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Bartłomiej Gardas, Jacek Dziarmaga, Wojciech H Zurek, Michael Zwolak
The shift of interest from general purpose quantum computers to adiabatic quantum computing or quantum annealing calls for a broadly applicable and easy to implement test to assess how quantum or adiabatic is a specific hardware. Here we propose such a test based on an exactly solvable many body system-the quantum Ising chain in transverse field-and implement it on the D-Wave machine. An ideal adiabatic quench of the quantum Ising chain should lead to an ordered broken symmetry ground state with all spins aligned in the same direction...
March 14, 2018: Scientific Reports
C E Matt, D Sutter, A M Cook, Y Sassa, M Månsson, O Tjernberg, L Das, M Horio, D Destraz, C G Fatuzzo, K Hauser, M Shi, M Kobayashi, V N Strocov, T Schmitt, P Dudin, M Hoesch, S Pyon, T Takayama, H Takagi, O J Lipscombe, S M Hayden, T Kurosawa, N Momono, M Oda, T Neupert, J Chang
The minimal ingredients to explain the essential physics of layered copper-oxide (cuprates) materials remains heavily debated. Effective low-energy single-band models of the copper-oxygen orbitals are widely used because there exists no strong experimental evidence supporting multi-band structures. Here, we report angle-resolved photoelectron spectroscopy experiments on La-based cuprates that provide direct observation of a two-band structure. This electronic structure, qualitatively consistent with density functional theory, is parametrised by a two-orbital ([Formula: see text] and [Formula: see text]) tight-binding model...
March 6, 2018: Nature Communications
A A Kalenyuk, A Pagliero, E A Borodianskyi, A A Kordyuk, V M Krasnov
Josephson current provides a phase-sensitive tool for probing the pairing symmetry. Here we present an experimental study of high-quality Josephson junctions between a conventional s-wave superconductor Nb and a multiband iron-pnictide Ba_{1-x}Na_{x}Fe_{2}As_{2}. Junctions exhibit a large enough critical current density to preclude the d-wave symmetry of the order parameter in the pnictide. However, the I_{c}R_{n} product is very small ≃3μV, which is not consistent with the sign-preserving s_{++} symmetry either...
February 9, 2018: Physical Review Letters
Igor Boettcher, Igor F Herbut
We investigate unconventional superconductivity in three-dimensional electronic systems with the chemical potential close to a quadratic band touching point in the band dispersion. Short-range interactions can lead to d-wave superconductivity, described by a complex tensor order parameter. We elucidate the general structure of the corresponding Ginzburg-Landau free energy and apply these concepts to the case of an isotropic band touching point. For a vanishing chemical potential, the ground state of the system is given by the superconductor analogue of the uniaxial nematic state, which features line nodes in the excitation spectrum of quasiparticles...
February 2, 2018: Physical Review Letters
Swagatam Nayak, Sanjeev Kumar
We show that the extended attractive Hubbard model on a square lattice allows for a variety of superconducting phases, including exotic mixed-symmetry phases with $d_{x^2-y^2} + {\rm i} [s + s^*]$ and $ d_{x^2-y^2} + p_{x}$ symmetries, and a novel $p_x + {\rm i} p_y$ state. The calculations are performed within the Hartree-Fock Bardeen-Cooper-Schrieffer (HF-BCS) framework. The ground states of the mean-field Hamiltonian are obtained via a minimization scheme that relaxes the symmetry constraints on the superconducting solutions, hence allowing for a mixing of $s$-, $p$- and $d$-wave order parameters...
February 13, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
András Gyenis, Benjamin E Feldman, Mallika T Randeria, Gabriel A Peterson, Eric D Bauer, Pegor Aynajian, Ali Yazdani
Layered material structures play a key role in enhancing electron-electron interactions to create correlated metallic phases that can transform into unconventional superconducting states. The quasi-two-dimensional electronic properties of such compounds are often inferred indirectly through examination of bulk properties. Here we use scanning tunneling microscopy to directly probe in cross-section the quasi-two-dimensional electronic states of the heavy fermion superconductor CeCoIn5. Our measurements reveal the strong confined nature of quasiparticles, anisotropy of tunneling characteristics, and layer-by-layer modulated behavior of the precursor pseudogap gap phase...
February 7, 2018: Nature Communications
Jingxiang Zhao, Qiang Gu
We study the two-dimensional Hubbard model with the Rashba type spin-orbit coupling within and beyond the mean-field theory. The antiferromagnetic ground state for the model at half-filling and the Cooper pairing induced by antiferromagnetic spin fluctuations near half-filling are examined based on the random-phase approximation. We show that the antiferromagnetic order is suppressed and the magnetic susceptibility turns out to be anisotropic in the presence of the spin-orbit coupling. Energy spectrums of transverse spin fluctuations are obtained and the effective interactions between holes mediated by antiferromagnetic spin fluctuations are deduced in the case of low hole doping...
