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Nontrivial Boundary-Mediated Superconducting Transport in a TRSB Topological Iron-Based Superconductor
Authors:
Wenyao Liu,
Gabriel Natale,
Camron Farhang,
Michael Geiwitz,
Qishuo Tan,
Xingyao Guo,
Mason Gray,
Vincent LambertiJazzmin Victorin,
Huairuo Zhang,
James L. Hart,
Vsevolod Belosevich,
Xi Ling,
Qiong Ma,
Wan Kyu Park,
Kenji Watanabe,
Takashi Taniguchi,
Judy J. Cha,
Albert V. Davydov,
Kin Chung Fong,
Ethan Arnault,
Genda Gu,
Rui-Xing Zhang,
Enrico Rossi,
Jing Xia,
Kenneth S. Burch
Abstract:
The interplay of superconductivity, band topology, and spontaneous time-reversal-symmetry breaking (TRSB) is expected to enable topological superconducting boundary states. FeTe0.55Se0.45 provides a promising single-material platform because it combines superconductivity, nontrivial band topology, and spontaneous magnetization in the superconducting state. Here we report evidence for a boundary-me…
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The interplay of superconductivity, band topology, and spontaneous time-reversal-symmetry breaking (TRSB) is expected to enable topological superconducting boundary states. FeTe0.55Se0.45 provides a promising single-material platform because it combines superconductivity, nontrivial band topology, and spontaneous magnetization in the superconducting state. Here we report evidence for a boundary-mediated superconducting transport response in exfoliated Fe(Te,Se) devices. Polar Kerr measurements show that TRSB emerges below TKerr < Tc and coexists with superconductivity across multiple compositions, providing an independent symmetry-breaking scale for transport. Using crystallographically sharp, continuous edges and side-surface-dominant contacts, we find that topological FeTe0.55Se0.45 exhibits an anomalous conductance plateau absent in topologically trivial FeTe0.40Se0.60 and Fe1.02Te0.55Se0.45 under comparable measurements. This plateau requires uninterrupted sharp edges connecting source and drain, persists over micrometer-scale separations far exceeding the bulk coherence length, shows strongly suppressed thermal broadening, and collapses when the drain is moved to the top surface. Its temperature evolution follows the TRSB scale: the plateau remains weakly broadened below T*Kerr and disappears near TKerr rather than Tc. These doping-selective, edge-geometry-dependent, TRSB-correlated, and long-range nonlocal signatures establish experimental criteria for identifying boundary-mediated superconducting transport in FeTe0.55Se0.45 and motivate phase-sensitive and theoretical studies of its microscopic origin.
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Submitted 19 June, 2026;
originally announced June 2026.
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Weyl-Superconductivity revealed by Edge Mode mediated Nonlocal Transport
Authors:
Wenyao Liu,
Gabriel Natale,
Camron Farhang,
Michael Geiwitz,
Kewen Huang,
Qishuo Tan,
Xingyao Guo,
Mason Gray,
Vincent Lamberti,
Jazzmin Victorin,
Huairuo Zhang,
James L. Hart,
Vsevolod Belosevich,
Xi Ling,
Qiong Ma,
Wan Kyu Park,
Kenji Watanabe,
Takashi Taniguchi,
Judy J. Cha,
Albert V. Davydov,
Kin Chung Fong,
Ethan Arnault,
Genda Gu,
Rui-Xing Zhang,
Enrico Rossi
, et al. (2 additional authors not shown)
Abstract:
Topological superconductivity (TSC) hosts exotic modes enabling error-free quantum computation and low-temperature spintronics. Despite preliminary evidence of edge modes, unambiguous signatures remain undetected. Here, we report the first observation of protected, non-local transport from the edge modes of the potential Weyl-superconductor \ch{FeTe_{0.55}Se_{0.45}}. Namely resonant charge injecti…
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Topological superconductivity (TSC) hosts exotic modes enabling error-free quantum computation and low-temperature spintronics. Despite preliminary evidence of edge modes, unambiguous signatures remain undetected. Here, we report the first observation of protected, non-local transport from the edge modes of the potential Weyl-superconductor \ch{FeTe_{0.55}Se_{0.45}}. Namely resonant charge injection, ballistic transport, and extraction via edge modes. An anomalous conductance plateau emerges only when topological, superconducting, and magnetic phases coexist, with source-drain contacts coupled via the edge. Moving the drain to the bulk switches the non-local transport process to a local Andreev process, generating a zero-bias conductance peak (ZBCP). The edge mode's topological protection is confirmed by its insensitivity to external magnetic fields and increasing temperatures until the spontaneous magnetization is substantially suppressed. Our findings provide a new methodology to demonstrate TSC edge states in \ch{FeTe_{0.55}Se_{0.45}} via topologically protected non-local transport.
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Submitted 1 July, 2025;
originally announced July 2025.
