations. The relevant length scales of magnonic spin transport in antiferromagnets are determined. We demonstrate the transfer of angular momentum from a ferromagnet into an antiferromagnet due to the excitation of only one magnon branch in the antiferromagnet. As an experimental system, we ascertain the transport across an antiferromagnet in Y3Fe5O12 |Ir20Mn80|Pt heterostructures. We determine the spin transport signals for spin currents generated in the Y3Fe5O12 by the spin Seebeck effect and compare to measurements of the spin Hall magnetoresistance in the heterostructure stack. By means of temperature-dependent and thickness-dependent measurements, we deduce conclusions on the spin transport mechanism across Ir20Mn80 and furthermore correlate it to its paramagnetic-antiferromagnetic phase transition.

Spin-orbit induced electronic spin separation in semiconductor nanostructures.

PubMed

Kohda, Makoto; Nakamura, Shuji; Nishihara, Yoshitaka; Kobayashi, Kensuke; Ono, Teruo; Ohe, Jun-ichiro; Tokura, Yasuhiro; Mineno, Taiki; Nitta, Junsaku

2012-01-01

The demonstration of quantized spin splitting by Stern and Gerlach is one of the most important experiments in modern physics. Their discovery was the precursor of recent developments in spin-based technologies. Although electrical spin separation of charged particles is fundamental in spintronics, in non-uniform magnetic fields it has been difficult to separate the spin states of charged particles due to the Lorentz force, as well as to the insufficient and uncontrollable field gradients. Here we demonstrate electronic spin separation in a semiconductor nanostructure. To avoid the Lorentz force, which is inevitably induced when an external magnetic field is applied, we utilized the effective non-uniform magnetic field which originates from the Rashba spin-orbit interaction in an InGaAs-based heterostructure. Using a Stern-Gerlach-inspired mechanism, together with a quantum point contact, we obtained field gradients of 10(8) T m(-1) resulting in a highly polarized spin current.

Robust and Efficient Spin Purification for Determinantal Configuration Interaction.

PubMed

Fales, B Scott; Hohenstein, Edward G; Levine, Benjamin G

2017-09-12

The limited precision of floating point arithmetic can lead to the qualitative and even catastrophic failure of quantum chemical algorithms, especially when high accuracy solutions are sought. For example, numerical errors accumulated while solving for determinantal configuration interaction wave functions via Davidson diagonalization may lead to spin contamination in the trial subspace. This spin contamination may cause the procedure to converge to roots with undesired ⟨Ŝ 2 ⟩, wasting computer time in the best case and leading to incorrect conclusions in the worst. In hopes of finding a suitable remedy, we investigate five purification schemes for ensuring that the eigenvectors have the desired ⟨Ŝ 2 ⟩. These schemes are based on projection, penalty, and iterative approaches. All of these schemes rely on a direct, graphics processing unit-accelerated algorithm for calculating the S 2 c matrix-vector product. We assess the computational cost and convergence behavior of these methods by application to several benchmark systems and find that the first-order spin penalty method is the optimal choice, though first-order and Löwdin projection approaches also provide fast convergence to the desired spin state. Finally, to demonstrate the utility of these approaches, we computed the lowest several excited states of an open-shell silver cluster (Ag 19 ) using the state-averaged complete active space self-consistent field method, where spin purification was required to ensure spin stability of the CI vector coefficients. Several low-lying states with significant multiply excited character are predicted, suggesting the value of a multireference approach for modeling plasmonic nanomaterials.

