arXiv subjects

D. Lacour

Publications and source records attributed to D. Lacour.

At least 19 recordsLinked to original sources

arXiv2025

Beam-test evaluation of pre-production Low Gain Avalanche Detectors for the ATLAS High Granularity Timing Detector

The High Granularity Timing Detector (HGTD) will be installed in the ATLAS experiment as part of the Phase-II upgrade for the High Luminosity-Large Hadron Collider (HL-LHC). It will mitigate pile-up effects in the forward region, and measure per bunch luminosity. The design of HGTD is based on Low Gain Avalanche Detector (LGAD) sensors. This paper presents the results of beam-test campaigns conducted at CERN and DESY in 2023 and 2024 on single LGADs from HGTD pre-production test structures, before and after neutron irradiation up to fluences of $2.5 \times 10^{15}~\mathrm{n_{eq}/cm^2}$. The tested LGADs can meet HGTD requirements in terms of charge collection, time resolution, and hit efficiency, even under HL-LHC end-of-life conditions, supporting their deployment in the final detector.

physics.ins-det↗

arXiv2025

Dissipation properties of anomalous Hall effect: intrinsic vs. extrinsic magnetic materials

A comparative study of anomalous-Hall current injection and anisotropic current injection (through planar Hall effect) are studied in Hall devices contacted to a lateral load circuit. Hall currents are injected into the load circuit from three different kinds of magnetic Hall bars: Mn5Si3 altermagnet, Co75Gd25 ferrimagnet, and Ni80Fe20 ferromagnet. The current, the voltage and the power are measured as a function of the load resistance and the Hall angle. It is observed that the power dissipated for the three kinds of materials fellow the same law as a function of load resistance and Hall angle, at the leading order in the Hall angle. Since the anomalous Hall effect in the altermagnetic Hall-bar is due to the intrinsic topological structure (i.e. due to the presence of a Berry phase in the reciprocal space), these observations suggest that the dissipative properties of anomalous Hall effect are dominated by the injection of electric charges accumulated at the edges (including electric screening), instead of the very mechanism responsible for it.

cond-mat.mes-hall↗

arXiv2025

Thermal Cycling Reliability of Hybrid Pixel Sensor Modules for The ATLAS High Granularity Timing Detector

The reliability of bump connection structures has become a critical aspect of future silicon detectors for particle physics. The High Granularity Timing Detector (HGTD) for the ATLAS experiment at the High-Luminosity Large Hadron Collider will require 8032 hybrid pixel sensor modules, composed of two Low Gain Avalanche Diode sensors bump-bonded to two readout ASICs and glued to a passive PCB. The detector will operate at low temperature (-30 degrees Celsius) to mitigate the impact of irradiation. The thermomechanical reliability of flip-chip bump connections in HGTD modules is a critical concern, particularly due to their characteristically lower bump density (pixel pitch dimensions of 1.3 mm by 1.3 mm). This paper elaborates on the challenges arising from this design characteristic. Finite element analysis and experimental testing were employed to investigate failure modes in the flip-chip bump structures under thermal cycling from -45 degrees Celsius to 40 degrees Celsius and to guide the module redesign. The optimized design demonstrates significantly enhanced robustness and is projected to fulfill the full lifetime requirements of the HGTD.

physics.ins-det↗

arXiv2025

Controlling Single-Pulse Magnetization Switching through Angular Momentum Reservoir Engineering

We report a systematic study of single pulse all optical helicity independent switching in CoGd bilayers, revealing that the magnetization reversal dynamics can be tuned over more than three orders of magnitude. By varying the Gd thickness or inserting a Pt spacer layer between Co and Gd, we control the angular momentum transferred from the rare earth sublattice to the transition metal sublattice. Our results show that when Gd is abundant and strongly coupled to Co, angular momentum is efficiently transferred during Gd demagnetization, leading to ultrafast Co reversal. In contrast, reducing the Gd thickness or introducing a Pt barrier impedes this transfer, resulting in a domain growth mediated reversal on nanosecond and possibly to microsecond timescales as previously observed in CoDy and CoHo alloys. As a result, in rare earth transition metal systems, replacing Gd with heavier rare-earth elements such as Dy or Ho slows down the switching due to a reduced angular momentum transfer towards Co upon demagnetization as demonstrated in CoGdDy alloys. Our findings establish angular momentum availability and transfer pathways as key parameters governing AO HIS dynamics, offering a unified framework for fast and slow magnetization reversal across rare earth transition metal systems.

