arXiv subjects

Surajit Mandal

Publications and source records attributed to Surajit Mandal.

13 recordsLinked to original sources

arXiv2026

Fidelity susceptibility of Su-Schrieffer-Heeger model with further neighbour hopping term

In this study, topological phase transition in Su-Schrieffer-Heeger (SSH) model with a further neighbour hopping term has been studied in terms of fidelity susceptibility. Topological phase transition point in the standard SSH model has been identified before by noting the divergence of fidelity susceptibility. The same approach has been employed here where fidelity susceptibility is found to diverge at the phase transition points. Additionally, effect of staggered potential on the fidelity susceptibility has been explored. Analytic expression for fidelity susceptibility has been obtained along with its numerical estimation on finite chains by exact diagonalization. Fidelity susceptibility exhibits sharp peaks at the phase transition points in both approaches. Scaling exponent of this divergence has been obtained numerically which is found to agree to that of the standard SSH model without further neighbour terms.

cond-mat.mes-hall↗

arXiv2026

Transitions and Critical Divergences in Periodically Hopping Modulated Su-Schrieffer-Heeger Chains

We use a curvature renormalization group (CRG) approach to study the topological phase transitions in a Su-Schrieffer-Heeger chain and its extensions coming from periodic hopping modulations. A curvature function is defined in terms of system parameters near high-symmetry points where the divergence of this function at critical points, in analogy to usual phase transitions, signals a topological phase transition. According to this theory, the phase transition line for the two-site Su-Schrieffer-Heeger (SSH) model is visible at the critical line \Delta = 0 where the curvature function diverges. Our study involves this model and also the modulated one with periodicity of four lattice spacing where the curvature function not only diverges at the topological phase transition point (Dirac-like) |\Delta/t| = \sqrt(2) but also shows faster divergence at the non-topological gapless point \Delta = 0. We further notice faster divergence of correlation length for \Delta -> 0 as compared to that for the |\Delta/t| -> \sqrt(2) resulting in two different sets of critical exponents making them lie in different universality classes. The edge state exhibits very slow decay into the bulk near the \Delta = 0 point while a much quicker decay from edge into bulk is discernible around the |\Delta/t| = \sqrt(2) point. We also continue similar analysis for a SSH model with hopping periodicity of eight lattice spacing.

cond-mat.str-el↗

arXiv2026

Quantum Tunneling-induced Hybridization and Coherent Dynamics of Jackiw-Rebbi Zero Modes in a Modified Su-Schrieffer-Heeger Chain

We investigate analytically and numerically the tunneling-induced hybridization and coherent dynamics of Jackiw-Rebbi (JR) zero modes in a modified Su-Schrieffer-Heeger (SSH) model. Unlike the conventional SSH model, this modified system possess two bulk gap closing points, namely, the quadratic-type gap closing point at $k=0$ and the Dirac-type gap closing point at $k=\pm\pi/4a$. While the quadratic point does not support a topological domain wall due to the absence of mass inversion, the low-energy Dirac theory around $k=\pm\pi/4a$ predicts an effective mass that changes sign at two spatially separated interfaces under a kink profile, generating a pair of JR bound states localized at those interfaces. We show that finite overlap between the JR zero modes lifts the zero-energy degeneracy through quantum tunneling, producing symmetric-antisymmetric hybridized states analogous to a quantum mechanical double-well system. An effective two-level description reveals coherent oscillations of the occupation probability between the two JR modes, accompanied by periodic transfer of sublattice polarization between the (A,C) and (B,D) sectors. The oscillation period is governed by the hybridization gap, providing a tunable route for controlling topological bound states. Our results establish a unified framework connecting JR zero modes, quantum tunneling, and coherent dynamics in modified SSH systems, offering a promising platform for controllable topological quantum-state transfer in engineered lattice structures.

