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Nature Physics

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https://www.readbyqxmd.com/read/29861780/observation-of-roton-mode-population-in-a-dipolar-quantum-gas
#1
L Chomaz, R M W van Bijnen, D Petter, G Faraoni, S Baier, J H Becher, M J Mark, F Wächtler, L Santos, F Ferlaino
The concept of a roton, a special kind of elementary excitation, forming a minimum of energy at finite momentum, has been essential to understand the properties of superfluid 4 He 1. In quantum liquids, rotons arise from the strong interparticle interactions, whose microscopic description remains debated 2. In the realm of highly-controllable quantum gases, a roton mode has been predicted to emerge due to magnetic dipole-dipole interactions despite of their weakly-interacting character 3. This prospect has raised considerable interest 4-12; yet roton modes in dipolar quantum gases have remained elusive to observations...
May 2018: Nature Physics
https://www.readbyqxmd.com/read/29760764/human-brain-organoids-on-a-chip-reveal-the-physics-of-folding
#2
Eyal Karzbrun, Aditya Kshirsagar, Sidney R Cohen, Jacob H Hanna, Orly Reiner
Human brain wrinkling has been implicated in neurodevelopmental disorders and yet its origins remain unknown. Polymer gel models suggest that wrinkling emerges spontaneously due to compression forces arising during differential swelling, but these ideas have not been tested in a living system. Here, we report the appearance of surface wrinkles during the in vitro development and self-organization of human brain organoids in a micro-fabricated compartment that supports in situ imaging over a timescale of weeks...
May 2018: Nature Physics
https://www.readbyqxmd.com/read/29736183/universality-of-clone-dynamics-during-tissue-development
#3
Steffen Rulands, Fabienne Lescroart, Samira Chabab, Christopher J Hindley, Nicole Prior, Magdalena K Sznurkowska, Meritxell Huch, Anna Philpott, Cedric Blanpain, Benjamin D Simons
The emergence of complex organs is driven by the coordinated proliferation, migration and differentiation of precursor cells. The fate behaviour of these cells is reflected in the time evolution their progeny, termed clones, which serve as a key experimental observable. In adult tissues, where cell dynamics is constrained by the condition of homeostasis, clonal tracing studies based on transgenic animal models have advanced our understanding of cell fate behaviour and its dysregulation in disease (1, 2). But what can be learned from clonal dynamics in development, where the spatial cohesiveness of clones is impaired by tissue deformations during tissue growth? Drawing on the results of clonal tracing studies, we show that, despite the complexity of organ development, clonal dynamics may converge to a critical state characterized by universal scaling behaviour of clone sizes...
May 2018: Nature Physics
https://www.readbyqxmd.com/read/29736182/robust-integer-and-fractional-helical-modes-in-the-quantum-hall-effect
#4
Yuval Ronen, Yonatan Cohen, Daniel Banitt, Moty Heiblum, Vladimir Umansky
Electronic systems harboring one-dimensional helical modes, where spin and momentum are locked, have lately become an important field of its own. When coupled to a conventional superconductor, such systems are expected to manifest topological superconductivity; a unique phase hosting exotic Majorana zero modes. Even more interesting are fractional helical modes, yet to be observed, which open the route for realizing generalized parafermions. Possessing non-abelian exchange statistics, these quasiparticles may serve as building blocks in topological quantum computing...
April 2018: Nature Physics
https://www.readbyqxmd.com/read/29910827/synthetic-antiferromagnetic-spintronics
#5
R A Duine, Kyung-Jin Lee, Stuart S P Parkin, M D Stiles
Spintronic and nanomagnetic devices often derive their functionality from layers of different materials and the interfaces between them. This is especially true for synthetic antiferromagnets - two or more ferromagnetic layers that are separated by metallic spacers or tunnel barriers and which have antiparallel magnetizations. Here, we discuss the new opportunities that arise from synthetic antiferromagnets, as compared to crystal antiferromagnets or ferromagnets.
