129 research outputs found
Three-dimensional dispersion induced by extreme tensile strain in La_(2āx)Sr_xCuO_4 films
The electronic band structure probed by angle-resolved photoemission spectroscopy on thin epitaxial La2āxSrxCuO4 films under extreme tensile strain shows anomalous features compatible with c-axis dispersion. This result is in striking contrast with the usual quasi-two-dimensional (2D) dispersion observed up to now in most superconducting cuprates, including relaxed and compressively strained La2āxSrxCuO4 films grown under the same conditions. The data were analyzed using a 3D tight-binding dispersion for a body-centered-tetragonal lattice. We relate the enhancement of the c-axis dispersion to the significant displacement of the apical oxygen induced by epitaxial strain
On field effect studies and superconductor-insulator transition in high-Tc cuprates
We summarize previous field effect studies in high-T c cuprates and then discuss our method to smoothly tune the carrier concentration of a cuprate film over a wide range using an applied electric field. We synthesized epitaxial one-unit-cell thick films of La2āx Sr x CuO4 and from them fabricated electric double layer transistor devices utilizing various gate electrolytes. We were able to vary the carrier density by about 0.08 carriers per Cu atom, with the resulting change in T c of 30 K. The superconductor-insulator transition occurred at the critical resistance very close to the quantum resistance for pairs, R Q = h/(2e)2 = 6.5 kĪ©. This is suggestive of a quantum phase transition, possibly driven by quantum phase fluctuations, between a "Bose insulatorā and a high-T c superconductor stat
On Fractal Geometry for Water Implosion Engineering
Summary Historically water engineering was predominantly treated within a conventional mathematical framework, like Bernoulli approach or more advanced Navier-Stokes equations; lately by various numerical modeling schemes. Here we outline how the natural, yet complex water (and related fluids) flow and implosion engineering can successfully be treated by contemporary fractal mathematics. Such an approach could gradually improve our fluid engineering and the planetary use of natural water in bio-medical, transport and energy context
Experimental Electronic Structure and Interband Nesting in BaVS_3
The correlated 3d sulphide BaVS_3 is a most interesting compound because of
the apparent coexistence of one-dimensional and three-dimensional properties.
Our experiments explain this puzzle and shed new light on its electronic
structure. High-resolution angle-resolved photoemission measurements in a 4eV
wide range below the Fermi level explored the coexistence of weakly correlated
a_1g wide-band and strongly correlated e_g narrow-band d-electrons that is
responsible for the complicated behavior of this material. The most relevant
result is the evidence for a_1g--e_g inter-band nesting condition.Comment: 4 pages, 3 figure
Promjene spektralnih svojstava kuprata visokog Tc izazvane defektima
Superconductivity in high-Tc cuprates is particularly sensitive to disorder due to the unconventional d-wave pairing symmetry. We investigated effects of disorder on the spectral properties of Bi2Sr2CaCu2O8+x high-Tc superconductor. We found that already small defect densities suppress the characteristic spectral signature of the superconducting state. The spectral line shape clearly reflects new excitations within the gap, as expected for defect-induced pair breaking. At the lowest defect concentrations the normal state remains unaffected, while increased disorder leads to suppression of the normal quasiparticle peaks.Zbog nekonvencionalne d-valne simetrije, supravodljivost u visokotemperaturnim kupratima je posebno osjetljiva na neureÄenost. Ispitivali smo utjecaj neureÄenosti na spektralna svojstva Bi2Sr2CaCu2O8+x supravodiÄa primjenom ARPES metode. VeÄ mala gustoÄa defekata smanjuje karakteristiÄni spektralni odziv supravodljivog stanja. Oblik spektralne linije oÄito reflektira nova pobuÄenja unutar zabranjene vrpce, kako se i oÄekuje u sluÄaju razbijanja Cooperovih parova izazvanog defektima. Za male koncentracije defekata, normalno stanje ostaje nepromijenjeno, dok viÅ”i stupanj neureÄenosti smanjuje intenzitet spektralnih linija kvaziÄestica
On field effect studies and superconductor-insulator transition in high-Tc cuprates
We summarize previous field effect studies in high-T (c) cuprates and then discuss our method to smoothly tune the carrier concentration of a cuprate film over a wide range using an applied electric field. We synthesized epitaxial one-unit-cell thick films of La2-x Sr (x) CuO4 and from them fabricated electric double layer transistor devices utilizing various gate electrolytes. We were able to vary the carrier density by about 0.08 carriers per Cu atom, with the resulting change in T (c) of 30 K. The superconductor-insulator transition occurred at the critical resistance very close to the quantum resistance for pairs, R (Q) = h/(2e)(2) = 6.5 k Omega. This is suggestive of a quantum phase transition, possibly driven by quantum phase fluctuations, between a "Bose insulator" and a high-T (c) superconductor state
Insulator to metal transition in WO3 induced by electrolyte gating
Tungsten oxide and its associated bronzes (compounds of tungsten oxide and an alkali metal) are well known for their interesting optical and electrical characteristics. We have modified the transport properties of thin WO3 films by electrolyte gating using both ionic liquids and polymer electrolytes. We are able to tune the resistivity of the gated film by more than five orders of magnitude, and a clear insulator-to-metal transition is observed. To clarify the doping mechanism, we have performed a series of incisive operando experiments, ruling out both a purely electronic effect (charge accumulation near the interface) and oxygen-related mechanisms. We propose instead that hydrogen intercalation is responsible for doping WO3 into a highly conductive ground state and provide evidence that it can be described as a dense polaronic gas
Ruthenocuprates RuSr2(Eu,Ce)2Cu2O10: Intrinsic magnetic multilayers
We report ac susceptibility data on RuSr_2(Eu,Ce)_2Cu_2O_(10-y) (Ru-1222, Ce
content x=0.5 and 1.0), RuSr_2GdCu_2O_8 (Ru-1212) and SrRuO_3. Both Ru-1222
(x=0.5, 1.0) sample types exhibit unexpected magnetic dynamics in low magnetic
fields: logarithmic time relaxation, switching behavior, and `inverted'
hysteresis loops. Neither Ru-1212 nor SrRuO_3 exhibit such magnetic dynamics.
The results are interpreted as evidence of the complex magnetic order in
Ru-1222. We propose a specific multilayer model to explain the data, and note
that superconductivity in the ruthenocuprate is compatible with both the
presence and absence of the magnetic dynamics.Comment: 9 pages, 11 figures, Revtex; submitted to Phys.Rev.
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