cond-mat.mtrl-sci↗

arXiv2025

Single-laser pulse toggle switching in CoHo and CoDy single layer alloys : when domain wall motion matters

Single pulse All Optical Helicity-Independent Toggle Switching is observed in CoHo and CoDy alloys single layers. An original reversal mechanism is reported which contrasts with those observed to date. It is shown that the reversal process is on the {\mu}s timescale involving the reorganization / coalescence of domains and domain walls. The toggle switching is explained considering the unbalanced magnetization distribution stabilized after the ultrashort laser pulse.

cond-mat.mtrl-sci↗

arXiv2024

Single-shot all-optical magnetization switching in in-plane magnetized magnetic tunnel junction

Single pulse All Optical Helicity-Independent Switching is demonstrated in an in-plane magnetized magnetic tunnel junction. A toggle switching of the 2nm thick Co40Fe40B20 soft layer could be achieved by exchange coupling the Co40Fe40B20 with a 10nm thick Co85Gd15 layer monitored by measuring the Tunnel magneto resistance of the device. The use of in plane magnetized electrodes relaxes the constrains linked to perpendicular magnetic anisotropy systems while achieving a tunneling magnetoresistance (TMR) ratio exceeding 100%. The influence of the upper electrical electrode, which is opaque to the laser beam in this study, is also discussed.

cond-mat.mtrl-sci↗

arXiv2023

Electric-power efficiency of anomalous Hall current

The electric-power dissipation of the anomalous-Hall current injected into a lateral load circuit is studied. The anomalous-Hall current is generated by a $\mathrm{Co_{75}Gd_{25}}$ ferrimagnetic Hall bar and injected into lateral contacts lithographied at the two edges. The current, the voltage and the power injected in the lateral circuit are studied as a function of the magnetization state, the load resistance $R_l$, and the temperature. The power efficiency shows a sharp maximum as a function $R_l$, which corresponds to the condition of the resistance matching of the two sub-circuits. The maximum power efficiency is of the order of the square of anomalous-Hall angle. The observations are in agreement with recent predictions based on a non-equilibrium variational approach.

cond-mat.mes-hall↗

arXiv2020

Laser-induced ultrafast demagnetization and perpendicular magnetic anisotropy reduction in a Co$_{88}$Tb$_{12}$ thin film with stripe domains

We use time-resolved x-ray resonant magnetic scattering (tr-XRMS) at the Co M$_{2,3}$- and Tb O$_1$-edges to study ultrafast demagnetization in an amorphous Co$_{88}$Tb$_{12}$ alloy with stripe domains. Combining the femtosecond temporal with nanometer spatial resolution of our experiment, we demonstrate that the equilibrium spin texture of the thin film remains unaltered by the optical pump-pulse on ultrashort timescales ($<$1 ps). However, after $\simeq$ 4 ps, we observe the onset of a significant domain wall broadening, which we attribute to a reduction of the uniaxial magnetic anisotropy of the system, due to energy transfer to the lattice. Static temperature dependent magnetometry measurements combined with analytical modeling of the magnetic structure of the thin film corroborate this interpretation.

cond-mat.mes-hall↗

arXiv2020

Electrical spectroscopy of forward volume spin waves in perpendicularly magnetized materials

We study the potential of all-electrical inductive techniques for the spectroscopy of propagating forward volume spin waves. We develop a one-dimensional model to account for the electrical signature of spin-wave reflection and transmission between inductive antennas and validate it with experiments on a perpendicularly magnetized Co/Ni multilayer. We describe the influence of the antenna geometry and antenna-to-antenna separation, as well as that of the material parameters on the lineshape of the inductive signals. For a finite damping, the broadband character of the antenna emission in the wave vector space imposes to take into account the growing decoherence of the magnetization waves upon their spatial propagation. The transmission signal can be viewed as resulting from two contributions: a first one from propagating spin-waves leading to an oscillatory phase of the broadband transmission coefficient, and another one originating from the distant induction of ferromagnetic resonance because of the long-range stray fields of realistic antennas. Depending on the relative importance of these two contributions, the decay of the transmitted signal with the propagation distance may not be exponential and the oscillatory character of the spin-wave phase upon propagation may be hidden. Our model and its experimental validation allow to define geometrical and material specifications to be met to enable the use of forward volume spin waves as efficient information carriers.

cond-mat.mes-hall↗

arXiv2019

Magnetoresistance and spintronic anisotropy induced by spin excitations along molecular spin chains

