Articolele autorului Costel R Rotundu
Link la profilul stiintific al lui Costel R Rotundu

High-pressure resistivity technique for quasi-hydrostatic compression experiments

Diamond anvil cell techniques are now well established and powerful methods for measuring materials properties to very high pressure. However, high pressure resistivity measurements are challenging because the electrical contacts attached to the sample have to survive to extreme stress conditions. Until recently, experiments in a diamond anvil cell were mostly limited to non-hydrostatic or quasihydrostatic pressure media other than inert gases. We

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Comment on “Retention of the Tetragonal to Orthorhombic Structural Transition in F-Substituted SmFeAsO: A New Phase Diagram for SmFeAs(O1-xFx)”
Photoelectron spin-flipping and texture manipulation realized in a topological insulator

Recently discovered materials called three-dimensional topological insulators constitute examples of symmetry protected topological states in the absence of applied magnetic fields and cryogenic temperatures. A hallmark characteristic of these non-magnetic bulk insulators is their protected metallic Dirac fermion-like surface states. Electrons in these surface states are spin polarized with their spins governed by their momentum, resulting in a helical

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Measurement of Ba(Fe1-xCox)2As2 critical-magnetic exponents for x = 0.039, 0.022, and 0.021

We present temperature dependent magnetic neutron diffraction measurements on Ba(Fe1−xCox)2As2 for x=0.039, 0.022, and 0.021 as-grown single crystals. Our investigations probe the behavior near the magnetic tricritical point in the (x,T) plane, xtr≈0.022, as well as systematically exploring the character of the magnetic phase transition across a range of doping values. All samples show long-range antiferromagnetic order that may be described

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Effect of electron correlations on the spin excitations in isovalently doped iron based superconductor Ba(Fe1-xRux)2As2

Magnetic correlations in isovalently doped Ba(Fe1-xRux)2As2 (x=0.25, Tc=14.5  K; x=0.35, Tc=20  K) are studied by elastic and inelastic neutron scattering techniques. A relatively large superconducting spin gap accompanied by a weak resonance mode is observed in the superconducting state in both samples. In the normal state, the magnetic excitation intensity is dramatically reduced with increasing Ru doping toward the optimally doped regime.

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High-pressure effects on single crystals of electron-doped Pr2-xCexCuO4

We present high-pressure diamond-anvil cell synchrotron x-ray, resistivity, and ac-susceptibility measurements on the electron-doped cuprate Pr2-xCexCuO4 to much higher pressures than previously reported. At 2.72 GPa between 88 and 98% of the superconducting T phase of the optimally doped Pr1.85Ce0.15CuO4 transforms into the insulating phase T . With application of pressure, the T phase becomes more insulating, so we present here an example of electron

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A neutron scattering study of the under-doped Ba1-xKxFe2As2, x=0.09 and 0.17 self-flux grown single crystals and the universality of the tricritical point

We present a combination of elastic neutron scattering measurements in zero and 14.5 T and magnetization measurements in zero and 14 T on underdoped superconducting Ba1−xKxFe2As2 (x = 0.17), and the same measurements in zero field on a nonsuperconducting crystal with x = 0.09. The data suggest that the underdoped materials may not be electronic phase separated but rather have slightly inhomogeneous potassium doping. The temperature dependence of

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Low temperature transport properties of Ce-Al metallic glasses

The low temperature transport properties of Ce75-xAl25+x (x=0, 10, and 15 at. %) metallic glasses were investigated. Magnetic field and composition tuned magnetoresistances changing from negative to positive values were observed at low temperature. It was suggested that these peculiar phenomena were caused by the tunable competition between the Kondo effect and the Ruderman-Kittel-Kasuya-Yoshida interaction in Ce-Al metallic glass with the variation

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Specific heat of the S=1/2 two-dimensional Shastry-Sutherland antiferromagnet SrCu2(BO3)2 in high magnetic fields

We characterize the field-induced magnetic phases of SrCu2(BO3)2, a frustrated spin-1/2 Heisenberg antiferromagnet in the two-dimensional Shastry–Sutherland lattice, using specific heat in magnetic fields up to 33 T. We find that the spin gap persists above the expected critical field Hc=Delta/(g*mu_B) of 21 T despite the appearance of magnetic moment in the ground state. At the magnetization plateau at 1/8 of the saturation, the triplets that

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Widespread spin polarization effects in photoemission from topological insulators

High-resolution spin- and angle-resolved photoemission spectroscopy (spin-ARPES) was performed on the three-dimensional topological insulator Bi2Se3 using a recently developed high-efficiency spectrometer. The topological surface state’s helical spin structure is observed, in agreement with theoretical prediction. Spin textures of both chiralities, at energies above and below the Dirac point, are observed, and the spin structure is found to persist

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