Specific heat investigation of superconducting properties in 2H-NbSe2 single crystals

초록

We report on the crystal growth and superconducting properties of the transition-metal dichalcogenide 2H-NbSe2. Millimeter scale 2H-NbSe2 single crystals with well-defined hexagonal platelets were grown by chemical vapor transport with iodine (I2) as the transport agent. Rietveld analysis of X-ray powder diffraction confirms the single-phase P63/mmc space group with a = b = 3.443 Å and c = 12.542 Å. Electrical transport and magnetic measurements confirm bulk superconductivity (Tc = 7.06 K), coexistence of charge density wave order (TCDW = 33 K), and nearly ideal diamagnetism (4πχ ~ 0.98 at 2 K). Temperature-dependent specific heat shows a clear jump at Tc, which can be analyzed using a two-gap s + s-wave model with different weights. Approximately 97% of the total Sommerfeld coefficient is associated with the larger-gap ( Δ1 ∼ 1.68 meV), while the smaller-gap ( Δ2 ∼ 0.27 meV) accounts for the remaining 3%. This work provides useful quantitative information on multiband superconductivity in 2H-NbSe2 single crystals.

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