arXiv subjects

Nguyen Duy Khanh

Publications and source records attributed to Nguyen Duy Khanh.

7 recordsLinked to original sources

arXiv2026

Intra-unit-cell resolved intertwining of multi-$Q$ charge and spin textures in an itinerant skyrmion magnet

The mechanisms stabilizing non-collinear magnetism in centrosymmetric crystals remain unclear, but likely involve spin-spin interactions mediated by itinerant electrons, such as the RKKY interaction. Finite-$Q$ magnetic order may then be accompanied by electronic modulations that are observable using a scanning tunneling microscope. In five successive magnetic phases of GdRu$_{2}$Ge$_{2}$, including two nano-scale skyrmion crystal phases, we show that multi-$Q$ magnetism among Gd 4$f$ spins entails a corresponding multi-$Q$ texture among the Ru 4$d$ orbitals that contribute itinerant electron bands. With atomically-resolved images of each electronic texture's motif, and a simple numerical modeling scheme drawing on the underlying spin structures, we infer their key relationship: The alignment between nearest-neighbor Gd spins tightly correlates with the local density-of-states of the Ru 4$d$ orbitals on the two bond-centered sublattices of the Gd square net. These analyses offer a microscopic view of the atomic-scale intertwining of charge and spin degrees-of-freedom in non-collinear itinerant magnets.

cond-mat.mtrl-sci↗

arXiv2026

Piezomagnetic transport in van der Waals noncoplanar Antiferromagnets

The piezomagnetic effect-strain-induced linear modulation of magnetization, arises in magnets with broken time-reversal symmetry (BTRS), offering a pathway to bidirectional strain-based control of magnetism, which is an essential straintronic and spintronic functionality in solids. Metallic antiferromagnets with BTRS provide an ideal platform to study this effect through transport measurements, yet experimental demonstrations are limited. Van der Waals (vdW) nanomagnets, with their mechanical flexibility, are particularly promising for realizing large piezomagnetic responses and effective transport control. Here we demonstrate piezomagnetic control of electronic transport in nano-devices of the vdW antiferromagnets CoNb$_3$S$_6$ and CoTa$_3$S$_6$, archetypal vdW metals with BTRS that exhibit a spontaneous Hall effect. Applying uniaxial strain linearly modulates both the antiferromagnetic transition temperature and coercive field, consistent with strain-driven tuning of exchange coupling, key signatures of the piezomagnetic effect. Moreover, spontaneous Hall effect is controllable via strain, evidencing piezomagnetic tuning of Berry curvature and its associated geometric transport. These findings establish piezomagnetism as a powerful route to manipulate antiferromagnetic transport, opening avenues for straintronic and spintronic applications in vdW magnetic systems.

cond-mat.mes-hall↗

arXiv2025

Triangular lattice magnet GdGa$_2$ with short-period spin cycloids and possible skyrmion phases

The two-dimensional triangular lattice (TAL) is a model system of magnetic frustration and competing interactions, where skyrmion spin vortices can be induced by a vertical magnetic field $B$. We target the binary compound GdGa$_2$ with an undistorted TAL of Gd$^{3+}$ Heisenberg moments. At higher temperature ($T > 5$ K, $B = 0$, phase II), we reveal the cycloidal spin textures in GdGa$_2$ via resonant elastic X-ray scattering (REXS). Further, a transition with strong magneto-elastic response occurs when cooling into the zero-field ground state ($T < 5$ K, phase I). We also report the thermodynamic phase boundaries of $B$-induced magnetic A-phases, which are suppressed by an in-plane magnetic field and which have enhanced resistivity due to the partial opening of a charge gap. In analogy to Gd$_2$PdSi$_3$ and GdRu$_2$Si$_2$, these phases may represent a superposition of various cycloids, possibly a Néel skyrmion lattice. Our work lays the basis for further studies of the magnetic phase diagram of GdGa$_2$.

