arXiv subjects

Manoranjan Kumar

Publications and source records attributed to Manoranjan Kumar.

At least 19 recordsLinked to original sources

arXiv2026

Semi-Dirac States and Quantum Linear Magnetoresistance in Helimagnetic Pnictide MnP

Large linear positive magnetoresistance (LPMR) in topological and magnetic materials remains a subject of intense debate, particularly in noncollinear spin systems where spin-dependent scattering complicates charge transport. Manganese phosphide (MnP), a helimagnetic binary pnictide with multiple field-induced magnetic transitions, provides a useful platform to investigate the interplay between complex magnetism and electronic topology. Here, we present a comprehensive experimental and theoretical investigation of phase-dependent magnetotransport in high-quality MnP single crystals. Hall measurements reveal an anomalous Hall effect dominated by skew scattering at high temperatures and a finite topological Hall effect in the noncollinear fan (FAN) and low-temperature screw (SCR) phases. At low temperatures, we observe a large, non-saturating LPMR reaching nearly 800 percent at 4 K and 15 T, with a pronounced linear field dependence in the field-polarized ferromagnetic (FM2) state. First-principles calculations reveal a strongly anisotropic semi-Dirac-like band at the Y point that progressively approaches the Fermi level from the SCR to FAN and FM2 states. Our analysis indicates that the resulting small Fermi pocket can access the extreme quantum-limit regime at experimentally accessible fields, providing a microscopic framework for the observed LPMR within Abrikosov's quantum magnetoresistance theory.

cond-mat.str-el↗

arXiv2026

Anomalous magnetotransport in a non-collinear correlated kagome ferromagnet MgMn6Sn6

Magnetic kagome metals provide a fertile platform for exploring unusual magnetotransport phenomena arising from the intricate interplay between electronic topology, electron correlations, and magnetic order. MgMn6Sn6 is a room-temperature kagome ferromagnet with strong in-plane magnetic anisotropy. Here, we report a combined study of single-crystal neutron diffraction (SCND) and magnetotransport properties of MgMn6Sn6, supported by first-principles calculations. Our SCND measurements reveal a non-collinear arrangement of Mn magnetic moments within the basal plane of the kagome bilayer. The Hall conductivity shows a substantial intrinsic contribution of approximately 0.29 e^2/h per kagome layer, which is nearly isotropic with respect to the field orientation. At low temperatures, the anomalous Hall conductivity develops a pronounced anisotropic extrinsic component, highlighting the directional sensitivity of scattering processes. The significantly large value of the Sommerfeld coefficient, in the absence of f-electrons, underscores enhanced electron correlation. Therefore, the non-collinear kagome ferromagnet MgMn6Sn6 is a promising candidate for studying the effects of electron correlation on magnetotransport properties.

cond-mat.mtrl-sci↗

arXiv2026

Nanoscale Electronic Phase Separation Driven by Fe-site Ordering in Fe\textsubscript{5-x}GeTe\textsubscript{2}

Understanding how local structural order governs electronic correlations is essential for revealing the microscopic mechanism underlying emergent behavior in two-dimensional magnets. In the layered van der Waals ferromagnet Fe\textsubscript{5-x}GeTe\textsubscript{2}, intrinsic Fe-site disorder provides a natural platform to probe this interplay. Here, we establish a direct atomic scale correlation between Fe-site ordering and local electronic structure by combining high-resolution scanning tunneling microscopy with density functional theory calculations. Scanning tunneling microscopy resolves two coexisting surface phases, a $\sqrt{3} \times \sqrt{3}$ superstructure associated with ordered Fe(1) configurations and an undistorted $1 \times 1$ hexagonal Te lattice in Fe(1)-deficient regions. Spatially resolved spectroscopy shows that the $\sqrt{3}$-ordered domains exhibit metallic behavior, whereas Fe(1) vacant areas display a suppressed density of states(DOS) near the Fermi level, indicative of pseudogapped electronic states. The nanoscale coexistence of these distinct electronic responses provides direct evidence of electronic phase separation driven by Fe-site ordering. First-principles calculations reveal that symmetry allowed hybridization between Fe 3d and Te 5p orbitals reconstructs the low-energy electronic structure, giving rise to the contrasting tunneling signatures of ordered and disordered phases. Bias-dependent local DOS simulations reproduce the experimentally observed contrast evolution and reveal that hybridization induced out of plane orbital character governs the spatial modulation of tunneling conductance. These results provide a microscopic framework linking atomic-scale structural order to nanoscale electronic inhomogeneity in van der Waals magnets.