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Cavity Soliton-Induced Topological Edge States
Authors:
Christian R. Leefmans,
Nicolas Englebert,
James Williams,
Robert M. Gray,
Nathan Goldman,
Simon-Pierre Gorza,
François Leo,
Alireza Marandi
Abstract:
Over the past decade, cavity solitons have attracted substantial attention for their rich dynamics and their myriad potential applications. Recently, there has been growing interest in understanding cavity solitons in systems of coupled resonators, where both new physics and applications can emerge. While numerous works have theoretically studied the interplay between cavity solitons and lattice t…
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Over the past decade, cavity solitons have attracted substantial attention for their rich dynamics and their myriad potential applications. Recently, there has been growing interest in understanding cavity solitons in systems of coupled resonators, where both new physics and applications can emerge. While numerous works have theoretically studied the interplay between cavity solitons and lattice topology, experimental demonstrations of cavity solitons in topological lattices remain elusive. Here, we experimentally realize cavity solitons in a Su-Schrieffer-Heeger (SSH) lattice and illustrate that the synergy between topology and soliton formation dynamics can induce soliton formation at the boundaries of a topological SSH lattice. Our work illustrates the rich physics of cavity solitons in topological lattices and demonstrates a flexible approach to study solitons in large-scale coupled resonator arrays.
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Submitted 8 November, 2023;
originally announced November 2023.
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Dislocation healing during hydrogen absorption and desorption in palladium
Authors:
T. A. Webb,
C. J. Webb,
E. MacA. Gray
Abstract:
An in-situ neutron diffraction investigation of the annealing and healing of dislocations in the bulk Pd-D2 system was carried out. Lattice misfit between the alpha and beta hydride phases produces dislocations during the phase transition in either direction, relieving elastic strain, which is reflected in reduced pressure hysteresis compared to the spinodal hysteresis. The effects on the dislocat…
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An in-situ neutron diffraction investigation of the annealing and healing of dislocations in the bulk Pd-D2 system was carried out. Lattice misfit between the alpha and beta hydride phases produces dislocations during the phase transition in either direction, relieving elastic strain, which is reflected in reduced pressure hysteresis compared to the spinodal hysteresis. The effects on the dislocation density of annealing the metal under vacuum, of annealing in the beta hydride phase, and of the phase transformation itself were investigated by measuring diffraction peak breadths during annealing and hydrogen cycling. During annealing under vacuum the dislocations were removed at a lower temperature than was previously reported, but annealing in the beta phase gave nearly the same result. However, when cycling hydrogen in and out of the sample, the dislocation density decreased much faster with increasing temperature compared to annealing. In other words the process of phase transformation allows for healing of dislocations at lower temperatures than would be required to anneal them purely by heating. This healing effect was observed during both absorption and desorption. This result illuminates the mechanism by which misfit dislocations can be healed at the same rate that they are created in a sample undergoing absorption-desorption cycling, as proposed in theoretical models of the origin of pressure hysteresis.
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Submitted 18 April, 2022;
originally announced April 2022.
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AC susceptometry of 2D van der Waals magnets enabled by the coherent control of quantum sensors
Authors:
Xin-Yue Zhang,
Yu-Xuan Wang,
Thomas A. Tartaglia,
Thomas Ding,
Mason J. Gray,
Kenneth S. Burch,
Fazel Tafti,
Brian B. Zhou
Abstract:
Precision magnetometry is fundamental to the development of novel magnetic materials and devices. Recently, the nitrogen-vacancy (NV) center in diamond has emerged as a promising probe for static magnetism in 2D van der Waals materials, capable of quantitative imaging with nanoscale spatial resolution. However, the dynamic character of magnetism, crucial for understanding the magnetic phase transi…
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Precision magnetometry is fundamental to the development of novel magnetic materials and devices. Recently, the nitrogen-vacancy (NV) center in diamond has emerged as a promising probe for static magnetism in 2D van der Waals materials, capable of quantitative imaging with nanoscale spatial resolution. However, the dynamic character of magnetism, crucial for understanding the magnetic phase transition and achieving technological applications, has rarely been experimentally accessible in single 2D crystals. Here, we coherently control the NV center's spin precession to achieve ultra-sensitive, quantitative ac susceptometry of a 2D ferromagnet. Combining dc hysteresis with ac susceptibility measurements varying temperature, field, and frequency, we illuminate the formation, mobility, and consolidation of magnetic domain walls in few-layer CrBr3. We show that domain wall mobility is enhanced in ultrathin CrBr3, with minimal decrease for excitation frequencies exceeding hundreds of kilohertz, and is influenced by the domain morphology and local pinning of the flake. Our technique extends NV magnetometry to the multi-functional ac and dc magnetic characterization of wide-ranging spintronic materials at the nanoscale.
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Submitted 17 May, 2021;
originally announced May 2021.
