Point contact spectroscopy studies of the iron based superconductors
type: CreativeWork
description: Point contact spectroscopy (PCS) is used to probe both the normal and superconducting phases of the iron based superconductors. It is shown that apart from probing superconductors by Andreev reflection, PCS is also a useful technique to study exotic electron matter in correlated materials. The point contact junctions are made by two separate techniques: needle-anvil PCS and soft PCS. $dI/dV$ measured in the superconducting phase is sensitive to the magnitude and symmetry of the superconducting order parameter. Andreev reflection spectra for the 122 and 111 families of the iron based superconductors is presented. The 122 crystals probed include electron doped $\rm{Ba(Fe_{1-x}Co_x)_2As_2}$ ($\rm{x = 0.05, 0.055, 0.07, 0.08}$), hole doped $\rm{Ba_{0.8}K_{0.2}Fe_2As_2}$, and isoelectronic doped $\rm{BaFe_2(As_{1-x}P_{x})_2}$ ($\rm{x = 0.24, 0.43}$). The 111 crystals studied are electron doped $\rm{NaFe_{1-x}Co_xAs}$ ($\rm{x = 0.02, 0.06}$). The Andreev spectra show clear features corresponding to multiple, nodeless superconducting gaps. The $dI/dV$ curves are fit to the independent two band BTK model assuming isotropic s-wave order parameters. The normal state spectra of certain iron based superconductors shows a conductance enhancement around zero bias above the structural transition temperature, $T_S$. Theoretical analysis showing that this enhancement is likely a consequence of orbital fluctuations is discussed. The nonsuperconducting compounds probed are $\rm{AEFe_2As_2}$ ($\rm{AE=Ca,Sr,Ba}$) and $\rm{Fe_{1+y}Te}$. For $\rm{AE=Sr,Ba}$ orbital fluctuations are detected above $T_S$ while for $\rm{AE=Ca}$ these fluctuations start below $T_S$. Co doping preserves the orbital fluctuations while K doping suppresses it. The fluctuations are only seen at those dopings and temperatures where for detwinned crystals, an in-plane resistive anisotropy is known to exist. The normal state spectra thus provides evidence that PCS is sensitive to orbital fluctuations in the iron base…
abstract: Point contact spectroscopy (PCS) is used to probe both the normal and superconducting phases of the iron based superconductors. It is shown that apart from probing superconductors by Andreev reflection, PCS is also a useful technique to study exotic electron matter in correlated materials. The point contact junctions are made by two separate techniques: needle-anvil PCS and soft PCS. $dI/dV$ measured in the superconducting phase is sensitive to the magnitude and symmetry of the superconducting order parameter. Andreev reflection spectra for the 122 and 111 families of the iron based superconductors is presented. The 122 crystals probed include electron doped $\rm{Ba(Fe_{1-x}Co_x)_2As_2}$ ($\rm{x = 0.05, 0.055, 0.07, 0.08}$), hole doped $\rm{Ba_{0.8}K_{0.2}Fe_2As_2}$, and isoelectronic doped $\rm{BaFe_2(As_{1-x}P_{x})_2}$ ($\rm{x = 0.24, 0.43}$). The 111 crystals studied are electron doped $\rm{NaFe_{1-x}Co_xAs}$ ($\rm{x = 0.02, 0.06}$). The Andreev spectra show clear features corresponding to multiple, nodeless superconducting gaps. The $dI/dV$ curves are fit to the independent two band BTK model assuming isotropic s-wave order parameters. The normal state spectra of certain iron based superconductors shows a conductance enhancement around zero bias above the structural transition temperature, $T_S$. Theoretical analysis showing that this enhancement is likely a consequence of orbital fluctuations is discussed. The nonsuperconducting compounds probed are $\rm{AEFe_2As_2}$ ($\rm{AE=Ca,Sr,Ba}$) and $\rm{Fe_{1+y}Te}$. For $\rm{AE=Sr,Ba}$ orbital fluctuations are detected above $T_S$ while for $\rm{AE=Ca}$ these fluctuations start below $T_S$. Co doping preserves the orbital fluctuations while K doping suppresses it. The fluctuations are only seen at those dopings and temperatures where for detwinned crystals, an in-plane resistive anisotropy is known to exist. The normal state spectra thus provides evidence that PCS is sensitive to orbital fluctuations in the iron base…
author: Arham, Hamood Zafir
language: en
keywords: Superconductivity, Point Contact Spectroscopy, Iron Based Superconductors, Andreev Reflection, Orbital Fluctuations, Nematicity, Correlated Electron Matter
date published: 2014-05-30T16:44:43Z
date modified: 2026-07-22T22:25:38Z
provider: University of Illinois - Urbana-Champaign
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Illinois at Urbana-Champaign

PropertyValue
property ID: Handle
value: http://hdl.handle.net/2142/49451