March 2018: Nature Physics
https://www.readbyqxmd.com/read/29422941/role-of-graph-architecture-in-controlling-dynamical-networks-with-applications-to-neural-systems
#6
Jason Z Kim, Jonathan M Soffer, Ari E Kahn, Jean M Vettel, Fabio Pasqualetti, Danielle S Bassett
Networked systems display complex patterns of interactions between components. In physical networks, these interactions often occur along structural connections that link components in a hard-wired connection topology, supporting a variety of system-wide dynamical behaviors such as synchronization. While descriptions of these behaviors are important, they are only a first step towards understanding and harnessing the relationship between network topology and system behavior. Here, we use linear network control theory to derive accurate closed-form expressions that relate the connectivity of a subset of structural connections (those linking driver nodes to non-driver nodes) to the minimum energy required to control networked systems...
2018: Nature Physics
https://www.readbyqxmd.com/read/29983725/coherent-control-of-an-opsin-in-living-brain-tissue
#7
Kush Paul, Parijat Sengupta, Eugene D Ark, Haohua Tu, Youbo Zhao, Stephen A Boppart
Retinal-based opsins are light-sensitive proteins. The photoisomerization reaction of these proteins has been studied outside cellular environments using ultrashort tailored light pulses1-5 . However, how living cell functions can be modulated via opsins by modifying fundamental nonlinear optical properties of light interacting with the retinal chromophore has remained largely unexplored. We report the use of chirped ultrashort near-infrared pulses to modulate light-evoked ionic current from Channelrhodopsin-2 (ChR2) in brain tissue, and consequently the firing pattern of neurons, by manipulating the phase of the spectral components of the light...
November 2017: Nature Physics
https://www.readbyqxmd.com/read/29109755/geometrical-frustration-yields-fiber-formation-in-self-assembly
#8
Martin Lenz, Thomas A Witten
Controlling the self-assembly of supramolecular structures is vital for living cells, and a central challenge for engineering at the nano- and microscales [1, 2]. Nevertheless, even particles without optimized shapes can robustly form well-defined morphologies. This is the case in numerous medical conditions where normally soluble proteins aggregate into fibers [3, 4]. Beyond the diversity of molecular mechanisms involved [5, 6], we propose that fibers generically arise from the aggregation of irregular particles with short-range interactions...
November 2017: Nature Physics
https://www.readbyqxmd.com/read/28883888/spectroscopic-evidence-of-a-new-energy-scale-for-superconductivity-in-h3s
#9
F Capitani, B Langerome, J-B Brubach, P Roy, A Drozdov, M I Eremets, E J Nicol, J P Carbotte, T Timusk
The discovery of a superconducting phase in sulfur hydride under high pressure with a critical temperature above 200 K has provided fresh impetus to the search for superconductors at ever higher temperatures. Although this systems displays all the hallmarks of superconductivity, the mechanism through which it arises remains to be determined. Here we provide a first optical spectroscopy study of this superconductor. Experimental results for the optical reflectivity of H3S, under hydrostatic pressure of 150 GPa, for several temperatures and over the range 60 to 600 meV of photon energies, are compared with theoretical calculations based on Eliashberg theory...
September 2017: Nature Physics
https://www.readbyqxmd.com/read/28781605/mottness-at-finite-doping-and-charge-instabilities-in-cuprates
#10
S Peli, S Dal Conte, R Comin, N Nembrini, A Ronchi, P Abrami, F Banfi, G Ferrini, D Brida, S Lupi, M Fabrizio, A Damascelli, M Capone, G Cerullo, C Giannetti
The influence of the Mott physics on the doping-temperature phase diagram of copper oxides represents a major issue that is subject of intense theoretical and experimental effort. Here, we investigate the ultrafast electron dynamics in prototypical single-layer Bi-based cuprates at the energy scale of the O-2p→Cu-3d charge-transfer (CT) process. We demonstrate a clear evolution of the CT excitations from incoherent and localized, as in a Mott insulator, to coherent and delocalized, as in a conventional metal...
