arXiv subjects

Marek Mihalkovič

Publications and source records attributed to Marek Mihalkovič.

9 recordsLinked to original sources

arXiv2026

Prediction of coherent interfaces between diamond and clathrate structures

Diamond (or its binary zincblende variant)-type structure can form coherent interface with clathrate type II via the common transitional layer known previously as a $(3\times 3)$-dimer-stacking fault (DS) reconstruction of the (111)-diamond surface. The generic $\sim 11\%$ lattice misfit can be eliminated in multicomponent heterostructures such as Ge(diamond)/CsSn(clathrate) or InN(zincblende)/Ge(clathrate). Interface models subjected to ab-initio molecular dynamics annealing are stable up to the temperatures approaching melting point of the constituent systems, and in some studied cases the diamond/clathrate bonding is stronger than the intra-clathrate bonding, as evidenced by simulated crack experiments. Composition-calibrated lattice-matching can stabilize even metastable clathrates as epitaxially grown films on the diamond/zincblende substrate.

cond-mat.mtrl-sci↗

arXiv2026

Reversible non-equilibrium phase transformation in amorphous germanium

First principles molecular dynamics simulations of germanium reveal a reversible liquid-glass transition below the equilibrium melting point with a wide hysteresis loop. Direct calculation of the liquid and amorphous state free energies, enabled by absolute entropy calculations, verify that the transition is first order in character between two metastable phases. These results lend credence to models of explosive recrystallization from amorphous Ge thin films, through a metastable liquid state and finally reaching the low temperature crystalline structure.

cond-mat.mtrl-sci↗

arXiv2026

Atomic structure and formation mechanism of a newly discovered charge density wave in the m=2 monophosphate tungsten bronze

The $m$=2 member of the monophosphate tungsten bronze family has been considered the only one in the family without an electronic instability at low temperature. In this paper, we report the discovery of a charge density wave phase in this compound, with a transition temperature of 290 K and an incommensurate modulation vector \textbf{q}=0.245\textbf{b*}+ $\upxi$\textbf{c*}. The presence of this new phase is confirmed by diffraction and resistivity measurements. Pre-transitional dynamics are investigated using diffuse and inelastic x-ray scattering, revealing a clear Kohn anomaly. We analyze both structural and electronic contributions to the phase transition, providing a comprehensive picture of the mechanism driving this newly identified instability.

cond-mat.str-el↗

arXiv2025

First-Principles Thermodynamics of Al$_{10}$V: An Analytical Treatment of Localized Anharmonic Modes

Many complex intermetallic structures possess cage-like environments that can host additional guest atoms. In Al$_{10}$V, these atoms give rise to low-frequency, localized vibrations (Einstein modes) that dominate the thermodynamic response at low temperature. They become imaginary under volume expansion as temperature rises, invalidating the harmonic approximation. We develop a framework to incorporate these strongly anharmonic vibrational modes into first-principles thermodynamic calculations. By explicitly modeling the cage potential and solving the associated Schrödinger equation numerically, we compute the full anharmonic free energy contribution and demonstrate its impact on thermodynamic phase stability. Our results reproduce key experimental signatures, including the anomalous rise in the thermal expansion coefficient and specific heat at low temperatures, and reveal that the presence of guest atoms is essential to stabilizing the Al$_{10}$V phase at elevated temperatures.

cond-mat.mtrl-sci↗

arXiv2022

Ordered ground state configurations of the asymmetric Wigner bilayer system -- revisited: an unsupervised clustering algorithm analysis

We have re-analysed the rich plethora of ground state configurations of the asymmetric Wigner bilayer system that we had recently published in a related diagram of states [M. Antlanger \textit{et al.}, Phys. Rev. Lett. \textbf{117}, 118002 (2016)], comprising roughly 60~000 state points in the phase space spanned by the distance between the plates and the charge asymmetry parameter of the system. In contrast to this preceding contribution where the classification of the emerging structures was carried out ``by hand'', we have used this time machine learning concepts, notably based on a principal component analysis and a $k$-means clustering approach: using a 30-dimensional feature vector for each emerging structure (containing relevant information, such as the composition of the configuration as well as the most relevant order parameters) we were able to re-analyse these ground state configurations in a considerably more systematic and comprehensive manner than we could possibly do in the previously published classification scheme. Indeed we were now able to identify new structures in previously unclassified regions of the parameter space and could considerably refine the previous classification scheme, identifying thereby a rich wealth of new emerging ground state configurations. Thorough consistency checks confirm the validity of the newly defined diagram of states.

