Combined external pressure and Cu-substitution studies on BaFe₂As₂single crystals

Abstract

We report a combined study of external pressure and Cu-substitution on BaFe 2 As 2 single crystals grown by the in-flux technique. At ambient pressure, the Cu-substitution is known to suppress the spin density wave (SDW) phase in pure BaFe 2 As 2 (T SDW ≈ 140 K) and to induce a superconducting (SC) dome with a maximum transition temperature T max c 4.2 K. This T max c is much lower than the T c ∼ 15-28 K achieved in the case of Ru, Ni and Co substitutions. Such a lower T c is attributed to a Cu 2+ magnetic pair-breaking effect. The latter is strongly suppressed by applied pressure, as shown herein, T c can be significantly enhanced by applying high pressures. In this work, we investigated the pressure effects on Cu 2+ magnetic pair-breaking in the BaFe 2−x Cu x As 2 series. Around the optimal concentration (x opd = 0.11), all samples showed a substantial increase of T c as a function of pressure. Yet for those samples with a slightly higher doping level (over-doped regime), T c presented a dome-like shape with maximum T c 8 K. Remarkably interesting, the under-doped samples, e.g. x = 0.02 display a maximum pressure induced T c 30 K which is comparable to the maximum T c 's found for the pure compound under external pressures. Furthermore, the magnetoresistance effect as a function of pressure in the normal state of the x = 0.02 sample also presented an evolution consistent with the screening of the Cu 2+ local moments. These findings demonstrate that the Cu 2+ magnetic pair-breaking effect is completely suppressed by applying pressure in the low concentration regime of Cu 2+ substituted BaFe 2 As 2 .

The role of magnetic excitations in magnetoresistance and Hall effect of slightly TM-substituted BaFe2As2 compounds (TM = Mn, Cu, Ni)

“…The first case is represented by the partial substitution of Ba atoms by K atoms (hole doping). Substitution inside the planes are achieved by partially substituting the Fe atoms by Co, Ni, Cu, Rh or Pd [2,8,9,10,11,12] (electron doping), or the As atoms by P atoms (isovalent substitution). All these substitutions disrupt the magnetic order and, depending on the impurity concentration, induce superconductivity.…”

Copper Doping of BaNi$_{2}$As$_{2}$: Giant Phonon Softening and Superconductivity Enhancement

“…Interestingly, transition-metal doping resulted in superconductivity with maximum transition temperatures of T c = 23 and 20.5 K for Ba(Fe 1−x Co x ) 2 As 2 [27,28] and Ba(Fe 1−x Ni x ) 2 As 2 [29,30], respectively. On the other hand, copper doping resulted in a reduced superconducting transition temperature T c ≃ 2-4 K of resistivity even though superconducting diamagnetic signals were not observed in Ba(Fe 1−x Cu x ) 2 As 2 [30][31][32].…”

Evidence of precursor orthorhombic domains well above the electronic nematic transition temperature in Sr(Fe1−x Co x )2As2

“…Undoped 122-compounds show nearly coincident T AF and T o [5,15], whereas well separated transition temperatures are observed in other series, such as in Ba(Fe 1−x Co x ) 2 As 2 [16][17][18], Sr(Fe 1−x Co x ) 2 As 2 [6,42,43,49], NaFe 1−x T x As (T = Co, Rh) [19,20] and even in parent oxypnictides such as LnFeAsO (Ln = La,Ce,Pr,Nd) [21][22][23][24][25][26]. So far, the origin of this large separation in some cases and its possible relation with lattice disorder has not been fully understood.…”