2,718 research outputs found
Scanning Tunneling Microscopy in the superconductor LaSb2
We present very low temperature (0.15 K) scanning tunneling microscopy and
spectroscopy experiments in the layered superconductor LaSb. We obtain
topographic microscopy images with surfaces showing hexagonal and square atomic
size patterns, and observe in the tunneling conductance a superconducting gap.
We find well defined quasiparticle peaks located at a bias voltage comparable
to the weak coupling s-wave BCS expected gap value (0.17 meV). The amount of
states at the Fermi level is however large and the curves are significantly
broadened. We find T of 1.2 K by following the tunneling conductance with
temperature.Comment: 5 pages, 4 figure
Signatures of quantum criticality in the thermopower of Ba(Fe(1-x)Co(x))2As2
We demonstrate that the thermopower (S) can be used to probe the spin
fluctuations (SFs) in proximity to the quantum critical point (QCP) in Fe-based
superconductors. The sensitivity of S to the entropy of charge carriers allows
us to observe an increase of S/T in Ba(Fe(1-x)Co(x))2As2 close to the
spin-density-wave (SDW) QCP. This behavior is due to the coupling of low-energy
conduction electrons to two-dimensional SFs, similar to heavy-fermion systems.
The low-temperature enhancement of S/T in the Co substitution range 0.02 < x <
0.1 is bordered by two Lifshitz transitions, and it corresponds to the
superconducting region, where a similarity between the electron and
non-reconstructed hole pockets exists. The maximal S/T is observed in proximity
to the commensurate-to-incommensurate SDW transition, for critical x_c ~ 0.05,
close to the highest superconducting T_c. This analysis indicates that low-T
thermopower is influenced by critical spin fluctuations which are important for
the superconducting mechanism
Crystal growth and annealing study of fragile, non-bulk superconductivity in YFeGe
We investigated the occurrence and nature of superconductivity in single
crystals of YFeGe grown out of Sn flux by employing x-ray diffraction,
electrical resistivity, and specific heat measurements. We found that the
residual resistivity ratio (RRR) of single crystals can be greatly improved,
reaching as high as 60, by decanting the crystals from the molten Sn at
350C and/or by annealing at temperatures between 550C and
600C. We found that samples with RRR 34 showed resistive
signatures of superconductivity with the onset of the superconducting
transition K. RRR values vary between 35 and 65 with, on
average, no systematic change in value, indicating that systematic
changes in RRR do not lead to comparable changes in . Specific heat
measurements on samples that showed clear resistive signatures of a
superconducting transition did not show any signature of a superconducting
phase transition, which suggests that the superconductivity observed in this
compound is either some sort of filamentary, strain stabilized
superconductivity associated with small amounts of stressed YFeGe
(perhaps at twin boundaries or dislocations) or is a second crystallographic
phase present at levels below detection capability of conventional powder x-ray
techniques.Comment: 8 pages, 11 figure
Local superconducting density of states of ErNi2B2C
We present local tunnelling microscopy and spectroscopy measurements at low
temperatures in single crystalline samples of the magnetic superconductor
ErNi2B2C. The electronic local density of states shows a striking departure
from s-wave BCS theory with a finite value at the Fermi level, which amounts to
half of the normal phase density of states.Comment: 9 pages, 3 figure
Research on applied bioelectrochemistry First quarterly progress report, 14 Mar. - 30 Jun. 1963
Optimum use of human waste as electrochemical fuels by urea bacterial organism conversion
Anisotropic Hc2 of K0.8Fe1.76Se2 determined up to 60 T
The anisotropic upper critical field, Hc2(T), curves for K0.8Fe1.76Se2 are
determined over a wide range of temperatures down to 1.5 K and magnetic fields
up to 60 T. Anisotropic initial slopes of Hc2 ~ -1.4 T/K and -4.6 T/K for
magnetic field applied along c-axis and ab-plane, respectively, were observed.
