arXiv subjects

Arijit Saha

Publications and source records attributed to Arijit Saha.

At least 37 records · Page 2Linked to original sources

arXiv2025

Transport signatures of single and multiple Floquet Majorana modes in one-dimensional Rashba nanowire and Shiba chain

We theoretically investigate the transport signature of single and multiple Floquet Majorana end modes~(FMEMs), appearing in an experimentally feasible setup with Rashba nanowire~(NW) placed in closed proximity to a conventional $s$-wave superconductor, in the presence of an external Zeeman field. Periodic drive causes the anomalous $π$-modes to emerge in addition to the regular $0$-modes in the driven system where the former does not exhibit any static analog. For single $0$- and/or $π$-FMEM, differential conductance exhibits a quantized value of $2e^{2}/h$ while we consider the sum over all the photon sectors, supporting Floquet sum rule. We examine the stability of this summed conductance against random onsite disorder. We further investigate the summed conductance in several cases hosting multiple~(more than one) $0$- or $π$-modes at the end of the NW. In these cases, we obtain quantized values of $n_{M}\times 2e^{2}/h$ in summed differential conductance with $n_{M}$ being the number of modes~($0$ or $π$) localized at one end of the NW. We repeat our analysis for another experimentally realizable model system known as helical Shiba chain. Moreover, we corroborate our results by computing the differential conductance for FMEMs using non-equilibrium Green's function method. Our work opens up the possibility of studying the transport signatures of FMEMs in these realistic models.

cond-mat.mes-hall↗

arXiv2025

Topological Majorana zero modes and the superconducting diode effect driven by Fulde-Ferrell-Larkin-Ovchinnikov pairing in a helical Shiba chain

We propose a theoretical framework for the realization of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing in a helical Shiba chain subjected to an out-of-plane Zeeman field, analyzed through a self-consistent Bogoliubov-de-Gennes (BdG) mean-field formalism approach. A chain of magnetic adatoms with helical spin texture deposited on the surface of a common $s$-wave superconductor, has emerged as a pivotal platform for realizing topological Majorana zero modes (MZMs). Our study reveals the crucial role of finite momentum pairing of Cooper pairs in the form of FFLO state which also supports topological MZMs at the ends of the chain. Interestingly, we demonstrate that FFLO pairing facilitates non-reciprocal charge transport, giving rise to superconducting diode effect in our system where both time-reversal and inversion symmetries are broken. Such diode effect stems directly from the presence of finite Cooper pair momentum of the FFLO ground state. Our comprehensive analysis highlights the intricate interplay between the richness of helical Shiba chain, the out-of-plane Zeeman field, and FFLO pairing in the emergence of MZMs and driving the superconducting diode effect. These findings offer valuable insights into the design and realization of topological superconducting devices with diode-like properties, potentially advancing technological applications in quantum computing and superconducting electronics.

cond-mat.supr-con↗

arXiv2025

Distinguishing between topological Majorana and trivial zero modes via transport and shot noise study in an altermagnet heterostructure

We theoretically investigate the transport and shot noise properties of a one-dimensional semiconducting nanowire with Rashba spin-orbit coupling~(SOC) placed in closed proximity to a bulk $s$-wave superconductor and an altermagnet with $d$-wave symmetry. Such heterostructure with vanishing net magnetization manifests itself as an alternative route to anchor Majorana zero modes~(MZMs) characterized by appropriate topological index~(winding number $W$). Interestingly, this system also hosts accidental zero modes~(AZMs) emerged with vanishing topological index indicating their non-topological nature. Furthermore, by incorporating three terminal setup, we explore the transport and shot noise signatures of these zero modes. At zero temperature, we obtain zero bias peak (ZBP) in differential conductance to be quantized with value $|W|\times 2 e^{2}/h$ for MZMs. On the other hand, AZMs exhibit non-quantized value at zero bias. Moreover, zero temperature shot noise manifests negative~(positive) value for MZMs~(AZMs) within the bulk gap. At finite temperature, shot noise exhibits negative value~(negative to positive transition) concerning MZMs~(AZMs). Thus, the obtained signatures clearly distinguish between the MZMs and non-topological AZMs. We extend our analysis by switching on the next to nearest neighbor hopping amplitude and SOC. Our conclusion remains unaffected for this case as well. Hence, our work paves the way to differentiate between emergent MZMs and AZMs in a semiconductor/ superconductor/ altermagnet heterostructure.

