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Signatures of Spin Coherence in Chiral Coupled Quantum Dots
Authors:
Hanna T. Fridman,
Rotem Malkinson,
Amir Hen,
Shira Yochelis,
Yossi Paltiel,
Nir Bar-gill
Abstract:
Chiral-induced spin selectivity (CISS) enables spin selectivity of charge carriers in chiral molecular systems without magnetic materials. While spin selectivity has been widely investigated, its quantum coherence has not yet been explored. Here, we investigate spin-dependent photoluminescence (PL) dynamics in multilayer quantum-dot (QD) assemblies coupled by chiral linkers. Using circularly polar…
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Chiral-induced spin selectivity (CISS) enables spin selectivity of charge carriers in chiral molecular systems without magnetic materials. While spin selectivity has been widely investigated, its quantum coherence has not yet been explored. Here, we investigate spin-dependent photoluminescence (PL) dynamics in multilayer quantum-dot (QD) assemblies coupled by chiral linkers. Using circularly polarized excitation in the presence of an external magnetic field, we observe a pronounced modulation of the PL lifetime that depends on the magnetic field magnitude and geometry. The lifetime difference between left- and right-circularly polarized excitations exhibits a field-angle dependence, consistent with spin precession driven by the transverse magnetic-field component relative to the chiral axis. A model incorporating coupled spin precession and decay processes reproduces the experimental trends. These results establish chiral QD assemblies as a room-temperature platform for probing quantum coherent manifestations of the CISS effect, with implications for spintronic and quantum technologies.
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Submitted 8 January, 2026;
originally announced January 2026.
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Spin and Orbital Magnetism in UH2 Thin Films Studied by X-ray Magnetic Circular Dichroism
Authors:
Evgenia A. Tereshina-Chitrova,
Mykhaylo Paukov,
Oleksandra Koloskova,
Amir Hen,
Fabrice Wilhelm,
Lukas Horak,
Mayerling Martinez Celis,
Miroslav Cieslar,
Ladislav Havela,
Andrei Rogalev,
Thomas Gouder
Abstract:
Uranium dihydride UH2 is a metastable phase unknown in bulk form but accessible through thin-film synthesis. We prepared UH2 films by reactive dc sputtering on CaF2(001) or Si(001) substrates, the latter equipped with a Mo buffer layer to suppress a U-Si interdiffusion. On CaF2, UH2 adopts the fluorite-type structure with a near-[1 1 1] out-of-plane texture, four rotational domains, and a lattice…
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Uranium dihydride UH2 is a metastable phase unknown in bulk form but accessible through thin-film synthesis. We prepared UH2 films by reactive dc sputtering on CaF2(001) or Si(001) substrates, the latter equipped with a Mo buffer layer to suppress a U-Si interdiffusion. On CaF2, UH2 adopts the fluorite-type structure with a near-[1 1 1] out-of-plane texture, four rotational domains, and a lattice parameter a = 539 +- 3 pm without measurable strain, whereas the Mo-buffered film is polycrystalline. X-ray photoelectron spectroscopy confirmed complete hydrogenation and minimal oxidation. Magnetization and XMCD measurements show ferromagnetic ordering with Curie temperatures of 120-130 K and a uranium 5f moment of 0.9 μB/U, dominated by the orbital contribution (μL ~ 1.4 μB, μS ~ -0.5 μB), in a good agreement with GGA+U computations, which otherwise overestimate absolute values of the spin and orbital components. The slightly reduced moment in thinner CaF2-supported films is attributed to surface U(IV) species. These results demonstrate that thin-film synthesis enables stabilization of UH2 and direct probing of 5f magnetism, opening pathways toward higher uranium hydrides and interface-engineered actinide systems.
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Submitted 8 December, 2025;
originally announced December 2025.
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Quantum Imaging of Ferromagnetic van der Waals Magnetic Domain Structures at Ambient Conditions
Authors:
Bindu,
Amandeep Singh,
Amir Hen,
Lukas Drago Cavar,
Sebastian Maria Ulrich Schultheis,
Shira Yochelis,
Yossi Paltiel,
Andrew F. May,
Angela Wittmann,
Mathias Klaui,
Dmitry Budker,
Hadar Steinberg,
Nir Bar-Gill
Abstract:
Recently discovered 2D van der Waals magnetic materials, and specifically Iron-Germanium-Telluride ($\rm Fe_{5}GeTe_{2}$), have attracted significant attention both from a fundamental perspective and for potential applications. Key open questions concern their domain structure and magnetic phase transition temperature as a function of sample thickness and external field, as well as implications fo…
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Recently discovered 2D van der Waals magnetic materials, and specifically Iron-Germanium-Telluride ($\rm Fe_{5}GeTe_{2}$), have attracted significant attention both from a fundamental perspective and for potential applications. Key open questions concern their domain structure and magnetic phase transition temperature as a function of sample thickness and external field, as well as implications for integration into devices such as magnetic memories and logic. Here we address key questions using a nitrogen-vacancy center based quantum magnetic microscope, enabling direct imaging of the magnetization of $\rm Fe_{5}GeTe_{2}$ at sub-micron spatial resolution as a function of temperature, magnetic field, and thickness. We employ spatially resolved measures, including magnetization variance and cross-correlation, and find a significant spread in transition temperature yet with no clear dependence on thickness down to 15 nm. We also identify previously unknown stripe features in the optical as well as magnetic images, which we attribute to modulations of the constituting elements during crystal synthesis and subsequent oxidation. Our results suggest that the magnetic anisotropy in this material does not play a crucial role in their magnetic properties, leading to a magnetic phase transition of $\rm Fe_{5}GeTe_{2}$ which is largely thickness-independent down to 15 nm. Our findings could be significant in designing future spintronic devices, magnetic memories and logic with 2D van der Waals magnetic materials.
