Virtual Journal of Applications of Superconductivity

Type-1.5 Superconducting State from an Intrinsic Proximity Effect in Two-Band Superconductors

Egor Babaev, Johan Carlstrom, and Martin Speight
We show that in multiband superconductors, even an extremely small interband proximity effect can lead to a qualitative change in the interaction potential between superconducting vortices by producing long-range intervortex attraction. This type of vortex interaction results in an unusual response ... [Phys. Rev. Lett. 105, 067003 ] published .

Proposal to detect vortices above the superconducting transition temperature

Zoran Ristivojevic and M. R. Norman
We propose a simple experiment to determine whether vortices persist above the superconducting transition temperature T in the pseudogap phase of high-temperature cuprate superconductors. This involves using a magnetic dot to stabilize a vortex in a thin cuprate film beneath the dot. We calculate th ... [Phys. Rev. B 82, 060506 ] published .

Fracture behaviors induced by electromagnetic force in a long cylindrical superconductor

Jun Zeng, You-He Zhou, and Hua-Dong Yong
In the present work, the crack problem of a long cylindrical superconductor with a center crack is investigated. The Bean and Kim model of critical state are considered, and the stress intensity factors are calculated for zero-field cooling (ZFC) and field cooling (FC) magnetization processes, respe ... [J. Appl. Phys. 108, 033901 (2010)] published Wed Aug 4, 2010.

Doping evolution of the absolute value of the London penetration depth and superfluid density in single crystals of Ba(FeCo)As

R. T. Gordon, H. Kim, N. Salovich, R. W. Giannetta, R. M. Fernandes et al.
The zero-temperature value of the in-plane London penetration depth, lambda(0), has been measured in single crystals of Ba(FeCo)As as a function of the Co concentration, x, across both the underdoped and overdoped superconducting regions of the phase diagram. For x>~0.047, lambda(0) has been found t ... [Phys. Rev. B 82, 054507 ] published .

In-Plane Resistivity Anisotropy in an Underdoped Iron Arsenide Superconductor

Jiun-Haw Chu, James G. Analytis, Kristiaan De Greve, Peter L. McMahon, Zahirul Islam et al.
High-temperature superconductivity often emerges in the proximity of a symmetry-breaking ground state. For superconducting iron arsenides, in addition to the antiferromagnetic ground state, a small structural distortion breaks the crystal's C4 rotational symmetry in the underdoped part of the phase ... [Science 329, 824 ] published .

Nodes in the gap structure of the iron arsenide superconductor Ba(FeCo)As from c-axis heat transport measurements

J.-Ph. Reid, M. A. Tanatar, X. G. Luo, H. Shakeripour, N. Doiron-Leyraud et al.
The thermal conductivity kappa of the iron-arsenide superconductor Ba(FeCo)As was measured down to 50 mK for a heat current parallel (kappa) and perpendicular (kappa) to the tetragonal c axis for seven Co concentrations from underdoped to overdoped regions of the phase diagram (0.038<=x<=0.127). A r ... [Phys. Rev. B 82, 064501 ] published .

Angle-resolved specific heat in iron-based superconductors: The case for a nodeless extended s-wave gap

A. V. Chubukov and I. Eremin
We consider the variation in the field-induced component of the specific heat C(H) with the direction of the applied field in Fe pnictides within quasiclassical Doppler-shift approximation with special emphasis to recent experiments on FeSeTe. We show that for extended s-wave gap with no nodes, C(H) ... [Phys. Rev. B 82, 060504 ] published .

Charge dynamics of Co-doped BaFeAs

A Lucarelli, A Dusza, F Pfuner, P Lerch, J Analytis et al.
We report on a thorough optical investigation over a broad spectral range and as a function of temperature of the charge dynamics in Ba(CoFe)As compounds for Co-doping ranging between 0 and 18%. For the parent compound as well as for x=0.025, we observe the opening of a pseudogap, due to the spin-de ... [New J. Phys. 12, 073036 (2010)] published Wed Aug 4, 2010.

Flux dynamics associated with the second magnetization peak in the iron pnictide BaKFeAs

S. Salem-Sugui, Jr., L. Ghivelder, A. D. Alvarenga, L. F. Cohen, K. A. Yates et al.
We report on isofield magnetic relaxation data on a single crystal of BaKFeAs with superconducting transition temperature T=32.7 K which exhibit the so-called fish-tail effect. A surface map of the superconducting transition temperature shows that the superconducting properties are close to homogen ... [Phys. Rev. B 82, 054513 ] published .

Thermoelectric properties of LaFeAsO at low temperature

K. Kihou, C. H. Lee, K. Miyazawa, P. M. Shirage, A. Iyo et al.
We have studied the thermoelectric properties of LaFeAsO in the temperature range 10300 K. The resistivity decreases with carrier doping induced by oxygen deficiency up to y=0.16. On the other hand, the Seebeck coefficient shows a maximum absolute value at a finite doping level. The power factor (PF ... [J. Appl. Phys. 108, 033703 (2010)] published Wed Aug 4, 2010.

