Suchergebnisse

We directly visualize and identify the capacitive coupling of infrared dimer antennas in the near field by employing scattering-type scanning near-field optical microscopy (s-SNOM). The coupling is identified by (i) resolving the strongly enhanced nano-localized near fields in the antenna gap and by (ii) tracing the red shift of the dimer resonance when compared to the resonance of the single antenna constituents. Furthermore, by modifying the illumination geometry we break the symmetry, providing a means to excite both the bonding and the >dark> anti-bonding modes. By spectrally matching both modes, their interference yields an enhancement or suppression of the near fields at specific locations, which could be useful in nanoscale coherent control applications. © 2013 Optical Society of America. ; We acknowledge support from the European FP7 projects "Nanoantenna" (FP7-HEALTHF5-2009-241818-NANOANTENNA), NMP (NMP3-SL-2011-263104- HINTS), and "SPINTROS" (257654), and the National Projects MAT2009-08398, MAT2009-08494 and FIS2010-19609-C02-C01 from the Spanish Ministerio de Ciencia e Innovacion. We also acknowledge the Marie Curie Actions PIRG06-GA-2009-25647, ITAMOSCINOM, as well as the Basque Government Program PI2011-1 and Etortek-2011 (nanoiker). ; Peer Reviewed

The spin Hall magnetoresistance (SMR) emerged as a reference tool to investigate the magnetic properties of materials with an all-electrical setup. Its sensitivity to the magnetization of thin films and surfaces may turn it into a valuable technique to characterize van der Waals magnetic materials, which support long-range magnetic order in atomically thin layers. However, realistic surfaces can be affected by defects and disorder, which may result in unexpected artifacts in the SMR, rather than the sole appearance of electrical noise. Here, we study the SMR response of heterostructures combining a platinum (Pt) thin film with the van der Waals antiferromagnet MnPSe3 and observe a robust SMR-like signal, which turns out to originate from the presence of strong interfacial disorder in the system. We use transmission electron microscopy (TEM) to characterize the interface between MnPSe3 and Pt, revealing the formation of a few nanometer-thick platinum–chalcogen amorphous layer. The analysis of the transport and TEM measurements suggests that the signal arises from a disordered magnetic system formed at the Pt/MnPSe3 interface, washing out the interaction between the spins of the Pt electrons and the MnPSe3 magnetic lattice. Our results show that the damaged interfaces can yield an important contribution to SMR, questioning a widespread assumption on the role of disorder in such measurements. ; The authors also thank SGIker Medidas Magneticas Gipuzkoa (UPV/EHU/ ERDF, EU) for the technical and human support. This work is supported by the European Union H2020 under the Marie Sklodowska-Curie Actions (796817-ARTEMIS and 748971-SUPER2D) and by the Spanish MICINN under project nos. RTI2018-094861-B-I00, PID2019-108153GA-I00, and the Maria de Maeztu Units of Excellence Programme (MDM-2016-0618 and CEX2020-001038-M). J.M.G.-P. and M.X.A.-P. thank the Spanish MICINN for a Ph.D. fellowship (grants no. BES-2016-077301 and PRE-2019-089833, respectively). M.G. acknowledges support from la Caixa Foundation for a Junior Leader ...

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY). ; We propose and demonstrate spin manipulation by magnetically controlled modulation of pure spin currents in cobalt/copper lateral spin valves, fabricated on top of the magnetic insulator Y3Fe5O12 (YIG). The direction of the YIG magnetization can be controlled by a small magnetic field. We observe a clear modulation of the nonlocal resistance as a function of the orientation of the YIG magnetization with respect to the polarization of the spin current. Such a modulation can only be explained by assuming a finite spin-mixing conductance at the Cu/YIG interface, as it follows from the solution of the spin-diffusion equation. These results open a path towards the development of spin logics. ; This work was supported by the European Commission under the Marie Curie Actions (256470-ITAMOSCINOM), NMP Project (263104-HINTS) and the European Research Council (257654-SPINTROS), by the Spanish MINECO under Projects No. MAT2012-37638, No. MAT2012-36844, and No. FIS2011-28851-C02-02, and by the Basque Government under Project No. PI2012-47 and UPV/EHU Project No. IT-756-13. E.V. and M.I. thank the Basque Government for support through a Ph.D. fellowship (Grants No. BFI-2010-163 and No. BFI-2011-106). ; Peer Reviewed

