arXiv subjects

Awadhesh Narayan

Publications and source records attributed to Awadhesh Narayan.

At least 37 records · Page 2Linked to original sources

arXiv2025

Extremely Large and Angle-Dependent Magnetoresistance in Kagome Dirac Semimetal RFe$_6$Sn$_6$ (R=Ho, Dy)

We report on the electronic, magnetic, and magneto-transport properties of Fe-based kagome Dirac system, RFe$_6$Sn$_6$ (R = Ho, Dy). Magnetic properties study reveals an antiferromagnetic order with N$\acute{e}$el temperature of $T_N \approx$ 570 K. Additionally, a weak ferromagnetic order emerge at low temperatures. Magnetotransport measurements demonstrate an extremely large magnetoresistance (XMR) reaching as high as $3\times 10^{3} \%$ for HoFe$_6$Sn$_6$ and $ 1\times 10^{3} \%$ for DyFe$_6$Sn$_6$ when measured at 2 K with 9 T of magnetic field. The semi-classical two-band model fitting of the Hall conductivity reveals nearly perfect electron-hole compensation and high carrier mobility, which leads to XMR behaviour in these system. Further, we identify large magnetoresistance anisotropy for the magnetic fields applied in different crystallographic orientations. In addition, considerable modification in the angle-dependent magnetoresistance (ADMR) pattern has been noticed between 2 and 50 K, indicating temperature-dependent changes in the Fermi surface topology of these systems.

cond-mat.mtrl-sci↗

arXiv2025

Chiral damping with persistent edge states: interplay of spectral topology and band topology in open quantum systems

We study the dynamical consequences of combining the non-Hermitian skin effect with topological edge states. Focusing on the paradigmatic dissipative Hofstadter model, we find that the time-dependent particle density exhibits both chiral damping (due to the non-Hermitian skin effect) and edge-selective extremal damping (rooted in persistent topological edge states). We find that the time scales of chiral damping and edge-selective extremal damping decouple due to boundary-induced spectral topology, thus allowing observation of both effects under dynamics. We identify intermediate magnetic fields as the most favorable regime, since chiral damping is then partially recovered. More generally, our work sheds light on how open quantum systems are impacted by the combined presence of spectral and band topologies, and how their interplay can be probed directly.

cond-mat.mes-hall↗

arXiv2024

Emergence of tunable exceptional points in altermagnet-ferromagnet junctions

The existence of exceptional points (EPs) ${-}$ where both eigenvalues and eigenvectors converge ${-}$ is a key characteristic of non-Hermitian physics. A newly-discovered class of magnets ${-}$ termed as altermagnets (AMs) ${-}$ are characterized by a net zero magnetization as well as spin-split bands. In this study, we propose the emergence of non-Hermitian physics at AM-ferromagnet (FM) junctions. We discover that such a junction hosts tunable EPs. We demonstrate that the positions of these emergent EPs can be tuned using an external applied magnetic field and show that for a critical value of the applied magnetic field the EPs can annihilate. Notably, the number and position of the EPs crucially depends on the type of AM and its orientation with respect to the FM. Our work puts forth a promising platform of exploration of non-Hermitian physics in an emerging class of magnetic materials.

cond-mat.mes-hall↗

arXiv2024

Interplay of altermagnetism and pressure in hexagonal and orthorhombic MnTe

Alternative magnetic materials or ``altermagnets", characterized by their non-relativistic, momentum-dependent spin-split states, represent a cutting-edge advancement in the field of magnetism, offering promising avenues for spintronic applications. Among these materials, hexagonal MnTe has emerged as a standout material candidate for its substantial spin-splitting. In this study, employing first-principles electronic structure calculations and spin group symmetry analysis, we delve into the interplay of altermagnetism and pressure in two main phases of MnTe. Our relativistic calculations demonstrate the presence of tunable anomalous Hall effect (AHE) in hexagonal MnTe. In addition, our results underscore the pivotal role of pressure as a tuning parameter for the alternative magnetic traits in the system. Furthermore, we identify another phase of MnTe with orthorhombic structure, namely $γ$-MnTe, hosting altermagnetic characteristics. We study, in detail, its response in AHE and spin-spliting due to magnetization and pressure variations, respectively. Our study highlights the substantial impact of pressure on the properties of alternative magnetic materials, particularly emphasizing the pronounced tuning effect observed in the hexagonal and orthorhombic MnTe.