Large decrease in the critical temperature of superconducting LaFeAsO compounds doped with 3% atomic weight of nonmagnetic Zn impurities

Y. F. Guo, Y. G. Shi, S. Yu, A. A. Belik, Y. Matsushita et al.
We observed a large decrease in T by no more than 3 at. % of Zn doped into the T-optimized superconductor LaFeAsO (T=26 K), confirmed by measurements of electrical resistivity, magnetic susceptibility, specific heat, Mossbauer spectroscopy, Hall coefficient, and an electron probe microanalysis. Th ... [Phys. Rev. B 82, 054506 ] published .

Nanoscopic coexistence of magnetic and superconducting states within the FeAs layers of CeFeAsOF

S. Sanna, R. De Renzi, T. Shiroka, G. Lamura, G. Prando et al.
We report on the coexistence of magnetic and superconducting states in CeFeAsOF for x=0.06(2), characterized by transition temperatures T=30 K and T=18 K, respectively. Zero-field and transverse-field muon-spin-relaxation measurements show that below 10 K the two phases coexist within a nanoscopic ... [Phys. Rev. B 82, 060508 ] published .

Phase transitions and iron-ordered moment form factor in LaFeAsO

H.-F. Li, W. Tian, J.-Q. Yan, J. L. Zarestky, R. W. McCallum et al.
Elastic neutron-scattering studies of single-crystal LaFeAsO reveal that upon cooling, an onset of the tetragonal (T)-to-orthorhombic (O) structural transition occurs at T[approximate]156 K, and it exhibits a sharp transition at T[approximate]148 K. We argue that in the temperature range T to T, T ... [Phys. Rev. B 82, 064409 ] published .

Superconductivity without Nesting in LiFeAs

S. V. Borisenko, V. B. Zabolotnyy, D. V. Evtushinsky, T. K. Kim, I. V. Morozov et al.
We have studied the electronic structure of the nonmagnetic LiFeAs (T~18 K) superconductor using angle-resolved photoemission spectroscopy. We find a notable absence of the Fermi surface nesting, strong renormalization of the conduction bands by a factor of 3, high density of states at the Fermi le ... [Phys. Rev. Lett. 105, 067002 ] published .

Macroscopic physical properties and spin dynamics in the layered superconductor FeTeSe

Chishiro Michioka, Hiroto Ohta, Mami Matsui, Jinhu Yang, Kazuyoshi Yoshimura et al.
Macroscopic physical properties of the novel layered superconducting system FeTeSe were investigated by means of magnetic-susceptibility, electric resistivity, and heat-capacity measurements. In addition to the substitution effect of the Te site, intercalated excess irons would suppress the bulk sup ... [Phys. Rev. B 82, 064506 ] published .

Iron isotope effect on the superconducting transition temperature and the crystal structure of FeSe

R Khasanov, M Bendele, K Conder, H Keller, E Pomjakushina et al.
The Fe isotope effect (Fe-IE) on the transition temperature T and the crystal structure was studied in the Fe chalcogenide superconductor FeSe by means of magnetization and neutron powder diffraction (NPD). The substitution of natural Fe (containing ~=92% of Fe) by its lighter Fe isotope leads to a ... [New J. Phys. 12, 073024 (2010)] published Wed Aug 4, 2010.

Quantum chemical formulation of high-T superconductivity applied to alpha-FeSe

Itai Panas
High-T superconductivity (HTS) in the cuprates is revisited and employed to interpret the superconductivity phenomenon in alpha-FeSe. HTS in alpha-FeSe is proposed to emerge from accidental near degeneracy among spin zero Fe states on a magnetic sublattice in a magnetically inhomogeneous reference s ... [Phys. Rev. B 82, 064508 ] published .

Saw-tooth pattern from flux jumps observed by high resolution M-H curves in MgB thin films

Jae-Yeap Lee, Hu-Jong Lee, Myung-Hwa Jung, Sung-Ik Lee, Eun-Mi Choi et al.
While flux jumps have been observed in the magnetic hysteresis loops of superconductors, a saw-tooth pattern of the flux jump is known to appear only in a bulk superconductor. But in this study, we were able to observe the saw-tooth pattern in MgB thin film with the careful data acquisition method e ... [J. Appl. Phys. 108, 033909 (2010)] published Fri Aug 6, 2010.

Response of Cu(TlHg)BaCaZnCuO (y=0, 0.15, 0.25 and 0.35) superconductors in electric and magnetic fields

Adnan Younis and Shama Seher
The superconducting properties of the Cu(TlHg)BaCaZnCuO compound have been studied by resistivity and ac magnetic susceptibility measurements. Mercury substitution has been found to improve the superconductivity of the CuTlBaCaZnCuO (CuTl-1234) compound, which is evidenced by the improvement of phys ... [Phys. Scr. 82, 025701 (2010)] published Wed Aug 11, 2010.

Evidence for a temperature dependent anisotropy of the superconducting state parameters in underdoped SmBaCuO

A. Kortyka, R. Puzniak, A. Wisniewski, M. Zehetmayer, H. W. Weber et al.
The temperature dependence of the anisotropy of the superconducting state parameters, gamma, was studied by torque magnetometry for the high-temperature superconductor SmBaCuO in magnetic fields of up to 9 T. The measurements were performed on four underdoped single crystals with oxygen contents cor ... [Phys. Rev. B 82, 054510 ] published .