Universal scheme for finite-probability perfect transfer of arbitrary multispin states through spin chains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Man, Zhong-Xiao, E-mail: zxman@mail.qfnu.edu.cn; An, Nguyen Ba, E-mail: nban@iop.vast.ac.vn; Xia, Yun-Jie, E-mail: yjxia@mail.qfnu.edu.cn

In combination with the theories of open system and quantum recovering measurement, we propose a quantum state transfer scheme using spin chains by performing two sequential operations: a projective measurement on the spins of ‘environment’ followed by suitably designed quantum recovering measurements on the spins of interest. The scheme allows perfect transfer of arbitrary multispin states through multiple parallel spin chains with finite probability. Our scheme is universal in the sense that it is state-independent and applicable to any model possessing spin–spin interactions. We also present possible methods to implement the required measurements taking into account the current experimental technologies.more » As applications, we consider two typical models for which the probabilities of perfect state transfer are found to be reasonably high at optimally chosen moments during the time evolution. - Highlights: • Scheme that can achieve perfect quantum state transfer is devised. • The scheme is state-independent and applicable to any spin-interaction models. • The scheme allows perfect transfer of arbitrary multispin states. • Applications to two typical models are considered in detail.« less

Rotational Invariance of the 2d Spin - Spin Correlation Function

NASA Astrophysics Data System (ADS)

Pinson, Haru

2012-09-01

At the critical temperature in the 2d Ising model on the square lattice, we establish the rotational invariance of the spin-spin correlation function using the asymptotics of the spin-spin correlation function along special directions (McCoy and Wu in the two dimensional Ising model. Harvard University Press, Cambridge, 1973) and the finite difference Hirota equation for which the spin-spin correlation function is shown to satisfy (Perk in Phys Lett A 79:3-5, 1980; Perk in Proceedings of III international symposium on selected topics in statistical mechanics, Dubna, August 22-26, 1984, JINR, vol II, pp 138-151, 1985).

Spin-independent transparency of pure spin current at normal/ferromagnetic metal interface

NASA Astrophysics Data System (ADS)

Hao, Runrun; Zhong, Hai; Kang, Yun; Tian, Yufei; Yan, Shishen; Liu, Guolei; Han, Guangbing; Yu, Shuyun; Mei, Liangmo; Kang, Shishou

2018-03-01

The spin transparency at the normal/ferromagnetic metal (NM/FM) interface was studied in Pt/YIG/Cu/FM multilayers. The spin current generated by the spin Hall effect (SHE) in Pt flows into Cu/FM due to magnetic insulator YIG blocking charge current and transmitting spin current via the magnon current. Therefore, the nonlocal voltage induced by an inverse spin Hall effect (ISHE) in FM can be detected. With the magnetization of FM parallel or antiparallel to the spin polarization of pure spin currents ({{\\boldsymbol{σ }}}sc}), the spin-independent nonlocal voltage is induced. This indicates that the spin transparency at the Cu/FM interface is spin-independent, which demonstrates that the influence of spin-dependent electrochemical potential due to spin accumulation on the interfacial spin transparency is negligible. Furthermore, a larger spin Hall angle of Fe20Ni80 (Py) than that of Ni is obtained from the nonlocal voltage measurements. Project supported by the National Basic Research Program of China (Grant No. 2015CB921502), the National Natural Science Foundation of China (Grant Nos. 11474184 and 11627805), the 111 Project, China (Grant No. B13029), and the Fundamental Research Funds of Shandong University, China.

Spin-resolved inelastic electron scattering by spin waves in noncollinear magnets

NASA Astrophysics Data System (ADS)

dos Santos, Flaviano José; dos Santos Dias, Manuel; Guimarães, Filipe Souza Mendes; Bouaziz, Juba; Lounis, Samir

2018-01-01

Topological noncollinear magnetic phases of matter are at the heart of many proposals for future information nanotechnology, with novel device concepts based on ultrathin films and nanowires. Their operation requires understanding and control of the underlying dynamics, including excitations such as spin waves. So far, no experimental technique has attempted to probe large wave-vector spin waves in noncollinear low-dimensional systems. In this paper, we explain how inelastic electron scattering, being suitable for investigations of surfaces and thin films, can detect the collective spin-excitation spectra of noncollinear magnets. To reveal the particularities of spin waves in such noncollinear samples, we propose the usage of spin-polarized electron-energy-loss spectroscopy augmented with a spin analyzer. With the spin analyzer detecting the polarization of the scattered electrons, four spin-dependent scattering channels are defined, which allow us to filter and select specific spin-wave modes. We take as examples a topological nontrivial skyrmion lattice, a spin-spiral phase, and the conventional ferromagnet. Then we demonstrate that, counterintuitively and in contrast to the ferromagnetic case, even non-spin-flip processes can generate spin waves in noncollinear substrates. The measured dispersion and lifetime of the excitation modes permit us to fingerprint the magnetic nature of the substrate.

