arXiv subjects

Aalok Tiwari

Publications and source records attributed to Aalok Tiwari.

6 recordsLinked to original sources

arXiv2026

Element-Specific Visualization of Layer-Parity and Twist-Dependent Magnetism in CrSBr

Van der Waals (vdW) based antiferromagnets (AFMs) are an ideal platform for probing and understanding thickness- and twist-angle-dependent emergent spin phenomena. However, element-specific nanoscale characterization of the spin structure in atomically thin vdW-based AFMs systems and layer-parity effects remain elusive, making them crucial for both fundamental insight into low-dimensional magnetism and the rational design of spintronic devices based on these materials. Here, we utilize X-ray magnetic circular and linear dichroisms paired with photoemission electron microscopy to resolve the magnetic order in atomically thin CrSBr. Our comprehensive measurements reveal CrSBr magnetic structure at the nanoscale and its dependence on the layer number, surface encapsulation, temperature, and applied field. Moreover, in the orthogonally twisted bilayer configuration, obtained by twisting two CrSBr ferromagnetic monolayers by 90$^\circ$, the magnetic easy axis fundamentally differs from the individual monolayers, unlocking a new pathway for moiré magnetism.

cond-mat.mes-hall↗

arXiv2026

Enabling Electrical Readout of Néel vector reversal in a van der Waals Antiferromagnet

Owing to its robustness against external perturbations and intrinsically ultrafast dynamics, the Néel vector in antiferromagnets (AFMs) can enable the development of next-generation spintronic and magnonic devices for memory and computing applications. To realize AFM-based magnetic memory devices, one of the key requirements is to demonstrate electrical readout of 180-degree reversal of Néel vector in thin film AFMs, which remains critically missing. In this work, we report experimental demonstration of a novel transport methodology to detect Néel vector reversal in atomically thin films of a van der Waals (vdW) based A-type AFM. For this, we utilize spin-dependent electronic band properties of CrSBr by coupling it to a spin-polarized layer, separated by a tunnel barrier. In this configuration, the spin-dependent tunnelling magnetoresistance (MR) becomes sensitive to the relative orientation between the magnetization of the reference electrode and the interfacial sublattice magnetization of the AFM layer, in turn enabling electrical detection of the Néel vector orientation. Importantly, the observed MR can also reveal 180-degree reversal of Néel vector in even-layers of CrSBr, wherein adjacent sublattice magnetic layers are exactly compensated and the net magnetization vanishes and thus establishes a broadly applicable strategy for electrical detection of Néel vector in vdW-based AFMs.

cond-mat.mes-hall↗

arXiv2026

Visualization of Tunable Electronic Structure of Monolayer TaIrTe$_4$

Monolayer TaIrTe$_4$ has emerged as an attractive material platform to study intriguing phenomena related to topology and strong electron correlations. Recently, strong interactions have been demonstrated to induce strain and dielectric screening tunable topological phases such as quantum spin Hall insulator (QSHI), trivial insulator, higher-order topological insulator, and metallic phase, in the ground state of monolayer TaIrTe$_4$. Moreover, charge dosing has been demonstrated to convert the QSHI into a dual QSHI state. Although the band structure of monolayer TaIrTe$_4$ is central to interpreting its topological phases in transport experiments, direct experimental access to its intrinsic electronic structure has so far remained elusive. Here we report direct measurements of the monolayer TaIrTe$_4$ band structure using spatially resolved micro-angle-resolved photoemission spectroscopy (microARPES) with micrometre-scale resolution. The observed dispersions show quantitative agreement with density functional theory calculations using the Heyd-Scuseria-Ernzerhof hybrid functional, establishing the insulating ground state and revealing no evidence for strong electronic correlations. We further uncover a pronounced electron-hole asymmetry in the doping response. Whereas hole doping is readily induced by electrostatic gating, attempts to introduce electrons via gating or alkali metal deposition do not yield a rigid upward shift of the Fermi level. Fractional charge calculations demonstrate that added electrons instead drive band renormalization and shrink the band gap. Taken together, our experimental and theoretical results identify the microscopic mechanism by which induced charges reshape the band topology of monolayer TaIrTe$_4$, showing that doping can fundamentally alter the electronic structure beyond the rigid band behaviour that is typically assumed.

cond-mat.str-el↗

arXiv2025

Temperature and Pressure Dependent Vibrational Properties of Pristine and Doped Vacancy-Ordered Double Perovskite

