Scaling of the physical properties in Ba(Fe,Ni)2As2single crystals: Evidence for quantum fluctuations

Abstract

We report on local magnetization, tunnel diode oscillators, and specific-heat measurements in a series of Ba(Ni x Fe 1−x ) 2 As 2 single crystals (0.26 x 0.74). We show that the London penetration depth λ(T ) = λ(0) + λ(T ) scales as λ (0) in both underdoped and overdoped samples. Moreover, the slope of the upper critical field [H c2 = −(dH c2 /dT ) |T →Tc ] decreases with T c in overdoped samples but increases with decreasing T c in underdoped samples. The remarkable variation of λ(0) with T c and the nonexponential temperature dependence of λ clearly indicates that pair-breaking effects are important in this system. We show that the observed scalings strongly suggest that those pair-breaking effects could be associated with quantum fluctuations near three-dimensional superconducting critical points.

Analysis of Electronic Properties from Magnetotransport Measurements on Ba(Fe1−xNix)2As2 Thin Films

“…In our calculations, we considered a gap value of ∆ = 2.6 k B T c , which is consistent with experimental data for pnictides [24]. However, Rodière et al [31] estimated the paramagnetic limit H p (0) based on the Bardeen-Cooper-Schrieffer (BCS) theory (∆ = 1.86 k B T c ) and if we use the same approach, we get H p (0) = 39.7 T (Ba(Fe 0.95 Ni 0.05 ) 2 As 2 ) and H p (0) = 20.08 T (Ba(Fe 0.92 Ni 0.08 ) 2 As 2 ), which is in good agreement with the values for single crystals. Furthermore, some inconsistency between the results is mainly associated with the lower T c in single crystals compared to the obtained films, and with the structural inhomogeneities of the latter.…”

Type II superconductivity in SrPd2Ge2

“…When the field increased above B p , the local magnetization sensor started to read increasing voltage as the number of vortices grew. The local magnetization measurements were performed at various temperatures for several different positions of the sensor with respect to the sample edge, as described more in detail by Rodière et al [30] The temperature dependence of B c1 measured at two different sensor positions is displayed in the inset of figure 2…”

“…When the field increased above B p , the local magnetization sensor started to read increasing voltage as the number of vortices grew. The local magnetization measurements were performed at various temperatures for several different positions of the sensor with respect to the sample edge, as described more in detail by Rodière et al [30] The temperature dependence of B c1 measured at two different sensor positions is displayed in the inset of Figure 2 permitted us to gain the effective Ginzburg -Landau parameter  = 13.5 ± 1 along with the effective penetration depth  =  = 345 ± 30 nm, much larger than  0 . The value of  is in accordance with the expected type II superconductivity in SrPd 2 Ge 2 and in steep contrast to  0 = 0.11 estimated from the penetration depth  0 and the coherence length  0 .…”

Nodeless superconductivity in the presence of spin-density wave in pnictide superconductors: The case ofBaFe2−xNixAs2

“…Additionally, the temperature dependence of the first vortex penetration field has been experimentally obtained by measuring the onset of the trapped flux moment M t as described in Refs. [52,53]. In contrast to tracking, the virgin M(H ) curves at low fields at several temperatures where a heavy data postprocessing is needed now a careful measurement protocol needs to be followed with little data analysis.…”