1,396 research outputs found
Disorder versus two transport lifetimes in a strongly correlated electron liquid
We report on angle-dependent measurements of the sheet resistances and Hall
coefficients of electron liquids in SmTiO3/SrTiO3/SmTiO3 quantum well
structures, which were grown by molecular beam epitaxy on (001) DyScO3. We
compare their transport properties with those of similar structures grown on
LSAT [(La0.3Sr0.7)(Al0.65Ta0.35)O3]. On DyScO3, planar defects normal to the
quantum wells lead to a strong in-plane anisotropy in the transport properties.
This allows for quantifying the role of defects in transport. In particular, we
investigate differences in the longitudinal and Hall scattering rates, which is
a non-Fermi liquid phenomenon known as lifetime separation. The residuals in
both the longitudinal resistance and Hall angle were found to depend on the
relative orientations of the transport direction to the planar defects. The
Hall angle exhibited a robust T2 temperature dependence along all directions,
whereas no simple power law could describe the temperature dependence of the
longitudinal resistances. Remarkably, the degree of the carrier lifetime
separation, as manifested in the distinctly different temperature dependences
and diverging residuals near a critical quantum well thickness, was completely
insensitive to disorder. The results allow for a clear distinction between
disorder-induced contributions to the transport and intrinsic, non-Fermi liquid
phenomena, which includes the lifetime separation.Comment: In press, Sci. Re
Growth of strontium ruthenate films by hybrid molecular beam epitaxy
We report on the growth of epitaxial Sr2RuO4 films using a hybrid molecular
beam epitaxy approach in which a volatile precursor containing RuO4 is used to
supply ruthenium and oxygen. The use of the precursor overcomes a number of
issues encountered in traditional MBE that uses elemental metal sources.
Phase-pure, epitaxial thin films of Sr2RuO4 are obtained. At high substrate
temperatures, growth proceeds in a layer-by-layer mode with intensity
oscillations observed in reflection high-energy electron diffraction. Films are
of high structural quality, as documented by x-ray diffraction, atomic force
microscopy, and transmission electron microscopy. The method should be suitable
for the growth of other complex oxides containing ruthenium, opening up
opportunities to investigate thin films that host rich exotic ground states.Comment: In press, APL Mate
Response of the lattice across the filling-controlled Mott metal-insulator transition of a rare earth titanate
The lattice response of a prototype Mott insulator, SmTiO3, to hole doping is
investigated with atomic-scale spatial resolution. SmTiO3 films are doped with
Sr on the Sm site with concentrations that span the insulating and metallic
sides of the filling-controlled Mott metal-insulator transition (MIT). The
GdFeO3-type distortions are investigated using an atomic resolution scanning
transmission electron microscopy technique that can resolve small lattice
distortions with picometer precision. We show that these distortions are
gradually and uniformly reduced as the Sr concentration is increased without
any phase separation. Significant distortions persist into the metallic state.
The results present a new picture of the physics of this prototype
filling-controlled MIT, which is discussed.Comment: Accepted, Phys. Rev. Let
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Controlling a Van Hove singularity and Fermi surface topology at a complex oxide heterostructure interface.
The emergence of saddle-point Van Hove singularities (VHSs) in the density of states, accompanied by a change in Fermi surface topology, Lifshitz transition, constitutes an ideal ground for the emergence of different electronic phenomena, such as superconductivity, pseudo-gap, magnetism, and density waves. However, in most materials the Fermi level, [Formula: see text], is too far from the VHS where the change of electronic topology takes place, making it difficult to reach with standard chemical doping or gating techniques. Here, we demonstrate that this scenario can be realized at the interface between a Mott insulator and a band insulator as a result of quantum confinement and correlation enhancement, and easily tuned by fine control of layer thickness and orbital occupancy. These results provide a tunable pathway for Fermi surface topology and VHS engineering of electronic phases
3C 273 Host Galaxy with Hubble Space Telescope Coronagraphy
The close-in regions of bright quasars' host galaxies have been difficult to
image due to the overwhelming light from the quasars. With coronagraphic
observations in visible light using the Space Telescope Imaging Spectrograph
(STIS) on the Hubble Space Telescope, we removed 3C 273 quasar light using
color-matching reference stars. The observations revealed the host galaxy from
60" to 0.2" with nearly full angular coverage. Isophote modeling revealed a new
core jet, a core blob, and multiple smaller-scale blobs within 2.5". The blobs
could potentially be satellite galaxies or infalling materials towards the
central quasar. Using archival STIS data, we constrained the apparent motion of
its large scale jets over a 22 yr timeline. By resolving the 3C 273 host galaxy
with STIS, our study validates the coronagraph usage on extragalactic sources
in obtaining new insights into the central ~kpc regions of quasar hosts.Comment: 13 pages, 11 figures, 2 tables, A&A Letters accepte
Development of cyclobutene- and cyclobutane-functionalized fatty acids with inhibitory activity against \u3ci\u3eMycobacterium tuberculosis\u3c/i\u3e
Eleven fatty acid analogs incorporating four-membered carbocycles (cyclobutenes, cyclobutanes, cyclobutanones, and cyclobutanols) were investigated for the ability to inhibit growth of Mycobacterium smegmatis (Msm) and Mycobacterium tuberculosis (Mtb). A number of the analogs displayed inhibitory activity against both mycobacterial species in minimal media. Several of the molecules displayed potent levels of inhibition against Mtb with MIC values equal to or below those obtained with the anti-tuberculosis drugs D-cycloserine and isoniazid. In contrast, two of the analogs displaying the greatest activity against Mtb failed to inhibit E. coli growth under either set of conditions. Thus, the active molecules identified here (1, 2, 6, and 8) may provide the basis for development of anti-mycobacterial agents against Mtb
The Optical-Near-IR Spectrum of the M87 Jet From HST Observations
We present 1998 HST observations of M87 which yield the first single-epoch
optical and radio-optical spectral index images of the jet at
resolution. We find , comparable to previous
measurements, and (),
slightly flatter than previous workers. Reasons for this discrepancy are
discussed. These observations reveal a large variety of spectral slopes. Bright
knots exhibit flatter spectra than interknot regions. The flattest spectra
(; comparable to or flatter than ) are
found in two inner jet knots (D-East and HST-1) which contain the fastest
superluminal components. In knots A, B and C, and are
essentially anti-correlated. Near the flux maxima of knots HST-1 and F, changes
in lag changes in , but in knots D and E, the opposite
relationship is observed. This is further evidence that radio and optical
emissions in the M87 jet come from substantially different physical regions.
The delays observed in the inner jet are consistent with localized particle
acceleration, with for optically emitting electrons in
knots HST-1 and F, and for optically emitting electrons
in knots D and E. Synchrotron models yield \nu_B \gsim 10^{16} Hz for knots
D, A and B, and somewhat lower values, Hz, in
other regions. If X-ray emissions from knots A, B and D are co-spatial with
optical and radio emission, we can strongly rule out the ``continuous
injection'' model. Because of the short lifetimes of X-ray synchrotron emitting
particles, the X-ray emission likely fills volumes much smaller than the
optical emission regions.Comment: Text 17 pages, 3 Tables, 11 figures, accepted by Ap
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