Understanding lattice dynamics and structural transitions in vacancy-ordered double perovskites is crucial for developing lead-free optoelectronic materials, yet the role of dopants in modulatingthese properties remains poorly understood. We investigate the vibrational and optical properties of pristine and Antimony(Sb)-doped Cs$_2$TiCl$_6$ vacancy-ordered double perovskite through temperature-dependent Raman spectroscopy (4-273 K), high-pressure studies (0- \~30 GPa), ambient powder XRD, and photoluminescence measurements. Sb doping improves phase purity, reducing impurity-related Raman modes present in pristine samples. Most notably, Sb-doped samples exhibit an anomalous Raman mode M$_1$ appearing exclusively below 100 K at 314-319 cm$^{-1}$, accompanied by changes in the temperature coefficient $χ$ and anharmonic constant $A$ across this threshold. This behavior is absent in pristine Cs$_2$TiCl$_6$. While these observations suggest possible structural changes at low temperature, the origin of the M$_1$ mode remains unclear and may arise from disorder-activated vibrations, symmetry breaking, or dopant-induced local distortions. Low-temperature structural characterization is needed to confirm the nature of this transition. Photoluminescence shows broad self-trapped exciton emission at 448 nm with broader FWHM in Sb-doped samples (164.73 nm) compared to Bi-doped samples (138.2 nm), consistent with enhanced structural disorder. High-pressure Raman measurements reveal continuous mode hardening to 30 GPa with no phase transitions. These results demonstrate that Sb doping modulates the vibrational properties of Cs$_2$TiCl$_6$, though further investigation is required to establish the underlying mechanisms.

cond-mat.mtrl-sci↗

arXiv2025

Magnetization Dependent In-plane Anomalous Hall Effect in a Low-dimensional System

Anomalous Hall Effect (AHE) response in magnetic systems is typically proportional to an out-of-plane magnetization component because of the restriction imposed by system symmetries, which demands that the magnetization, applied electric field, and induced Hall current are mutually orthogonal to each other. Here, we report experimental realization of an unconventional form of AHE in a low-dimensional heterostructure, wherein the Hall response is not only proportional to the out-of-plane magnetization component but also to the in-plane magnetization component. By interfacing a low-symmetry topological semimetal (TaIrTe4) with the ferromagnetic insulator (Cr2Ge2Te6), we create a low-dimensional magnetic system, where only one mirror symmetry is preserved. We show that as long as the magnetization has a finite component in the mirror plane, this last mirror symmetry is broken, allowing the emergence of an AHE signal proportional to in-plane magnetization. Our experiments, conducted on multiple devices, reveal a gate-voltage-dependent AHE response, suggesting that the underlying mechanisms responsible for the Hall effect in our system can be tuned via electrostatic gating. A minimal microscopic model constrained by the symmetry of the heterostructure shows that both interfacial spin-orbit coupling and time-reversal symmetry breaking via the exchange interaction from magnetization are responsible for the emergence of the in-plane AHE. Our work highlights the importance of system symmetries and exchange interaction in low-dimensional heterostructures for designing novel and tunable Hall effects in layered quantum systems.

cond-mat.mes-hall↗

arXiv2024

Revealing the EuCd_{2}As_{2} Semiconducting Band Gap via n-type La-Doping

EuCd_{2}As_{2} has attracted considerable interest as one of the few magnetic Weyl semimetal candidate materials, although recently there have been emerging reports that claim it to have a semiconducting electronic structure. To resolve this debate, we established the growth of n-type EuCd_{2}As_{2} crystals, to directly visualize the nature of the conduction band using angle resolve photoemission spectroscopy (ARPES). We show that La-doping leads to n-type transport signatures in both the thermopower and Hall effect measurements, in crystals with doping levels at 2 - 6 x 10^{17} e^{-} cm^{-3}. Both p-type and n-type doped samples exhibit antiferromagnetic ordering at 9 K. ARPES experiments at 6 K clearly show the presence of the conduction band minimum at 0.8 eV above the valence band maximum, which is further corroborated by the observation of a 0.71 - 0.72 eV band gap in room temperature diffuse reflectance absorbance measurements. Together these findings unambiguously show that EuCd_{2}As_{2} is indeed a semiconductor with a substantial band gap and not a topological semimetal.

cond-mat.mtrl-sci↗