arXiv subjects

Dominique Mailly

Publications and source records attributed to Dominique Mailly.

At least 19 recordsLinked to original sources

arXiv2025

Mapping the twist angle dependence of quasi-Brillouin zones in doubly aligned graphene/BN heterostructures

When monolayer graphene is crystallographically aligned to hexagonal boron nitride (BN), a moir\'e superlattice is formed, producing characteristic satellite Dirac peaks in the electronic band structure. Aligning a second BN layer to graphene creates two coexisting moir\'e patterns, which can interfere to produce periodic, quasi-periodic or non-periodic superlattices, depending on their relative alignment. Here, we investigate one of the simplest realizations of such a double-moir\'e structure, graphene encapsulated between two BN layers, using dynamically rotatable van der Waals heterostructures. Our setup allows \textit{in situ} control of the top BN alignment while keeping the bottom BN fixed. By systematically mapping the charge transport as a function of BN angular alignment, we identify the simultaneous signatures of the original moir\'es, super-moir\'es, and a third set of features corresponding to quasi-Brillouin zones (qBZ) formed when the system's periodicity becomes ill-defined. Comparing our measurements with theoretical models, we provide the first experimental mapping of the qBZs as a function of angular alignment. Our results establish a direct experimental link between moir\'e interference and qBZ formation, opening new avenues for engineering electronic structures in multi-aligned 2D heterostructures.

cond-mat.mes-hall↗

arXiv2025

Robust quantum Hall resistance standard from uniform wafer-scale epitaxial graphene on SiC

We report high-precision resistance measurements on quantum Hall resistance devices fabricated from uniform epitaxial graphene grown by propane-hydrogen chemical vapor deposition on a two-inch silicon carbide substrate. Through molecular doping, we achieve a low carrier density regime ($n_\mathrm s < $ 1.5 \textperiodcentered 10$^{11}$ cm$^{-2}$) combined with high mobility ($\upmu \geq$ 6000 cm$^2$ V$^{-1}$ s$^{-1}$) at low temperature. Accurate quantization of the Hall resistance is demonstrated at magnetic flux densities as low as 3.5 T, temperatures up to 8 K, and measurement currents up to 325 $\upmu$A, with relative measurement uncertainties of a few parts per billion. A stability diagram mapping dissipation as a function of temperature and current provides insight into optimal doping conditions that maximize the breakdown current. All measurements were carried out in a pulse-tube-based cryomagnetic system, enabling simplified and continuous operation of the quantum Hall resistance standard without liquid helium consumption.

cond-mat.mes-hall↗

arXiv2024

Magnetic memory and distinct spin populations in ferromagnetic Co3Sn2S2

Co3Sn2S2, a ferromagnetic Weyl semi-metal with Co atoms on a kagome lattice, has generated much recent attention. Experiments have identified a temperature scale below the Curie temperature. Here, we find that this magnet keeps a memory, when not exposed to a magnetic field sufficiently large to erase it. We identify the driver of this memory effect as a small secondary population of spins, whose coercive field is significantly larger than that of the majority spins. The shape of the magnetization hysteresis curve has a threshold magnetic field set by the demagnetizing factor. These two field scales set the hitherto unidentified temperature scale, which is not a thermodynamic phase transition, but a crossing point between meta-stable boundaries. Global magnetization is well defined, even when it is non-uniform, but drastic variations in local magnetization point to a coarse energy landscape, with the thermodynamic limit not achieved at micrometer length scales.

cond-mat.mtrl-sci↗

arXiv2023

Observation of non-Hermitian topology in a multi-terminal quantum Hall device

Quantum devices characterized by non-Hermitian topology are predicted to show highly robust and potentially useful properties, but realizing them has remained a daunting experimental task. This is because non-Hermiticity is often associated with gain and loss, which would require precise tailoring to produce the signatures of nontrivial topology. Here, instead of gain/loss, we use the nonreciprocity of the quantum Hall edge states to directly observe non-Hermitian topology in a multi-terminal quantum Hall ring. Our transport measurements evidence a robust, non-Hermitian skin effect: currents and voltages show an exponential profile, which persists also across Hall plateau transitions away from the regime of maximum non-reciprocity. Our observation of non-Hermitian topology in a quantum device introduces a scalable experimental approach to construct and investigate generic non-Hermitian systems.

cond-mat.mes-hall↗

arXiv2019

Chiral domain walls of Mn$_3$Sn and their memory

Magnetic domain walls are topological solitons whose internal structure is set by competing energies which sculpt them. In common ferromagnets, domain walls are known to be of either Bloch or Néel types. Little is established in the case of Mn$_3$Sn, a triangular antiferromagnet with a large room-temperature anomalous Hall effect, where domain nucleation is triggered by a well-defined threshold magnetic field. Here, we show that the domain walls of this system generate an additional contribution to the Hall conductivity tensor and a transverse magnetization. The former is an electric field lying in the same plane with the magnetic field and electric current and therefore a planar Hall effect. We demonstrate that in-plane rotation of spins inside the domain wall would explain both observations and the clockwise or anticlockwise chirality of the walls depends on the history of the field orientation and can be controlled.

