Showing 1–45 of 45 results for author: Gray, B

Physical Characterization of Moon Impactor 2025-010D

Authors: Tanner Campbell, Adam Battle, Bill Gray, Juan A. Sanchez, David Cantillo, Lucille LeCorre, Vishnu Reddy

Abstract: Renewed interest in lunar exploration is creating a growing population of poorly tracked cislunar objects, some of which will ultimately impact the Moon$^{1}$. The ultimate fate of rocket upper stages or failed mission payloads is often unknown and unplanned. Determining the origin and physical properties of such objects will become increasingly important as sustained lunar exploration places huma… ▽ More Renewed interest in lunar exploration is creating a growing population of poorly tracked cislunar objects, some of which will ultimately impact the Moon$^{1}$. The ultimate fate of rocket upper stages or failed mission payloads is often unknown and unplanned. Determining the origin and physical properties of such objects will become increasingly important as sustained lunar exploration places humans and infrastructure on the surface$^{2;3;4;5}$. Here we present a ground-based physical and dynamical characterization of 2025-010D, a Falcon 9 upper stage predicted to impact the lunar farside on 2026 August 05. Backward propagation of its orbit independently links the object to the ``Ghost Riders in the Sky'' launch, while visible and near-infrared spectroscopy distinguishes it from natural objects and reveals absorption bands consistent with spacecraft thermal control materials. Photometric lightcurves confirm its elongated shape and reveal an unexpected change of more than 8 s in its $\sim$7 min rotation period during observations. We predict an impact between Bell and Einstein craters at $\sim$2.4 km s$^{-1}$, producing a crater $\sim$40 m in diameter. Since its provenance is independently known, 2025-010D provides a benchmark for identifying and characterizing future cislunar objects of uncertain origin. △ Less

Submitted 31 July, 2026; originally announced August 2026.

Control of protein activity by photoinduced spin polarized charge reorganization

Authors: Shirsendu Ghosh, Koyel Banerjee-Ghosh, Dorit Levy, David Scheerer, Inbal Riven, Jieun Shin, Harry B. Gray, Ron Naaman, Gilad Haran

Abstract: Considerable electric fields are present within living cells, and the role of bioelectricity has been well established at the organismal level. Yet little is known about electric-field effects on protein function. Here we use phototriggered charge injection from a site-specifically attached ruthenium photosensitizer to directly demonstrate the effects of charge redistribution within a protein. We… ▽ More Considerable electric fields are present within living cells, and the role of bioelectricity has been well established at the organismal level. Yet little is known about electric-field effects on protein function. Here we use phototriggered charge injection from a site-specifically attached ruthenium photosensitizer to directly demonstrate the effects of charge redistribution within a protein. We find that binding of an antibody to phosphoglycerate kinase (PGK) is increased two folds under illumination. Remarkably, illumination is found to suppress the enzymatic activity of PGK by a factor as large as three. These responses are sensitive to the photosensitizer position on the protein. Surprisingly, left (but not right) circularly polarized light elicits these responses, indicating that the electrons involved in the observed dynamics are spin polarized, due to spin filtration by protein chiral structures. Our results directly establish the contribution of electrical polarization as an allosteric signal within proteins. Future experiments with phototriggered charge injection will allow delineation of charge rearrangement pathways within proteins and will further depict their effects on protein function. △ Less

Submitted 1 June, 2026; originally announced June 2026.

Journal ref: PNAS 119, 2022, e2204735119

Astrometric follow-up of near-Earth asteroid 2024 YR4 during a Torino scale level 3 alert

Authors: Marco Micheli, Maxime Devogèle, Larry Denneau, Eileen V. Ryan, William H. Ryan, Petr Pravec, Kamil Hornoch, Hana Kučáková, Petr Fatka, Melissa J. Brucker, Cassandra Lejoly, Nicholas Moskovitz, Mikael Granvik, Zuri Gray, Grigori Fedorets, Anlaug Amanda Djupvik, Carson Fuls, David Rankin, Kacper Wierzchoś, Bill Gray, Tim Lister, Richard J. Wainscoat, Robert Weryk, Olivier R. Hainaut, Federica Spoto , et al. (16 additional authors not shown)

Abstract: The discovery of 2024 YR4 presented the planetary defense community with the most significant impact threat in almost two decades, reaching level 3 on the Torino scale. The community, now mature and well-organized, responded with a global observational effort. Astrometric measurements, forming the basis for orbital refinement and impact prediction, were a central component of this response. In thi… ▽ More The discovery of 2024 YR4 presented the planetary defense community with the most significant impact threat in almost two decades, reaching level 3 on the Torino scale. The community, now mature and well-organized, responded with a global observational effort. Astrometric measurements, forming the basis for orbital refinement and impact prediction, were a central component of this response. In this paper, we present the astrometric data collected by the international community, from the time of discovery until the object became too faint for all existing observational assets, including JWST. We also discuss the coordination role played by the International Asteroid Warning Network, and the importance of publicly available image archives to enable precovery searches. △ Less

Submitted 6 February, 2026; originally announced February 2026.

Journal ref: J Astronaut Sci 73, 8 (2026)

FLASH: Faint Lenses from Associated Selection with Herschel

Authors: Tom J. L. C. Bakx, Bethany S. Gray, Joaquin González-Nuevo, Laura Bonavera, Aristeidis Amvrosiadis, Stephen Eales, Masato Hagimoto, Stephen Serjeant

Abstract: We report the ALMA Band 7 observations of 86 Herschel sources that likely contain gravitationally-lensed galaxies. These sources are selected with relatively faint 500 $μ$m flux densities between 15 to 85 mJy in an effort to characterize the effect of lensing across the entire million-source Herschel catalogue. These lensed candidates were identified by their close proximity to bright galaxies in… ▽ More We report the ALMA Band 7 observations of 86 Herschel sources that likely contain gravitationally-lensed galaxies. These sources are selected with relatively faint 500 $μ$m flux densities between 15 to 85 mJy in an effort to characterize the effect of lensing across the entire million-source Herschel catalogue. These lensed candidates were identified by their close proximity to bright galaxies in the near-infrared VISTA Kilo-Degree Infrared Galaxy Survey (VIKING) survey. Our high-resolution observations (0.15 arcsec) confirm 47 per cent of the initial candidates as gravitational lenses, while lensing cannot be excluded across the remaining sample. We find average lensing masses (log M/M$_{\odot}$ = 12.9 $\pm$ 0.5) in line with previous experiments, although direct observations might struggle to identify the most massive foreground lenses across the remaining 53 per cent of the sample, particularly for lenses with larger Einstein radii. Our observations confirm previous indications that more lenses exist at low flux densities than expected from strong galaxy-galaxy lensing models alone, where the excess is likely due to additional contributions of cluster lenses and weak lensing. If we apply our method across the total 660 sqr. deg. H-ATLAS field, it would allow us to robustly identify 3000 gravitational lenses across the 660 square degree Herschel ATLAS fields. △ Less

Submitted 28 November, 2023; originally announced November 2023.

Comments: Accepted for publication in MNRAS. Comments and discussion are welcome

Observation of Coherently Coupled Cation Spin Dynamics in an Insulating Ferrimagnetic Oxide

Authors: C. Klewe, P. Shafer, J. E. Shoup, C. Kons, Y. Pogoryelov, R. Knut, B. A. Gray, H. -M. Jeon, B. M. Howe, O. Karis, Y. Suzuki, E. Arenholz, D. A. Arena, S. Emori

Abstract: Many technologically useful magnetic oxides are ferrimagnetic insulators, which consist of chemically distinct cations. Here, we examine the spin dynamics of different magnetic cations in ferrimagnetic NiZnAl-ferrite (Ni$_{0.65}$Zn$_{0.35}$Al$_{0.8}$Fe$_{1.2}$O$_4$) under continuous microwave excitation. Specifically, we employ time-resolved x-ray ferromagnetic resonance to separately probe Fe… ▽ More Many technologically useful magnetic oxides are ferrimagnetic insulators, which consist of chemically distinct cations. Here, we examine the spin dynamics of different magnetic cations in ferrimagnetic NiZnAl-ferrite (Ni$_{0.65}$Zn$_{0.35}$Al$_{0.8}$Fe$_{1.2}$O$_4$) under continuous microwave excitation. Specifically, we employ time-resolved x-ray ferromagnetic resonance to separately probe Fe$^{2+/3+}$ and Ni$^{2+}$ cations on different sublattice sites. Our results show that the precessing cation moments retain a rigid, collinear configuration to within $\approx$2$^\circ$. Moreover, the effective spin relaxation is identical to within $<$10% for all magnetic cations in the ferrite. We thus validate the oft-assumed ``ferromagnetic-like'' dynamics in resonantly driven ferrimagnetic oxides, where the magnetic moments from different cations precess as a coherent, collective magnetization. △ Less

Submitted 6 February, 2023; originally announced February 2023.