cond-mat.mes-hall↗

arXiv2025

Tailoring topological band properties of twisted double bilayer graphene: effects due to spin-orbit coupling

Our theoretical study unfolds the topological phase transitions (within bands of the Moiré super-lattice) in small angle twisted double bilayer graphene (tDBLG) under the influence of external gate voltage and intrinsic spin-orbit coupling (SOC) for both AB-AB and AB-BA stacking configurations. Utilizing a low-energy continuum model, we investigate the band structure and perform a comprehensive topological characterization of the system by analysing the direct band gap closing as well as various Chern numbers. In the absence of SOC, the tDBLG exhibits characteristics of a valley Hall insulator. However, in the presence of SOC, we observe a transition to a quantum spin Hall insulator state and band topology emerges in the parameter spaces of non-topological regime without SOC. Furthermore, we conduct a comparative analysis between untwisted double bilayer graphene and tDBLG to assess the impact of twisting on the system's properties. Our findings reveal the construction of topological phase diagrams that showcase distinct phases arising from changes in the twist angle compared to the untwisted case. These phase diagrams provide valuable insights into the diverse topological phases achievable in tDBLG with SOC. Our findings contribute to the understanding of the interplay between small twist angle, SOC, and external electric field on the topological band properties of twisted multilayer graphene systems.

cond-mat.mes-hall↗

arXiv2024

Identifying Bogoliubov Fermi surfaces via thermoelectric response in a $d$-wave superconductor heterostructure

We theoretically investigate the thermoelectric response of Bogoliubov Fermi surfaces (BFSs) generated in a two dimensional unconventional $d$-wave superconductor subjected to an external in-plane Zeeman field. These BFSs exhibiting the same dimension as the underlying normal state Fermi surface are topologically protected by combinations of discrete symmetries. Utilizing the Blonder-Tinkham-Klapwijk formalism and considering normal-$d$-wave superconductor hybrid junction, we compute the thermoelectric coefficients including thermal conductance, Seebeck coefficient, figure of merit ($zT$), and examine the validation of Widemann-Franz law in the presence of both voltage and temperature bias. Importantly, as a signature of anisotropic nature of $d$-wave pairing, Andreev bound states (ABSs) formed at the normal-superconductor interface play a significant role in the thermoelectric response. In the presence of ABSs, we observe a substantial enhancement in Seebeck coefficient ($\sim 200\,μ$V/K) and $zT$ ($\sim 3.5$) due to the generation of the BFSs and thus making such setup a potential candidate for device applications. Finally, we strengthen our continuum model results by computing the thermoelectric coefficients based on a lattice-regularized version of our continuum model.

cond-mat.supr-con↗

arXiv2024

Floquet second-order topological Anderson insulator hosting corner localized modes

The presence of random disorder in a metallic system accounts for the localization of extended states in general. On the contrary, the presence of disorder can induce topological phases hosting metallic boundary states out of a non-topological system, giving birth to the topological Anderson insulator phase. In this context, we theoretically investigate the generation of an out of equilibrium higher-order topological Anderson phase in the presence of disorder potential in a time-periodic dynamical background. In particular, the time-dependent drive and the disorder potential concomitantly render the generation of Floquet higher-order topological Anderson insulator~(FHOTAI) phase, while the clean, undriven system is topologically trivial. We showcase the generation of FHOTAI hosting both $0$- and $π$-modes. Most importantly, we develop the real space topological invariant -- a winding number based on chiral symmetry to characterize the Floquet $0$- and $π$-modes distinctly. This chiral winding number serves the purpose of the indicator for the topological phase transition in the presence of drive as well as disorder and appropriately characterizes the FHOTAI.