January 17, 2018: Scientific Reports
D F Agterberg, T Shishidou, J O'Halloran, P M R Brydon, M Weinert
Monolayer FeSe exhibits the highest transition temperature among the iron based superconductors and appears to be fully gapped, seemingly consistent with s-wave superconductivity. Here, we develop a theory for the superconductivity based on coupling to fluctuations of checkerboard magnetic order (which has the same translation symmetry as the lattice). The electronic states are described by a symmetry based k·p-like theory and naturally account for the states observed by angle resolved photoemission spectroscopy...
December 29, 2017: Physical Review Letters
Xiang Chen, Julian L Schmehr, Zahirul Islam, Zach Porter, Eli Zoghlin, Kenneth Finkelstein, Jacob P C Ruff, Stephen D Wilson
Materials that exhibit both strong spin-orbit coupling and electron correlation effects are predicted to host numerous new electronic states. One prominent example is the Jeff = 1/2 Mott state in Sr2IrO4, where introducing carriers is predicted to manifest high temperature superconductivity analogous to the S = 1/2 Mott state of La2CuO4. While bulk superconductivity currently remains elusive, anomalous quasiparticle behaviors paralleling those in the cuprates such as pseudogap formation and the formation of a d-wave gap are observed upon electron-doping Sr2IrO4...
January 9, 2018: Nature Communications
D G Mazzone, S Raymond, J L Gavilano, P Steffens, A Schneidewind, G Lapertot, M Kenzelmann
Unconventional superconductivity in many materials is believed to be mediated by magnetic fluctuations. It is an open question how magnetic order can emerge from a superconducting condensate and how it competes with the magnetic spin resonance in unconventional superconductors. Here we study a model d-wave superconductor that develops spin-density wave order, and find that the spin resonance is unaffected by the onset of static magnetic order. This result suggests a scenario, in which the resonance in Nd_{0...
November 3, 2017: Physical Review Letters
A DeGrush, A Maschinot, T Akdogan, R Alarcon, W Bertozzi, E Booth, T Botto, J R Calarco, B Clasie, C Crawford, K Dow, M Farkhondeh, R Fatemi, O Filoti, W Franklin, H Gao, E Geis, S Gilad, D K Hasell, P Karpius, M Kohl, H Kolster, T Lee, J Matthews, K McIlhany, N Meitanis, R Milner, J Rapaport, R Redwine, J Seely, A Shinozaki, A Sindile, S Širca, E Six, T Smith, B Tonguc, C Tschalär, E Tsentalovich, W Turchinetz, Y Xiao, W Xu, Z-L Zhou, V Ziskin, T Zwart
We report the measurement of the beam-vector and tensor asymmetries A_{ed}^{V} and A_{d}^{T} in quasielastic (e[over →],e^{'}p) electrodisintegration of the deuteron at the MIT-Bates Linear Accelerator Center up to missing momentum of 500  MeV/c. Data were collected simultaneously over a momentum transfer range 0.1<Q^{2}<0.5  (GeV/c)^{2} with the Bates Large Acceptance Spectrometer Toroid using an internal deuterium gas target polarized sequentially in both vector and tensor states. The data are compared with calculations...
November 3, 2017: Physical Review Letters
Yilin Wang, Hongming Weng, Liang Fu, Xi Dai
The magnetic properties of the pyrochlore iridate material Eu_{2}Ir_{2}O_{7} (5d^{5}) have been studied based on first principles calculations, where the crystal field splitting Δ, spin-orbit coupling (SOC) λ, and Coulomb interaction U within Ir 5d orbitals all play significant roles. The ground state phase diagram has been obtained with respect to the strength of SOC and Coulomb interaction U, where a stable antiferromagnetic ground state with all-in-all-out (AIAO) spin structure has been found. In addition, another antiferromagnetic state with energy close to AIAO has also been found to be stable...
November 3, 2017: Physical Review Letters
Yue Cui, Chuyang Shen, Min Deng, Shen Dong, Cheng Chen, Rong Lü, Bo Gao, Meng Khoon Tey, Li You
High partial-wave (l≥2) Feshbach resonance (FR) in an ultracold mixture of ^{85}Rb-^{87}Rb atoms is investigated experimentally aided by a partial-wave insensitive analytic multichannel quantum-defect theory. Two "broad" resonances from coupling between d waves in both the open and closed channels are observed and characterized. One of them shows a fully resolved triplet structure with a splitting ratio well explained by the perturbation to the closed channel due to interatomic spin-spin interaction...
