Virtual Journal of Applications of Superconductivity

Generation and Characterization of Electron Bunches with Ramped Current Profiles in a Dual-Frequency Superconducting Linear Accelerator

P. Piot, C. Behrens, C. Gerth, M. Dohlus, F. Lemery et al.
We report on the successful experimental generation of electron bunches with ramped current profiles. The technique relies on impressing nonlinear correlations in the longitudinal phase space using a superconducing radio frequency linear accelerator operating at two frequencies and a current-enhanci ... [Phys. Rev. Lett. 108, 034801 ] published .

Determination of critical current density from arbitrary flux relaxation process

Rongchao Ma
The current-carrying ability of a type-II superconductor is generally represented by its critical current density. This can be determined by measuring a flux relaxation process starting with a testing current density that is greater than or equal to the critical value. Here we show that a flux relax ... [AIP Advances 2, 012125 (2012)] published Thu Jan 19, 2012.

Longitudinal Magnetic Field Effect in Superconductors

Teruo Matsushita
Characteristic electromagnetic phenomena called longitudinal magnetic field effect are observed for a current-carrying superconductor in a parallel magnetic field. These phenomena and the mechanism of the longitudinal magnetic field effect are generally discussed from the viewpoint of flux motion in ... [Jpn. J. Appl. Phys. 51, 010111 (2012)] published Tue Jan 24, 2012.

Resistive current state of a wide superconducting film

I. V. Zolochevskii
The current-voltage characteristics (CVCs) of vortex superconducting films are investigated in a wide temperature range. It is shown for the first time that the experimental CVCs and their parameters are described well enough by asymptotic formulas within the theory of the vortex resistive state of ... [Low Temp. Phys. 37, 979 (2012)] published Wed Jan 25, 2012.

Critical State Theory in Superconductors

Teruo Matsushita
It is well known that the phenomenological balance equation between the Lorentz force and pinning force determines the electric current flow in superconductors in the mixed state. This equation is derived by using the variation principle for isolated or non-isolated flux line system. It might be que ... [Jpn. J. Appl. Phys. 51, 010109 (2012)] published Tue Jan 24, 2012.

Guided vortex motion in YBaCuO thin films with collective ratchet pinning potentials

A. Palau, C. Monton, V. Rouco, X. Obradors, and T. Puig
We investigate guided vortex motion in high-temperature YBaCuO thin films patterned with an array of asymmetric blind antidots. A preferential vortex motion along spatial asymmetric pinning potentials has been directly observed by changing the driving current direction. Transport measurements reveal ... [Phys. Rev. B 85, 012502 ] published .

Erratum: Magnetotransport in La(Fe,Ru)AsO as a probe of band structure and mobility [Phys. Rev. B 84, 134524 (2011)]

I. Pallecchi, F. Bernardini, M. Tropeano, A. Palenzona, A. Martinelli et al.
Abstract not available. [Phys. Rev. B 85, 019902 ] published .

Molecular Beam Epitaxy Growth of Superconducting BaKFeAs and SmFeAs(O,F) Films

Shinya Ueda, Soichiro Takeda, Shiro Takano, Akihiro Mitsuda, and Michio Naito
We report the molecular beam epitaxy (MBE) growth of the iron-based superconductors, BaKFeAs and SmFeAs(O,F). In the growth of BaKFeAs films, the key to incorporating volatile K in films is low-temperature ({\leq}350 degrees C) growth in reduced As flux. The highest T_{\text{c}} thus far obtained i ... [Jpn. J. Appl. Phys. 51, 010103 (2012)] published Tue Jan 24, 2012.

Thin Film Growth and Device Fabrication of Iron-Based Superconductors

Hidenori Hiramatsu, Takayoshi Katase, Toshio Kamiya, and Hideo Hosono
Iron-based superconductors have received much attention as a new family of high-temperature superconductors owing to their unique properties and distinct differences from cuprates and conventional superconductors. This paper reviews progress in thin film research on iron-based superconductors since ... [J. Phys. Soc. Jpn. 81, 011011 (2012)] published Thu Jan 26, 2012.

Influence of random point defects introduced by proton irradiation on critical current density and vortex dynamics of Ba(FeCo)As single crystals

N. Haberkorn, B. Maiorov, I. O. Usov, M. Weigand, W. Hirata et al.
In this work we analyze the influence of random point defects introduced by 3 MeV proton irradiation on the critical current density (J) and vortex dynamics of a Ba(FeCo)As single crystal. The results show that at low temperatures (T) the irradiation produces an enhancement of J of up to 2.6 times. ... [Phys. Rev. B 85, 014522 ] published .

