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Abstract:
Copper doping of FeSe destroys its superconductivity at ambient
pressure, even at low doping levels. Here we report the
pressure-dependent transport and structural properties of Fe(1.01-x)
Cu(x) Se with 3% and 4% Cu doping and find that the superconductivity is
restored. Metallic resistivity behavior, absent in Cu-doped FeSe, is
also restored. At the low pressure of 1.5 GPa, superconductivity is seen
at 6 K for 4% Cu doping, somewhat lower than the 8 K T(c) of undoped
FeSe. T(c) reaches its maximum of 31.3 K at 7.8 GPa, lower than the
maximum superconducting temperature in the undoped material under
pressure (T(c) max of 37 K) but still very high. X-ray diffraction shows
that applied pressure decreases the lattice parameter in the basal
plane, counteracting the structural effect of Cu doping, providing a
possible explanation for the restoration of the superconductivity.