cond-mat.str-el↗

arXiv2025

Hawking Temperature of Massive Charged Ads Black Hole: a Topological Treatment

In this work, we investigate the Hawking temperature of a charged Ads black hole (spherically symmetric) on the basis of a completely topological method introduced by Robson, Villari, and Biancalana (RVB). This topological method can give the exact Hawking temperature of the charged Ads black hole. We have also derived the Hawking temperature of a charged Ads black hole considering massive gravity. Due to the presence of mass term in the metric function of the charged Ads black hole in massive gravity, the effect of mass term can't be neglected when calculating the Hawking temperature. In massive gravity, the accurate Hawking temperature can be obtained by including an integral constant term, which can be derived from the standard definition.

gr-qc↗

arXiv2025

Topology and Localizations in a 2D Su-Schrieffer-Heeger Model with Domain Walls, Quasi-periodic Disorder and Periodic Hopping Modulations

We study a two dimensional (2D) Su-Schrieffer-Heeger (SSH) model on a square lattice in presence of domain walls (DW) / vortices or quasi-periodic disorders to investigate the nature of topology and localizations in its quantum states. While in a pure 2D SSH model, zero energy states (ZES) lie within the dispersion continuum and the bound states in continuum (BIC) are localized at the corners, a continuous distributions of DWs can produce localized ZES along the DW lines or at the DW center depending on the orientations of the DWs. Moreover with such DWs, one can witness nonzero energy in-gap states showing localizations at the edges, along the DWs or at the DW center. For probing disorder effect, we introduce on-site quasiperiodic potentials (QP) in such systems that show the usual tendency of the states to localize. But exotic reentrant localization behavior is also captured for judicious choice of the QP term. We also examine the scenario for different hopping periodicities in the SSH Hamiltonian. Interestingly for anisotropic hopping modulations, the bulk ZES gets exhausted leaving only topological boundary modes at zero energies. The fate of these states in presence of the DWs are also discussed. Our present study with its plethora of exotic outcomes can thus inspire varied applications in the field of topological quantum computations.

cond-mat.str-el↗

arXiv2024

Zero Energy States for Commensurate Hopping Modulation of a Generalized Su-Schrieffer-Heeger Chain in the Presence of a Domain Wall

We study the effect of domain wall (DW) on zero-energy states (ZESs) in the Su-Schrieffer-Heeger (SSH) chain. The chain features two fractional ZESs in the presence of such DW, one of which is localized at the edge and the other bound at the location of DW. This zero-energy DW state exhibits interesting modifications when hopping modulation is tuned periodically. We studied the energy spectra for commensurate frequencies $\theta=\pi,\pi/2,\pi/3$ and $\pi/4$. Following the recent study by the author of this paper [S. Mandal, S. Kar, Phys. Rev. B 109, 195124 (2024)], we showed numerically, along with physical intuition, that one ZES can bound at the DW position only for commensurate frequency $\theta=\frac{\pi}{2s+1}$ for zero or an integer $s$ values, while for $\theta=\frac{\pi}{2s}$ with nonzero or an integer $s$ value they appear only at the edges of the chain. We verify our numerical results by using exact analytical techniques. Both analyses indicate the realization of the Jackiw-Rebbi modes for our model only with $\theta=\frac{\pi}{2s+1}$. Moreover, the localization of zero-energy edge and DW states are investigated which reveals their localized (extended) nature for smaller (larger) $\Delta_{0}$ (amplitude of DW). The localization of topological DW states is suppressed as the width of DW ($\xi$) increases (typically scaled as $\sim 1/\xi$) while the edge state shows an extended behavior only for the large $\xi$ limit.

cond-mat.str-el↗

arXiv2024

Topological Solitons in Su-Schrieffer-Heeger Chain with periodic hopping modulation, domain walls and disorder

A chiral symmetric Su-Schrieffer-Heeger (SSH) chain features topological end states in one of its dimerized configurations. Those mid-gap zero energy states show interesting modifications upon a periodic tuning of the hopping modulations. Besides, more and more in-gap end modes appear at nonzero energies for further partitioning of the Brillouin zone (BZ) due to increased hopping periodicity. The new topological phases are identified with a detailed analysis of the topological invariants namely, winding number and Zak phases. The spectra and topology of these systems with periodically modulated hopping are studied also in the presence of a single static domain wall, separating two topologically inequivalent dimerized structures. The domain wall causes additional in-gap modes in the spectrum as well as zero energy domain wall solitonic states for specific hopping periodicities. We also study the effect of disorder, particularly the chirality breaking onsite ones, on the edge and domain wall states. Other than the SSH type we also consider random, Rice-Mele or AI type disorder to do a comparative analysis of the evolution of chirality and zero energy states as the strength of disorder and hopping periodicity is varied. Our findings can add important feedback in utilizing topological phases in various fields including quantum computations while the results can be easily verified in a cold atom set up within optical lattices.