Dynamics of a localized spin excitation close to the spin-helix regime

NASA Astrophysics Data System (ADS)

Salis, Gian; Walser, Matthias; Altmann, Patrick; Reichl, Christian; Wegscheider, Werner

2014-03-01

The time evolution of a local spin excitation in a (001)-confined two-dimensional electron gas subjected to Rashba and Dresselhaus spin-orbit interactions of similar strength is investigated theoretically and compared with experimental data. Specifically, the consequences of a finite spatial extension of the initial spin polarization are studied for non-balanced Rashba and Dresselhaus terms and for finite cubic Dresselhaus spin-orbit interaction. We show that the initial out-of-plane spin polarization evolves into a helical spin pattern with a wave number that gradually approaches the value q0 of the persistent spin helix mode. In addition to an exponential decay of the spin polarization that is proportional to both the spin-orbit imbalance and the cubic Dresselhaus term, the finite width w of the spin excitation reduces the spin polarization by a factor that approaches exp(-q02w2 / 2) at longer times. This result bridges the gap between the formation of a long-lived helical spin mode and a spatially homogeneous spin decay described by the Dyakonov-Perel mechanism. This work is financially supported by NCCR QSIT.

Hard-spin mean-field theory: A systematic derivation and exact correlations in one dimension

PubMed

Kabakcioglu

2000-04-01

Hard-spin mean-field theory is an improved mean-field approach which has proven to give accurate results, especially for frustrated spin systems, with relatively little computational effort. In this work, the previous phenomenological derivation is supplanted by a systematic and generic derivation that opens the possibility for systematic improvements, especially for the calculation of long-range correlation functions. A first level of improvement suffices to recover the exact long-range values of the correlation functions in one dimension.

Nonreciprocal Transverse Photonic Spin and Magnetization-Induced Electromagnetic Spin-Orbit Coupling

PubMed Central

Levy, Miguel; Karki, Dolendra

2017-01-01

We present a formulation of electromagnetic spin-orbit coupling in magneto-optic media, and propose an alternative source of spin-orbit coupling to non-paraxial optics vortices. Our treatment puts forth a formulation of nonreciprocal transverse-spin angular-momentum-density shifts for evanescent waves in magneto-optic waveguide media. It shows that magnetization-induced electromagnetic spin-orbit coupling is possible, and that it leads to unequal spin to orbital angular momentum conversion in magneto-optic media evanescent waves in opposite propagation-directions. Generation of free-space helicoidal beams based on this conversion is shown to be spin-helicity- and magnetization-dependent. We show that transverse-spin to orbital angular momentum coupling into magneto-optic waveguide media engenders spin-helicity-dependent unidirectional propagation. This unidirectional effect produces different orbital angular momenta in opposite directions upon excitation-spin-helicity reversals. PMID:28059120

Enhanced spin pumping into superconductors provides evidence for superconducting pure spin currents

NASA Astrophysics Data System (ADS)

Jeon, Kun-Rok; Ciccarelli, Chiara; Ferguson, Andrew J.; Kurebayashi, Hidekazu; Cohen, Lesley F.; Montiel, Xavier; Eschrig, Matthias; Robinson, Jason W. A.; Blamire, Mark G.

