arXiv subjects

A. Bruchhausen

Publications and source records attributed to A. Bruchhausen.

11 recordsLinked to original sources

arXiv2026

In-plane magnetic field control of anomalous Hall response enabled by magnetic anisotropy engineering

Engineering magnetic anisotropy provides a powerful route to control magnetization orientation and unlock emerging functionalities in opto-spintronic and current-driven devices. Beyond its role in magnetization reversal, the effective anisotropy can strongly influence the magnetotransport response, offering an additional degree of freedom to tune new device functionalities. In this work, we report a magnetotransport study of a ferrimagnetic [Tb/Co]$_{\times 5}$ multilayer grown with a Tb thickness gradient, whose wedge-shaped tilts the uniaxial anisotropy axis slightly away from the film normal. Anomalous Hall resistivity measurements from 80 K to 300 K reveal a spin reorientation transition, while the angular dependence of the magnetotransport responses exposes the crucial role of the tilted anisotropy. A simplified macrospin model reproduces the full angular response across the transition and shows that the observed anomalous Hall effect when the in-plane magnetic field is applied originates from the tilt of the uniaxial anisotropy axis, which supplies a built-in symmetry-breaking mechanism, enabling in-plane field control over the out-of-plane anomalous Hall response, sign included. These findings establish tilted magnetic anisotropy as a promising route toward Hall effect-based sensor applications and highlight Tb/Co multilayers as a versatile platform for anisotropy-engineered spintronic devices.

cond-mat.mes-hall↗

arXiv2026

Synchronization in coherently and dissipatively coupled spinor polariton time crystals

The spinor degree of freedom associated to exciton-polariton condensates can spontaneously self-oscillate breaking time translation symmetry, thus showing a continuous time-crystal (CTC) behavior. An open question in such driven-dissipative and non-linear quantum open systems is what happens when CTCs are brought together to interact. Here we experimentally study polariton condensates in coupled traps, evidencing mutual induction and synchronization of the pseudospin temporal GHz dynamics in the CTC phase. The individual and relative orientation of the (limit cycle) precessing pseudospins can be tuned by the optical excitation power, displaying both ferro and anti-ferro dynamical configurations. We theoretically show that the exciton reservoir, and both the coherent and long-range dissipative inter-trap coupling, play important roles in the CTC dynamics. The investigation of time-broken symmetry is thus extended here to more complex non-hermitian systems opening the path to study self-sustained collective dynamics in lattices of non-linear quantum condensates.

cond-mat.other↗

arXiv2022

Probing Gigahertz Coherent Acoustic Phonons in TiO$_{2}$ Mesoporous Thin Films

Ultrahigh-frequency acoustic-phonon resonators usually require atomically flat interfaces to avoid phonon scattering and dephasing, leading to expensive fabrication processes, such as molecular beam epitaxy. In contrast, mesoporous thin films are based on inexpensive wet chemical fabrication techniques. Here, we report mesoporous titanium dioxide-based acoustic resonators with resonances up to 90 GHz, and quality factors from 3 to 7. Numerical simulations show a good agreement with the picosecond ultrasonics experiments. We also numerically study the effect of changes in the speed of sound on the performance of the resonator. This change could be induced by liquid infiltration into the mesopores. Our findings constitute the first step towards the engineering of building blocks based on mesoporous thin films for reconfigurable optoacoustic sensors.

cond-mat.mes-hall↗

arXiv2020

Mesoporous Thin-Films for Acoustic Devices in the Gigahertz Range

The coherent manipulation of acoustic waves on the nanoscale usually requires multilayers with thicknesses and interface roughness defined down to the atomic monolayer. This results in expensive devices with predetermined functionality. Nanoscale mesoporous materials present high surface-to-volume ratio and tailorable mesopores, which allow the incorporation of chemical functionalization to nanoacoustics. However, the presence of pores with sizes comparable to the acoustic wavelength is intuitively perceived as a major roadblock in nanoacoustics. Here we present multilayered nanoacoustic resonators based on mesoporous SiO$_2$ thin-films showing acoustic resonances in the 5-100 GHz range. We characterize the acoustic response of the system using coherent phonon generation experiments. Despite resonance wavelengths comparable to the pore size, we observe for the first time unexpectedly well-defined acoustic resonances with Q-factors around 10. Our results open the path to a promising platform for nanoacoustic sensing and reconfigurable acoustic nanodevices based on soft, inexpensive fabrication methods.

