Alex Fainstein - Academia.edu (original) (raw)
Papers by Alex Fainstein
Journal of The Optical Society of America B-optical Physics, Mar 31, 2023
South American optics research has seen remarkable growth over the past 50 years, with significan... more South American optics research has seen remarkable growth over the past 50 years, with significant contributions in areas such as quantum optics, holography, spectroscopy, nonlinear optics, statistical optics, nanophotonics and integrated photonics. The research has driven economic development in sectors like telecom, biophotonics, biometrics, and agri-sensing. This joint feature issue between JOSA A and JOSA B exhibits cutting-edge optics research from the region, fostering a sense of community and promoting collaboration among researchers.
Chinese Journal of Physics, Feb 1, 2011
The acoustic phonons in epitaxial ferroelectric (BaTiO 3) n /(SrTiO 3) m superlattices (SLs) are ... more The acoustic phonons in epitaxial ferroelectric (BaTiO 3) n /(SrTiO 3) m superlattices (SLs) are investigated by high-resolution ultraviolet Raman scattering. The temperature dependence of the folded acoustic (FA) phonon Raman intensity through the ferroelectric transition is addressed. A comparison of this behavior between SLs with different number of ferroelectric BaTiO 3 unit cells n and spacer SrTiO 3 unit cells m is presented. A mechanism involving the strain modulation of the spatially varying ferroelectric polarization is introduced to explain the temperature dependence of the FA phonon scattering. The temperature dependence of the polarization can be derived from an analysis of the first-order optical phonon spectra. Using this information, the observed temperature dependence of the whole set of SLs with different n can be consistently accounted for with the presented model. Atomistic shell-model simulations of the spatial pattern of the SL polarization are presented to explain the variation of the FA-spectral intensity for SLs with different m and the experimental fact that no high-order FA-replicas are observed. These results demonstrate the strong coupling between THz hypersound, charge, and light in these multifunctional nanoscale ferroelectrics.
HAL (Le Centre pour la Communication Scientifique Directe), 2011
ABSTRACT
In this work we study the effects of the presence of built-in electric fields, in piezoelectric s... more In this work we study the effects of the presence of built-in electric fields, in piezoelectric strained heterostructures, on the interaction between light and sound. In that sense, we propose that a novel electric-field-induced piezoelectric interaction, involving acoustic phonons, can be important in such structures. Taking advantage of the unique vibrational properties of superlattices and phonon cavities, we design and study GaInAs/AlAs-based multilayers, grown along [001] and [311] directions, in order to prove this hypothesis.
Cornell University - arXiv, Dec 1, 2021
Phonons, the quanta of vibrations, are very important for the equilibrium and dynamical propertie... more Phonons, the quanta of vibrations, are very important for the equilibrium and dynamical properties of matter. GHz coherent phonons can also interact with and act as interconnects in a wide range of quantum systems. Harnessing and tailoring their coupling to opto-electronic excitations thus becomes highly relevant for engineered materials for quantum technologies. With this perspective we introduce polaromechanical metamaterials, twodimensional arrays of µm-size zero-dimensional traps confining light-matter polariton fluids and GHz phonons. A strong exciton-mediated polariton-phonon interaction determines the inter-site polariton coupling with remarkable consequences for the dynamics. When locally perturbed by optical excitation, polaritons respond by locking the energy detuning between neighbor sites at integer multiples of the phonon energy, evidencing synchronization involving the polariton and phonon fields. These results open the path for the coherent control of quantum light fluids with hypersound in a scalable platform.
2020 International Conference Laser Optics (ICLO), 2020
Providing a fast, reliable, and sensitive alternative to methods of detecting and characterizing ... more Providing a fast, reliable, and sensitive alternative to methods of detecting and characterizing analytes in solution will be invaluable to the healthcare services. Currently, analysis techniques may take several weeks providing either qualitative (analyte make-up) or quantitative (concentration) information for a given sample. Here, we present a method to simultaneously acquire both, by utilizing the Kretschmann configuration and combining SERS and plasmonic spectroscopic techniques into a single unit. The proposed method is based on the use of a plasmonic substrate consisting of metallic nanoparticles on a film geometry.
