Multigap nodeless superconductivity in nickel chalcogenideTlNi2Se2

Abstract

Low-temperature thermal conductivity measurements were performed on single crystals of TlNi2Se2, a nickel-chalcogenide heavy-electron superconductor with Tc ≃ 3.7 K. In zero field, the residual electronic contribution at T → 0 K (κ0/T ) was well separated from the total thermal conductivity, which is less than 0.45% of its normal-state value. Such a tiny residual κ0/T is unlikely contributed by the nodal quasiparticles. Nodeless gap structure is supported by the very weak field dependence of κ0(H)/T in low magnetic fields. In the whole field range, κ0(H)/T exhibits an "S"-shape curve, as in the case of nickel pnictides BaNi2As2 and SrNi2P2. This common feature of nickel-based superconductors can be explained by multiple nodeless superconducting gaps.

Optical properties ofTlNi2Se2: Observation of pseudogap formation

“…This model includes Drude and Lorentz terms, which approximately capture the contribution by free carriers and interband transitions. Both transport 14,23 and ARPES 18 results suggest the multiband character of TlNi 2 Se 2 , therefore we applied two Drude components analysis here, similar to the other members of "122" system [25][26][27] . Even though the Drude-Lorentz fit is somewhat arbitrary and the accuracy of the derived fit parameters is uncertain, it will not modify the key outcomes of the analysis.…”

“…Their structure, transport, magnetic and thermodynamic properties were already reported 14,23 . The frequency-dependent reflectance spectra at different temperature were measured by Bruker IFS 113v and 80v spectrometers in the frequency range from 30 to 20 000 cm −1 (4 meV∼2.5 eV), and then the reflectance was extended to 50 000 cm −1 (∼6.1 eV) at room temperature with a grating-type spectrometer.…”

Structural, electrical, and optical properties of polycrystalline NbO2 thin films grown on glass substrates by solid phase crystallization

“…Oxygen-poor films prepared at P O2 < 1 Â 10 À6 Torr showed much lower r of around 1 V cm. Such low r compared with the bulk value was also reported for epitaxial NbO 2 thin films [14,15]. Electrical properties that are sensitive to oxygen nonstoichiometry are advantageous for electrical switching applications [16,19].…”

“…Recently, epitaxial [11][12][13][14][15][16] and polycrystalline [17][18][19][20][21][22][23][24] thin films of NbO 2 have attracted attention from both fundamental and practical viewpoints [1]. For example, we demonstrated that a 10-nm-thick NbO 2 seed layer improved the mobility of rutile SnO 2 thin films [20], which are promising for use as the transparent conductive electrodes of photovoltaic cells.…”

Structural and electrical characterization of polycrystalline NbO2 thin film vertical devices grown on TiN-coated SiO2/Si substrates

“…Other authors have reported the estimated thickness of the top Nb2O5 layer to be 2 nm. 24 The exact estimation of the oxygen stoichiometry, however, is difficult via ex-situ measurements due to the possibility of the film surface oxidation after exposure to the air. .…”