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A Cleanroom in a Glovebox
Authors:
Mason J. Gray,
Narendra Kumar,
Ryan O'Connor,
Marcel Hoek,
Erin Sheridan,
Meaghan C. Doyle,
Marisa L. Romanelli,
Gavin B. Osterhoudt,
Yiping Wang,
Vincent Plisson,
Shiming Lei,
Ruidan Zhong,
Bryan Rachmilowitz,
He Zhao,
Hikari Kitadai,
Steven Shepard,
Leslie M. Schoop,
G. D. Gu,
Ilija Zeljkovic,
Xi Ling,
K. S. Burch
Abstract:
The exploration of new materials, novel quantum phases, and devices requires ways to prepare cleaner samples with smaller feature sizes. Initially, this meant the use of a cleanroom that limits the amount and size of dust particles. However, many materials are highly sensitive to oxygen and water in the air. Furthermore, the ever-increasing demand for a quantum workforce, trained and able to use t…
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The exploration of new materials, novel quantum phases, and devices requires ways to prepare cleaner samples with smaller feature sizes. Initially, this meant the use of a cleanroom that limits the amount and size of dust particles. However, many materials are highly sensitive to oxygen and water in the air. Furthermore, the ever-increasing demand for a quantum workforce, trained and able to use the equipment for creating and characterizing materials, calls for a dramatic reduction in the cost to create and operate such facilities. To this end, we present our cleanroom-in-a-glovebox, a system which allows for the fabrication and characterization of devices in an inert argon atmosphere. We demonstrate the ability to perform a wide range of characterization as well as fabrication steps, without the need for a dedicated room, all in an argon environment. Connection to a vacuum suitcase is also demonstrated to enable receiving from and transfer to various ultra-high vacuum (UHV) equipment including molecular-beam epitaxy (MBE) and scanning tunneling microscopy (STM).
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Submitted 27 July, 2020;
originally announced July 2020.
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Modulation Doping via a 2d Atomic Crystalline Acceptor
Authors:
Yiping Wang,
Jesse Balgley,
Eli Gerber,
Mason Gray,
Narendra Kumar,
Xiaobo Lu,
Jia-Qiang Yan,
Arash Fereidouni,
Rabindra Basnet,
Seok Joon Yun,
Dhavala Suri,
Hikari Kitadai,
Takashi Taniguchi,
Kenji Watanabe,
Xi Ling,
Jagadeesh Moodera,
Young Hee Lee,
Hugh O. H. Churchill,
Jin Hu,
Li Yang,
Eun-Ah Kim,
David G. Mandrus,
Erik A. Henriksen,
Kenneth S. Burch
Abstract:
Two-dimensional (2d) nano-electronics, plasmonics, and emergent phases require clean and local charge control, calling for layered, crystalline acceptors or donors. Our Raman, photovoltage, and electrical conductance measurements combined with \textit{ab initio} calculations establish the large work function and narrow bands of $α$-RuCl$_3$ enable modulation doping of exfoliated, chemical vapor de…
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Two-dimensional (2d) nano-electronics, plasmonics, and emergent phases require clean and local charge control, calling for layered, crystalline acceptors or donors. Our Raman, photovoltage, and electrical conductance measurements combined with \textit{ab initio} calculations establish the large work function and narrow bands of $α$-RuCl$_3$ enable modulation doping of exfoliated, chemical vapor deposition (CVD), and molecular beam epitaxy (MBE) materials. Short-ranged lateral doping (${\leq}65\ \text{nm}$) and high homogeneity are achieved in proximate materials with a single layer of \arucl. This leads to the highest monolayer graphene (mlg) mobilities ($4,900\ \text{cm}^2/ \text{Vs}$) at these high hole densities ($3\times10^{13}\ \text{cm}^{-2}$); and yields larger charge transfer to bilayer graphene (blg) ($6\times10^{13}\ \text{cm}^{-2}$). We further demonstrate proof of principle optical sensing, control via twist angle, and charge transfer through hexagonal boron nitride (hBN).
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Submitted 15 July, 2020; v1 submitted 13 July, 2020;
originally announced July 2020.
