Nonzero isotope effect inLa1.85Sr0.15

B. Batlogg

¹

,

G. A. Kourouklis

²

,

W. Weber

³

et al.

Perspective on RBa2Cu3Ox materials from oxygen deficiency studies

“…5. In agreement with earlier reports [9,17] wefindaplateauin TCfor6.66x56.8 that is accompanied by a minimum in the resistivity at 250 K which suggests a new ordered oxygen deficient structure having a transition temperature of 2 60 K. Extrapolating T, to zero gives a critical ox- ygen concentration for superconductivity of N 6.4, which is in the composition range where an orthorhombic-to-tetragonal transition is reported [ 7 ] to occur. X-ray analysis of our x= 6.33 sample confirmed that it was tetragonal and that there were less than 10% other phases present.…”

Intrinsic and structural isotope effects in iron-based superconductors

“…5,6 The cuprate high-temperature superconductors (HTS) are characterized by a vanishingly small but positive isotope effect exponent in optimally doped compounds which increases in a monotonic way upon decreasing doping. [7][8][9][10][11][12][13][14] For the optimally doped cuprate HTS the smallest value of the oxygen-isotope exponent α O ≃ 0.02 was obtained for YBa 2 Cu 3 O 7−δ and Bi 2 Sr 2 Ca 2 Cu 3 O 10+δ , while it reaches α O ≃ 0.25 for Bi 2 Sr 1.6 La 0.4 CuO 6+δ . [7][8][9]13,14 In addition, it was demonstrated that in underdoped materials α O exceeds substantially the BCS limit α BCS ≡ 0.5.…”

“…[7][8][9][10][11][12][13][14] For the optimally doped cuprate HTS the smallest value of the oxygen-isotope exponent α O ≃ 0.02 was obtained for YBa 2 Cu 3 O 7−δ and Bi 2 Sr 2 Ca 2 Cu 3 O 10+δ , while it reaches α O ≃ 0.25 for Bi 2 Sr 1.6 La 0.4 CuO 6+δ . [7][8][9]13,14 In addition, it was demonstrated that in underdoped materials α O exceeds substantially the BCS limit α BCS ≡ 0.5. 8,10,14 It is important to note here that the values of both, the oxygen and the copper isotope exponents in cuprate HTS are always positive.…”

Properties of La2CuO4 and related compounds

“…Isotope experiments [84,85] using t60 and 180 find T~ vc M-o.~6, where the exponent is reduced from the maximum value (-0.5) expected for a phonon mechanism. However, what one really expects is that the sum of the partial isotope effects over all the atoms will be -0.5.…”