2020 International Conference Laser Optics (ICLO), 2020
In this talk I will discuss some of the research directions of my group in the area of biosensing... more In this talk I will discuss some of the research directions of my group in the area of biosensing. Specifically, I will discuss: the development of hybrid plasmonic substrates that can be implemented into the Krechmann configuration for simultaneous qualitative and quantitative detection of analytes; the use of combinatory techniques based on plasmonic structures that enable control of analyte motion and thus concentration of analytes in the sensing area; and finally, the development of a theranostic agent based on conjugated polymer nanoparticles.
Physical Review Materials, 2018
The engineering of phononic resonances in ferroelectric structures appears as a new knob in the d... more The engineering of phononic resonances in ferroelectric structures appears as a new knob in the design and realization of novel multifunctional devices. In this work we experimentally study phononic resonators based on insulating (BaTiO 3 , SrTiO 3) and metallic (SrRuO 3) oxides. We experimentally demonstrate the confinement of acoustic waves in the 100 GHz frequency range in a phonon nanocavity, the time and spatial beatings resulting from the coupling of two different hybrid nanocavities forming an acoustic molecule, and the direct measurement of Bloch-like oscillations of acoustic phonons in a system formed by 10 coupled resonators. By means of coherent phonon generation techniques we study the phonon dynamics directly in the time-domain. The metallic SrRuO 3 introduces a local phonon generator and transducer that allows for the spatial, spectral and time-domain monitoring of the complex generated waves. Our results introduce ferroelectric cavity systems as a new tool for the study of complex wave localization phenomena at the nanoscale.
Physical Review B, 2019
When light is confined in all three directions and in dimensions of the order of the light wavele... more When light is confined in all three directions and in dimensions of the order of the light wavelength, discretization of the photon spectra and distinctive phenomena occur, the Purcell effect and the inhibition of emission of atoms being two paradigmatic examples. Diverse solid-state devices that confine light in all three dimensions have been developed and applied. Typically the confinement volume, operating wavelength, and quality factor of these resonators are set by construction, and small variations of these characteristics with external perturbations are targeted for applications including light modulation and control. Here we describe full 3D light trapping, that is set and tuned by laser excitation in an all-optical scheme. The proposed device is based on a planar distributed Bragg reflector GaAs semiconductor microcavity operated at room temperature. Lateral confinement is generated by an in-plane gradient in the refractive index of the structure's materials due to localized heating, which is in turn induced by carriers photoexcited by a focused laser. Strong three dimensional trapping of light is evidenced by the laser-induced changes on the spectral, spatial, and k-space distribution of the emission. The dynamics of the laser induced photonic potential is studied using modulated optical excitation, highlighting the central role of thermal effects at the origin of the observed phenomena.
ACS Photonics, 2019
Enhancing light−molecule interactions requires the efficient transfer of energy between the labor... more Enhancing light−molecule interactions requires the efficient transfer of energy between the laboratory macroscale and the molecule nanoscale. Multiscale designs have been proposed as a means to efficiently connect these two worlds. Metallic sphere-segment void (SSV) cavities constitute plasmonic substrates in which light wavelength scale cavity-like modes and nanoscale roughness operate in conjunction as a multiscale antenna to provide larger surface-enhanced Raman scattering efficiency than the two mechanisms considered separately. We study the selective resonant coupling to cavity modes with different spatial distributions in SSV arrays with tailored nanoscale roughness. Cavity modes that are spatially more confined to the surface are demonstrated to lead to more efficient channeling of energy from the far to the near field, a synergy that scales with the degree of roughness. Finiteelement modeling of the spatially varying local fields in rough SSV arrays allows for a microscopic description of the results, opening promising paths for the design of spatially and spectrally optimized multiscale antennas for efficient sensing with far-to near-field channeling of light.
Physical Review B, 1999
By means of X-and Q-band magnetic-resonance measurements we have investigated the magnetic intera... more By means of X-and Q-band magnetic-resonance measurements we have investigated the magnetic interactions and derived the magnon gap in the ferromagnetic superconductor RuSr 2 GdCu 2 O 8. Two microwave absorptions are observed: first, a paramagnetic resonance of the Gd 3ϩ ions, and second, appearing below the Curie temperature (T Curie), a ferromagnetic resonance due to the ruthenium lattice. Located between the superconducting CuO 2 planes, the Gd ions serve as intrinsic probes of the internal magnetic fields near the Cu sites. Below T Curie the Gd 3ϩ signal shifts, evidencing the appearance of a homogeneous internal field, H Ru-Gd ϳ600 Oe. We show that H Ru-Gd is due to a Ru-Gd ferromagnetic exchange interaction. The Ru ferromagnetic resonance indicates the existence of a magnon anisotropy gap /␥տ4600 Oe. We estimate the out-of-plane and in-plane anisotropy fields to be, respectively, H z ϳ110 kOe and H x ϳ200 Oe.