Whereas the c-axis Hc2|c(T) increases quasi-linearly with decreasing
temperature, the ab-plane Hc2|ab(T) shows a flattening, starting near 25 K
above 30 T. This leads to a non-monotonic temperature dependence of the
anisotropy parameter \gamma= Hc2|ab/Hc2|c. The anisotropy parameter is ~ 2 near
Tc ~ 32 K and rises to a maximum \gamma ~ 3.6 around 27 K. For lower
temperatures, \gamma decreases with T in a linear fashion, dropping to \gamma ~
2.5 by T ~ 18 K. Despite the apparent differences between the K0.8Fe1.76Se2 and
(Ba0.55K0.45)Fe2As2 or Ba(Fe0.926Co0.074)2As2, in terms of the magnetic state
and proximity to an insulating state, the Hc2(T) curves are remarkably similar.Comment: slightly modified version, accepted to PRB, Rapid Communication
Ferromagnetism or slow paramagnetic relaxation in Fe-doped LiN?
We report on isothermal magnetization, M\"ossbauer spectroscopy, and
magnetostriction as well as temperature-dependent alternating-current (ac)
susceptibility, specific heat, and thermal expansion of single crystalline and
polycrstalline Li(LiFe)N with and .
Magnetic hysteresis emerges at temperatures below K with
coercivity fields of up to T at K and magnetic
anisotropy energies of K (meV). The ac susceptibility is strongly
frequency dependent (--Hz) and reveals an effective energy
barrier for spin reversal of K. The relaxation times
follow Arrhenius behavior for K. For K, however, the
relaxation times of s are only weakly
temperature-dependent indicating the relevance of a quantum tunneling process
instead of thermal excitations. The magnetic entropy amounts to more than
J molK which significantly exceeds ln2, the
value expected for the entropy of a ground state doublet. Thermal expansion and
magnetostriction indicate a weak magneto-elastic coupling in accordance with
slow relaxation of the magnetization. The classification of
Li(LiFe)N as ferromagnet is stressed and contrasted with highly
anisotropic and slowly relaxing paramagnetic behavior.Comment: 12 pages, 10 figure
Anisotropic transport and magnetic properties, and magnetic-field tuned states of CeZn11 single crystals
We present detailed temperature and field dependent data obtained from
magnetization, resistivity, heat capacity, Hall resistivity and thermoelectric
power measurements performed on single crystals of CeZn11. The compounds orders
antiferromagnetically at 2 K. The zero-field resistivity and TEP data
show features characteristic of a Ce-based intermetallic with crystal electric
field splitting and possible correlated, Kondo lattice effects. We constructed
the T-H phase diagram for the magnetic field applied along the easy, [110],
direction which shows that the magnetic field required to suppress T_N below
0.4 K is in the range of 45-47.5 kOe. A linear behavior of the rho(T) data,
H||[110], was observed only for H=45 kOe for 0.46 K<T<1.96 K followed by the
Landau-Fermi-liquid regime for a limited range of fields, 47.5 kOe< H<60 kOe.
From the analysis of our data, it appears that CeZn11 is a weakly to moderately
correlated local moment compound with rather small Kondo temperature. The
thermoelectric and transport properties of CeZn11 are mostly governed by the
CEF effects. Given the very high quality of our single crystals, quantum
oscillations are found for both CeZn11 and its non-magnetic analogue, LaZn11
Magnetic and superconducting phase diagrams in ErNi2B2C
We present measurements of the superconducting upper critical field Hc2(T)
and the magnetic phase diagram of the superconductor ErNi2B2C made with a
scanning tunneling microscope (STM). The magnetic field was applied in the
basal plane of the tetragonal crystal structure. We have found large gapless
regions in the superconducting phase diagram of ErNi2B2C, extending between
different magnetic transitions. A close correlation between magnetic
transitions and Hc2(T) is found, showing that superconductivity is strongly
linked to magnetism.Comment: 5 pages, 4 figure
H. Spofford Canfield to Jean Allen, 26 July 1974
Typed letter signed dated 26 July 1974 from H. Spofford Canfield, Legislative Assistant to the President of the Senate, to Jean Allen, Executive Secretary to Eastland, re: signed photographs of Vice-President Ford\u27s swearing-in ceremony.https://egrove.olemiss.edu/joecorr_f/1019/thumbnail.jp
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