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38 results on '"Mayr F"'

9. Lattice modes and the Jahn-Teller ferroelectric transition ofGaV4S8

Author

Hlinka, J., primary, Borodavka, F., additional, Rafalovskyi, I., additional, Docekalova, Z., additional, Pokorny, J., additional, Gregora, I., additional, Tsurkan, V., additional, Nakamura, H., additional, Mayr, F., additional, Kuntscher, C. A., additional, Loidl, A., additional, Bordács, S., additional, Szaller, D., additional, Lee, H.-J., additional, Lee, J. H., additional, and Kézsmárki, I., additional

Published
2016
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11. Spin-orbiton and quantum criticality inFeSc2S4

Author

Mittelstädt, L., primary, Schmidt, M., additional, Wang, Zhe, additional, Mayr, F., additional, Tsurkan, V., additional, Lunkenheimer, P., additional, Ish, D., additional, Balents, L., additional, Deisenhofer, J., additional, and Loidl, A., additional

Published
2015
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13. Erratum: Orbital fluctuations and orbital order below the Jahn-Teller transition in Sr3Cr2O8[Phys. Rev. B83, 201102(R) (2011)]

Author

Wang, Zhe, primary, Schmidt, M., additional, Günther, A., additional, Schaile, S., additional, Pascher, N., additional, Mayr, F., additional, Goncharov, Y., additional, Quintero-Castro, D. L., additional, Islam, A. T. M. N., additional, Lake, B., additional, Krug von Nidda, H.-A., additional, Loidl, A., additional, and Deisenhofer, J., additional

Published
2012
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31. Metal-to-insulator transition inLa1−xBaxTiO3

Author

Fritsch, V., primary, Hemberger, J., additional, Brando, M., additional, Engelmayer, A., additional, Horn, S., additional, Klemm, M., additional, Knebel, G., additional, Lichtenberg, F., additional, Mandal, P., additional, Mayr, F., additional, Nicklas, M., additional, and Loidl, A., additional

Published
2001
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34. Electronic and phonon excitations in α - RuCl3.

Author

Reschke, S., Mayr, F., Zhe Wang, Seung-Hwan Do, Choi, K.-Y., and Loidl, A.

Subjects
*PHONONS, *WAVENUMBER, *PHASE transitions
Abstract

We report on terahertz (THz), infrared reflectivity, and transmission experiments for wavenumbers from 10 to 8000 cm-1 (~1 meV - 1 eV) and for temperatures from 5 to 295 K on the Kitaev candidate material α - 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. [ABSTRACT FROM AUTHOR]

Published
2017
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35. Optical conductivity in multiferroic GaV4S8 and GeV4S8: Phonons and electronic transitions.

Author

Reschke, S., Mayr, F., Zhe Wang, Lunkenheimer, P., Weiwu Li, Szaller, D., Bordács, S., Kézsmárki, I., Tsurkan, V., and Loidl, A.

Subjects
*OPTICAL conductivity, *GALLIUM compounds, *MULTIFERROIC materials
Abstract

We report on optical spectroscopy on the lacunar spinels GaV4S8 and GeV4S8 in the spectral range from 100 to 23 000 cm-1 and for temperatures from 5 to 300 K. These multiferroic spinel systems reveal Jahn-Teller driven ferroelectricity and complex magnetic order at low temperatures. We study the infrared-active phonon modes and the low-lying electronic excitations in the cubic high-temperature phase, as well as in the orbitally and in the magnetically ordered low-temperature phases. We compare the phonon modes in these two compounds, which undergo different symmetry-lowering Jahn-Teller transitions into ferroelectric and orbitally ordered phases, and exhibit different magnetic ground states. We follow the splitting of the phonon modes at the structural phase transition and detect additional splittings at the onset of antiferromagnetic order in GeV4S8. We observe electronic transitions within the d-derived bands of the V4 clusters and document a significant influence of the structural and magnetic phase transitions on the narrow electronic band gaps. [ABSTRACT FROM AUTHOR]

Published
2017
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36. Excitations and relaxation dynamics in multiferroic GeV4S8 studied by terahertz and dielectric spectroscopy.

Author

Reschke, S., Zhe Wang, Mayr, F., Ruff, E., Lunkenheimer, P., Tsurkan, V., and Loidl, A.

