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Search Results: 1 - 10 of 144408 matches for " B. Maiorov "
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Novel Vortex Solid State in YBa$_2$Cu$_3$O$_{7 - δ}$ Twinned Crystals
B. Maiorov,E. Osquiguil
Physics , 2001, DOI: 10.1103/PhysRevB.64.052511
Abstract: We report on the scaling of transport properties around the vortex melting in YBa$_2$Cu$_3$O$_{7- \delta}$ oriented-twin single crystals in applied magnetic fields between 1T and 18T. We find that for all the measured field range the linear resistivity scales as $\rho (t,\theta) \sim t^{sy} {\cal F}_{\pm} (\sin(\theta)t^{-sx})$, with $t=|T-T_{BG}|$ and $\theta$ the angle between de planar defects and the magnetic field. The scaling is valid only for angles where the transition temperature $T_{BG} (\theta)$ shows a cusp. The critical exponents $sx$ and $sy$ are in agreement with the values predicted by Lidmar and Wallin only at magnetic fields below 4T. A change in the value of $sx$ from $sx = 1 \pm 0.2$ to $sx = 3 \pm 0.2$ at around $H^{cr} \approx $ 4T when the magnetic field is increased, is responsible for changes in the shape of the $T_{BG} (\theta)$ curve and in the dependence of the linear dissipation on temperature and angle. The results strongly suggest the existence of a different vortex glassy phase in twinned crystals compared to the Bose-glass state found in samples with linear defects.
First order phase transition of the vortex lattice in twinned YBa2Cu3O7 single crystals in tilted magnetic fields
B. Maiorov,G. Nieva,E. Osquiguil
Physics , 1999, DOI: 10.1103/PhysRevB.61.12427
Abstract: We present an exhaustive analysis of transport measurements performed in twinned YBa2Cu3O7 single crystals which stablishes that the vortex solid-liquid transition is first order when the magnetic field H is applied at an angle theta away from the direction of the twin planes. We show that the resistive transitions are hysteretic and the V-I curves are non-linear, displaying a characteristic s-shape at the melting line Hm(T), which scales as epsilon(theta)Hm(T,theta). These features are gradually lost when the critical point H*(theta) is approached. Above H*(theta) the V-I characteristics show a linear response in the experimentally accessible V-I window, and the transition becomes reversible. Finally we show that the first order phase transition takes place between a highly correlated vortex liquid in the field direction and a solid state of unknown symmetry. As a consequence, the available data support the scenario for a vortex-line melting rather than a vortex sublimation as recently suggested [T.Sasagawa et al. PRL 80, 4297 (1998)].
Correlated enhancement of Hc2 and Jc in carbon nanotube-doped MgB2
A. Serquis,G. Serrano,S. Moreno,; L. Civale,B. Maiorov,; F. Balakirev,M. Jaime
Physics , 2006, DOI: 10.1088/0953-2048/20/4/L02
Abstract: The use of MgB2 in superconducting applications still awaits for the development of a MgB2-based material where both current-carrying performance and critical magnetic field are optimized simultaneously. We achieved this by doping MgB2 with double-wall carbon nanotubes (DWCNT) as a source of carbon in polycrystalline samples. The optimum nominal DWCNT content for increasing the critical current density, Jc is in the range 2.5-10%at depending on field and temperature. Record values of the upper critical field, Hc2(4K) = 41.9 T (with extrapolated Hc2(0) ~ 44.4 T) are reached in a bulk sample with 10%at DWCNT content. The measured Hc2 vs T in all samples are successfully described using a theoretical model for a two-gap superconductor in the dirty limit first proposed by Gurevich et al.
Psuedo-isotropic upper critical field in cobalt-doped SrFe2As2 epitaxial films
S. A. Baily,Y. Kohama,H. Hiramatsu,B. Maiorov,F. F. Balakirev,M. Hirano,H. Hosono
Physics , 2008, DOI: 10.1103/PhysRevLett.102.117004
Abstract: The temperature and angular dependence of the upper critical field (Hc2) is reported for cobalt-doped SrFe2As2 epitaxial films between Tc and 0.5 K in pulsed magnetic fields up to 50 T. For H parallel c, Hc2 is close to a linear function of temperature, while in the perpendicular direction there is significant downward curvature that results in an Hc2 ratio (gamma = Hc2(perpendicular)/Hc2(parallel) that decreases nearly linearly with temperature, approaching gamma = 1 at low temperature with Hc2(0) = 47 T. We measure the complete upper-critical field phase diagram including angular dependence and model the data using a two band theory allowing us to determine the anisotropy of both bands, their relative diffusivities, and the relationship between BCS coupling constant matrix elements. We find an unusual relationship between the diffusivities of the two bands, with two anisotropic and opposite bands. This relationship is supported by the observation of a local maximum for Hc2(parallel) at low temperature.
