arXiv subjects

Jun-Hyung Cho

Publications and source records attributed to Jun-Hyung Cho.

58 records · Page 4Linked to original sources

arXiv2011

Atomic structure, energetics, and dynamics of topological solitons in Indium chains on Si(111) surfaces

Based on scanning tunneling microscopy and first-principles theoretical studies, we characterize the precise atomic structure of a topological soliton in In chains grown on Si(111) surfaces. Variable-temperature measurements of the soliton population allow us to determine the soliton formation energy to be ~60 meV, smaller than one half of the band gap of ~200 meV. Once created, these solitons have very low mobility, even though the activation energy is only about 20 meV; the sluggish nature is attributed to the exceptionally low attempt frequency for soliton migration. We further demonstrate local electric field-enhanced soliton dynamics.

cond-mat.mes-hall↗

arXiv2011

Quantum Size Effect and Electronic Stability of Freestanding Metal Atom Wires

Using DFT calculations, we present a thorough study of the quantum size effects on the stability of freestanding metal atom wires. Our systems include Na, Ag, Au, In, Ga and Pb atom wires, i.e. $s$, $sd$, and $sp$ electron prototypes. We found that the total energy always oscillates with the wire length, which clearly indicates the existence of preferred lengths. Increasing the length, the s-system exhibits even-odd oscillations following a $a/x +b/x^2$ decay law in the stability, which can be attributed to electron band filling and quantum confinement along the wire. The $sd$-system exhibits a similar oscillation pattern, even in the presence of $sd$ hybridization. In $sp$-system, the energy oscillations are beyond the simple even-odd nature, likely due to unpaired p orbitals and the corresponding nontrival band filling. Our findings clearly demonstrate that electronic contribution is quite critical to the stability of freestanding wires, and this stability may be important even when wires are deposited on substrates or strained. This study sheds light on the underlying formation mechanism of metal atom wires.

cond-mat.mtrl-sci↗

arXiv1997

Surface relaxation and ferromagnetism of Rh(001)

The significant discrepancy between first-principles calculations and experimental analyses for the relaxation of the (001) surface of rhodium has been a puzzle for some years. In this paper we present density functional theory calculations using the local-density approximation and the generalized gradient approximation of the exchange-correlation functional. We investigate the thermal expansion of the surface and the possibility of surface magnetism. The results throw light on several, hitherto overlooked, aspects of metal surfaces. We find, that, when the free energy is considered, density-functional theory provides results in good agreement with experiments.

cond-mat.mtrl-sci↗

arXiv1995

Ab initio pseudopotential study of Fe, Co, and Ni employing the spin-polarized LAPW approach

The ground-state properties of Fe, Co, and Ni are studied with the linear-augmented-plane-wave (LAPW) method and norm-conserving pseudopotentials. The calculated lattice constant, bulk modulus, and magnetic moment with both the local-spin-density approximation (LSDA) and the generalized gradient approximation (GGA) are in good agreement with those of all-electron calculations, respectively. The GGA results show a substantial improvement over the LSDA results, i.e., better agreement with experiment. The accurate treatment of the nonlinear core-valence exchange and correlation interaction is found to be essential for the determination of the magnetic properties of 3d transition metals. The present study demonstrates the successful application of the LAPW pseudopotential approach to the calculation of ground-state properties of magnetic 3d transition metals.

mtrl-th↗