• Progress in Superconductivity
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• v.11 no.2
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• pp.135-140
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• 2010

We propose a variational wave function for the ground state of the magnetic heavy fermion (HF) systems, in which both the Kondo and the RKKY interactions are variationally incorporated and the local f-orbital state exists as a linear combination of a full local moment state and a fully compensated state (mixed wave state). We describe the mechanism for the mixed wave ground state based on the large-N treatment of the Kondo lattice Hamiltonian added with RKKY interaction. With the mixed wave ground state we can explain several puzzling experiments in magnetic HF compounds such as a small value of local moment, coexistence of the antiferromagnetic (AFM) and the paramagnetic (PM) phases, local quantum criticality, etc.

• Progress in Superconductivity
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• v.14 no.1
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• pp.17-23
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• 2012

The heavy-fermion compound $CeRhIn_5$ is a prototypical antiferromagnet where Ce 4f moments align antiferromagnetically below 3.8 K. When doped with Hg, the antiferromagnetic transition $T_N$ initially decreases, becomes flat, and increases again with further increasing Hg concentration. Here we report pressure effects on the electrical resistivity of a 0.45 % Hg-doped $CeRhIn_5$, where $T_N$ is 3.4 K and the magnetic structure is same as that of the undoped compound with Q=(1/2, 1/2, 0.298). With increasing pressure, $T_N$ is suppressed and a superconducting state emerges. The temperature dependence of the electrical resistivity near an optimal pressure shows a power-law behavior that deviates from a $T^2$ dependence, indicating presence of abundant quantum fluctuations near the optimal pressure.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.5
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• pp.399-402
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• 2019

The electromagnetic properties of heavy fermion $CePd_2Si_2$ are investigated using density functional theory using the local density approximation (LDA) and LDA+U methods. The Ce f-bands are located near the Fermi energy and hybridized with the Pd-3d states. This hybridization plays an important role in generating the physical characteristics of this compound. The magnetic moment of $CePd_2Si_2$ calculated within the LDA scheme does not match with the experimental result because of the strong correlation interaction between the f orbitals. The calculation shows that the specific heat coefficient underestimates the experimental value by a factor of 5.98. This discrepancy is attributed to the formation of quasiparticles. The exchange interaction between the local f electrons and the conduction d electrons is the reason for the formation of quasiparticles. The exchange interaction is significant in $CePd_2Si_2$, which makes the quasiparticle mass increase. This enhances the specific heat coefficient.

• Korean Journal of Materials Research
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• v.29 no.7
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• pp.451-455
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• 2019

The electromagnetic and thermal properties of a heavy fermion $CeNi_2Ge_2$ are investigated using first-principle methods with local density approximation (LDA) and fully relativistic approaches. The Ce f-bands are located near the Fermi energy $E_F$ and hybridized with the Ni-3d states. This hybridization plays important roles in the characteristics of this material. The fully relativistic approach shows that the 4f states split into $4f_{7/2}$ and $4f_{5/2}$ states due to spin-orbit coupling effects. It can be found that within the LDA calculation, the density of states near the Fermi level are mainly of Ce-derived 4f states. The Ni-derived 3d states have high peaks around -1.7eV and spreaded over wide range around the Fermi level. The calculated magnetic of $CeNi_2Ge_2$ with LDA method does not match with that of experimental result because of strong correlation interaction between electrons in f orbitals. The calculations show that the specific heat coefficient underestimates the experimental value by a factor of 19.1. The discrepancy between the band calculation and experiment for specific heat coefficient is attributed to the formation of a quasiparticle. Because of the volume contraction, the exchange interaction between the f states and the conduction electrons is large in $CeNi_2Ge_2$, which increases the quasiparticle mass. This will result in the enhancement of the specific hear coefficient.

• 한국초전도학회:학술대회논문집
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• v.16
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• pp.36-36
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• 2006

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.753-757
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• 1995

Systematic studies on the crystal structure and magnetic properties of light rare earth element(RE) compounds with Pb, $REPb_{2}$, have been carried out. Their crystal structure has been identified to be a $MoSi_{2}$-type. The values of the effective magnetic moment for $CePb_{2},\;PrPb_{2}\;and\;NdPb_{2}$ are respectively very close to the theoretical values of $RE^{3+}$. These three compounds are antiferromagnetic and exhibit a metamagnetic transition. The magnitude of the Neel temperature is proportional to two-thirds of the de Gennes factor. The magnetic entropy change for $NdPb_{2}$ is contrast to the value for $CePb_{2}$ heavy-fermion compound, comparable to the theoretical value. The magnetic contribution to the temperature dependence of resistivity for $PrPb_{2}$ is given by a form of -lnT in a wide temperature range, implying the Kondo system in analogy with $Cepb_{2}$.

• Progress in Superconductivity and Cryogenics
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• v.23 no.3
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• pp.41-44
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• 2021

We developed an optimization process of the pulsed laser deposition method to grow epitaxial CeCoIn₅ thin films on MgF₂ substrates. The effects of different deposition parameters on film growth were extensively studied by analyzing the measured X-ray diffraction patterns. All the deposited films contained small amounts of CeIn₃ impurity phase and misoriented CeCoIn₅, for which the c-axis of the unit cell is perpendicular to the normal vector of the substrate surface. The deposition temperature, target composition, laser energy density, and repetition rate were found effective in the formation of (00l)-oriented CeCoIn₅ as well as the undesired phases such as CeIn₃, misoriented CeCoIn₅ along the (112) and (h00). Our results provide a set of deposition parameters that produce high-quality epitaxial CeCoIn₅ thin films with sufficiently low amounts of impurity phases and can serve as a reference for future studies to optimize the deposition process further.