Anomalous Proximity Effect in Underdoped YBaCuO Josephson Junctions
R. S. Decca,H. D. Drew,E. Osquiguil,B. Maiorov,J. Guimpel
Physics , 2000, DOI: 10.1103/PhysRevLett.85.3708
Abstract: Josephson junctions were photogenerated in underdoped thin films of the YBa$_2$Cu$_3$O$_{6+x}$ family using a near-field scanning optical microscope. The observation of the Josephson effect for separations as large as 100 nm between two wires indicates the existence of an anomalously large proximity effect and show that the underdoped insulating material in the gap of the junction is readily perturbed into the superconducting state. The critical current of the junctions was found to be consistent with the conventional Josephson relationship. This result constrains the applicability of SO(5) theory to explain the phase diagram of high critical temperature superconductors.
Photoinduced superconducting nanowires in Gd-Ba-Cu-O films
R. S. Decca,H. D. Drew,B. Maiorov,J. Guimpel,E. Osquiguil
Physics , 1998, DOI: 10.1063/1.121787
Abstract: We report the fabrication of high Tc superconducting wires by photodoping a GdBa2Cu3O{6.5} thin film. An optical near-field probe was used to locally excite carriers in the system at room temperature. Trapping of the photogenerated electrons define a confining potential for the conducting holes in the CuO planes. Spatially resolved reflectance measurements show the photogenerated nanowires to be ~ 250 nm wide. Electron diffusion, before electron capture, is believed to be responsible for the observed width of the wires.
Comment on `Strong Vortex Liquid Correlation' from Multiterminal Measurements on Untwinned YBa$_2$Cu$_3$O$_{7-δ}$ Single Crystals'
B. Maiorov,A. V. Silhanek,F. de la Cruz,E. Osquiguil
Physics , 2002, DOI: 10.1103/PhysRevLett.88.139703
Abstract: A.Rydh and \"O.Rapp [Phys. Rev. Lett. {\bf 86}, 1873 (2001).] claim that the vortex liquid in untwinned YBa$_2$Cu$_3$O$_{7-\delta}$ crystals is correlated above the melting transition, in striking contrast to previous work [D.L\'opez {\it et al.}, Phys. Rev. Lett. {\bf 76}, 4034 (1996).]. In this Comment we present new measurements using the same experimental technique on twinned and untwinned YBa$_2$Cu$_3$O$_{7-\delta}$ crystals with similar overall characteristics as those reported by Rydh and Rapp . The comparison of the vortex correlation response in both cases indicates that the central conclusion of their work is not correct. Our results reconfirm the work by L\'opez {\it et al.} and points on the origin of the misinterpretation in the work of Rydh and Rapp.
Doping-Dependent Nonlinear Meissner Effect and Spontaneous Currents in High-Tc Superconductors
Sheng-Chiang Lee,Mathew Sullivan,Gregory R. Ruchti,Steven M. Anlage,Benjamin Palmer,B. Maiorov,E. Osquiguil
Physics , 2004, DOI: 10.1103/PhysRevB.71.014507
Abstract: We measure the local harmonic generation from superconducting thin films at microwave frequencies to investigate the intrinsic nonlinear Meissner effect near Tc in zero magnetic field. Both second and third harmonic generation are measured to identify time-reversal symmetry breaking (TRSB) and time-reversal symmetric (TRS) nonlinearities. We perform a systematic doping-dependent study of the nonlinear response and find that the TRS characteristic nonlinearity current density scale follows the doping dependence of the de-pairing critical current density. We also extract a spontaneous TRSB characteristic current density scale that onsets at Tc, grows with decreasing temperature, and systematically decreases in magnitude (at fixed T/Tc) with under-doping. The origin of this current scale could be Josephson circulating currents or the spontaneous magnetization associated with a TRSB order parameter.
Strong Enhancement of the Critical Current at the Antiferromagnetic Transition in ErNi2B2C Single Crystals
M. Weigand,L. Civale,F. J. Baca,Jeehoon Kim,S. L. Bud'ko,P. C. Canfield,B. Maiorov
Physics , 2013, DOI: 10.1103/PhysRevB.87.140506
Abstract: We report on transport and magnetization measurements of the critical current density Jc in ErNi2B2C single crystals that show strongly enhanced vortex pinning at the Neel temperature TN and low applied fields. The height of the observed Jc peak decreases with increasing magnetic field in clear contrast with that of the peak effect found at the upper critical field. We also performed the first angular transport measurements of Jc ever conducted on this compound. They reveal the correlated nature of this pinning enhancement, which we attribute to the formation of antiphase boundaries at TN.
Magneto-optical evidence for a gapped Fermi surface in underdoped YBa2Cu3O6+x
L. B. Rigal,D. C. Schmadel,H. D. Drew,B. Maiorov,E. Osquigil,J. S. Preston,R. Hughes,G. D. Gu
Physics , 2003, DOI: 10.1103/PhysRevLett.93.137002
Abstract: The infrared (900-1100 cm-1) Faraday rotation and circular dichroism are measured in the normal state of underdoped High Tc superconductors and used to study the magneto-transport. YBa2Cu3O6+x thin films are investigated in the temperature range 10-300 K in magnetic fields up to 8 Tesla and as a function of oxygen concentration. A dramatic increase of the Hall frequency is observed for underdoped samples which is not consistent with the approach to a Mott transition but is consistent with a partial gapping of the Fermi surface as predicted in charge density wave models.
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