Can spintronics and quantum technologies help to mitigate the energy crisis?

Our modern, highly technological societies have developed within the paradigm of cheap, unlimited energy thanks to fossil fuel extraction. The resulting energy-driven human activity within the closed ecosystem that is Earth has caused multiple planetary boundaries to be exceeded. The wide-ranging impacts on our daily lives of the war-fueled and systemic, long-term energy crises have underscored our societal addiction to energy. Solving this conundrum will almost certainly require a systemic change in our society. This can occur through a combination of temperance, an astute use of existing energy solutions within planetary boundaries, and the development of radically new energy sources — if used wisely.

Molecule-based engines with a quantum advantage are implemented using spin electronics to harvest the most basic form of energy: ambient heat. This groundbreaking interdisciplinary approach enables electrical output above room temperature using nanoscale electrical devices. This opens quantum technologies and spintronics toward disruptive energy applications, as a possible technological game-changer to help mitigate the energy/climate crises.

A multi-lab team of scientists, led by CNRS Senior Researcher Martin Bowen of the Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), has experimentally demonstrated a new, industrially promising approach to harvest the most basic form of energy available: ambient heat.  Heat is the energy wasted in any process that transforms energy from one type to another while generating work. Typical processes involve the cycles of an engine, e.g in cars, refrigerators, etc… The team’s nanoscale devices output around 10nW of dc electrical power at room temperature. The resulting power density is much greater than that using conventional thermoelectric approaches that convert heat gradients into electricity. And in this case, no heat gradient was applied nominally. To achieve this remarkable, counterintuitive result, which was published in the top-tier journal Advanced Materials, the team combined two heretofore non-interacting branches of physics. Quantum thermodynamics is a rapidly developing field that has recently begun reexamining how an engine operates when its components are reduced to excited electrons on single atoms. “At this scale, an engine’s efficiency can be increased by the quantum mechanical interactions between the engine parts. One boost can arise upon measuring the state of a quantum object that acts as the engine’s working substance”, explains Andrew Jordan, a leading quantum thermodynamics theoretician from Chapman University, CA USA.

Typically, these engine cycles are studied using well-controlled, model experiments in which an ensemble of atoms is excited using optical and microwave light. Achieving an electronic counterpart would open promising possibilities for industrialization. However, so far, semiconductor physics approaches have failed to generate a quantum advantage. “This is likely because these engines typically utilize electrons that mostly behave like classical, charged particles without strong quantum interactions,” explains Heiner Linke, a leading quantum engine experimentalist at Lund University in Sweden.

The Bowen team’s solution is to implement the electronic engine using spintronics, a green nanotechnology that exploits the electron’s quantum spin property in addition to its charge. The electron is a Fermion particle, meaning that its spin can exist in one of two possible states… when measured! Between measurements, it can exist in a superposition of these two states. In atomic magnets called paramagnets, this superposition arises from the energy of ambient heat. To harvest this heat, in the team’s design, engine-fueling quantum measurements on the atom-borne spin are performed by electronically connecting the atom to the outside world using electrodes that only allow electrons of one spin type to flow within a narrow energy window. “We believe that quantum measurements, together with other quantum forms of engine fuel, can account for our experimental results”, explains Martin Bowen.

Another quantum engine fuel has been predicted to arise when the spins forming the working substance experience quantum coupling between one another. “Using electron paramagnetic resonance, we discovered that the temperature at which this transition occurs in our chains of atomic magnets matches a change in the temperature dependence of the device’s output power”, adds teammate Bertrand Vileno of the University of Strasbourg.

To build these concept features into a nanoelectronic device, the Bowen team used molecules. Indeed, phthalocyanine molecules are not only quite commonplace, but can host magnetic atoms so as to form spin chains. Also, molecules can more easily be positioned within a vertical nanopillar device than by working with single atoms directly. In addition, over the past 10 years, the Bowen-led IPCMS team has extensively researched — and patented, the spin selective properties of the interface between molecules and simple ferromagnetic metals like iron (which is plentiful). “These latest results, with a 89% spin polarization of the current, showcase how competitive this so-called ‘spinterface’ is relative to other solutions for a spin-selecting device electrode”, comments IPCMS teammate Wolfgang Weber.

