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Choi, Seongil,Sim, Hasung,Kang, Soonmin,Choi, Ki-Young,Park, Je-Geun Institute of Physics 2017 Journal of Physics, Condensed Matter Vol.29 No.9
<P>Hexagonal RMnO<SUB>3</SUB> is a multiferroic compound with a giant spin–lattice coupling at an antiferromagnetic transition temperature, Lee <I>et al</I> (2008 <I>Nature</I> <B>451</B> 805). Despite extensive studies over the past two decades, the origin and underlying microscopic mechanism of strong spin–lattice coupling remain very much elusive. In this study, we have tried to address this problem by measuring the thermal expansion and dielectric constant of doped single crystals Y<SUB>1−<I>x</I> </SUB>Lu<SUB> <I>x</I> </SUB>MnO<SUB>3</SUB> where <I>x</I> = 0, 0.25, 0.5, 0.75, and 1.0. From these measurements, we confirm that there is a progressive change in the physical properties with doping. At the same time, all our samples exhibit clear anomalies at <I>T</I> <SUB>N</SUB>, even in the samples where <I>x</I> = 0.5 and 0.75. This is opposed to some earlier ideas, which suggests an unusual doping dependence of the anomaly. Our work reveals yet another interesting facet of the spin–lattice coupling issue in hexagonal RMnO<SUB>3</SUB>.</P>
The contribution of polar C–H hydrogen bonds to anion binding
Choi, Yusun,Kim, Taehoon,Jang, Soonmin,Kang, Jongmin The Royal Society of Chemistry 2016 NEW JOURNAL OF CHEMISTRY Vol.40 No.1
<P>The contribution of C-H hydrogen bonds is one of the key factors to consider in anion binding receptor design. To investigate the participation of C-H hydrogen bonds through C-H polarization in an anion binding event, we have designed and synthesized three new anion receptors (receptors 1, 2 and 3). Essentially, the only difference between these receptors is the relative magnitude of the C-H(H-a) polarization. These receptors utilize two amide N-H, two aromatic C-H(H-a), anthracene 9-C-H and possibly two methyl groups as hydrogen bonding moieties. From the titrations and DFT calculations, we found that the anion binding abilities of these receptors mainly depend on the magnitude of the polarization of C-H(H-a) and receptors 1 and 2 are selective for H2PO4-.</P>
Duvjir, Ganbat,Choi, Byoung Ki,Jang, Iksu,Ulstrup, Søren,Kang, Soonmin,Thi Ly, Trinh,Kim, Sanghwa,Choi, Young Hwan,Jozwiak, Chris,Bostwick, Aaron,Rotenberg, Eli,Park, Je-Geun,Sankar, Raman,Kim, Ki-Seo American Chemical Society 2018 NANO LETTERS Vol.18 No.9
<P>Emergent phenomena driven by electronic reconstructions in oxide heterostructures have been intensively discussed. However, the role of these phenomena in shaping the electronic properties in van der Waals heterointerfaces has hitherto not been established. By reducing the material thickness and forming a heterointerface, we find two types of charge-ordering transitions in monolayer VSe<SUB>2</SUB> on graphene substrates. Angle-resolved photoemission spectroscopy (ARPES) uncovers that Fermi-surface nesting becomes perfect in ML VSe<SUB>2</SUB>. Renormalization-group analysis confirms that imperfect nesting in three dimensions universally flows into perfect nesting in two dimensions. As a result, the charge-density wave-transition temperature is dramatically enhanced to a value of 350 K compared to the 105 K in bulk VSe<SUB>2</SUB>. More interestingly, ARPES and scanning tunneling microscopy measurements confirm an unexpected metal-insulator transition at 135 K that is driven by lattice distortions. The heterointerface plays an important role in driving this novel metal-insulator transition in the family of monolayer transition-metal dichalcogenides.</P> [FIG OMISSION]</BR>
Ising-Type Magnetic Ordering in Atomically Thin FePS<sub>3</sub>
Lee, Jae-Ung,Lee, Sungmin,Ryoo, Ji Hoon,Kang, Soonmin,Kim, Tae Yun,Kim, Pilkwang,Park, Cheol-Hwan,Park, Je-Geun,Cheong, Hyeonsik American Chemical Society 2016 NANO LETTERS Vol.16 No.12
<P>Magnetism in two-dimensional materials is not only of fundamental scientific interest but also a promising candidate for numerous applications. However, studies so far, especially the experimental ones, have been mostly limited to the magnetism arising from defects, vacancies, edges, or chemical dopants which are all extrinsic effects. Here, we report on the observation of intrinsic antiferromagnetic ordering in the two-dimensional limit. By monitoring the Raman peaks that arise from zone folding due to antiferromagnetic ordering at the transition temperature, we demonstrate that FePS3 exhibits an Ising-type antiferromagnetic ordering down to the monolayer limit, in good agreement with the Onsager solution for two-dimensional order disorder transition. The transition temperature remains almost independent of the thickness from bulk to the monolayer limit with T-N similar to 118 K, indicating that the weak interlayer interaction has little effect on the antiferromagnetic ordering.</P>