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Grain size segregation during bedload transport on steep slopes
Authors:
Rémi Chassagne,
Raphaël Maurin,
Julien Chauchat,
J. M. N. T. Gray,
Philippe Frey
Abstract:
Size segregation in bedload transport is studied numerically with a coupled fluid-discrete element model. Starting from an initial deposit of small spherical particles on top of a large particle bed, the segregation dynamics of the bed is studied as it is driven by the fluid flow. Focusing on the quasi-static part of the bed, the small particles are observed to segregate as a layer of constant thi…
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Size segregation in bedload transport is studied numerically with a coupled fluid-discrete element model. Starting from an initial deposit of small spherical particles on top of a large particle bed, the segregation dynamics of the bed is studied as it is driven by the fluid flow. Focusing on the quasi-static part of the bed, the small particles are observed to segregate as a layer of constant thickness at a velocity constant in time and independent of the number of small particles. The segregation velocity is observed to be directly linked to the inertial number at the bottom of the layer, and to increase linearly with the size ratio. While the macroscopic behavior is independent of the concentration in small particles, an analysis in the framework of the continuous model of (Thornton et al. 2006) shows that the dynamics results from an equilibrium between the influence of the local concentration and the inertial number forcing. Deriving an analytical solution of the continuous model, it is shown that the diffusion coefficient should have the same dependency on the inertial number as the segregation flux. Implementing the segregation and the diffusive fluxes in the continuous model, it is shown that they quantitatively reproduce the discrete simulations. These results improve the understanding of the size segregation dynamics and represent a step forward in the upscaling process of polydisperse granular flow in the context of turbulent bedload transport.
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Submitted 17 September, 2019;
originally announced September 2019.
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High mobility in a van der Waals layered antiferromagnetic metal
Authors:
Shiming Lei,
Jingjing Lin,
Yanyu Jia,
Mason Gray,
Andreas Topp,
Gelareh Farahi,
Sebastian Klemenz,
Tong Gao,
Fanny Rodolakis,
Jessica L. McChesney,
Christian R. Ast,
Ali Yazdani,
Kenneth S. Burch,
Sanfeng Wu,
N. Phuan Ong,
Leslie M. Schoop
Abstract:
Magnetic van der Waals (vdW) materials have been heavily pursued for fundamental physics as well as for device design. Despite the rapid advances, so far magnetic vdW materials are mainly insulating or semiconducting, and none of them possesses a high electronic mobility - a property that is rare in layered vdW materials in general. The realization of a magnetic high-mobility vdW material would op…
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Magnetic van der Waals (vdW) materials have been heavily pursued for fundamental physics as well as for device design. Despite the rapid advances, so far magnetic vdW materials are mainly insulating or semiconducting, and none of them possesses a high electronic mobility - a property that is rare in layered vdW materials in general. The realization of a magnetic high-mobility vdW material would open the possibility for novel magnetic twistronic or spintronic devices. Here we report very high carrier mobility in the layered vdW antiferromagnet GdTe3. The electron mobility is beyond 60,000 cm2 V-1 s-1, which is the highest among all known layered magnetic materials, to the best of our knowledge. Among all known vdW materials, the mobility of bulk GdTe3 is comparable to that of black phosphorus, and is only surpassed by graphite. By mechanical exfoliation, we further demonstrate that GdTe3 can be exfoliated to ultrathin flakes of three monolayers, and that the magnetic order and relatively high mobility is retained in approximately 20-nm-thin flakes.
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Submitted 14 August, 2019; v1 submitted 7 March, 2019;
originally announced March 2019.
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Evidence for Helical Hinge Zero Modes in an Fe-Based Superconductor
Authors:
Mason J. Gray,
Josef Freudenstein,
Shu Yang F. Zhao,
Ryan OConnor,
Samuel Jenkins,
Narendra Kumar,
Marcel Hoek,
Abigail Kopec,
Takashi Taniguchi,
Kenji Watanabe,
Ruidan Zhong,
G. D. Gu,
K. S. Burch
Abstract:
Combining topology and superconductivity provides a powerful tool for investigating fundamental physics as well as a route to fault-tolerant quantum computing. There is mounting evidence that the Fe-Based Superconductor FeTe$_{0.55}$Se$_{0.45}$ (FTS) may also be topologically non-trivial. Should the superconducting order be s$^{\pm}$, then FTS could be a higher order topological superconductor wit…
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Combining topology and superconductivity provides a powerful tool for investigating fundamental physics as well as a route to fault-tolerant quantum computing. There is mounting evidence that the Fe-Based Superconductor FeTe$_{0.55}$Se$_{0.45}$ (FTS) may also be topologically non-trivial. Should the superconducting order be s$^{\pm}$, then FTS could be a higher order topological superconductor with Helical Hinge Zero Modes (HHZM).To test the presence of these modes we developed a new method for making normal metal/superconductor junctions via 2D atomic crystal heterostructures. As expected,junctions in contact with the hinge reveal a sharp zero-bias anomaly whose suppression with temperature and magnetic field only along the c-axis are completely consistent with the presence of HHZM. This feature is completely absent when tunneling purely into the c-axis, and its characteristics are also inconsistent with other origins of zero bias anomalies. Furthermore, additional measurements with soft-point contacts in bulk samples with various Fe interstitial contents demonstrate the intrinsic nature of the observed mode. Thus we provide evidence that FTS is indeed a higher order topological superconductor as well as a new method for probing 2D atomic crystals.
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Submitted 10 July, 2019; v1 submitted 27 February, 2019;
originally announced February 2019.