August 2017: Nature Physics
https://www.readbyqxmd.com/read/28781604/high-frequency-microrheology-reveals-cytoskeleton-dynamics-in-living-cells
#11
Annafrancesca Rigato, Atsushi Miyagi, Simon Scheuring, Felix Rico
Living cells are viscoelastic materials, with the elastic response dominating at long timescales (≳1 ms)1. At shorter timescales, the dynamics of individual cytoskeleton filaments are expected to emerge, but active microrheology measurements on cells accessing this regime are scarce2. Here, we develop high-frequency microrheology (HF-MR) to probe the viscoelastic response of living cells from 1Hz to 100 kHz. We report the viscoelasticity of different cell types and upon cytoskeletal drug treatments. At previously inaccessible short timescales, cells exhibit rich viscoelastic responses that depend on the state of the cytoskeleton...
August 2017: Nature Physics
https://www.readbyqxmd.com/read/28781603/hot-spot-mediated-non-dissipative-and-ultrafast-plasmon-passage
#12
Eva-Maria Roller, Lucas V Besteiro, Claudia Pupp, Larousse Khosravi Khorashad, Alexander O Govorov, Tim Liedl
Plasmonic nanoparticles hold great promise as photon handling elements and as channels for coherent transfer of energy and information in future all-optical computing devices.1-5 Coherent energy oscillations between two spatially separated plasmonic entities via a virtual middle state exemplify electron-based population transfer, but their realization requires precise nanoscale positioning of heterogeneous particles.6-10 Here, we show the assembly and optical analysis of a triple particle system consisting of two gold nanoparticles with an inter-spaced silver island...
August 2017: Nature Physics
https://www.readbyqxmd.com/read/28706560/experimental-realization-and-characterization-of-an-electronic-lieb-lattice
#13
Marlou R Slot, Thomas S Gardenier, Peter H Jacobse, Guido C P van Miert, Sander N Kempkes, Stephan J M Zevenhuizen, Cristiane Morais Smith, Daniel Vanmaekelbergh, Ingmar Swart
Geometry, whether on the atomic or nanoscale, is a key factor for the electronic band structure of materials. Some specific geometries give rise to novel and potentially useful electronic bands. For example, a honeycomb lattice leads to Dirac-type bands where the charge carriers behave as massless particles [1]. Theoretical predictions are triggering the exploration of novel 2D geometries [2-10], such as graphynes, Kagomé and the Lieb lattice. The latter is the 2D analogue of the 3D lattice exhibited by perovskites [2]; it is a square-depleted lattice, which is characterised by a band structure featuring Dirac cones intersected by a flat band...
July 2017: Nature Physics
https://www.readbyqxmd.com/read/28890730/quantifying-the-quantum
#14
Stephan Schlamminger
No abstract text is available yet for this article.
June 2017: Nature Physics
https://www.readbyqxmd.com/read/27917231/magnetotail-energy-dissipation-during-an-auroral-substorm
#15
E V Panov, W Baumjohann, R A Wolf, R Nakamura, V Angelopoulos, J M Weygand, M V Kubyshkina
Violent releases of space plasma energy from the Earth's magnetotail during substorms produce strong electric currents and bright aurora. But what modulates these currents and aurora and controls dissipation of the energy released in the ionosphere? Using data from the THEMIS fleet of satellites and ground-based imagers and magnetometers, we show that plasma energy dissipation is controlled by field-aligned currents (FACs) produced and modulated during magnetotail topology change and oscillatory braking of fast plasma jets at 10-14 Earth radii in the nightside magnetosphere...
