New High-T_c Superconductor Family of Cu-Based Cu_1-xBa₂Ca_n-1Cu_nO_2n+4-δ with T_c>116 K

Abstract

The question of localisation of spin wave states is considered in a dilute Heisenberg ferromagnet with nearest-neighbour exchange near the percolation threshold. Using a geometrical model of the percolating cluster introduced by de Gennes which assumes that it is connected by effectively one-dimensional chains, together with Dyson's solution for the properties of states on a disordered chain, we find that the mobility edge drops to zero energy as p --* p , like exp( -A/@ -P,)''~),

A Search for a Low Anisotropic Superconductor

“…The relationship between valence state z of copper and number of CuO 2 layers follows following empirical rule z=2+4/(n+1) Among all the superconducting phases in this family the highest critical temperature is achieved in a phase with n=3 phase, Cu-1223 (T c (0)~120K); in four CuO 2 plane Cu-based superconductor (Cu-1234) T c (0) is around 18K. These two compounds have least anisotropy (γ=5 and 1.6 respectively) and long coherence length along c-axis [123][124][125][126]. The high-pressure synthesis of these compounds is not economically viable but by introducing thallium (which acts as structure stabilizer and reaction rate accelerator) into the charge reservoir layer, the superconductor phases can easily be obtained by normal pressure synthesis.…”

“…The members of Cu-based superconductors follow the formula Cu-12(n-1)n with n denoting the number of conducting CuO 2 planes; the higher number of CuO 2 planes are thought to have higher T c (0) since the optimum valency of copper for higher critical temperature is suggested to be z=2.33. The maximum increase of critical temperature is theoretically predicted for phase with n=11 [124]. The relationship between valence state z of copper and number of CuO 2 layers follows following empirical rule z=2+4/(n+1) Among all the superconducting phases in this family the highest critical temperature is achieved in a phase with n=3 phase, Cu-1223 (T c (0)~120K); in four CuO 2 plane Cu-based superconductor (Cu-1234) T c (0) is around 18K.…”

“…Therefore, the search for a superconductor material with low anisotropy and higher critical temperature was not stopped. A new family of superconductor materials, CuBa 2 Ca n-1 Cu n O 2n+2 (n=1,2,3…) [Cu-12(n-1)n] prepared under high pressure (4-6 GPa), is thought to be the most promising due to its higher critical temperature and critical current density [118][119][120][121][122][123][124]. The members of Cu-12(n-1)n family has the same tetragonal structure as Tl-12(n-1)n compounds have copper in their charge reservoir layer, CuBa 2 O4 n+δ .…”

“…The substitution of Tl in Cu-12(n-1)n compounds results in emergence of a new subfamily Cu 1-x Tl x -12(n-1)n which is the close derivative of these compounds. These com-pounds are prepared under high as well as normal pressure and have superconducting properties very close to Cu-based compounds [124,[127][128][129][130]. The members of this family have semi insulating charge reservoir layer Cu 1-x Tl x Ba 2 O 4n-δ which slightly increases the anisotropy but their anisotropy remains lower than that of Tl-based compounds.…”

Two-dimensional nature of four-layer cuprate superconductors

“…With this aim, we measured the reversible and fluctuation-induced magnetization of another four-layer system CuBa 2 Ca 3 Cu 4 O 12−δ [6][7][8][9][10] The c-axis parameter of Cu-1234 is shorter than that of Hg-1234 by about 1Å due to the relatively thin CRB. The T c , 117 K, of Cu-1234 is known not to vary even after post annealings under various conditions.…”