cond-mat.soft↗

arXiv2022

Decagonal Sn clathrate on $d$-Al-Ni-Co

Decagonal quasiperiodic ordering of Sn thin film on $d$-Al-Ni-Co, is shown based on scanning tunneling microscopy (STM), low-energy electron diffraction and density functional theory (DFT). Interestingly, the decagonal structural correlations are partially retained up to a large film thickness of 10 nm grown at a 165$\pm$10 K. The nucleation centers called 'Sn white flowers' identified by STM at submonolayer thickness are recognized as valid patches of the decagonal clathrate structure with low adsorption energies. Due to the excellent lattice matching (to within 1%) between columns of Sn dodecahedra in the clathrate structure and pentagonal motifs at the $d$-Al-Ni-Co surface, the interfacial energy favors clathrate over the competing Sn crystalline forms. DFT study of the Sn/Al-Ni-Co composite model shows good mechanical stability, as shown by the work of separation of Sn from Al-Ni-Co slab that is comparable to clathrate self-separation energy. The relaxed surface terminations of the R$_2$T$_4$ clathrate approximant are in self-similarity correspondence with the motifs observed in the STM images from monolayer to thickest Sn film.

cond-mat.mtrl-sci↗

arXiv2021

Planar defect in approximant: the case of Cu-Al-Sc alloy

The {110} planar defect formed in the Cu-Al-Sc 1/1 approximant has been studied by means of electron microscopy and 6-dimensional analysis. As the displacement vector of the planar defect, 1/2 <τ, 1/τ, 0> has been proposed. Here τ denotes the golden ratio. This vector corresponds to a 6-dimensional translation of type [111000] and also to the c-linkage of Tsai-type clusters. An atomic structure model of the planar defect has been constructed referring to the structural properties of the regular 1/1 approximant; namely truncated triacontahedron framework and embedded clusters. This structural model was validated by the agreement between the observed and simulated HAADF-STEM images. Models of the intersection of two planar defects and the triple point, where three planar defects intersect, were also proposed. All local structures formed at these defects are understood by the concept of so-called canonical cell tiling.

cond-mat.mtrl-sci↗

arXiv2018

Interpretation of some Yb-based valence-fluctuating crystals as approximants to a dodecagonal quasicrystal

The hexagonal ZrNiAl-type (space group: P-62m) and the tetragonal Mo2FeB2-type (space group: P4/mbm) structures, which are frequently formed in the same Yb-based alloys and exhibit physical properties related to valence-fluctuation, can be regarded as approximants of a hypothetical dodecagonal quasicrystal. Using Pd-Sn-Yb system as an example, a model of quasicrystal structure has been constructed, of which 5-dimensional crystal (space group: P12/mmm, aDD=5.66 Å and c=3.72 Å) consists of four types of acceptance regions located at the following crystallographic sites; Yb [00000], Pd[1/3 0 1/3 0 1/2], Pd[1/3 1/3 1/3 1/3 0] and Sn[1/2 00 1/2 1/2]. In the 3-dimensional space, the quasicrystal is composed of three types of columns, of which c-projections correspond to a square, an equilateral triangle and a 3-fold hexagon. They are fragments of two known crystals, the hexagonal α-YbPdSn and the tetragonal Yb2Pd2Sn structures. The model of the hypothetical quasicrystal may be applicable as a platform to treat in a unified manner the heavy fermion properties in the two types of Yb-based crystals.

cond-mat.str-el↗

arXiv2012

Caged clusters in Al$_{11}$Ir$_4$: structural transition and insulating phase

Using pair potentials fitted to an ab--initio database, combined with replica--exchange simulated annealing, we show the complex, quasicrystal-related Al$_{11}$Ir$_4$ compound contains a new version of the "pseudo-Mackay" icosahedral cluster, with non-icosahedral inner Al$_{10}$Ir and/or Al$_9$Ir clusters that exist in various orientations and account for partial occupancies in the reported structure. Two different compositions show first-order transitions to orientationally ordered phases doubling the (cubic) unit cell, which are respectively metallic and insulating.

cond-mat.mtrl-sci↗