GAP DETERMINATION IN THE FIELD-INDUCED-SPIN-DENSITY-WAVE STATE OF (TMTSF)2CLO4 VIA FAR-INFRARED PHOTOCONDUCTIVITY

We report the determination of the field-induced-spin-density-wave opt ical gap of the organic superconductor (TMTSF)2ClO4, by direct measure ment of the far-infrared photoconductivity. The energy spectrum shows a sharp resonance of photoconductivity centered at 19 cm-1 attributed to the single-particle gap. Its amplitude in the symmetry breaking pha ses is independent of temperature (for 2-5 K) and magnetic field (to 1 4 T). This is consistent with previous far-infrared transmission studi es suggesting that in contrast to the predictions of existing models, the condensate fraction rather than the gap should represent the order parameter of the cascade of phase transitions.