cond-mat.mtrl-sci↗

arXiv2024

Anomalous and parallel Hall effects in ferromagnetic Weyl semimetal Cr$_3$Te$_4$

Recently, time-reversal symmetry broken magnetic Weyl semimetals (WSMs) have attracted extensive attention and have provided an intriguing platform for exploring fundamental physical phenomena. The study of chromium telluride-based systems has also drawn significant interest towards spintronics applications owing to their high Curie temperatures. Here, using \textit{ab initio} calculations, we propose the emergence of multiple Weyl points (WPs) near the Fermi level in such an intrinsic ferromagnetic system, Cr$_3$Te$_4$. The large, well-separated, nontrivial Fermi arcs and surface states, suggest that the WPs are highly robust and resilient to perturbations. A substantial Berry curvature contribution in the vicinity of the Fermi energy not only serves as the origin of large conventional anomalous Hall conductivity (AHC), but also produces unconventional parallel AHC in this material, owing to the low structural symmetry. In addition to the charge Hall conductivity, we also find significant anomalous Nernst conductivities originating from the Berry curvature. Alongside our theoretical predictions, we present complementary experimental results, including X-ray diffraction (XRD) analysis and an examination of the magnetic properties, which demonstrate a Curie temperature of 327 K. Our study advances the understanding of magnetic WSMs, and also encourages further studies in the context of topological properties of our proposed material.

cond-mat.mtrl-sci↗

arXiv2024

Floquet engineering of topological semimetals with bicircularly polarized light

We study the effect of illumination of bicircularly polarized light (BCL) on topological semimetals, namely multifold fermion and line-node semimetals. We demonstrate, by means of both low-energy and lattice models, that the band-structures of both multifold fermions and line-node semimetal exhibit rich features with BCL illumination. For multifold fermions, we show that if the relative amplitude, $r$, between the two frequency components of the BCL is related to the relative frequency, $η$, in such a way that $r^2 = η$, then the band touching points remain unchanged without any shift or band gap opening for any choice of the material-dependent parameters. For other choices of the BCL parameters, we find both gapped phases as well as gapless phases with shifted band touching points. Line-node semimetals also exhibit diverse phases, ranging from protected line-nodes under illumination to point nodes, by tuning the BCL parameters $r$ and $η$. Overall, our analytical and numerical results establish BCL as a versatile tool for obtaining tunable topological phases.

cond-mat.mes-hall↗

arXiv2024

Dopant-induced modulation of ferroelectricity in perovskite nitride LaWN$_3$

Perovskite nitrides are starting to be explored for their promising properties distinct from their oxide counterparts. Here, through first-principles density functional computations, we study the intricate relationship between ferroelectricity and metallicity in the ferroelectric nitride LaWN$_3$. We systematically assess the impact of electron and hole doping via the background charge method, revealing that both types of charge carriers diminish the propensity for ferroelectricity in LaWN$_3$, although to remarkably different extents. Specifically, the introduction of electrons leads to centrosymmetry at a lower concentration value of nearly 0.2 electrons per formula unit. In contrast, the addition of holes does not result in centrosymmetry at reasonable doping values of up to 0.3 holes per formula unit. We present the underlying mechanisms behind these findings, noting that adding electrons fills the valence orbitals of both W and N atoms. This filling leads to a screening effect on the long-range repulsion between these atoms, thereby reducing the off-centering of W. On the other hand, hole doping does not significantly alter the W-N bonding nature, resulting in a more robust off-centering. Furthermore, we introduce explicit impurity atoms and analyze the influence of the different factors contributing to the change in polarization, namely, the size of the dopant, charge carriers introduced by the dopant, and changes in lattice constants. We discover that doped LaWN$_3$ can be a promising polar metal, especially with acceptor dopants. Our study comprehensively shows the interplay between polarity and metallicity in this prototypical perovskite nitride.