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 reviewed

Strong coupling between molecular vibrations and microcavity modes has been demonstrated to modify physical and chemical properties of the molecular material. Here, we study the less explored coupling between lattice vibrations (phonons) and microcavity modes. Embedding thin layers of hexagonal boron nitride (hBN) into classical microcavities, we demonstrate the evolution from weak to ultrastrong phonon-photon coupling when the hBN thickness is increased from a few nanometers to a fully filled cavity. Remarkably, strong coupling is achieved for hBN layers as thin as 10 nm. Further, the ultrastrong coupling in fully filled cavities yields a polariton dispersion matching that of phonon polaritons in bulk hBN, highlighting that the maximum light-matter coupling in microcavities is limited to the coupling strength between photons and the bulk material. Tunable cavity phonon polaritons could become a versatile platform for studying how the coupling strength between photons and phonons may modify the properties of polar crystals. ; This work is supported by the Spanish Ministry of Science and Innovation under the María de Maeztu Units of Excellence Program (MDM-2016-0618), and Projects PID2019-107432GB-I00 and RTI2018-094861-B-100; by the European Union H2020 under the Marie Curie Actions (796817-ARTEMIS); and by Project PI2017-30 and Grant IT1164-19 for the research groups of the Basque University System from the Department of Education of the Basque Government. ; Peer reviewed

We study the spin Hall magnetoresistance (SMR) in Pt grown in situ on CoFe2O4 (CFO) ferrimagnetic insulating films. A careful analysis of the angle-dependent and field-dependent longitudinal magnetoresistance indicates that the SMR contains a contribution that does not follow the bulk magnetization of CFO, but it is a fingerprint of the complex magnetism at the surface of the CFO layer, thus signaling SMR as a tool for mapping surface magnetization. A systematic study of the SMR for different temperatures and CFO thicknesses gives us information impossible to obtain with any standard magnetometry technique. On one hand, the surface magnetization behaves independently of the CFO thickness and does not saturate up to high fields, evidencing that the surface has its own anisotropy. On the other hand, characteristic zero-field magnetization steps are not present at the surface while they are relevant in the bulk, strongly suggesting that antiphase boundaries are responsible for such intriguing features. In addition, a contribution from the ordinary magnetoresistance of Pt is identified, which is distinguishable only due to the low resistivity of the in situ grown Pt. ; This work is supported by the European Union under the NMP project (263104-HINTS) and the European Research Council (257654-SPINTROS), by the Spanish MINECO (MAT2012-37638, MAT2015-65159-R, MAT2014-56063- C2-1R, and SEV-2015-0496), by the Basque Government (PC2015-1-01), and by the Catalan Government (2014 SGR 734). M. I. and E. S. acknowledge the Basque Government and the Spanish MECD, respectively, for a Ph.D. fellowship (BFI-2011-106 and FPU14/03102). J. F. acknowledges stimulating discussions with Xavier Martí. ; Peer reviewed