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Coulomb blockade in an atomically thin quantum dot coupled to a tunable Fermi reservoir
Authors:
Mauro Brotons-Gisbert,
Artur Branny,
Santosh Kumar,
Raphaël Picard,
Raphaël Proux,
Mason Gray,
Kenneth S. Burch,
Kenji Watanabe,
Takashi Taniguchi,
Brian D. Gerardot
Abstract:
Gate-tunable quantum-mechanical tunnelling of particles between a quantum confined state and a nearby Fermi reservoir of delocalized states has underpinned many advances in spintronics and solid-state quantum optics. The prototypical example is a semiconductor quantum dot separated from a gated contact by a tunnel barrier. This enables Coulomb blockade, the phenomenon whereby electrons or holes ca…
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Gate-tunable quantum-mechanical tunnelling of particles between a quantum confined state and a nearby Fermi reservoir of delocalized states has underpinned many advances in spintronics and solid-state quantum optics. The prototypical example is a semiconductor quantum dot separated from a gated contact by a tunnel barrier. This enables Coulomb blockade, the phenomenon whereby electrons or holes can be loaded one-by-one into a quantum dot. Depending on the tunnel-coupling strength, this capability facilitates single spin quantum bits or coherent many-body interactions between the confined spin and the Fermi reservoir. Van der Waals (vdW) heterostructures, in which a wide range of unique atomic layers can easily be combined, offer novel prospects to engineer coherent quantum confined spins, tunnel barriers down to the atomic limit or a Fermi reservoir beyond the conventional flat density of states. However, gate-control of vdW nanostructures at the single particle level is needed to unlock their potential. Here we report Coulomb blockade in a vdW heterostructure consisting of a transition metal dichalcogenide quantum dot coupled to a graphene contact through an atomically thin hexagonal boron nitride (hBN) tunnel barrier. Thanks to a tunable Fermi reservoir, we can deterministically load either a single electron or a single hole into the quantum dot. We observe hybrid excitons, composed of localized quantum dot states and delocalized continuum states, arising from ultra-strong spin-conserving tunnel coupling through the atomically thin tunnel barrier. Probing the charged excitons in applied magnetic fields, we observe large gyromagnetic ratios (~8). Our results establish a foundation for engineering next-generation devices to investigate either novel regimes of Kondo physics or isolated quantum bits in a vdW heterostructure platform.
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Submitted 24 April, 2019; v1 submitted 5 October, 2018;
originally announced October 2018.
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Colossal Bulk Photovoltaic Effect in a Weyl Semimetal
Authors:
Gavin B. Osterhoudt,
Laura K. Diebel,
Mason J. Gray,
Xu Yang,
John Stanco,
Xiangwei Huang,
Bing Shen,
Ni Ni,
Philip J. W. Moll,
Ying Ran,
Kenneth S. Burch
Abstract:
Broadband, efficient and fast conversion of light to electricity is crucial for sensing and clean energy. Here we reveal the largest observed bulk photo-voltaic effect (BPVE), an intrinsic mechanism predicted to be ultrafast and exceed the Shockley-Quiesser limit. This discovery results from combining recent developments in the connection of BPVE to topology, Weyl semimetals and focused-ion beam f…
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Broadband, efficient and fast conversion of light to electricity is crucial for sensing and clean energy. Here we reveal the largest observed bulk photo-voltaic effect (BPVE), an intrinsic mechanism predicted to be ultrafast and exceed the Shockley-Quiesser limit. This discovery results from combining recent developments in the connection of BPVE to topology, Weyl semimetals and focused-ion beam fabrication. Our room temperature observation of the first BPVE in the mid-IR, is enabled by microscopic devices of the Weyl semimetal TaAs. Detailed symmetry analysis enables unambiguous separation of this response from competing photo-thermal effects. The size and wavelength range of the shift current offers new opportunities in optical detectors, clean energy, and topology, while directly demonstrating the utility of Weyl semimetals for applications.
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Submitted 16 October, 2018; v1 submitted 13 December, 2017;
originally announced December 2017.