cond-mat.mtrl-sci↗

arXiv2024

Sn$_{0.06}$Cr$_3$Te$_4$: A Skyrmion Superconductor

Topological superconductors are an exciting class of quantum materials from the point of view of the fundamental sciences and potential technological applications. Here, we report on the successful introduction of superconductivity in a ferromagnetic layered skyrmion system Cr$_3$Te$_4$, obtained by the Sn intercalation, below a transition temperature of $T_c$$\approx$3.5 K. We observe several interesting physical properties, such as superconductivity, magnetism, and the topological Hall effect, simultaneously in this system. Despite the magnetism and Meissner effects being anisotropic, the superconductivity observed from the in-plane electrical resistivity ($ρ_{\it{bc}}$) is nearly isotropic between $H\parallel \it{bc}$ and $H\parallel \it{a}$, suggesting separate channels of conduction electrons responsible for the superconductivity and magnetism of this system, which is also supported by our spin-resolved DFT calculations. We identify two orders of higher carrier density in superconducting Sn$_{0.06}$Cr$_{3}$Te$_4$ than the parent Cr$_3$Te$_4$. A jump in the specific heat is noticed around the $T_c$ with a volume fraction of 33\%, confirming the bulk superconductivity in Sn$_{0.06}$Cr$_{3}$Te$_4$. In addition to the introduction of superconductivity, tuning of topological Hall properties is noticed with Sn intercalation. Our observation of superconductivity in a skyrmion lattice brings up a new class of topological quantum materials.

cond-mat.supr-con↗

arXiv2024

Chirality-tunable non-linear Hall effect

The non-linear generalization of the Hall effect has recently gained much attention, with a rapidly growing list of non-centrosymmetric materials that display higher-order Hall responses under time-reversal invariant conditions. The intrinsic second-order Hall response arises due to the first-order moment of Berry curvature -- termed Berry curvature dipole -- which requires broken inversion and low crystal symmetries. Chiral materials are characterized by their lack of improper symmetries such as inversion, mirror plane, and roto-inversion. Owing to this absence of symmetries, in this work, we propose chiral systems as ideal platforms to study the Berry curvature dipole-induced non-linear Hall effects. We use state-of-the-art first-principles computations, in conjunction with symmetry analyses, to explore a variety of chiral material classes -- metallic \ch{NbSi2}, semiconducting elemental Te, insulating HgS, and topological multifold semimetal CoSi. We present the emergence and tunability of the Berry curvature dipole in these chiral materials. In particular, we demonstrate that the two enantiomeric pairs exhibit an exactly opposite sign of the Berry curvature dipole. We complement our \textit{ab initio} findings with a general tight-binding minimal model and give estimates for non-linear Hall voltages, which are experimentally accessible. Our predictions put forward chiral materials as an emerging class of materials to realize non-linear Hall phenomena and highlight an as-yet-unexplored aspect of these systems.

cond-mat.mtrl-sci↗

arXiv2024

Non-linear Hall Effects: Mechanisms and Materials

This review presents recent breakthroughs in the realm of nonlinear Hall effects, emphasizing central theoretical foundations and recent experimental progress. We elucidate the quantum origin of the second-order Hall response, focusing on the Berry curvature dipole, which may arise in inversion symmetry broken systems. The theoretical framework also reveals the impact of disorder scattering effects on the nonlinear response. We further discuss the possibility of obtaining nonlinear Hall responses beyond the second order. We examine symmetry-based indicators essential for the manifestation of nonlinear Hall effects in time-reversal symmetric crystals, setting the stage for a detailed exploration of theoretical models and candidate materials predicted to exhibit sizable and tunable Berry curvature dipole. We summarize groundbreaking experimental reports on measuring both intrinsic and extrinsic nonlinear Hall effects across diverse material classes. Finally, we highlight some of the other intriguing nonlinear effects, including nonlinear planar Hall, nonlinear anomalous Hall, and nonlinear spin and valley Hall effects. We conclude with an outlook on pivotal open questions and challenges, marking the trajectory of this rapidly evolving field.

cond-mat.mes-hall↗

arXiv2024

Emergence of two-fold non-Hermitian spectral topology through synthetic spin engineering

