Physical Review Letters

Lee, SungBin; Paramekanti, Arun; Kim, Yong

doi: 10.1103/PhysRevLett.111.196601pmid: 24266480

Motivated by experiments on Pr 2 Ir 2 O 7 , we consider metallic pyrochlore systems A 2 B 2 O 7 , where the A sites are occupied by rare-earth local moments and the B sites host 5 d transition metal ions with itinerant strongly spin-orbit coupled electrons. Assuming non-Kramers doublets on the A site, we derive the RKKY interaction between them mediated by the B -site itinerant electrons and find extended non-Heisenberg interactions. Analyzing a simplified model of the RKKY interaction, we uncover a local moment phase with coexisting spiral Ising-like magnetic dipolar and X Y -like quadrupolar ordering. This state breaks time-reversal and lattice symmetries, and reconstructs the B -site electronic band structure, producing a Weyl metallic phase with an intrinsic anomalous Hall effect and an undetectably small magnetization. <?format ?>We discuss implications of our results for Pr 2 Ir 2 O 7 .

Becher, Thomas ; Neubert, Matthias

doi: 10.1103/PhysRevLett.111.199905pmid: N/A

Fert, Albert ; Levy, Peter M

doi: 10.1103/PhysRevLett.111.199904pmid: N/A

Motter, Adilson E; Gruiz, Márton E; Károlyi, György E; Tél, Tamás E

doi: 10.1103/PhysRevLett.111.194101pmid: 24266475

Chaos is an inherently dynamical phenomenon traditionally studied for trajectories that are either permanently erratic or transiently influenced by permanently erratic ones lying on a set of measure zero. The latter gives rise to the final state sensitivity observed in connection with fractal basin boundaries in conservative scattering systems and driven dissipative systems. Here we focus on the most prevalent case of undriven dissipative systems, whose transient dynamics fall outside the scope of previous studies since no time-dependent solutions can exist for asymptotically long times. We show that such systems can exhibit positive finite-time Lyapunov exponents and fractal-like basin boundaries which nevertheless have codimension one. In sharp contrast to its driven and conservative counterparts, the settling rate to the (fixed-point) attractors grows exponentially in time, meaning that the fraction of trajectories away from the attractors decays superexponentially. While no invariant chaotic sets exist in such cases, the irregular behavior is governed by transient interactions with transient chaotic saddles, which act as effective, time-varying chaotic sets.

Si, Chen; Liu, Zheng; Duan, Wenhui; Liu, Feng

doi: 10.1103/PhysRevLett.111.196802pmid: 24266482

Graphene has exhibited a wealth of fascinating properties, but is also known not to be a superconductor. Remarkably, we show that graphene can be made a conventional Bardeen-Cooper-Schrieffer superconductor by the combined effect of charge doping and tensile strain. While the effect of doping obviously enlarges the Fermi surface, the effect of strain profoundly increases the electron-phonon coupling. At the experimental accessible doping ( <?format ?>∼ <?format ?> 4 × 10 14 cm - 2 ) and strain ( <?format ?>∼ <?format ?> 16 % ) levels, the superconducting critical temperature T c is estimated to be as high as ∼ 30 K , the highest for a single-element material above the liquid hydrogen temperature.

Ito, Atsuya; Nakamura, Yuto; Nakamura, Arao; Kishida, Hideo

doi: 10.1103/PhysRevLett.111.197801pmid: 24266489

Nonlinear conducting states in a strongly correlated organic electronic system α - ( BEDT - TTF ) 2 I 3 ( BEDT - TTF = bis ( ethylenedithio ) -tetrathiafulvalene) are studied by Raman spectroscopy. Wide-range Raman spectra of nonlinear conducing states provide direct information about conducting properties through the electronic Raman process. A comparison between the behaviors of the electronic modes of BEDT-TTF layers and the vibrational mode of I 3 molecules reveals the formation of nonequilibrium states in which only the electronic parts show the change of states. We obtained a spatial map of the conducting regions of the nonlinear conducting states by utilizing the electronic Raman intensity as a measure of the highly conducting states. A spatially inhomogeneous formation of nonlinear conducting states was observed.

Kim, Chulki; Prada, Marta; Platero, Gloria; Blick, Robert

doi: 10.1103/PhysRevLett.111.197202pmid: 24266485

We demonstrate the transition of a coupled electron shuttle from a stable to a strongly nonlinear response at room temperature. Within this transition we observe the coupled shuttle’s response to change from Coulomb controlled to conventional field emission. This parametric process is fully reversible and occurs within a broad frequency range. In combination, the large current and wide frequency band enable energy harvesting applications. The experimental data and the numerical calculations both indicate that the source of the nonlinearity is given by the electromechanical coupling of electron shuttling.

Kulić, Igor; Kulić, Miodrag

doi: 10.1103/PhysRevLett.111.198301pmid: 24266491

From microscopic fluid clusters to macroscopic droplets, the structure of fluids is governed by the van der Waals force, a force that acts between polarizable objects. In this Letter, we derive a general theory that describes the nonequilibrium counterpart to the van der Waals force, which emerges in spatially coherently fluctuating electromagnetic fields. We describe the formation of a novel and complex hierarchy of self-organized morphologies in magnetic and dielectric colloid systems. Most striking among these morphologies are dipolar foams—colloidal superstructures that swell against gravity and display a high sensitivity to the applied field. We discuss the dominance of many-body forces and derive the equation of state for a material formed by the coherent van der Waals force. Our theory is applied to recent experiments in paramagnetic colloidal systems and a new experiment is suggested to test the theory.

Wenk, H.-R; Kaercher, P; Kanitpanyacharoen, W; Zepeda-Alarcon, E; Wang, Y

doi: 10.1103/PhysRevLett.111.195701pmid: 24266478

Transition metals Ti, Zr, and Hf have a hexagonal close-packed structure ( α ) at ambient conditions, but undergo phase transformations with increasing temperature and pressure. Of particular significance is the high-pressure hexagonal ω phase which is brittle compared to the α phase. There has been a long debate about transformation mechanisms and orientation relations between the two crystal structures. Here we present the first high pressure experiments with in situ synchrotron x-ray diffraction texture studies on polycrystalline aggregates. We follow crystal orientation changes in Zr, confirming the original suggestion by Silcock for an α → ω martensitic transition for Ti, with ( 0001 ) α | | ( 11 2 ¯ 0 ) ω , and a remarkable orientation memory when ω reverts back to α .

Allam, J.; Sajjad, M.; Sutton, R.; Litvinenko, K.; Wang, Z.; Siddique, S.; Yang, Q.-H.; Loh, W.; Brown, T.

doi: 10.1103/PhysRevLett.111.197401pmid: 24266488

Exciton-exciton recombination in isolated semiconducting single-walled carbon nanotubes was studied using femtosecond transient absorption. Under sufficient excitation to saturate the optical absorption, we observed an abrupt transition between reaction- and diffusion-limited kinetics, arising from reactions between incoherent localized excitons with a finite probability of ∼ 0.2 per encounter. This represents the first experimental observation of a crossover between classical and critical kinetics in a 1D coalescing random walk, which is a paradigm for the study of nonequilibrium systems.