Spintronic technology is normally used to encode and transmit information at a low energy cost. “When in contact with a molecular spin chain, the spinterface can help to spintronically encode information onto the chain’s quantum excited state. To promote the thermal fluctuations on the 3-member chain that are to be harvested, it was necessary to weaken the magnetic coupling between them by intercalating monolayers of non-magnetic fullerenes,” explains IPCMS teammate Samy Boukari.

This highlights the need, when designing quantum spintronic engines, to exquisitely control the quality of the heterostructure stack used to make the device.  “Spintronics is already present in hard disk drives and magnetic memories. This makes it a natural vector to industrialize quantum physics… if you can controllably insert quantum spin states within a device on an industrial scale”, adds Martin Bowen. At present, crafting vertical nanopillars that contain molecules remain an academic tour-de-force that only two labs worldwide master the technology for. Both are run by the Centre National de la Recherche Scientifique (CNRS), a French research agency. To transform entire, pristine heterostructures into nanoscale vertical devices without exposing the delicate molecular layer to degrading solvents, the IPCMS nanotechnological process utilizes several steps of macroscale and nanoscale masking. For co-author Armel Bahouka of the laser-cutting firm IREPA LASER near Strasbourg who provided the high-precision shadow-masks, “these results illustrate the potential that technological solutions have to help solve fundamental problems.

A challenging but industrially promising alternative to molecules is to directly work with individual atoms. “Magnetic tunnel junctions comprising a magnesium oxide (MgO) barrier are found in hard drive read heads and magnetic memories. They constitute a prime industrialization vector for spintronic concepts”, reminds Shinji Yuasa, director of the Research Center for Emerging Computing Technologies at the Japanese National Institute of Advanced Industrial Science and Technology (AIST). The major hurdle is now to control the insertion of magnetic atoms into these devices. “Our 10-year collaboration with the IPCMS’s Bowen team has generated precious knowledge into how oxygen vacancies in the MgO barrier drive the device performance. Switching from an information technology to an energy technology use will require mastering how to fill these oxygen vacancies with appropriately placed magnetic atoms”, explains teammate Daniel Lacour of the Institut Jean Lamour in Nancy, France. The Bowen-led team had already reported first results into a more industrializable spintronic quantum engine using MgO magnetic tunnel junctions containing magnetic carbon atoms. What plagued those fortuitous results from 2019 was that energy output was observed on only one device.

The present study bolsters the case for other academic and industrial entities to further explore this new implementation of quantum energy technologies using spintronics. This could require accessing the properties of the spintronic quantum engine’s magnetic atoms while the engine is in operation.  “This very challenging experiment is precisely what the Bowen team unsuccessfully set out to undertake, using their unique prior expertise on device in-operando characterization techniques at our synchrotron facility”, remarks co-author Philippe Ohresser of Synchrotron SOLEIL near Paris, France.

Looking ahead, the Bowen-led team plans to study both the molecular and the MgO approaches, thanks to research consortiums built using fresh funding from French agencies. “This second set of results presents us with the challenge of clarifying which resources are powering these quantum spintronic engines”, remarks project consortium member Robert Whitney, who develops quantum thermodynamical theory at the LPMMC at Grenoble. “Our plans to study the engine’s magnetic atoms while in operation using microwaves could be very insightful”, adds project consortium member Joris Van Slageren, who studies quantum magnetism at the Institute of Physical Chemistry in Stuttgart, Germany. For Martin Bowen, the results are the natural progression of his 20+ year career focus on how spin-polarized currents that run across spintronic devices interact with quantum states. “What’s new is that I now get to interact with a whole new scientific community, and research technological solutions to society’s energy-driven crises. But you’ll be seeing me at Scientist Rebellion protests too, because technology alone won’t avert the major planetary catastrophe in progress.

