We present here a wide experimental study of the microwave complex resistivity r(T,H), performed on different superconducting films (Re-BaCuO cuprates and MgB2), with two different, complementary experimental techniques. The first set of measurement is performed using an end-wall cavity technique, which allows us to determine the complex resistivity at fixed frequency (48 GHz) in moderate applied magnetic fields (H < 0.7 T). The second set of data is obtained through a Corbino disc technique, which allows for a continuous frequency spectrum measurement between 5 and 20 GHz. In this latter case, the magnetic field can vary between zero and 12 T. In absence of an applied magnetic field, the real part of the conductivity shows an enhancement below the critical temperature Tc in all superconductor under investigation. The physical origin of this enhancement is still under debate [1], and some indications will be obtained from the observed frequency dependence. On the other hand, the imaginary part of the conductivity shows the expected behavior, allowing for the determination of the temperature dependence of the superfluid density. Measurements in presence of an applied field show further puzzling characteristics. On general grounds, the variation of the resistivity with the field can be due to both vortex motion and quasiparticle fractional density variation. These two phenomena contribute to both the real and the imaginary part of the resistivity, so that the beahvior of the quantity Dr=r(B)-r(0) can be in general rather complex. The standard approach to this problem [2] is to assume that the quasiparticle contribution can be neglected with respect to vortex motion, at least at low enough temperatures and magnetic fields (B<<Bc2). We show that within this approach the data for YBCO can be reasonably understood, so that one may conclude that most of the observed resistivity is due to vortex motion. This is however not the case for SmBaCuO and MgB2, where, by making use of this assumption, contradictory results are obtained from the data. In particular, in SmBaCuO, we observe a sublinear field dependence of both the real and imaginary part of Dr, which cannot be accounted for through flux motion only. In MgB2, on the other hand, both the high frequency limit and the frequency dependence itself are not consistent with the predictions of the vortex motion resistivity. We will show that in both cases the measured resistivity can be described if one takes into account the variation of the quasiparticle density with the applied magnetic field. 1. A. Hosseini et al., Phys. Rev. B 60 (1999) 1349.
Sarti, S., Amabile, C., Fastampa, R., Giura, M., Silva, E., Pompeo, N. (2004). Microwave resistivity and quasiparticle transport properties in Re-BCO and MgB2.
Microwave resistivity and quasiparticle transport properties in Re-BCO and MgB2
POMPEO, NICOLA
2004-01-01
Abstract
We present here a wide experimental study of the microwave complex resistivity r(T,H), performed on different superconducting films (Re-BaCuO cuprates and MgB2), with two different, complementary experimental techniques. The first set of measurement is performed using an end-wall cavity technique, which allows us to determine the complex resistivity at fixed frequency (48 GHz) in moderate applied magnetic fields (H < 0.7 T). The second set of data is obtained through a Corbino disc technique, which allows for a continuous frequency spectrum measurement between 5 and 20 GHz. In this latter case, the magnetic field can vary between zero and 12 T. In absence of an applied magnetic field, the real part of the conductivity shows an enhancement below the critical temperature Tc in all superconductor under investigation. The physical origin of this enhancement is still under debate [1], and some indications will be obtained from the observed frequency dependence. On the other hand, the imaginary part of the conductivity shows the expected behavior, allowing for the determination of the temperature dependence of the superfluid density. Measurements in presence of an applied field show further puzzling characteristics. On general grounds, the variation of the resistivity with the field can be due to both vortex motion and quasiparticle fractional density variation. These two phenomena contribute to both the real and the imaginary part of the resistivity, so that the beahvior of the quantity Dr=r(B)-r(0) can be in general rather complex. The standard approach to this problem [2] is to assume that the quasiparticle contribution can be neglected with respect to vortex motion, at least at low enough temperatures and magnetic fields (B<I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
