Carl Peter Romao

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Romao

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Carl Peter

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0000-0002-5519-2519

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Publications 1 - 10 of 11

Tuning chirality amplitude at ultrafast timescales in chiral CsCuCl₃
Ueda, Hiroki; Sato, Takahiro; Nguyen, Quynh L.; et al. (2025)
Physical Review Research
Chirality is a fundamental symmetry concept relevant to many scientific fields. It describes discrete states, i.e., left-handed, right-handed, or achiral. In contrast to this discrete classification, objects can be continuously distorted. To describe the deviation from an achiral state, the chirality amplitude has to be addressed, similarly to magnetization being the "amplitude"for time-reversal symmetry breaking. Even though symmetry breaking is the base for many phenomena in science in general, symmetry cannot quantitatively predict measurable quantities. Chirality amplitude is the key quantity for quantifying chirality-related emergent phenomena. Here, we propose two types of chiral lattice distortions and report their ultrafast dynamics. We determine the ultrafast reduction of the chirality amplitude in CsCuCl₃ after an optical excitation by using resonant x-ray diffraction with circular polarization. An additional symmetry breaking representing a nonhanded chiral structure is observed by resonant x-ray diffraction when exciting the material with an intense, low-cycle terahertz pulse. The latter demonstrates a hidden enantiomorphic pair in a nonhanded chiral structure. The concept of chirality amplitude, as well as the decomposition into two different types of chiral lattice distortions, suggests a unique approach toward controlling chirality-induced emergent phenomena.
Preparation, photoluminescence and excited state properties of the homoleptic cluster cation [(W₆I₈)(CH₃CN)₆]⁴⁺
Pachel, Florian; Frech, Philipp; Ströbele, Markus; et al. (2023)
Dalton Transactions
Solvated tungsten iodide cluster compounds are presented with the homoleptic cluster cation [(W6I8)(CH3CN)6]4+ and the heteroleptic [(W6I8)I(CH3CN)5]3+, synthesized from W6I22 in acetonitrile. Crystal structures were solved and refined on deep red single-crystals of [(W6I8)(CH3CN)6](I3)(BF4)3·H2O, [(W6I8)I(CH3CN)5](I3)2(BF4), and on a yellow single-crystal of [W6I8(CH3CN)6](BF4)4·2(CH3CN) on the basis of X-ray diffraction data. The structure of the homoleptic [(W6I8)(CH3CN)6]4+ cluster is based on the octahedral [W6I8]4+ tungsten iodide cluster core, coordinated by six apical acetonitrile ligands. The electron localisation function of [(W6I8)(CH3CN)6]4+ is calculated and solid-state photoluminescence and its temperature depedence are reported. Additionally, photoluminescence and transient absorption measurements in acetonitrile are shown. Results of the obtained data are compared to compounds containing [(M6I8)I6]2− and [(M6I8)L6]2− (M = Mo or W; L = ligand) clusters.
Phonon-Induced Geometric Chirality
Romao, Carl Peter; Juraschek, Dominik M. (2024)
ACS Nano
Chiral properties have seen increasing use in recent years, leading to the emerging fields of chiral quantum optics, plasmonics, and phononics. While these fields have achieved manipulation of the chirality of light and lattice vibrations, controlling the chirality of materials on demand has yet remained elusive. Here, we demonstrate that linearly polarized phonons can be used to induce geometric chirality in achiral crystals when excited with an ultrashort laser pulse. We show that nonlinear phonon coupling quasistatically displaces the crystal structure along phonon modes that reduce the symmetry of the lattice to that of a chiral point group corresponding to a chiral crystal. By reorienting the polarization of the laser pulse, the two enantiomers can be induced selectively. Therefore, geometric chiral phonons enable the light-induced creation of chiral crystal structures and therefore the engineering of chiral electronic states and optical properties.
Formation of a Polar Structure in the Metallic Niobium Sulfide Nb₄S₃
Grahlow, Fabian; Dorsch, Eric; Ströbele, Markus; et al. (2021)
Inorganic Chemistry
The synthesis of Nb4S3, a previously undiscovered binary sulfide, was achieved using Nb3Br7S as a precursor. Its structure is composed of Nb6S triangular prisms arranged in a polar (Imm2) configuration, with sulfur atoms lying in channels along the a axis. Electrical resistivity measurements and density functional theory calculations were used to determine that Nb4S3 is metallic and therefore a polar metal, with metallic bands occupied by electrons with primarily niobium character. The electrons near the Fermi level are so closely associated with the niobium sublattice that the sulfur atoms have positive Born effective charges, indicating that the electrostatic interactions between sulfur atoms are unscreened. Calculations of the dependence of the electron density on the sulfur atomic positions confirm that the metallic electrons do not screen the dipole-dipole interactions between sulfur atoms, which allows polarity and metallicity to coexist in Nb4S3. These findings suggest that applied electric fields might be able to reverse the polarity of thin films of Nb4S3.
The Rectangular Niobium Oxyiodide Cluster Nb₄OI₁₀ – A Narrow Band-Gap Semiconductor
Beitlberger, Jan; Ströbele, Markus; Strauss, Fabian; et al. (2024)
European Journal of Inorganic Chemistry
A metal-rich niobium oxyiodide was prepared by soft reduction of NbI4. 4 . The structure of the new compound Nb4OI10 was determined by single-crystal X-ray diffraction and contains a rectangular Nb-4(mu(4)-O) cluster that is interconnected into layers by iodide ligands. The local structure of the Nb4OI10 cluster bears a close relationship to a defect Nb6I11 structure. The twodimensional van der Waals material (2)(infinity)[Nb4OI8I4/2]is a small band-gap semiconductor ( < 1 eV), as analysed by electrical conductivity measurements, photoresponse, experimental band gap determination, and band structure calculation.
Chiral phonons as dark matter detectors
Romao, Carl Peter; Catena, Riccardo; Spaldin, Nicola; et al. (2023)
Physical Review Research
We propose a method for detecting single chiral phonons that will enable their use as dark-matter detectors. We suggest metal–organic frameworks (MOFs) as detector materials, as their flexibility yields low-energy chiral phonons with measurable magnetic moments, and their anisotropy leads to directional sensitivity, which mitigates background contamination. To demonstrate our proposal, we calculate the phononic structure of the MOF InF₃(4,4′-bipyridine), and show that it has highly chiral acoustic phonons. Detection of such chiral phonons via their magnetic moments would dramatically lower the excitation energy threshold for dark matter detection to the energy of a single phonon. We show that single-phonon detection in a MOF would extend detector reach ten or more orders of magnitude below current limits, enabling exploration of a multitude of as-yet-unprobed dark matter candidates.
Negative and Near-Zero Thermal Expansion in A2M3O12 and Related Ceramic Families: A Review
Marinkovic, Bojan A.; Pontón, Patricia I.; Romao, Carl Peter; et al. (2021)
Frontiers in Materials
This review presents the history of materials in the A2M3O12 and related ceramic families, including their unusual thermal expansion and the present understanding of its mechanism, and related factors such as hydroscopicity and the monoclinic to orthorhombic phase transition. Other properties, including thermomechanical, thermal and ionic conduction and optical properties, are presented in terms of current knowledge, challenges and opportunities for applications. One of the largest challenges is the production of monoliths, and various methods for consolidation and sintering are summarized. These ceramics have considerable promise when combined with other materials, and recent advances in such composites are presented. These matters are placed in the context of the potential applications of negative and near-zero thermal expansion ceramics, which still present challenges for future materials researchers.
The Remarkably Robust, Photoactive Tungsten Iodide Cluster [W6I12(NCC6H5)2]
Pachel, Florian; Ströbele, Markus; Romao, Carl Peter; et al. (2023)
European Journal of Inorganic Chemistry
The new heteroleptic tungsten iodide cluster compound [W6I12(NCC6H5)(2)] is presented. The synthesis is carried-out from Cs2W6I14 and ZnI2 under solvothermal conditions in benzonitrile solution, yielding red cube-shaped crystals. [W6I12(NCC6H5)(2)] represents a heteroleptic [W6I8]-type cluster bearing four apical iodides and two benzonitrile ligands. Molecular [W6I12(NCC6H5)(2)] clusters form a robust hydrogen bridged crystal structure with high thermal stability and high resistibility against hydrolysis. The electronic structure is analyzed by quantum chemical methods of the calculated electron localization function (ELF) and the band structure. Photoluminescence measurements are performed to verify and describe the photophysical properties of [W6I12(NCC6H5)(2)]. Finally, the photocatalytic properties of [W6I12(NCC6H5)(2)] are evaluated as a proof-of-concept.
Synthesis, Structure, and Thermoelastic Properties of LiSn2Br3(CN2) and Sn4Br2(CN2)(3)
Löber, Manuel; Ströbele, Markus; Romao, Carl Peter; et al. (2021)
European Journal of Inorganic Chemistry
Tin carbodiimides have been reported with various compositions, prepared via solid-state metathesis reactions by heating tin halides and lithium carbodiimide at moderate temperatures. The formations of two new compounds, LiSn2Br3(CN2) and Sn4Br2(CN2)(3) are monitored by differential thermal analysis (DTA), and crystal structures are reported as refined on basis of X-ray diffraction studies. The structure of LiSn2Br3(CN2) can be described by two interpenetrating frameworks of corner-linked coordination polyhedra, raising the possibility of negative thermal expansion (NTE) as investigated by density functional perturbation theory (DFPT). Like some previously reported tin carbodiimide compounds, LiSn2Br3(CN2) was also found to be a semiconductor with an indirect band gap of 2.5 eV, as determined by DFT calculations.
Light makes atoms behave like electromagnetic coils
Romao, Carl Peter; Juraschek, Dominik M. (2024)
Nature
Microscopic magnetic fields form in non-magnetic materials when light makes the atoms rotate. A similar macroscopic effect has long been known, but proof of its atomic equivalent could give rise to ultrafast data processing.

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Carl Peter Romao

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