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY). ; We report measurements of a new type of magnetoresistance in Pt and Ta thin films. The spin accumulation created at the surfaces of the film by the spin Hall effect decreases in a magnetic field because of the Hanle effect, resulting in an increase of the electrical resistance as predicted by Dyakonov [Phys. Rev. Lett. 99, 126601 (2007)]. The angular dependence of this magnetoresistance resembles the recently discovered spin Hall magnetoresistance in Pt/Y3Fe5O12 bilayers, although the presence of a ferromagnetic insulator is not required. We show that this Hanle magnetoresistance is an alternative simple way to quantitatively study the coupling between charge and spin currents in metals with strong spin-orbit coupling. ; This work was supported by the European Union 7th Framework Programme under NMP Project No. 263104-HINTS and the European Research Council (Project No. 257654-SPINTROS), by the Spanish Ministry of Economy and Competitiveness under Projects No. MAT2012-37638, No. FIS2011-28851-C02-02, No. FIS2014-55987-P, and No. MAT2013-46593-C6-4-P, and by the Basque Government under UPV/EHU Projects No. IT-756-13 and No. IT-621-13. M. I. and E. S. thank the Basque Government and the Spanish Ministry of Education, Culture and Sport, respectively, for a Ph.D. fellowship (Grants No. BFI-2011-106 and No. FPU14/03102). ; Peer Reviewed

We report the spin Hall magnetoresistance (SMR) in Pt deposited on a tensile-strained LaCoO3 (LCO) thin film, which is a ferromagnetic insulator with a Curie temperature Tc=85K. The SMR displays a strong magnetic-field dependence below Tc, with the SMR amplitude continuing to increase (linearly) with increasing the field far beyond the saturation value of the ferromagnet. The SMR amplitude decreases gradually with raising the temperature across Tc and remains measurable even above Tc. Moreover, no hysteresis is observed in the field dependence of the SMR. These unusual behaviors indicate that a low-dimensional magnetic system forms at the surface of LCO and that the LCO/Pt interface decouples magnetically from the rest of the LCO thin film. Transmission electron microscopy analysis of the heterostructure reveals that an ultrathin Co-rich layer forms at the LCO surface upon deposition of Pt, which is separated from the rest of the LCO film by a ∼1-nm La/O-rich layer, thus supporting the presence of a low-dimensional ferromagnetic system. To explain the magnetoresistance measurements, we revisit the derivation of the SMR corrections and relate the spin-mixing conductances to the spin-spin correlation functions and microscopic quantities describing the magnetism at the interface. Comparisons between theory and experiment confirm the existence of a low-dimensional Heisenberg ferromagnet at the interface. Our results pave the way for exploring complex magnetic textures of insulating films by simple transport measurements. ; This work was supported by the European Union 7th Framework Programme under the Marie Curie Actions (607904- 13-SPINOGRAPH), the European Research Council (257654-SPINTROS), and the European Regional Development Fund (ERDF), by the Spanish Ministry of Economy, Industry and Competitiveness (MAT2015-65159-R, FIS2014-55987-P, MAT2013-46593-C6-4-P, MAT2016-80762-R and FIS2017-82804-P), by the Basque Government (UPV/EHU Project IT-756-13 and IT-621-13), by the Regional Council of Gipuzkoa (100/16), and by the Xunta de Galicia (Centro singular de investigación de Galicia accreditation 2016–2019, ED431G/09).

Theory predicts a distinct spectral shift between the near- and far-field optical response of plasmonic antennas. Here we combine near-field optical microscopy and far-field spectroscopy of individual infrared-resonant nanoantennas to verify experimentally this spectral shift. Numerical calculations corroborate our experimental results. We furthermore discuss the implications of this effect in surface-enhanced infrared spectroscopy. © 2013 American Physical Society. ; This work was supported by the European FP7 Project ''Nanoantenna'' (No. FP7-HEALTH-F5-2009-241818-NANOANTENNA), the Spanish National Projects No. MAT2009-08398 and No. FIS2010-19609-C02-01, and the Basque Government Projects ETORTEK (nanoIKER) and excellence program IT756-13. ; Peer Reviewed