How grain boundaries limit supercurrents in high-temperature superconductors

S. Graser, P. J. Hirschfeld, T. Kopp, R. Gutser, B. M. Andersen et al.
The interface properties of high-temperature (high-T) copper oxide superconductors have been of interest for many years, and play an essential role in Josephson junctions, superconducting cables and microwave electronics. In particular, the maximum critical current achievable in high-T wires and tap ... [Nature Phys. 6, 609 (2010)] published Wed Aug 4, 2010.

Effect of LaAlO twin-domain topology on local dc and microwave properties of cuprate films

A. P. Zhuravel, Steven M. Anlage, Stephen K. Remillard, A. V. Lukashenko, and A. V. Ustinov
Different imaging modes of low temperature laser scanning microscopy (LTLSM) have been applied to probe local optical and superconducting properties, as well as the spatial variations in thermoelectric and electronic (both dc and rf) transport, in a YBaCuO/LaAlO (YBCO/LAO) superconducting microstrip ... [J. Appl. Phys. 108, 033920 (2010)] published Fri Aug 13, 2010.

Strength of correlations in electron- and hole-doped cuprates

Cdric Weber, Kristjan Haule, and Gabriel Kotliar
The introduction of holes in a parent compound consisting of copper oxide layers results in high-temperature superconductivity. It is also possible to dope the cuprate parent compound with electrons. The physical properties of these electron-doped materials bear some similarities to but also signif ... [Nature Phys. 6, 574 (2010)] published Wed Aug 4, 2010.

Publisher's Note: Coherent Terahertz Emission of Intrinsic Josephson Junction Stacks in the Hot Spot Regime [Phys. Rev. Lett. 105, 057002 (2010)]

H. B. Wang, S. Guenon, B. Gross, J. Yuan, Z. G. Jiang et al.
Abstract not available. [Phys. Rev. Lett. 105, 069902 ] published .

Evidence for triplet superconductivity in Josephson junctions with barriers of the ferromagnetic Heusler alloy CuMnAl

D. Sprungmann, K. Westerholt, H. Zabel, M. Weides, and H. Kohlstedt
We have studied Josephson junctions with barriers prepared from the Heusler compound CuMnAl. In the as-prepared state the CuMnAl layers are nonferromagnetic and the critical Josephson current density j decreases exponentially with the thickness of the Heusler layers d. On annealing the junctions at ... [Phys. Rev. B 82, 060505 ] published .

Electromagnetically Induced Transparency with Amplification in Superconducting Circuits

Jaewoo Joo, Jerome Bourassa, Alexandre Blais, and Barry C. Sanders
We show that controlling relative phases of electromagnetic fields driving an atom with a Delta-configuration energy-level structure enables optical susceptibility to be engineered in novel ways. In particular, relative-phase control can yield electromagnetically induced transparency but with the be ... [Phys. Rev. Lett. 105, 073601 ] published .

Measurement of the effect of quantum phase slips in a Josephson junction chain

I. M. Pop, I. Protopopov, F. Lecocq, Z. Peng, B. Pannetier et al.
The interplay between superconductivity and Coulomb interactions has been studied for more than 20 years now. In low-dimensional systems, superconductivity degrades in the presence of Coulomb repulsion: interactions tend to suppress fluctuations of charge, thereby increasing fluctuations of phase. ... [Nature Phys. 6, 589 (2010)] published Wed Aug 4, 2010.

Implementation of superconductor/ferromagnet/ superconductor -shifters in superconducting digital and quantum circuits

A. K. Feofanov, V. A. Oboznov, V. V. Bolginov, J. Lisenfeld, S. Poletto et al.
High operation speed and low energy consumption may allow the superconducting digital single-flux-quantum circuits to outperform traditional complementary metaloxidesemiconductor logic. The remaining major obstacle towards high element densities on-chip is a relatively large cell size necessary to ... [Nature Phys. 6, 593 (2010)] published Wed Aug 4, 2010.

Quantum logical gates with four-level superconducting quantum interference devices coupled to a superconducting resonator

Xiao-Ling He, Chui-Ping Yang, Sheng Li, Jun-Yan Luo, and Siyuan Han
We propose a way for realizing a two-qubit controlled phase gate with superconducting quantum interference devices (SQUIDs) coupled to a superconducting resonator. In this proposal, the two lowest levels of each SQUID serve as the logical states and two intermediate levels of each SQUID are used for ... [Phys. Rev. A 82, 024301 ] published .

Strong Coupling of a Quantum Oscillator to a Flux Qubit at Its Symmetry Point

A. Fedorov, A. K. Feofanov, P. Macha, P. Forn-Diaz, C. J. P. M. Harmans et al.
A flux qubit biased at its symmetry point shows a minimum in the energy splitting (the gap), providing protection against flux noise. We have fabricated a qubit of which the gap can be tuned fast and have coupled this qubit strongly to an LC oscillator. We show full spectroscopy of the qubit-oscilla ... [Phys. Rev. Lett. 105, 060503 ] published .