arXiv subjects

Artem V. Tarasov

Publications and source records attributed to Artem V. Tarasov.

4 recordsLinked to original sources

arXiv2026

Magneto-spin-orbit graphene: Chern topology and photoinduced Hall response

Magneto-spin-orbit graphene can host Chern phases due to proximity interactions, but in realistic heterostructures these depend on substrate chemistry, local stacking registry and may be altered by buried-interface reconstruction. Investigation of these effects requires special efforts to take into account the long-range moire patterns that often arise for these heterostructures. We address this question using first-principles calculations and effective four-band models for four out-of-plane magnetized Gr/(Au, Pt)/(Co, Mn) heterostructures in commensurate (2 x 2) and moire (9 x 9) supercells where the latter include misfit dislocations for the Co-based interfaces. The commensurate cells overestimate charge transfer and exaggerate valley asymmetry, whereas moire averaging strongly reduces both effects while preserving sizable spin splittings. The Pt spacer mediates stronger proximity interactions than Au, while replacing Co by Mn substantially changes the balance of the effective exchange interactions in a spacer-dependent manner. Introduction of misfit dislocations into the Co-based structures is selective and tunes the Dirac gap in Gr/Au/Co or spin splittings in Gr/Pt/Co. Graphene in Gr/Pt/Co exhibits effective ferromagnetic Chern phase with C = 2 in all studied supercells. By contrast, the moire models of the other three compositions are ferrimagnetic and topologically trivial, with C = 0. Nevertheless, they exhibit helicity-dependent photoinduced Hall responses, which are strongly enhanced by misfit-dislocation reconstruction in Gr/Au/Co. This work demonstrates that moire-scale stacking controls the effective Chern phase and Hall conductivity, whereas buried-interface defects tune the photoinduced Hall response without changing the topology.

cond-mat.mtrl-sci↗

arXiv2024

Magnetism, heat capacity and electronic structure of EuCd$_2$P$_2$ in view of its colossal magnetoresistance

The mechanism of the peculiar transport properties around the magnetic ordering temperature of semiconducting antiferromagnetic EuCd$_2$P$_2$ is not yet understood. With a huge peak in the resistivity observed above the Néel temperature, $T_{\rm N}=10.6\,\rm K$, it exhibits a colossal magnetoresistance effect. Recent reports on observations of ferromagnetic contributions above $T_{\rm N}$ as well as metallic behavior below this temperature have motivated us to perform a comprehensive characterization of this material, including its resistivity, heat capacity, magnetic properties and electronic structure. Our transport measurements revealed quite different temperature dependence of resistivity with the maximum at $14\,\rm K$ instead of previously reported $18\,\rm K$. Low-field susceptibility data support the presence of static ferromagnetism above $T_{\rm N}$ and show a complex behavior of the material at small applied magnetic fields. Namely, signatures of reorientation of magnetic domains are observed up to $T=16\,\rm K$. Our magnetization measurements indicate a magnetocrystalline anisotropy which also leads to a preferred alignment of the magnetic clusters above $T_{\rm N}$. The momentum-resolved photoemission experiments at temperatures from $24\,\rm K$ down to $2.5\,\rm K$ indicate the permanent presence of a fundamental band gap without change of the electronic structure when going through $T_N$ that is in contradiction with previous results. We performed \textit{ab initio} band structure calculations which are in good agreement with the measured photoemission data when assuming an antiferromagnetic ground state. Calculations for the ferromagnetic phase show a much smaller bandgap, indicating the importance of possible ferromagnetic contributions for the explanation of the colossal magnetoresistance effect in the related EuZn$_2$P$_2$.

cond-mat.str-el↗

arXiv2023

Colossal magnetoresistance in EuZn$_2$P$_2$ and its electronic and magnetic structure

We investigate single crystals of the trigonal antiferromagnet EuZn$_2$P$_2$ ($P\overline{3}m1$) by means of electrical transport, magnetization measurements, X-ray magnetic scattering, optical reflectivity, angle-resolved photoemission spectroscopy (ARPES) and ab-initio band structure calculations (DFT+U). We find that the electrical resistivity of EuZn$_2$P$_2$ increases strongly upon cooling and can be suppressed in magnetic fields by several orders of magnitude (CMR effect). Resonant magnetic scattering reveals a magnetic ordering vector of $q = (0\, 0\, \frac{1}{2})$, corresponding to an $A$-type antiferromagnetic (AFM) order, below $T_{\rm N} = 23.7\,\rm K$. We find that the moments are canted out of the $a-a$ plane by an angle of about $40^{\circ}\pm 10^{\circ}$ degrees and aligned along the [100] in the $a-a$ plane. We observe nearly isotropic magnetization behavior for low fields and low temperatures which is consistent with the magnetic scattering results. The magnetization measurements show a deviation from the Curie-Weiss behavior below $\approx 150\,\rm K$, the temperature below which also the field dependence of the material's resistivity starts to increase. An analysis of the infrared reflectivity spectrum at $T=295\,\rm K$ allows us to resolve the main phonon bands and intra-/interband transitions, and estimate indirect and direct band gaps of $E_i^{\mathrm{opt}}=0.09\,\rm{eV}$ and $E_d^{\mathrm{opt}}=0.33\,\rm{eV}$, respectively, which are in good agreement with the theoretically predicted ones. The experimental band structure obtained by ARPES is nearly $T$-independent above and below $T_{\rm N}$. The comparison of the theoretical and experimental data shows a weak intermixing of the Eu 4$f$ states close to the $Γ$ point with the bands formed by the phosphorous 3$p$ orbitals leading to an induction of a small magnetic moment at the P sites.

cond-mat.str-el↗

arXiv2023

Magnetic Dirac semimetal state of (Mn,Ge)Bi$_2$Te$_4$

For quantum electronics, the possibility to finely tune the properties of magnetic topological insulators (TIs) is a key issue. We studied solid solutions between two isostructural Z$_2$ TIs, magnetic MnBi$_2$Te$_4$ and nonmagnetic GeBi$_2$Te$_4$, with Z$_2$ invariants of 1;000 and 1;001, respectively. For high-quality, large mixed crystals of Ge$_x$Mn$_{1-x}$Bi$_2$Te$_4$, we observed linear x-dependent magnetic properties, composition-independent pairwise exchange interactions along with an easy magnetization axis. The bulk band gap gradually decreases to zero for $x$ from 0 to 0.4, before reopening for $x>0.6$, evidencing topological phase transitions (TPTs) between topologically nontrivial phases and the semimetal state. The TPTs are driven purely by the variation of orbital contributions. By tracing the x-dependent $6p$ contribution to the states near the fundamental gap, the effective spin-orbit coupling variation is extracted. As $x$ varies, the maximum of this contribution switches from the valence to the conduction band, thereby driving two TPTs. The gapless state observed at $x=0.42$ closely resembles a Dirac semimetal above the Neel temperature and shows a magnetic gap below, which is clearly visible in raw photoemission data. The observed behavior of the Ge$_x$Mn$_{1-x}$Bi$_2$Te$_4$ system thereby demonstrates an ability to precisely control topological and magnetic properties of TIs.

cond-mat.mtrl-sci↗