cond-mat.mes-hall↗

arXiv2024

Corner modes in non-Hermitian next-nearest-neighbor hopping model

We consider a non-Hermitian (NH) analog of a second-order topological insulator, protected by chiral symmetry, in the presence of next-nearest neighbor hopping elements to theoretically investigate the interplay beyond the first nearest neighbor hopping amplitudes and topological order away from Hermiticity. In addition to the four zero-energy corner modes present in the first nearest neighbor hopping model, we uncover that the second nearest neighbor hopping introduces another topological phase with sixteen zero-energy corner modes. Importantly, the NH effects are manifested in altering the Hermitian phase boundaries for both the models. While comparing the complex energy spectrum under open boundary conditions, and bi-orthogonalized quadrupolar winding number in real space, we resolve the apparent anomaly in the bulk boundary correspondence of the NH system as compared to the Hermitian counterpart by incorporating the effect of non-Bloch form of momentum into the mass term. The above invariant is also capable of capturing the phase boundaries between the two different topological phases where the degeneracy of the corner modes is evident, as exclusively observed for the second nearest neighbor model.

cond-mat.mes-hall↗

arXiv2024

Optimizing one dimensional superconducting diodes: Interplay of Rashba spin-orbit coupling and magnetic fields

The superconducting diode effect (SDE) refers to the non-reciprocal nature of the critical current (maximum current that a superconductor can withstand before turning into a normal metal) of a superconducting device. Here, we investigate SDE in helical superconductors with broken inversion and time-reversal symmetry, focusing on a prototypical Rashba nanowire device proximitized by an s-wave superconductor and subjected to external magnetic fields. Using a self-consistent Bogoliubov-de Gennes mean-field formalism, we analyze the interplay between linear and higher-order spin-orbit coupling (SOC), bulk supercurrents, and external magnetic fields. Our results demonstrate that Rashba nanowires with only linear SOC can achieve incredibly large diode efficiencies > 45% through the interplay of longitudinal and transverse magnetic fields. Notably, higher-order SOC introduces qualitatively different behavior, enabling finite diode efficiency even in the absence of a longitudinal Zeeman field due to inherent energy dispersion asymmetry. We present a comprehensive phase diagram of the device elucidating the emergent Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state and demonstrate that proximitized Rashba nanowires offer a versatile, practical platform for SDE, with potential realizations in existing material systems. These results provide crucial insights for optimizing SDE in nanoscale superconducting devices, paving the way for next-generation dissipationless quantum electronics.

cond-mat.supr-con↗

arXiv2024

Fermi arcs mediated transport in inversion symmetry-broken Weyl semimetal nanowire and its hybrid junctions

The emergence of gapless surface states, known as Fermi arcs (FAs), is one of the unique properties of the novel topological Weyl semimetal (WSM). However, extracting the signatures of FAs from the bulk states has always been a challenge as both of them are gapless in nature and connected to each other. We capture the signatures of FAs via transport in an inversion symmetry (IS)-broken WSM. We study the band structure and the properties of FAs like shape, spin polarization considering slab and nanowire (NW) geometry, and then compute the two-terminal conductance in WSM NW in terms of the scattering coefficients within the Landauer formalism. We find the FA-mediated conductance to be quantized in units of $2e^2/h$. We extend our study to the transport in WSM/Weyl superconductor (WSC) NW hybrid junction using the Blonder-Tinkham-Klapwijk (BTK) formalism. We show that due to the intricate spin textures, the signatures of the FAs can be captured via Andreev reflection process. We also show that our results of conductance are robust against delta-correlated quenched disorder and thus enhancing the experimental feasibility.

cond-mat.mes-hall↗

arXiv2024

Transport signatures of Bogoliubov Fermi surfaces in normal metal/time-reversal symmetry broken $d$-wave superconductor junctions

