arXiv subjects

Nirman Chakraborty

Publications and source records attributed to Nirman Chakraborty.

5 recordsLinked to original sources

arXiv2026

Spectrally Programmable Spin-Polarized Photocurrents in WSe$_2$-NiPS$_3$ Magnetic van der Waals Heterostructures

Efficient generation and control of spin-polarized currents in semiconductors remain central challenges for spin-based electronics, particularly due to impedance mismatch and the reliance on magnetic fields or ferromagnetic contacts. Here, we introduce a materials platform for spectrally programmable spin transport based on a van der Waals heterostructure combining the antiferromagnetic semiconductor NiPS$_3$ with WSe$_2$. In a p-n diode architecture, circularly polarized excitation produces pronounced photoconductive resonances with spin polarization reaching 80% near the Neel temperature and persisting at 30% at room temperature. Remarkably, selected spectral bands retain their polarization sign across the magnetic phase transition, evidencing robust, spectrally protected spin-polarized current generation. Polarization-resolved photogalvanic measurements reveal a dominant circular injection-current mechanism, confirming spin-polarized carrier transport. First-principles calculations show that an applied electric field induces interfacial hybridization and spin-layer locking, giving rise to localized symmetry breaking and enhanced optical absorption while preserving global time-reversal symmetry. These results establish spectral tuning of excitation as a new control knob for spin transport, enabling spin-current generation without magnetic fields or polarization switching. Our findings position magnetic van der Waals heterostructures as a versatile platform for opto-spintronic functionality and spectrally programmable spintronic devices.

cond-mat.mtrl-sci↗

arXiv2026

Localized Exciton Emission with Spontaneous Circular Polarization in NiPS3/WSe2 Heterostructures

Two-dimensional (2D) van der Waals (vdW) heterostructures (HSs) provide a versatile platform for tailoring electronic, optical, and magnetic properties via proximity effects at their interfaces. In this work, we explore the optical response of few-layer NiPS3/WSe2 HSs using low-temperature micro-photoluminescence (μ-PL) and magneto-PL spectroscopy. The HSs exhibit multiple sharp excitonic peaks that do not appear in the individual constituent materials, indicating the emergence of localized intralayer WSe2 excitons confined by interface-induced potentials. Notably, these excitons exhibit spontaneous circular polarization even in the absence of an external magnetic field, suggesting a magnetic proximity effect induced by uncompensated spins at the NiPS3 interface. Magneto-PL measurements further reveal nonlinear Zeeman splitting, consistent with the presence of an interfacial exchange field that alters the valley exciton dynamics. Density functional theory (DFT) calculations confirm the intralayer origin of the PL and reveal interfacial hybridization and spin texture modifications, supporting the experimental findings. These results highlight how combining a 2D semiconductor with a layered antiferromagnet enables control over valley polarization and spin degrees of freedom, offering new opportunities for chiral light sources and magnetically tunable optoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2024

Change in Magnetic Order in NiPS3 Single Crystals Induced by a Molecular Intercalation

Intercalation is a robust method for tuning the physical properties of a vast number of van der Waals (vdW) materials. However, the prospects of using intercalation to modify magnetism in vdWs systems and the associated mechanisms have not been investigated adequately. In this work, we modulate magnetic order in an XY antiferromagnet NiPS3 single crystals by introducing pyridine molecules into the vdWs gap under different thermal conditions. X-ray diffraction measurements indicated pronounced changes in the lattice parameter beta, while magnetization measurements at in-plane and out-of-plane configurations exposed reversal trends in the crystals Neel temperatures through intercalation-de-intercalation processes. The changes in magnetic ordering were also supported by three-dimensional thermal diffusivity experiments. The preferred orientation of the pyridine dipoles within vdW gaps was deciphered via polarized Raman spectroscopy. The results highlight the relation between the preferential alignment of the intercalants, thermal transport, and crystallographic disorder along with the modulation of anisotropy in the magnetic order. The theoretical concept of double-exchange interaction in NiPS3 was employed to explain the intercalation-induced magnetic ordering. The study uncovers the merit of intercalation as a foundation for spin switches and spin transistors in advanced quantum devices.

cond-mat.mtrl-sci↗

arXiv2022

High-resolution surface structure determination from bulk X-ray diffraction data

The key to most surface phenomenon lies with the surface structure. Particularly it is the charge density distribution over surface that primarily controls overall interaction of the material with external environment. It is generally accepted that surface structure cannot be deciphered from conventional bulk X-ray diffraction data. Thus, when we intend to delineate the surface structure in particular, we are technically compelled to resort to surface sensitive techniques like High Energy Surface X-ray Diffraction (HESXD), Low Energy Electron Diffraction (LEED), Scanning Transmission Electron Microscopy (STEM) and Grazing Incidence Small Angle X-ray Scattering (GISAXS). In this work, using aspherical charge density models of crystal structures in different molecular and extended solids, we show a convenient and complementary way of determining high-resolution experimental surface charge density distribution from conventional bulk X-ray diffraction (XRD) data. The usefulness of our method has been validated on surface functionality of boron carbide. While certain surfaces in boron carbide show presence of substantial electron deficient centers, it is absent in others. Henceforth, a plausible correlation between the calculated surface structures and corresponding functional property has been identified.

cond-mat.mtrl-sci↗

arXiv2021

Material surface -- analyte interactions with similar energy rates vary as univariate quadratic function of topological polar surface area of analytes

Material surface - analyte interactions play important roles in numerous processes including gas sensing. However, the effects of topological polar surface area (TPSA) of analytes on surface interactions during gas sensing have been so far largely disregarded. In this work, based on experimental observations on changes in electrical resistance of cadmium sulphide (CdS) due to surface interactions during gas sensing, we found that unexpected univariate quadratic correlation exists between changes in resistance of CdS and TPSA of analytes. Further experiments on four other material systems showed the same trend, revealing a generalized picture of TPSA dependence of surface interactions.

physics.chem-ph↗