Coherent Phononics of van der Waals Layers on Nanogratings

Strain engineering can be used to control the physical properties of two-dimensional van der Waals (2D-vdW) crystals. Coherent phonons, which carry dynamical strain, could push strain engineering to control classical and quantum phenomena in the unexplored picosecond temporal and nanometer spatial regimes. This intriguing approach requires the use of coherent GHz and sub-THz 2D phonons. Here, we report on nanostructures that combine nanometer thick vdW layers and nanogratings. Using an ultrafast pump-probe technique, we generate and detect in-plane coherent phonons with frequency up to 40 GHz and hybrid flexural phonons with frequency up to 10 GHz. The latter arises from the periodic modulation of the elastic coupling of the vdW layer at the grooves and ridges of the nanograting. This creates a new type of a tailorable 2D periodic phononic nanoobject, a flexural phononic crystal, offering exciting prospects for the ultrafast manipulation of states in 2D materials in emerging quantum technologies

Real-space observation of ultraconfined in-plane anisotropic acoustic terahertz plasmon polaritons

Thin layers of in-plane anisotropic materials can support ultraconfined polaritons, whose wavelengths depend on the propagation direction. Such polaritons hold potential for the exploration of fundamental material properties and the development of novel nanophotonic devices. However, the real-space observation of ultraconfined in-plane anisotropic plasmon polaritons (PPs)-which exist in much broader spectral ranges than phonon polaritons-has been elusive. Here we apply terahertz nanoscopy to image in-plane anisotropic low-energy PPs in monoclinic Ag2Te platelets. The hybridization of the PPs with their mirror image-by placing the platelets above a Au layer-increases the direction-dependent relative polariton propagation length and the directional polariton confinement. This allows for verifying a linear dispersion and elliptical isofrequency contour in momentum space, revealing in-plane anisotropic acoustic terahertz PPs. Our work shows high-symmetry (elliptical) polaritons on low-symmetry (monoclinic) crystals and demonstrates the use of terahertz PPs for local measurements of anisotropic charge carrier masses and damping.The work was financially supported by the Spanish Ministry of Science and Innovation under the María de Maeztu Units of Excellence Program (CEX2020-001038-M/MCIN/AEI/10.13039/501100011033) (R.H., A.C., L.E.H. and E.A.); Projects PID2021-123949OB-I00 (R.H.), PID2019-109905GB-C21 (M.G.V. and I.E.), RTI2018-094861-B-100 (L.E.H.), PID2019-107432GB-I00 (J.A.) and PID2019-107338RB-C61 (E.A.) funded by MCIN/AEI/10.13039/501100011033 and by ‘ERDF—A Way of Making Europe’; the National Natural Science Foundation of China (NSFC) (52225207 and 11934005) and the Shanghai Pilot Program for Basic Research—Fudan University 21TQ1400100 (21TQ006) (F.X.X.); NSFC grant no. 61988102 and the Science and Technology Commission of Shanghai Municipality (nos. 23010503400 and 23ZR1443500) (S.C.); the Czech Science Foundation GACR under the Junior Star grant no. 23-05119M (A.K.); the European Research Council (ERC) under grant agreement no. 101020833 (M.G.V.); the German Research Foundation (DFG) under project nos. 467576442 (I.N.) and GA 3314/1-1–FOR 5249 (QUAST) (M.G.V.); the Gipuzkoa Council (Spain) in the frame of the Gipuzkoa Fellows Program (B.M.-G.); and the University groups of the Basque Government (IT1526-22) (J.A.).Peer reviewe

Tuning phonon-microcavity photon polaritons in the weak, strong and ultrastrong coupling regimes

Resumen del trabajo presentado a la Conferencia Española de Nanofotónica (CEN), celebrada en Vigo del 20 al 22 de septiembre de 2021.Department of Education of the Basque Government (Project PI2017-30 and Grant IT1164-19); Spanish Ministry of Science and Innovation (PID2019-107432GB-I00, RTI2018-094861-B-100, MDM-2016-0618); European Union H2020 (796817-ARTEMIS).Peer reviewe

Tailoring photoluminescence by strain-engineering in layered perovskite flakes

Strain is an effective strategy to modulate the optoelectronic properties of 2D materials, but it has been almost unexplored in layered hybrid organic–inorganic metal halide perovskites (HOIPs) due to their complex band structure and mechanical properties. Here, we investigate the temperature-dependent microphotoluminescence (PL) of 2D (C6H5CH2CH2NH3)2Cs3Pb4Br13 HOIP subject to biaxial strain induced by a SiO2 ring platform on which flakes are placed by viscoelastic stamping. At 80 K, we found that a strain of <1% can change the PL emission from a single peak (unstrained) to three well-resolved peaks. Supported by micro-Raman spectroscopy, we show that the thermomechanically generated strain modulates the bandgap due to changes in the octahedral tilting and lattice expansion. Mechanical simulations demonstrate the coexistence of tensile and compressive strain along the flake. The observed PL peaks add an interesting feature to the rich phenomenology of photoluminescence in 2D HOIPs, which can be exploited in tailored sensing and optoelectronic devices.This work is supported by the Spanish MICINN under Project PID2019-108153GA-I00 and under the María de Maeztu Units of Excellence Programme (MDM-2016-0618). B.M-G. thanks Gipuzkoa Council (Spain) in the frame of Gipuzkoa Fellows Program and to Prof. A. Mateo-Alonso (Molecular and Supramolecular Materials Group - POLYMAT) for the access to the Chemistry Lab to grow the crystals. M.G. acknowledges support from la Caixa Foundation (ID 0010434) for a Junior Leader fellowship (Grant No. LCF/BQ/PI19/11690017).Peer reviewe

Research data supporting "Characterizing the Backscattered Spectrum of Mie Spheres"

Each folder contains .txt files of the data for each of the figures indicated on its name, together with README instructions on each case.The file contains the dataset corresponding to the figures of the article "Characterizing the Backscattered Spectrum of Mie Spheres" written by Martín Molezuelas-Ferreras, Álvaro Nodar, María Barra-Burillo, Jorge Olmos-Trigo, Jon Lasa-Alonso, Iker Gómez-Viloria, Elena Posada, J. J. Miguel Varga, Rubén Esteban, Javier Aizpurua, Luis E. Hueso, Cefe Lopez, and Gabriel Molina-Terriza (DOI: 10.1002/lpor.202300665). The data is organized into different folders, and each folder contains .txt files of the data for each of the figures indicated on its name, together with README instructions on each case.PRE2018-085136. MCIN/AEI/10.13039 /501100011033 through Project Ref. No. FIS2017-87363-P. MCIN/AEI/10.13039/501100011033 and “ESF Investing in your future” through Project Ref. No. BES-2017-080073. MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe” through Project Ref. No. PID2022-139579NB-I00. Department of Education, Research and Universities of the Basque Government through Project Ref. No. IT 1526-22. CSIC Research Platform PTI-001. MCIN/AEI/10.13039/501100011033 through Project Ref. No. MDM-2016-0618. MCIN/AEI/10.13039/501100011033 and the European UnionNextGenerationEU/PRTR through the Juan de la Cierva Fellowship Ref. No. FJC2021-047090-I. MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe” through Project Ref. No. PID-2022-137569NBC43. MCIN/AEI/10.13039/501100011033 through Project Ref. No. PID2021-124814NB-C21.Peer reviewe