In recent times, Bogoliubov Fermi surfaces (BFSs) in superconductors (SCs) have drawn significant attention due to a substantial population of Bogoliubov quasiparticles (BQPs) together with Cooper pairs (CPs) in them. The BQPs as zero energy excitations give rise to captivating and intricate charge dynamics within the BFSs. In this theoretical study, we propose to reveal the unique signatures of the topologically protected BFSs in bulk $d$-wave SCs using normal metal/time-reversal symmetry (TRS) broken $d$-wave SC hybrid setup, in terms of the differential conductance and Fano factor (FF). Orientation of crystal $a$ axis with respect to junction normal, quantified by the parameter $α$, is crucial for transport properties in these hybrid devices. For $α=0$, an enhancement in zero-bias conductance (ZBC) can be identified as a key signature of BFSs. However, for $α\ne0$, this feature does not replicate due to the presence of the localized Andreev bound state (ABS) at the interface. The interplay of ABS and BFSs gives rise to an anomalous behavior in ZBC compared to the $α=0$ case. This behavior remains qualitatively similar even at finite temperatures. Finally, we explain this anomalous behavior by analyzing the effective charge of the carriers in terms of the FF. The simplicity of our setup based on $d$-wave SC makes our proposal persuasive.

cond-mat.supr-con↗

arXiv2024

Multiple Topological Phase Transitions Unveiling Gapless Topological Superconductivity in Magnet/Unconventional Superconductor Hybrid Platform

We propose a theoretical framework for generating gapless topological superconductivity (GTSC) hosting Majorana flat edge modes (MFEMs) in the presence of a two-dimensional (2D) array of magnetic adatoms with noncollinear spin texture deposited on top of a unconventional superconductor. Our observations reveal two distinct topological phase transitions within the emergent Shiba band depending on the exchange coupling strength ($J$) between magnetic adatom spins and superconducting electrons: the first one designates transition from gapless non-topological to gapless topological phase at lower $J$, while the second one denotes transition from gapless topological to a trivial gapped superconducting phase at higher $J$. The gapless topological superconducting phase survives at intermediate values of $J$, hosting MFEMs. Further, we investigate the nature of the bulk effective pairings which indicate that GTSC appears due to the interplay between pseudo "$s$-wave" and pseudo "$p_{x}+p_y$" types of pairing. Consequently, our study opens a promising avenue for the experimental realization of GTSC in 2D Shiba lattice based on $d$-wave superconductors as a high-temperature platform.

cond-mat.supr-con↗

arXiv2024

Higher-order topological corner and bond-localized modes in magnonic insulators

We theoretically investigate a two-dimensional decorated honeycomb lattice framework to realize a second-order topological magnon insulator (SOTMI) phase featuring distinct corner-localized modes. Our study emphasizes the pivotal role of spin-magnon mapping in characterizing bosonic topological properties, which exhibit differences from their fermionic counterparts. We employ a symmetry indicator topological invariant to identify and characterize this SOTMI phase, particularly for systems respecting time-reversal and ${\sf{C}}_6$ rotational symmetry. Using a spin model defined on a honeycomb lattice geometry, we demonstrate that introducing ``\textit{kekulé}'' type distortions yields a topological phase. In contrast, ``\textit{anti-kekulé}'' distortions result in a non-topological magnonic phase. The presence of kekulé distortions manifests in two distinct topologically protected bosonic corner modes - an \textit{intrinsic} and a \textit{pseudo}, based on the specific edge terminations. On the other hand, anti-kekulé distortions give rise to \SW{\textit{Tamm/Shockley}} type bond-localized boundary modes, which are non-topological and reliant on particular edge termination. We further investigate the effects of random out-of-plane exchange anisotropy disorder on the robustness of these bosonic corner modes. The distinction between SOTMIs and their fermionic counterparts arises due to the system-specific magnonic onsite energies, a crucial feature often overlooked in prior literature. Our study unveils exciting prospects for engineering higher-order topological phases in magnon systems and enhances our understanding of their unique behavior within decorated honeycomb lattices.