Journal ref: Appl. Phys. Lett. 122, 132401 (2023)

Performance of the CMS High Granularity Calorimeter prototype to charged pion beams of 20$-$300 GeV/c

Authors: B. Acar, G. Adamov, C. Adloff, S. Afanasiev, N. Akchurin, B. Akgün, M. Alhusseini, J. Alison, J. P. Figueiredo de sa Sousa de Almeida, P. G. Dias de Almeida, A. Alpana, M. Alyari, I. Andreev, U. Aras, P. Aspell, I. O. Atakisi, O. Bach, A. Baden, G. Bakas, A. Bakshi, S. Banerjee, P. DeBarbaro, P. Bargassa, D. Barney, F. Beaudette , et al. (435 additional authors not shown)

Abstract: The upgrade of the CMS experiment for the high luminosity operation of the LHC comprises the replacement of the current endcap calorimeter by a high granularity sampling calorimeter (HGCAL). The electromagnetic section of the HGCAL is based on silicon sensors interspersed between lead and copper (or copper tungsten) absorbers. The hadronic section uses layers of stainless steel as an absorbing med… ▽ More The upgrade of the CMS experiment for the high luminosity operation of the LHC comprises the replacement of the current endcap calorimeter by a high granularity sampling calorimeter (HGCAL). The electromagnetic section of the HGCAL is based on silicon sensors interspersed between lead and copper (or copper tungsten) absorbers. The hadronic section uses layers of stainless steel as an absorbing medium and silicon sensors as an active medium in the regions of high radiation exposure, and scintillator tiles directly readout by silicon photomultipliers in the remaining regions. As part of the development of the detector and its readout electronic components, a section of a silicon-based HGCAL prototype detector along with a section of the CALICE AHCAL prototype was exposed to muons, electrons and charged pions in beam test experiments at the H2 beamline at the CERN SPS in October 2018. The AHCAL uses the same technology as foreseen for the HGCAL but with much finer longitudinal segmentation. The performance of the calorimeters in terms of energy response and resolution, longitudinal and transverse shower profiles is studied using negatively charged pions, and is compared to GEANT4 predictions. This is the first report summarizing results of hadronic showers measured by the HGCAL prototype using beam test data. △ Less

Submitted 27 May, 2023; v1 submitted 9 November, 2022; originally announced November 2022.

Comments: Accepted for publication by JINST

Response of a CMS HGCAL silicon-pad electromagnetic calorimeter prototype to 20-300 GeV positrons

Authors: B. Acar, G. Adamov, C. Adloff, S. Afanasiev, N. Akchurin, B. Akgün, F. Alam Khan, M. Alhusseini, J. Alison, A. Alpana, G. Altopp, M. Alyari, S. An, S. Anagul, I. Andreev, P. Aspell, I. O. Atakisi, O. Bach, A. Baden, G. Bakas, A. Bakshi, S. Bannerjee, P. Bargassa, D. Barney, F. Beaudette , et al. (364 additional authors not shown)

Abstract: The Compact Muon Solenoid Collaboration is designing a new high-granularity endcap calorimeter, HGCAL, to be installed later this decade. As part of this development work, a prototype system was built, with an electromagnetic section consisting of 14 double-sided structures, providing 28 sampling layers. Each sampling layer has an hexagonal module, where a multipad large-area silicon sensor is glu… ▽ More The Compact Muon Solenoid Collaboration is designing a new high-granularity endcap calorimeter, HGCAL, to be installed later this decade. As part of this development work, a prototype system was built, with an electromagnetic section consisting of 14 double-sided structures, providing 28 sampling layers. Each sampling layer has an hexagonal module, where a multipad large-area silicon sensor is glued between an electronics circuit board and a metal baseplate. The sensor pads of approximately 1 cm$^2$ are wire-bonded to the circuit board and are readout by custom integrated circuits. The prototype was extensively tested with beams at CERN's Super Proton Synchrotron in 2018. Based on the data collected with beams of positrons, with energies ranging from 20 to 300 GeV, measurements of the energy resolution and linearity, the position and angular resolutions, and the shower shapes are presented and compared to a detailed Geant4 simulation. △ Less

Submitted 31 March, 2022; v1 submitted 12 November, 2021; originally announced November 2021.

Ferromagnetic dynamics detected via one- and two-magnon NV relaxometry

Authors: Brendan A. McCullian, Ahmed M. Thabt, Benjamin A. Gray, Alex L. Melendez, Michael S. Wolf, Vladimir L. Safonov, Denis V. Pelekhov, Vidya P. Bhallamudi, Michael R. Page, P. Chris Hammel

Abstract: The NV center in diamond has proven to be a powerful tool for locally characterizing the magnetic response of microwave excited ferromagnets. To date, this has been limited by the requirement that the FMR excitation frequency be less than the NV spin resonance frequency. Here we report NV relaxometry based on a two-magnon Raman-like process, enabling detection of FMR at frequencies higher than the… ▽ More The NV center in diamond has proven to be a powerful tool for locally characterizing the magnetic response of microwave excited ferromagnets. To date, this has been limited by the requirement that the FMR excitation frequency be less than the NV spin resonance frequency. Here we report NV relaxometry based on a two-magnon Raman-like process, enabling detection of FMR at frequencies higher than the NV frequency. For high microwave drive powers, we observe an unexpected field-shift of the NV response relative to a simultaneous microwave absorption signal from a low damping ferrite film. We show that the field-shifted NV response is due to a second order Suhl instability. The instability creates a large population of non-equilibrium magnons which relax the NV spin, even when the uniform mode FMR frequency exceeds that of the NV spin resonance frequency, hence ruling out the possibility that the NV is relaxed by a single NV-resonant magnon. We argue that at high frequencies the NV response is due to a two-magnon relaxation process in which the difference frequency of two magnons matches the NV frequency, and at low frequencies we evaluate the lineshape of the one-magnon NV relaxometry response using spinwave instability theory. △ Less

Submitted 3 November, 2019; originally announced November 2019.

On the Insufficiency of the Large Margins Theory in Explaining the Performance of Ensemble Methods

Authors: Waldyn Martinez, J. Brian Gray

Abstract: Boosting and other ensemble methods combine a large number of weak classifiers through weighted voting to produce stronger predictive models. To explain the successful performance of boosting algorithms, Schapire et al. (1998) showed that AdaBoost is especially effective at increasing the margins of the training data. Schapire et al. (1998) also developed an upper bound on the generalization error… ▽ More Boosting and other ensemble methods combine a large number of weak classifiers through weighted voting to produce stronger predictive models. To explain the successful performance of boosting algorithms, Schapire et al. (1998) showed that AdaBoost is especially effective at increasing the margins of the training data. Schapire et al. (1998) also developed an upper bound on the generalization error of any ensemble based on the margins of the training data, from which it was concluded that larger margins should lead to lower generalization error, everything else being equal (sometimes referred to as the ``large margins theory''). Tighter bounds have been derived and have reinforced the large margins theory hypothesis. For instance, Wang et al. (2011) suggest that specific margin instances, such as the equilibrium margin, can better summarize the margins distribution. These results have led many researchers to consider direct optimization of the margins to improve ensemble generalization error with mixed results. We show that the large margins theory is not sufficient for explaining the performance of voting classifiers. We do this by illustrating how it is possible to improve upon the margin distribution of an ensemble solution, while keeping the complexity fixed, yet not improve the test set performance. △ Less

Submitted 10 June, 2019; originally announced June 2019.

