In: Journal of Superconductivity and Novel Magnetism, 2015, vol. 28, no. 4, p. 1231-1236
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In: npj Quantum Materials, 2021, vol. 6, no. 1, p. 51
Investigations of magnetically ordered phases on the femtosecond timescale have provided significant insights into the influence of charge and lattice degrees of freedom on the magnetic sub-system. However, short-range magnetic correlations occurring in the absence of long-range order, for example in spin-frustrated systems, are inaccessible to many ultrafast techniques. Here, we show how...
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In: Physical Review Letters, 2021, vol. 126, no. 15, p. 157401
Terahertz vortex beams with different superposition of the orbital angular momentum $l={\pm}1$, ${\pm}2$, ${\pm}3$, and ${\pm}4$ and spin angular momentum ${\sigma}={\pm}1$ were used to study antiferromagnetic (AFM) resonances in TbFe$_3$(BO$_3$)$_4$ and Ni$_3$TeO$_6$ single crystals. In both materials we observed a strong vortex beam dichroism for the AFM resonances that are split in ...
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In: Applied Physics Letters, 2020, vol. 117, no. 6, p. 062401
The binary compound V3Ga can exhibit two near-equilibrium phases, the A15 structure that is superconducting and the Heusler D03 structure that is semiconducting and antiferromagnetic. Density functional theory calculations show that these two phases are nearly degenerate, being separated in energy by only ±10 meV/atom. Our magnetization measurements on bulk-grown samples show ...
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In: Physical Review B, 2020, vol. 101, no. 21, p. 214512
We studied the infrared response of polycrystalline samples of the iron arsenide superconductor (Rb,Cs)Ca2Fe4As4F2 (Rb,Cs-12442), which has a bilayer structure similar to the high-Tc cuprates YBa2Cu3O7 (YBCO) and Bi2Sr2CaCu2O8. The c-axis reflectivity spectra Rc have been derived from the reflectivity spectra of the polycrystalline samples Rpoly and the in-plane spectrum of a corresponding...
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In: Physical Review Research, 2020, vol. 2, no. 2, p. 023218
With terahertz and infrared spectroscopy we studied the in-plane response of an underdoped, twinned YBa2Cu3O6.6 single crystal with Tc=58(1)K in high magnetic fields up to B=30 Tesla (T) applied along the c axis. Our goal was to investigate the field-induced suppression of superconductivity and to observe the signatures of the three-dimensional (3D) incommensurate copper charge density wave...
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In: Physical Review B, 2020, vol. 101, no. 19, p. 195118
We consider a two-band spinless model describing an excitonic insulator (EI) on the two-dimensional square lattice with anisotropic hopping parameters and electron-phonon (el-ph) coupling, inspired by the EI candidate Ta2NiSe5. We systematically study the nature of the collective excitations in the ordered phase which originates from the interband Coulomb interaction and the el-ph coupling. ...
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In: Physical Review Letters, 2019, vol. 122, no. 21, p. 217002
By means of infrared spectroscopy, we determine the temperature-doping phase diagram of the Fano effect for the in-plane Fe-As stretching mode in Ba1−xKxFe2As2. The Fano parameter 1=q2, which is a measure of the phonon coupling to the electronic particle-hole continuum, shows a remarkable sensitivity to the magnetic and structural orderings at low temperatures. Most strikingly, at elevated...
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In: Journal of Superconductivity and Novel Magnetism, 2014, vol. 27, no. 10, p. 2163-2179
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In: Physical Review B, 2019, vol. 99, no. 15, p. 155107
We investigate the excited state electronic structure of the model phase transition system In/Si(111) using femtosecond time- and angle-resolved photoemission spectroscopy (trARPES). An extreme ultraviolet 500 kHz laser source at 21.7 eV is utilized both to map the energy of excited states above the Fermi level and follow the momentum-resolved population dynamics on a femtosecond timescale....
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