Far-infrared investigations of eta-Mo4O11: using a magnetic field to open the gap

eta -Mo4O11 has been of recent interest as both a charge density wave (CDW) and a quantum limit material. Indeed, previous low temperature far-infrare d measurements have highlighted the unusual spectroscopic response, while t ransport studies have identified low-field quantum Hall behavior as well as a semimetal to semiconductor transition above 19 T. In order to explore th e low-temperature electrodynamics in this prototype system, we have measure d the unpolarized far-infrared response (30-400 cm(-1)) of eta -Mo4O11 in a n applied magnetic field (0-17 T). The reflectance ratio of eta -Mo4O11 cha nges systematically at low fields, saturating above 7 T. Here, a small rise in ratio spectra is found near 120 cm(-1), whereas the reflectance ratio d rops below 70 cm(-1). Combining this data with the low-temperature power re flectance, we have used a Kramers-Kronig analysis to calculate the frequenc y dependent conductivity in the magnetic field. The preliminary data shows that the main effect of the field is related to the CDW2 gap.