Evolution of transport properties of BaFeRuAs in a wide range of isovalent Ru substitution

M. J. Eom, S. W. Na, C. Hoch, R. K. Kremer, and J. S. Kim
The effects of isovalent Ru substitution at the Fe sites of BaFeRuAs are investigated by measuring resistivity (rho) and Hall coefficient (R) on high-quality single crystals in a wide range of doping (0 <= x <= 1.4). Ru substitution weakens the antiferromagnetic (AFM) order, inducing superconductivi ... [Phys. Rev. B 85, 024536 ] published .

Frontiers of Research on Iron-Based Superconductors toward Their Application

Keiichi Tanabe and Hideo Hosono
The recent discovery of iron-based superconductors has evoked enthusiasm for extensive research on these materials because they form the second high-temperature superconductor family after the copper oxide superconductors and impart an expectation for materials with a higher transition temperature ( ... [Jpn. J. Appl. Phys. 51, 010005 (2012)] published Tue Jan 24, 2012.

Evolution of Tetragonal Phase in the FeSe Wire Fabricated by a Novel Chemical-Transformation Powder-in-Tube Process

Hiroki Izawa, Yoshikazu Mizuguchi, Toshinori Ozaki, Yoshihiko Takano, and Osuke Miura
We fabricated superconducting FeSe wires by the chemical-transformation powder-in-tube (PIT) process. The obvious correlation between annealing temperature and phase transformation was observed. Annealing above 500 degrees C produced wire-core transformation from hexagonal to tetragonal phase. Furt ... [Jpn. J. Appl. Phys. 51, 010101 (2012)] published Tue Jan 24, 2012.

Forefront in the Elucidation of the Mechanism of High-Temperature Superconductivity

Shin-ichi Uchida
The mechanism underlying the high-temperature (T_{\text{c}}) superconductivity of copper oxides has remained unelucidated and is one of the most difficult challenges of physics remaining in the 21st century. Various types of advanced spectroscopy have been employed to clarify the mechanism, resultin ... [Jpn. J. Appl. Phys. 51, 010002 (2012)] published Tue Jan 24, 2012.

Recent Progress in Physics of High-Temperature Superconductors

Takami Tohyama
One hundred years after the discovery of superconductivity, we are now facing a new era that demands an increase in the superconducting transition temperature T_{\text{c}}. In addition to copper-based superconductors, iron-based superconductors that have been discovered recently have been considered ... [Jpn. J. Appl. Phys. 51, 010004 (2012)] published Tue Jan 24, 2012.

Development of High Performance MgB Tapes and Wires

Hiroaki Kumakura
MgB shows no weak coupling of grains, indicating that grain alignment is not essential to obtain large current transfer from one grain to adjacent grain. This is a very big advantage because a simple process, such as powder-in-tube (PIT) method, can be applied for the fabrication of wires and tapes. ... [J. Phys. Soc. Jpn. 81, 011010 (2012)] published Thu Jan 26, 2012.

Superior MgB Superconducting Wire Performance through Oxygen-Free Pyrene Additive

Minoru Maeda, Jung Ho Kim, Yoon-Uk Heo, Se Kyun Kwon, Hiroaki Kumakura et al.
There is great potential to further enhance the critical current density (J_{\text{c}}) performance of MgB wires. Herein, MgB wires were fabricated by using oxygen-free pyrene as dopant, and field and temperature dependences of J_{\text{c}} were systematically evaluated. In addition, a strong correl ... [Appl. Phys. Express 5, 013101 (2012)] published Thu Jan 26, 2012.

High-T_{\text{c}} Superconductivity and Antiferromagnetism in Multilayered Copper Oxides ---A New Paradigm of Superconducting Mechanism---

Hidekazu Mukuda, Sunao Shimizu, Akira Iyo, and Yoshio Kitaoka
High-temperature superconductivity (HTSC) in copper oxides emerges on a layered CuO plane when an antiferromagnetic Mott insulator is doped with mobile hole carriers. We review extensive studies of multilayered copper oxides by site-selective nuclear magnetic resonance (NMR), which have uncovered th ... [J. Phys. Soc. Jpn. 81, 011008 (2012)] published Thu Jan 26, 2012.