November 17, 2017: Physical Review Letters
Jun Li, Paulo J Pereira, Jie Yuan, Yang-Yang Lv, Mei-Ping Jiang, Dachuan Lu, Zi-Quan Lin, Yong-Jie Liu, Jun-Feng Wang, Liang Li, Xiaoxing Ke, Gustaaf Van Tendeloo, Meng-Yue Li, Hai-Luke Feng, Takeshi Hatano, Hua-Bing Wang, Pei-Heng Wu, Kazunari Yamaura, Eiji Takayama-Muromachi, Johan Vanacken, Liviu F Chibotaru, Victor V Moshchalkov
Nematic order often breaks the tetragonal symmetry of iron-based superconductors. It arises from regular structural transition or electronic instability in the normal phase. Here, we report the observation of a nematic superconducting state, by measuring the angular dependence of the in-plane and out-of-plane magnetoresistivity of Ba0.5 K0.5 Fe2 As2 single crystals. We find large twofold oscillations in the vicinity of the superconducting transition, when the direction of applied magnetic field is rotated within the basal plane...
December 1, 2017: Nature Communications
Niclas Niemann, Patrick Wiegel, Alexander Kurz, John C Rothwell, Christian Leukel
Transcranial magnetic stimulation (TMS) of motor cortex produces a series of descending volleys known as D- (direct) and I- (indirect) waves. In the present study, we questioned whether spinal H-reflexes can be used to dissect D-waves, early and late I-waves from TMS. We therefore probed H-reflex facilitation at arrival times of D- and I-waves at the spinal level and thereby changed TMS parameters that have previously been shown to have selective effects on evoked D- and different I-waves. We changed TMS intensity and current direction, and applied a double-pulse paradigm known as short-interval intracortical inhibition (SICI)...
November 15, 2017: Journal of Neurophysiology
Ke-Gao Liu, Xiao-Yan Peng, Zheng Zhang, Hua Sun, Di-Ya Yang, Ning-Li Wang
BACKGROUND: There are ON- and OFF-pathways in the normal vertebrate retina. Short- and long-flash electroretinogram (ERG) are suitable methods to observe the function of ON- and OFF-pathways in vivo, respectively. It is clear that high intraocular pressure (IOP) might cause dysfunction of cone-dominated photopic negative response (PhNR) in monkeys with high IOP in ON-pathway. However, whether cone-dominated OFF-responses are also affected is less known. The aim of this study was to observe photopic OFF-responses of ERG in monkeys with high IOP...
November 20, 2017: Chinese Medical Journal
T Ekino, A M Gabovich, Mai Suan Li, H Szymczak, A I Voitenko
Quasiparticle tunnel conductance-voltage characteristics (CVCs), [Formula: see text], were calculated for break junctions (BJs) made up of layered d-wave superconductors partially gapped by charge-density waves (CDWs). The current is assumed to flow in the ab-plane of electrodes. The influence of CDWs is analyzed by comparing the resulting CVCs with CVCs calculated for BJs made up of pure d-wave superconductors with relevant parameters. The main CDW-effects were found to be the appearance of new CVC peculiarities and the loss of CVC symmetry with respect to the V-sign...
December 20, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Xiao-Shan Ye, Yong-Jun Liu, Xiu Yun Zhang, Guoqing Wu
We explore the topological phase, which involves Majorana type topological zero mode fermions (MTZFs) at the edge, using d-wave superfluid with Rashba spin-orbit coupling (SOC) interactions. The self-Hermitian of this MTZF([Formula: see text]) is similar to that of the Majorana fermions (MFs) ([Formula: see text]). We show that, to realize a single MTZF at each edge in superfluid with d-wave pairing in a Majorana type Kramers Doublet (MTKD) state, it is important to lift both the spin and the Dirac Cones degeneracies...
October 19, 2017: Scientific Reports
Petia Kupenova, Elka Popova, Liliya Vitanova
The contribution of the purinergic receptors P2X7 (P2X7Rs) to the electroretinographic (ERG) responses was studied by testing the effects of the selective P2X7R antagonist A438079 and the selective P2X7R agonist Bz-ATP on the electroretinograms obtained in perfused frog (Rana ridibunda) eyecup preparations under a variety of stimulation conditions. The P2X7R blockade by 200 µM A438079 diminished the amplitude of the photoreceptor components: the a-wave and the pharmacologically isolated mass receptor potential...
January 2017: Visual Neuroscience
Tao Li, Yuehua Su
The electronic nematic responses in Fe-based superconductors have been observed ubiquitously in various experimental probes. One novel nematic character is the d-wave bond orbital-relevant nematic charge order which was firstly proposed by symmetry analysis and then conformed by angle-resolved photoemission spectroscopy. In this paper, we present a mechanism that the driving force of the orbital-relevant nematic charge order is the reduction of the large Hubbard energy in the particle-hole charge channel by virtual hopping processes...
August 14, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
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