Journal of Nanomaterials, 2016
Surface Plasmon Resonance assays are being developed as alternative biodetection methods for a gr... more Surface Plasmon Resonance assays are being developed as alternative biodetection methods for a great number of pesticides and toxins. These substances typically have low molecular weight, making it necessary to perform competitive inhibition immunoassays. In most of the cases, the strategy is to immobilize a protein derivative of the analyte, which usually involves the appearance of nonspecific protein binding which limits the detection range of the assay. In this work we present results of a poly-L-lysine (Au-MUA-PLL) based sensor platform for quantitative determination of 2,4-dinitrophenol as model system for small molecular weight substances detection. The prepared sensor chip was characterized by means of Atomic Force Microscopy, Surface Plasmon Resonance, and Surface Enhanced Raman Spectroscopy. Experiments verified the absence of nonspecific protein adsorption to Au-MUA-PLL surfaces and the improvement of the competitive inhibition assays performance in comparison with single ...
Ultrasonics, 2015
Resonators based on acoustic distributed Bragg reflectors (DBRs) were optimized to work in the GH... more Resonators based on acoustic distributed Bragg reflectors (DBRs) were optimized to work in the GHz-THz regime, and grown by molecular beam epitaxy. We show that in structures made of GaAlAs alloys a simultaneous optimal confinement of light in the visible range and phonons in the tens of GHz range can be achieved. We report time resolved differential optical reflectivity experiments performed with fs-ps laser pulses. The experimental results are in excellent agreement with simulations based on standard transfer matrix methods. The resonant behavior of the photoelastic coefficient is discussed. The perfect optic-acoustic mode overlapping, added to a strongly enhanced coupling mechanism, implies that these DBR-based cavities could be the base of highly efficient optomechanical resonators.
We present Raman measurements from ambient temperature to 10 K on single crystals of layered mang... more We present Raman measurements from ambient temperature to 10 K on single crystals of layered manganites R_2-2xSr_1+2xMn_2O7 (RSMO) (R = Nd, Pr, Dy) and of the pseudo-cubic La_1-xCa_xMnO3 (LCMO). The phonon frequencies and their dependencies on composition have been determined, allowing assignments for most modes. RSMO shows a multitude of complex phonon behaviours, which we relate to the many magnetic
Physica B: Condensed Matter, 2002
ABSTRACT We present a Raman scattering and dilatometry study of polycrystalline samples of the ma... more ABSTRACT We present a Raman scattering and dilatometry study of polycrystalline samples of the magnetic superconducting ruthenocuprates RuSr2Gd2−xCexCu2O10+δ (RuGd1222) and RuSr2GdCu2O8 (RuGd1212). In the Raman spectra a high-temperature diffusive-like laser-tail develops below the magnetic ordering temperature (TM) into an underdamped peak which shifts up to ∼130cm−1. A line assigned to O(Ru) phonons hardens, narrows and strengthens strongly below TM. Finally, a phonon peak appears below TM at ∼590cm−1. These three magnetic-order-dependent features are observed for RuGd1212 and for RuGd1222 with x=1.0, but do not appear for x=0.5. Dilatometry measurements, on the other hand, evidence a change of the expansion coefficient at TM. These results point to a structural effect accompanying the magnetic order, and suggest a complex interplay of spin and lattice degrees of freedom in these ruthenocuprates.