cond-mat.mes-hall↗

arXiv2025

Basis Adaptive Algorithm for Quantum Many-Body Systems on Quantum Computers

We introduce a Basis Adaptive (BA) algorithm for hybrid quantum-classical simulation of correlated quantum many-body systems. Starting from a small set of physically motivated bitstrings, the algorithm iteratively applies a single-step first-order Trotterized circuit on a quantum processor, filters the sampled configurations by enforcing $U(1)$ spin conservation and lattice reflection symmetry, and classically diagonalizes the Hamiltonian in the resulting reduced Hilbert space. This design avoids the variational optimization overhead of VQE, the deep coherent circuits required by QPE, and the symmetry-violating subspaces that arise in SKQD. The ground-state energy error is bounded analytically by $\sqrt{8}\,\|H\|\left(1-\sqrt{\alpha_{D_T}}\right)^{1/2}$, where $\alpha_{D_T}$ is the probability weight captured by the $D_T$ sampled basis states. This bound connects algorithm performance directly to ground-state sparsity and explains the observed accuracy hierarchy across different phases. Benchmarked on the spin-$1/2$ Heisenberg XXZ chain (up to $N=62$ qubits on the IBM Heron processor), the algorithm achieves a $3.5\%$ energy error in the gapped Neel phase ($\Delta=2.0$) and below $0.5\%$ at the ferromagnetic boundary ($\Delta=-1.0$). The accuracy degrades to $28.7\%$ in the strongly quasi-long-range-ordered regime ($\Delta=0.5$). Spin-spin correlation functions are reproduced across all regimes, confirming that symmetry-filtered real-time sampling provides a practical and noise-resilient pathway to ground-state properties on near-term quantum hardware.

cond-mat.str-el↗

arXiv2025

Interplay of Orbital Degeneracy and Vacancies in Stabilizing Collinear Magnetic Order in Cr$_{1+\delta}$Te$_2$

Cr$_{1+\delta}$Te$_2$, a two-dimensional van der Waals ferromagnet, displays a contested magnetic structure, poised between collinear and non-collinear spin configurations. In this work, we investigate the magnetic structure of Cr$_{1.33}$Te$_2$ at the microscopic level by combining single-crystal neutron diffraction, X-ray absorption spectroscopy, and first-principles calculations. Neutron diffraction measurements reveal a distinct collinear spin alignment, whereas spectroscopic analyses reveal inherent structural vacancies at both Cr and Te sites. These vacancies lead to local symmetry breaking that elevates the orbital degeneracy of the Cr 3$d$ states, as demonstrated by our first-principles analysis. The resulting modification of magnetocrystalline anisotropy emerges as the key mechanism stabilising the collinear magnetic ground state over the non-collinear one in the presence of vacancies. Our findings uncover a vacancy-driven route to control spin anisotropy and magnetic ordering in layered ferromagnets, offering new insights into the design of tunable 2D magnetic materials.

cond-mat.str-el↗

arXiv2025

Observation of a Novel Charge Density Wave Superstructure in Monolayer 1T-$VS_{2}$ at Room Temperature and its Evolution in Multilayers

Spontaneous formation of charge density wave (CDW) superstructures in monolayers (MLs) of a two-dimensional (2D) crystal lattice is fundamental in understanding its complex quantum states. We report a successful top-down liquid phase exfoliation and stamp transfer process (LPESTP) to create ML VS\textsubscript{2}, undergoing a CDW transition at room temperature. Using high-resolution transmission electron microscopy (HRTEM) and electron diffraction (ED), we observed the coexistence of 1T and 2H polymorphic phases in VS\textsubscript{2} at room temperature, and only the 1T phase undergoes CDW transition. We discovered a novel incommensurate CDW superstructure ($\sqrt{7} \times \sqrt{7}$) R19.1\textsuperscript{o} in ML 1T-VS\textsubscript{2}. With an increase in the number of layers, the CDW order changes to a commensurate ($2 \times 2\times 1$) superstructure. Using angle-dependent photoelectron spectroscopy and TEM, we have shown that vanadium atoms self-intercalate as V\textsuperscript{3+} ions in multilayer VS\textsubscript{2} and are responsible for the evolution of the CDW superstructure from the incommensurate ($\sqrt{7} \times \sqrt{7}$) R 19.1\textsuperscript{o} to the commensurate ($2\times2\times1$) order. We also report the observation of novel Moir\'e superlattices in twisted bilayer 1T-VS\textsubscript{2} flakes with trapped CDW superstructure of the monolayer. The density functional theory (DFT) calculation performed on ML 1T-VS\textsubscript{2} show that the observed ($\sqrt{7} \times \sqrt{7}$) R 19.1\textsuperscript{o} CDW superstructure has lower energy compared to that of the pristine undistorted ML and the CDW instability is driven by formation of strong soft-phonon modes. Our findings provide an important platform for understanding the evolution of CDW superstructures in 1T-VS\textsubscript{2} with layer numbers and V self-intercalation.

cond-mat.mtrl-sci↗

arXiv2025

Signatures of two ferromagnetic states and goniopolarity in LaCrGe3 in the Hall effect

LaCrGe3 has become a playground to understand quantum critical phenomena in ferromagnetic (FM) materials. It has also garnered attention due to its peculiar two FM phases. Here, we demonstrate the presence of these phases using the Hall effect. Continuous temperature-dependent Hall resistivity measurements at fixed magnetic fields clearly demonstrate the presence of these phases, regardless of the direction of the applied magnetic field. The remanent Hall resistivity and Hall coefficient undergo a maximum and a minimum, respectively, at the boundary between the two phases. We observe significantly large anomalous Hall conductivity of 1160 ohm-1cm-1 at 2 K when the magnetic field is applied along the magnetic easy axis, which is dominated by intrinsic effects, at least in the low-temperature FM phase. In the paramagnetic (PM) phase, hexagonal LaCrGe3 exhibits opposite charge carrier polarities along different crystallographic directions, attributed to the anisotropic Fermi surface geometry, a phenomenon known as "goniopolarity". The coexistence of goniopolar transport and unconventional magnetic phases may lead this material as a promising candidate for future electronic devices.

cond-mat.mtrl-sci↗

arXiv2025

A long-range model for the electron-nuclear coupling and two-stage order in TmVO$_4$

We study an infinite-range coupled electronic-quadrupole and nuclear-spin model for ferro-quadrupolar and nuclear-spin ordering in TmVO$_4$ in external magnetic and strain fields. This material is an experimental realization of a Transverse-Field Ising Model, where the Ising degree of freedom is quadrupolar and non-magnetic, but a transverse component is magnetic and couples both to external magnetic fields and to the nuclear spins via a hyperfine coupling. In zero external magnetic-field, there is a well-separated two-step order of the electronic and nuclear degrees of freedom and the release of their respective entropies. A transverse magnetic-field polarizes the electronic orbital moments and also the nuclear spins via the hyperfine coupling. The quadrupolar ordering temperature is gradually reduced to zero. But, there is no longer a nuclear transition in non-zero fields. Quantum fluctuations are magnified near the phase transitions and lead to peaks in the magnetic susceptibility. The spectral functions reveal a softening of a low-energy mode near the quantum critical point, consistent with the closing of the excitation gap and its reopening in the disordered phase, providing direct dynamical signatures of the field-driven quantum critical phenomena.

cond-mat.str-el↗

arXiv2025

Electronic and magnetic ground states of {112} grain boundary in graphene in the extended Hubbard model

We study the ground state phase diagram of the extended Hubbard model in a half-filled 5/7 skewed ladder, which is topologically equivalent to a \{112\} grain boundary in graphene and related systems. Using the mean-field method, we identify various electronic and magnetic phases in the U-V plane, by calculating the site charge and spin densities. The electronic phases include partially charge-ordered metal or insulator, and fully charge-ordered insulator. The different magnetic phases of the model are non-magnet, spin density wave, spin split compensated ferrimagnet or partial antiferromagnet. Analysis of the electronic band structure reveals that the partially charge-ordered compensated ferrimagnetic phase exhibits spin polarisation, which can be quite interesting for spintronics applications. We also compute the polarisation as a function of $U$ using the Berry phase formalism and show that the system exhibits multiferroicity with coexisting compensated ferrimagnetic spin order alongside electronic polarisations.

cond-mat.str-el↗

arXiv2025

Polarization-Driven Charge Frustration and Emergent Phases in the One-Dimensional Extended Hubbard Model

Frustration is a key driver of exotic quantum phases, yet its role in charge dynamics remains largely unexplored. We show that charge frustration - induced by electronic polarization effects - stabilizes unconventional insulating states in the one-dimensional extended Hubbard model. Using exact diagonalization and density-matrix renormalization group, we uncover a charge-disordered phase that remains insulating despite lacking long-range order and possessing an effectively attractive on-site interaction - a behavior reminiscent of gapful spin liquids in frustrated spin systems. We also identify a fragile ferroelectric phase and a charge-density-wave state with emergent eight-site periodicity. These findings establish charge frustration, driven by charge-dipole interactions, as a robust mechanism for realizing exotic phases in low-dimensional correlated systems, with implications for organic conductors, transition-metal oxides, and ultracold polar molecules.

cond-mat.str-el↗

arXiv2025

Accessing quasi-flat $\textit{f}$-bands to harvest large Berry curvature in NdGaSi

In typical rare-earth lanthanide compounds, the localized 4\textit{f}-electrons have a weak effect on the electrical conduction, limiting their influence on the Berry curvature and, hence, the intrinsic anomalous Hall effect. A comprehensive study of the magnetic, thermodynamic, and transport properties of single-crystalline NdGaSi, guided by first-principles calculations, reveals a ferromagnetic ground state that induces a splitting of quasi-flat 4\textit{f} electronic bands and positions them near the Fermi energy. The observation of an extraordinarily large intrinsic anomalous Hall conductivity of 1165 $\Omega^{-1}$ cm$^{-1}$ implies the direct involvement of localized states in the generation of non-trivial band crossings around the Fermi energy. The angle-resolved photoemission spectroscopy measurements provide direct evidence of non-trivial crossing of the 4\textit{f}-bands with dispersive bands. These results are remarkable when compared to ferrimagnetic NdAlSi, which differs only in a non-magnetic atom (a change in the principal quantum number \textit{n} of the outer \textit{p }orbital) with the same number of valence electrons and does not exhibit any measurable anomalous Hall conductivity.

cond-mat.mtrl-sci↗

arXiv2025

Emergent quasi-particles of spin-1 trimer chain

The recent experimental realization of emergent quasi-particles, such as spinons, doublons, and quartons, in a spin-$1/2$ trimer chain has spurred new interest in low dimensional magnetic systems. In this study, we investigate the dynamical properties of the isotropic spin-$1$ trimer chain with intra and inter-trimer antiferromagnetic exchange couplings, ($J >0$ and $J' >0$), respectively, unveiling various quasi-particles: magnons, singletons, triplons, pentons, and heptons. For weak inter-trimer exchange coupling $J'/J \ll 1$, it behaves as an effective spin-$1$ chain with valence bond solid (VBS) ground state. Employing density matrix renormalization group (DMRG) techniques, we compute the dynamic structure factor (DSF) which reveals a gapped magnon band alongside weakly dispersive singleton, excited triplon, and penton excitations. The evolution of these excitations with inter-trimer coupling $J'$ is also examined, providing insight into the underlying excitation mechanisms. For spin-$1$ chain, these exotic quasi-particles eventually reduce to conventional magnon excitations as $J'/J \rightarrow 1$. Our results shed light on the rich and complex excitation spectrum of spin-$1$ trimer chains and offer unique perspectives on the dynamics in quantum spin systems.

cond-mat.str-el↗

arXiv2025

Phase diagram of a coupled trimer system at half filling using the Hubbard model

Flat band systems have recently attracted significant attention due to their instability under small perturbations, which can lead to the stabilization of many exotic quantum phases. We study a trimer ladder which shows a middle flat band in the absence of onsite Coulomb interaction. We investigate the quantum phases of the Hubbard model on this geometry using exact diagonalization (ED), density matrix renormalization group (DMRG), and perturbation theory. We construct a quantum phase diagram in the plane of the next-nearest-neighbor hopping parameter $t_2$ and onsite Coulomb interaction $U$, revealing five distinct quantum phases. At low $U$ and moderate to high magnitude of $t_2$, the system exhibits metallic behavior, while at large $U$ and small magnitude of $t_2$, it transitions to a ferrimagnetic insulator phase, similar to those observed in certain trimer materials. In the small $t_2$ limit, the Fermi energy is in the flat band, leading to localization of the electrons within the trimer. At low $U$ and small magnitude of $t_2$, the flat band mechanism favors insulating ferrimagnetism, whereas at large $U$, ferrimagnetic states emerge from singlet dimer formation between neighboring sites of a trimer and an isolated corner spin, which connect ferromagnetically. The insulating cell spin density wave phase displays an up-up-down-down spin configuration due to competing nearest neighbor hopping, $t_1$. Interestingly, in moderate $U$ and $|t_2|>0.3$, the ground state behaves like metallic Tomonaga-Luttinger liquid.

cond-mat.str-el↗

arXiv2024

Suppression of Intrinsic Hall Effect through Competing Berry Curvature in Cr$_{1+\delta}$Te$_2$

We conducted a comprehensive analysis of the magnetic and electronic transport properties of the layered chalcogenide Cr$_{1+\delta}$Te$_2$ in its single crystalline form. This material exhibits a ferromagnetic transition at a critical temperature of $T_C = 191$ K, characterized by significant thermal hysteresis in the magnetization data below this temperature. Measurements of isothermal magnetization, magnetocaloric effect, and magnetoresistance indicate that the system exhibits strong magnetocrystalline anisotropy, with the $c$-axis serving as the easy axis of magnetization. The Cr$_{1+\delta}$Te$_2$ compound shows pronounced anomalous Hall effect (AHE); however, existing experimental and theoretical data do not provide a clear understanding of the nature and origin of this phenomenon. Our experimental findings suggest that the skew scattering mechanism primarily accounts for the observed AHE. In contrast, our theoretical study reveals the presence of gapped nodal points accompanied by non-zero Berry Curvature, which are expected to contribute towards intrinsic AHE. A detailed analysis of the electronic band structure, obtained through density functional theory calculations, reveals that the Berry Curvature at different nodal points exhibit both positive and negative signs. These opposing contributions largely cancel each other out, thereby significantly diminishing the intrinsic contribution to the AHE.

cond-mat.mtrl-sci↗

arXiv2024

Predicting Fractionalized Multi-Spin Excitations in Resonant Inelastic X-ray Spectra of Frustrated Spin-1/2 Trimer Chains

We theoretically investigate the resonant inelastic X-ray scattering (RIXS) spectra in a quasi-1D chain of weakly coupled frustrated spin-1/2 trimers, as realized in Na$_{2}$Cu$_{3}$Ge$_{4}$O$_{12}$, with Cu $d^{9}$ 1/2 spins. We compute multi-spin correlations contributing to spin-conserving (SC) and spin non-conserving (NSC) RIXS cross-sections using ultra-short core-hole lifetime expansion within the Kramer-Heisenberg formalism. These excitations involve flipping spins of up to three spin-1/2 trimers and include the inelastic neutron scattering (INS) single spin-flip excitations in the lowest order of the NSC channel. We identify the fractionalization of two coupled frustrated trimers in terms of spinons, doublons, and quartons in the spectra evaluated using exact diagonalization, complementing prior studies single spin-spin flip excitation in inelastic neutron scattering. Specifically, we uncover two new high-energy modes at $\omega \approx 2.4J_1$ and $3.0 J_1$ in the NSC and SC channels that are accessible at the Cu $K$-edge and $L$-edge RIXS spectra, which were missing in the INS study. This, therefore, provides pathways to uncover all the possible excitations in coupled trimers. Our work opens new opportunities for understanding the nature of fractionalization and RIXS spectra of frustrated, low-dimensional spin chains.

cond-mat.str-el↗

arXiv2024

Frustrated spin-1/2 Heisenberg model on a Kagome-strip chain: Dimerization and mapping to a spin-orbital Kugel-Khomskii model

We investigate the quantum phases of a frustrated antiferromagnetic Heisenberg spin-1/2 model Hamiltonian on a Kagome-strip chain (KSC), a one-dimensional analogue of the Kagome lattice, and construct its phase diagram in an extended exchange parameter space. The isolated unit cell of this lattice comprises of five spin-1/2 particles, giving rise to several types of magnetic ground states in a unit cell: a spin-$3/2$ state as well as spin-$1/2$ states with and without additional degeneracies. We explore the ground state properties of the fully connected thermodynamic system using exact diagonalization and density matrix renormalization group methods, identifying several distinct quantum phases. All but one of the phases exhibit gapless spin excitations. The exception is a dimerized spin-gapped phase that covers a large part of the phase diagram and includes the uniformly exchange coupled system. We argue that this phase can be understood by perturbing around the limit of decoupled unit cells where each unit cell has six degenerate ground states. We use degenerate perturbation theory to obtain an effective Hamiltonian, a Kugel-Khomskii model with an anisotropic spin-one orbital degree of freedom, which helps explain the origin of dimerization.

cond-mat.str-el↗

arXiv2024

Emergent scalar-chirality \& colossal transverse-magnetoresponse in strongly correlated nodal-line half-metal

Understanding the interplay of strong correlation and temperature in nodal-line semimetals can offer novel ways to control spin currents. Here we consider the 3d-5d double-perovskite Ba$_{2}$CoWO$_{6}$, which features mirror-symmetry-protected nodal-lines, strong Co-site interactions, and spin-orbit coupling (SOC) at W sites. Our first principles and exact diagonalization results reveal a half-metallic ground state with high-spin Co and topologically non-trivial bands. We demonstrate that SOC gaps out nodal points, causes band-inversion and generates anomalous Hall response. A semi-classical Monte Carlo finite-temperature simulation of five-orbital Hubbard model uncovers an emergent Co-spin scalar chirality and colossal positive transverse-magnetoresponse. We predict the temperature and magnetic field scales for the tunability of scalar-chirality and magnetoresponse.

cond-mat.str-el↗

arXiv2024

Exploring magnetic and topological complexity in MgMn$_6$Sn$_6$: from frustrated ground states to nontrivial Hall conductivity

We explore the intriguing topological itinerant magnet MgMn$_6$Sn$_6$, characterized by bilayer kagome Mn layers encasing a hexagonal Sn layer. Using \textit{ab initio} Density functional theory and Dynamical mean-field theory calculations, we uncover the complex electronic properties and many-body configuration of its magnetic ground state. Mn d-orbital electrons form a frustrated many-body ground state with significant quantum fluctuations, resulting in competing antiferromagnetic and ferromagnetic spin exchanges. Our band dispersion calculations reveal a mirror symmetry-protected nodal line in the \textit{k}$_z$ = 0 plane. When spin-orbit coupling (SOC) is introduced, the gap is formed along the nodal line lifted due to broken time-reversal symmetry with magnetic ordering, leading to substantial intrinsic Berry curvature. We identify Dirac fermions, van Hove singularities, and flat band near the Fermi energy (\textit{E}$_F$), with SOC introducing a finite gap at key points. The unique proximity of the flat band to \textit{E}$_F$ suggests potential instabilities. Spin-orbit coupling opens a 20 meV gap at the quadratic touching point between the Dirac and flat band, bestowing a nonzero Z$_2$ invariant. This leads to a significant spin Hall conductivity. Despite the presence of large incoherent scattering due to electronic interactions, band crossings and flat band features persist at finite temperatures. MgMn$_6$Sn$_6$ exhibits intriguing topological and magnetic properties, with promising applications in spintronics.

cond-mat.str-el↗