The history of physics publishing in the past century shows how the changing needs of the research community shaped the dissemination of knowledge through scientific journals.

]]>Author: Mark Buchanan

]]>Author: May Chiao

]]>Author: Bart Verberck

]]>Author: Abigail Klopper

]]>Author: Luke Fleet

]]>Author: Andrea Taroni

]]>Author: Roberta Citro

Two experiments with ultracold fermionic and bosonic atoms in optical superlattices demonstrate the quantized charge transport predicted by Thouless in the 1980s.

]]>Author: Luke Fleet

]]>Author: Nigel Hussey

Disentangling the physics of the pseudogap phase from the other electronic phases of high-temperature superconductors has long been a frustrating problem. A recent high-field experiment has isolated it completely — thus raising hopes that its origin can finally be understood.

]]>Author: Bart Verberck

]]>Author: Ben Still

The first results from the NOvA experiment confirm what we already know about neutrino oscillations. As data collection continues we are getting closer to finding the remaining unknown parameters.

]]>Author: Sabino Matarrese

The quality and quantity of current and forthcoming cosmological datasets call for both analytical and numerical modelling of the dynamics of nonlinear gravitational matter based on general relativity.

]]>Authors: Shuta Nakajima, Takafumi Tomita, Shintaro Taie, Tomohiro Ichinose, Hideki Ozawa, Lei Wang, Matthias Troyer & Yoshiro Takahashi

An electron gas in a one-dimensional periodic potential can be transported even in the absence of a voltage bias if the potential is slowly and periodically modulated in time. Remarkably, the transferred charge per cycle is sensitive only to the topology of the path in parameter space. Although this so-called Thouless charge pump was first proposed more than thirty years ago, it has not yet been realized. Here we report the demonstration of topological Thouless pumping using ultracold fermionic atoms in a dynamically controlled optical superlattice. We observe a shift of the atomic cloud as a result of pumping, and extract the topological invariance of the pumping process from this shift. We demonstrate the topological nature of the Thouless pump by varying the topology of the pumping path and verify that the topological pump indeed works in the quantum regime by varying the speed and temperature.

]]>Authors: A. Leblanc, S. Monchocé, C. Bourassin-Bouchet, S. Kahaly & F. Quéré

The extreme intensities now delivered by femtosecond lasers make it possible to drive and control relativistic motion of charged particles with light, opening a path to compact particle accelerators and coherent X-ray sources. Accurately characterizing the dynamics of ultrahigh-intensity laser–plasma interactions as well as the resulting light and particle emissions is an essential step towards such achievements. This remains a considerable challenge, as the relevant scales typically range from picoseconds to attoseconds in time, and from micrometres to nanometres in space. In these experiments, owing to the extreme prevalent physical conditions, measurements can be performed only at macroscopic distances from the targets, yielding only partial information at these microscopic scales. This letter presents a major advance by applying the concepts of ptychography to such measurements, and thus retrieving microscopic information hardly accessible until now. This paves the way to a general approach for the metrology of extreme laser–plasma interactions on very small spatial and temporal scales.

]]>Authors: Fahad Mahmood, Ching-Kit Chan, Zhanybek Alpichshev, Dillon Gardner, Young Lee, Patrick A. Lee & Nuh Gedik

The coherent optical manipulation of solids is emerging as a promising way to engineer novel quantum states of matter. The strong time-periodic potential of intense laser light can be used to generate hybrid photon–electron states. Interaction of light with Bloch states leads to Floquet–Bloch states, which are essential in realizing new photo-induced quantum phases. Similarly, dressing of free-electron states near the surface of a solid generates Volkov states, which are used to study nonlinear optics in atoms and semiconductors. The interaction of these two dynamic states with each other remains an open experimental problem. Here we use time- and angle-resolved photoemission spectroscopy (Tr-ARPES) to selectively study the transition between these two states on the surface of the topological insulator Bi2Se3. We find that the coupling between the two strongly depends on the electron momentum, providing a route to enhance or inhibit it. Moreover, by controlling the light polarization we can negate Volkov states to generate pure Floquet–Bloch states. This work establishes a systematic path for the coherent manipulation of solids via light–matter interaction.

]]>Authors: S. V. Borisenko, D. V. Evtushinsky, Z.-H. Liu, I. Morozov, R. Kappenberger, S. Wurmehl, B. Büchner, A. N. Yaresko, T. K. Kim, M. Hoesch, T. Wolf & N. D. Zhigadlo

Spin–orbit coupling is a fundamental interaction in solids that can induce a broad range of unusual physical properties, from topologically non-trivial insulating states to unconventional pairing in superconductors. In iron-based superconductors its role has, so far, not been considered of primary importance, with models based on spin- or orbital fluctuations pairing being used most widely. Using angle-resolved photoemission spectroscopy, we directly observe a sizeable spin–orbit splitting in all the main members of the iron-based superconductors. We demonstrate that its impact on the low-energy electronic structure and details of the Fermi surface topology is stronger than that of possible nematic ordering. The largest pairing gap is supported exactly by spin–orbit-coupling-induced Fermi surfaces, implying a direct relation between this interaction and the mechanism of high-temperature superconductivity.

]]>Authors: M. Ben Shalom, M. J. Zhu, V. I. Fal’ko, A. Mishchenko, A. V. Kretinin, K. S. Novoselov, C. R. Woods, K. Watanabe, T. Taniguchi, A. K. Geim & J. R. Prance

Graphene-based Josephson junctions provide a novel platform for studying the proximity effect due to graphene’s unique electronic spectrum and the possibility to tune junction properties by gate voltage. Here we describe graphene junctions with a mean free path of several micrometres, low contact resistance and large supercurrents. Such devices exhibit pronounced Fabry–Pérot oscillations not only in the normal-state resistance but also in the critical current. The proximity effect is mostly suppressed in magnetic fields below 10 mT, showing the conventional Fraunhofer pattern. Unexpectedly, some proximity survives even in fields higher than 1 T. Superconducting states randomly appear and disappear as a function of field and carrier concentration, and each of them exhibits a supercurrent carrying capacity close to the universal quantum limit. We attribute the high-field Josephson effect to mesoscopic Andreev states that persist near graphene edges. Our work reveals new proximity regimes that can be controlled by quantum confinement and cyclotron motion.

]]>Authors: Aaron M. Jones, Hongyi Yu, John R. Schaibley, Jiaqiang Yan, David G. Mandrus, Takashi Taniguchi, Kenji Watanabe, Hanan Dery, Wang Yao & Xiaodong Xu

Photon upconversion is an elementary light–matter interaction process in which an absorbed photon is re-emitted at higher frequency after extracting energy from the medium. This phenomenon lies at the heart of optical refrigeration in solids, where upconversion relies on anti-Stokes processes enabled either by rare-earth impurities or exciton–phonon coupling. Here, we demonstrate a luminescence upconversion process from a negatively charged exciton to a neutral exciton resonance in monolayer WSe2, producing spontaneous anti-Stokes emission with an energy gain of 30 meV. Polarization-resolved measurements find this process to be valley selective, unique to monolayer semiconductors. Since the charged exciton binding energy closely matches the 31 meV A1′ optical phonon, we ascribe the spontaneous excitonic anti-Stokes to doubly resonant Raman scattering, where the incident and outgoing photons are in resonance with the charged and neutral excitons, respectively. In addition, we resolve a charged exciton doublet with a 7 meV splitting, probably induced by exchange interactions, and show that anti-Stokes scattering is efficient only when exciting the doublet peak resonant with the phonon, further confirming the excitonic doubly resonant picture.

]]>Authors: D. K. Efetov, L. Wang, C. Handschin, K. B. Efetov, J. Shuang, R. Cava, T. Taniguchi, K. Watanabe, J. Hone, C. R. Dean & P. Kim

Electrons incident from a normal metal onto a superconductor are reflected back as holes—a process called Andreev reflection. In a normal metal where the Fermi energy is much larger than a typical superconducting gap, the reflected hole retraces the path taken by the incident electron. In graphene with low disorder, however, the Fermi energy can be tuned to be smaller than the superconducting gap. In this unusual limit, the holes are expected to be reflected specularly at the superconductor–graphene interface owing to the onset of interband Andreev processes, where the effective mass of the reflected holes changes sign. Here we present measurements of gate-modulated Andreev reflections across the low-disorder van der Waals interface formed between graphene and the superconducting NbSe2. We find that the conductance across the graphene–superconductor interface exhibits a characteristic suppression when the Fermi energy is tuned to values smaller than the superconducting gap, a hallmark for the transition between intraband retro Andreev reflections and interband specular Andreev reflections.

]]>Authors: S. DuttaGupta, S. Fukami, C. Zhang, H. Sato, M. Yamanouchi, F. Matsukura & H. Ohno

The dynamics of elastic interfaces is a general field of interest in statistical physics, where magnetic domain wall has served as a prototypical example. Domain wall ‘creep’ under the action of sub-threshold driving forces with thermal activation is known to be described by a scaling law with a certain universality class, which represents the mechanism of the interaction of domain walls with the applied forces over the disorder of the system. Here we show different universality classes depending on the driving forces, magnetic field or spin-polarized current, in a metallic system, which have hitherto been seen only in a magnetic semiconductor. We reveal that an adiabatic spin-transfer torque plays a major role in determining the universality class of current-induced creep, which does not depend on the intricacies of material disorder. Our results shed light on the physics of the creep motion of domain walls and other elastic systems.

]]>Authors: Ling Lu, Chen Fang, Liang Fu, Steven G. Johnson, John D. Joannopoulos & Marin Soljačić

Topology of electron wavefunctions was first introduced to characterize the quantum Hall states in two dimensions discovered in 1980 (ref. ). Over the past decade, it has been recognized that symmetry plays a crucial role in the classification of topological phases, leading to the broad notion of symmetry-protected topological phases. As a primary example, topological insulators are distinguished from normal insulators in the presence of time-reversal symmetry (nphys3611-m1gif1251211). A three-dimensional (3D) topological insulator exhibits an odd number of protected surface Dirac cones, a unique property that cannot be realized in any 2D systems. Importantly, the existence of topological insulators requires Kramers’ degeneracy in spin–orbit coupled electronic materials; this forbids any direct analogue in boson systems. In this report, we discover a 3D topological photonic crystal phase hosting a single surface Dirac cone, which is protected by a crystal symmetry—the nonsymmorphic glide reflection rather than nphys3611-m2gif1251211. Such a gapless surface state is fully robust against random disorder of any type. This bosonic topological band structure is achieved by applying alternating magnetization to gap out the 3D ‘generalized Dirac points’ discovered in the bulk of our crystal. The Z2 bulk invariant is characterized through the evolution of Wannier centres. Our proposal—readily realizable using ferrimagnetic materials at microwave frequencies—expands the scope of 3D topological materials from fermions to bosons.

]]>Authors: Hugo Wioland, Francis G. Woodhouse, Jörn Dunkel & Raymond E. Goldstein

Despite their inherently non-equilibrium nature, living systems can self-organize in highly ordered collective states that share striking similarities with the thermodynamic equilibrium phases of conventional condensed-matter and fluid systems. Examples range from the liquid-crystal-like arrangements of bacterial colonies, microbial suspensions and tissues to the coherent macro-scale dynamics in schools of fish and flocks of birds. Yet, the generic mathematical principles that govern the emergence of structure in such artificial and biological systems are elusive. It is not clear when, or even whether, well-established theoretical concepts describing universal thermostatistics of equilibrium systems can capture and classify ordered states of living matter. Here, we connect these two previously disparate regimes: through microfluidic experiments and mathematical modelling, we demonstrate that lattices of hydrodynamically coupled bacterial vortices can spontaneously organize into distinct patterns characterized by ferro- and antiferromagnetic order. The coupling between adjacent vortices can be controlled by tuning the inter-cavity gap widths. The emergence of opposing order regimes is tightly linked to the existence of geometry-induced edge currents, reminiscent of those in quantum systems. Our experimental observations can be rationalized in terms of a generic lattice field theory, suggesting that bacterial spin networks belong to the same universality class as a wide range of equilibrium systems.

]]>Authors: Julian Adamek, David Daverio, Ruth Durrer & Martin Kunz

Numerical simulations are a versatile tool for providing insight into the complicated process of structure formation in cosmology. This process is mainly governed by gravity, which is the dominant force on large scales. At present, a century after the formulation of general relativity, numerical codes for structure formation still employ Newton’s law of gravitation. This approximation relies on the two assumptions that gravitational fields are weak and that they originate from non-relativistic matter. Whereas the former seems well justified on cosmological scales, the latter imposes restrictions on the nature of the ‘dark’ components of the Universe (dark matter and dark energy), which are, however, poorly understood. Here we present the first simulations of cosmic structure formation using equations consistently derived from general relativity. We study in detail the small relativistic effects for a standard lambda cold dark matter cosmology that cannot be obtained within a purely Newtonian framework. Our particle-mesh N-body code computes all six degrees of freedom of the metric and consistently solves the geodesic equation for particles, taking into account the relativistic potentials and the frame-dragging force. This conceptually clean approach is very general and can be applied to various settings where the Newtonian approximation fails or becomes inaccurate, ranging from simulations of models with dynamical dark energy or warm/hot dark matter to core collapse supernova explosions.

]]>Authors: M. Lohse, C. Schweizer, O. Zilberberg, M. Aidelsburger & I. Bloch

]]>Authors: M. Thévenet, A. Leblanc, S. Kahaly, H. Vincenti, A. Vernier, F. Quéré & J. Faure

]]>Authors: LiDong Pan, N. J. Laurita, Kate A. Ross, Bruce D. Gaulin & N. P. Armitage

]]>Authors: Franck Raynaud, Mark E. Ambühl, Chiara Gabella, Alicia Bornert, Ivo F. Sbalzarini, Jean-Jacques Meister & Alexander B. Verkhovsky

]]>Author: Vincent Icke

Vincent Icke paints a portrait of the bewildering cosmological constant.

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