Subjects
*GERMANIUM compounds, *MULTIFERROIC materials, *JAHN-Teller effect
Abstract

We report on THz time-domain spectroscopy on multiferroic GeV4S8, which undergoes orbital ordering at a Jahn-Teller transition at 30.5 K and exhibits antiferromagnetic order below 14.6 K. The THz experiments are complemented by dielectric experiments at audio and radio frequencies. We identify a low-lying excitation close to 0.5 THz, which is only weakly temperature dependent and probably corresponds to a molecular excitation within the electronic level scheme of the V4 clusters. In addition, we detect complex temperature-dependent behavior of a low-lying phononic excitation, closely linked to the onset of orbitally driven ferroelectricity. In the high-temperature cubic phase, which is paramagnetic and orbitally disordered, this excitation is of relaxational character becomes an overdamped Lorentzian mode in the orbitally ordered phase below the Jahn-Teller transition, and finally appears as well-defined phonon excitation in the antiferromagnetic state. Abrupt changes in the real and imaginary parts of the complex dielectric permittivity show that orbital ordering appears via a structural phase transition with strong first-order character and that the onset of antiferromagnetic order is accompanied by significant structural changes, which are of first-order character, too. Dielectric spectroscopy documents that at low frequencies, significant dipolar relaxations are present in the orbitally ordered, paramagnetic phase only. In contrast to the closely related GaV4S8, this relaxation dynamics that most likely mirrors coupled orbital and polar fluctuations does not seem to be related to the dynamic processes detected in the THz regime. [ABSTRACT FROM AUTHOR]

Published
2017
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37. Lattice modes and the Jahn-Teller ferroelectric transition of GaV4S8.

Author

Hlinka, J., Borodavka, F., Rafalovskyi, I., Docekalova, Z., Pokorny, J., Gregora, I., Tsurkan, V., Nakamura, H., Mayr, F., Kuntscher, C. A., Loidl, A., Bordács, S., Szaller, D., Lee, H.-J., Lee, J. H., and Kézsmárki, I.

Subjects
*JAHN-Teller transitions, *FERROELECTRIC transitions, *LATTICE models (Statistical physics), *MULTIFERROIC materials, *POLARIZATION (Nuclear physics), *AB initio quantum chemistry methods
Abstract

Crystal of GaV4S8, a multiferroic system hosting a Néel-type skyrmion lattice phase, has been investigated by polarized Raman and IR spectroscopy above and below the ferroelectric phase transition. Counts of the observed IR and Raman-active modes belonging to distinct irreducible representations agree quite well with group-theory predictions. Phonon spectra are assigned and interpreted with the aid of ab initio calculations of the phonon spectra in the ferroelectric phase. Results allow appreciation of phonon frequencies of the modes involved in Jahn-Teller distortion and their contribution to the spontaneous polarization. [ABSTRACT FROM AUTHOR]

Published
2016
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38. Electromagnons, magnons, and phonons in Eu1-xHoxMn O3.

Author

Zhenyu Chen, Schmidt, M., Zhe Wang, Mayr, F., Deisenhofer, J., Mukhin, A. A., Balbashov, A. M., and Loidl, A.

Subjects
*ANTIFERROMAGNETIC resonance, *POLARIZATION (Nuclear physics), *MAGNONS
Abstract

Here we present a detailed study of the terahertz and far-infrared response of the mixed perovskite manganite system Eu1-xHoxMn O3 for holmium concentrations x=0.1 and 0.3. We compare the magnetic excitations of the four different magnetically ordered phases (A-type antiferromagnetic, sinusoidally modulated collinear, helical phases with spin planes perpendicular to the crystallographic a and c axes). The transition between the two latter phases goes hand in hand with a switching of the ferroelectric polarization from P∥a to P∥c. Special emphasis is paid to the temperature dependence of the excitations at this transition. We find a significant change of intensity indicating that the exchange-striction mechanism may not be the only mechanism to induce dipolar weight to spin-wave excitations. We also focus on excitations within the incommensurate collinear antiferromagnetic phase and find an excitation close to 40cm-1. A detailed analysis of optical weight gives a further unexpected result: In the multiferroic phase with P∥c all the spectral weight of the electromagnons comes from the lowest-phonon mode. However, for the phase with the polarization P∥a additional spectral weight must be transferred from higher frequencies. [ABSTRACT FROM AUTHOR]

Published
2016
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