Numéro |
J. Phys. IV France
Volume 12, Numéro 9, November 2002
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Page(s) | 361 - 361 | |
DOI | https://doi.org/10.1051/jp4:20020438 |
J. Phys. IV France 12 (2002) Pr9-361
DOI: 10.1051/jp4:20020438
Layered tungsten bronzes: Tuning the optical properties by changing the layer thickness
J.L. Musfeldt1, Z.T. Zhu1, Z.S. Teweldemedhin2 and M. Greenblatt21 University of Tennessee, U.S.A.
2 Rutgers University, NJ 08854, U.S.A.
Abstract
We investigated the optical properties of a series of monophosphate tungsten bronzes
(P02)4(W03)2m (m=2,4, 6,7) as a function of layer thickness, with special attention on the
m=7 density wave superconductor. These materials have several layers of corner-sharing
WO6 octahedra separated by one PO4 layer, leading to a tunable octahedral layer thickness
with m. In the optical regime, the spectra of the m=2, 4, 6, and 7 materials display an
anisotropic electronic excitation, originating from the W intra t2g d to d transition. The
intensities and frequencies of these excitations vary with the octahedral layer thickness,
consistent with a softer lattice with increasing m. The low-frequency electrodynamics of the
monophosphate tungsten bonzes show a gap or pseudogap feature in the infrared,
demonstrating a ubiquitous bound camer response. The m=7 density wave superconductor is
especially interesting. The variable temperature ab-plane spectra display a suppression of the
optical conductivity along the b-axis below 140 K, giving rise to charge localization and
anisotropic charge density wave gap formation near 1400 cm-1. This middle infrared charge
localization is directly related to the appearance of both flat and dispersive bands along b.
Although oscillator strength is redistributed among the free carrier response, charge density
wave gap absorption, and d to d transition in the density wave states, the spectral weight is
largely conserved below the plasma frequency. Based upon these observations, P4W 14050 is
another example of a superconductor with an unusual normal state.
© EDP Sciences 2002