arXiv subjects

Jungho Kim

Publications and source records attributed to Jungho Kim.

76 records · Page 5Linked to original sources

arXiv2008

Magnetic field dependence of charge stripe order in La2-xBaxCuO4 (x~1/8)

We have carried out a detailed investigation of the magnetic field dependence of charge ordering in La2-xBaxCuO4 (x~1/8) utilizing high-resolution x-ray scattering. We find that the charge order correlation length increases as the magnetic field greater than ~5T is applied in the superconducting phase (T=2K). The observed unusual field dependence of the charge order correlation length suggests that the static charge stripe order competes with the superconducting ground state in this sample.

cond-mat.supr-con↗

arXiv2007

Reentrant spin glass transition in LuFe2O4

We have carried out a comprehensive investigation of magnetic properties of LuFe$_2$O$_4$, using AC susceptibility, DC magnetization and specific heat. A magnetic phase transition around $\sim$236 K was observed with DC magnetization and specific heat measurements, which is identified as a paramagnetic to ferrimagnetic transition based on the nonlinear susceptibility data. Upon further cooling below this temperature, we also observed highly relaxational magnetic behavior: the DC magnetization exhibits history and time dependence, and the real and imaginary part of the AC susceptibility shows large frequency dependence. Dynamic scaling of the AC susceptibility data suggests that this low temperature phase can be described as a reentrant spin glass phase. We also discuss magnetic field dependence of the spin glass transition and aging, memory and rejuvenation effect below the glass transition temperature around 228 K.

cond-mat.str-el↗

arXiv2007

Multiple-source optical spectral weight transfer in ferromagnetic EuB6

We present the first wide range (2 meV$-$5.5 eV) optical conductivity of EuB$_6$ from reflectivity and ellipsometry measurements. Upon the ferromagnetic transition at T$_{c}$=15.5 K, interband transition $σ_{1}(ω)$ decreases at three different energy $ω$=0.5, 1.4, 2.75 eV and the lost spectral weight is transferred to the Drude $σ_{1}(ω)$ at $ω<$0.33 eV. We succeeded in explaining this unprecedented multiple-energy $σ_{1}(ω)$ change using LDA+U calculated band structure by Kunes and Pickett (Phys. Rev. B, $\textbf{69}$,165111). Our finding supports strongly that (1) EuB$_6$ is a semimetal and (2) the exchange-driven band splitting is the primary source of the drastic $ρ(T)$ and $ω_{p}^{2}$ changes at T $<$ T$_{c}$.

cond-mat.str-el↗

arXiv2004

Optical spectroscopy study on the electronic structure of $Eu_{1-x} Ca_x B_6$

The optical conductivity $σ_{1}(ω)$ of Eu$_{1-x}$Ca$_{x}$B$_{6}$ has been obtained from reflectivity and ellipsometry measurements for series of compositions, $0\leq x\leq 1$. The interband part of $σ_{1}(ω) $ shifts continuously to higher frequency as Ca-content $x$ increases. Also the intraband spectral weight of $σ_{1}(ω)$ decreases rapidly and essentially vanishes for $x\geq x_{c}=0.35$. These results show that the valence band and the conduction band of Eu$_{1-x}$Ca$_{x}$B$_{6}$ move away from each other such that their band overlap decreases with increasing Ca-substitution. As a result, the electronic state evolves from the semimetallic structure of EuB$_{6}$ to the insulating CaB$_{6}$ where the two bands are separated to open a finite gap ($\simeq 0.25$ eV) at the X-point of the Brillouin zone.

cond-mat.str-el↗