Published paper:

Quantum advantage in a molecular spintronic engine that harvests thermal fluctuation energy
Advanced Materials


Le comportement ferroélectrique unique du ferrite de gallium enfin démontré

Lire l’article sur le site de l’INC

Référence : Anna Demchenko, Suvidyakumar Homkar, Corinne Bouillet, Christophe Lefèvre, François Roulland, Daniele Preziosi, Gilles Versini, Cédric Leuvrey, Philippe Boullay, XavierDevaux & Nathalie Viart
Unveiling unconventional ferroelectric switching in multiferroic Ga0.6 Fe1.4O3 thin films through multiscale electron microscopy investigations
Acta Materialia 2022

Contact : Nathalie Viart (PR – IPCMS/DCMI)

Ultrafast electron microscopy sees photo-thermal switching of single spin-crossover nanoparticles

Fast photon-induced switching phenomena are the basis of nanodevices that can be operated by laser pulses. Highly promising materials for these applications are spin-crossover (SCO) compounds where a spin transition, e.g., from a diamagnetic s = 0 state to a paramagnetic s = 2 state, changes the bond length between a central metal atom and organic ligands. This transition can be induced by light or heat pulses and changes the size of the molecules. In SCO nanoparticles, reversible size changes can therefore be induced by laser pulses. While macroscopic techniques such as X-ray diffraction or magnetic measurements have already given time-resolved information on bulk ensembles of SCO nanoparticles, expansion effects at the level of individual SCO nanoparticles has so far remained difficult to study.

In a collaboration with researchers at the University of Bordeaux, ultrafast transmission electron microscopy (UTEM) at the IPCMS was applied to reveal the expansion mechanisms of individual SCO particles under nanosecond laser pulses. To facilitate the heat absorption in SCO, gold nanorods were embedded in SCO nanocrystals. Plasmonic heating of the gold rods under laser pulses leads to a controllable transfer of heat to the SCO nanoparticles which then expand rapidly due to the thermal spin transition and subsequently shrink upon cooling. With the ultrafast TEM, we are now able to measure the size of individual particles with high spatial precision and nanosecond time resolution. In this study, it is seen that elliptical SCO crystals with lengths of 200 – 500 nm expand by up to 5% within 10 – 20 ns. It is shown that the presence of plasmonic gold rods speeds up and enhances the expansion of SCO which is governed by collective effects within the nanoparticles.

Reference : Y. Hu, M. Picher, N. M. Tran, M. Palluel, L. Stoleriu, N. Daro, S. Mornet, C. Enachescu, E. Freysz, F. Banhart, G. Chastanet: Photo-Thermal Switching of Individual Plasmonically Activated Spin Crossover Nanoparticle Imaged by Ultrafast Transmission Electron Microscopy, Advanced Materials,  

Understanding energy transfers during photosynthesis

Read more on Actualité Scientifique de l’INP

This work was carried out by a team from Institut de physique et chimie des matériaux de Strasbourg (IPCMS, CNRS/Univ. de Strasbourg) associated with a team from Institut Franche-Comté électronique mécanique thermique et optique – sciences et technologies  (FEMTO-ST, CNRS/COMUE UBFC) and have been published in Nature Chemistry

Référence :

Energy funnelling within multichromophore architectures monitored with subnanometre resolution. S. Cao, A. Rosławska, B. Doppagne, M. Romeo, M. Féron, F. Chérioux, H. Bulou, F. Scheurer, G. Schull, Nature Chemistry. Publié le 24 mai 2021.
DOI : 10.1038/s41557-021-00697-z

Article available on arXiv

Read also the article on “L’Actualité de la Recherche à l’Unistra

Contact : Guillaume Schull | Directeur de recherche CNRS l IPCMS

A new generation of nanocrystals photodetector pushes the boundaries of infrared devices

In a nanocrystal array, transport occurs though hopping mechanism, leading to limited carrier diffusion length, in the 10 to 100 nm range. In the case of HgTe nanocrystals, Lan et al. [1] recently proposed that transport actually occurs between island of strongly coupled nanocrystals. In other word, partly delocalize states are formed within these islands and the bottleneck for conduction becomes the link between these islands. Based on this idea, it becomes of utmost interest to probe transport at the scale of a single island where transport can efficiently occur.

IPCMS recently collaborated with Emmanuel Lhuillier team of INSP (Paris), together with ONERA (Gregory Vincent, Palaiseau) and IEMN (Christophe Delerue, Lille) to address this technological lock. [2]

The authors exploited a smart concept of “nanotrench” electrodes, previously introduced by Dayen et al. [3] and developed at StNano plateform,  to build high aspect ratio electrodes spaced by few nanometers only and expanding over several tenths of µm. Device size resolution is no longer set by the wavelength of the light used for the lithography but rather by device geometrical factor, down to few nanometers resolution.

