| This dissertation focus on the studies of transport properties and Nernst effect of high-Tc superconductors such as underdoped SmBa2Cu3O6+δsingle crystals and overdoped c-axis oriented Y1-xCaxBa2Cu3O7-δ(x=0.05,0.1,0.2) thin films on LAO substrate. Besides this, the effect of Te substitution on two-band superconductivity in NbSe2 is studied. The purpose of the first study is to investigate the phase fluctuations above Tc and the relationship between pseudogap phase and superconducting state, and second one is for our understanding of two-band superconductivity in low dimensional materials.Due to low dimensional nature and low charge carriers, the phase fluctuation of Cooper pairs plays a crucial role in high-Tc cuprates. The novel scenario in which the electrons starts to form Cooper pairs at a characteristic temperature Tonset much higher than Tc and long range phase coherence establishes at Tc is proposed by many theorists. In conventional superconductors Cooper pair formation and condensation occur simultaneously. For high-Tc, there is a large pseudogap (PG) region (Tc |
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