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Spin transport and dynamics in all-oxide perovskite La$_{2/3}$Sr$_{1/3}$MnO$_3$/SrRuO$_3$ bilayers probed by ferromagnetic resonance
Authors:
Satoru Emori,
Urusa S. Alaan,
Matthew T. Gray,
Volker Sluka,
Yizhang Chen,
Andrew D. Kent,
Yuri Suzuki
Abstract:
Thin films of perovskite oxides offer the possibility of combining emerging concepts of strongly correlated electron phenomena and spin current in magnetic devices. However, spin transport and magnetization dynamics in these complex oxide materials are not well understood. Here, we experimentally quantify spin transport parameters and magnetization damping in epitaxial perovskite ferromagnet/param…
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Thin films of perovskite oxides offer the possibility of combining emerging concepts of strongly correlated electron phenomena and spin current in magnetic devices. However, spin transport and magnetization dynamics in these complex oxide materials are not well understood. Here, we experimentally quantify spin transport parameters and magnetization damping in epitaxial perovskite ferromagnet/paramagnet bilayers of La$_{2/3}$Sr$_{1/3}$MnO$_3$/SrRuO$_3$ (LSMO/SRO) by broadband ferromagnetic resonance spectroscopy. From the SRO thickness dependence of Gilbert damping, we estimate a short spin diffusion length of $\lesssim$1 nm in SRO and an interfacial spin-mixing conductance comparable to other ferromagnet/paramagnetic-metal bilayers. Moreover, we find that anisotropic non-Gilbert damping due to two-magnon scattering also increases with the addition of SRO. Our results demonstrate LSMO/SRO as a spin-source/spin-sink system that may be a foundation for examining spin-current transport in various perovskite heterostructures.
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Submitted 20 October, 2016;
originally announced October 2016.
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Well-posed continuum equations for granular flow with compressibility and $μ(I)$-rheology
Authors:
T. Barker,
D. G. Schaeffer,
M. Shearer,
J. M. N. T Gray
Abstract:
Continuum modelling of granular flow has been plagued with the issue of ill-posed equations for a long time. Equations for incompressible, two-dimensional flow based on the Coulomb friction law are ill-posed regardless of the deformation, whereas the rate-dependent $μ(I)$-rheology is ill-posed when the non-dimensional strain-rate $I$ is too high or too low. Here, incorporating ideas from Critical-…
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Continuum modelling of granular flow has been plagued with the issue of ill-posed equations for a long time. Equations for incompressible, two-dimensional flow based on the Coulomb friction law are ill-posed regardless of the deformation, whereas the rate-dependent $μ(I)$-rheology is ill-posed when the non-dimensional strain-rate $I$ is too high or too low. Here, incorporating ideas from Critical-State Soil Mechanics, we derive conditions for well-posedness of PDEs that combine compressibility with $I$-dependent rheology. When the $I$-dependence comes from a specific friction coefficient $μ(I)$, our results show that, with compressibility, the equations are well-posed for all deformation rates provided that $μ(I)$ satisfies certain minimal, physically natural, inequalities.
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Submitted 14 October, 2016;
originally announced October 2016.
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Kinetics of dislocation annealing and the effect of trapped hydrogen, investigated with in-situ diffraction
Authors:
T. A. Webb,
C. J. Webb,
C. V. Tapia-Bastidas,
E. MacA. Gray
Abstract:
In-situ powder diffraction was used to study the annealing of dislocations in the archetypal hydrogen absorbers Pd and LaNi5. The relationship between dislocations and trapped hydrogen was explored using thermally induced desorption. It was found that the dislocations in Pd caused by hydrogen absorption anneal over a wide range of temperatures and that although they start to anneal below 250…
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In-situ powder diffraction was used to study the annealing of dislocations in the archetypal hydrogen absorbers Pd and LaNi5. The relationship between dislocations and trapped hydrogen was explored using thermally induced desorption. It was found that the dislocations in Pd caused by hydrogen absorption anneal over a wide range of temperatures and that although they start to anneal below 250 $^\circ$C, temperatures well above 750 $^\circ$C are required to fully anneal the metal. It was shown that allowing further time at lower temperatures does not further anneal the metal. It is suggested that this is due to dislocation tangling and pinning, causing different temperatures to be required for different pinning defects. It was found that hydrogen trapped in LaNi5 is released in a wide range of temperatures and it was therefore concluded that hydrogen is trapped in the dislocation strain field and dislocation core as well as vacancies. The direct comparison of deuterium release and dislocation density showed no correlation, in agreement with previous indirect comparisons. Dislocations in LaNi5 were shown to anneal at temperatures as low as 150 $^\circ$C, in contrast to previous reports which suggested more than 500 $^\circ$C was required. This lower annealing temperature for dislocations at least partly explains why low temperature ageing increases the pressure hysteresis in hydrogen cycled LaNi5.
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Submitted 18 September, 2016;
originally announced September 2016.
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Superconductivity in palladium hydride and deuteride at 52-61 kelvin
Authors:
H. M. Syed,
T. J. Gould,
C. J. Webb,
E. MacA. Gray
Abstract:
We report the observation of conventional superconductivity at the highest temperature yet attained without mechanical compression, around 54 kelvin in palladium-hydride and 60 kelvin in palladium-deuteride. The remarkable increase in Tc compared to the previously known value was achieved by rapidly cooling the hydride and deuteride after loading with hydrogen or deuterium at elevated temperature.…
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We report the observation of conventional superconductivity at the highest temperature yet attained without mechanical compression, around 54 kelvin in palladium-hydride and 60 kelvin in palladium-deuteride. The remarkable increase in Tc compared to the previously known value was achieved by rapidly cooling the hydride and deuteride after loading with hydrogen or deuterium at elevated temperature. Our results encourage hope that conventional superconductivity under ambient conditions will be discovered in materials with very high hydrogen density, as predicted more than a decade ago.
