arXiv subjects

Z. Z. Alisultanov

Publications and source records attributed to Z. Z. Alisultanov.

10 recordsLinked to original sources

arXiv2026

Quasi-1D Planar Magnetic Topological Heterostructure

We theoretically introduce a quasi-1D magnetic heterostructure of alternating 2D topological and normal insulator strips. Its low-energy physics is governed by a hybrid Hamiltonian intertwining the Su-Schrieffer-Heeger and Shockley models, with spin-momentum locking and local Zeeman splitting. Symmetry analysis places it in class AIII, characterized by chiral symmetry and a $\mathbb{Z}$ topological invariant. Computing the winding number from the block-off-diagonal structure of the Hamiltonian reveals topological phases characterized by invariants $ν= 0$, $1$, and $2$. Furthermore, a single magnetic defect acts as a sensitive local probe, whose in-gap spectrum provides a spectroscopic fingerprint to distinguish topological phases. Extending the platform to a multilayer geometry uncovers a nonsymmorphic projective symmetry that gives rise to Möbius band topology, with the Brillouin zone compactifying into a Klein bottle. Our work establishes a platform for higher-order topology via heterostructure design and magnetic patterning.

cond-mat.mes-hall↗

arXiv2026

Geometric oscillations of local Hall and Nernst effects in ballistic graphene at weak magnetic fields

We predict a novel class of magnetotransport oscillations in ballistic graphene specific for a ring-shape geometry. Using the Büttiker-Landauer formalism, we analytically obtain the local Hall and Nernst coefficients in the weak-field ballistic regime. These coefficients exhibit pronounced oscillations as functions of both the magnetic field and the angular positions of the measurement probes. The oscillations originate from the discrete set of skipping orbits that geometrically connect the contacts, with resonances occurring when the angular separation between contacts times the radius of the disk equals an integer number of cyclotron diameters. Unlike conventional quantum oscillations in conductivity, this effect is robust at room temperature and can dominate local thermoelectric signals. This geometric control of ballistic flow provides a platform for studying electron hydrodynamics and engineering phase-coherent devices, with potential applications in sensitive terahertz detectors and thermal management systems.

cond-mat.mes-hall↗

arXiv2026

Resonant absorption and linear photovoltaic effect in ferroelectric moiré heterostructures

Twisted bilayers, featuring interfacial ferroelectricity in the form of array of polar domains, combined with incommensurate two-dimensional layers in a single van der Waals heterostructures allows for generation of purely electrostatic moiré superlattice potentials in the latter. We study electronic and optoelectronic properties of such heterostructures composed of graphene stacked with the twisted ferroelectric bilayers and show that doping of graphene substantially affects mini-band structures because of screening of free carriers. We demonstrate that formation of van Hove singularities in density of states modifies linear and second-order responses of the structures leading to resonant absorption and linear photovoltaic effect, respectively. The latter is generated solely by a shift photocurrent, arising only with account of virtual optical transitions, whereas an injection photocurrent is forbidden by symmetry.

cond-mat.mes-hall↗

arXiv2025

Theory of off-diagonal disorder in multilayer topological insulator

We study multilayer topological insulators with random interlayer tunneling, known as off-diagonal disorder. Within the Burkov-Balents model a single Hermitian defect creates a bound state whose energy crosses the middle of the gap in the trivial phase but never in the topological phase; a non-Hermitian defect splits this level yet preserves the same crossing rule, so the effect serves as a local marker of topology. However, the key distinction persists: the bound state crosses zero in the trivial phase but not in the topological phase. Two complementary diagrammatic approaches give matching densities of states for the normal, topological, Weyl and anomalous quantum Hall regimes. Off diagonal disorder inserts bulk states into the gap and can close it: the Weyl phase remains robust under strong disorder, whereas the anomalous quantum Hall phase survives only for weak fluctuations, and the added bulk states shrink the Hall plateau, clarifying experimental deviations. Finally, we analyze edge modes. Uniform disorder shortens their localization length slightly, while Gaussian and Lorentzian disorder enlarge it and in the Gaussian case can even delocalize the edges. Although chirality is maintained, the enhanced overlap permits tunneling between opposite edges and pulls the longitudinal conductance away from its quantized value.

cond-mat.mes-hall↗

arXiv2025

Thermoelectric effects in two-dimensional topological insulators

We explore the nontrivial thermoelectric properties of two-dimensional topological systems. For the Chern insulator, we show that the Seebeck coefficient is fully determined by the Kelvin formula, while the Nernst coefficient vanishes. For a two-dimensional electron gas with Rashba spin-orbit interactions we reveal how the Berry curvature affects the thermoelectric coefficients, and derive the Mott-like equation for thermopower. We predict a strong variation of the thermopower of a two-dimensional topological insulator with time-reversal symmetry in the ballistic and dissipative regimes. The Kelvin formula applies in the ballistic regime, while the Mott formula holds in the dissipative regime. Importantly, in a system with trapezoidal geometry, the combination of ballistic and dissipative regimes leads to the anomalous Nernst effect. Finally, we analyze a two-dimensional Anderson insulator, where edge modes show distinct temperature behavior of the Seebeck coefficient near the weak localization-strong localization transition temperatures. In the trivial phase, the thermopower exhibits a strong power law temperature dependence, while in the topological phase both power law and exponential dependences coexist.