Photonic crystals (PCs) are periodically patterned dielectrics providing opportunities to shape and slow down the light for processing of optical signals, lasing and spontaneous emission control. Unit cells of conventional PCs are comparable to the wavelength of light and are not suitable for subwavelength scale applications. We engineer a nanoscale hole array in a van der Waals material (h-BN) supporting ultra-confined phonon polaritons (PhPs)—atomic lattice vibrations coupled to electromagnetic fields. Such a hole array represents a polaritonic crystal for mid-infrared frequencies having a unit cell volume of 10−5λ30 (with λ0 being the free-space wavelength), where PhPs form ultra-confined Bloch modes with a remarkably flat dispersion band. The latter leads to both angle- and polarization-independent sharp Bragg resonances, as verified by far-field spectroscopy and near-field optical microscopy. Our findings could lead to novel miniaturized angle- and polarization-independent infrared narrow-band couplers, absorbers and thermal emitters based on van der Waals materials and other thin polar materials. ; The authors acknowledge financial support from the European Commission under the Graphene Flagship (GrapheneCore2), the Spanish Ministry of Economy and Competitiveness (national projects MAT2017-88358-C3,MAT 2015-65159-R, MAT2014-53432-C5, FIS2014-60195-JIN), the Basque government (PhD fellowship PRE-2016-1-0150) and the European Research Council under the starting grants SPINTROS (Grant no. 257654) and 2DNANOPTICA (Grant no. 715496). ; Peer reviewed

The authors acknowledge support from the European Commission under the Graphene Flagship (GrapheneCore1, Grant no. 696656), the Marie Sklodowska-Curie individual fellowship (SGPCM-705960), the ERC starting grants SPINTROS (Grant no. 257654) and 2DNANOPTICA (Grant no. 715496), the Spanish Ministry of Economy and Competitiveness (national projects FIS2014-60195-JIN, MAT2014-53432-C5-4-R, MAT2015-65525-R, MAT2012-37638 and MAT2015-65159-R), the Basque government (PhD fellowship PRE-2016-1-0150), and the Regional Council of Gipuzkoa (Project No. 100/16)

We acknowledge stimulating discussions with Prof. FJ Garcia-Vidal (Madrid). We also acknowledge support from the European Commission under the Graphene Flagship (GrapheneCore1, Grant no. 696656), the Marie Sklodowska-Curie individual fellowship (SGPCM-705960), the Spanish Ministry of Economy and Competitiveness (Maria de Maetzu Units of Excellence Programme MDM-2016-0618 and national projects FIS2014-60195-JIN, MAT2014-53432-C5-4-R, MAT2015-65525-R, MAT2015-65159-R, FIS2016-80174-P, MAT2017-88358-C3-3-R), the Basque government (PhD fellowship PRE-2016-1-0150, PRE-2016-2-0025), the Department of Industry of the Basque Government (ELKARTEK project MICRO4FA), the Regional Council of Gipuzkoa (project no. 100/16) and the ERC starting grant 715496, 2DNANOPTICA.

Enhanced light-matter interactions are the basis of surface-enhanced infrared absorption (SEIRA) spectroscopy, and conventionally rely on plasmonic materials and their capability to focus light to nanoscale spot sizes. Phonon polariton nanoresonators made of polar crystals could represent an interesting alternative, since they exhibit large quality factors, which go far beyond those of their plasmonic counterparts. The recent emergence of van der Waals crystals enables the fabrication of high-quality nanophotonic resonators based on phonon polaritons, as reported for the prototypical infrared-phononic material hexagonal boron nitride (h-BN). In this work we use, for the first time, phonon-polariton-resonant h-BN ribbons for SEIRA spectroscopy of small amounts of organic molecules in Fourier transform infrared spectroscopy. Strikingly, the interaction between phonon polaritons and molecular vibrations reaches experimentally the onset of the strong coupling regime, while numerical simulations predict that vibrational strong coupling can be fully achieved. Phonon polariton nanoresonators thus could become a viable platform for sensing, local control of chemical reactivity and infrared quantum cavity optics experiments. ; We also acknowledge support from the European Commission under the Graphene Flagship (GrapheneCore1, Grant no. 696656), the Marie SklodowskaCurie individual fellowship (SGPCM-705960), the Spanish Ministry of Economy and Competitiveness (Maria de Maetzu Units of Excellence Programme MDM-2016-0618 and national projects FIS2014-60195-JIN, MAT2014-53432- C5-4-R, MAT2015-65525-R, MAT2015-65159-R, FIS2016-80174-P, MAT2017- 88358-C3-3-R), the Basque government (PhD fellowship PRE-2016-1-0150, PRE-2016-2-0025), the Department of Industry of the Basque Government (ELKARTEK project MICRO4FA), the Regional Council of Gipuzkoa (project no. 100/16) and the ERC starting grant 715496, 2DNANOPTICA. ; Peer Reviewed

