Experimental Studies of the Anomalous Sign Reversal in the Vortex-State Hall Conductivity of YBa₂2Cu₃O₇

Author: Beam, David Alan

Year: 1997

Degree: Dissertation (Ph.D.)

Advisor: Yeh, Nai-Chang

Committee Members: Yeh, Nai-Chang; Cross, Michael Clifford; Eisenstein, James P.; Frautschi, Steven C.

Option: Physics

DOI: 10.7907/aak2-p702

Abstract

The DC vortex-state Hall conductivity (σxy) of YBa2Cu3O7 single crystals is found to be independent of the density and orientation of correlated disorder. A universal σxy is observed for a given reduced temperature (T/Tc), magnetic field strength (H), and magnetic field orientation (ϴ), in five samples of different controlled defects, using direct current transport measurements. Transport scattering times (τ), derived from our data using the model describing the origin of the anomalous sign reversal in the vortex-state σxy by Feigel'man et al.1, are consistent in magnitude with those derived from other measurements. Experimental issues unresolved by the Feigel'man et al. model are also presented.

The complex Hall conductivity, σxy (≡ σxy' + iσxy"),of a YBa2Cu3O1 thin film is measured in the frequency range of 100 Hz to 7 MHz. A frequency independent σxy', and a frequency dependent σxy" ∝ w are observed, in agreement with an extension of the Feigel'man et al. model to finite frequencies, and using the Drude approximation2 by Yeh3.. Finally, the magnetic field (B) dependence of the complex Hall conductivity is compared with the model used by Spielman et al.4, where the Hall conductivity was attributed solely to a quasiparticle contribution, predicting a linear dependence on B for T « Tc. We observe σxy' ∝ 1/Bα and σxy" ∝ 1/Bβ, where α, β > 1, and α ≠ β, for T < Tc, in sharp contrast to the prediction from the model assuming only quasiparticle contributions. This provides support for any model which requires that both vortices and quasiparticles contribute to the Hall conductivity at low temperatures.

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1 M. V. Feigel'man et al., Pis'ma Zh. Teor. Fiz. 62, 811 (1995) [JETP Lett. 62, 835 (1995)].

2 P. Drude, Annalen der Physik 1, 566, and 3, 369 (1900).

3 Yeh, N.-C., private communications (1997).

4 S. Spielman et al., Phys. Rev. Lett. 73, 1537 (1994)

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