Present Status and Future Perspective of Bismuth-Based High-Temperature Superconducting Wires Realizing Application Systems

Ken-ichi Sato, Shin-ichi Kobayashi, and Takayoshi Nakashima
Among a series of high-temperature superconducting materials that have been discovered to date, (Bi,Pb)SrCaCuO is the best candidate for superconducting wires that are long with commercial productivity, and critical current performance. In particular, the controlled overpressure (CT-OP) sintering te ... [Jpn. J. Appl. Phys. 51, 010006 (2012)] published Tue Jan 24, 2012.

Overview of Materials and Power Applications of Coated Conductors Project

Yuh Shiohara, Takahiro Taneda, and Masateru Yoshizumi
There are high expectations for coated conductors in electric power applications such as superconducting magnetic energy storage (SMES) systems, power cables, and transformers owing to their ability to contribute to stabilizing and increasing the capacity of the electric power supply grid as well as ... [Jpn. J. Appl. Phys. 51, 010007 (2012)] published Tue Jan 24, 2012.

Development and Prospects for the Future of Superconducting Wires

Hiroaki Kumakura
Superconducting wires are important from the viewpoints of energy saving and the realization of a low-carbon society, because their applications in various types of electric power applications enable not only improved efficiency but also the reduction of size and weight owing to the fact that they c ... [Jpn. J. Appl. Phys. 51, 010003 (2012)] published Tue Jan 24, 2012.

High Temperature Superconductor Terahertz Emitters: Fundamental Physics and Its Applications

Takanari Kashiwagi, Manabu Tsujimoto, Takashi Yamamoto, Hidetoshi Minami, Kazuhiro Yamaki et al.
Coherent and continuous radiation sources of the electromagnetic (EM) waves at terahertz (1 THz = 10^{12} c/s) frequencies using a mesa structure fabricated from high temperature superconducting BiSrCaCuO single crystals are described with a special emphasis on the physics of the radiation mechanism ... [Jpn. J. Appl. Phys. 51, 010113 (2012)] published Tue Jan 24, 2012.

Low-loss terahertz metamaterial from superconducting niobium nitride films

C. H. Zhang, J. B. Wu, B. B. Jin, Z. M. Ji, L. Kang et al.
This paper reports a type of low Ohmic loss terahertz (THz) metamaterials made from low-temperature superconducting niobium nitride (NbN) films. Its resonance properties are studied by THz time domain spectroscopy. Our experiments show that its unloaded quality factor reaches as high as 178 at 8 K w ... [Opt. Express 20, 42 (2012)] published Tue Jan 24, 2012.

A superconducting focal plane array for ultraviolet, optical, and near-infrared astrophysics

Benjamin A. Mazin, Bruce Bumble, Seth R. Meeker, Kieran O'Brien, Sean McHugh et al.
Microwave Kinetic Inductance Detectors, or MKIDs, have proven to be a powerful cryogenic detector technology due to their sensitivity and the ease with which they can be multiplexed into large arrays. A MKID is an energy sensor based on a photon-variable superconducting inductance in a lithographed ... [Opt. Express 20, 1503 (2012)] published Tue Jan 24, 2012.

Characterization of escape times of Josephson junctions for signal detection

Paolo Addesso, Giovanni Filatrella, and Vincenzo Pierro
The measurement of the escape time of a Josephson junction might be used to detect the presence of a sinusoidal signal embedded in noise when use of standard signal processing tools can be prohibitive due to the extreme weakness of the source or to the huge amount of data. In this paper we show that ... [Phys. Rev. E 85, 016708 ] published .

Review of Josephson Waveform Synthesis and Possibility of New Operation Method by Multibit Delta--Sigma Modulation and Thermometer Code for Its Further Advancement

Nobu-hisa Kaneko, Michitaka Maruyama, Chiharu Urano, and Shogo Kiryu
A method of AC waveform synthesis with quantum--mechanical accuracy has been developed on the basis of the Josephson effect in national metrology institutes, not only for its scientific interest but its potential benefit to industries. In this paper, we review the development of Josephson arbitrary ... [Jpn. J. Appl. Phys. 51, 010116 (2012)] published Tue Jan 24, 2012.

