Interplay of chemical disorder and electronic inhomogeneity in unconventional superconductors

Abstract

Many of today's forefront materials, such as high-T c superconductors, doped semiconductors, and colossal magnetoresistance materials, are structurally, chemically and/or electronically inhomogeneous at the nanoscale. Although inhomogeneity can degrade the utility of some materials, defects can also be advantageous. Quite generally, defects can serve as nanoscale probes and facilitate quasiparticle scattering used to extract otherwise inaccessible electronic properties. In superconductors, nonstoichiometric dopants are typically necessary to achieve a high transition temperature, while both structural and chemical defects are used to pin vortices and increase critical current. Scanning tunneling microscopy (STM) has proven to be an ideal technique for studying these processes at the atomic scale.In this perspective, we present an overview of STM studies on chemical disorder in unconventional superconductors, and discuss how dopants, impurities and adatoms may be used to probe, pin or enhance the intrinsic electronic properties of these materials.

Spatial distribution of superconducting and charge-density-wave order parameters in cuprates and its influence on the quasiparticle tunnel current (Review Article)

“…In other words, the measured quasiparticle tunnel current is actually averaged over rather a large region of the electrode surface. Nevertheless, while scanning along the sample surfaces of various cuprates, the measured CVCs change appreciably [34,[39][40][41][42][43][44][45][46][47][48][49]55], which brings us to a conclusion that SCDWs are really electronically inhomogeneous objects characterized by certain distributions of their parameters. As a result, the calculation of the tunnel current should include averaging over those distributions.…”

“…The most compelling origin of this inhomogeneity is the non-uniform distribution of oxygen atoms in those non-stoichiometric materials. However, the inhomogeneity may be traced to other causes of the nanoscale phase separation observed not only in superconducting and magnetic oxides [33][34][35][36][37]118,119] but also in other magnets [120,121], non-equilibrium alloys [122], porous systems [123,124], and colloids [125,126]. In the case of STM spectroscopy, the tunnel current is apparently harvested from a small area of the atomic size on the substrate [127].…”

“…The existence of intrinsic disorder in high-c T oxides is another factor, which makes the identification of CDW gaps more complicated than that of their superconducting counterparts [33][34][35][36][37][38] as comes about from the scanningtunnel-microscopy (STM) measurements. The spread of the latter over the sample surface is also quite wide, although the distribution histogram for the superconducting gaps is narrower than that for the CDW ones in the cases when the both kinds can be distinguished [39].…”

Multiband thermal transport in the iron-based superconductorBa1−xKxFe2Matusiak1, Wolf2 2015Phys. Rev. B11070View full textAdd to dashboardCite

“…The phase diagrams of these compounds generally look alike, often with a magnetically ordered non-superconducting parent compound and a superconducting dome developing upon doping or pressure [1]. The iron-based superconductors are no exception here, but there are some aspects that distinguish them from another numerous family of high-Tc superconductors -copper-based compounds.…”

Electronic Structure of HgBa2CuO4+δ with Self-organized Interstitial Oxygen Wires in the Hg Spacer Planes

“…The defects self organization controlling the critical temperature has been found in Sr 2 CuO 4−y [16], in Sr 2−x Ba x CuO 3+y [17], in (Cu 0.75 M o 0.25 Sr 2 YCu 2 O 7+y with 0 < y < 0.5 [18,19], and in BaP b 1−x Bi x O 3 [20]. The oxygen interstitial organization in oxygen doped cuprates La 2 CuO 4+y has been studied by scanning micro x-ray diffraction [2,3,[21][22][23][24][25][26], and by STM [27][28][29] showing superconductivity emerging in a nanoscale phase separation with a complex geometry [30][31][32][33][34]. The phase separation is determined by the proximity to a electronic topological Lifshitz transition in strongly correlated electronic systems [35][36][37] .…”