physics.app-ph↗

arXiv2017

Optomechanical properties of GaAs/AlAs micropillar resonators operating in the 18 GHz range

Recent experiments demonstrated that GaAs-AlAs based micropillar cavities are promising systems for quantum optomechanics, allowing the simultaneous three-dimensional confinement of near-infrared photons and acoustic phonons in the 18-100 GHz range. Here, we investigate through numerical simulations the optomechanical properties of this new platform. We evidence how the Poisson's ratio and semiconductor-vacuum boundary conditions lead to very distinct features in the mechanical and optical three dimensional confinement. We find a strong dependence of the mechanical quality factor and strain distribution on the micropillar radius, in great contrast to what is predicted and observed in the optical domain. The derived optomechanical coupling constants g_0 reach ultra-large values in the 10^6 rad/s range.

cond-mat.mes-hall↗

arXiv2016

Acoustic Localization Phenomena in Ferroelectric Nanophononic Devices

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 (BaTiO3, SrTiO3) and metallic (SrRuO3) 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 SrRuO3 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.

cond-mat.mes-hall↗

arXiv2010

Sub-harmonic resonant excitation of confined acoustic modes at GHz frequencies with a high-repetition-rate femtosecond laser

We propose sub-harmonic resonant optical excitation with femtosecond lasers as a new method for the characterization of phononic and nanomechanical systems in the gigahertz to terahertz frequency range. This method is applied for the investigation of confined acoustic modes in a free-standing semiconductor membrane. By tuning the repetition rate of a femtosecond laser through a sub-harmonic of a mechanical resonance we amplify the mechanical amplitude, directly measure the linewidth with megahertz resolution, infer the lifetime of the coherently excited vibrational states, accurately determine the system's quality factor, and determine the amplitude of the mechanical motion with femtometer resolution.

cond-mat.mes-hall↗

arXiv2009

Microcavity exciton-polariton mediated Raman scattering: Experiments and theory

We studied the intensity of resonant Raman scattering due to optical phonons in a planar II-VI-type semiconductor microcavity in the regime of strong coupling between light and matter. Two different sets of independent experiments were performed at near outgoing resonance with the middle polariton (MP)branch of the cavity. In the first, the Stokes-shifted photons were kept at exact resonance with the MP, varying the photonic or excitonic character of the polariton. In the second, only the incoming light wavelength was varied, and the resonant profile of the inelastic scattered intensity was studied when the system was tuned out of the resonant condition. Taking some matrix elements as free parameters, both independent experiments are quantitatively described by a model which incorporates lifetime effects in both excitons and photons, and the coupling of the cavity photons to the electron-hole continuum. The model is solved using a Green's function approach which treats the exciton-photon coupling nonperturbatively.

cond-mat.str-el↗

arXiv2009

Polariton-mediated Raman scattering in microcavities: A Green's function approach

We present calculations of the intensity of polariton-mediated inelastic light scattering in semiconductor microcavities within a Green's function framework. In addition to reproducing the strong coupling of light and matter, this method also enables the inclusion of damping mechanisms in a consistent way. Our results show excellent agreement with recent Raman scattering experiments.

cond-mat.str-el↗

arXiv2007

Theory of polariton mediated Raman scattering in microcavities

We calculate the intensity of the polariton mediated inelastic light scattering in semiconductor microcavities. We treat the exciton-photon coupling nonperturbatively and incorporate lifetime effects in both excitons and photons, and a coupling of the photons to the electron-hole continuum. Taking the matrix elements as fitting parameters, the results are in excellent agreement with measured Raman intensities due to optical phonons resonant with the upper polariton branches in II-VI microcavities with embedded CdTe quantum wells.

cond-mat.str-el↗

arXiv2002

Confinement of acoustical vibrations in a semiconductor planar phonon cavity

Extending the idea of optical microcavities to sound waves, we propose a {\it phonon cavity} consisting of two semiconductor superlattices enclosing a spacer with thickness determined by the acoustic wavelength at the center of the first zone-center folded minigap. We show that acoustical phonons can be confined in these layered structures, and propose Raman experiments which are able to probe these novel excitations. The Raman experiments take profit of an optical microcavity scattering geometry that, through the forward-scattering contribution, gives access to the zone-center excitations. We report experimental results of Raman scattering in a structure based in GaAs/AlAs materials that demonstrate unambiguously the observation of phonon cavity confined acoustical vibrations. The experimental results compare precisely with photoelastic model calculations of the Raman spectra of the proposed phonon-cavity embedded optical microcavity.

cond-mat↗