Byeong Hun Min

Existence of Heavy Fermions in the Antiferromagnetic Phase of CeIn3

We report the pressure-dependent optical conductivity spectra of the heavy-fermion (HF) compound CeIn 3 below the Neel temperature of 10 K to investigate the existence of the HF state in the antiferromagnetic (AFM) phase. The peak due to the interband transition in the hybridization gap between the conduction band and the nearly localized 4 f states ( c – f hybridization) appears at a photon energy of about 20 meV, not only in the HF regime but also in the AFM regime. Both the energy and intensity of the c – f hybridization peak continuously increase with the application of pressure from the AFM phase to the HF regime. This result suggests that c – f hybridization, as well as heavy fermions, exists even in the AFM phase of CeIn 3 .

Optical properties of the iron-based superconductor LiFeAs single crystal

We have measured the reflectivity spectra of the LiFeAs (Tc = 17.6 K) single crystal in the temperature range from 4 to 300 K. In the superconducting (SC) state (T Tc), the optical conductivity spectra display typical metallic behavior with the Drude-type spectra at low frequencies, but we found that the introduction of the two Drude components best fits the data, indicating the multiband nature of this compound. A theoretical analysis of the low-temperature data (T = 4 K 200 cm−1), we have also performed the local-density approximation band calculation and calculated the optical spectra of the interband transitions. This theoretical result provided qualitative agreement with the experimental data below 4000 cm−1 .

Vortex fluctuation effect evaluated using reversible magnetization in optimally doped single crystal NaFe0.97Co0.03As superconductor

The reversible magnetization curves for various magnetic fields are investigated for a single crystal of the optimally doped NaFe0.97Co0.03As superconductor with the superconducting transition temperature Tc?=?20.9 K (?(T)?=?0) in the case where H is parallel to c-axis. A well-formed rounding effect is observed in the temperature dependence of the magnetization, and it widens on increasing the strength of the applied magnetic fields. At 20.2 K, we observe a crossing of the M(T) curves for different applied magnetic fields, indicating important fluctuation effects. The irreversibility line Hirr(T) obeys a universal scaling relation Hirr(T)??=??H0(1???T/Tc)n characterized by n?????1.537, which confirms the moderately anisotropic nature of the sample. The scaling analysis of the reversible magnetization in the region near Tc(H) supports the three-dimensional nature of the vortex fluctuations in NaFe0.97Co0.03As.

Superconducting states study in electron-overdoped BaFe1.8Co0.2As2 using terahertz and far-infrared spectroscopy

Terahertz and far-infrared spectroscopy in the temperature range, 4–300 K were used to study the normal and superconducting states of superconductor BaFe1.8Co0.2As2 with Tc = 22.5 K. At T < Tc, the vanishing of optical conductivity caused by the unity approach and flat behavior in reflectivity were observed below 45 cm−1. This feature indicates the formation of a superconducting energy gap due to the formation of Cooper pairs. The introduction of the two Drudes model well reproduced the normal state optical conductivity, indicating the multiband nature of this superconductor. Two superconducting energy gaps were estimated as = 2.90 meV and = 6.75 meV by the BCS model. Using the sum rule and dielectric function, the superconducting plasma frequency () can be estimated as 5170 ± 270 cm−1, yielding that the magnetic penetration depth (λ) is 3090 ± 160 A. This material was observed to fall on the universal scaling line, Nc ~ 4.4 .

Polarization-Dependent Three-Dimensional Angle-Resolved Photoemission Spectroscopy of BaFe1.8Co0.2As2

We performed polarization- and photon-energy-dependent angle-resolved photoemission spectroscopy of a slightly overdoped iron pnictide superconductor, BaFe

Critical current density and lower critical field in a superconducting Ca10(Pt4As8) (Fe2−x Ptx As2)5 single crystal

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Anomalous Superconducting-Gap Structure of Slightly Overdoped Ba(Fe1−xCox)2As2

Co

Polarization-dependent three-dimensional angle-resolved photoemission study on LiFeAs

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Superconductivity-induced Phonon Renormalization on NaFe1 xCoxAs

As

Three-dimensional electronic structure and interband nesting in the stoichiometric superconductor LiFeAs

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