arXiv subjects

Amartya Pal

Publications and source records attributed to Amartya Pal.

12 recordsLinked to original sources

arXiv2026

Current switching behavior mediated via hinge modes in higher-order topological phases using altermagnets

We propose a theoretical framework to engineer hybrid-order and higher-order topological phases in three-dimensional topological insulators by coupling to $d$-wave altermagnets (AMs). Presence of only $d_{x^2-y^2}$-type AM drives the system into a hybrid-order topological phase where both first-order and second-order topological phases coexist. This phase is characterized by spectral analysis, low-energy surface theory, dipolar and quadrupolar winding numbers, and it's signature is further confirmed by two-terminal differential conductance calculations. Incorporation of the $d_{x^2-z^2}$-type AM drives the system into two second-order topological insulator phases hosting distinct type of hinge modes. These two variants of second-order topological phases are also topologically characterized by spectral analysis, topological invariants, low-energy surface thoery, and transport calculations. Importantly, the localization and direction of propagation of these one-dimensional hinge modes are controllable by tuning the relative strengths of the alermagnetic exchange orders. We utilize this feature to propose a tunable current-switching behaviour mediated via the hinge modes. Our results establish AMs based hybrid structure as a versatile platform for controllable higher-order topology and hinge-mediated device applications.

cond-mat.mes-hall↗

arXiv2026

Topological superconductivity and superconducting diode effect mediated via unconventional magnet and Ising spin-orbit coupling

We propose a theoretical framework in which a one-dimensional (1D) tight-binding model incorporating unconventional magnetic order together with Rashba and Ising spin-orbit couplings are considered to realize two key phenomena in condensed matter systems: topological superconductivity and the superconducting diode effect (SDE). We first elucidate the underlying band topology of the normal-state Hamiltonian and subsequently introduce an on-site attractive Hubbard interaction. Performing a a self-consistent mean-field analysis, we establish superconducting order parameters in both the conventional Bardeen-Cooper-Schrieffer (BCS) and finite-momentum Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing channels. Intriguingly, both pairing states can support topological superconductivity, characterized by a nontrivial winding number, and lead to the emergence of four zero-energy Majorana modes localized at the ends of the 1D chain. The FFLO state further gives rise to an intrinsic field-free SDE, manifested as a nonreciprocal supercurrent and quantified by the diode efficiency $η$. Notably, our model yields a large diode efficiency $η\sim 65\%$, highlighting its potential for realising topological superconductivity and highly efficient superconducting devices.

cond-mat.mes-hall↗

arXiv2026

Proximity-induced superconductivity and emerging topological phases in altermagnet-based heterostructures

We present a theoretical framework for investigating superconducting proximity effect in altermagnet (AM)-superconductor (SC) heterostructures. In general, AMs, characterized by vanishing net magnetization but spin-split electronic spectra, provide a promising platform for realizing unconventional magnetic phases. We consider a two-dimensional $d$-wave AM proximity coupled to a three dimensional ordinary $s$-wave SC. By integrating out the superconducting degrees of freedom, we derive an effective Hamiltonian that describes the proximity-induced modifications in the AM layer in the form of a self-energy. We then derive an effective Green's function to obtain the proximity-induced pairing amplitudes in the AM layer and classify the induced pairing amplitudes according to their parity, frequency, and spin. We find the presence of even-parity singlet and triplet pairing amplitudes in the AM layer. To achieve the odd-parity triplet components, important to realize topological superconductivity, we introduce a layer of Rashba spin-orbit coupling (RSOC) in the heterostructure. We analyse the band topology of this proximity-induced AM-RSOC layer and demonstrate the emergence of both weak and strong topological superconducting phases with edge-localized modes, characterized by winding number and Chern number. These findings highlight the role of AM-SC hybrid setup as a versatile platform for realizing odd-parity triplet pairings and engineering topological superconductivity in two-dimension.

cond-mat.supr-con↗

arXiv2026

Emergent superconducting phases in unconventional $p$-wave magnets: Topological superconductivity, Bogoliubov Fermi surfaces and superconducting diode effect

