910 research outputs found
Tailoring a two-dimensional electron gas at the LaAlO3/SrTiO3 (001) interface by epitaxial strain
Recently a metallic state was discovered at the interface between insulating
oxides, most notably LaAlO3 and SrTiO3. Properties of this two-dimensional
electron gas (2DEG) have attracted significant interest due to its potential
applications in nanoelectronics. Control over this carrier density and mobility
of the 2DEG is essential for applications of these novel systems, and may be
achieved by epitaxial strain. However, despite the rich nature of strain
effects on oxide materials properties, such as ferroelectricity, magnetism, and
superconductivity, the relationship between the strain and electrical
properties of the 2DEG at the LaAlO3/SrTiO3 heterointerface remains largely
unexplored. Here, we use different lattice constant single crystal substrates
to produce LaAlO3/SrTiO3 interfaces with controlled levels of biaxial epitaxial
strain. We have found that tensile strained SrTiO3 destroys the conducting
2DEG, while compressively strained SrTiO3 retains the 2DEG, but with a carrier
concentration reduced in comparison to the unstrained LaAlO3/SrTiO3 interface.
We have also found that the critical LaAlO3 overlayer thickness for 2DEG
formation increases with SrTiO3 compressive strain. Our first-principles
calculations suggest that a strain-induced electric polarization in the SrTiO3
layer is responsible for this behavior. It is directed away from the interface
and hence creates a negative polarization charge opposing that of the polar
LaAlO3 layer. This both increases the critical thickness of the LaAlO3 layer,
and reduces carrier concentration above the critical thickness, in agreement
with our experimental results. Our findings suggest that epitaxial strain can
be used to tailor 2DEGs properties of the LaAlO3/SrTiO3 heterointerface
Suppression of Superconducting Critical Current Density by Small Flux Jumps in Thin Films
By doing magnetization measurements during magnetic field sweeps on thin
films of the new superconductor , it is found that in a low temperature
and low field region small flux jumps are taking place. This effect strongly
suppresses the central magnetization peak leading to reduced nominal
superconducting critical current density at low temperatures. A borderline for
this effect to occur is determined on the field-temperature (H-T) phase
diagram. It is suggested that the small size of the flux jumps in films is due
to the higher density of small defects and the relatively easy thermal
diffusion in thin films in comparison with bulk samples.Comment: 7 figures Phys. Rev. B accepted scheduled issue: 01 Feb 200
Interface structure and strain relaxation in BaTiO3 thin films grown on GdScO3 and DyScO3 substrates with buried coherent SrRuO3 layer
To obtain the electrical properties of strained ferroelectric thin films, bottom electrodes with lattice constants and thermal coefficients matched to both films and substrates are needed. The interface structure, strain configuration, and strain relaxation in such bilayer systems are different from those in single layer systems. Here, we report transmission electron microscopy studies of epitaxial BaTiO3 films grown on GdScO3 and DyScO3 substrates with buried SrRuO3 layers. We found that the different strain relaxation behaviors observed in the bilayer are mainly dependent on lattice mismatch of each layer to the substrate and the thicknesses of each layer.open7
Non-Fermi liquid behavior and scaling of low frequency suppression in optical conductivity spectra of CaRuO
Optical conductivity spectra of paramagnetic CaRuO are
investigated at various temperatures. At T=10 K, it shows a non-Fermi liquid
behavior of , similar to the case
of a ferromagnet SrRuO. As the temperature () is increased, on the other
hand, in the low frequency region is progressively
suppressed, deviating from the 1/{\omega}^{\frac 12%}-dependence.
Interestingly, the suppression of is found to scale with
at all temperatures. The origin of the scaling
behavior coupled with the non-Fermi liquid behavior is discussed.Comment: 4 pages, 3 figure
Statistics of Heat Transfer in Mesoscopic Circuits
A method to calculate the statistics of energy exchange between quantum
systems is presented. The generating function of this statistics is expressed
through a Keldysh path integral. The method is first applied to the problem of
heat dissipation from a biased mesoscopic conductor into the adjacent
reservoirs. We then consider energy dissipation in an electrical circuit around
a mesoscopic conductor. We derive the conditions under which measurements of
the fluctuations of heat dissipation can be used to investigate higher order
cumulants of the charge counting statistics of a mesoscopic conductor.Comment: 9 pages, 6 figure
Non-resonant microwave absorption studies of superconducting MgB_2
Non-resonant microwave absorption(NRMA) studies of superconducting MgB_2 at a
frequency of 9.43 GHz in the field range -50 Gauss to 5000 Gauss are reported.
The NRMA results indicate near absence of intergranular weak links. A linear
temperature dependence of the lower critical field H_c1 is observed indicating
a non s-wave superconductivity. However, the phase reversal of the NRMA signal
which could suggest d-wave symmetry is also not observed.Comment: 8 pages, 2 figure
Direct Imaging of Graphene Edges: Atomic Structure and Electronic Scattering
We report an atomically-resolved scanning tunneling microscopy (STM)
investigation of the edges of graphene grains synthesized on Cu foils by
chemical vapor deposition (CVD). Most of the edges are macroscopically parallel
to the zigzag directions of graphene lattice. These edges have microscopic
roughness that is found to also follow zigzag directions at atomic scale,
displaying many ~120 degree turns. A prominent standing wave pattern with
periodicity ~3a/4 (a being the graphene lattice constant) is observed near a
rare-occurring armchair-oriented edge. Observed features of this wave pattern
are consistent with the electronic intervalley backscattering predicted to
occur at armchair edges but not at zigzag edges
75As NMR probe of antiferromagnetic fluctuations in Ba(Fe1-xRux)2As2
The evolution of 75As NMR parameters with composition and temperature was
probed in the Ba(Fe1-xRux)2As2 system where Fe is replaced by isovalent Ru.
While the Ru-end member was found to be a conventional Fermi liquid, the
composition (x=0.5) corresponding to the highest Tc (20K) in this system shows
an upturn in 75As 1/T1T below about 80 K evidencing the presence of
antiferromagnetic (AFM) fluctuations. These results are similar to those
obtained in another system with isovalent substitution BaFe2(As1-xPx)2 [Y.
Nakai, T. Iye, S. Kitagawa, K. Ishida, H. Ikeda, S. Kasahara, H. Shishido, T.
Shibauchi, Y. Matsuda, and T. Terashima, Phys. Rev. Lett. 105, 107003 (2010)]
and point to the possible role of AFM fluctuations in driving
superconductivity.Comment: 5 pages, 4 figure
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