Far-Infrared Optical Conductivity Gap in Superconducting MgB2 Films

Robert A. Kaindl; Marc A. Carnahan; Joseph Orenstein; Daniel S. Chemla; Hans M. Christen; Hong-Ying Zhai; Mariappan Paranthaman; Doug H. Lowndes

doi:10.1103/PhysRevLett.88.027003

Far-Infrared Optical Conductivity Gap in Superconducting MgB2 Films

Robert A. Kaindl, Marc A. Carnahan, Joseph Orenstein, Daniel S. Chemla, Hans M. Christen, Hong-Ying Zhai, Mariappan Paranthaman, Doug H. Lowndes

DOI 10.1103/PhysRevLett.88.027003 · Physical Review Letters

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Abstract

We report the first study of the optical conductivity of MgB2 covering the range of its lowest-energy superconducting gap. Terahertz time-domain spectroscopy is utilized to determine the complex, frequency-dependent conductivity σ(ω) of thin films. The imaginary part reveals an inductive response due to the emergence of the superconducting condensate. The real part exhibits a strong depletion of oscillator strength near 5 meV resulting from the opening of a superconducting energy gap. The gap ratio of 2Δ0/kBTC≈1.9 is well below the weak-coupling value, pointing to complex behavior in this novel superconductor.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
MgB2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	30.5	Pressure not reported	zero_resistance
MgB2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	34	Pressure not reported	zero_resistance
MgB2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	39	Pressure not reported	unknown