Condensed Matter Physics Seminars

Atomic and molecular spins on surfaces offer a uniquely powerful platform to investigate magnetism and quantum behaviour at the ultimate length scale, where adsorption geometry, symmetry, and coupling to the environment can be engineered one building block at a time. This controllability makes surface spins an ideal testbed to explore coherent spin phenomena and identify practical strategies to preserve coherence while maintaining fast, local addressability and scalability.

In this talk, I will present how we drive and coherently control molecular and atomic spins on surfaces using electron spin resonance (ESR). First, I will introduce our surface-sensitive ensemble ESR spectrometer, which offers low-temperature X-band operation under ultra-high-vacuum conditions on single-crystal surfaces, with sensitivity reaching below a single molecular layer [1]. We employ this setup to explore how the spins of metal–organic complexes are altered when interfaced with solid-state surfaces. Using ESR and surface characterisation, we identify decoupling strategies to preserve the YPc₂ radical spin from quenching in close proximity to a metallic substrate, highlighting the central role of interfacial hybridisation in spin protection [2]. In contrast, for the molecular spin-qubit candidate FluTi(CoT) [3], where the spin is localised on the metal centre, we observe a robust spin response even in contact with metal surfaces. Moreover, the anisotropy of its g-tensor provides a direct spectroscopic fingerprint to distinguish molecular orientations within a single layer.

In the second part, I will move to the single-spin regime and discuss all-electrical ESR scanning tunnelling microscopy (ESR-STM) of individual Er atoms on MgO/Ag(100) [4], where the lanthanide ground state can be engineered to couple efficiently to microwaves [5]. We demonstrate coherent manipulation with sub-GHz Rabi frequencies, an unusually fast regime for a 4f spin system, establishing that atoms on surfaces can enable highly efficient coherent drive beyond traditional approaches. By exploiting atomic-precision assembly and symmetry control at the adsorption complex, this platform provides a clean route to study and optimise the microscopic mechanisms that set driving efficiency and coherence in surface-based atomic qubits.

References
_{[1] F. H. Cho et al., Rev. Sci. Instrum. 95, 063904 (2024). [2] S. Oh et al., Nanoscale 17, 22163 (2025). [3] S. Wisbeck et al., Chem. Sci. 15, 14390 (2024). [4] S. Reale et al., Nat. Commun. 15, 5289 (2024). [5] S. Reale et al., Phys. Rev. B 107, 045427 (2023).}

With Moore’s law approaching its physical limit, beyond-CMOS concepts are needed to address the rising power demands of Internet of Things (IoT) and artificial intelligence (AI) systems [1]. Among these concepts, magnetoelectric spin-orbit (MESO) logic offers a promising route by harnessing electric-field control of magnetism via multiferroics [2]. The room-temperature multiferroic BiFeO₃ is central to this approach as a magnetoelectric medium due to the coupling between its antiferromagnetic spin cycloid and ferroelectric polarization. However, the coexistence of multiple ferroelectric variants in bulk crystals [3] and thin films [4,5] leads to complex switching pathways. Achieving deterministic, energy-efficient operation therefore requires stabilization of ferroelectric-domain-wall-free, single-variant BiFeO₃ that enables reproducible magnetoelectric control.

In this talk, I will present two parts. First, I will show how we simplified the multiferroic landscape of epitaxial BiFeO₃ thin films by engineering them into single-domain variants through anisotropic-strain strategies. These single-domain systems allowed us to identify the fundamental limit of the magnetoelectric interaction and enabled narrow-band THz emission from this configuration [6,7]. The second part revolves around the deterministic electric-field control of ferroelectric polarization in substrate-vicinality-driven single ferroelectric variants (P) as well as single spin-cycloid propagation directions (k). In these heterostructures, we achieved nonvolatile, and deterministic toggle switching between two distinct antiferromagnetic states [8]. This heterostructure provides a promising platform for magnetoelectric-based devices, advancing the development of MESO technology toward practical applications.