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Submitted 27 July, 2025;
originally announced July 2025.
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Probing Magnetic Sublattices in Multiferroic Ho$_{0.5}$Nd$_{0.5}$Fe$_{3}$(BO$_{3}$)$_{4}$ Single Crystal using X-ray Magnetic Circular Dichroism
Authors:
Mikhail Platunov,
Natalia Kazak,
Viacheslav Dudnikov,
Fabrice Wilhelm,
Amir Hen,
Vadim Diadkin,
Iurii Dovgaliuk,
Alexey Bosak,
Vladislav Temerov,
Irina Gudim,
Yurii Knyazev,
Sergey Gavrilkin,
Andrei Rogalev,
Sergei Ovchinnikov
Abstract:
Using element-specific X-ray magnetic circular dichroism (XMCD) technique we have studied different magnetic sublattices in a multiferroic Ho$_{0.5}$Nd$_{0.5}$Fe$_{3}$(BO$_{3}$)$_{4}$ single crystal. The XMCD measurements at the \emph{L}$_{2,3}$-edges of Ho and Nd, and at the Fe \emph{K}-edge have been performed at \emph{T}=2~K under a magnetic field up to 17~T applied along the trigonal \emph{c}-…
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Using element-specific X-ray magnetic circular dichroism (XMCD) technique we have studied different magnetic sublattices in a multiferroic Ho$_{0.5}$Nd$_{0.5}$Fe$_{3}$(BO$_{3}$)$_{4}$ single crystal. The XMCD measurements at the \emph{L}$_{2,3}$-edges of Ho and Nd, and at the Fe \emph{K}-edge have been performed at \emph{T}=2~K under a magnetic field up to 17~T applied along the trigonal \emph{c}-axis as well as in the basal \emph{ab}-plane. All three magnetic sublattices are shown to undergo a spin-reorientation transition under magnetic field applied along the \emph{c}-axis. On the contrary, when magnetic field is applied in the \emph{ab}-plane only the holmium atoms exhibit a magnetization jump. Thus, the element-specific magnetization curves revealed the Ho sublattice to be much stronger coupled to the Fe one than the Nd sublattice. The results demonstrate that the Ho$^{3+}$ subsystem plays even more dominant role in magnetic behavior of Ho$_{0.5}$Nd$_{0.5}$Fe$_{3}$(BO$_{3}$)$_{4}$ crystal than in pure HoFe$_{3}$(BO$_{3}$)$_{4}$ crystal.
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Submitted 19 April, 2018;
originally announced April 2018.
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Low temperature magnetic properties of NpNi$_5$
Authors:
A. Hen,
E. Colineau,
R. Eloirdi,
J. -C. Griveau,
N. Magnani,
F. Wilhelm,
A. Rogalev,
J. -P. Sanchez,
A. B. Shick,
I. Halevy,
I. Orion,
R. Caciuffo
Abstract:
We present the result of an extended experimental characterization of the hexagonal intermetallic Haucke compound NpNi$_{5}$. By combining macroscopic and shell-specific techniques, we determine the 5$f$-shell occupation number $n_f$ close to 4 for the Np ions, together with orbital and spin components of the ordered moment in the ferromagnetic phase below T$_C$ = 16 K ($μ_{S}$ = -1.88~$μ_{B}$ and…
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We present the result of an extended experimental characterization of the hexagonal intermetallic Haucke compound NpNi$_{5}$. By combining macroscopic and shell-specific techniques, we determine the 5$f$-shell occupation number $n_f$ close to 4 for the Np ions, together with orbital and spin components of the ordered moment in the ferromagnetic phase below T$_C$ = 16 K ($μ_{S}$ = -1.88~$μ_{B}$ and $μ_{L}$ = 3.91~$μ_{B}$). The apparent coexistence of ordered and disordered phases observed in the Mössbauer spectra is explained in terms of slow relaxation between the components of a quasi-triplet ground state. The ratio between the expectation value of the magnetic dipole operator and the spin magnetic moment ($3\langle T_{z}\rangle/ \langle S_{z}\rangle$ = +1.43) is positive and large, suggesting a localized character of the 5$f$ electrons. The angular part of the spin-orbit coupling ($\langle\vec{\ell}\cdot\vec{s}\rangle$ = -5.55) is close to the value of -6.25 calculated for trivalent Np ions in intermediate coupling approximation. The results are discussed against the prediction of first-principle electronic structure calculations based on the spin-polarized local spin density approximation plus Hubbard interaction, and of a mean field model taking into account crystal field and exchange interactions.
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Submitted 25 July, 2014;
originally announced July 2014.