cond-mat.mes-hall↗

arXiv2024

Topological Superconductivity by Engineering Noncollinear Magnetism in Magnet/ Superconductor Heterostructures: A Realistic Prescription for 2D Kitaev Model

We report on a realistic and rather general scheme where noncollinear magnetic textures proximitized with the most common $s$-wave superconductor can appear as the alternative to $p$-wave superconductor{--}the prime proposal to realize two-dimensional (2D) Kitaev model for topological superconductors (TSCs) hosting Majorana flat edge mode (MFEM). A general minimal Hamiltonian suitable for magnet/superconductor heterostructures reveals robust MFEM within the gap of Shiba bands due to the emergence of an effective ``$p_x+p_y$"-type $p$-wave pairing, spatially localized at the edges of a 2D magnetic domain of spin-spiral. We finally verify this concept by considering Mn (Cr) monolayer grown on a $s$-wave superconducting substrate, Nb(110) under strain (Nb(001)). In both 2D cases, the antiferromagnetic spin-spiral solutions exhibit robust MFEM at certain domain edges that is beyond the scope of the trivial extension of 1D spin-chain model in 2D. This approach, particularly when the MFEM appears in the TSC phase for such heterostructure materials, offers a perspective to extend the realm of the TSC in 2D.

cond-mat.mes-hall↗

arXiv2024

Time-dependent droplet detachment behaviour from wettability-engineered fibers during fog harvesting

Water collection from natural and industrial fogs has recently been viewed as a viable freshwater source. An interesting outgrowth of the relevant research as focused on arresting of the drift losses (un-evaporated and re-condensed water droplets present in the exhaust plume from industrial cooling towers. Such exploits in fog collection have implemented metal and polyester meshes as fog water collectors (FWC). Fog droplets impinge and deposit on mesh fibers. They coalesce with previously deposited liquid to evolve as larger drops before detaching from the fibers under their own weight, an event largely dependent on the mesh fiber wettability, diameter and its arrangement relative to the fog flow. To better estimate drainage and hence collection from these fibers, the study, focuses on droplet detachment from differently wetted horizontally positioned cylindrical fibers of various diameters, placed orthogonally in the path of an oncoming fog. Droplet detachment volume is found to increase with fiber diameter and fiber surface wettability. Interestingly, in a typical fogging condition, the detachment volume is also found to exhibit a time-dependent behaviour, altering the droplet detachment criteria otherwise predicted from emulation. Our current study sheds light on this unexplored phenomenon.

physics.flu-dyn↗

arXiv2024

Second-order topological superconductor via noncollinear magnetic texture

We put forth a theoretical framework for engineering a two-dimensional (2D) second-order topological superconductor (SOTSC) by utilizing a heterostructure: incorporating noncollinear magnetic textures between an $s$-wave superconductor and a 2D quantum spin Hall insulator. It stabilizes the higher order topological superconducting phase, resulting in Majorana corner modes (MCMs) at four corners of a 2D domain. The calculated non-zero quadrupole moment characterizes the bulk topology. Subsequently, through a unitary transformation, an effective low-energy Hamiltonian reveals the effects of magnetic textures, resulting in an effective in-plane Zeeman field and spin-orbit coupling. This approach provides a qualitative depiction of the topological phase, substantiated by numerical validation within exact real-space model. Analytically calculated effective pairings in the bulk illuminate the microscopic behavior of the SOTSC. The comprehension of MCM emergence is supported by a low-energy edge theory, which is attributed to the interplay between effective pairings of $(p_x + p_y)$-type and $(p_x + i p_y)$-type. Our extensive study paves the way for practically attaining the SOTSC phase by integrating noncollinear magnetic textures.

