J.-G. Park

Current-carrying capacity of double-wall carbon nanotubes

We have studied electrical transport characteristics of individual double-wall carbon nanotubes (DWNT) under high bias voltages. As the bias voltage applied to the carbon nanotubes increases, the outermost shell of the DWNTs broke down sequentially, which enabled us to determine the current-carrying capacity of each shell. The maximum current-carrying capacity per shell was about 150??A, which is well above that of any other previous reports.

Unconventional superconductivity and magnetism in

Abstract CePt 3 Si is a novel ternary compound exhibiting antiferromagnetic order at T N ≈ 2.2 K and superconductivity (SC) at T c ≈ 0.75 K . Large values of H c 2 ′ ≈ - 8.5 T / K and H c 2 ( 0 ) ≈ 5 T indicate Cooper pairs formed out of heavy quasiparticles. The mass enhancement originates from Kondo interaction with a characteristic temperature T K ≈ 8 K . NMR and μ SR measurements evidence coexistence of SC and long-range magnetic order on a microscopic scale. Moreover, CePt 3 Si is the first heavy fermion SC without an inversion symmetry. This gives rise to a novel type of NMR relaxation rate 1 / T 1 which is very unique and never reported before for other heavy fermion superconductors. Studies of Si/Ge substitution allow us to establish a phase diagram.

Thermopower study of La- and Ce-doped URu2Si2

Abstract We have measured the thermopower of La-and Ce-doped URu 2 Si 2 . Since a feature distinctively related to an antiferromagnetic transition in URu 2 Si 2 disappears between 2% and 5% of doping, we conclude that a small amount of either La- or Ce-doping modifies the magnetic ground state of URu 2 Si 2 significantly. At higher concentrations, however, the thermopower data of La- and Ce-doped URu 2 Si 2 differ from each other. This suggests that although U moments in (U,La)Ru 2 Si 2 possibly become localised with increasing La concentration (U,Ce)Ru 2 Si 2 seems to remain strongly hybridised up to 40% of Ce.

Asymmetric magnetoconductance and magneto-Coulomb effect in a carbon nanotube single electron transistor

We report single step-like asymmetric magnetoconductance from a double-walled carbon nanotube single electron transistor contacted by ferromagnetic cobalt electrodes. The device conductance changed significantly when the direction of the applied magnetic field was reversed, but did not show the spin-valve-type double extrema feature near the coercive field of the electrodes. The magnetoconductance also showed quasi-periodic sign-reversing oscillations with respect to the applied bias. The bias-dependent oscillation of the magnetoconductance was compared with the quantum dot stability diagram for the device. As a result, it was confirmed that the asymmetric magnetoconductance was caused by the magneto-Coulomb effect.

Influence of field-dependent magnetic structure of CeTe2 on its resistivity

Abstract The tetragonal compound CeTe 2 has a magnetic ground state at low temperatures. Neutron-diffraction measurements have shown that CeTe 2 orders ferrimagnetically below 4.3 K. The magnetic moments lie along c in a down-up-up-down spin sequence A, B, B, A. The moment on the A sites is 0.40(6) μ B and that on the B sites is 0.98(6) μ B . We have also found a strong field dependence of the magnetic peaks, and discuss it with reference to the large magnetoresistance.

Understanding the origin of non-Fermi liquid behaviour in doped Kondo insulators

We have made inelastic neutron scattering measurements on the doped Kondo insulators Ce(Rh0.8Pd0.2)Sb and (Ce0.7Th0.3)RhSb. Previous bulk property measurements showed non-Fermi liquid (NFL) behaviour for both compositions. In our inelastic neutron scattering data these two compounds also show E/T scaling behaviour in the dynamical spin susceptibility with different exponents, which is considered a characteristic feature of NFL systems. We discuss how these two different exponents might be related to different microscopic mechanisms of the NFL behaviour in the bulk properties as well as the E/T scaling behaviour seen in the dynamical susceptibility.

Neutron scattering study of CeTe2

We give a report on our recent elastic and inelastic neutron studies of CeTe2. From the diffraction results, we found that CeTe2 shows two successive transitions and simultaneously undergoes a very large cia ratio change at low temperatures. These results suggest that the upper transition in CeTe2 should have strong magnetoelastic character. Our inelastic neutron study shows two well-defined excitations, which we attribute to the crystal field splitting of Ce3+ indicating that the Ce ions in CeTe2 are relatively well. localised

Spin dynamics of Gd in UAl2 and LaAl2

To investigate the spin dynamics of Gd-doped UAl2, we have studied two Gd-doped UAl2 samples; (Gd0.03U0.97)Al2 and (Gd0.1U0.9)Al2, using muon spin relaxation technique (μSR). For comparison, we also measured the spin dynamics of (Gd0.05La0.95)Al2. The three samples show a different temperature dependence of their initial asymmetry values. More importantly, the time dependence of the muon spin depolarisation differs significantly from one sample to another. We discuss our μSR data with reference to previous susceptibility measurements. Previous Gd-EPR results on similar compositions are also discussed.

Small moment ordering in U-doped CeNiSn a μSR study

Abstract Moment localization and magnetic order in U-doped CeNiSn have been studied using muon spin relaxation (μSR). CeNiSn and (Ce 0.95 U 0.05 )NiSn show similar spin dynamics down to lowest temperatures. Further increase in the U concentration leads to the onset of an inhomogeneous magnetically ordered state: in (Ce 0.9 U 0.1 )NiSn and (Ce 0.8 U 0.2 )NiSn regions of magnetic order are found to coexist with an essentially paramagnetic matrix. We discuss these results in the light of our previous resistivity, magnetization and thermopower data.

Unconventional superconductivity and magnetism in

Abstract CePt 3 Si is a novel ternary compound exhibiting antiferromagnetic order at T N ≈ 2.2 K and superconductivity (SC) at T c ≈ 0.75 K . Large values of H c 2 ′ ≈ - 8.5 T / K and H c 2 ( 0 ) ≈ 5 T indicate Cooper pairs formed out of heavy quasiparticles. The mass enhancement originates from Kondo interaction with a characteristic temperature T K ≈ 8 K . NMR and μ SR measurements evidence coexistence of SC and long-range magnetic order on a microscopic scale. Moreover, CePt 3 Si is the first heavy fermion SC without an inversion symmetry. This gives rise to a novel type of NMR relaxation rate 1 / T 1 which is very unique and never reported before for other heavy fermion superconductors. Studies of Si/Ge substitution allow us to establish a phase diagram.