Soft X-ray Detection Performance of Superconducting Tunnel Junction Arrays with Asymmetric Tunnel Junction Layer Structure

Masahiro Ukibe, Shigetomo Shiki, Yoshinori Kitajima, and Masataka Ohkubo
Superconducting tunnel junction (STJ) array detectors with an asymmetric tunnel junction layer structure have been fabricated for the soft X-ray region between 100 eV and 1 keV. The asymmetric layer design was effective in solving the problem of double peak response to monochromatic X-rays, which is ... [Jpn. J. Appl. Phys. 51, 010115 (2012)] published Tue Jan 24, 2012.

Engineering two-mode continuous-variable entangled states of distant atomic spin ensembles with superconducting quantum circuits

Peng-Bo Li, Shao-Yan Gao, and Fu-Li Li
We present an experimental feasible scheme to generate two-mode entangled states of two spatially separated atomic spin ensembles, using superconducting quantum circuits consisting of two coplanar waveguide resonators and a charge qubit. We show that, with the charge qubit as a tunable coupler and t ... [Phys. Rev. A 85, 014303 ] published .

Effect of control procedures on the evolution of entanglement in open quantum systems

Sandeep K. Goyal, Subhashish Banerjee, and Sibasish Ghosh
The effect of a number of mechanisms designed to suppress decoherence in open quantum systems are studied with respect to their effectiveness at slowing down the loss of entanglement. The effect of photonic band-gap materials and frequency modulation of the system-bath coupling are along expected li ... [Phys. Rev. A 85, 012327 ] published .

Gated mode superconducting nanowire single photon detectors

Mohsen K. Akhlaghi and A. Hamed Majedi
Single Photon Detectors are fundamental to quantum optics and quantum information. Superconducting nanowire detectors exhibit high performance in free-running mode, but have a limited maximum count rate. By exploiting a bistable superconducting nanowire system, we demonstrate the first gated-mode op ... [Opt. Express 20, 1608 (2012)] published Tue Jan 24, 2012.

Vortex-assisted photon counts and their magnetic field dependence in single-photon superconducting detectors

L. N. Bulaevskii, Matthias J. Graf, and V. G. Kogan
We argue that photon counts in a superconducting nanowire single-photon detector (SNSPD) are caused by the transition from a current-biased metastable superconducting state to the normal state. Such a transition is triggered by vortices crossing the thin and narrow superconducting strip from one edg ... [Phys. Rev. B 85, 014505 ] published .

Evidence for coherent quantum phase slips across a Josephson junction array

Vladimir E. Manucharyan, Nicholas A. Masluk, Archana Kamal, Jens Koch, Leonid I. Glazman et al.
Superconducting order in a sufficiently narrow and infinitely long wire is destroyed at zero temperature by quantum fluctuations, which induce 2pi slips of the phase of the order parameter. However, in a finite-length wire, coherent quantum phase slips would manifest themselves simply as shifts of e ... [Phys. Rev. B 85, 024521 ] published .

Shaping an Itinerant Quantum Field into a Multimode Squeezed Vacuum by Dissipation

Diego Porras and Juan Jose Garcia-Ripoll
We show that inducing sidebands in the emission of a single emitter into a one-dimensional waveguide, together with a dissipative repumping process, a photon field is cooled down to a multimode squeezed vacuum. Our method does not require being in the strong coupling regime, works with a continuum o ... [Phys. Rev. Lett. 108, 043602 ] published .

Quantum memory with a single two-level atom in a half cavity

Yimin Wang, Jiri Minar, Gabriel Hetet, and Valerio Scarani
We propose a setup for quantum memory based on a single two-level atom in a half cavity with a moving mirror. We show that various temporal shapes of incident photon can be efficiently stored and read out by shaping the time-dependent decay rate gamma(t) between the atom and the light. This is achie ... [Phys. Rev. A 85, 013823 ] published .

Dipole Coupling of a Double Quantum Dot to a Microwave Resonator

T. Frey, P. J. Leek, M. Beck, A. Blais, T. Ihn et al.
We demonstrate the realization of a hybrid solid-state quantum device, in which a semiconductor double quantum dot is dipole coupled to the microwave field of a superconducting coplanar waveguide resonator. The double dot charge stability diagram extracted from measurements of the amplitude and phas ... [Phys. Rev. Lett. 108, 046807 ] published .