On the Current State of Research in Explaining Ensemble Performance Using Margins

Authors: Waldyn Martinez, J. Brian Gray

Abstract: Empirical evidence shows that ensembles, such as bagging, boosting, random and rotation forests, generally perform better in terms of their generalization error than individual classifiers. To explain this performance, Schapire et al. (1998) developed an upper bound on the generalization error of an ensemble based on the margins of the training data, from which it was concluded that larger margins… ▽ More Empirical evidence shows that ensembles, such as bagging, boosting, random and rotation forests, generally perform better in terms of their generalization error than individual classifiers. To explain this performance, Schapire et al. (1998) developed an upper bound on the generalization error of an ensemble based on the margins of the training data, from which it was concluded that larger margins should lead to lower generalization error, everything else being equal. Many other researchers have backed this assumption and presented tighter bounds on the generalization error based on either the margins or functions of the margins. For instance, Shen and Li (2010) provide evidence suggesting that the generalization error of a voting classifier might be reduced by increasing the mean and decreasing the variance of the margins. In this article we propose several techniques and empirically test whether the current state of research in explaining ensemble performance holds. We evaluate the proposed methods through experiments with real and simulated data sets. △ Less

Submitted 7 June, 2019; originally announced June 2019.

A Convolutional Neural Network for Search Term Detection

Authors: Hojjat Salehinejad, Joseph Barfett, Parham Aarabi, Shahrokh Valaee, Errol Colak, Bruce Gray, Tim Dowdell

Abstract: Pathfinding in hospitals is challenging for patients, visitors, and even employees. Many people have experienced getting lost due to lack of clear guidance, large footprint of hospitals, and confusing array of hospital wings. In this paper, we propose Halo; An indoor navigation application based on voice-user interaction to help provide directions for users without assistance of a localization sys… ▽ More Pathfinding in hospitals is challenging for patients, visitors, and even employees. Many people have experienced getting lost due to lack of clear guidance, large footprint of hospitals, and confusing array of hospital wings. In this paper, we propose Halo; An indoor navigation application based on voice-user interaction to help provide directions for users without assistance of a localization system. The main challenge is accurate detection of origin and destination search terms. A custom convolutional neural network (CNN) is proposed to detect origin and destination search terms from transcription of a submitted speech query. The CNN is trained based on a set of queries tailored specifically for hospital and clinic environments. Performance of the proposed model is studied and compared with Levenshtein distance-based word matching. △ Less

Submitted 7 November, 2017; v1 submitted 6 August, 2017; originally announced August 2017.

Comments: This paper is accepted for presentation at 2017 IEEE 28th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications

Superconductor to Mott insulator transition in YBa$_2$Cu$_3$O$_7$/LaCaMnO$_3$ heterostructures

Authors: B. A. Gray, S. Middey, G. Conti, A. X. Gray, C. -T. Kuo, A. M. Kaiser, S. Ueda, K. Kobayashi, D. Meyers, M. Kareev, I. C. Tung, Jian Liu, C. S. Fadley, J. Chakhalian, J. W. Freeland

Abstract: The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high $T_c$ superconductor… ▽ More The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high $T_c$ superconductor YBa$_2$Cu$_3$O$_7$ (YBCO) and colossal magnetoresistance ferromagnet La$_{0.67}$Ca$_{0.33}$MnO$_3$ (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping in cuprate and manganite atomic layers, leading to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may response to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Such deterministic control of $T_c$ by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates. △ Less

Submitted 15 August, 2016; originally announced August 2016.

Comments: Accepted in Scientific Reports

Journal ref: Scientific Reports, 6, 33184 (2016)

Competition between heavy-fermion and Kondo interaction in isoelectronic A-site ordered perovskites

Authors: D. Meyers, S. Middey, J. -G. Cheng, Swarmakamal Mukherjee, B. A. Gray, Yanwei Cao, J. -S. Zhou, J. B. Goodenough, Yongseong Choi, D. Haskel, J. W. Freeland, T. Saha-Dasgupta, J. Chakhalian

Abstract: With current research efforts shifting towards the 4$d$ and 5$d$ transition metal oxides, understanding the evolution of the electronic and magnetic structure as one moves away from 3$d$ materials is of critical importance. Here we perform X-ray spectroscopy and electronic structure calculations on $A$-site ordered perovskites with Cu in the $A$-site and the $B$-sites descending along the 9th grou… ▽ More With current research efforts shifting towards the 4$d$ and 5$d$ transition metal oxides, understanding the evolution of the electronic and magnetic structure as one moves away from 3$d$ materials is of critical importance. Here we perform X-ray spectroscopy and electronic structure calculations on $A$-site ordered perovskites with Cu in the $A$-site and the $B$-sites descending along the 9th group of the periodic table to elucidate the emerging properties as $d$-orbitals change from partially filled 3$d$, 4$d$, to 5$d$. The results show that when descending from Co to Ir the charge transfers from the cuprate like Zhang-Rice state on Cu to the t$_{2g}$ orbital of the B site. As the Cu $d$-orbital occupation approaches the Cu$^{2+}$ limit, a mixed-valence state in CaCu$_3$Rh$_4$O$_{12}$ and heavy fermion state in CaCu$_3$Ir$_4$O$_{12}$ are obtained. The investigated d-electron compounds are mapped onto the Doniach phase diagram of the competing RKKY and Kondo interactions developed for f-electron systems. △ Less

Submitted 7 January, 2015; v1 submitted 24 April, 2014; originally announced April 2014.

Comments: 4 pages, 4 figures

Heterointerface engineered electronic and magnetic phases of NdNiO3 thin films

Authors: Jian Liu, Mehdi Kargarian, Mikhail Kareev, Ben Gray, Phil J. Ryan, Alejandro Cruz, Nadeem Tahir, Yi-De Chuang, Jinghua Guo, James M. Rondinelli, John W. Freeland, Gregory A. Fiete, Jak Chakhalian

Abstract: Mott physics is characterized by an interaction-driven metal-to-insulator transition in a partially filled band. In the resulting insulating state, antiferromagnetic orders of the local moments typically develop, but in rare situations no long-range magnetic order appears, even at zero temperature, rendering the system a quantum spin liquid. A fundamental and technologically critical question is w… ▽ More Mott physics is characterized by an interaction-driven metal-to-insulator transition in a partially filled band. In the resulting insulating state, antiferromagnetic orders of the local moments typically develop, but in rare situations no long-range magnetic order appears, even at zero temperature, rendering the system a quantum spin liquid. A fundamental and technologically critical question is whether one can tune the underlying energetic landscape to control both metal-to-insulator and Néel transitions, and even stabilize latent metastable phases, ideally on a platform suitable for applications. Here we demonstrate how to achieve this in ultrathin films of NdNiO3 with various degrees of lattice mismatch, and report on the quantum critical behaviours not reported in the bulk by transport measurements and resonant X-ray spectroscopy/scattering. In particular, on the decay of the antiferromagnetic Mott insulating state into a non-Fermi liquid, we find evidence of a quantum metal-to-insulator transition that spans a non-magnetic insulating phase. △ Less

Submitted 18 November, 2013; originally announced November 2013.

Comments: For updated published version see the link below

Journal ref: Nature Communications 4:2714 (2013)

Strain mediated suppression of the metal-insulator transition in EuNiO3 thin films

Authors: D. Meyers, S. Middey, M. Kareev, M. van Veenendaal, E. J. Moon, B. A. Gray, J. W. Freeland, J. Chakhalian

Abstract: Ultrathin epitaxial films of EuNiO3 were grown on a series of substrates traversing highly compressive (- 2.4%) to highly tensile (2.5%) lattice mismatch. X-ray diffraction measurements showed the expected c-lattice parameter shift for compressive strain, but no detectable shift for tensilely strained substrates, while reciprocal space mapping confirmed the tensile strained film maintained epitaxi… ▽ More Ultrathin epitaxial films of EuNiO3 were grown on a series of substrates traversing highly compressive (- 2.4%) to highly tensile (2.5%) lattice mismatch. X-ray diffraction measurements showed the expected c-lattice parameter shift for compressive strain, but no detectable shift for tensilely strained substrates, while reciprocal space mapping confirmed the tensile strained film maintained epitaxial coherence. Transport measurements showed a successively (from tensile to compressive) lower resistance and a complete suppression of the metalinsulator transition at highly compressive lattice mismatch. Corroborating these findings, X-ray absorption spectroscopy measurements revealed a strong multiplet splitting in the tensile samples that progressively weakens with increasing compressive strain that, combined with cluster calculations, showed enhanced covalence between Ni-d and O-p orbitals leads to the metallic state. △ Less

Submitted 29 July, 2013; v1 submitted 5 April, 2013; originally announced April 2013.

Enhanced Spin and Electronic Reconstructions at the Cuprate-Manganite Interface

Authors: B. A. Gray, E. J. Moon, I. C. Tung, M. Kareev, Jian Liu, D. J. Meyers, M. J. Bedzyk, J. W. Freeland, J. Chakhalian

Abstract: We report on a resonant soft X-ray spectroscopy study of the electronic and magnetic structure of the cuprate-manganite interface. Polarized X-ray spectroscopy measurements taken at the Cu L edge reveal up to a five-fold increase in the dichroic signal as compared to past experimental and theoretical values. Furthermore an increase in the degree of interlayer charge transfer up to 0.25e (where e i… ▽ More We report on a resonant soft X-ray spectroscopy study of the electronic and magnetic structure of the cuprate-manganite interface. Polarized X-ray spectroscopy measurements taken at the Cu L edge reveal up to a five-fold increase in the dichroic signal as compared to past experimental and theoretical values. Furthermore an increase in the degree of interlayer charge transfer up to 0.25e (where e is charge of an electron) per copper ion is observed leading to a profound reconstruction in the orbital scheme for these interfacial copper ions. It is inferred that these enhancement are related to an increase in TMI observed for manganite layers grown with rapidly modulated flux. △ Less

Submitted 16 January, 2013; originally announced January 2013.

Epitaxial growth of (111)-oriented LaAlO$_3$/LaNiO$_3$ ultra-thin superlattices

Authors: S. Middey, D. Meyers, M. Kareev, E. J. Moon, B. A. Gray, X. Liu, J. W. Freeland, J. Chakhalian

Abstract: The epitaxial stabilization of a single layer or superlattice structures composed of complex oxide materials on polar (111) surfaces is severely burdened by reconstructions at the interface, that commonly arise to neutralize the polarity. We report on the synthesis of high quality LaNiO$_3$/mLaAlO$_3$ pseudo cubic (111) superlattices on polar (111)-oriented LaAlO$_3$, the proposed complex oxide ca… ▽ More The epitaxial stabilization of a single layer or superlattice structures composed of complex oxide materials on polar (111) surfaces is severely burdened by reconstructions at the interface, that commonly arise to neutralize the polarity. We report on the synthesis of high quality LaNiO$_3$/mLaAlO$_3$ pseudo cubic (111) superlattices on polar (111)-oriented LaAlO$_3$, the proposed complex oxide candidate for a topological insulating behavior. Comprehensive X-Ray diffraction measurements, RHEED, and element specific resonant X-ray absorption spectroscopy affirm their high structural and chemical quality. The study offers an opportunity to fabricate interesting interface and topology controlled (111) oriented superlattices based on ortho-nickelates. △ Less

Submitted 3 December, 2012; originally announced December 2012.

Ultrafast pump-probe spectroscopic signatures of superconducting and pseudogap phases in YBa2Cu3O7-δ films

Authors: Chunfeng Zhang, Wei Li, B. Gray, Bin He, Ye Wang, Fan Yang, Xiaoyong Wang, J. Chakhalian, Min Xiao

Abstract: Femtosecond pump-probe spectroscopy is applied to identify transient optical signatures of phase transitions in optimally doped YBa2Cu3O7-δ films. To elucidate the dynamics of superconducting and pseudogap phases, the slow thermal component is removed from the time-domain traces of photo-induced reflectivity in a high-flux regime with low frequency pulse rate. The rescaled data exhibit distinct si… ▽ More Femtosecond pump-probe spectroscopy is applied to identify transient optical signatures of phase transitions in optimally doped YBa2Cu3O7-δ films. To elucidate the dynamics of superconducting and pseudogap phases, the slow thermal component is removed from the time-domain traces of photo-induced reflectivity in a high-flux regime with low frequency pulse rate. The rescaled data exhibit distinct signatures of the phase separation with abrupt changes at the onsets of TSC and TPG in excellent agreement with transport data. Compared to the superconducting phase, the response of the pseudogap phase is characterized by the strongly reduced reflectivity change accompanied by a faster recovery time. △ Less

Submitted 22 November, 2012; originally announced November 2012.

Comments: 14 pages, 3 figures

Journal ref: J. Appl.Phys. 113, 083901 (2013)

Abelian properties of Anick spaces

Authors: Brayton Gray

Abstract: The Anick spaces play a key role in an unstable filtration of the stable homotopy of V(0) to produce secondary EHP sequences. This work establishes that the Anick spaces are homotopy associative and homotopy commutative H-spaces, and that they have a universal mapping property for maps into a homotopy commutative and homotopy associative H-space with a (necessary) condition on the growth of the p… ▽ More The Anick spaces play a key role in an unstable filtration of the stable homotopy of V(0) to produce secondary EHP sequences. This work establishes that the Anick spaces are homotopy associative and homotopy commutative H-spaces, and that they have a universal mapping property for maps into a homotopy commutative and homotopy associative H-space with a (necessary) condition on the growth of the p torsion. This is utilized to establish an unstable composition theory. The techniques involve generalized Whitehead products based on co-H spaces, calculations in a congruence category that lies between the unstable category and the stable category, and a controlled version of the extension theorem for principal fibrations. △ Less

Submitted 4 August, 2014; v1 submitted 18 August, 2012; originally announced August 2012.

Comments: 125 pages

MSC Class: 55P45; 55Q15; 55Q25; 55Q51; 55R99

Metal-insulator transition and orbital reconstruction in Mott quantum wells of NdNiO$_{3}$

Authors: Jian Liu, M. Kareev, D. Meyers, B. Gray, P. Ryan, J. W. Freeland, J. Chakhalian

Abstract: The metal-insulator transition (MIT) and the underlying electronic and orbital structure in $e_{g}^{1}$ quantum wells based on NdNiO$_{3}$ was investigated by d.c. transport and resonant soft x-ray absorption spectroscopy. By comparing quantum wells of the same dimension but with two different confinement structures, we explicitly demonstrate that the quantum well boundary condition of correlated… ▽ More The metal-insulator transition (MIT) and the underlying electronic and orbital structure in $e_{g}^{1}$ quantum wells based on NdNiO$_{3}$ was investigated by d.c. transport and resonant soft x-ray absorption spectroscopy. By comparing quantum wells of the same dimension but with two different confinement structures, we explicitly demonstrate that the quantum well boundary condition of correlated electrons is critical to selecting the many-body ground state. In particular, the long-range orderings and the MIT are found to be strongly enhanced under quantum confinement by sandwiching NdNiO$_{3}$ with the wide-gap dielectric LaAlO$_{3}$, while they are suppressed when one of the interfaces is replaced by a surface (interface with vacuum). Resonant spectroscopy reveals that the reduced charge fluctuations in the sandwich structure are supported by the enhanced propensity to charge ordering due to the suppressed $e_g$ orbital splitting when interfaced with the confining LaAlO$_{3}$ layer. △ Less

Submitted 6 August, 2012; originally announced August 2012.