Electrically manipulating the quantum properties of nano-objects, such as atoms or molecules, is typically done using scanning tunnelling microscopes and lateral junctions. The resulting nanotransport path is well established in these model devices. Societal applications require transposing this knowledge to nano-objects embedded within vertical solid-state junctions, which can advantageously harness spintronics to address these quantum properties thanks to ferromagnetic electrodes and high-quality interfaces. The challenge here is to ascertain the device's effective, buried nanotransport path, and to electrically involve these nano-objects in this path by shrinking the device area from the macro- to the nano-scale while maintaining high structural/chemical quality across the heterostructure. We've developed a low-tech, resist- and solvent-free technological process that can craft nanopillar devices from entire in-situ grown heterostructures, and use it to study magnetotransport between two Fe and Co ferromagnetic electrodes across a functional magnetic CoPc molecular layer. We observe how spin-flip transport across CoPc molecular spin chains promotes a specific magnetoresistance effect, and alters the nanojunction's magnetism through spintronic anisotropy. In the process, we identify three magnetic units along the effective nanotransport path thanks to a macrospin model of magnetotransport. Our work elegantly connects the until now loosely associated concepts of spin-flip spectroscopy, magnetic exchange bias and magnetotransport due to molecular spin chains, within a solid-state device. We notably measure a 5.9meV energy threshold for magnetic decoupling between the Fe layer's buried atoms and those in contact with the CoPc layer forming the so-called 'spinterface'. This provides a first insight into the experimental energetics of this promising low-power information encoding unit.

cond-mat.mes-hall↗

arXiv2019

Beam test performance of the highly granular SiW-ECAL technological prototype for the ILC

The technological prototype of the CALICE highly granular silicon-tungsten electromagnetic calorimeter (SiW-ECAL) was tested in a beam at DESY in 2017. The setup comprised seven layers of silicon sensors. Each layer comprised four sensors, with each sensor containing an array of 256 $5.5\times5.5$ mm$^2$ silicon PIN diodes. The four sensors covered a total area of $18\times18$ cm$^2$, and comprised a total of 1024 channels. The readout was split into a trigger line and a charge signal line. Key performance results for signal over noise for the two output lines are presented, together with a study of the uniformity of the detector response. Measurements of the response to electrons for the tungsten loaded version of the detector are also presented.

physics.ins-det↗

arXiv2019

Commissioning of the highly granular SiW-ECAL technological prototype

In this article we describe the commissioning and a first analysis of the the beam test performance of a small prototype of a highly granular silicon tungsten calorimeter. The prototype features detector elements with a channel number similar to that envisaged for e.g. the ILD Detector of the International Linear Collider (ILC). The analysis demonstrates the capability of the detector to record signals as low as 0.5 MIP. Further, no loss of performance has been observed when operating the detector in a high magnetic field.

physics.ins-det↗

arXiv2019

Hole transport across MgO-based magnetic tunnel junctions with high resistance-area product due to oxygen vacancies

The quantum mechanical tunnelling process conserves the quantum properties of the particle considered. As applied to solid-state tunnelling (SST), this physical law was verified, within the field of spintronics, regarding the electron spin in early experiments across Ge tunnel barriers, and in the 90s across Al2O3 barriers. The conservation of the quantum parameter of orbital occupancy, as grouped into electronic symmetries, was observed in the '00s across MgO barriers, followed by SrTiO3 (STO). Barrier defects, such as oxygen vacancies, partly conserve this electronic symmetry. In the solid-state, an additional subtlety is the sign of the charge carrier: are holes or electrons involved in transport? We demonstrate that SST across MgO magnetic tunnel junctions (MTJs) with a large resistance-area (RA) product involves holes by examining how shifting the MTJ's Fermi level alters the ensuing barrier heights defined by the barrier's oxygen vacancies. In the process, we consolidate the description of tunnel barrier heights induced by specific oxygen-vacancy induced localized states. Our work opens prospects to understand the concurrent observation of high TMR and spin transfer torque across MgO-based nanopillars.