cond-mat.str-el↗

arXiv2024

SP-STM study of the multi-Q phases in GdRu2Si2

The two stable surfaces of GdRu2Si2 are studied using spin-polarized scanning tunneling microscopy (SP-STM). Depending on the applied magnetic field different magnetic phases have been found and the presented measurements are in agreement with the respective previously proposed multi-Q spin textures. In particular the multi-Q nature of the zero magnetic field state, for which previous experiments could not rule out the coexistence of single-Q states, can be confirmed by our spin-resolved measurements on the Si-terminated surface. The surfaces of GdRu2Si2 exhibit strong magnetism-induced modulations of the spin-averaged density of states. We find that while the magnetic contribution to the tunnel signal can be clearly identified for the Si-terminated surface this proves to be much more difficult for the Gd-terminated surface. However, the magnetic field dependent spatial modulations on the Gd-terminated surface demonstrate that additional magnetic phase transitions occur for the surface layer compared to those identified for bulk GdRu2Si2 and possible spin textures are presented.

cond-mat.mtrl-sci↗

arXiv2023

Unlocking the Potential of GeS Monolayer: Strain-Enabled Control of Electronic Transports and Exciton Radiative Lifetimes

Monolayer germanium sulfide is gaining significant attention for its exceptional anisotropic electronic conductance, notable excitonic effects, and wide range of potential applications. In our study, we used density functional theory, many-body perturbation theory, and non-equilibrium Green function to investigate electronic transport properties and exciton radiative lifetime of single-layer germanium sulfide. Our theoretical findings showed that applying up to 8 percent compressive strain increased carrier mobility by nearly threefold, and thus, dramatically enhance the device's current intensity. Moreover, we observed that strain engineering allowed fine-tuning of the electron-hole recombination time. At 6 percent tensile strain, the effective radiative lifetime was as short as 19 picoseconds, which is 4.5 times faster than the intrinsic state and 80 times faster than at 8 percent compressive strain. These results highlight the potential of strain engineering to customize the electronic and optical properties of GeS monolayer for specific electronic, optoelectronic, and photovoltaic device requirements

cond-mat.mtrl-sci↗

arXiv2020

Imaging the coupling between itinerant electrons and localised moments in the centrosymmetric skyrmion magnet GdRu2Si2

Magnetic skyrmions were thought to be stabilised only in inversion-symmetry breaking structures, but skyrmion lattices were recently discovered in inversion symmetric Gd-based compounds, spurring questions of the stabilisationmechanism. A natural consequence of a recent theoretical proposal, a coupling between itinerant electrons and localised magnetic moments, is that the skyrmions are amenable to detection using even non-magnetic probes such as spectroscopic-imaging scanning tunnellingmicroscopy (SI-STM). Here SI-STM observations of GdRu$_2$Si$_2$ reveal patterns in the local density of states that indeed vary with the underlying magnetic structures. These patterns are qualitatively reproduced by model calculations which assume exchange coupling between itinerant electrons and localised moments. These findings provide a clue to understand the skyrmion formation mechanism in GdRu$_2$Si$_2$.

cond-mat.str-el↗

arXiv2019

Diversified properties of carbon substitutions in silicene

The theoretical framework, which is built from the first-principles results, is successfully developed for investigating emergent two-dimensional (2D) materials, as it is clearly illustrated by carbon substitution in silicene. Computer coding with the aid of VASP in conjunction with data analysis from the multi-orbital hybridizations [spin configurations] are thoroughly identified from the optimal honeycomb lattices, the atom-dominated energy spectra, and the spatial charge density distributions. The atom and orbital-decomposed van Hove singularities [the net magnetic moments], being very sensitive to the concentration and arrangements of guest atoms. All the binary 2D silicon-carbon compounds belong to the finite- or zero-gap semiconductors, corresponding to the thoroughly/strongly/slightly modified Dirac-cone structures near the Fermi level. Additionally, there are frequent π and σ band crossings, but less anti-crossing behaviors. Apparently, our results indicate the well-defined π and σ bondings.

physics.comp-ph↗