2018-06-01

Unlike conventional spin-singlet Cooper pairs, spin-triplet pairs can carry spin1,2. Triplet supercurrents were discovered in Josephson junctions with metallic ferromagnet spacers, where spin transport can occur only within the ferromagnet and in conjunction with a charge current. Ferromagnetic resonance injects a pure spin current from a precessing ferromagnet into adjacent non-magnetic materials3,4. For spin-singlet pairing, the ferromagnetic resonance spin pumping efficiency decreases below the critical temperature (Tc) of a coupled superconductor5,6. Here we present ferromagnetic resonance experiments in which spin sink layers with strong spin-orbit coupling are added to the superconductor. Our results show that the induced spin currents, rather than being suppressed, are substantially larger in the superconducting state compared with the normal state; although further work is required to establish the details of the spin transport process, we show that this cannot be mediated by quasiparticles and is most likely a triplet pure spin supercurrent.

Bending strain engineering in quantum spin hall system for controlling spin currents

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Bing; Jin, Kyung-Hwan; Cui, Bin

Quantum spin Hall system can exhibit exotic spin transport phenomena, mediated by its topological edge states. The concept of bending strain engineering to tune the spin transport properties of a quantum spin Hall system is demonstrated. Here, we show that bending strain can be used to control the spin orientation of counter-propagating edge states of a quantum spin system to generate a non-zero spin current. This physics mechanism can be applied to effectively tune the spin current and pure spin current decoupled from charge current in a quantum spin Hall system by control of its bending curvature. Moreover, the curvedmore » quantum spin Hall system can be achieved by the concept of topological nanomechanical architecture in a controllable way, as demonstrated by the material example of Bi/Cl/Si(111) nanofilm. This concept of bending strain engineering of spins via topological nanomechanical architecture affords a promising route towards the realization of topological nano-mechanospintronics.« less

Bending strain engineering in quantum spin hall system for controlling spin currents

DOE PAGES

Huang, Bing; Jin, Kyung-Hwan; Cui, Bin; ...

2017-06-16

Quantum spin Hall system can exhibit exotic spin transport phenomena, mediated by its topological edge states. The concept of bending strain engineering to tune the spin transport properties of a quantum spin Hall system is demonstrated. Here, we show that bending strain can be used to control the spin orientation of counter-propagating edge states of a quantum spin system to generate a non-zero spin current. This physics mechanism can be applied to effectively tune the spin current and pure spin current decoupled from charge current in a quantum spin Hall system by control of its bending curvature. Moreover, the curvedmore » quantum spin Hall system can be achieved by the concept of topological nanomechanical architecture in a controllable way, as demonstrated by the material example of Bi/Cl/Si(111) nanofilm. This concept of bending strain engineering of spins via topological nanomechanical architecture affords a promising route towards the realization of topological nano-mechanospintronics.« less

Spin pumping and inverse spin Hall voltages from dynamical antiferromagnets

NASA Astrophysics Data System (ADS)

Johansen, Øyvind; Brataas, Arne

2017-06-01

Dynamical antiferromagnets can pump spins into adjacent conductors. The high antiferromagnetic resonance frequencies represent a challenge for experimental detection, but magnetic fields can reduce these resonance frequencies. We compute the ac and dc inverse spin Hall voltages resulting from dynamical spin excitations as a function of a magnetic field along the easy axis and the polarization of the driving ac magnetic field perpendicular to the easy axis. We consider the insulating antiferromagnets MnF2,FeF2, and NiO. Near the spin-flop transition, there is a significant enhancement of the dc spin pumping and inverse spin Hall voltage for the uniaxial antiferromagnets MnF2 and FeF2. In the uniaxial antiferromagnets it is also found that the ac spin pumping is independent of the external magnetic field when the driving field has the optimal circular polarization. In the biaxial NiO, the voltages are much weaker, and there is no spin-flop enhancement of the dc component.

Continuous quantum measurement in spin environments

NASA Astrophysics Data System (ADS)

Xie, Dong; Wang, An Min

2015-08-01

We derive a stochastic master equation (SME) which describes the decoherence dynamics of a system in spin environments conditioned on the measurement record. Markovian and non-Markovian nature of environment can be revealed by a spectroscopy method based on weak continuous quantum measurement. On account of that correlated environments can lead to a non-local open system which exhibits strong non-Markovian effects although the local dynamics are Markovian, the spectroscopy method can be used to demonstrate that there is correlation between two environments.

