Low-temperature far-infrared absorption in the antiferromagnetic organic superconductor κ-(BETS)2FeBr4
Abstract
Organic salt κ-(BETS)2FeBr4 is a unique compound in which local moment antiferromagnetism of Fe3+ ions (below Néel temperature TN of 2.5 K) coexists with bulk superconductivity (below the superconducting transition temperature TC=1.1K ). To probe this unique coexistence we studied the low-temperature far-infrared optical response in a frequency range of 7-40cm-1 , a characteristic energy range for superconducting and magnetic gaps. Measurements were undertaken using a polarizing interferometer and a He3 cryostat in a temperature range 0.5-2.8 K. The spectrum shows a clear change on crossing both TN and TC . An absorption feature below TN is interpreted as a signature for the formation of a magnetic pseudogap. The observed increased reflectance relative to the normal state at temperatures below TC sets a value of the superconducting energy gap Δ0 in the strong coupling regime, 2Δ0≈8kbTC .
- Publication:
-
Physical Review B
- Pub Date:
- March 2010
- DOI:
- 10.1103/PhysRevB.81.092508
- Bibcode:
- 2010PhRvB..81i2508K
- Keywords:
-
- 74.25.Gz;
- 74.70.Kn;
- 75.50.Ee;
- Optical properties;
- Organic superconductors;
- Antiferromagnetics