arXiv subjects

Alapan Bera

Publications and source records attributed to Alapan Bera.

5 recordsLinked to original sources

arXiv2026

Junction-free polarity-tunable superconducting diode effect enables XNOR logic operation

The realization of the superconducting diode effect (SDE), characterized by non-reciprocal supercurrent, is a major step towards dissipationless logic circuits. A polarity-tunable superconducting diode with high diode efficiency primarily consists of Josephson-junction architectures that couple two superconducting regions via a weak link. Realizing an SDE without a weak-link junction would reduce fabrication complexity, lower electrical noise, and minimize dependence on junction quality. Here, we report an all-vdW, highly efficient, junction-free SDE in NbSe2, enabled by proximity-induced symmetry breaking from a strong uniaxial ferromagnet Fe3GeTe2 (F3GT). Superconducting diode efficiency of up to 30% is achieved at a small magnetic field of 50 mT. A field-free diode rectification effect is realized with diode polarity that is tunable by the F3GT spin polarization. Furthermore, by employing the active-field dependence of the SDE, a two-input exclusive-NOR (XNOR) logic gate operation is demonstrated. The findings highlight the potential utilization of magnetic proximity effect towards realizing junction-free superconducting diodes for high-performance, energy-efficient logic circuits.

cond-mat.supr-con↗

arXiv2026

Room temperature intrinsic anomalous Hall effect in disordered half-metallic ferromagnetic quaternary Heusler alloy CoRuFeSi

Quaternary Heusler alloys offer a versatile platform for engineering magnetic and topological transport phenomena through chemical flexibility and tunable disorder. Here, we report a comprehensive experimental and theoretical investigation of the magnetic, magnetotransport, and anomalous Hall properties of the quaternary Heusler alloy CoRuFeSi. The compound crystallizes in the LiMgPdSn-type structure with significant Co--Ru antisite disorder and exhibits soft ferromagnetism with a saturation magnetization of $4.21~\mu_{\mathrm{B}}/\mathrm{f.u.}$ at low temperature and a Curie temperature well above room temperature. Hall measurements reveal a robust anomalous Hall effect persisting up to 300~K, with an anomalous Hall conductivity of $\sim 74$~S/cm that is nearly temperature independent. Scaling analysis demonstrates that the anomalous Hall response is dominated by the intrinsic Berry-curvature mechanism. First-principles calculations identify CoRuFeSi as a topologically nontrivial nodal-line semimetal in its ordered phase. Incorporation of experimentally relevant Co--Ru antisite disorder redistributes the Berry curvature and quantitatively reproduces the experimentally observed anomalous Hall conductivity, while preserving half-metallicity. These results establish CoRuFeSi as a disorder-tolerant half-metallic ferromagnet with a sizable intrinsic anomalous Hall effect at room temperature, highlighting its potential for spintronic and Hall-based device applications.

cond-mat.mtrl-sci↗

arXiv2025

Common topological origin of longitudinal and transverse magnetoresistance in Fe3GeTe2

In this work, we reveal the coexistence and correlation of a topological cusp anomaly in the planar Hall signal and a spin-flip scattering dominated positive longitudinal magnetoresistance (MR) across the entire temperature range below the Curie point in Fe3GeTe2. This correlation dies out exponentially as the magnetic field is directed away from the ab-plane, resulting in unusually sharp polar angle dependence of longitudinal MR and the Hall response.

cond-mat.mtrl-sci↗

arXiv2025

Spin-reorientation driven topological Hall effect in Fe4GeTe2

Iron-based van der Waals (vdW) ferromagnets with relatively high ordering temperatures are a current research focus due to their significance in fundamental physics and potential applications in spintronics. Competing magnetic interactions and anisotropies can give rise to nontrivial spin textures in these materials, resulting in novel topological features. Fe4GeTe2 (F4GT) is a nearly room-temperature vdW ferromagnet, well known for hosting a spin-reorientation transition (SRT) arising from the interplay of perpendicular magnetic anisotropy (PMA) and shape anisotropy. In this work, we investigate the angle-dependent magneto-transport properties of F4GT single crystals. We report a large topological Hall effect (THE) in a multi-layer F4GT originating from the SRT-driven non-coplanar spin textures. The THE appears at the in-plane orientation of the external magnetic field and persists over a wide range of temperatures around SRT. Additionally, we find a thickness-sensitive THE signal for the c axis orientation of the magnetic field at a low-temperature regime which is associated with a reentrant Lifshitz transition.

cond-mat.mtrl-sci↗

arXiv2024

Anisotropic magnetization dynamics in Fe5GeTe2 at room temperature

The determination of Lande's g-factor and the damping constant is central to extracting crucial information about the spin-spin and spin-orbit interactions in magnetically ordered systems. In insulating compounds based on 3d elements, the spin-orbit interaction can be effectively probed by investigating the ground state of the corresponding free 3d ion within the crystalline environment. For metallic systems, the problem is non-trivial because of additional band structure effects. Here, we investigate the anisotropic magnetization dynamics in bulk single crystalline Fe5GeTe2, a van der Waals 2D itinerant ferromagnet at room temperature, using broadband ferromagnetic resonance spectroscopy. Strikingly, contrary to the results of ab-initio calculations, we do not observe any intrinsic anisotropy of magnetization damping close to room temperature, suggesting diminished role of spin-orbit interaction. However, there is a sizable anisotropy in the Lande's g factor near room temperature which is attributed to anisotropic critical spin fluctuations.

cond-mat.mtrl-sci↗