The recent discovery of unconventional momentum-dependent magnetic orders has expanded the landscape of magnetism beyond conventional ferromagnetism and antiferromagnetism. Among them, $p$-wave magnets ($p$WMs) represent a novel class of odd-parity, non-collinear compensated magnetic order that generates spin-split electronic bands. In this work, our theoretical investigation establishes $p$WMs as a versatile platform for realizing intriguing superconducting phases including topological superconductivity (TSC), Bogoliubov Fermi surfaces (BFSs), and superconducting diode effect (SDE), within a unified microscopic framework. Employing a minimal model incorporating $p$-wave magnetic order, exchange coupling, and Zeeman fields, we perform a self-consistent mean-field analysis and uncover a rich phase diagram featuring unconventional finite-momentum Fulde-Ferrell (FF) and Larkin-Ovchinnikov (LO) superconducting phases. Remarkably, we also show that $p$WMs can undergo a transition to a TSC phase anchoring Majorana flat edge modes, a hallmark of two-dimensional TSCs, even without Rashba spin-orbit coupling and Zeeman field. Upon applying a Zeeman field, gapless FF and LO phases emerge with BFSs characterized by the appearance of finite zero-energy quasiparticle density of states. Furthermore, we demonstrate that SDE arises naturally in the asymmetric FF phase. Our analysis manifests that $p$WMs serve as a unique and novel platform to host TSC phase, gapless superconducting states, and non-reciprocal transport phenomena.

cond-mat.supr-con↗

arXiv2025

Josephson current signature of Floquet Majorana and topological accidental zero modes in altermagnet heterostructures

We theoretically investigate the generation and Josephson current signatures of Floquet Majorana end modes (FMEMs) in a periodically driven altermagnet (AM) heterostructure. Considering a one-dimensional (1D) Rashba nanowire (RNW) proximitized to a regular $s$-wave superconductor and a $d$-wave AM, we generate both $0$- and $π$-FMEMs by driving the nontopological phase of the static system. While the static counterpart hosts both topological Majorana zero modes (MZMs) and nontopological accidental zero modes (AZMs), the drive can gap out the static AZMs and generate robust $π$-FMEMs, termed as topological AZMs (TAZMs). We topologically characterize the emergent FMEMs via dynamical winding numbers exploiting chiral symmetry of the system. Moreover, we consider a periodically driven Josephson junction comprising of RNW/AM-based 1D topological superconduting setup. We identify the signature of MZMs and FMEMs utilizing $4π$-periodic Josephson effect, distinguishing them from trivial AZMs exhibiting $2π$-periodicty, in both static and driven platforms. This Josephson current signal due to Majorana modes survives even in presence of finite disorder. Our work establishes a route to realize and identify FMEMs in AM-based platforms through Floquet engineering and Josephson current response.

cond-mat.mes-hall↗

arXiv2025

Identifying Majorana edge and end modes in a Josephson junction of a $p$-wave superconductor with a magnetic barrier

We propose a theoretical model describing a Josephson junction featuring a magnetically textured barrier within two-dimensional (2D) $p$-wave superconductor, considering both $p_x + p_y$ and $p_x + ip_y$ type pairing symmetries. Our study reveals the influence of the magnetic barrier strength and its spatial periodicity on the system's topological properties, in terms of local density of states and Josephson current calculations. Notably, we demonstrate that these parameters regulate the number of Majorana zero modes at the junction in the topological regime. Our setup further allows for the identification of three distinct topological phases, the differentiation between one-dimensional (1D) Majorana edge (either flat/dispersive and arising from intrinsic 2D $p$-wave pairing) and localized Majorana end modes, and an analysis of their hybridization through the Josephson current. In particular, the Josephson current exhibits a discontinuous jump due to the edge modes and pronounced hump in the $p_x + ip_y$ pairing case, directly linked to the hybridized Majorana modes. Moreover, our study opens a possible interesting avenue to distinguish between 1D Majorana edge modes and zero-dimensional end modes via Josephson current signatures.

cond-mat.supr-con↗

arXiv2025

Multi higher-order Dirac and nodal line semimetals

In recent years, there has been a surge of interest in exploring higher-order topology and their semi-metallic counterparts, particularly in the context of Dirac, Weyl, and nodal line semimetals, termed as higher-order Dirac semimetal (HODSM), higher-order Weyl semimetal, and higher-order nodal line semimetal (HONLSM). The HODSM phase exhibits hinge Fermi arcs (FAs) with a quantized higher-order topological invariant. Conversely, the HONLSM phase is a hybrid-order topological phase manifesting both drumhead-like surface states and hinge FAs as a signature of first- and second-order topology, and also possesses both first- and second-order topological invariants. In this work, we investigate a tight binding model for multi-HODSM (mHODSM) hosting multiple hinge FAs having a quantized quadrupolar winding number (QWN) greater than one. Furthermore, we obtain a multi-HONLSM (mHONLSM) phase from the mHODSM by applying an external magnetic field, which breaks the $PT$-symmetry. The mHONLSM phase possesses both the dipolar winding number, non-vanishing only inside the nodal loops, being the representative invariant for first-order topology, and the QWN, featuring both drumhead-like surface states and multiple hinge FAs. We study the spectral properties of the mHODSM and mHONLSM in different geometries. We also investigate the hinge FA-mediated transport in HONLSM employing a two-terminal setup.

cond-mat.mes-hall↗

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↗

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

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.

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