Hamza Balci

Evidence of a d- to s-wave pairing symmetry transition in the electron-doped cuprate superconductor Pr(2-x)CexCuO4.

We present point contact spectroscopy (PCS) data for junctions between a normal metal and the electron-doped cuprate superconductor Pr(2-x)CexCuO4 (PCCO). For the underdoped compositions of this cuprate ( x approximately 0.13) we observe a peak in the conductance-voltage characteristics of the point contact junctions. The shape and magnitude of this peak suggest the presence of Andreev bound states at the surface of underdoped PCCO which is evidence for a d-wave pairing symmetry. For overdoped PCCO ( x approximately 0.17) the PCS data do not show any evidence of Andreev bound states at the surface suggesting an s-wave pairing symmetry.

Evolution of superconductivity in electron-doped cuprates: Magneto-Raman spectroscopy

The electron-doped cuprates Pr_{2-x}Ce_xCuO_4 and Nd_{2-x}Ce_xCuO_4 have been studied by electronic Raman spectroscopy across the entire region of the superconducting (SC) phase diagram. The SC pairing strength is found to be consistent with a weak-coupling regime except in the under-doped region where we observe an in-gap collective mode at 4.5 k_{B}T_c while the maximum amplitude of the SC gap is ~8 k_{B}T_{c}. In the normal state, doped carriers divide into coherent quasi-particles (QPs) and carriers that remain incoherent. The coherent QPs mainly reside in the vicinity of (\pi/2, \pi/2) regions of the Brillouin zone (BZ). We find that only coherent QPs contribute to the superfluid density in the B_{2g} channel. The persistence of SC coherence peaks in the B_{2g} channel for all dopings implies that superconductivity is mainly governed by interactions between the hole-like coherent QPs in the vicinity of (\pi/2, \pi/2) regions of the BZ. We establish that superconductivity in the electron-doped cuprates occurs primarily due to pairing and condensation of hole-like carriers. We have also studied the excitations across the SC gap by Raman spectroscopy as a function of temperature (T) and magnetic field (H) for several different cerium dopings (x). Effective upper critical field lines H*_{c2}(T, x) at which the superfluid stiffness vanishes and H^{2\Delta}_{c2}(T, x) at which the SC gap amplitude is suppressed by field have been determined; H^{2\Delta}_{c2}(T, x) is larger than H*_{c2}(T, x) for all doping concentrations. The difference between the two quantities suggests the presence of phase fluctuations that increase for x< 0.15. It is found that the magnetic field suppresses the magnitude of the SC gap linearly at surprisingly small fields.

Magnetic-field dependence of electronic specific heat in Pr 1.85 Ce 0.15 CuO 4

The specific heat of electron-doped Pr 1 . 8 5 Ce 0 . 1 5 CuO 4 single crystals is reported for the temperature range 2-7 K and magnetic field range 0-10 T. A nonlinear magnetic-field dependence is observed for the field range 0-2 T. Our data support a model with lines of nodes in the gap function of these superconductors. Theoretical calculations of the electronic specific heat for dirty d-wave, clean d-wave, and s-wave symmetries are compared to our data.

Magnetic contribution to the specific heat of Pb 1 − x Eu x Te ( x = 0.027 , 0.073 )

The temperature dependence of the magnetic specific heat has been studied experimentally and theoretically in the semimagnetic semiconductor

Nernst effect in electron-doped Pr 2 − x Ce x CuO 4

{\mathrm{Pb}}_{1\ensuremath{-}x}{\mathrm{Eu}}_{x}\mathrm{Te}

Inhomogeneous electronic structure probed by spin-echo experiments in the electron doped high-Tc superconductor Pr1.85Ce0.15CuO4-y.

for

Anomalous saturation of the phase coherence length in underdoped Pr 2 − x Ce x CuO 4 thin films

x=0.027

Anomalous Change in the Field Dependence of the Electronic Specific Heat of an Electron-Doped Cuprate Superconductor

and 0.073, over the temperature range from 0.5 to

Thermodynamic properties ofPr1.85Ce0.15CuO4−δ

10\phantom{\rule{0.3em}{0ex}}\mathrm{K}

Nernst effect in electron-dopedPr2−xCexCuO4

, in magnetic fields up to