Superconducting fluctuations and pseudogap in high-T_ccuprates

Abstract

Abstract. Large pulsed magnetic fields up to 60 Tesla are used to suppress the contribution of superconducting fluctuations (SCF) to the ab-plane conductivity above T c in a series of YBa 2 Cu 3 O 6+x . These experiments allow us to determine the field H ′ c (T ) and the temperature T ′ c above which the SCFs are fully suppressed. A careful investigation near optimal doping shows that T ′ c is higher than the pseudogap temperature T ⋆ , which is an unambiguous evidence that the pseudogap cannot be assigned to preformed pairs. Accurate determinations of the SCF contribution to the conductivity versus temperature and magnetic field have been achieved. They can be accounted for by thermal fluctuations following the Ginzburg-Landau scheme for nearly optimally doped samples. A phase fluctuation contribution might be invoked for the most underdoped samples in a T range which increases when controlled disorder is introduced by electron irradiation. Quantitative analysis of the fluctuating magnetoconductance allows us to determine the critical field H c2 (0) which is found to be be quite similar to H ′ c (0) and to increase with hole doping. Studies of the incidence of disorder on both T ′ c and T ⋆ allow us to to propose a three dimensional phase diagram including a disorder axis, which allows to explain most observations done in other cuprate families.

New insights into the phase diagram of the copper oxide superconductors from electronic Raman scattering

“…In our interpretation the superconducting gap and the pseudogap coexist and compete with each other below p c1 . This is also supported by previous studies [47][48][49][50][51][52][53][54][55].…”

Pseusogap in Cuprates by Electronic Raman Scattering

“…It is a foe. Our findings bring additional experimental evidence to recent studies in ARPES [37,38], STS [39],optics [40] and transport [41,42] all showing that the pseudogap and superconducting phases are in competition.…”

Quantum logic gates generated by SC-charge qubits coupled to a resonator

“…The operations of such gates may be affected considerably when the magnetic fluxes are subjected to fluctuations in either phase or amplitude. Quantitative evaluation of such fluctuations need further investigation [39,40].…”