December 2016: Nature Physics
https://www.readbyqxmd.com/read/27917230/local-equilibrium-in-bird-flocks
#16
Thierry Mora, Aleksandra M Walczak, Lorenzo Del Castello, Francesco Ginelli, Stefania Melillo, Leonardo Parisi, Massimiliano Viale, Andrea Cavagna, Irene Giardina
The correlated motion of flocks is an instance of global order emerging from local interactions. An essential difference with analogous ferromagnetic systems is that flocks are active: animals move relative to each other, dynamically rearranging their interaction network. The effect of this off-equilibrium element is well studied theoretically, but its impact on actual biological groups deserves more experimental attention. Here, we introduce a novel dynamical inference technique, based on the principle of maximum entropy, which accodomates network rearrangements and overcomes the problem of slow experimental sampling rates...
December 2016: Nature Physics
https://www.readbyqxmd.com/read/27833647/parametric-amplification-of-a-superconducting-plasma-wave
#17
S Rajasekaran, E Casandruc, Y Laplace, D Nicoletti, G D Gu, S R Clark, D Jaksch, A Cavalleri
Many applications in photonics require all-optical manipulation of plasma waves1, which can concentrate electromagnetic energy on sub-wavelength length scales. This is difficult in metallic plasmas because of their small optical nonlinearities. Some layered superconductors support Josephson plasma waves (JPWs)2,3, involving oscillatory tunneling of the superfluid between capacitively coupled planes. Josephson plasma waves are also highly nonlinear4, and exhibit striking phenomena like cooperative emission of coherent terahertz radiation5,6, superconductor-metal oscillations7 and soliton formation8...
November 2016: Nature Physics
https://www.readbyqxmd.com/read/28553364/crystal-structure-of-the-superconducting-phase-of-sulfur-hydride
#18
Mari Einaga, Masafumi Sakata, Takahiro Ishikawa, Katsuya Shimizu, Mikhail I Eremets, Alexander P Drozdov, Ivan A Troyan, Naohisa Hirao, Yasuo Ohishi
A superconducting critical temperature above 200 K has recently been discovered in H2S (or D2S) under high hydrostatic pressure1, 2. These measurements were interpreted in terms of a decomposition of these materials into elemental sulfur and a hydrogen-rich hydride that is responsible for the superconductivity, although direct experimental evidence for this mechanism has so far been lacking. Here we report the crystal structure of the superconducting phase of hydrogen sulfide (and deuterium sulfide) in the normal and superconducting states obtained by means of synchrotron X-ray diffraction measurements, combined with electrical resistance measurements at both room and low temperatures...
September 2016: Nature Physics
https://www.readbyqxmd.com/read/27610190/engineered-swift-equilibration-of-a-brownian-particle
#19
Ignacio A Martínez, Artyom Petrosyan, David Guéry-Odelin, Emmanuel Trizac, Sergio Ciliberto
A fundamental and intrinsic property of any device or natural system is its relaxation time relax, which is the time it takes to return to equilibrium after the sudden change of a control parameter [1]. Reducing τrelax, is frequently necessary, and is often obtained by a complex feedback process. To overcome the limitations of such an approach, alternative methods based on driving have been recently demonstrated [2, 3], for isolated quantum and classical systems [4-9]. Their extension to open systems in contact with a thermostat is a stumbling block for applications...
September 2016: Nature Physics
https://www.readbyqxmd.com/read/27610189/quantum-phase-transitions-with-parity-symmetry-breaking-and-hysteresis
#20
A Trenkwalder, G Spagnolli, G Semeghini, S Coop, M Landini, P Castilho, L Pezzè, G Modugno, M Inguscio, A Smerzi, M Fattori
Symmetry-breaking quantum phase transitions play a key role in several condensed matter, cosmology and nuclear physics theoretical models1-3. Its observation in real systems is often hampered by finite temperatures and limited control of the system parameters. In this work we report for the first time the experimental observation of the full quantum phase diagram across a transition where the spatial parity symmetry is broken. Our system is made of an ultra-cold gas with tunable attractive interactions trapped in a spatially symmetric double-well potential...
September 2016: Nature Physics
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