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Electronic and phonon excitations in α−RuCl3
Reschke, S.,Mayr, F.,Wang, Zhe,Do, Seung-Hwan,Choi, K.-Y.,Loidl, A. American Physical Society 2017 Physical Review B Vol.96 No.16
<P>We report on terahertz (THz), infrared reflectivity, and transmission experiments for wavenumbers from 10 to 8000 cm(-1) (similar to 1meV-1eV) and for temperatures from 5 to 295 K on the Kitaev candidate material alpha-RuCl3. As reported earlier, the compound under investigation passes through a first-order structural phase transition, from a monoclinic high-temperature to a rhombohedral low-temperature phase. The phase transition shows an extreme and unusual hysteretic behavior, which extends from 60 to 166 K. In passing this phase transition, in the complete frequency range investigated, we found a significant reflectance change, which amounts to almost a factor of two. We provide a broadband spectrum of dielectric constant, dielectric loss, and optical conductivity from the THz to the mid-infrared regime and study in detail the phonon response and the low-lying electronic density of states. We provide evidence for the onset of an optical energy gap, which is on the order of 200 meV, in good agreement with the gap derived from measurements of the dc electrical resistivity. Remarkably, the onset of the gap exhibits a strong blue shift on increasing temperatures.</P>
Optical and Magnetic Properties of MBE-Grown Manganese Sulfide Layers
W. Heimbrodt,L. Chen,H.-A. Krug Von Nidda,A. Loidl,P. J. Klar,L. David,K. A. Prior 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5
Metastable zinc-blende MnS layers of various thicknesses from 1:8 nm to 8:6 nm have been grown by molecular beam epitaxy on (100) GaAs between ZnSe cladding layers. We studied the dependences of the optical and the magnetic properties on the layer thickness. On the one hand, the non-exponential decay of the Mn internal transition is found to be faster for thick erlayer,which is a size effect and not caused by the interfaces. On the other hand, the Neel-temperature is not altered with decreasing layer thickness, but the phase-transition-induced shift of the internal Mn transitions is smaller for thinnerMnSlayers. Thisisexplainedbythedominatingin uenceofMn ions at the interface, which possess a reduced number of Mn neighbors. SQUID measurements in a weak external magnetic eld conrm the optical observations in zero field. However, applying a strong magnetic field reveals the metamagnetic character of these zinc-blende MnS layers. An antiferromagnetic-to-erromagnetic phase transitionis found with increasing external field. Metastable zinc-blende MnS layers of various thicknesses from 1:8 nm to 8:6 nm have been grown by molecular beam epitaxy on (100) GaAs between ZnSe cladding layers. We studied the dependences of the optical and the magnetic properties on the layer thickness. On the one hand, the non-exponential decay of the Mn internal transition is found to be faster for thick erlayer,which is a size effect and not caused by the interfaces. On the other hand, the Neel-temperature is not altered with decreasing layer thickness, but the phase-transition-induced shift of the internal Mn transitions is smaller for thinnerMnSlayers. Thisisexplainedbythedominatingin uenceofMn ions at the interface, which possess a reduced number of Mn neighbors. SQUID measurements in a weak external magnetic eld conrm the optical observations in zero field. However, applying a strong magnetic field reveals the metamagnetic character of these zinc-blende MnS layers. An antiferromagnetic-to-erromagnetic phase transitionis found with increasing external field.
Electron spin resonance in Eu-based iron pnictides
Krug von Nidda, H.-A.,Kraus, S.,Schaile, S.,Dengler, E.,Pascher, N.,Hemmida, M.,Eom, M. J.,Kim, J. S.,Jeevan, H. S.,Gegenwart, P.,Deisenhofer, J.,Loidl, A. American Physical Society 2012 Physical review. B, Condensed matter and materials Vol.86 No.9
Sub-gap optical response in the Kitaev spin-liquid candidate <i>α</i>-RuCl<sub>3</sub>
Reschke, Stephan,Mayr, Franz,Widmann, Sebastian,von Nidda, Hans-Albrecht Krug,Tsurkan, Vladimir,Eremin, Mikhail V,Do, Seung-Hwan,Choi, Kwang-Yong,Wang, Zhe,Loidl, Alois IOP 2018 Journal of physics, an Institute of Physics journa Vol.30 No.47
<P>We report detailed optical experiments on the layered compound <I>α</I>-RuCl<SUB>3</SUB> focusing on the THz and sub-gap optical response across the structural phase transition from the monoclinic high-temperature to the rhombohedral low-temperature structure, where the stacking sequence of the molecular layers is changed. This type of phase transition is characteristic for a variety of tri-halides crystallizing in a layered honeycomb-type structure and so far is unique, as the low-temperature phase exhibits the higher symmetry. One motivation is to unravel the microscopic nature of THz and spin-orbital excitations via a study of temperature and symmetry-induced changes. The optical studies are complemented by thermal expansion experiments. We document a number of highly unusual findings: A characteristic two-step hysteresis of the structural phase transition, accompanied by a dramatic change of the reflectivity. A complex dielectric loss spectrum in the THz regime, which could indicate remnants of Kitaev physics. Orbital excitations, which cannot be explained based on recent models, and an electronic excitation, which appears in a narrow temperature range just across the structural phase transition. Despite significant symmetry changes across the monoclinic to rhombohedral phase transition and a change of the stacking sequence, phonon eigenfrequencies and the majority of spin-orbital excitations are not strongly influenced. Obviously, the symmetry of a single molecular layer determines the eigenfrequencies of most of these excitations. Only one mode at THz frequencies, which becomes suppressed in the high-temperature monoclinic phase and one phonon mode experience changes in symmetry and stacking. Finally, from this combined terahertz, far- and mid-infrared study we try to shed some light on the so far unsolved low energy (<1 eV) electronic structure of the ruthenium 4<I>d</I> <SUP>5</SUP> electrons in <I>α</I>-RuCl<SUB>3</SUB>.</P>