cond-mat.mes-hall↗

arXiv2019

Spin-driven electrical power generation at room temperature

To mitigate climate change, our global society is harnessing direct (solar irradiation) and indirect (wind/water flow) sources of renewable electrical power generation. Emerging direct sources include current-producing thermal gradients in thermoelectric materials, while quantum physics-driven processes to convert quantum information into energy have been demonstrated at very low temperatures. The magnetic state of matter, assembled by ordering the electron's quantum spin property, represents a sizeable source of built-in energy. We propose to create a direct source of electrical power at room temperature (RT) by utilizing magnetic energy to harvest thermal fluctuations on paramagnetic (PM) centers. Our spin engine rectifies current fluctuations across the PM centers' spin states according to the electron spin by utilizing so-called 'spinterfaces' with high spin polarization. As a rare experimental event, we demonstrate how this path can generate 0.1nW at room temperature across a 20 micron-wide spintronic device called the magnetic tunnel junction, assembled using commonplace Co, C and MgO materials. The presence of this path in our experiment, which also generates very high spintronic performance, is confirmed by analytical and ab-initio calculations. Device downscaling, and the ability for other materials systems than the spinterface to select a transport spin channel at RT widens opportunities for routine device reproduction. The challenging control over PM centers within the tunnel barrier's nanotransport path may be addressed using oxide- and organic-based nanojunctions. At present densities in MRAM products, this spin engine could lead to 'always-on' areal power densities well beyond that generated by solar irradiation on earth. Further developing this concept can fundamentally alter our energy-driven society's global economic, social and geopolitical constructs.

cond-mat.mes-hall↗

arXiv2019

LPNHE scientific perspectives for the European Strategy for Particle Physics

This note summarizes the activities and the scientific and technical perspectives of the Laboratoire de Physique Nucleaire et de Hautes Energies (LPNHE) at Sorbonne University, Paris. Although the ESPP is specifically aimed at particle physics, we discuss in this note in parallel the three scientific lines developed at LPNHE (Particle Physics, Astroparticles, Cosmology), first with the current scientific activities, then for the future activities. However, our conclusions and recommendations are focused on the particle physics strategy.

hep-ph↗

arXiv2018

Beam test measurements of Low Gain Avalanche Detector single pads and arrays for the ATLAS High Granularity Timing Detector

For the high luminosity upgrade of the LHC at CERN, ATLAS is considering the addition of a High Granularity Timing Detector (HGTD) in front of the end cap and forward calorimeters at |z| = 3.5 m and covering the region 2.4 < |η| < 4 to help reducing the effect of pile-up. The chosen sensors are arrays of 50 μm thin Low Gain Avalanche Detectors (LGAD). This paper presents results on single LGAD sensors with a surface area of 1.3x1.3 mm2 and arrays with 2x2 pads with a surface area of 2x2 mm^2 or 3x3 mm^2 each and different implant doses of the p+ multiplication layer. They are obtained from data collected during a beam test campaign in Autumn 2016 with a pion beam of 120 GeV energy at the CERN SPS. In addition to several quantities measured inclusively for each pad, the gain, efficiency and time resolution have been estimated as a function of the position of the incident particle inside the pad by using a beam telescope with a position resolution of few μm. Different methods to measure the time resolution are compared, yielding consistent results. The sensors with a surface area of 1.3x1.3 mm^2 have a time resolution of about 40 ps for a gain of 20 and of about 27 ps for a gain of 50 and fulfill the HGTD requirements. Larger sensors have, as expected, a degraded time resolution. All sensors show very good efficiency and time resolution uniformity.

physics.ins-det↗

arXiv2017

SiW ECAL for future $e^+e^-$ collider

Calorimeters with silicon detectors have many unique features and are proposed for several world-leading experiments. We discuss the tests of the first three 18x18 cm$^2$ layers segmented into 1024 pixels of the technological prototype of the silicon-tungsten electromagnetic calorimeter for a future $e^+e^-$ collider. The tests have beem performed in November 2015 at CERN SPS beam line.

physics.ins-det↗

arXiv2015

Spin transport in molybdenum disulfide multilayer channel

Molybdenum disulfide has recently emerged as a promising two-dimensional semiconducting material for nano-electronic, opto-electronic and spintronic applications. However, demonstrating spin-transport through a semiconducting MoS2 channel is challenging. Here we demonstrate the electrical spin injection and detection in a multilayer MoS2 semiconducting channel. A magnetoresistance (MR) around 1% has been observed at low temperature through a 450nm long, 6 monolayer thick channel with a Co/MgO spin injector and detector. From a systematic study of the bias voltage, temperature and back-gate voltage dependence of MR, it is found that the hopping via localized states in the contact depletion region plays a key role for the observation of the two-terminal MR. Moreover, the electron spin-relaxation is found to be greatly suppressed in the multilayer MoS2 channel for in-plan spin injection. The underestimated long spin diffusion length (~235nm) and large spin lifetime (~46ns) open a new avenue for spintronic applications using multilayer transition metal dichalcogenides.

cond-mat.mtrl-sci↗