cond-mat.mes-hall↗

arXiv2024

Disorder-Induced Topological Transitions in a Multilayer Topological Insulator

We examine the impact of non-magnetic disorder on the electronic states of a multilayer structure comprising layers of both topological and conventional band insulators. Employing the Burkov-Balents model with renormalized tunneling parameters, we generate phase diagrams correlating with disorder, demonstrating that non-magnetic disorder can induce transitions between distinct topological phases. The subsequent section of our investigation focuses on the scenario where disorder is unevenly distributed across layers, resulting in fluctuations of the interlayer tunneling parameter - termed off-diagonal disorder. Furthermore, we determine the density of states employing the self-consistent single-site diagram technique, expanding the Green function in relation to the interlayer tunneling parameter (locator method). Our findings reveal that off-diagonal disorder engenders delocalized bulk states within the band gap. The emergence of these states may lead to the breakdown of the anomalous quantum Hall effect (AQHE) phase, a phenomenon that has garnered significant attention from researchers in the realm of topological heterostructures. Nonetheless, our results affirm the stability of the Weyl semimetal phase even under substantial off-diagonal disorder.

cond-mat.mes-hall↗

arXiv2023

Pressure-Induced Negative-Positive Magnetoresistance Crossover Near Metal-Insulator Transition in La_{0.8}Ag_{0.1}MnO_{3}

We investigated the effect of high pressure on the field dependences of magnetoresistance (MR) in La_{0.8}Ag_{0.1}MnO_{3} near the metal-insulator transition temperature. Our results showed that an increase in pressure results in a decrease in the magnitude of negative MR. At pressures $P\geqslant5.6$ GPa and magnetic fields up to 4 kOe, we observed a positive MR. However, with a further increase in magnetic field (>4 kOe), the MR again became negative. Therefore, we discovered a "negative-positive" MR crossover induced by high pressure near the transition temperature. We supported our experimental findings with a qualitative theoretical interpretation using the electron-hole model of MR. This theory explains observed the MR sign change.

cond-mat.str-el↗

arXiv2016

Graphene infrared light emitting diode (GILED)

The present Letter proposes a device based on graphene for infrared light emission. It is based on a n- and p-doped monolayer graphene (MGs), with Fermi energies $E_F$ and -$E_F$, respectively, sandwiching a bilayer graphene (BG) with bandgap $Λ=2|eV_g-Δ|\geq 2E_F$, where $V_g$ is the gate voltage across the BG and $Δ$ the sub-lattice energy difference into each layer of the BG. This device works as simple as tuning the gate voltage to decrease the BG bandgap down to $2E_F$; and, once this condition is fulfilled, a current flows from the n-doped MG to the p-doped MG. However, when electrons achieve the other side of the device, i.e., into the p-doped MG, their energies ($E_F$) are much bigger than the holes energies ($-E_F$), and thus these electrons decay emitting infrared photons.

cond-mat.mes-hall↗

arXiv2015

Quantum capacitance oscillations in graphene under crossed magnetic and electric fields

Quantum oscillations of metallic systems at low temperatures is one of the key rules to experimentally access their electronic properties, such as energy spectrum, scattering mechanisms, geometry of Fermi surface and many other features. The importance of these knowledge is enormous, since from these a thorough understanding of anomalous Hall effect, thermopower and Nernst coefficients, just to name a few, is possible; and from those knowledge, a plenty of applications arise as emerging technologies. In this direction, the present contribution focus on a complete description of quantum capacitance oscillations of monolayer and bilayer graphenes under crossed electric and magnetic fields. We found a closed theoretical expression for the quantum capacitance and highlight their amplitude, period and phase - important parameters to access the electronic properties of graphenes. These results open doors for further experimental studies.

cond-mat.mes-hall↗

arXiv2015

Magneto-oscillations on specific heat of graphene monolayer

Measurement of magnetic oscillations on thermodynamic quantities (like magnetization and specific heat), is one of the experimental methods to access the density of states of electronic systems. In the present paper we therefore theoretically explore the oscillatory phenomena on the specific heat of graphenes considering gapped and gapless cases in a quantized magnetic field. Further situations is also considered, as the influence of impurities, Coulomb interaction and phonons. We could then map the magnetic oscillations on the specific heat of graphenes under these constraints and the obtained results are a good starting point and guide for further experimental works.

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