Benchmarking a Quantum Teleportation Protocol in Superconducting Circuits Using Tomography and an Entanglement Witness

M. Baur, A. Fedorov, L. Steffen, S. Filipp, M. P. da Silva et al.
Teleportation of a quantum state may be used for distributing entanglement between distant qubits in quantum communication and for quantum computation. Here we demonstrate the implementation of a teleportation protocol, up to the single-shot measurement step, with superconducting qubits coupled to a ... [Phys. Rev. Lett. 108, 040502 ] published .

Fast generation of multiparticle entangled state for flux qubits in a circle array of transmission line resonators with tunable coupling

Z. H. Peng, Yu-xi Liu, Y. Nakamura, and J. S. Tsai
We study a one-step approach to the fast generation of Greenberger-Horne-Zeilinger (GHZ) states in a circuit QED system with superconducting flux qubits. The GHZ state can be generated in about 10 ns, which is much shorter than the coherence time of flux qubits and comparable with the time of single ... [Phys. Rev. B 85, 024537 ] published .

Quantum state transfer between hybrid qubits in a circuit QED

Zhi-Bo Feng
In this Brief Report, we propose a theoretical scheme to transfer quantum states between superconducting charge qubits and semiconductor spin qubits in a circuit QED device. Under dispersive conditions, resonator-assisted state transfer between qubits can be performed controllably only by addressing ... [Phys. Rev. A 85, 014302 ] published .

Low noise MgB terahertz hot-electron bolometer mixers

S. Bevilacqua, S. Cherednichenko, V. Drakinskiy, J. Stake, H. Shibata et al.
We report on low noise terahertz bolometric mixers made of MgB superconducting thin films. For a 10-nm-thick MgB film, the lowest mixer noise temperature was 600 K at 600 GHz. For 30 to 10-nm-thick films, the mixer gain bandwidth is an inverse function of the film thickness, reaching 3.4 GHz for the ... [Appl. Phys. Lett. 100, 033504 (2012)] published Thu Jan 19, 2012.

Short-Pulse Intrinsic Tunneling Spectroscopy in BiSrCaCuO under Suppressed Self Heating

Minoru Suzuki, Ryota Takemura, Kenji Hamada, Masayuki Ohmaki, and Takao Watanabe
Short-pulse tunneling spectroscopy on a time scale of 300 ns has been conducted using intrinsic Josephson junctions naturally built in the crystal structure of a slightly underdoped BiSrCaCuO (Bi2212) by fabricating a very small and thin mesa of 6 nm in thickness and less than 5 [mu]m in square widt ... [Jpn. J. Appl. Phys. 51, 010112 (2012)] published Tue Jan 24, 2012.

Colloquium: Stimulating uncertainty: Amplifying the quantum vacuum with superconducting circuits

P. D. Nation, J. R. Johansson, M. P. Blencowe, and Franco Nori
The ability to generate particles from the quantum vacuum is one of the most profound consequences of Heisenberg's uncertainty principle. Although the significance of vacuum fluctuations can be seen throughout physics, the experimental realization of vacuum amplification effects has until now been l ... [Rev. Mod. Phys. 84, 1 ] published .

Emergent phenomena at oxide interfaces

H. Y. Hwang, Y. Iwasa, M. Kawasaki, B. Keimer, N. Nagaosa et al.
Recent technical advances in the atomic-scale synthesis of oxide heterostructures have provided a fertile new ground for creating novel states at their interfaces. Different symmetry constraints can be used to design structures exhibiting phenomena not found in the bulk constituents. A characteristi ... [Nature Mater. 11, 103 (2012)] published Thu Jan 26, 2012.

Meissner effect, diamagnetism, and classical physicsa review

Hanno Essen and Miguel C. N. Fiolhais
We review the literature on what classical physics says about the Meissner effect and the London equations. We discuss the relevance of the Bohr-van Leeuwen theorem for the perfect diamagnetism of superconductors and conclude that the theorem is based on invalid assumptions. We also point out result ... [Am. J. Phys. 80, 164 (2012)] published Fri Jan 20, 2012.

Superconductivity: 100th Anniversary of Its Discovery and Its Future

Koichi Kitazawa
Superconducting technologies are reviewed as the integration of various technologies by considering its research history, present status, future prospects, and the application to energy, transportation, and communications. Superconductivity involves a persistent current, perfect diamagnetism, and th ... [Jpn. J. Appl. Phys. 51, 010001 (2012)] published Tue Jan 24, 2012.