Unusual Normal and Superconducting State Properties Observed in Hydrothermal Fe_1-\deltaSe Flakes

The electronic and superconducting properties of Fe_1-\deltaSe single-crystal flakes grown hydrothermally are studied by the transport measurements under zero and high magnetic fields up to 38.5 T. The results contrast sharply with those previously reported for nematically ordered FeSe by chemical-vapor-transport (CVT) growth. No signature of the electronic nematicity, but an evident metal-to-nonmetal crossover with increasing temperature, is detected in the normal state of the present hydrothermal samples. Interestingly, a higher superconducting critical temperature T_\rm c of 13.2 K is observed compared to a suppressed T_\rm c of 9 K in the presence of the nematicity in the CVT FeSe. Moreover, the upper critical field in the zero-temperature limit is found to be isotropic with respect to the field direction and to reach a higher value of \sim 42 T, which breaks the Pauli limit by a factor of 1.8.