Epitaxial Tl2CaBa2Cu2O8 thin films with low 9.6 GHz surface resistance at high power and above 77 K

Abstract

We report measurements of the dc and microwave properties of epitaxial thin films of Tl2CaBa2Cu2O8 on LaAlO3. ac magnetic susceptibility measurements yield critical temperatures at the transition midpoint Tc∼100 K and 10–90% transition widths of ∼1.0 K. We observed a critical current density of 1.06×106 A/cm2 at 77 K measured by dc transport. We measured a low-power surface resistance of Rs=0.2 mΩ at 9.55 GHz and 77 K. This is ∼50 times lower than oxygen-free high-conductivity (OFHC) Cu at the same frequency and temperature. At 90 K, RS rises to 0.4 mΩ, and at 95 K, RS=0.7 mΩ. We measured the microwave power dependence of RS at 77, 90, and 95 K. At high microwave field (≳30 G, 77 K) Rs=0.8 mΩ, more than ten times lower than OFHC Cu.

Microwave Surface Impedance of High Temperature Superconductors

“…An early measurement at 9.5 GHz by Hammond et al 144 A material that has come under some scrutiny for reasons other than the potential for applications is Ndi.^Ceo.i^CuOi. As already discussed in Section 3.3 there is a fairly strong case for a sizeable energy gap in this material and no evidence as yet of the presence of nodes in the gap.…”

Effect of single crystal substrates on the growth and properties of superconducting Tl2Ba2CaCu2O8 films

“…Yet, these angular shifts can account only for a small part of the large peak width in the rocking curve measured here. In one previous study of Tl 2 Ba 2 CaCu 2 0 8 on LaA10 3 , the rocking curve full width at half maximum has been reported to be as narrow as 0.3 °, 8 although the same group has reported values to be more typically in the range O.8-1.O 0 . 12 The T c of the Tl 2 Ba 2 CaCu 2 0 8 film on LaA10 3 was measured inductively and by ac magnetic susceptibility to be 103 K. In previous studies T c has been reported to be 102 K, 8 103 K, 7 and 106.5 K. 6 The narrow transition width in the inductive measurement of T c is the signature of a high quality film with few weak junctions between grains.…”

The nucleation and growth mechanism of the electrodeposition of Tl2Ba2Ca2Cu3O10superconducting thin films on Al-substrate

“…The easiest films to prepare as single-phase material, however, are the Tl 2 Ba 2 CaCu 2 O 8 compounds, whereas the growth of single-phase Tl 2 Ba 2 Ca 2 Cu 3 O 10 films is somewhat more difficult. The primary techniques for the preparation of Tl-based thin films are laser ablation [11,12], electron beam evaporation [13,14], organic chemical vapor deposition [15,16] and sputtering [17][18][19]. Holstein et al [20], prepared Tl-2212 films by a two-step post-annealing process.…”