New features are reported in precision measurements of the complex microwave conductivity of high-quality YBa 2 Cu 3 O 6.95 crystals grown in BaZrO 3 crucibles. A third peak in the normal conductivity, 1 (T), at around 80 K, and enhanced pair conductivity 2 (T) below ϳ65 K are observed. The data are inconsistent with a single order parameter, and instead are indicative of multicomponent superconductivity. Overall, these results point to the presence of multiple pairing interactions in YBa 2 Cu 3 O 6.95 and also provide a natural explanation to account for the low-temperature 35-K conductivity peak observed in all YBa 2 Cu 3 O 6.95 crystals. ͓S0163-1829͑97͒52322-8͔The mechanism for superconductivity and the nature of the superconducting state in the cuprates continue to be prime issues that are being debated. 1 Microwave measurements have yielded important information on the nature of the pairing, the quasiparticle density of states, and scattering in the cuprate superconductors. 2-4 Surface impedance of YBa 2 Cu 3 O 6.95 ͑YBCO͒ single crystals in the past have consistently shown two features: A linear penetration depth ͓(T)ϰT͔ over a limited low T range, and the presence of a bump in the surface resistance R s (T) which results in a peak in the normal conductivity 1 (T) at ϳ35 K, well below the superconducting T c ϳ93 K. 2,5 The former behavior has been attributed to d-wave order-parameter symmetry or, in general, the presence of nodes in the gap. A rapidly decreasing quasiparticle scattering rate below T c has been proposed to account for the latter feature. 5,6 There is a general consensus that the experimental results can be explained in the framework of a single d-wave order parameter with inclusion of effects due to strong coupling, scattering with strong temperature dependence, and fluctuation. 5,7 In this paper, we present results on the microwave response of high-quality YBa 2 Cu 3 O 6.95 single crystals grown by a new method that avoids crucible corrosion. We measure the temperature-dependent surface impedance Z s ϭR s ϩiX s and penetration depth (ϭX s / 0 ) from which we extract the complex conductivity s ϭ 1 Ϫi 2 . The two features mentioned above, (T)ϰT at low T and the 35-K peak in 1 , are still present in these crystals. However, in addition, a new peak in 1 (T) at ϳ80 K and a distinct increase in 2 (T) below ϳ65 K are observed. A single d-wave order parameter is insufficient to describe the new data, and instead we show that an analysis in terms of two-component superconductivity is necessary.The single crystals ͑typically 1.3ϫ1.3ϫ0.1 mm 3 in size͒ used in this work were of very high quality grown from BaZrO 3 crucibles ͑BZO͒. 8 This growth method leads to crystals with extremely clean surfaces and exceptional purity exceeding 99.995% ͑Ref. 9͒, in contrast to crystals grown in other crucibles which have final reported purities of 99.5-99.95%. 10,11 As shown in this paper, this difference in purity appears to play a significant role in the microwave properties. Standard oxygen annealing procedures w...