Journal of Applied Physics, 1993
ABSTRACT dc magnetization measurements in a Gd doped Eu 2 CuO 4 single crystal indicate the appea... more ABSTRACT dc magnetization measurements in a Gd doped Eu 2 CuO 4 single crystal indicate the appearance below T N =243 K, of a weak ferromagnetic component M s (T), in addition to the Van Vleck paramagnetism of the Eu3+ ions. M s (T) is oriented parallel to the (001) plane and its magnitude and in‐plane angular dependence are strongly dependent on the cooling conditions. For samples cooled in zero magnetic field the magnetization is isotropic in the (001) plane with M s (0)=2.2(4)×10-3 μ B /formula unit. For samples cooled in a field (FC), M s (T) increases as a function of the field applied for cooling, H FC , reaching M s (0)=5.0(5)×10-3 μ B /formula unit for H FC =10 kG. A uniaxial magnetic anisotropy develops in this case with an easy axis along the [110] crystallographic direction lying closer to the orientation of H FC . A magnetic free energy including second and fourth order in‐plane anisotropy terms provides a good description of the experimental results, with H(2)=-85(5) G and H(4)=10(3) G.
Journal of Applied Physics, 2001
ABSTRACT Magnetic resonance techniques at frequencies of 9.4, 34, 110, and 219 GHz were used to i... more ABSTRACT Magnetic resonance techniques at frequencies of 9.4, 34, 110, and 219 GHz were used to investigate the magnetism of the recently discovered ferromagnetic superconducting system RuSr2RECu2O8 (RE=Eu, Gd). One absorption is observed in both compounds below the magnetic ordering temperature, TM∼135 K, and can be ascribed to the ferromagnetic resonance of the ordered Ru ions. The resonance field of this absorption is frequency dependent and is well described assuming an in-plane ferromagnetic component with strong out-of-plane (Hz) and weak in-plane (Hx) anisotropy fields. We have derived almost the same anisotropy fields for both compounds at 70 K (〈Hz〉∼250 kOe and 〈Hx〉∼165 Oe). Another absorption is observed only in the Gd compound and arises from the paramagnetic resonance of the Gd3+ ions. Below TM the Gd3+ signal shifts from g=2 evidencing the appearance of a homogeneous internal field, Hi,Gd, that is frequency (and hence field) dependent. This variation is probably due to the nonsaturated nature of the Ru lattice. Below 10 K there is an additional shift of the Gd3+ line arising from the Gd dipole-dipole interaction. © 2001 American Institute of Physics.
Physical Review B, 2018
Radiation pressure, electrostriction, and photothermal forces have been investigated to evidence ... more Radiation pressure, electrostriction, and photothermal forces have been investigated to evidence backaction, non-linearities and quantum phenomena in cavity optomechanics. We show here through a detailed study of the relative intensity of the cavity mechanical modes observed when exciting with pulsed lasers close to the GaAs optical gap that optoelectronic forces involving real carrier excitation and deformation potential interaction are the strongest mechanism of light-to-sound transduction in semiconductor GaAs/AlAs distributed Bragg reflector optomechanical resonators. We demonstrate that the ultrafast spatial redistribution of the photoexcited carriers in microcavities with massive GaAs spacers leads to an enhanced coupling to the fundamental 20 GHz vertically polarized mechanical breathing mode. The carrier diffusion along the growth axis of the device can be enhanced by increasing the laser power, or limited by embedding GaAs quantum wells in the cavity spacer, a strategy used here to prove and engineer the optoelectronic forces in phonon generation with real carriers. The wavelength dependence of the observed phenomena provide further proof of the role of optoelectronic forces. The optical forces associated to the different intervening mechanisms and their relevance for dynamical backaction in optomechanics are evaluated using finite-element methods. The results presented open the path to the study of hitherto seldom investigated dynamical backaction in optomechanical solid-state resonators in the presence of optoelectronic forces. I. MOTIVATION
Nature Communications, 2020
Efficient generation of phonons is an important ingredient for a prospective electrically-driven ... more Efficient generation of phonons is an important ingredient for a prospective electrically-driven phonon laser. Hybrid quantum systems combining cavity quantum electrodynamics and optomechanics constitute a novel platform with potential for operation at the extremely high frequency range (30–300 GHz). We report on laser-like phonon emission in a hybrid system that optomechanically couples polariton Bose-Einstein condensates (BECs) with phonons in a semiconductor microcavity. The studied system comprises GaAs/AlAs quantum wells coupled to cavity-confined optical and vibrational modes. The non-resonant continuous wave laser excitation of a polariton BEC in an individual trap of a trap array, induces coherent mechanical self-oscillation, leading to the formation of spectral sidebands displaced by harmonics of the fundamental 20 GHz mode vibration frequency. This phonon “lasing” enhances the phonon occupation five orders of magnitude above the thermal value when tunable neighbor traps ar...
