70 research outputs found
Non-conservation of Density of States in BiSrCaCuO: Coexistence of Pseudogap and Superconducting gap
The tunneling spectra obtained within the ab-plane of
BiSrCaCuO (Bi2212) for temperatures below and above the
critical temperature (T) are analyzed. We find that the tunneling
conductance spectra for the underdoped compound in the superconducting state do
not follow the conservation of states rule. There is a consistent loss of
states for the underdoped BI2212 implying an underlying depression in the
density of states (DOS) and hence the pseudogap near the Fermi energy (E).
Such an underlying depression can also explain the peak-dip-hump structure
observed in the spectra. Furthermore, the conservation of states is recovered
and the dip-hump structure disappears after normalizing the low temperature
spectra with that of the normal state. We argue that this is a direct evidence
for the coexistence of a pseudogap with the superconducting gap.Comment: 5 pages, 4 figure
Josephson Coupling in the Dissipative State of a Thermally Hysteretic -SQUID
Micron-sized superconducting interference devices (-SQUIDs) based on
constrictions optimized for minimizing thermal runaway are shown to exhibit
voltage oscillations with applied magnetic flux despite their hysteretic
behavior. We explain this remarkable feature by a significant supercurrent
contribution surviving deep into the resistive state, due to efficient heat
evacuation. A resistively shunted junction model, complemented by a thermal
balance determining the amplitude of the critical current, describes well all
experimental observations, including the flux modulation of the (dynamic)
retrapping current and voltage by introducing a single dimensionless parameter.
Thus hysteretic -SQUIDs can be operated in the voltage read-out mode with
a faster response. The quantitative modeling of this regime incorporating both
heating and phase dynamics paves the way for further optimization of
-SQUIDs for nano-magnetism.Comment: 10 pages, 11 figures, Revise
Controlling hysteresis in superconducting constrictions with a resistive shunt
We demonstrate control of the thermal hysteresis in superconducting
constrictions by adding a resistive shunt. In order to prevent thermal
relaxation oscillations, the shunt resistor is placed in close vicinity of the
constriction, making the inductive current-switching time smaller than the
thermal equilibration time. We investigate the current-voltage characteristics
of the same constriction with and without the shunt-resistor. The widening of
the hysteresis-free temperature range is explained on the basis of a simple
model.Comment: 6 pages, 7 figures, including Supplementary Informatio
Evidence of mobile carriers with Charge Ordering gap in Epitaxial PrCaMnO Thin Films
Epitaxial thin films of charge-ordered PrCaMnO have
been studied using variable temperature Scanning tunneling microscopy and
spectroscopy (STM/STS). The as grown films were found to be granular while the
annealed films show atomic terraces at all temperatures and are found to be
electronically homogeneous in 78-300K temperature range. At high temperatures
(TT 230 K) the local tunnel spectra of the annealed films show
a depression in the density of states (DOS) near Fermi energy implying a
pseudogap with a significant DOS at E. The gap feature becomes more robust
with cooling with a sharp jump in DOS at E at T and with a gap value
of 0.3 eV at 78K. At low temperatures we find a small but finite DOS at
E indicative of some delocalized carriers in the CO phase together with an
energy gap. This is consistent with bulk transport, which shows weakening of
the activation gap with cooling below 200K, and indicates the presence of two
types of carriers at low temperatures.Comment: 4 pages, 4 figure
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