cond-mat.mes-hall↗

arXiv2023

Generation of higher-order topological insulators using periodic driving

Topological insulators~(TIs) are a new class of materials that resemble ordinary band insulators in terms of a bulk band gap but exhibit protected metallic states on their boundaries. In this modern direction, higher-order TIs~(HOTIs) are a new class of TIs in dimensions $d>1$. These HOTIs possess $(d - 1)$-dimensional boundaries that, unlike those of conventional TIs, do not conduct via gapless states but are themselves TIs. Precisely, an $n^{\rm th}$ order $d$-dimensional higher-order topological insulator is characterized by the presence of boundary modes that reside on its $d_c=(d-n)$-dimensional boundary. For instance, a three-dimensional second (third) order TI hosts gapless (localized) modes on the hinges (corners), characterized by $d_c = 1 (0)$. Similarly, a second-order TI in two dimensions only has localized corner states ($d_c = 0$). These higher-order phases are protected by various crystalline as well as discrete symmetries. The non-equilibrium tunability of the topological phase has been a major academic challenge where periodic Floquet drive provides us golden opportunity to overcome that barrier. Here, we discuss different periodic driving protocols to generate Floquet higher-order TIs while starting from a non-topological or first-order topological phase. Furthermore, we emphasize that one can generate the dynamical anomalous $π$-modes along with the concomitant $0$-modes. The former can be realized only in a dynamical setup. We exemplify the Floquet higher-order topological modes in two and three dimensions in a systematic way. Especially, in two dimensions, we demonstrate a Floquet second-order TI hosting $0$- and $π$ corner modes. Whereas a three-dimensional Floquet second-order TI and Floquet third-order TI manifest one- and zero-dimensional hinge and corner modes, respectively.

cond-mat.mes-hall↗

arXiv2023

Engineering anomalous Floquet Majorana modes and their time evolution in helical Shiba chain

We theoretically explore the Floquet generation of Majorana end modes~(MEMs) (both regular $0$- and anomalous $π$-modes) implementing a periodic sinusoidal modulation in chemical potential in an experimentally feasible setup based on a one-dimensional chain of magnetic impurity atoms having spin spiral configuration (out-of-plane Néel-type) fabricated on the surface of most common bulk $s$-wave superconductor. We obtain a rich phase diagram in the parameter space, highlighting the possibility of generating multiple $0$-/$π$-MEMs localized at the end of the chain. We also study the real-time evolution of these emergent MEMs, especially when they start to appear in the time domain. These MEMs are topologically characterized by employing the dynamical winding number. We observe that the existing perturbative analysis is unable to explain the numerical findings, indicating the complex mechanism behind the formation of the Floquet Shiba minigap, which is characteristically distinct from other setup e.g. Rashba nanowire model. We also discuss the possible experimental parameters in connection to our model. Our work paves the way to realize the Floquet MEMs in a magnet-superconductor heterostructure.

cond-mat.mes-hall↗

arXiv2023

Thermoelectric properties of inversion symmetry broken Weyl semimetal-Weyl superconductor hybrid junctions

We theoretically investigate the thermoelectric properties (electronic contribution) of a hybrid structure comprising of an inversion symmetry broken Weyl semimetal (WSM) and intrinsic Weyl superconductor (WSC) with $s$-wave pairing, employing the Blonder-Tinkham-Klapwijk formulation for non-interacting electrons. Our study unfolds interesting features for various relevant physical quantities such as the thermal conductance, the thermoelectric coefficient and the corresponding figure of merit. We also explore the effects of an interfacial insulating (I) barrier (WSM-I-WSC set-up) on the thermoelectric response in the thin barrier limit. Further, we compute the ratio of the thermal to the electrical conductance in different temperature regimes and find that the Wiedemann-Franz law is violated for small temperatures (below critical temperature $T_{c}$) near the Weyl points while it saturates to the Lorentz number, away from the Weyl points, at all temperatures irrespective of the barrier strength. We compare and contrast this behaviour with other Dirac material heterostructures and provide a detailed analysis of the thermal transport. Our study can facilitate the fabrication of mesoscopic thermoelectric devices based on WSMs.

cond-mat.mes-hall↗