Spin-lattice relaxation of individual solid-state spins

NASA Astrophysics Data System (ADS)

Norambuena, A.; Muñoz, E.; Dinani, H. T.; Jarmola, A.; Maletinsky, P.; Budker, D.; Maze, J. R.

2018-03-01

Understanding the effect of vibrations on the relaxation process of individual spins is crucial for implementing nanosystems for quantum information and quantum metrology applications. In this work, we present a theoretical microscopic model to describe the spin-lattice relaxation of individual electronic spins associated to negatively charged nitrogen-vacancy centers in diamond, although our results can be extended to other spin-boson systems. Starting from a general spin-lattice interaction Hamiltonian, we provide a detailed description and solution of the quantum master equation of an electronic spin-one system coupled to a phononic bath in thermal equilibrium. Special attention is given to the dynamics of one-phonon processes below 1 K where our results agree with recent experimental findings and analytically describe the temperature and magnetic-field scaling. At higher temperatures, linear and second-order terms in the interaction Hamiltonian are considered and the temperature scaling is discussed for acoustic and quasilocalized phonons when appropriate. Our results, in addition to confirming a T5 temperature dependence of the longitudinal relaxation rate at higher temperatures, in agreement with experimental observations, provide a theoretical background for modeling the spin-lattice relaxation at a wide range of temperatures where different temperature scalings might be expected.

Relaxation-optimized transfer of spin order in Ising spin chains

NASA Astrophysics Data System (ADS)

Stefanatos, Dionisis; Glaser, Steffen J.; Khaneja, Navin

2005-12-01

In this paper, we present relaxation optimized methods for the transfer of bilinear spin correlations along Ising spin chains. These relaxation optimized methods can be used as a building block for the transfer of polarization between distant spins on a spin chain, a problem that is ubiquitous in multidimensional nuclear magnetic resonance spectroscopy of proteins. Compared to standard techniques, significant reduction in relaxation losses is achieved by these optimized methods when transverse relaxation rates are much larger than the longitudinal relaxation rates and comparable to couplings between spins. We derive an upper bound on the efficiency of the transfer of the spin order along a chain of spins in the presence of relaxation and show that this bound can be approached by the relaxation optimized pulse sequences presented in the paper.

Spin Currents and Ferromagnetic Resonance in Magnetic Thin Films

NASA Astrophysics Data System (ADS)

Ellsworth, David

Spin currents represent a new and exciting phenomenon. There is both a wealth of new physics to be discovered and understood, and many appealing devices which may result from this area of research. To fully realize the potential of this discipline it is necessary to develop new methods for realizing spin currents and explore new materials which may be suitable for spin current applications. Spin currents are an inherently dynamic phenomenon involving the transfer of angular momentum within and between different thin films. In order to understand and optimize such devices the dynamics of magnetization must be determined. This dissertation reports on novel approaches for spin current generation utilizing the magnetic insulators yttrium iron garnet (YIG) and M-type barium hexagonal ferrite (BaM). First, the light-induced spin Seebeck effect is reported for the first time in YIG. Additionally, the first measurement of the spin Seebeck effect without an external magnetic field is demonstrated. To accomplish this the self-biased BaM thin films are utilized. Second, a new method for the generation of spin currents is presented: the photo-spin-voltaic effect. In this new phenomenon, a spin current may be generated by photons in a non-magnetic metal that is in close proximity to a magnetic insulator. On exposure to light, there occurs a light induced, spin-dependent excitation of electrons in a few platinum layers near the metal/magnetic insulator interface. This excitation gives rise to a pure spin current which flows in the metal. This new effect is explored in detail and extensive measurements are carried out to confirm the photonic origin of the photo-spin-voltaic effect and exclude competing effects. In addition to the spin current measurements, magnetization dynamics were probed in thin films using ferromagnetic resonance (FMR). In order to determine the optimal material configuration for magnetic recording write heads, FMR measurements were used to perform damping

Free-Spinning-Tunnel Tests of a 0.057-Scale Model of the Chance Vought XF7U-1 Airplane

NASA Technical Reports Server (NTRS)

Daughtridge, Lee T., Jr.

1948-01-01

An investigation of the spin and recovery characteristics of a 0.057-scale model of the Chance Vought XF7U-1 airplane has been conducted in the Langley 20-foot free-spinning tunnel. The effects of control settings and movements on the erect and inverted spin and recovery characteristics were determined, as were also the effects of extending the wing slats, of center-of-gravity movement, and-of variation in the mass distribution. The investigation also included wing-tip spin-recovery-parachute tests, pilot-escape tests, and rudder-control-force tests. The investigation indicated that the spin and recovery characteristics of the airplane will be satisfactory for all conditions. It was found that a single 4.24-foot (full-scale) parachute when opened alone from the outboard wing tip or two 8.77-foot (full-scale) parachutes when opened simultaneously, one from each wing tip, would effect satisfactory emergency recoveries (the drag coefficients of the parachutes, based on the surface area of the parachute, were 0.83 and 0.70 for the 4.24- and 8.77-foot parachutes, respectively). The towline length in both cases was 25 feet (full scale). Tests results showed that, if the pilot should have to leave the airplane during a spin, he should jump from the outboard side (left side in a right spin) of the cockpit. The rudder-control force necessary for recovery from a spin was found to be rather high but appeared to be within the upper limits of a pilot's capabilities.

Efficient micromagnetic modelling of spin-transfer torque and spin-orbit torque

NASA Astrophysics Data System (ADS)

Abert, Claas; Bruckner, Florian; Vogler, Christoph; Suess, Dieter

2018-05-01

While the spin-diffusion model is considered one of the most complete and accurate tools for the description of spin transport and spin torque, its solution in the context of dynamical micromagnetic simulations is numerically expensive. We propose a procedure to retrieve the free parameters of a simple macro-spin like spin-torque model through the spin-diffusion model. In case of spin-transfer torque the simplified model complies with the model of Slonczewski. A similar model can be established for the description of spin-orbit torque. In both cases the spin-diffusion model enables the retrieval of free model parameters from the geometry and the material parameters of the system. Since these parameters usually have to be determined phenomenologically through experiments, the proposed method combines the strength of the diffusion model to resolve material parameters and geometry with the high performance of simple torque models.

Moderate MAS enhances local (1)H spin exchange and spin diffusion.

PubMed

Roos, Matthias; Micke, Peter; Saalwächter, Kay; Hempel, Günter

2015-11-01

Proton NMR spin-diffusion experiments are often combined with magic-angle spinning (MAS) to achieve higher spectral resolution of solid samples. Here we show that local proton spin diffusion can indeed become faster at low (<10 kHz) spinning rates as compared to static conditions. Spin diffusion under static conditions can thus be slower than the often referred value of 0.8 nm(2)/ms, which was determined using slow MAS (Clauss et al., 1993). The enhancement of spin diffusion by slow MAS relies on the modulation of the orientation-dependent dipolar couplings during sample rotation and goes along with transient level crossings in combination with dipolar truncation. The experimental finding and its explanation is supported by density matrix simulations, and also emphasizes the sensitivity of spin diffusion to the local coupling topology. The amplification of spin diffusion by slow MAS cannot be explained by any model based on independent spin pairs; at least three spins have to be considered. Copyright © 2015 Elsevier Inc. All rights reserved.

Spin Rotation of Formalism for Spin Tracking

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luccio,A.

The problem of which coefficients are adequate to correctly represent the spin rotation in vector spin tracking for polarized proton and deuteron beams in synchrotrons is here re-examined in the light of recent discussions. The main aim of this note is to show where some previous erroneous results originated and how to code spin rotation in a tracking code. Some analysis of a recent experiment is presented that confirm the correctness of the assumptions.

Spin valves with spin-engineered domain-biasing scheme

NASA Astrophysics Data System (ADS)

Lu, Z. Q.; Pan, G.

2003-06-01

Synthetic spin-filter spin valves with spin-engineered biasing scheme "sub/Ta/NiFe/IrMn/NiFe/NOL/Cu1/CoFe/Cu2/CoFe/Ru/CoFe/IrMn/Ta" were developed. In the structure, the orthogonal magnetic configuration for biasing and pinning field was obtained by one-step magnetic annealing process by means of spin flop, which eliminated the need for two antiferromagnetic materials with distinctively different blocking temperatures and two-step magnetic annealing as in conventional exchange biasing scheme. The longitudinal domain biasing of spin valves was achieved by using interlayer coupling field through Cu1 spacer. By adjusting the thickness of the Cu1 layer, the interlayer coupling biasing field can provide domain stabilization and was sufficiently strong to constrain the magnetization in coherent rotation. This can prevent Barkhausen noises associated with magnetization reversal. We report here a proof of concept study of such a domain-biasing scheme, which has its important technological applications in nanoscale spin valve and magnetic tunneling junction read heads and other spintronic devices.

Lifting SU(2) spin networks to projected spin networks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dupuis, Maiete; Livine, Etera R.

2010-09-15

Projected spin network states are the canonical basis of quantum states of geometry for the recent EPRL-FK spinfoam models for quantum gravity introduced by Engle-Pereira-Rovelli-Livine and Freidel-Krasnov. They are functionals of both the Lorentz connection and the time-normal field. We analyze in detail the map from these projected spin networks to the standard SU(2) spin networks of loop quantum gravity. We show that this map is not one to one and that the corresponding ambiguity is parameterized by the Immirzi parameter. We conclude with a comparison of the scalar products between projected spin networks and SU(2) spin network states.

Conduction-band valley spin splitting in single-layer H-T l2O

NASA Astrophysics Data System (ADS)

Ma, Yandong; Kou, Liangzhi; Du, Aijun; Huang, Baibiao; Dai, Ying; Heine, Thomas

2018-02-01

Despite numerous studies, coupled spin and valley physics is currently limited to two-dimensional (2D) transition-metal dichalcogenides (TMDCs). Here, we predict an exceptional 2D valleytronic material associated with the spin-valley coupling phenomena beyond 2D TMDCs—single-layer (SL) H-T l2O . It displays large valley spin splitting (VSS), significantly larger than that of 2D TMDCs, and a finite band gap, which are both critically attractive for the integration of valleytronics and spintronics. More importantly, in sharp contrast to all the experimentally confirmed 2D valleytronic materials, where the strong valence-band VSS (0.15-0.46 eV) supports the spin-valley coupling, the VSS in SL H-T l2O is pronounced in its conduction band (0.61 eV), but negligibly small in its valence band (21 meV), thus opening a way for manipulating the coupled spin and valley physics. Moreover, SL H-T l2O possesses extremely high carrier mobility, as large as 9.8 ×103c m2V-1s-1 .

Two-Component Noncollinear Time-Dependent Spin Density Functional Theory for Excited State Calculations.

PubMed

Egidi, Franco; Sun, Shichao; Goings, Joshua J; Scalmani, Giovanni; Frisch, Michael J; Li, Xiaosong

2017-06-13

We present a linear response formalism for the description of the electronic excitations of a noncollinear reference defined via Kohn-Sham spin density functional methods. A set of auxiliary variables, defined using the density and noncollinear magnetization density vector, allows the generalization of spin density functional kernels commonly used in collinear DFT to noncollinear cases, including local density, GGA, meta-GGA and hybrid functionals. Working equations and derivations of functional second derivatives with respect to the noncollinear density, required in the linear response noncollinear TDDFT formalism, are presented in this work. This formalism takes all components of the spin magnetization into account independent of the type of reference state (open or closed shell). As a result, the method introduced here is able to afford a nonzero local xc torque on the spin magnetization while still satisfying the zero-torque theorem globally. The formalism is applied to a few test cases using the variational exact-two-component reference including spin-orbit coupling to illustrate the capabilities of the method.

The Scattering of Particles with Spin from Targets with Spin

ERIC Educational Resources Information Center

Stewart, Noel M.

1978-01-01

The density matrix is used to obtain an expression for the mean value of any spin operator in the scattering of particles with arbitrary spin. The example of spin-1/2-spin-1 scattering is developed and physical information obtained by establishing connections with the polarization tensor and Wolfenstein observables. (Author/GA)

Simulation Study on Understanding the Spin Transport in MgO Adsorbed Graphene Based Magnetic Tunnel Junction

NASA Astrophysics Data System (ADS)

Raturi, Ashish; Choudhary, Sudhanshu

2016-11-01

First principles calculations of spin-dependent electronic transport properties of magnetic tunnel junction (MTJ) consisting of MgO adsorbed graphene nanosheet sandwiched between two CrO2 half-metallic ferromagnetic (HMF) electrodes is reported. MgO adsorption on graphene opens bandgap in graphene nanosheet which makes it more suitable for use as a tunnel barrier in MTJs. It was found that MgO adsorption suppresses transmission probabilities for spin-down channel in case of parallel configuration (PC) and also suppresses transmission in antiparallel configuration (APC) for both spin-up and spin-down channel. Tunnel magneto-resistance (TMR) of 100% is obtained at all bias voltages in MgO adsorbed graphene-based MTJ which is higher than that reported in pristine graphene-based MTJ. HMF electrodes were found suitable to achieve perfect spin filtration effect and high TMR. I-V characteristics for both parallel and antiparallel magnetization states of junction are calculated. High TMR suggests its usefulness in spin valves and other spintronics-based applications.

Spin Transport in Nondegenerate Si with a Spin MOSFET Structure at Room Temperature

NASA Astrophysics Data System (ADS)

Sasaki, Tomoyuki; Ando, Yuichiro; Kameno, Makoto; Tahara, Takayuki; Koike, Hayato; Oikawa, Tohru; Suzuki, Toshio; Shiraishi, Masashi

2014-09-01

Spin transport in nondegenerate semiconductors is expected to pave the way to the creation of spin transistors, spin logic devices, and reconfigurable logic circuits, because room-temperature (RT) spin transport in Si has already been achieved. However, RT spin transport has been limited to degenerate Si, which makes it difficult to produce spin-based signals because a gate electric field cannot be used to manipulate such signals. Here, we report the experimental demonstration of spin transport in nondegenerate Si with a spin metal-oxide-semiconductor field-effect transistor (MOSFET) structure. We successfully observe the modulation of the Hanle-type spin-precession signals, which is a characteristic spin dynamics in nondegenerate semiconductors. We obtain long spin transport of more than 20 μm and spin rotation greater than 4π at RT. We also observe gate-induced modulation of spin-transport signals at RT. The modulation of the spin diffusion length as a function of a gate voltage is successfully observed, which we attribute to the Elliott-Yafet spin relaxation mechanism. These achievements are expected to lead to the creation of practical Si-based spin MOSFETs.

Anisotropic interactions of a single spin and dark-spin spectroscopy in diamond

NASA Astrophysics Data System (ADS)

Epstein, R. J.; Mendoza, F. M.; Kato, Y. K.; Awschalom, D. D.

2005-11-01

Experiments on single nitrogen-vacancy (N-V) centres in diamond, which include electron spin resonance, Rabi oscillations, single-shot spin readout and two-qubit operations with a nearby13C nuclear spin, show the potential of this spin system for solid-state quantum information processing. Moreover, N-V centre ensembles can have spin-coherence times exceeding 50 μs at room temperature. We have developed an angle-resolved magneto-photoluminescence microscope apparatus to investigate the anisotropic electron-spin interactions of single N-V centres at room temperature. We observe negative peaks in the photoluminescence as a function of both magnetic-field magnitude and angle that are explained by coherent spin precession and anisotropic relaxation at spin-level anti-crossings. In addition, precise field alignment unmasks the resonant coupling to neighbouring `dark' nitrogen spins, otherwise undetected by photoluminescence. These results demonstrate the capability of our spectroscopic technique for measuring small numbers of dark spins by means of a single bright spin under ambient conditions.