arXiv subjects

Andrei Kogan

Publications and source records attributed to Andrei Kogan.

6 recordsLinked to original sources

arXiv2026

Negative magnetoresistance in strained $\alpha$-Sn and $\alpha$-SnGe films in an in-plane magnetic field

To test the hypothesis that the chiral anomaly is responsible for negative magnetoresitance (MR) in \atn{}, we have studied magnetotransport in strained, epitaxial films of pure \aSn{} and the alloy \aSnGe{} that are in the Dirac semimetal and 3D topological insulator state, respectively. We have observed for both states a negative MR with current either parallel or transverse to the in-plane magnetic field, but with a different dependence of MR on $\vec{B}$ strength. Our results are inconsistent with the chiral anomaly and suggest that other mechanisms may be responsible for negative MR in the Dirac/Weyl semimetal phase of \aSn{}. We also discuss several factors in sample design and material quality that may be contributing to the incongruous observations of MR reported in studies of strained \atn{} films.

cond-mat.mtrl-sci↗

arXiv2025

Polycrystalline Morphology and Anomalous Hall Effect in RF-Sputtered Co2MnGa Films

The Heusler compound Co2MnGa is a topological semimetal with intriguing electronic and magnetic properties, making it a promising candidate for spintronic applications. This study systematically investigates the effects of substrate temperature and RF sputtering power on the structure, morphology, and anomalous Hall effect (AHE) in Co2MnGa thin films. Using X-ray diffraction line analysis, we identify variations in film orientation and crystallinity, revealing the emergence of high-index textures at specific growth conditions. Atomic force microscopy imaging provide insight into grain morphology and size distributions demonstrating a correlation between deposition parameters and film texture. Hall transport measurements confirm a strong dependence of AHE on growth conditions, exhibiting a non-monotonic relationship with RF power and temperature. Despite significant variations in microstructure, a striking linear relationship between AHE and the zero-field slope of the Hall resistivity is observed, suggesting an underlying universal mechanism. These findings provide a foundation for investigating the complex interplay of CMG thin film conditions and transport for next-generation magnetic and electronic devices.

cond-mat.mtrl-sci↗

arXiv2014

Dynamic response of a spin-1/2 Kondo singlet

We present a study of spin 1/2 Kondo singlets in single electron transistors under a microwave frequency bias excitation. We compare time-averaged conductance $G$ to predicted universal response with respect to microwave frequency, oscillation amplitude and the Kondo temperature and find a non-adiabatic response when the microwave photon energy $hf$ is comparable to the Kondo temperature $k_B T_K$. We show that our measurements are qualitatively consistent with the predictions for the radiation-induced decoherence rate of the Kondo spin.

cond-mat.str-el↗

arXiv2012

A quantitative study of spin-flip co-tunneling transport in a quantum dot

We report detailed transport measurements in a quantum dot in a spin-flip co-tunneling regime, and a quantitative comparison of the data to microscopic theory. The quantum dot is fabricated by lateral gating of a GaAs/AlGaAs heterostructure, and the conductance is measured in the presence of an in-plane Zeeman field. We focus on the ratio of the nonlinear conductance values at bias voltages exceeding the Zeeman threshold, a regime that permits a spin flip on the dot, to those below the Zeeman threshold, when the spin flip on the dot is energetically forbidden. The data obtained in three different odd-occupation dot states show good quantitative agreement with the theory with no adjustable parameters. We also compare the theoretical results to the predictions of a phenomenological form used previously for the analysis of non-linear co-tunneling conductance, specifically the determination of the heterostructure g-factor, and find good agreement between the two.

cond-mat.mes-hall↗

arXiv2011

Magnetic Splitting of the Zero Bias Peak in a Quantum Point Contact with a Variable Aspect Ratio

We report a zero-bias peak in the differential conductance of a Quantum Point Contact (QPC), which splits in an external magnetic field. The peak is observed over a range of device conductance values starting significantly below $2e^2/h$. The observed splitting closely matches the Zeeman energy and shows very little dependence on gate voltage, suggesting that the mechanism responsible for the formation of the peak involves electron spin. Precision Zeeman energy data for the experiment are obtained from a separately patterned single-electron transistor located a short distance away from the QPC. The QPC device has four gates arranged in a way that permits tuning of the longitudinal potential, and is fabricated in a GaAs/AlGaAs heterostructure containing 2-dimenional electron gas. We show that the agreement between the peak splitting and the Zeeman energy is robust with respect to moderate distortions of the QPC potential. We also show that the mechanism that leads to the formation of the ZBP is different from the conventional Kondo effect found in quantum dots.

cond-mat.mes-hall↗

arXiv2009

Magnetic-Field-Induced Crossover to a Nonuniversal Regime in a Kondo Dot

We have measured the magnetic splitting, $Δ_K$, of a Kondo peak in the differential conductance of a Single-Electron Transistor while tuning the Kondo temperature, $T_K$, along two different paths in the parameter space: varying the dot-lead coupling at a constant dot energy, and vice versa. At a high magnetic field, $B$, the changes of $Δ_K$ with $T_K$ along the two paths have opposite signs, indicating that $Δ_K$ is not a universal function of $T_K$. At low $B$, we observe a decrease in $Δ_K$ with $T_K$ along both paths, in agreement with theoretical predictions. Furthermore, we find $Δ_K/Δ<1$ at low $B$ and $Δ_K/Δ>1$ at high $B$, where $Δ$ is the Zeeman energy of the bare spin, in the same system.

cond-mat.mes-hall↗