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Submitted 5 August, 2016;
originally announced August 2016.
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Metallicity in Ultra-Thin Oxygen-Deficient SrTiO$_3$ Thin Films
Authors:
Purnima P. Balakrishnan,
Urusa S. Alaan,
Matthew T. Gray,
Yuri Suzuki
Abstract:
We report on the observation of metallic behavior in thin films of oxygen-deficient SrTiO$_3$ - down to 9 unit cells - when coherently strained on (001) SrTiO$_3$ or DyScO$_3$-buffered (001) SrTiO$_3$ substrates. These films have carrier concentrations of up to 2$\times10^{22}$ cm$^{-3}$ and mobilities of up to 19,000 cm$^2$/V-s at 2 K. There exists a non-conducting layer in our SrTiO$_{3-δ}$ film…
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We report on the observation of metallic behavior in thin films of oxygen-deficient SrTiO$_3$ - down to 9 unit cells - when coherently strained on (001) SrTiO$_3$ or DyScO$_3$-buffered (001) SrTiO$_3$ substrates. These films have carrier concentrations of up to 2$\times10^{22}$ cm$^{-3}$ and mobilities of up to 19,000 cm$^2$/V-s at 2 K. There exists a non-conducting layer in our SrTiO$_{3-δ}$ films that is larger in films with lower carrier concentrations. This non-conducting layer can be attributed to a surface depletion layer due to a Fermi level pinning potential. The depletion width, transport, and structural properties are not greatly affected by the insertion of a DyScO$_3$ buffer between the SrTiO$_3$ film and SrTiO$_3$ substrate.
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Submitted 3 June, 2016;
originally announced June 2016.
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Magneto-Elastic Coupling in a potential ferromagnetic 2D Atomic Crystal
Authors:
Yao Tian,
Mason J. Gray,
Huiwen Ji,
R. J. Cava,
Kenneth S. Burch
Abstract:
Cr2Ge2Te6 has been of interest for decades, as it is one of only a few naturally forming ferromagnetic semiconductors. Recently, this material has been revisited due to its potential as a 2 dimensional semiconducting ferromagnet and a substrate to induce anomalous quantum Hall states in topological insulators. However, many relevant properties of Cr2Ge2Te6 still remain poorly understood, especiall…
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Cr2Ge2Te6 has been of interest for decades, as it is one of only a few naturally forming ferromagnetic semiconductors. Recently, this material has been revisited due to its potential as a 2 dimensional semiconducting ferromagnet and a substrate to induce anomalous quantum Hall states in topological insulators. However, many relevant properties of Cr2Ge2Te6 still remain poorly understood, especially the spin-phonon coupling crucial to spintronic, multiferrioc, thermal conductivity, magnetic proximity and the establishment of long range order on the nanoscale. We explore the interplay between the lattice and magnetism through high resolution micro-Raman scattering measurements over the temperature range from 10 K to 325 K. Strong spin-phonon coupling effects are confirmed from multiple aspects: two low energy modes splits in the ferromagnetic phase, magnetic quasielastic scattering in paramagnetic phase, the phonon energies of three modes show clear upturn below Tc, and the phonon linewidths change dramatically below Tc as well. Our results provide the first demonstration of spin-phonon coupling in a potential 2 dimensional atomic crystal.
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Submitted 29 April, 2016;
originally announced April 2016.
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Stabilizing membrane domains antagonizes n-alcohol anesthesia
Authors:
Benjamin B. Machta,
Ellyn Gray,
Mariam Nouri,
Nicola L. C. McCarthy,
Erin M. Gray,
Ann L. Miller,
Nicholas J. Brooks,
Sarah L. Veatch
Abstract:
Diverse molecules induce general anesthesia with potency strongly correlated both with their hydrophobicity and their effects on certain ion channels. We recently observed that several n-alcohol anesthetics inhibit heterogeneity in plasma membrane derived vesicles by lowering the critical temperature ($T_c$) for phase separation. Here we exploit conditions that stabilize membrane heterogeneity to…
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Diverse molecules induce general anesthesia with potency strongly correlated both with their hydrophobicity and their effects on certain ion channels. We recently observed that several n-alcohol anesthetics inhibit heterogeneity in plasma membrane derived vesicles by lowering the critical temperature ($T_c$) for phase separation. Here we exploit conditions that stabilize membrane heterogeneity to further test the correlation between the anesthetic potency of n-alcohols and effects on $T_c$. First we show that hexadecanol acts oppositely to n-alcohol anesthetics on membrane mixing and antagonizes ethanol induced anesthesia in a tadpole behavioral assay. Second, we show that two previously described `intoxication reversers' raise $T_c$ and counter ethanol's effects in vesicles, mimicking the findings of previous electrophysiological and behavioral measurements. Third, we find that hydrostatic pressure, long known to reverse anesthesia, also raises $T_c$ in vesicles with a magnitude that counters the effect of butanol at relevant concentrations and pressures. Taken together, these results demonstrate that $ΔT_c$ predicts anesthetic potency for n-alcohols better than hydrophobicity in a range of contexts, supporting a mechanistic role for membrane heterogeneity in general anesthesia.
