146 research outputs found
Mobility gap in intermediate valent TmSe
The infrared optical conductivity of intermediate valence compound TmSe
reveals clear signatures for hybridization of light - and heavy f-electronic
states with m* ~ 1.6 m_0 and m* ~ 16 m_0, respectively. At moderate and high
temperatures, the metal-like character of the heavy carriers dominate the
low-frequency response while at low temperatures (T_N < T < 100 K) a gap-like
feature is observed in the conductivity spectra below 10 meV which is assigned
to be a mobility gap due to localization of electrons on local Kondo singlets,
rather than a hybridization gap in the density of states
Comment on ''Phase Diagram of LaSrCuO Probed in the Infrared: Imprints of Charge Stripe Excitations''
Recently Lucarelli {\it et al.} have reported\cite{lucarelli}
temperature-dependence of the in-plane optical reflectivity of
LaSrCuO over a wide doping range, focusing on the infrared
peaks at 30 cm (for =0.12), 250 cm and 510 cm. They
interpreted the first peak (30 cm) as a signature of charge stripe
ordering, while the latter two (250 cm and 510 cm) are attributed
to the polaronic charge excitations. However, careful readers would notice that
the reported spectra are largely different from those so far measured on the
same system. As we illustrate below, all these peaks are caused by an
uncontrolled leakage of the c-axis reflectivity into the measured spectra.Comment: 1 page, 1 figure, accepted for publication in Phys. Rev. Lett 91
(2003
Suppression of the charge-density-wave state in Sr_14Cu_24O_41 by calcium doping
The charge response in the spin chain/ladder compound Sr_14-xCa_xCu_24O_41 is
characterized by DC resistivity, low-frequency dielectric spectroscopy and
optical spectroscopy. We identify a phase transition below which a
charge-density wave (CDW) develops in the ladder arrays. Calcium doping
suppresses this phase with the transition temperature decreasing from 210 K for
x=0 to 10 K for x=9, and the CDW gap from 130 meV down to 3 meV, respectively.
This suppression is due to the worsened nesting originating from the increase
of the inter-ladder tight-binding hopping integrals, as well as from disorder
introduced at the Sr sites. These results altogether speak in favor of
two-dimensional superconductivity under pressure.Comment: 4 pages, 4 figures, accepted for publication in PR
Anisotropic Charge Modulation in Ladder Planes of Sr_14-xCa_xCu_24O_41
The charge response of the ladders in Sr_14-xCa_xCu_24O_41 is characterized
by dc resistivity, low frequency dielectric and optical spectroscopy in all
three crystallographic directions. The collective charge-density wave screened
mode is observed in the direction of the rungs for x=0, 3 and 6, in addition to
the mode along the legs. For x=8 and 9, the charge-density-wave response along
the rungs fully vanishes, while the one along the legs persists. The transport
perpendicular to the planes is always dominated by hopping.Comment: 4 pages, 3 figures, submitted to PRB R
Spin excitations of the correlated semiconductor FeSi probed by THz radiation
By direct measurements of the complex optical conductivity of
FeSi we have discovered a broad absorption peak centered at frequency
that develops at temperatures below 20 K.
This feature is caused by spin-polaronic states formed in the middle of the gap
in the electronic density of states. We observe the spin excitations between
the electronic levels split by the exchange field of . Spin
fluctuations are identified as the main factor determining the formation of the
spin polarons and the rich magnetic phase diagram of FeSi.Comment: 5 pages, 4 figure
B-T phase diagram of CoCr2O4 in magnetic fields up to 14 T
We have measured the magnetization and specific heat of multiferroic CoCr2O4
in magnetic fields up to 14 T. The high-field magnetization measurements
indicate a new phase transition at T* = 5 - 6 K. The phase between T* and the
lock-in transition at 15 K is characterized by magnetic irreversibility. At
higher magnetic fields, the irreversibility increases. Specific-heat
measurements confirm the transition at T*, and also show irreversible behavior.
We construct a field-temperature phase diagram of CoCr2O4.Comment: 4 page
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