Drastic effect of impurity scattering on the electronic and superconducting properties of Cu-doped FeSe

Abstract

Nonmagnetic impurities in iron-based superconductors can provide an important tool to understand the pair symmetry and they can significantly influence the transport and the superconducting behavior. Here, we present a study of the role of strong impurity potential in the Fe plane, induced by Cu substitution, on the electronic and superconducting properties of single crystals of FeSe. The addition of Cu quickly suppresses both the nematic and superconducting states and increases the residual resistivity due to enhanced impurity scattering. Using magnetotransport data up to 35 T for a small amount of Cu impurity, we detect a significant reduction in the mobility of the charge carriers by a factor of ∼3. While the electronic conduction is strongly disrupted by Cu substitution, we identify additional signatures of anisotropic scattering which manifest in linear resistivity at low temperatures and H 1.6 dependence of magnetoresistance. The suppression of superconductivity by Cu substitution is consistent with a sign-changing s ± order parameter. Additionally, in the presence of compressive strain, the superconductivity is enhanced, similar to FeSe.

Unconventional localization of electrons inside of a nematic electronic phase

“…Fig. 1 B shows the variation of and as a function of inverse thickness ( ) for different devices, revealing that both are suppressed for thinner flakes; interestingly, we find a linear dependence between and , as found in Cu-substituted FeSe ( 33 ) ( SI Appendix , Fig. S4 B ).…”

“…In thinner flakes, the RRR value falls as a function of decreasing thickness, reducing to 5.5 in the -nm device, as shown in SI Appendix , Fig. S4 C , being similar to the effect of impurity scattering by Cu doping in FeSe ( 32 , 33 ). Similarly, the emergence of the nematic phase at , which results in significant in-plane distortion of the Fermi surface and orbitally dependent band shifts ( 10 ), becomes smeared and less defined for thinner flakes.…”

“…3 D . A cross-over transition to the Fermi liquid behavior occurs below 5 K for nm, but this cross-over is highly sensitive to the degree of impurity scattering, as found in FeSe S x ( 22 ) and Cu-substituted FeSe ( 33 ). Linear dependence at the lowest temperature is found for a flake with 100 nm ( SI Appendix , Fig.…”

“…The sign of the Hall coefficient is always positive in thin flakes, but negative in the bulk below K, despite having similar RRR values. The Hall coefficient is also positive in Cu-substituted FeSe with large impurity scattering ( 32 , 33 ) and in thin films of FeSe S x ( 63 ). Furthermore, it also becomes positive by using the isoelectronic sulfur substitution in single crystals of FeSe S x (for x > 0.11) ( 22 , 64 , 65 ), due to subtle changes in the band structure and spin-fluctuation scattering ( 13 , 22 ).…”

Влияние частичного замещения железа на элементы IV группы на структуру и сверхпроводящие свойства соединения Fe(Se-=SUB=-0.2-=/SUB=-Te-=SUB=-0.8-=/SUB=-)-=SUB=-0.82-=/SUB=-

“…Зависимость R(T ) для исходного Fe(Se 0.2 Te 0.8 ) 0.82 и для образцов Fe 0.9 Pb 0.1 (Se 0.2 Te 0.8 ) 0.82 , Fe 0.95 Cu 0.05 (Se 0.2 Te 0.8 ) 0.82 и Fe 0.9 Ge 0.1 (Se 0.2 Te 0.8 ) 0.82 .СП переход не наблюдается до T ∼ 2 K. В работе[11] при исследовании монокристаллов Fe 1−x Cu x Te 0.67 Se 0.33 было обнаружено, что сверхпроводимость подавлялась уже при замещении на 1.5% меди. Обсуждение причин подавления сверхпроводимостью при замещении железа на медь проведено в работе[22].На рис. 2 приведена зависимость R(T ) для исходного соединения Fe(Se 0.2 Te 0.8 ) 0.82 и для соединения с 5%-ным замещением атомов железа на атомы меди, и 10%-ным замещением на атомы германия и свинца.При замещении железа на висмут наблюдался разброс свойств образцов, полученных в одном технологическом цикле.…”