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY). ; The spin transport and spin-to-charge current conversion properties of bismuth are investigated using permalloy/copper/bismuth (Py/Cu/Bi) lateral spin valve structures. The spin current is strongly absorbed at the surface of Bi, leading to ultrashort spin-diffusion lengths. A spin-to-charge current conversion is measured, which is attributed to the inverse Rashba-Edelstein effect at the Cu/Bi interface. The spin-current-induced charge current is found to change direction with increasing temperature. A theoretical analysis relates this behavior to the complex spin structure and dispersion of the surface states at the Fermi energy. The understanding of this phenomenon opens novel possibilities to exploit spin-orbit coupling to create, manipulate, and detect spin currents in two-dimensional systems. ; This work was supported by the European Commission under the Marie Curie Actions (Grant No. 256470-ITAMOSCINOM), the SUDOE (Grant No. TRAIN2-SOE2/P1/E-280), and the European Research Council (Grant No. 257654-SPINTROS), by the Spanish MINECO under Projects No. MAT2012-37638, No. MAT2011-13099-E, No. MAT2011-27553-C02, No. MAT2014-51982-C2-1-R, No. MAT2015-69725-REDT, and No. FIS2013-48286-C2-1-P, including FEDER funds, by the Basque Government under Project No. PI2011-1, and by the Aragon Regional Government under Project No. E26. M.I. and E.V. thank the Basque Government for Ph.D. fellowships (Grants No. BFI-2011-106 and No. BFI-2010-163). ; Peer Reviewed

Launching and manipulation of polaritons in van der Waals materials offers novel opportunities for field-enhanced molecular spectroscopy and photodetection, among other applications. Particularly, the highly confined hyperbolic phonon polaritons (HPhPs) in h-BN slabs attract growing interest for their capability of guiding light at the nanoscale. An efficient coupling between free space photons and HPhPs is, however, hampered by their large momentum mismatch. Here, we show —by far-field infrared spectroscopy, infrared nanoimaging and numerical simulations— that resonant metallic antennas can efficiently launch HPhPs in thin h-BN slabs. Despite the strong hybridization of HPhPs in the h-BN slab and Fabry-Pérot plasmonic resonances in the metal antenna, the efficiency of launching propagating HPhPs in h-BN by resonant antennas exceeds significantly that of the non-resonant ones. Our results provide fundamental insights into the launching of HPhPs in thin polar slabs by resonant plasmonic antennas, which will be crucial for phonon-polariton based nanophotonic devices. ; The authors acknowledge financial support from the European Commission under the Graphene Flagship (GrapheneCore2), the Spanish Ministry of Science, Innovation and Universities (national projects MAT2017-88358-C3, MAT2015-65159-R, MAT2015-65525-R, RTI2018-094830-B-100, RTI2018-094861-B-100, and the project MDM-2016-0618 of the Marie de Maeztu Units of Excellence Program) the Marie Sklodowska-Curie individual fellowship (SGPCM-705960), the Basque Government (PhD fellowship PRE 2018 2 0253), and the project PIC201660E046 from CSIC. M.M.W. acknowledges support from the Konrad-Adenauer-Stiftung. P.A.G. acknowledges support from the European Research Council under Starting Grant 715496, 2DNANOPTICA. ; Peer reviewed