The union of topology and non-Hermiticity has led to the unveiling of many intriguing phenomena. We introduce a synthetic spin-engineered model belonging to symmetry class AI, which is a rare occurrence, and demonstrate the emergence of a multi-fold spectral topology. As an example of our proposal, we engineer non-Hermiticity in the paradigmatic Su-Schrieffer-Heeger (SSH) model by introducing a generalized synthetic spin, leading to an emergent two-fold spectral topology that governs the decoupled behaviour of the corresponding non-Hermitian skin effect. As a consequence of the spin choice, our model exhibits a rich phase diagram consisting of distinct topological phases, which we characterize by introducing the notion of paired winding numbers, which, in turn, predict the direction of skin localization under open boundaries. We demonstrate that the choice of spin parameters enables control over the directionality of the skin effect, allowing for it to be unilateral or bilateral. Furthermore, we discover non-dispersive flat bands emerging within the inherent SSH model framework, arising from the spin-engineering approach. We also introduce a simplified toy model to capture the underlying physics of the emergent flat bands and direction-selective skin effect. As an illustration of experimental feasibility, we present a topoelectric circuit that faithfully emulates the underlying spin-engineered Hamiltonian, providing a viable platform for realizing our predicted effects. Our findings pave way for the exploration of unconventional spectral topology through spin-designed models.

cond-mat.mes-hall↗

arXiv2024

Observation of quantum oscillations near the Mott-Ioffe-Regel limit in CaAs3

The Mott-Ioffe-Regel limit sets the lower bound of carrier mean free path for coherent quasiparticle transport. Metallicity beyond this limit is of great interest because it is often closely related to quantum criticality and unconventional superconductivity. Progress along this direction mainly focuses on the strange-metal behaviors originating from the evolution of quasiparticle scattering rate such as linear-in-temperature resistivity, while the quasiparticle coherence phenomena in this regime are much less explored due to the short mean free path at the diffusive bound. Here we report the observation of quantum oscillations from Landau quantization near the Mott-Ioffe-Regel limit in CaAs3. Despite the insulator-like temperature dependence of resistivity, CaAs3 presents giant magnetoresistance and prominent Shubnikov-de Haas oscillations from Fermi surfaces, indicating highly coherent band transport. In contrast, the quantum oscillation is absent in the magnetic torque. The quasiparticle effective mass increases systematically with magnetic fields, manifesting a much larger value than the expectation given by magneto-infrared spectroscopy. It suggests a strong many-body renormalization effect near Fermi surface. We find that these unconventional behaviors may be explained by the interplay between the mobility edge and the van Hove singularity, which results in the formation of coherent cyclotron orbits emerging at the diffusive bound. Our results call for further study on the electron correlation effect of the van Hove singularity.

cond-mat.str-el↗

arXiv2023

Characterizing Exceptional Points Using Neural Networks

One of the key features of non-Hermitian systems is the occurrence of exceptional points (EPs), spectral degeneracies where the eigenvalues and eigenvectors merge. In this work, we propose applying neural networks to characterize EPs by introducing a new feature -- summed phase rigidity (SPR). We consider different models with varying degrees of complexity to illustrate our approach, and show how to predict EPs for two-site and four-site gain and loss models. Further, we demonstrate an accurate EP prediction in the paradigmatic Hatano-Nelson model for a variable number of sites. Remarkably, we show how SPR enables a prediction of EPs of orders completely unseen by the training data. Our method can be useful to characterize EPs in an automated manner using machine learning approaches.

cond-mat.dis-nn↗

arXiv2023

Nonlinear Hall effect in Rashba systems with hexagonal warping

Rashba spin-orbit coupled systems are an important class of materials noted for diverse fundamental and applied phenomena. Recently, the emergence of non-linear Hall effect under conditions of time-reversal symmetry has been discovered in materials with broken inversion symmetry. In this work, we study the second- and third-order Hall response in Rashba systems with hexagonal warping. Starting with a low-energy model, we obtain the analytic expressions and discover the unique dipole profile in Rashba systems with hexagonal warping. Furthermore, we extend the analysis using a realistic tight-binding model. Next, we predict the existence of a third-order Hall effect in these systems, and calculate the Berry connection polarizability tensor analytically. We also show how the model parameters affect the third-order conductivity. Our predictions can help in the experimental realization of Berry curvature multipole physics in Rashba materials with hexagonal warping, and provide a new platform for engineering the non-linear Hall effects.