cond-mat.str-el↗

arXiv2017

Superfluid density and carrier concentration across a superconducting dome: the case of SrTi$_{1-x}$Nb$_{x}$O$_{3}$

We present a study of the lower critical field, \hc1, of \STO as a function of carrier concentration with the aim of quantifying the superfluid density. At low carrier concentration (i.e. the underdoped side), superfluid density and the carrier concentration in the normal state are equal within experimental margin. A significant deviation between the two numbers starts at optimal doping and gradually increases with doping. The inverse of the penetration depth and the critical temperature follow parallel evolutions as in the case of cuprate superconductors. In the overdoped regime, the zero-temperature superfluid density becomes much lower than the normal-state carrier density before vanishing all together. We show that the density mismatch and the clean-to-dirty crossover are concomitant. Our results imply that the discrepancy between normal and superconducting densities is expected whenever the superconducting gap becomes small enough to put the system in the dirty limit. A quantitative test of the dirty BCS theory is not straightforward, due to he multiplicity of the bands in superconducting strontium titanate.

cond-mat.supr-con↗

arXiv2017

A comparative study of resists and lithographic tools using the Lumped Parameter Model

A comparison of the performance of high resolution lithographic tools is presented here. We use extreme ultraviolet interference lithography, electron beam lithography, and He ion beam lithography tools on two different resists that are processed under the same conditions. The dose-to-clear and the lithographic contrast are determined experimentally and are used to compare the relative efficiency of each tool. The results are compared to previous studies and interpreted in the light of each tool-specific secondary electron yield. In addition, the patterning performance is studied by exposing dense line/spaces patterns and the relation between critical dimension and exposure dose is discussed. Finally, the Lumped Parameter Model is employed in order to quantitatively estimate the critical dimension of line/spaces, using each tool specific aerial image. Our implementation is then validated by fitting the model to the experimental data from interference lithography exposures, and extracting the resist contrast.

physics.chem-ph↗

arXiv2013

Ergodic vs diffusive decoherence in mesoscopic devices

We report on the measurement of phase coherence length in a high mobility two-dimensional electron gas patterned in two different geometries, a wire and a ring. The phase coherence length is extracted both from the weak localization correction in long wires and from the amplitude of the Aharonov-Bohm oscillations in a single ring, in a low temperature regime when decoherence is dominated by electronic interactions. We show that these two measurements lead to different phase coherence lengths, namely $L_Φ^\mathrm{wire}\propto T^{-1/3}$ and $L_Φ^\mathrm{ring}\propto T^{-1/2}$. This difference reflects the fact that the electrons winding around the ring necessarily explore the whole sample (ergodic trajectories), while in a long wire the electrons lose their phase coherence before reaching the edges of the sample (diffusive regime).

cond-mat.mes-hall↗

arXiv2011

Quasi one-dimensional transport in single GaAs/AlGaAs core-shell nanowires

We present an original approach to fabricate single GaAs/AlGaAs core-shell nanowire with robust and reproducible transport properties. The core-shell structure is buried in an insulating GaAs overlayer and connected as grown in a two probe set-up using the highly doped growth substrate and a top diffused contact. The measured conductance shows a non-ohmic behavior with temperature and voltage-bias dependences following power laws, as expected for a quasi-1D system.

cond-mat.mtrl-sci↗

arXiv2010

Quantum Coherence at Low Temperatures in Mesoscopic Systems: Effect of Disorder

We study the disorder dependence of the phase coherence time of quasi one-dimensional wires and two-dimensional (2D) Hall bars fabricated from a high mobility GaAs/AlGaAs heterostructure. Using an original ion implantation technique, we can tune the intrinsic disorder felt by the 2D electron gas and continuously vary the system from the semi-ballistic regime to the localized one. In the diffusive regime, the phase coherence time follows a power law as a function of diffusion coefficient as expected in the Fermi liquid theory, without any sign of low temperature saturation. Surprisingly, in the semi-ballistic regime, it becomes independent of the diffusion coefficient. In the strongly localized regime we find a diverging phase coherence time with decreasing temperature, however, with a smaller exponent compared to the weakly localized regime.

cond-mat.mes-hall↗

arXiv2009

Towards a monolithic optical cavity for atom detection and manipulation

We study a Fabry-Perot cavity formed from a ridge waveguide on a AlGaAs substrate. We experimentally determined the propagation losses in the waveguide at 780 nm, the wavelength of Rb atoms. We have also made a numerical and analytical estimate of the losses induced by the presence of the gap which would allow the interaction of cold atoms with the cavity field. We found that the intrinsic finesse of the gapped cavity can be on the order of F ~ 30, which, when one takes into account the losses due to mirror transmission, corresponds to a cooperativity parameter for our system C ~ 1.

quant-ph↗

arXiv2006

Dimensional crossover in quantum networks: from macroscopic to mesoscopic Physics

We report on magnetoconductance measurements of metallic networks of various sizes ranging from 10 to $10^{6}$ plaquettes, with anisotropic aspect ratio. Both Altshuler-Aronov-Spivak (AAS) $h/2e$ periodic oscillations and Aharonov-Bohm (AB) $h/e$ periodic oscillations are observed for all networks. For large samples, the amplitude of both oscillations results from the incoherent superposition of contributions of phase coherent regions. When the transverse size becomes smaller than the phase coherent length $L_ϕ$, one enters a new regime which is phase coherent (mesoscopic) along one direction and macroscopic along the other, leading to a new size dependence of the quantum oscillations.

cond-mat.mes-hall↗

arXiv2006

Experimental Test of the Numerical Renormalization Group Theory for Inelastic Scattering from Magnetic Impurities

We present measurements of the phase coherence time \tauphi in quasi one-dimensional Au/Fe Kondo wires and compare the temperature dependence of \tauphi with a recent theory of inelastic scattering from magnetic impurities (Phys. Rev. Lett. 93, 107204 (2004)). A very good agreement is obtained for temperatures down to 0.2 $T_K$. Below the Kondo temperature $T_K$, the inverse of the phase coherence time varies linearly with temperature over almost one decade in temperature.

cond-mat.mes-hall↗

arXiv2005

Atom chips in the real world: the effects of wire corrugation

We present a detailed model describing the effects of wire corrugation on the trapping potential experienced by a cloud of atoms above a current carrying micro wire. We calculate the distortion of the current distribution due to corrugation and then derive the corresponding roughness in the magnetic field above the wire. Scaling laws are derived for the roughness as a function of height above a ribbon shaped wire. We also present experimental data on micro wire traps using cold atoms which complement some previously published measurements and which demonstrate that wire corrugation can satisfactorily explain our observations of atom cloud fragmentation above electroplated gold wires. Finally, we present measurements of the corrugation of new wires fabricated by electron beam lithography and evaporation of gold. These wires appear to be substantially smoother than electroplated wires.

physics.atom-ph↗

arXiv2005

Direct measurement of the phase coherence length in a GaAs/GaAlAs square network

The low temperature magnetoconductance of a large array of quantum coherentloops exhibits Altshuler-Aronov-Spivak oscillations which periodicitycorresponds to 1/2 flux quantum per loop.We show that the measurement of the harmonics content in a square networkprovides an accurate way to determine the electron phase coherence length$L\_ϕ$ in units of the lattice length without any adjustableparameters.We use this method to determine $L\_ϕ$ in a network realised from a 2Delectron gas (2DEG) in a GaAS/GaAlAs heterojunction. The temperaturedependence follows a power law $T^{-1/3}$ from 1.3 K to 25 mK with nosaturation, as expected for 1D diffusive electronic motion andelectron-electron scattering as the main decoherence mechanism.

cond-mat.mes-hall↗

arXiv2004

The role of wire imperfections in micro magnetic traps for atoms

We present a quantitative study of roughness in the magnitude of the magnetic fieldproduced by a current carrying microwire, i.e. in the trapping potential for paramagnetic atoms.We show that this potential roughness arises from deviations in the wire current flow due to geometric fluctuations of the edges of the wire : a measurement of the potentialusing cold trapped atoms agrees with the potential computed from the measurement of the wire edge roughness by a scanning electronmicroscope.

physics.atom-ph↗

arXiv2004

Direct observation of vortices in an array of holes at low temperature: temperature dependance and first visualization of localized superconductivity

A scanning micro superconducting quantum interference device (microSQUID) microscope is used to directly image vortices in a superconducting Al thin film. We observe the temperature dependence of the vortex distribution in a regular defect (hole) array patterned into the Al film. The first direct observation of the localized superconducting state around the holes is shown as well as the effect of the hole size on nucleation of the superconducting state.

cond-mat.supr-con↗

arXiv2000

First observation of Aharonov-Bohm cages in 2-D normal metal networks

We report on magnetoresistance transport measurements performed on a bipartite tiling of rhombus in the GaAs/GaAlAs system. We observe for the first time large amplitude $h/e$ oscillations in this network as compared to the one measured in square lattices of similar size. These oscillations are the signature of a recently predicted localization phenomenon induced by Aharonov-Bohm interferences in this peculiar network.

cond-mat.mes-hall↗