3,767 research outputs found
Anomalous relaxation kinetics and charge density wave correlations in underdoped BaPb1-xBixO3
Superconductivity often emerges in proximity of other symmetry-breaking
ground states, such as antiferromagnetism or charge-density-wave (CDW) order.
However, the subtle inter-relation of these phases remains poorly understood,
and in some cases even the existence of short-range correlations for
superconducting compositions is uncertain. In such circumstances, ultrafast
experiments can provide new insights, by tracking the relaxation kinetics
following excitation at frequencies related to the broken symmetry state. Here,
we investigate the transient terahertz conductivity of BaPb1-xBixO3 - a
material for which superconductivity is adjacent to a competing CDW phase -
after optical excitation tuned to the CDW absorption band. In insulating BaBiO3
we observed an increase in conductivity and a subsequent relaxation, which are
consistent with quasiparticles injection across a rigid semiconducting gap. In
the doped compound BaPb0.72Bi0.28O3 (superconducting below Tc=7K), a similar
response was also found immediately above Tc. This observation evidences the
presence of a robust gap up to T=40 K, which is presumably associated with
short-range CDW correlations. A qualitatively different behaviour was observed
in the same material fo T>40 K. Here, the photo-conductivity was dominated by
an enhancement in carrier mobility at constant density, suggestive of melting
of the CDW correlations rather than excitation across an optical gap. The
relaxation displayed a temperature dependent, Arrhenius-like kinetics,
suggestive of the crossing of a free-energy barrier between two phases. These
results support the existence of short-range CDW correlations above Tc in
underdoped BaPb1-xBixO3, and provide new information on the dynamical interplay
between superconductivity and charge order.Comment: 19 pages, 4 figure
Measles in Italy: Viral strains and crossing borders.
In 2017, Italy experienced one of the largest outbreaks of measles in recent years, with 5404 notified cases and 4347 confirmed cases. A further 2029 cases were notified during the first 6 months of 2018, and 1516 of them were laboratory-confirmed. The B3 and D8 genotypes were identified as those responsible for the outbreak. Possible transmission routes can be established by monitoring the circulating measles virus strains in support of the national health authorities to warn people and travellers
Far-infrared absorption and the metal-to-insulator transition in hole-doped cuprates
By studying the optical conductivity of BSLCO and YCBCO, we show that the
metal-to-insulator transition (MIT) in these hole-doped cuprates is driven by
the opening of a small gap at low T in the far infrared. Its width is
consistent with the observations of Angle-Resolved Photoemission Spectroscopy
in other cuprates, along the nodal line of the k-space. The gap forms as the
Drude term turns into a far-infrared absorption, whose peak frequency can be
approximately predicted on the basis of a Mott-like transition. Another band in
the mid infrared softens with doping but is less sensitive to the MIT.Comment: To be published on Physical Review Letter
Infrared study of the charge-ordered multiferroic LuFe(2)O(4)
The reflectivity of a large LuFe(2)O(4) single crystal has been measured with
the radiation field either perpendicular or parallel to the c axis of its
rhombohedral structure, from 10 to 500K, and from 7 to 16000 cm-1. The
transition between the two-dimensional and the three-dimensional charge order
at T_(CO) = 320 K is found to change dramatically the phonon spectrum in both
polarizations. The number of the observed modes above and below T_(CO),
according to a factor-group analysis, is in good agreement with a transition
from the rhombohedral space group R{bar 3}m to the monoclinic C2/m. In the
sub-THz region a peak becomes evident at low temperature, whose origin is
discussed in relation with previous experiments.Comment: Physical Review B in pres
Optical properties of V2O3 in its whole phase diagram
Vanadium sesquioxide V2O3 is considered a textbook example of Mott-Hubbard
physics. In this paper we present an extended optical study of its whole
temperature/doping phase diagram as obtained by doping the pure material with
M=Cr or Ti atoms (V1-xMx)2O3. We reveal that its thermodynamically stable
metallic and insulating phases, although macroscopically equivalent, show very
different low-energy electrodynamics. The Cr and Ti doping drastically change
both the antiferromagnetic gap and the paramagnetic metallic properties. A
slight chromium content induces a mesoscopic electronic phase separation, while
the pure compound is characterized by short-lived quasiparticles at high
temperature. This study thus provides a new comprehensive scenario of the
Mott-Hubbard physics in the prototype compound V2O3
Pressure tuning of light-induced superconductivity in K3C60
Optical excitation at terahertz frequencies has emerged as an effective means
to manipulate complex solids dynamically. In the molecular solid K3C60,
coherent excitation of intramolecular vibrations was shown to transform the
high temperature metal into a non-equilibrium state with the optical
conductivity of a superconductor. Here we tune this effect with hydrostatic
pressure, and we find it to disappear around 0.3 GPa. Reduction with pressure
underscores the similarity with the equilibrium superconducting phase of K3C60,
in which a larger electronic bandwidth is detrimental for pairing. Crucially,
our observation excludes alternative interpretations based on a high-mobility
metallic phase. The pressure dependence also suggests that transient, incipient
superconductivity occurs far above the 150 K hypothesised previously, and
rather extends all the way to room temperature.Comment: 33 pages, 17 figures, 2 table
High-temperature optical spectral weight and Fermi liquid renormalization in Bi-based cuprates
The optical conductivity and the spectral weight W(T) of two superconducting
cuprates at optimum doping, Bi2Sr2-xLaxCuO6 and Bi2Sr2CaCu2O8, have been first
measured up to 500 K. Above 300 K, W(T) deviates from the usual T2 behavior in
both compounds, even though the zero-frequency extrapolation of the optical
conductivity remains larger than the Ioffe-Regel limit. The deviation is
surprisingly well described by the T4 term of the Sommerfeld expansion, but its
coefficients are enhanced by strong correlation. This renormalization is due to
strong correlation, as shown by the good agreement with dynamical mean field
calculations.Comment: 5 pages, 3 figures, Physical Review Letters in pres
Electrodynamics near the Metal-to-Insulator Transition in V3O5
The electrodynamics near the metal-to-insulator transitions (MIT) induced, in
V3O5 single crystals, by both temperature (T) and pressure (P) has been studied
by infrared spectroscopy. The T- and P-dependence of the optical conductivity
may be explained within a polaronic scenario. The insulating phase at ambient T
and P corresponds to strongly localized small polarons. Meanwhile the T-induced
metallic phase at ambient pressure is related to a liquid of polarons showing
incoherent dc transport, in the P-induced metallic phase at room T strongly
localized polarons coexist with partially delocalized ones. The electronic
spectral weight is almost recovered, in both the T and P induced metallization
processes, on an energy scale of 1 eV, thus supporting the key-role of
electron-lattice interaction in the V3O5 metal-to-insulator transition.Comment: 7 pages, 5 figure
Pharmacogenetics of Bisphosphonate-associated Osteonecrosis of the Jaw
Osteonecrosis of the jaws (ONJ) is a potentially severe disorder that develops in a subgroup of individuals who have used bisphosphonate (BP) medications. Several clinical risk factors have been associated with the risk of ONJ development, but evidence is limited and in most instances ONJ remains an unpredictable adverse drug reaction. Interindividual genetic variability can contribute to explaining ONJ development in a subset of BP users and the discovery of relevant associated gene variants could lead to the identification of individuals at higher risk. No genetic variant has been found to be robustly associated with susceptibility to ONJ
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