cond-mat.mes-hall↗

arXiv2023

Uncovering Exceptional Contours in non-Hermitian Hyperbolic Matter

Hyperbolic lattices are starting to be explored in search of novel phases of matter. At the same time, non-Hermitian physics has come to the forefront in photonic, optical, phononic, and condensed matter systems. In this work, we introduce non-Hermitian hyperbolic matter and elucidate its exceptional properties in depth. We use hyperbolic Bloch theory to investigate band structures of hyperbolic lattices in the presence of non-Hermitian on-site gain and loss as well as non-reciprocal hopping. Using various analytical and numerical approaches we demonstrate widely accessible and tunable exceptional points and contours in {10,5} tessellations, which we characterize using phase rigidity, energy scaling, and vorticity. We further demonstrate the occurrence of higher-order exceptional points and contours in the {8,4} tessellations using the method of Newton polygons, supported by vorticity and phase rigidity computations. Finally, we investigate the open boundary spectra and densities of states to compare with results from band theory, along with a demonstration of boundary localisation. Our results unveil an abundance of exceptional degeneracies in hyperbolic non-Hermitian matter.

cond-mat.mes-hall↗

arXiv2023

Weak Electronic Correlations Observed in Magnetic Weyl Semimetal Mn$_3$Ge

Using angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations, we systematically studied the electronic band structure of Mn$_3$Ge in the vicinity of the Fermi level. We observe several bands crossing the Fermi level, confirming the metallic nature of the studied system. We further observe several flat bands along various high symmetry directions, consistent with the DFT calculations. The calculated partial density of states (PDOS) suggests a dominant Mn $3d$ orbital contribution to the total valence band DOS. With the help of orbital-resolved band structure calculations, we qualitatively identify the orbital information of the experimentally obtained band dispersions. Out-of-plane electronic band dispersions are explored by measuring the ARPES data at various photon energies. Importantly, our study suggests relatively weaker electronic correlations in Mn$_3$Ge compared to Mn$_3$Sn.

cond-mat.mtrl-sci↗

arXiv2023

Origin of flat bands and non-trivial topology in coupled kagome lattices

We propose an exact analytical decimation transformation scheme to explore the fascinating coexistence of flat bands and Dirac fermions in three-dimensional coupled kagome systems. Our method allows coarse-graining of the parameter space that maps the original system to an equivalent low-level lattice. The decimated system enables defining a quantity in the tight-binding parameter space that predominantly controls the emergence of a flat band (FB) and provides a specific criterion for absolute flatness. Likewise, in terms of atomic separations, we develop a quantity that primarily controls the FB width in real materials and thus can be helpful in predicting new systems hosting FB as well as in tuning the FB width. Our predictions on the emergence of the flat band and Dirac fermions are confirmed for M$_3$X (M= Ni, Mn, Co, Fe; X= Al, Ga, In, Sn, Cr,...) family of materials, leveraging materials databases and first-principles calculations. Our work provides an analytical formalism that enables accurate predictions of FBs in real materials.

cond-mat.mtrl-sci↗

arXiv2023

Berry Curvature Dipole and its Strain Engineering in Layered Phosphorene

The emergence of the fascinating non-linear Hall effect intrinsically depends on the non-zero value of the Berry curvature dipole. In this work, we predict that suitable strain engineering in layered van der Waals material phosphorene can give rise to a significantly large Berry curvature dipole. Using symmetry design principles, and a combination of feasible strain and staggered on-site potentials, we show how a substantial Berry curvature dipole may be engineered at the Fermi level. We discover that monolayer phosphorene exhibits the most intense Berry curvature dipole peak near 11.8% strain, which is also a critical point for the topological phase transition in pristine phosphorene. Furthermore, we have shown that the necessary strain value to achieve substantial Berry curvature dipole can be reduced by increasing the number of layers. We have revealed that strain in these van der Waals systems not only alters the magnitude of Berry curvature dipole to a significant value but allows control over its sign. We are hopeful that our predictions will pave way to realize the non-linear Hall effect in such elemental van der Waals systems.

cond-mat.mes-hall↗