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Submitted 5 June, 2016; v1 submitted 1 April, 2016;
originally announced April 2016.
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An Underlying Asymmetry within Particle-size Segregation
Authors:
Kasper van der Vaart,
Parmesh Gajjar,
Gaël Epely-Chauvin,
Nicolas Andreini,
J. M. N. T. Gray,
Christophe Ancey
Abstract:
We experimentally study particle scale dynamics during segregation of a bidisperse mixture under oscillatory shear. Large and small particles show an underlying asymmetry that is dependent on the local particle concentration, with small particles segregating faster in regions of many large particles and large particles segregating slower in regions of many small particles. We quantify the asymmetr…
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We experimentally study particle scale dynamics during segregation of a bidisperse mixture under oscillatory shear. Large and small particles show an underlying asymmetry that is dependent on the local particle concentration, with small particles segregating faster in regions of many large particles and large particles segregating slower in regions of many small particles. We quantify the asymmetry on bulk and particle scales, and capture it theoretically. This gives new physical insight into segregation and reveals a similarity with sedimentation, traffic flow and particle diffusion.
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Submitted 8 May, 2015; v1 submitted 27 January, 2015;
originally announced January 2015.
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An accurate determination of the Avogadro constant by counting the atoms in a 28Si crystal
Authors:
B. Andreas,
Y. Azuma,
G. Bartl,
P. Becker,
H. Bettin,
M. Borys,
I. Busch,
M. Gray,
P. Fuchs,
K. Fujii,
H. Fujimoto,
E. Kessler,
M. Krumrey,
U. Kuetgens,
N. Kuramoto,
G. Mana,
P. Manson,
E. Massa,
S. Mizushima,
A. Nicolaus,
A. Picard,
A. Pramann,
O. Rienitz,
D. Schiel,
S. Valkiers
, et al. (1 additional authors not shown)
Abstract:
The Avogadro constant links the atomic and the macroscopic properties of matter. Since the molar Planck constant is well known via the measurement of the Rydberg constant, it is also closely related to the Planck constant. In addition, its accurate determination is of paramount importance for a definition of the kilogram in terms of a fundamental constant. We describe a new approach for its determ…
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The Avogadro constant links the atomic and the macroscopic properties of matter. Since the molar Planck constant is well known via the measurement of the Rydberg constant, it is also closely related to the Planck constant. In addition, its accurate determination is of paramount importance for a definition of the kilogram in terms of a fundamental constant. We describe a new approach for its determination by "counting" the atoms in 1 kg single-crystal spheres, which are highly enriched with the 28Si isotope. It enabled isotope dilution mass spectroscopy to determine the molar mass of the silicon crystal with unprecedented accuracy. The value obtained, 6.02214084(18) x 10^23 mol^-1, is the most accurate input datum for a new definition of the kilogram.
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Submitted 12 October, 2010;
originally announced October 2010.
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Residual attractive force between superparamagnetic nanoparticles
Authors:
John F. Dobson,
Evan MacA. Gray
Abstract:
A superparamagnetic nanoparticle (SPN) is a nanometre-sized piece of a material that would, in bulk, be a permanent magnet. In the SPN the individual atomic spins are aligned via Pauli effects into a single giant moment that has easy orientations set by shape or magnetocrystalline anisotropy. Above a size-dependent blocking temperature $T_{b}(V,τ_{obs})$, thermal fluctuations destroy the average…
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A superparamagnetic nanoparticle (SPN) is a nanometre-sized piece of a material that would, in bulk, be a permanent magnet. In the SPN the individual atomic spins are aligned via Pauli effects into a single giant moment that has easy orientations set by shape or magnetocrystalline anisotropy. Above a size-dependent blocking temperature $T_{b}(V,τ_{obs})$, thermal fluctuations destroy the average moment by flipping the giant spin between easy orientations at a rate that is rapid on the scale of the observation time $τ_{obs}$.
We show that, depite the vanising of the average moment, two SPNs experience a net attractive force of magnetic origin, analogous to the van der Waals force between molecules that lack a permanent electric dipole. This could be relevant for ferrofluids, for the clumping of SPNs used for drug delivery, and for ultra-dense magnetic recording media.
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Submitted 20 February, 2009;
originally announced February 2009.