We observe that for such small devices the light responsivity of a thin film of HgTe nanocrystals exposed to infrared light is strongly enhanced compared to the same film deposited on µm-spaced electrodes. Because the device is small, gain is generated and quantum efficiency above 105 are achieved (corresponding to 105 electrons flowing per absorbed photons). This large gain enables large signal to noise ratio reaching 2×1012 Jones at 200 K for a device with 2.5 µm cut-off wavelength, see figure 1b. This result over-performs the best photodiodes operating at the same wavelength. [2]

Figure 1 a Schematic of the nanotrench device: two electrodes spaced by a few 10s of nm and where the interelectrode gap is infilled by HgTe nanocrystals. b Detectivity (i.e. signal to noise ratio) for a film of HgTe nanocrystals as a function of the electrode spacin

Carefull optoelectronics study and theoretical modeling demonstrates that transport is only driven by the part of the nanocrystal film located within the nanogap, and asset the top-notched performances of our device to the ultimate length scale of the photoactive channel. This result is important since it contradicts a common thought in the field that only photodiodes enable highest performances. The next challenge will be to achieve a matrix of such electrodes.

These result, published in Nature Communications, are important since it contradicts a common thought in the field that only photodiodes enable highest performances. The next challenge will be to achieve a matrix of such electrodes, and to address new generation of photovoltaic cells.

Read our article in


[1] Quantum dot solids showing state-resolved band-like transport, X. Lan et al., Nature materials 19, 323 (2020)

[2] Infrared photoconduction at the diffusion length limit in HgTe nanocrystal arrays.  Chu, A., et al. Nat Commun 12, 1794 (2021).

[3] Nanotrench for nano and microparticle electrical interconnects, J-F. Dayen et al., Nanotechnology 21, 335303 (2010)

Electron spins compatible with magnetic memories

Read the article on “Actualités de l’INC” (in french)

Représentation de la précession du spin (flèches colorées) d’un électron (boules grises) dans le champ moléculaire (flèches pastel) d’un matériau ferromagnétique (boules bleues). © Vautrin et al.

Référence :

Low-energy spin precession in the molecular field of a magnetic thin film Christopher Vautrin, Daniel Lacour, Coriolan Tiusan, Yuan Lu, François Montaigne, Mairbek Chshiev, Wolfgang Weber, Michel Hehn Annalen der Physik, 10 décembre 2020.

Playing atomically thin drums

Measuring vibration-induced strain in an atomically-thin drum

Physicists have demonstrated efficient mechanical strain-mediated coupling between the quantized microscopic vibrations (optical phonons) and the macroscopic oscillations of an atomically-thin membrane made from a graphene monolayer. This fundamental work holds promise for the development of 2D-systems with mechanically tunable light-matter interactions.

Recent progress in photonics, optoelectronics and optomechanics has been enabled by improvements in the quality of low-dimensional materials. Two-dimensional (2D) materials (semiconducting transition metal dichalcogenides (TMD) and graphene) are examples of choice. They display remarkable electronic properties and interact strongly with light. At the same time, 2D materials are lightweight, ultrasensitive nanomechanical systems that are controllable by externally applied strain. Although a variety of opto-electronic devices and nano-mechanical resonators made from 2D materials have been demonstrated, the subtle connections between the microscopic properties (e.g., excitons, phonons, interlayer coupling) of these atomically thin crystals and their macroscopic mechanical figures of merit remain unexplored.

In this work, physicists from Université de Strasbourg and CNRS, in collaboration with the University of Nottingham (UK) demonstrate efficient strain-mediated coupling between microscopic quantum degrees of freedom of a 2D resonator (here the phonons, i.e., the quantized vibrations of the 2D atomic registry) and its macroscopic, flexural modes. This work has been published in Nature Communications.

