arXiv subjects

Amarjyoti Choudhury

Publications and source records attributed to Amarjyoti Choudhury.

4 recordsLinked to original sources

arXiv2026

Quasi-one-dimensional topological band structure and van Hove singularities in monolayer TaIrTe$_4$ from laser $μ$-ARPES

Recent transport experiments reported a quantum spin Hall insulator phase in monolayer 1T-TaIrTe$_4$ gated away from charge neutrality. This phase is not predicted by band structure calculations and has been attributed to an electronic instability induced by strong correlations at a putative van Hove singularity. Here, we investigate the electronic structure of exfoliated monolayer 1T-TaIrTe$_4$ using micro-focus laser angle resolved photoemission. We find a strongly anisotropic band structure susceptible to density wave instabilities. Our data further reveal a saddle point singularity in the density of states. However, we find that the saddle point lies at a density for which transport experiments found no anomalies. Moreover, the quasiparticle line widths suggest weak electron correlations only. This points to a secondary role of van Hove singularities and electron correlations in the transport phase diagram of monolayer 1T-TaIrTe$_4$.

cond-mat.mtrl-sci↗

arXiv2026

Topological Surface States and Anisotropic Magnetotransport in SnSb$_6$Te$_{10}$

We have investigated the electronic structure and magnetotransport properties of SnSb$_6$Te$_{10}$ single crystals using density functional theory (DFT), synchrotron-based angle-resolved photoemission spectroscopy (ARPES), and quantum transport measurements. Our DFT calculations reveal a clear spin-orbit coupling driven band inversion between the Sb-$p$ and Te-$p$ states together with a non-trivial $\mathbb{Z}_2$ topological invariant. The calculated surface-state dispersion and hexagonally warped Fermi surface contours agree well with the ARPES measurements. Temperature-dependent transport measurements indicate dominant electron-phonon scattering, while Hall measurements confirm hole-type carriers with carrier density of the order of $10^{21}$ cm$^{-3}$. Both transverse and longitudinal magnetotransport exhibit weak antilocalization behavior, while Shubnikov-de Haas oscillations observed for $H \parallel c$ yield a Berry phase close to $π$, consistent with Dirac-like surface states. Furthermore, angle-dependent magnetotransport measurements reveal pronounced anisotropy associated with an anisotropic Fermi surface topology and mixed bulk-surface transport behavior. Our combined theoretical and experimental results establish SnSb$_6$Te$_{10}$ as a strong topological insulator and a promising platform for investigating topological transport phenomena in layered telluride systems.

cond-mat.mtrl-sci↗

arXiv2024

Emerging topological states in EuMn$_2$Bi$_2$: A first principles prediction

New materials with magnetic order driven topological phases are hugely sought after for their immense application potential. In this work, we propose a new compound EuMn$_2$Bi$_2$ from our first principles density functional theory calculations to host novel topological phases such as Dirac/Weyl semimetal and topological insulator in its different magnetic states which are energetically close to one another. We started with an isostructural compound EuMn$_2$As$_2$ where the magnetic structure has been studied experimentally. From our calculations we could explain the nature of two magnetic transitions observed experimentally in this system and could also establish the correct magnetic ground state. Our electronic structure calculations reveal the insulating nature of the ground state consistent with the experiments. By replacing all As by Bi in EuMn$_2$As$_2$ and by optimizing the new structure, we obtained the new compound EuMn$_2$Bi$_2$. We observe this compound to be dynamically stable from our phonon calculations supporting its experimental preparation in future. By comparing the total energies of various possible magnetic structures we identified the ground state. Though the magnetic ground state is found to be insulating in nature with tiny band gap which is an order of magnitude less than the same in EuMn$_2$As$_2$, there were other magnetic states energetically very close to the ground state which display remarkable non-trivial band topology such as Dirac/Weyl points close to the Fermi level and topological insulator state. The energetic proximity of these magnetic order driven topological phases makes them tunable via external handle which indicates that the proposed new material EuMn$_2$Bi$_2$ would be a very versatile magnetic topological material.

cond-mat.mtrl-sci↗

arXiv2022

Interplay of magnetism and band topology in Eu$_{1-x}$Ca$_x$Mg$_2$Bi$_2$ (x=0, 0.5) from first principles study

Recent discovery of the time reversal symmetry breaking magnetic Weyl semimetals has created a huge surge of activities in the field of quantum topological materials. In this work, we have studied systematically the ground state magnetic order, electronic structure and the interplay between the magnetic order and band topology in one such materials, EuMg$_2$Bi$_2$ (EMB) and its Ca doped variant using first principles method within the framework of density functional theory (DFT). The detailed investigation unravels the existence of different topological phases in this single material which can be tuned by an external probe such as magnetic field or chemical substitution. Our DFT calculations including Coulomb correlation (U) and spin-orbit (SO) interaction within GGA+U+SO approximation confirms that the magnetic ground state of EMB is A-type Antiferromagnetic (A-AFM) with Eu magnetic moments aligned along the crystallographic $a$ or $b$ direction. Although the ground state of EMB is A-AFM, the Ferromagnetic (FM) state lies very close in energy. We observe a single pair of Weyl points connecting valence and conduction band very close to the Fermi level (FL) along $Γ$-A direction in the FM state of EuMg$_2$Bi$_2$ with Eu moments aligned along crystallographic $c$ direction. On doping 50\% Ca at Eu sites, we observe single pair of Weyl points moving closer to the FL which is highly desirable for application purposes. Further we observe that the separation between the Weyl points in the pair decreases in doped compound compared to that in the parent compound which has direct consequence on anomalous Hall conductivity (AHC). Our first principles calculation of AHC shows high peak values exactly at these Weyl points and the peak height decreases when we dope the system with Ca. Therefore, Ca doping can be a good external handle to tune AHC in this system.

cond-mat.mtrl-sci↗