In-plane resistivity anisotropy in underdoped Ba(Fe1-xNix)2As2 and Ba(Fe1-xCux)2As2 (original) (raw)
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In-plane resistivity anisotropy in an underdoped iron arsenide superconductor
Science (New York, N.Y.), 2010
High-temperature superconductivity often emerges in the proximity of a symmetry-breaking ground state. For superconducting iron arsenides, in addition to the antiferromagnetic ground state, a small structural distortion breaks the crystal's C(4 )rotational symmetry in the underdoped part of the phase diagram. We reveal that the representative iron arsenide Ba(Fe(1)(-x)Co(x))(2)As(2) develops a large electronic anisotropy at this transition via measurements of the in-plane resistivity of detwinned single crystals, with the resistivity along the shorter b axis rho(b) being greater than rho(a). The anisotropy reaches a maximum value of ~2 for compositions in the neighborhood of the beginning of the superconducting dome. For temperatures well above the structural transition, uniaxial stress induces a resistivity anisotropy, indicating a substantial nematic susceptibility.
Physical Review B, 2011
The in-plane resistivity anisotropy has been measured for detwinned single crystals of Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$ and Ba(Fe$_{1-x}$Cu$_x$)$_2$As$_2$. The data reveal a non-monotonic doping dependence, similar to previous observations for Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$. Magnetotransport measurements of the parent compound reveal a non-linear Hall coefficient and a strong linear term in the transverse magnetoresistance. Both effects are rapidly suppressed with chemical substitution over a similar compositional range as the onset of the large in-plane resistivity anisotropy. It is suggested that the relatively small in-plane anisotropy of the parent compound in the spin density wave state is due to the presence of an isotropic, high mobility pocket of reconstructed Fermi surface. Progressive suppression of the contribution to the conductivity arising from this isotropic pocket with chemical substitution eventually reveals the underlying in-plane anisotropy associated with the remaining FS pockets.
The evolution of antiferromagnetic susceptibility to uniaxial pressure in Ba(Fe1-xCox)2As2
2014
Neutron diffraction measurements are presented measuring the responses of both magnetic and structural order parameters of parent and lightly Co-doped Ba(Fe1-xCox)2As2 under the application of uniaxial pressure. We find that the uniaxial pressure induces a thermal shift in the onset of antiferromagnetic order that grows as a percentage of T_N as Co-doping is increased and the superconducting phase is approached. Additionally, as uniaxial pressure is increased within parent and lightly-doped Ba(Fe1-xCox)2As2 on the first order side of the tricritical point, we observe a decoupling between the onsets of the orthorhombic structural distortion and antiferromagnetism. Our findings place needed constraints on models exploring the nematic susceptibility of the bilayer pnictides in the tetragonal, paramagnetic regime.
Phys Rev B, 2010
We present results of angle-dependent magnetoresistance measurements and direct optical images of underdoped Ba(Fe1-xCox)2As2 which reveal partial detwinning by action of a 14 T magnetic field. The relative change in the twin domain population for the given field is modest, of order 5-15% . The associated field-induced hysteretic changes in the resistivity are up to 5% for intermediate Co concentrations, implying a large in-plane resistivity anisotropy in the broken-symmetry state. Based on the generic anisotropic susceptibility of collinear antiferromagnets, we infer a smaller resistivity along the antiferromagnetic ordering direction. The observation of field-induced motion of twin boundaries indicates a substantial magnetoelastic coupling in this material.
Probing Local Variations of Superconductivity on the Surface of Ba (Fe1-xCox) 2As2 Single Crystals
2010
The spatially resolved electrical transport properties have been studied on the surface of optimally-doped superconducting Ba(Fe 1-x Co x ) 2 As 2 single crystal by using a four-probe scanning tunneling microscopy. While some non-uniform contrast appears near the edge of the cleaved crystal, the scanning electron microscopy (SEM) reveals mostly uniform contrast. For the regions that showed uniform SEM contrast, a sharp superconducting transition at T C = 22.1 K has been observed with a transition width ΔT C = 0.2 K. In the non-uniform contrast region, T C is found to vary between 19.6 and 22.2 K with ΔT C from 0.3 to 3.2 K. The wavelength dispersive x-ray spectroscopy reveals that Co concentration remains 7.72% in the uniform region, but changes between 7.38% and 7.62% in the non-* Corresponding author. apli@ornl.gov 2 uniform region. Thus the variations of superconductivity are associated with local compositional change.
Physical Review B Condensed Matter and Materials Physics, 2009
The spatially resolved electrical transport properties have been studied on the surface of optimally doped superconducting Ba(Fe1-xCox)2As2 single crystal by using a four-probe scanning tunneling microscopy. While some nonuniform contrast appears near the edge of the cleaved crystal, the scanning electron microscopy (SEM) reveals mostly uniform contrast. For the regions that showed uniform SEM contrast, a sharp superconducting transition at TC=22.1K has been observed with a transition width ΔTC=0.2K . In the nonuniform contrast region, TC is found to vary between 19.6 and 22.2 K with ΔTC from 0.3 to 3.2 K. The wavelength dispersive x-ray spectroscopy reveals that Co concentration remains 7.72% in the uniform region, but changes between 7.38% and 7.62% in the nonuniform region. Thus the variations of superconductivity are associated with local compositional change.
Thermoelectric power and Hall coefficient measurements on Ba(Fe1−xTx)2As2 (T=Co and Cu
Physical Review B, 2009
Temperature dependent thermoelectric power (TEP) data on Ba(Fe1-xTMx)2As2 (TM = Co and Cu), complemented by the Hall coefficient data on the samples from the same batches, have been measured. For Co-doping we clearly see a change in the temperature dependent TEP and Hall coefficient data when the sample is doped to sufficient eee (the number of extra electrons associated with the TM doping) so as to stabilize low temperature superconductivity. Remarkably, a similar change is found in the Cu-doped samples at comparable e-value, even though these compounds do not superconduct. These changes possibly point to a significant modification of the Fermi surface / band structure of Ba(Fe1-xTM_x)2As2 at small electron doping, that in the case of Co-doping is just before, and probably allows for, the onset of superconductivity. These data further suggest that suppression of the structural / magnetic phase transition and the establishment of a proper e-value are each necessary but, individually, not sufficient conditions for superconductivity.