For their project, the physicists have used circular drums made from pristine graphene monolayers. These one atom thick membranes are suspended over micrometric cavities and capacitively driven by a sinusoidal voltage whose frequency is in the vicinity of a mechanical resonance, as are many “nano-electromechanical systems” (NEMS). The frequency-dependent mechanical response of these drums is monitored using an optical interferometric method, which allows us to probe displacements as small as a few picometers (see Fig. 1a). When the frequency of the actuation matches a resonant mode of the drum (typically a few 107Hz), one observes a maximal displacement, as in any driven oscillator. The specificity of this work is to perform, in operando, an optical measurement of the optical phonon frequency using inelastic light scattering spectroscopy (a technique that is more commonly known as Raman scattering spectroscopy). Optical phonons in graphene have well-defined frequencies near 40 THz, i.e. six orders of magnitude higher than the resonance frequency.

The measurements make use of the same laser beam for interferometric readout of the graphene drum displacement and, at the same time, to locally probe its optical phonon frequencies with a spatial resolution near 1 µm, given by the laser spot size. The optical phonons “emitted” by graphene give rise to sharp peaks in the spectrum of the backscattered light that are shifted relative to the laser line by an amount that directly yields the phonon frequency (Fig. 1b). The resonant motion of the graphene drum leads to tensile strain, i.e. an increase of the lattice parameter that results in a well-defined downshift of the phonon frequency. In the linear regime (that is, when the driven vibrations are harmonic with small amplitudes, typically near 1 nm), the level of dynamically-induced strain falls below the sensitivity of our setup. However, when graphene is driven strongly enough (with amplitudes approaching 10 nm), its oscillations become non-linear and one can measure dynamically-induced strain above 200 ppm (or 0.02 %, see Fig. 1c). This value is anomalously large as it exceeds the strain that would be expected under harmonic oscillations with the same amplitude. This intriguing result sheds new light on the mechanical non-linearities of 2D materials as it may arise from existence of localised strain fields that develop under strong non-linear driving. Although these strain fields could not be resolved in the present study, further spatially-resolved and phase-resolved (i.e., stroboscopic) studies on custom-designed drums may will help clear this interesting question.

Strain-mediated coupling in 2D materials will help develop the blooming field of hybrid optomechanics, which consists in manipulating quantum degrees of freedom (excitons, spins, pseudo-spins,…) coupled to macroscopic mechanical modes. Indeed, nanoresonators made from 2D materials host “built-in” quantum degrees of freedom that can yield enhanced strain-mediated coupling as compared to bulkier systems, e.g., comprising a single quantum emitter implanted in or coupled to a nano-mechanical system. More broadly, the highly tunable light emission and light scattering characteristics of 2D materials pave the way for a novel class of atomically-thin opto-electro-mechanical systems, which will also be ultra-sensitive probes of their nanoscale environment.

a – Sketch of our experiment combining electrostatic actuation, optical readout of the displacement and micro-Raman spectroscopy of a circular graphene drum. The graphene layer is represented by the dark grey dashed line; its flexural motion is sketched with the light grey shade. M, DM, APD represent a mirror, a dichroic mirror, an avalanche photodiode, respectively. Upper inset: optical image of a suspended graphene monolayer (1L) contacted by a Ti/Au lead (scale bar: 2 μm). b – Raman spectra recorded at a non-resonant drive frequency of Ω/2π = 32 MHz (open symbols) and under resonant non-linear driving at 34.3 MHz (filled symbols, vertically flipped for clarity). The G- and 2D-modes correspond to the atomic displacements shown in the lower inset in a. c – (up) Mechanical root mean square (RMS) displacement of a non-linearly driven graphene drum (same as in b) showing a hysteretic behavior. (down) Frequency of the Raman 2D mode recorded during the frequency sweep. The dynamically-induced local strain is deduced directly from the 2D-mode frequency shift and is anomalously large.

More information:

Zhang, X., Makles, K., Colombier, L. et al., Dynamically-enhanced strain in atomically thin resonators. Nature Communications 11, 5526 (2020).

Preprint :

Contact : Stéphane Berciaud, Professor at l’Université de Strasbourg.

Xin Zhang, first author (1st on the left) Stéphane Berciaud (3rd from the left) et Kevin Makles, second author, (on the right)
Read also the article published on the University of Strasbourg’s “L’Actualité de la Recherche” site: