arXiv subjects

Narayan Mohanta

Publications and source records attributed to Narayan Mohanta.

At least 19 recordsLinked to original sources

arXiv2026

Topological Hall plateau in quasi-2D kagome magnet YMn$_6$Sn$_6$

We examine the impact of the Dzyaloshinskii-Moriya interaction (DMI) in kagome magnets and show that a predominantly planar DMI together with ferromagnetic exchange stabilizes a disordered skyrmion phase in quasi-two-dimensional (2D) YMn$_6$Sn$_6$. Within an ab initio framework combining density functional theory and spin-dynamics simulations, we generate realistic spin textures of disordered skyrmion and find that this phase persists for $B_{ext} < 0.5$ T, with a decreasing skyrmion size as magnetic field increases. We demonstrate the emergence of topological Hall plateau in the range $-0.5 \leq B_{ext} < 0.5$ T, driven by nearly uniform scalar spin chirality and the resulting constant real-space Berry curvature. This response is anti-symmetric with magnetic field while magnitude and sign of these plateau are determined by a complex interplay between Hund's coupling strength and chemical potential signifying the role of Dirac points and van Hove singularities. In addition, we reveal topological magnon excitations in the disordered skyrmion phase of quasi-2D YMn$_6$Sn$_6$.

cond-mat.mtrl-sci↗

arXiv2026

Double-peak Majorana bound states in altermagnet--superconductor heterostructures

We study Majorana bound states in a planar Josephson junction in which the middle channel is a $d$-wave altermagnetic metal deposited on a proximitized two-dimensional electron gas. In the topological regime, the near-zero-energy states reveals a characteristic double-peak spatial profile, with the Majorana wavefunction localized near the altermagnet--superconductor interfaces. Using simplified theoretical models, we show that anisotropic hopping intrinsic to altermagnetism naturally generates interface-localized low-energy states, providing the natural explanation for the double-peak structure. In a nanowire geometry with extended normal metallic regions, the same feature persists but the Majorana bound states become more sensitive to the chemical potential compared to the case in planar Josephson junction. In a T-shaped Josephson junction, multiple near-zero-energy states appear, and the Majorana bound state expected at the crossing point is found to be localized near the interfaces, demonstrating that the localization of the Majorana bound states is primarily governed by interface boundaries rather than by the junction geometry. These results show that anisotropic hopping and interface structure play a central role in altermagnet-based topological superconductors and provide a promising route toward a network of controllable Majorana bound states without external magnetic fields.

cond-mat.supr-con↗

arXiv2025

Selective Amplification of the Topological Hall Signal in Cr$_2$Te$_3$: The Role of Molecular Exchange Coupling

Layered magnetic transition-metal chalcogenides (TMCs) are a focal point of research, revealing a variety of intriguing magnetic and topological ground states. Within this family of TMCs, chromium telluride has garnered significant attention because of its excellent tunability in magnetic response, owing to the presence of competing magnetic exchange interactions. We here demonstrate the manipulation of magnetic anisotropy in ultra-thin Cr$_2$Te$_3$ films through growth engineering leading to a controlled transition from in-plane to out-of-plane orientation with an intermediate non-coplanar magnetic ground phase characterized by a topological Hall effect. Moreover, interfacing these films with Vanadyl phthalocyanine (VOPc) molecules prominently enhances the non-coplanar magnetic phase, attributing its presence to the competing interfacial magnetic exchange interactions over the spin-orbit-driven interfacial effects. These findings pave the way for the realization of novel topological spintronic devices through interface-modulated exchange coupling.

cond-mat.mtrl-sci↗

arXiv2025

Interface controlled Berry phase and anisotropic spin-charge conversion in altermagnet-topological insulator bilayers

We propose an altermagnet-topological insulator bilayer as a platform to engineer Berry phase driven spin-charge responses using an interfacial buffer layer. Using a momentum-space lattice model and linear-response theory, we investigate a $d$-wave altermagnet coupled to a topological insulator and highlight the crucial role of spin-flip tunneling in shaping its electronic and transport properties. Interfacial hybridization strongly modifies the band structure, leading to anisotropic Rashba-Edelstein and Hall responses. The spin-flip component of the coupling induces an inverse $d$-wave spin texture in the altermagnetic bands, signaling the onset of an altermagnetic topological phase. This coupling also renders the Rashba-Edelstein effect strongly in-plane anisotropic, enhancing the transverse response relative to ferromagnetic or antiferromagnetic analogues. These results establish interfacial spin-flip tunneling as a practical control knob for direction-sensitive, stray-field-free spin-charge conversion in correlated topological heterostructures.

cond-mat.mes-hall↗

arXiv2025

Diode effect in a skyrmion-coupled high-temperature Josephson junction

We show that a planar Josephson junction having $d$-wave superconducting regions, with a skyrmion crystal placed underneath, produces a robust gate-tunable superconducting diode effect. The spatially-varying exchange field of the skyrmion crystal breaks both inversion and time-reversal symmetries, leading to an asymmetric current-phase relation with an anomalous phase shift. Our theoretical calculations, obtained using resistively and capacitively shunted junction model combined with Bogoliubov-de Gennes method, reveal that the diode efficiency is largely tunable by controlling external gate voltage and skyrmion radius. Incorporation of a $d$-wave superconductor such as high-$T_c$ Cuprate enables the diode to function at higher operating temperatures. Our results establish a unique and practically-realizable mechanism for devising tunable field-free superconducting diodes based on magnetic texture-superconductor hybrid platforms.

cond-mat.supr-con↗

arXiv2025

Multiple Majorana bound states and their resilience against disorder in planar Josephson junctions

Planar Josephson junctions are theoretically predicted to harbor zero-energy Majorana bound states (MBS) in a tunable two-dimensional geometry, at the two ends of the middle metallic channel. Here we show that three distinct topological superconducting regimes, governing the localization of the near-zero-energy MBS, appear in these planar Josephson junctions. The topologically-protected MBS appear near the narrow edges of the junction -- not only in the middle metallic channel but also in the superconducting leads which have widths similar to the values used in recent experiments. We incorporate random fluctuation in the chemical potential to investigate the influence of non-magnetic disorder on the localization of the MBS in different topological regimes and find that the MBS are quite robust against disorder because of the two-dimensional geometry. Interestingly, moderate amount of disorder reduces the splitting between the MBS pairs, possibly by minimizing the wave function overlap of the MBS. We also discuss the changes in the topological superconducting phases when the superconducting lead width is varied. Our results reveal a rich structure of the localization of topologically protected multiple MBS in experimentally-accessible planar Josephson junctions, and call for their experimental confirmation.

cond-mat.supr-con↗

arXiv2025

Superconducting pairing symmetries in charge-ordered kagomé metals

We investigate the superconducting state in a kagomé lattice, with intertwined charge order and time-reversal symmetry-breaking loop current, using self-consistent Bogoliubov-de Gennes formalism to find the emergent pairing symmetries. Using local and nearest-neighbor attractive interactions, treated within Hartree-Fock mean-field approximation, we obtain all possible pairing symmetries in position space. Our findings indicate that the uniform $s$-wave symmetry, arising in the absence of the charge order and the loop current, modifies to a pair density wave of $s$-wave symmetry of 2$\times$2 lattice periodicity in the presence of the charge order, and a chiral pair density wave of $d_{x^2-y^2}\!+\!id_{xy}$-wave symmetry of the same 2$\times$2 periodicity in the presence of the charge order and loop current order, in both onsite and nearest-neighbor channels. In the absence of inversion symmetry, such as in the thin-film geometry, Rashba spin-orbit coupling appears, inducing an additional nearest-neighbor triplet $p_x\pm ip_y$-wave pairing. The results are relevant to superconductivity found in $A$V$_{3}$Sb$_{5}$ ($A$ = K, Rb, Cs), coexisting with a charge order that breaks time-reversal symmetry. We discuss fingerprints of these different pairing symmetries in scanning tunneling microscopy experiments.

cond-mat.supr-con↗

arXiv2025

Magnetic field-free braiding and nontrivial fusion of Majorana bound states in high-temperature planar Josephson junctions

Demonstration of non-Abelian statistics of Majorana bound states (MBS) is crucial for the realization of fault-tolerant topological quantum computation. Two-dimensional platforms such as planar Josephson junctions require an in-plane magnetic field to generate a pair of MBS at its non-superconducting channel ends; however, the fixed direction of the in-plane magnetic field puts a constraint on the realization of a multi-terminal topological planar junction, and hence its ability to physically move multiple MBS -- which is necessary for performing the fusion and braiding operations. Here we show that in a planar Josephson junction coupled to a skyrmion crystal, which can generate multiple pairs of MBS in the absence of any external magnetic field, the non-trivial fusion and braiding operations can be performed. Our numerical calculations, designed for realistic two-dimensional quantum systems, certify the feasibility of experimental realization of the proposed device schemes. We find that both $s$-wave and $d$-wave superconducting leads can generate the MBS; indicating that the MBS movement operations can be performed at higher temperatures using $d$-wave superconducting leads. Our results establish that the skyrmion crystal-coupled planar Josephson junction is a viable platform for the generation and controlled movement of the MBS.

cond-mat.supr-con↗

arXiv2025

Novel phenomena in transition-metal oxide thin films and heterostructures with strong correlations and spin-orbit coupling

Transition-metal oxides have been a central subject of condensed matter physics for decades. In addition to novel electronic states driven by the influence of strong correlation, relativistic spin-orbit coupling effects have recently attracted much attention for their potential to explore topological phenomena. In this article, we review various experimental and theoretical studies on transition-metal oxides with focus on thin films and heterostructures where their physics is much influenced by correlation effects and spin-orbit coupling. The combination of the heterostructure geometry together with correlation and topology leads to a variety of novel states here reviewed. We also discuss perspectives for future research in this broad promising area.

cond-mat.mtrl-sci↗

arXiv2024

Anisotropic planar Hall effects in Bi$_2$Se$_3$/EuS interfaces: Deciphering the role of proximity induced spin canting and topological spin texture

Proximity coupling of ferromagnetic insulator EuS to the topological insulator Bi$_2$Se$_3$ has been proposed to break time-reversal symmetry near the surface of Bi$_2$Se$_3$, introducing an energy gap or a tilt in the surface Dirac cone. As an inverse proximity effect, strong spin-orbit coupling available in the topological surface states can enhance the Curie temperature of ferromagnetism in EuS largely beyond its bulk value, and also generate a magnetic anisotropy. This can result in a canting of the magnetic moment of Eu ions in a plane perpendicular to the interface. Here, we investigate theoretically electronic transport properties arising from the Bi$_2$Se$_3$/EuS interfaces in the planar Hall geometry. Our analysis, based on a realistic model Hamiltonian and a semi-classical formalism for the Boltzmann transport equation, reveals distinct intriguing features of anisotropic planar Hall conductivity, depending on different scenarios for the canting of the Eu moments: fixed Eu moment canting, and freely-orientable Eu moment in response to the external in-plane magnetic field. The anisotropy in the planar Hall conductivity arises from the asymmetric Berry curvature of the gapped topological surface states. We also explore topological Hall effect of the Dirac surface states, coupled to a skyrmion crystal which can emerge in the EuS due to the interplay of ferromagnetic Heisenberg exchange, interfacial Dzyaloshinskii-Moriya interaction, and perpendicular alignment of the Eu moment. Our study provides new impetus for probing complex interplay between magnetic exchange interactions and topological surface states via anisotropic planar Hall effects.

cond-mat.mes-hall↗

arXiv2024

Layer-dependent electronic structures and magnetic ground states of polar-polar $\rm{LaVO_3/KTaO_3}$ (001) heterostructures

Employing a first-principles and model Hamiltonian approach, we work out the electronic properties of polar-polar LaVO$_3$/KTaO$_3$ (LVO/KTO, 001) heterostrctures, with up to six layers of KTO and five layers of LVO. Our analyses indicate the existence of multiple Lifshitz transitions (LTs) within the $t_{2g}$ bands, which can be fine-tuned by adjusting the number of LVO layers or applying gate voltage. Contrary to the experimental report, spin-orbit coupling is found to be negligible, originating solely from the Ta $5d_{xy}$-derived band of KTO, while the 5$d_{xz}$ and 5$d_{yz}$ bands are considerably away from the Fermi level while LVO overlayers having no role in it. Magnetic properties of the heterostructures, due to Vanadium ions, exhibit a pronounced sensitivity to the number of LVO and KTO layers. Our calculations indicate that the interlayer AFM, (so called A-AFM), is energetically most favorable. This is further supported by ground state energy calculations on extended $\sqrt{2}\times\sqrt{2}$ supercells. Moreover, we find that an insulator to metal transition at the interface requires four LVO layers, corroborating the experimental observation. The interfaces featuring ferromagnetic (FM) ground states turn out to be \textit{half-metallic} after the critical thickness is reached. Considerations of the magnetic interactions appear crucial for the experimentally observed critical thickness for metallicity.

cond-mat.mtrl-sci↗

arXiv2024

Anomalous magnetoentropic response of skrymion crystals

We investigate theoretically magnetoentropic signatures of the crystal phase of magnetic skyrmions of various kinds, commonly appearing in two dimensions, \textit{viz.}, Néel, Bloch and anti skyrmions. Using Monte Carlo calculations based on spin Hamiltonians, we obtain magnetic entropy change $ΔS_m$ in the presence of three different types of Dzyaloshinskii-Moriya interactions responsible for these skyrmions. The phase mapping of $ΔS_m$ using skyrmion counting number $N_{sk}$ in temperature-magnetic field plane reveals fluctuation-dominated weak first-order transition in the precursor phase of the skyrmions, and a sign change in $ΔS_m$ when the system enters into the skyrmion crystal phase -- in agreement with recent experimental findings. We also find that the fractional entropy change in going from a ferromagnetic phase to the skyrmion crystal phase is much larger compared to the conventional route of paramagnetic phase to ferromagnetic phase, used for the purpose of magnetic cooling. The magnetoentropic signatures of the different types of skyrmion crystals are found to be similar. Our results indicate that the skyrmion crystals exhibit enhanced cooling efficiency and have the potential to upgrade the existing magnetic cooling methods.

cond-mat.str-el↗

arXiv2024

Challenges in detecting topological superconducting transitions via supercurrent and phase probes in planar Josephson junctions

Topological superconductors harbor, at their boundaries and vortex cores, zero-energy Majorana bound states, which can be the building blocks in fault-tolerant topological quantum computing. Planar Josephson junctions host such topological superconducting phases, highly tunable by external magnetic field or phase difference between the superconducting leads. Despite many theoretical and experimental studies, the signatures of the transition to a topological superconducting phase, based on minima in the critical supercurrent $I_c$ flowing across the junction, $0$-$π$ transition in the ground state junction phase and their anisotropic magnetic-field response have remained unsettled. Using rigorous numerical calculations with several experimentally-relevant parameter settings, we show that $I_c$ and $φ_{_{\rm GS}}$ cannot indicate unambiguously topological transition in any realistic planar junctions. Furthermore, the anisotropic variations of $I_c$ and $φ_{_{\rm GS}}$ with in-plane magnetic field appear in junctions that are undoubtedly in trivial superconducting phase, raising concerns on the effectiveness of these probes in identifying topological transitions in planar junctions. We discuss possible strategies to confirm a topological superconducting phase in these platforms.

cond-mat.supr-con↗

arXiv2023

Chiral pair density wave as a precursor of the pseudogap in kagomé superconductors

Motivated by scanning tunneling microscopy experiments on $A$V$_3$Sb$_5$ ($A$ = Cs, Rb, K) that revealed periodic real-space modulation of electronic states at low energies, I show using model calculations that a triple-{\bf Q} chiral pair density wave (CPDW) is generated in the superconducting state by a charge order of $2a\! \times \!2a$ superlattice periodicity, intertwined with a time-reversal symmetry breaking orbital loop current. In the presence of such a charge order and orbital loop current, the superconducting critical field is enhanced beyond the Chandrasekhar-Clogston limit. The CPDW correlation survives even when the long-range superconducting phase coherence is diminished by a magnetic field or temperature, stabilizing an exotic granular superconducting state above and in the vicinity of the superconducting transition. The presented results suggest that the CPDW can be regarded as the origin of the pseudogap observed near the superconducting transition.

cond-mat.supr-con↗

arXiv2023

Majorana corner states on the dice lattice

Lattice geometry continues providing exotic topological phases in condensed matter physics. Exciting recent examples are the higher-order topological phases, manifesting via localized lower-dimensional boundary states. Moreover, flat electronic bands with a non-trivial topology arise in various lattices and can hold a finite superfluid density, bounded by the Chern number $C$. Here we consider attractive interaction in the dice lattice that hosts flat bands with $C=\pm2$ and show that the induced superconducting state exhibits a second-order topological phase with mixed singlet-triplet pairing. The second-order nature of the topological superconducting phase is revealed by the zero-energy Majorana bound states at the lattice corners. Hence, the topology of the normal state dictates the nature of the Majorana localization. These findings suggest that flat bands with a higher Chern number provide feasible platforms for inducing higher-order topological superconductivity.

cond-mat.supr-con↗

arXiv2022

Out of Equilibrium Majoranas in Interacting Kitaev Chains

We employ a time-dependent real-space local density-of-states method to study the movement and fusion of Majorana zero modes in the 1D interacting Kitaev model, based on the time evolution of many-body states. We analyze the dynamics and both fusion channels of Majoranas using time-dependent potentials, either creating {\it Walls} or {\it Wells}. % focusing on the local density-of-states and charge-density of fermions varying with time. For fast moving Majoranas, we unveil non-equilibrium signatures of the ``strong-zero mode'' operator (quasi parity degeneracy in the full spectrum) and its breakdown in the presence of repulsive Coulomb interactions. Focusing on forming a full electron after fusion, we also discuss upper and lower limits on the Majorana speed needed to reduce non-adiabatic effects and to avoid poisoning due to decoherence.

cond-mat.supr-con↗

arXiv2022

Topological flat bands in a kagomé lattice multiorbital system

Flat bands and dispersive Dirac bands are known to coexist in the electronic bands in a two-dimensional kagome lattice. Including the relativistic spin-orbit coupling, such systems often exhibit nontrivial band topology, allowing for gapless edge modes between flat bands at several locations in the band structure, and dispersive bands or at the Dirac band crossing. Here, we theoretically demonstrate that a multiorbital system on a kagome lattice is a versatile platform to explore the interplay between nontrivial band topology and electronic interaction. Specifically, here we report that the multiorbital kagome model with the atomic spin-orbit coupling naturally supports topological bands characterized by nonzero Chern numbers $\cal C$, including a flat band with $|{\cal C}| =1$. When such a flat band is $1/3$ filled, the non-local repulsive interactions induce a fractional Chern insulating state. We also discuss the possible realization of our findings in real kagome materials.

cond-mat.str-el↗

arXiv2022

Interfacial phase frustration stabilizes unconventional skyrmion crystals

Chiral magnetic phases with an unconventional topological twist in the magnetization are of huge interest due to their potential in spintronics applications. Here, we present a general method to induce such exotic magnetic phases using interfacial phase frustration within artificially grown superlattices. To demonstrate our method, we consider a multilayer with two different chiral magnetic phases as the competing orders at the top and bottom and show, using Monte Carlo calculations, that the interfacial phase frustration is realized at the central layer. In particular, we obtain three unconventional phases: a checkerboard skyrmion crystal, an incommensurate skyrmion stripe, and a ferrimagnetic skyrmion crystal. In these frustration-induced phases, the spin chirality driven topological Hall conductivity can be largely enhanced. This method provides a playground to realize unconventional magnetic phases in any family of materials that can be grown in superlattices.

cond-mat.str-el↗