Journal of The Optical Society of America B-optical Physics, Mar 31, 2023
South American optics research has seen remarkable growth over the past 50 years, with significan... more South American optics research has seen remarkable growth over the past 50 years, with significant contributions in areas such as quantum optics, holography, spectroscopy, nonlinear optics, statistical optics, nanophotonics and integrated photonics. The research has driven economic development in sectors like telecom, biophotonics, biometrics, and agri-sensing. This joint feature issue between JOSA A and JOSA B exhibits cutting-edge optics research from the region, fostering a sense of community and promoting collaboration among researchers.
Chinese Journal of Physics, Feb 1, 2011
The acoustic phonons in epitaxial ferroelectric (BaTiO 3) n /(SrTiO 3) m superlattices (SLs) are ... more The acoustic phonons in epitaxial ferroelectric (BaTiO 3) n /(SrTiO 3) m superlattices (SLs) are investigated by high-resolution ultraviolet Raman scattering. The temperature dependence of the folded acoustic (FA) phonon Raman intensity through the ferroelectric transition is addressed. A comparison of this behavior between SLs with different number of ferroelectric BaTiO 3 unit cells n and spacer SrTiO 3 unit cells m is presented. A mechanism involving the strain modulation of the spatially varying ferroelectric polarization is introduced to explain the temperature dependence of the FA phonon scattering. The temperature dependence of the polarization can be derived from an analysis of the first-order optical phonon spectra. Using this information, the observed temperature dependence of the whole set of SLs with different n can be consistently accounted for with the presented model. Atomistic shell-model simulations of the spatial pattern of the SL polarization are presented to explain the variation of the FA-spectral intensity for SLs with different m and the experimental fact that no high-order FA-replicas are observed. These results demonstrate the strong coupling between THz hypersound, charge, and light in these multifunctional nanoscale ferroelectrics.
HAL (Le Centre pour la Communication Scientifique Directe), 2011
ABSTRACT
In this work we study the effects of the presence of built-in electric fields, in piezoelectric s... more In this work we study the effects of the presence of built-in electric fields, in piezoelectric strained heterostructures, on the interaction between light and sound. In that sense, we propose that a novel electric-field-induced piezoelectric interaction, involving acoustic phonons, can be important in such structures. Taking advantage of the unique vibrational properties of superlattices and phonon cavities, we design and study GaInAs/AlAs-based multilayers, grown along [001] and [311] directions, in order to prove this hypothesis.
Cornell University - arXiv, Dec 1, 2021
Phonons, the quanta of vibrations, are very important for the equilibrium and dynamical propertie... more Phonons, the quanta of vibrations, are very important for the equilibrium and dynamical properties of matter. GHz coherent phonons can also interact with and act as interconnects in a wide range of quantum systems. Harnessing and tailoring their coupling to opto-electronic excitations thus becomes highly relevant for engineered materials for quantum technologies. With this perspective we introduce polaromechanical metamaterials, twodimensional arrays of µm-size zero-dimensional traps confining light-matter polariton fluids and GHz phonons. A strong exciton-mediated polariton-phonon interaction determines the inter-site polariton coupling with remarkable consequences for the dynamics. When locally perturbed by optical excitation, polaritons respond by locking the energy detuning between neighbor sites at integer multiples of the phonon energy, evidencing synchronization involving the polariton and phonon fields. These results open the path for the coherent control of quantum light fluids with hypersound in a scalable platform.
2020 International Conference Laser Optics (ICLO), 2020
Providing a fast, reliable, and sensitive alternative to methods of detecting and characterizing ... more Providing a fast, reliable, and sensitive alternative to methods of detecting and characterizing analytes in solution will be invaluable to the healthcare services. Currently, analysis techniques may take several weeks providing either qualitative (analyte make-up) or quantitative (concentration) information for a given sample. Here, we present a method to simultaneously acquire both, by utilizing the Kretschmann configuration and combining SERS and plasmonic spectroscopic techniques into a single unit. The proposed method is based on the use of a plasmonic substrate consisting of metallic nanoparticles on a film geometry.
2020 International Conference Laser Optics (ICLO), 2020
In this talk I will discuss some of the research directions of my group in the area of biosensing... more In this talk I will discuss some of the research directions of my group in the area of biosensing. Specifically, I will discuss: the development of hybrid plasmonic substrates that can be implemented into the Krechmann configuration for simultaneous qualitative and quantitative detection of analytes; the use of combinatory techniques based on plasmonic structures that enable control of analyte motion and thus concentration of analytes in the sensing area; and finally, the development of a theranostic agent based on conjugated polymer nanoparticles.
Physical Review Materials, 2018
The engineering of phononic resonances in ferroelectric structures appears as a new knob in the d... more The engineering of phononic resonances in ferroelectric structures appears as a new knob in the design and realization of novel multifunctional devices. In this work we experimentally study phononic resonators based on insulating (BaTiO 3 , SrTiO 3) and metallic (SrRuO 3) oxides. We experimentally demonstrate the confinement of acoustic waves in the 100 GHz frequency range in a phonon nanocavity, the time and spatial beatings resulting from the coupling of two different hybrid nanocavities forming an acoustic molecule, and the direct measurement of Bloch-like oscillations of acoustic phonons in a system formed by 10 coupled resonators. By means of coherent phonon generation techniques we study the phonon dynamics directly in the time-domain. The metallic SrRuO 3 introduces a local phonon generator and transducer that allows for the spatial, spectral and time-domain monitoring of the complex generated waves. Our results introduce ferroelectric cavity systems as a new tool for the study of complex wave localization phenomena at the nanoscale.
Physical Review B, 2019
When light is confined in all three directions and in dimensions of the order of the light wavele... more When light is confined in all three directions and in dimensions of the order of the light wavelength, discretization of the photon spectra and distinctive phenomena occur, the Purcell effect and the inhibition of emission of atoms being two paradigmatic examples. Diverse solid-state devices that confine light in all three dimensions have been developed and applied. Typically the confinement volume, operating wavelength, and quality factor of these resonators are set by construction, and small variations of these characteristics with external perturbations are targeted for applications including light modulation and control. Here we describe full 3D light trapping, that is set and tuned by laser excitation in an all-optical scheme. The proposed device is based on a planar distributed Bragg reflector GaAs semiconductor microcavity operated at room temperature. Lateral confinement is generated by an in-plane gradient in the refractive index of the structure's materials due to localized heating, which is in turn induced by carriers photoexcited by a focused laser. Strong three dimensional trapping of light is evidenced by the laser-induced changes on the spectral, spatial, and k-space distribution of the emission. The dynamics of the laser induced photonic potential is studied using modulated optical excitation, highlighting the central role of thermal effects at the origin of the observed phenomena.
ACS Photonics, 2019
Enhancing light−molecule interactions requires the efficient transfer of energy between the labor... more Enhancing light−molecule interactions requires the efficient transfer of energy between the laboratory macroscale and the molecule nanoscale. Multiscale designs have been proposed as a means to efficiently connect these two worlds. Metallic sphere-segment void (SSV) cavities constitute plasmonic substrates in which light wavelength scale cavity-like modes and nanoscale roughness operate in conjunction as a multiscale antenna to provide larger surface-enhanced Raman scattering efficiency than the two mechanisms considered separately. We study the selective resonant coupling to cavity modes with different spatial distributions in SSV arrays with tailored nanoscale roughness. Cavity modes that are spatially more confined to the surface are demonstrated to lead to more efficient channeling of energy from the far to the near field, a synergy that scales with the degree of roughness. Finiteelement modeling of the spatially varying local fields in rough SSV arrays allows for a microscopic description of the results, opening promising paths for the design of spatially and spectrally optimized multiscale antennas for efficient sensing with far-to near-field channeling of light.
Physical Review B, 1999
By means of X-and Q-band magnetic-resonance measurements we have investigated the magnetic intera... more By means of X-and Q-band magnetic-resonance measurements we have investigated the magnetic interactions and derived the magnon gap in the ferromagnetic superconductor RuSr 2 GdCu 2 O 8. Two microwave absorptions are observed: first, a paramagnetic resonance of the Gd 3ϩ ions, and second, appearing below the Curie temperature (T Curie), a ferromagnetic resonance due to the ruthenium lattice. Located between the superconducting CuO 2 planes, the Gd ions serve as intrinsic probes of the internal magnetic fields near the Cu sites. Below T Curie the Gd 3ϩ signal shifts, evidencing the appearance of a homogeneous internal field, H Ru-Gd ϳ600 Oe. We show that H Ru-Gd is due to a Ru-Gd ferromagnetic exchange interaction. The Ru ferromagnetic resonance indicates the existence of a magnon anisotropy gap /␥տ4600 Oe. We estimate the out-of-plane and in-plane anisotropy fields to be, respectively, H z ϳ110 kOe and H x ϳ200 Oe.
Journal of Nanomaterials, 2016
Surface Plasmon Resonance assays are being developed as alternative biodetection methods for a gr... more Surface Plasmon Resonance assays are being developed as alternative biodetection methods for a great number of pesticides and toxins. These substances typically have low molecular weight, making it necessary to perform competitive inhibition immunoassays. In most of the cases, the strategy is to immobilize a protein derivative of the analyte, which usually involves the appearance of nonspecific protein binding which limits the detection range of the assay. In this work we present results of a poly-L-lysine (Au-MUA-PLL) based sensor platform for quantitative determination of 2,4-dinitrophenol as model system for small molecular weight substances detection. The prepared sensor chip was characterized by means of Atomic Force Microscopy, Surface Plasmon Resonance, and Surface Enhanced Raman Spectroscopy. Experiments verified the absence of nonspecific protein adsorption to Au-MUA-PLL surfaces and the improvement of the competitive inhibition assays performance in comparison with single ...
Ultrasonics, 2015
Resonators based on acoustic distributed Bragg reflectors (DBRs) were optimized to work in the GH... more Resonators based on acoustic distributed Bragg reflectors (DBRs) were optimized to work in the GHz-THz regime, and grown by molecular beam epitaxy. We show that in structures made of GaAlAs alloys a simultaneous optimal confinement of light in the visible range and phonons in the tens of GHz range can be achieved. We report time resolved differential optical reflectivity experiments performed with fs-ps laser pulses. The experimental results are in excellent agreement with simulations based on standard transfer matrix methods. The resonant behavior of the photoelastic coefficient is discussed. The perfect optic-acoustic mode overlapping, added to a strongly enhanced coupling mechanism, implies that these DBR-based cavities could be the base of highly efficient optomechanical resonators.
We present Raman measurements from ambient temperature to 10 K on single crystals of layered mang... more We present Raman measurements from ambient temperature to 10 K on single crystals of layered manganites R_2-2xSr_1+2xMn_2O7 (RSMO) (R = Nd, Pr, Dy) and of the pseudo-cubic La_1-xCa_xMnO3 (LCMO). The phonon frequencies and their dependencies on composition have been determined, allowing assignments for most modes. RSMO shows a multitude of complex phonon behaviours, which we relate to the many magnetic
Physica B: Condensed Matter, 2002
ABSTRACT We present a Raman scattering and dilatometry study of polycrystalline samples of the ma... more ABSTRACT We present a Raman scattering and dilatometry study of polycrystalline samples of the magnetic superconducting ruthenocuprates RuSr2Gd2−xCexCu2O10+δ (RuGd1222) and RuSr2GdCu2O8 (RuGd1212). In the Raman spectra a high-temperature diffusive-like laser-tail develops below the magnetic ordering temperature (TM) into an underdamped peak which shifts up to ∼130cm−1. A line assigned to O(Ru) phonons hardens, narrows and strengthens strongly below TM. Finally, a phonon peak appears below TM at ∼590cm−1. These three magnetic-order-dependent features are observed for RuGd1212 and for RuGd1222 with x=1.0, but do not appear for x=0.5. Dilatometry measurements, on the other hand, evidence a change of the expansion coefficient at TM. These results point to a structural effect accompanying the magnetic order, and suggest a complex interplay of spin and lattice degrees of freedom in these ruthenocuprates.