References:

_{[1] G. E. Moore: Electronics 38, 8 (1965); [2] S. Manipatruni, et. al., Nat. Phys., 14, 338 (2018); [3] JT. Heron, et. al., Nat., 516, 370 (2014); [4] A. Haykal, et. al., Nat. Commun. 11, 1704 (2020); [5] P. Dufour*, A. Abdelsamie*, et. al., Nano Lett. 23, 9073 (2023).; [6] A. Abdelsamie, et. al., Appl. Phys. Lett. 24, 242902 (2024); [7] S. Massabeau, A. Abdelsamie, et. al., submitted (2025); [8] A. Abdelsamie, et. al., under review (2026).}

Operando electrochemical characterisation aims to reveal catalytic mechanisms under working conditions in reactions such as electrochemical CO2 reduction and water splitting. However, many operando measurements are still performed under conditions that differ substantially from those used for catalytic performance evaluation. First, operando measurements are often conducted at relatively low current densities, whereas product selectivity is evaluated at much higher, practically relevant current densities. Second, operando measurements are commonly performed in H-cells or modified flow cells, while catalytic selectivity is often assessed in fundamentally different reaction environments, such as practical flow-cell or membrane-electrode-assembly systems. As a result, the interface probed during operando measurements may not be the same interface that governs catalytic performance under realistic operating conditions. This presentation discusses strategies to make operando electrochemical characterisation more truly operando by bridging the gap between mechanistic measurements and practical reaction environments. I will highlight our first demonstration of operando proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS) for electrochemical CO2 reduction and its subsequent development for quantitative, time-resolved detection of complex intermediates and products under operating conditions. I will then present recent advances in operando Raman spectroscopy under practically relevant electrochemical conditions, enabling direct observation of catalyst surface restructuring and evolution of the local interfacial chemical environment. Finally, I will discuss data analysis strategies developed for these measurements to more clearly resolve mechanistic evolution and improve the reliability of structure–performance interpretation under real operating conditions.

Electrocaloric cooling is an emerging solid-state refrigeration technology that offers low energy consumption, high efficiency, and operation without greenhouse-gas refrigerants. It relies on ferroelectric materials, in which an applied electric field induces a reversible phase transition, resulting in heat absorption and release. In recent years, multilayer ceramic capacitors, or MLCCs, have attracted significant attention as a promising platform for electrocaloric cooling because they can generate high electric fields within a compact geometry. However, high-performance EC devices still mainly rely on lead scandium tantalate, which contains toxic lead as well as relatively expensive elements such as scandium and tantalum. At the same time, commercial lead-free barium titanate-based MLCCs are not optimized for electrocaloric cooling, particularly in terms of their thermal mass, heat transfer, and electrocaloric performance. I will first present recent advances in electrocaloric cooling, including various materials and laboratory-scale prototypes. Then, I will show our recent progress in developing lead-free, manganese-doped barium strontium titanate MLCCs with a protective-layer-free architecture, using an industrially scalable fabrication process. The resulting device achieves both a higher regeneration factor and a higher specific cooling power compared with state-of-the-art lead scandium tantalate-based prototypes. These results demonstrate the potential of scalable, lead-free MLCC technology for high-performance electrocaloric cooling. Finally, I will discuss possible approaches to further enhance the cooling performance of electrocaloric systems and improve their compatibility with practical applications.

The cell plasma membrane and its underlying actin cytoskeleton are the central processing platform for any signalling going into or out of the cell. Growing evidence highlights that mechanical forces are driving signalling and that local membrane organisation is driven by actin cytoskeleton dynamics. Our focus lies to understand how the force generating machinery of the cell cortex, actin filaments and motor proteins, govern and regulate the mechanical properties of the cell membrane and dynamics of cell membrane components, and vice versa, how membrane organisation and signalling events feed-back to the regulation of the cortex machinery. Using reconstituted minimal systems of the membrane – cortex composite, we shed light on the physical mechanisms that govern the active cell membrane organisation. We use quantitative imaging approaches, controlled mechanical and biochemical manipulations and work with theoretical physicists to understand how cells might use the active cell cortex to locally and temporally alter membrane-protein organisation in the cell plasma membrane. In a second part, we discuss how simplified cell surface mimicking substrates offer insights into the cell cortex dynamics during E-cadherin mediated cell-cell adhesion.

Nearly half of the world’s CO₂ emissions can be attributed to heating and cooling [1]. This is primarily due to heating with natural gas and cooling with compression of greenhouse gases, which are neither environmentally friendly nor energy efficient. Therefore there is great interest in developing alternative technologies that can replace these gas-based environmentally damaging systems [2,3]. Barocaloric materials are at the core of novel solid-state heat-pump technologies [4]. During this talk I will describe our work on mechanically responsive barocaloric materials, and present our recent advances on barocaloric systems for heating and cooling applications.

_{[1] Climate change: science and solutions low-carbon heating and cooling, Royal Society, 2021.
[2] X. Moya, S. Kar-Narayan and N. D. Mathur, Nature Materials 13, 439 (2014).
[3] X. Moya and N. D. Mathur, Science 370, 797 (2020).
[4] www.barocal.com.}