Strain-controlled band engineering and self-doping in ultrathin LaNiO$_3$ films

Authors: E. J. Moon, J. M. Rondinelli, N. Prasai, B. A. Gray, M. Kareev, J. Chakhalian, J. L. Cohn

Abstract: We report on a systematic study of the temperature-dependent Hall coefficient and thermoelectric power in ultra-thin metallic LaNiO$_3$ films that reveal a strain-induced, self-doping carrier transition that is inaccessible in the bulk. As the film strain varies from compressive to tensile at fixed composition and stoichiometry, the transport coefficients evolve in a manner strikingly similar to t… ▽ More We report on a systematic study of the temperature-dependent Hall coefficient and thermoelectric power in ultra-thin metallic LaNiO$_3$ films that reveal a strain-induced, self-doping carrier transition that is inaccessible in the bulk. As the film strain varies from compressive to tensile at fixed composition and stoichiometry, the transport coefficients evolve in a manner strikingly similar to those of bulk hole-doped superconducting cuprates with varying doping level. Density functional calculations reveal that the strain-induced changes in the transport properties are due to self-doping in the low-energy electronic band structure. The results imply that thin-film epitaxy can serve as a new means to achieve hole-doping in other (negative) charge-transfer gap transition metal oxides without resorting to chemical substitution. △ Less

Submitted 10 April, 2012; originally announced April 2012.

Journal ref: http://link.aps.org/doi/10.1103/PhysRevB.85.121106 (2012)

Thermal instability and runaway criteria: the dangers of disregarding dynamics

Authors: Rowena Ball, Brian F. Gray

Abstract: Two exemplary exothermic processes, synthesis of nitroglycerine in a continuous stirred tank reactor (CSTR) and synthesis of the explosive RDX in a CSTR, are used to demonstrate the dangers of ignoring the system dynamics when defining criteria for thermal criticality or runaway. Stability analyses are necessary to prescribe such criteria, and for these systems prove the presence of dangerous osci… ▽ More Two exemplary exothermic processes, synthesis of nitroglycerine in a continuous stirred tank reactor (CSTR) and synthesis of the explosive RDX in a CSTR, are used to demonstrate the dangers of ignoring the system dynamics when defining criteria for thermal criticality or runaway. Stability analyses are necessary to prescribe such criteria, and for these systems prove the presence of dangerous oscillatory thermal instability which cannot be detected using the steady state thermal balances. △ Less

Submitted 23 February, 2012; originally announced February 2012.

Comments: Submitted 23 Feb 2012 to Process Safety & Environmental Protection. Research highlights: *We adjure the use of stability analysis in specifying thermal runaway conditions. *Two recent works that disregarded stability were re-examined. *Oscillatory thermal instability is shown to be endemic to these systems. *It is real, not an artefact, it may occur with violent abruptness, it is dangerous

Epitaxial Stabilization of Ultrathin Films of Rare-Earth Nickelates

Authors: D. J. Meyers, E. J. Moon, M. Kareev, I. C. Tung, B. A. Gray, Jian Liu, M. J. Bedzyk, J. W. Freeland, J. Chakhalian

Abstract: We report on the synthesis of ultrathin films of highly distorted EuNiO3 (ENO) grown by interrupted pulse laser epitaxy on YAlO3 (YAO) substrates. Through mapping the phase space of nickelate thin film epitaxy, the optimal growth temperatures were found to scale linearly with the Goldschmidt tolerance factor. Considering the gibbs energy of the expanding film, this empirical trend is discussed in… ▽ More We report on the synthesis of ultrathin films of highly distorted EuNiO3 (ENO) grown by interrupted pulse laser epitaxy on YAlO3 (YAO) substrates. Through mapping the phase space of nickelate thin film epitaxy, the optimal growth temperatures were found to scale linearly with the Goldschmidt tolerance factor. Considering the gibbs energy of the expanding film, this empirical trend is discussed in terms of epitaxial stabilization and the escalation of the lattice energy due to lattice distortions and decreasing symmetry. These findings are fundamental to other complex oxide perovskites, and provide a route to the synthesis of other perovskite structures in ultrathin-film form. △ Less

Submitted 22 December, 2011; originally announced December 2011.

Comments: 7 pages, 3 figures

Strain dependent transport properties of the quasi two-dimensional correlated metal, LaNiO$_{3}$

Authors: E. J. Moon, B. A. Gray, M. Kareev, J. Liu, S. G. Altendorf, F. Strigari, L. H. Tjeng, J. W. Freeland, J. Chakhalian

Abstract: We explore the electrical transport and magneto-conductance in quasi two-dimensional strongly correlated ultrathin films of LaNiO$_{3}$ (LNO) to investigate the effect of hetero-epitaxial strain on electron-electron and electron-lattice interactions from the low to intermediate temperature range (2K$\sim$170K). The fully epitaxial 10 unit cell thick films spanning tensile strain up to $\sim4%$ are… ▽ More We explore the electrical transport and magneto-conductance in quasi two-dimensional strongly correlated ultrathin films of LaNiO$_{3}$ (LNO) to investigate the effect of hetero-epitaxial strain on electron-electron and electron-lattice interactions from the low to intermediate temperature range (2K$\sim$170K). The fully epitaxial 10 unit cell thick films spanning tensile strain up to $\sim4%$ are used to investigate effects of enhanced carrier localization driven by a combination of weak localization and electron-electron interactions at low temperatures. The magneto-conductance data shows the importance of the increased contribution of weak localization to low temperature quantum corrections. The obtained results demonstrate that with increasing tensile strain and reduced temperature the quantum confined LNO system gradually evolves from the Mott into the Mott-Anderson regime. △ Less

Submitted 27 May, 2011; originally announced May 2011.

Universal Abelian H-spaces

Authors: Brayton Gray

Abstract: The question of the existence of Universal homotopy commutative and homotopy associative H-spaces (called Abelian H-spaces) is studied. Such a space T(X) would prolong a map from X into an Abelian H-space to a unique H-map from T into X. Examples of such pairs (X,T) are given and conditions are discussed which limit the possible spaces X for which such a T can exist. The Anick spaces are shown not… ▽ More The question of the existence of Universal homotopy commutative and homotopy associative H-spaces (called Abelian H-spaces) is studied. Such a space T(X) would prolong a map from X into an Abelian H-space to a unique H-map from T into X. Examples of such pairs (X,T) are given and conditions are discussed which limit the possible spaces X for which such a T can exist. The Anick spaces are shown not to be universal Abelian H-spaces for the corresponding Moore spaces, but conditions are discussed which could lead to a universal property with respect to a more limited range of targets. △ Less

Submitted 3 February, 2011; originally announced February 2011.

Comments: 22 pages

MSC Class: 55Q40; 55Q51; 55P45

Quantum confinement of Mott electrons in ultrathin LaNiO3/LaAlO3 superlattice

Authors: Jian Liu, S. Okamoto, M. van Veenendaal, M. Kareev, B. Gray, P. Ryan, J. W. Freeland, J. Chakhalian

Abstract: We investigate the electronic reconstruction in (LaNiO$_{3}$)$_n$/(LaAlO$_{3}$)$_3$ (n=3, 5 and 10) superlattices due to the quantum confinement (QC) by d.c. transport and resonant soft x-ray absorption spectroscopy. In proximity to the QC limit, a Mott-type transition from an itinerant electron behavior to a localized state is observed. The system exhibits tendency towards charge-order during the… ▽ More We investigate the electronic reconstruction in (LaNiO$_{3}$)$_n$/(LaAlO$_{3}$)$_3$ (n=3, 5 and 10) superlattices due to the quantum confinement (QC) by d.c. transport and resonant soft x-ray absorption spectroscopy. In proximity to the QC limit, a Mott-type transition from an itinerant electron behavior to a localized state is observed. The system exhibits tendency towards charge-order during the transition. ab initio cluster calculations are in good agreement with the absorption spectra, indicating that the apical ligand hole density is highly suppressed resulting in a strong modification of the electronic structure. At the dimensional crossover cellular dynamical-mean-field calculations support the emergence of a Mott insulator ground state in the heterostructured ultra-thin slab of LaNiO$_{3}$. △ Less

Submitted 28 January, 2011; originally announced January 2011.

Comments: 4 pages, 3 figures

Orbital control in strained ultra-thin LaNiO$_3$/LaAlO$_3$ superlattices

Authors: J. W. Freeland, Jian Liu, M. Kareev, B. Gray, J. W. Kim, P. Ryan, R. Pentcheva, J. Chakhalian

Abstract: In pursuit of rational control of orbital polarization, we present a combined experimental and theoretical study of single unit cell superlattices of the correlated metal LaNiO$_3$ and the band insulator LaAlO$_3$. Polarized x-ray absorption spectra show a distinct asymmetry in the orbital response under strain. A splitting of orbital energies consistent with octahedral distortions is found for th… ▽ More In pursuit of rational control of orbital polarization, we present a combined experimental and theoretical study of single unit cell superlattices of the correlated metal LaNiO$_3$ and the band insulator LaAlO$_3$. Polarized x-ray absorption spectra show a distinct asymmetry in the orbital response under strain. A splitting of orbital energies consistent with octahedral distortions is found for the case of compressive strain. In sharp contrast, for tensile strain, no splitting is found although a strong orbital polarization is present. Density functional theory calculations including a Hubbard U term reveal that this asymmetry is a result of the interplay of strain and confinement induces octahedral rotations and distortions and altered covalency in the bonding across the interfacial Ni-O-Al apical oxygen, leading to a charge disporportionation at the Ni sites for tensile strain. △ Less

Submitted 19 January, 2012; v1 submitted 9 August, 2010; originally announced August 2010.

Comments: 4 pages. 5 figures

Journal ref: Europhysics Letters vol. 96 p. 57004 (2011)

Asymmetric orbital-lattice interactions in ultra-thin correlated oxide films

Authors: J. Chakhalian, J. M. Rondinelli, Jian Liu, B. A. Gray, M. Kareev, E. J. Moon, N. Prasai, J. L. Cohn, M. Varela, I. C. Tung, M. J. Bedzyk, S. G. Altendorf, F. Strigari, B. Dabrowski, L. H. Tjeng, P. J. Ryan, J. W. Freeland

Abstract: Using resonant X-ray spectroscopies combined with density functional calculations, we find an asymmetric bi-axial strain-induced $d$-orbital response in ultra-thin films of the correlated metal LaNiO$_3$ which are not accessible in the bulk. The sign of the misfit strain governs the stability of an octahedral "breathing" distortion, which, in turn, produces an emergent charge-ordered ground state… ▽ More Using resonant X-ray spectroscopies combined with density functional calculations, we find an asymmetric bi-axial strain-induced $d$-orbital response in ultra-thin films of the correlated metal LaNiO$_3$ which are not accessible in the bulk. The sign of the misfit strain governs the stability of an octahedral "breathing" distortion, which, in turn, produces an emergent charge-ordered ground state with an altered ligand-hole density and bond covalency. Control of this new mechanism opens a pathway to rational orbital engineering, providing a platform for artificially designed Mott materials. △ Less

Submitted 25 August, 2011; v1 submitted 7 August, 2010; originally announced August 2010.

Journal ref: Phys. Rev. Lett. 107, 116805 (2011)

Sub-monolayer nucleation and growth of complex oxide heterostructures at high supersaturation and rapid flux modulation

Authors: M. Kareev, S. Prosandeev, Jian Liu, B. Gray, P. Ryan, A. Kareev, Eun Ju Moon, J. Chakhalian

Abstract: We report on the non-trivial nanoscale kinetics of the deposition of novel complex oxide heterostructures composed of a unit-cell thick correlated metal LaNiO3 and dielectric LaAlO3. The multilayers demonstrate exceptionally good crystallinity and surface morphology maintained over the large number of layers, as confirmed by AFM, RHEED, and synchrotron X-ray diffraction. To elucidate the physic… ▽ More We report on the non-trivial nanoscale kinetics of the deposition of novel complex oxide heterostructures composed of a unit-cell thick correlated metal LaNiO3 and dielectric LaAlO3. The multilayers demonstrate exceptionally good crystallinity and surface morphology maintained over the large number of layers, as confirmed by AFM, RHEED, and synchrotron X-ray diffraction. To elucidate the physics behind the growth, the temperature of the substrate and the deposition rate were varied over a wide range and the results were treated in the framework of a two-layer model. These results are of fundamental importance for synthesis of new phases of complex oxide heterostructures. △ Less

Submitted 4 May, 2010; originally announced May 2010.

Comments: 13 pages, 6 figures

Local Electronic and Magnetic Studies of an Artificial La2FeCrO6 Double Perovskite

Authors: Benjamin Gray, Ho Nyung Lee, Jian Liu, J. Chakhalian, J. W. Freeland

Abstract: Through the utilization of element-resolved polarized x-ray probes, the electronic and magnetic state of an artificial La2FeCrO6 double perovskite were explored. Applying unit-cell level control of thin film growth on SrTiO3 (111), the rock salt double perovskite structure can be created for this system, which does not have an ordered perovskite phase in the bulk. We find that the Fe and Cr are in… ▽ More Through the utilization of element-resolved polarized x-ray probes, the electronic and magnetic state of an artificial La2FeCrO6 double perovskite were explored. Applying unit-cell level control of thin film growth on SrTiO3 (111), the rock salt double perovskite structure can be created for this system, which does not have an ordered perovskite phase in the bulk. We find that the Fe and Cr are in the proper 3+ valence state, but, contrary to previous studies, the element-resolved magnetic studies find the moments in field are small and show no evidence of a sizable magnetic moment in the remanent state. △ Less

Submitted 19 April, 2010; originally announced April 2010.

Comments: 3 pages, 4 figures

Strain-mediated metal-insulator transition in epitaxial ultra-thin films of NdNiO3

Authors: Jian Liu, M. Kareev, B. Gray, J. W. Kim, P. Ryan, B. Dabrowski, J. W. Freeland, J. Chakhalian

Abstract: We have synthesized epitaxial NdNiO$_{3}$ ultra-thin films in a layer-by-layer growth mode under tensile and compressive strain on SrTiO$_{3}$ (001) and LaAlO$_3$ (001), respectively. A combination of X-ray diffraction, temperature dependent resistivity, and soft X-ray absorption spectroscopy has been applied to elucidate electronic and structural properties of the samples. In contrast to the bu… ▽ More We have synthesized epitaxial NdNiO$_{3}$ ultra-thin films in a layer-by-layer growth mode under tensile and compressive strain on SrTiO$_{3}$ (001) and LaAlO$_3$ (001), respectively. A combination of X-ray diffraction, temperature dependent resistivity, and soft X-ray absorption spectroscopy has been applied to elucidate electronic and structural properties of the samples. In contrast to the bulk NdNiO$_{3}$, the metal-insulator transition under compressive strain is found to be completely quenched, while the transition remains under the tensile strain albeit modified from the bulk behavior. △ Less

Submitted 17 March, 2010; v1 submitted 16 March, 2010; originally announced March 2010.

Comments: 4 pages, 4 figures

Effect of polar discontinuity on the growth of LaNiO3/LaAlO3 superlattices

Authors: Jian Liu, M. Kareev, S. Prosandeev, B. Gray, P. Ryan, J. W. Freeland, J. Chakhalian

Abstract: We have conducted a detailed microscopic investigation of [LaNiO3(1 u.c.)/LaAlO3(1 u.c.)]N superlattices grown on (001) SrTiO3 and LaAlO3 to explore the influence of polar mismatch on the resulting electronic and structural properties. Our data demonstrate that the initial growth on the non-polar SrTiO3 surface leads to a rough morphology and unusual 2+ valence of Ni in the first LaNiO3 layer, w… ▽ More We have conducted a detailed microscopic investigation of [LaNiO3(1 u.c.)/LaAlO3(1 u.c.)]N superlattices grown on (001) SrTiO3 and LaAlO3 to explore the influence of polar mismatch on the resulting electronic and structural properties. Our data demonstrate that the initial growth on the non-polar SrTiO3 surface leads to a rough morphology and unusual 2+ valence of Ni in the first LaNiO3 layer, which is not observed after growth on the polar surface of LaAlO3. A newly devised model suggests that the polar mismatch can be resolved if the perovskite layers grow with an excess of LaO, which also accounts for the observed electronic, chemical, and structural effects. △ Less

Submitted 5 January, 2010; originally announced January 2010.

Comments: 3 pages, 3 figures

On Generalized Whitehead Products

Authors: Brayton Gray

Abstract: A symmetric monoidal pairing is defined among simply connected co-H spaces and this is used to generalize the Whitehead product map S(X ^ Y) --> SX v SY to co-H spaces. A symmetric monoidal pairing is defined among simply connected co-H spaces and this is used to generalize the Whitehead product map S(X ^ Y) --> SX v SY to co-H spaces. △ Less

Submitted 17 November, 2009; v1 submitted 16 November, 2009; originally announced November 2009.

Comments: 16 pages

MSC Class: 55Q15; 55P40; 55Q20; 55P99; 55P45

Filtering the fiber of the pinch map

Authors: Brayton Gray

Abstract: A new type of Hopf invariant is described for the fiber of the pinch map from the mapping cone of a map from A to X onto to the suspension of A; this is then used to study the boundary map in the fibration sequence of Cohen, Moore and Neisendorfer in the case that the mapping cone is an odd dimensional Moore space. The components of the boundary map are then shown to be compatible with Hopf inva… ▽ More A new type of Hopf invariant is described for the fiber of the pinch map from the mapping cone of a map from A to X onto to the suspension of A; this is then used to study the boundary map in the fibration sequence of Cohen, Moore and Neisendorfer in the case that the mapping cone is an odd dimensional Moore space. The components of the boundary map are then shown to be compatible with Hopf invariants and a filtered splitting of the loops on the fiber is obtained. △ Less

Submitted 5 April, 2009; v1 submitted 11 April, 2008; originally announced April 2008.

Comments: This is the version published by Geometry & Topology Monographs on 22 2008

MSC Class: 55P99; 55Q20; 55Q25

Journal ref: Geom. Topol. Monogr. 13 (2008) 203-227

Decompositions involving Anick's spaces

Authors: Brayton Gray

Abstract: Recently Stephen Theriault and I found an elementary construction of Anick's spaces and proved their main properties(arXiv:0710.1024).In this work the fundamental fibration is decomposed. This is useful in studying maps out of Anick's spaces and will be needed in order to determine it's universal properties. Recently Stephen Theriault and I found an elementary construction of Anick's spaces and proved their main properties(arXiv:0710.1024).In this work the fundamental fibration is decomposed. This is useful in studying maps out of Anick's spaces and will be needed in order to determine it's universal properties. △ Less

Submitted 4 April, 2008; originally announced April 2008.

Comments: 20 pages

MSC Class: 55P35; 55P40; 55P45

An elementary construction of Anick's fibration

Authors: Brayton Gray, Stephen Theriault

Abstract: Cohen, Moore, and Neisendorfer's work on the odd primary homotopy theory of spheres and Moore spaces, as well as the first author's work on the secondary suspension, predicted the existence of a p-local fibration S^2n-1 --> T --> ΩS^2n+1 whose connecting map is degree p^r. In a long and complex monograph, Anick constructed such a fibration for p>= 5 and r>= 1. Using new methods we give a much mo… ▽ More Cohen, Moore, and Neisendorfer's work on the odd primary homotopy theory of spheres and Moore spaces, as well as the first author's work on the secondary suspension, predicted the existence of a p-local fibration S^2n-1 --> T --> ΩS^2n+1 whose connecting map is degree p^r. In a long and complex monograph, Anick constructed such a fibration for p>= 5 and r>= 1. Using new methods we give a much more conceptual construction which is also valid for p=3 and r>= 1. We go on to establish several properties of the space T. △ Less

Submitted 4 October, 2007; originally announced October 2007.

Comments: 30 pages

MSC Class: 55P45; 55P40; 55P35

Journal ref: Geom. Topol. 14 (2010) 243-275

Compensation of Strong Thermal Lensing in High Optical Power Cavities

Authors: C. Zhao, J. Degallaix, L. Ju, Y. Fan, D. G. Blair, B. J. J. Slagmolen, M. B. Gray, C. M. Mow Lowry, D. E. McClellandl, D. J. Hosken, D. Mudge, A. Brooks, J. Munch, P. J. Veitch, M. A. Barton, G. Billingsley

Abstract: In an experiment to simulate the conditions in high optical power advanced gravitational wave detectors such as Advanced LIGO, we show that strong thermal lenses form in accordance with predictions and that they can be compensated using an intra-cavity compensation plate heated on its cylindrical surface. We show that high finesse ~1400 can be achieved in cavities with internal compensation plat… ▽ More In an experiment to simulate the conditions in high optical power advanced gravitational wave detectors such as Advanced LIGO, we show that strong thermal lenses form in accordance with predictions and that they can be compensated using an intra-cavity compensation plate heated on its cylindrical surface. We show that high finesse ~1400 can be achieved in cavities with internal compensation plates, and that the cavity mode structure can be maintained by thermal compensation. It is also shown that the measurements allow a direct measurement of substrate optical absorption in the test mass and the compensation plate. △ Less

Submitted 28 February, 2006; v1 submitted 24 February, 2006; originally announced February 2006.

Comments: 8 pages

Journal ref: Phys.Rev.Lett.96:231101,2006

Quantum Noise Locking

Authors: Kirk McKenzie, Eugeniy Mikhailov, Keisuke Goda, Ping Koy Lam, Nicolai Grosse, Malcolm B. Gray, Nergis Mavalvala, David E. McClelland

Abstract: Quantum optical states which have no coherent amplitude, such as squeezed vacuum states, can not rely on standard readout techniques to generate error signals for control of the quadrature phase. Here we investigate the use of asymmetry in the quadrature variances to obtain a phase-sensitive readout and to lock the phase of a squeezed vacuum state, a technique which we call noise locking (NL). W… ▽ More Quantum optical states which have no coherent amplitude, such as squeezed vacuum states, can not rely on standard readout techniques to generate error signals for control of the quadrature phase. Here we investigate the use of asymmetry in the quadrature variances to obtain a phase-sensitive readout and to lock the phase of a squeezed vacuum state, a technique which we call noise locking (NL). We carry out a theoretical derivation of the NL error signal and the associated stability of the squeezed and anti-squeezed lock points. Experimental data for the NL technique both in the presence and absence of coherent fields are shown, including a comparison with coherent locking techniques. Finally, we use NL to enable a stable readout of the squeezed vacuum state on a homodyne detector. △ Less

Submitted 22 May, 2005; originally announced May 2005.

Comments: Accepted for publication in Journal of Optics:B special issue on Quantum Control

Journal ref: J. Opt. B: Quantum Semiclass. Opt. 7, S421-S428, (2005).

Demonstration of a passive sub-picostrain fiber strain sensor

Authors: Jong H. Chow, Ian C. M. Littler, David E. McClelland, Malcolm B. Gray

Abstract: We demonstrate a fiber Fabry-Perot (FFP) sensor capable of detecting sub-picostrain signals, from 100 Hz and extending beyond 100 kHz, using the Pound-Drever-Hall frequency locking technique. A low power diode laser at 1550 nm is locked to a free-space reference cavity to suppress its free-running frequency noise, thereby stabilizing the laser. The stabilized laser is then used to interrogate a… ▽ More We demonstrate a fiber Fabry-Perot (FFP) sensor capable of detecting sub-picostrain signals, from 100 Hz and extending beyond 100 kHz, using the Pound-Drever-Hall frequency locking technique. A low power diode laser at 1550 nm is locked to a free-space reference cavity to suppress its free-running frequency noise, thereby stabilizing the laser. The stabilized laser is then used to interrogate a FFP where the PDH error signal yields the instantaneous fiber strain. △ Less

Submitted 11 April, 2005; originally announced April 2005.

Comments: 3 pages, 4 figure, to appear in Optics Letters

Pump-probe differencing technique for cavity-enhanced, noise-canceling saturation laser spectroscopy

Authors: Glenn de Vine, David E. McClelland, John D. Close, Malcolm B. Gray

Abstract: We present an experimental technique enabling mechanical-noise free, cavity-enhanced frequency measurements of an atomic transition and its hyperfine structure. We employ the 532nm frequency doubled output from a Nd:YAG laser and an iodine vapour cell. The cell is placed in a traveling-wave Fabry-Perot interferometer (FPI) with counter-propagating pump and probe beams. The FPI is locked using th… ▽ More We present an experimental technique enabling mechanical-noise free, cavity-enhanced frequency measurements of an atomic transition and its hyperfine structure. We employ the 532nm frequency doubled output from a Nd:YAG laser and an iodine vapour cell. The cell is placed in a traveling-wave Fabry-Perot interferometer (FPI) with counter-propagating pump and probe beams. The FPI is locked using the Pound-Drever-Hall (PDH) technique. Mechanical noise is rejected by differencing pump and probe signals. In addition, this differenced error signal gives a sensitive measure of differential non-linearity within the FPI. △ Less

Submitted 10 November, 2004; originally announced November 2004.

Comments: 3 pages, 5 figures, submitted to Optics Letters

Phase-sensitive interrogation of fiber Bragg grating resonators for sensing applications

Authors: Jong H. Chow, Ian C. M. Littler, Glenn de Vine, David E. McClelland, Malcolm B. Gray

Abstract: We discuss a phase-sensitive technique for remote interrogation of passive Bragg grating Fabry-Perot resonators. It is based on Pound-Drever-Hall laser frequency locking, using radio-frequency phase modulation sidebands to derive an error signal from the complex optical response, near resonance, of a Fabry-Perot interferometer. We examine how modulation frequency and resonance bandwidth affect t… ▽ More We discuss a phase-sensitive technique for remote interrogation of passive Bragg grating Fabry-Perot resonators. It is based on Pound-Drever-Hall laser frequency locking, using radio-frequency phase modulation sidebands to derive an error signal from the complex optical response, near resonance, of a Fabry-Perot interferometer. We examine how modulation frequency and resonance bandwidth affect this error signal. Experimental results are presented that demonstrate when the laser is locked, this method detects differential phase shifts in the optical carrier relative to its sidebands, due to minute fiber optical path displacements. △ Less

Submitted 9 November, 2004; originally announced November 2004.

Comments: Submitted to Journal of Lightwave Technology

Interrogation of a fiber Fabry-Perot sensor by current modulation of a diode laser

Authors: Jong H. Chow, Jeff S. Cumpston, Ian C. M. Littler, David E. McClelland, Malcolm B. Gray

Abstract: We present a method for remote interrogation of passive fiber Bragg grating Fabry-Perot resonators, employing current modulation of the diode laser source. With the presence of both RF amplitude and frequency modulation, it is a variant of the ultra-sensitive Pound-Drever-Hall laser frequency locking technique. We demonstrate that current modulation and interferometric demodulation removes the n… ▽ More We present a method for remote interrogation of passive fiber Bragg grating Fabry-Perot resonators, employing current modulation of the diode laser source. With the presence of both RF amplitude and frequency modulation, it is a variant of the ultra-sensitive Pound-Drever-Hall laser frequency locking technique. We demonstrate that current modulation and interferometric demodulation removes the need for a phase modulator in the sensing architecture. △ Less

Submitted 9 November, 2004; originally announced November 2004.

Comments: Submitted to IEEE Photonics Technology Letters

Squeezing in the audio gravitational wave detection band

Authors: K. McKenzie, N. Grosse, W. P. Bowen, S. E. Whitcomb, M. B. Gray, D. E. McClelland, P. K. Lam

Abstract: We demonstrate the generation of broad-band continuous-wave optical squeezing down to 200Hz using a below threshold optical parametric oscillator (OPO). The squeezed state phase was controlled using a noise locking technique. We show that low frequency noise sources, such as seed noise, pump noise and detuning fluctuations, present in optical parametric amplifiers have negligible effect on squee… ▽ More We demonstrate the generation of broad-band continuous-wave optical squeezing down to 200Hz using a below threshold optical parametric oscillator (OPO). The squeezed state phase was controlled using a noise locking technique. We show that low frequency noise sources, such as seed noise, pump noise and detuning fluctuations, present in optical parametric amplifiers have negligible effect on squeezing produced by a below threshold OPO. This low frequency squeezing is ideal for improving the sensitivity of audio frequency measuring devices such as gravitational wave detectors. △ Less

Submitted 25 May, 2004; v1 submitted 24 May, 2004; originally announced May 2004.

Comments: 5 pages, 6 figures

Report number: LIGO-P040018-00-R

Journal ref: Phys.Rev.Lett. 93 (2004) 161105

Study of an electro-optic modulator capable of generating simultaneous amplitude and phase modulations

Authors: Benedict J Cusack, Benjamin S Sheard, Daniel A Shaddock, Malcolm B Gray, Ping Koy Lam, Stan E Whitcomb

Abstract: We report on the analysis and prototype-characterization of a dual-electrode electro-optic modulator that can generate both amplitude and phase modulations with a selectable relative phase, termed a universally tunable modulator (UTM). All modulation states can be reached by tuning only the electrical inputs, facilitating real-time tuning, and the device is shown to have good suppression and sta… ▽ More We report on the analysis and prototype-characterization of a dual-electrode electro-optic modulator that can generate both amplitude and phase modulations with a selectable relative phase, termed a universally tunable modulator (UTM). All modulation states can be reached by tuning only the electrical inputs, facilitating real-time tuning, and the device is shown to have good suppression and stability properties. A mathematical analysis is presented, including the development of a geometric phase representation for modulation. The experimental characterization of the device shows that relative suppressions of 38 dB, 39 dB and 30 dB for phase, single-sideband and carrier-suppressed modulations, respectively, can be obtained, as well as showing the device is well-behaved when scanning continuously through the parameter space of modulations. Uses for the device are discussed, including the tuning of lock points in optical locking schemes, single sideband applications, modulation fast-switching applications, and applications requiring combined modulations. △ Less

Submitted 8 August, 2003; v1 submitted 17 June, 2003; originally announced June 2003.

Comments: 12 pages, 8 figures, 1 table

Suppression of Classical and Quantum Radiation Pressure Noise via Electro-Optic Feedback

Authors: Ben C. Buchler, Malcolm B. Gray, Daniel A. Shaddock, Timothy C. Ralph, David E. McClelland

Abstract: We present theoretical results that demonstrate a new technique to be used to improve the sensitivity of thermal noise measurements: intra-cavity intensity stabilisation. It is demonstrated that electro-optic feedback can be used to reduce intra-cavity intensity fluctuations, and the consequent radiation pressure fluctuations, by a factor of two below the quantum noise limit. We show that this i… ▽ More We present theoretical results that demonstrate a new technique to be used to improve the sensitivity of thermal noise measurements: intra-cavity intensity stabilisation. It is demonstrated that electro-optic feedback can be used to reduce intra-cavity intensity fluctuations, and the consequent radiation pressure fluctuations, by a factor of two below the quantum noise limit. We show that this is achievable in the presence of large classical intensity fluctuations on the incident laser beam. The benefits of this scheme are a consequence of the sub-Poissonian intensity statistics of the field inside a feedback loop, and the quantum non-demolition nature of radiation pressure noise as a readout system for the intra-cavity intensity fluctuations. △ Less

Submitted 25 November, 1998; v1 submitted 5 November, 1998; originally announced November 1998.

Comments: 4 pages, 1 figure