Journal of Applied Physics, 1993
ABSTRACT dc magnetization measurements in a Gd doped Eu 2 CuO 4 single crystal indicate the appea... more ABSTRACT dc magnetization measurements in a Gd doped Eu 2 CuO 4 single crystal indicate the appearance below T N =243 K, of a weak ferromagnetic component M s (T), in addition to the Van Vleck paramagnetism of the Eu3+ ions. M s (T) is oriented parallel to the (001) plane and its magnitude and in‐plane angular dependence are strongly dependent on the cooling conditions. For samples cooled in zero magnetic field the magnetization is isotropic in the (001) plane with M s (0)=2.2(4)×10-3 μ B /formula unit. For samples cooled in a field (FC), M s (T) increases as a function of the field applied for cooling, H FC , reaching M s (0)=5.0(5)×10-3 μ B /formula unit for H FC =10 kG. A uniaxial magnetic anisotropy develops in this case with an easy axis along the [110] crystallographic direction lying closer to the orientation of H FC . A magnetic free energy including second and fourth order in‐plane anisotropy terms provides a good description of the experimental results, with H(2)=-85(5) G and H(4)=10(3) G.
Journal of Applied Physics, 2001
ABSTRACT Magnetic resonance techniques at frequencies of 9.4, 34, 110, and 219 GHz were used to i... more ABSTRACT Magnetic resonance techniques at frequencies of 9.4, 34, 110, and 219 GHz were used to investigate the magnetism of the recently discovered ferromagnetic superconducting system RuSr2RECu2O8 (RE=Eu, Gd). One absorption is observed in both compounds below the magnetic ordering temperature, TM∼135 K, and can be ascribed to the ferromagnetic resonance of the ordered Ru ions. The resonance field of this absorption is frequency dependent and is well described assuming an in-plane ferromagnetic component with strong out-of-plane (Hz) and weak in-plane (Hx) anisotropy fields. We have derived almost the same anisotropy fields for both compounds at 70 K (〈Hz〉∼250 kOe and 〈Hx〉∼165 Oe). Another absorption is observed only in the Gd compound and arises from the paramagnetic resonance of the Gd3+ ions. Below TM the Gd3+ signal shifts from g=2 evidencing the appearance of a homogeneous internal field, Hi,Gd, that is frequency (and hence field) dependent. This variation is probably due to the nonsaturated nature of the Ru lattice. Below 10 K there is an additional shift of the Gd3+ line arising from the Gd dipole-dipole interaction. © 2001 American Institute of Physics.
Physical Review B, 2018
Radiation pressure, electrostriction, and photothermal forces have been investigated to evidence ... more Radiation pressure, electrostriction, and photothermal forces have been investigated to evidence backaction, non-linearities and quantum phenomena in cavity optomechanics. We show here through a detailed study of the relative intensity of the cavity mechanical modes observed when exciting with pulsed lasers close to the GaAs optical gap that optoelectronic forces involving real carrier excitation and deformation potential interaction are the strongest mechanism of light-to-sound transduction in semiconductor GaAs/AlAs distributed Bragg reflector optomechanical resonators. We demonstrate that the ultrafast spatial redistribution of the photoexcited carriers in microcavities with massive GaAs spacers leads to an enhanced coupling to the fundamental 20 GHz vertically polarized mechanical breathing mode. The carrier diffusion along the growth axis of the device can be enhanced by increasing the laser power, or limited by embedding GaAs quantum wells in the cavity spacer, a strategy used here to prove and engineer the optoelectronic forces in phonon generation with real carriers. The wavelength dependence of the observed phenomena provide further proof of the role of optoelectronic forces. The optical forces associated to the different intervening mechanisms and their relevance for dynamical backaction in optomechanics are evaluated using finite-element methods. The results presented open the path to the study of hitherto seldom investigated dynamical backaction in optomechanical solid-state resonators in the presence of optoelectronic forces. I. MOTIVATION
Nature Communications, 2020
Efficient generation of phonons is an important ingredient for a prospective electrically-driven ... more Efficient generation of phonons is an important ingredient for a prospective electrically-driven phonon laser. Hybrid quantum systems combining cavity quantum electrodynamics and optomechanics constitute a novel platform with potential for operation at the extremely high frequency range (30–300 GHz). We report on laser-like phonon emission in a hybrid system that optomechanically couples polariton Bose-Einstein condensates (BECs) with phonons in a semiconductor microcavity. The studied system comprises GaAs/AlAs quantum wells coupled to cavity-confined optical and vibrational modes. The non-resonant continuous wave laser excitation of a polariton BEC in an individual trap of a trap array, induces coherent mechanical self-oscillation, leading to the formation of spectral sidebands displaced by harmonics of the fundamental 20 GHz mode vibration frequency. This phonon “lasing” enhances the phonon occupation five orders of magnitude above the thermal value when tunable neighbor traps ar...