cond-mat.str-el↗

arXiv2024

Topology and $\mathcal{PT}$ Symmetry in a Non-Hermitian Su-Schrieffer-Heeger Chain with Periodic Hopping Modulation

We study the effect of periodic but commensurate hopping modulation on a Su-Schrieffer-Heeger (SSH) chain with an additional onsite staggered imaginary potential. Such dissipative, non-Hermitian (NH) extension amply modifies the features of the topological trivial phase (TTP) and the topological nontrivial phase (TNP) of the SSH chain, more so with the periodic hopping distribution. Generally a weak potential can respect the parity-time (PT ) symmetry keeping the energy eigenvalues real, while a strong potential breaks PT conservation leading to imaginary end state and complex bulk state energies in the system. We find that this PT breaking with imaginary potential strength \gamma show interesting dependence on the hopping modulation \Delta for different hoping modulations. In-gap states, that appear also in the \gamma = 0 limit, take either purely real or purely imaginary eigenvalues depending on the strength of both \gamma and \Delta. The localization of end states (in-gap states) at the boundaries are investigated which show extended nature not only near topological transitions (further away from |\Delta/t| = 1) but also near the unmodulated limit of \Delta = 0. Moreover, localization of the bulk states is observed at the maximally dimerized limit of |\Delta/t| = 1, which also have a {\gamma} dependence. Analyzing further the dissipation caused by the complex eigenvalues in this problem with different hopping periodicity can be essential in modulating the gain-loss contrast in optical systems or in designing various quantum information processing and storage devices.

cond-mat.mes-hall↗

arXiv2023

Weak Deflection Angle, Hawking Radiation, Greybody Bound and Shadow Cast for Static Black Hole in the Framework of $f(R)$ Gravity

In this work, we probe the weak gravitational lensing by a static spherically symmetric black hole in view of $f(R)$ gravity in the background of the non-plasma medium (vacuum). We provide a discussion on a light ray in a static black hole solution in $f(R)$ gravity. To adore this purpose, we find the Gaussian optical curvature in weak gravitational lensing by utilizing the optical geometry of this black hole solution. Furthermore, we find the deflection angle up to the leading order by employing the Gauss-Bonnet theorem. We present the graphical analysis of the deflection angle with respect to the various parameters that govern the black hole. Further, we calculate the Hawking temperature for this black hole via a topological method and compare it with a standard method of deriving the Hawking temperature. We also analyze the Schrödinger-like Regge-Wheeler equation and derive a bound on the greybody factor for a static black hole in the framework of $f(R)$ gravity and graphically inquire that bound converges to 1. We also investigate the silhouette or shadow generated by this static $f(R)$ black hole. Moreover, we constrain the non-negative real constant and cosmological constant from the observed angular diameters of M87* and Sgr A* released by the EHT. We then probe how cosmological constant, non-negative real constant and mass affected the radius of shadow. Finally, we demonstrate that, in the eikonal limit, the real part of scalar field quasinormal mode frequency can be determined from the shadow radius.

gr-qc↗

arXiv2023

Leading-order corrections to the thermodynamics of Rindler modified Schwarzschild black hole

In this work, we present a thermodynamical study of a Rindler modified Schwarzschild black hole under the consideration of small thermal fluctuations. In particular, we compute various stable macroscopic thermodynamic variables such as Hawking temperature, entropy, Helmholtz free energy, internal energy, enthalpy, and Gibbs free energy. To explore the effects of small statistical thermal fluctuations on stable thermodynamical parameters, we estimated the corrections to the various thermodynamical potentials of Rindler modified Schwarzschild black hole up to the first (leading) order and do a comparative study for the different values of correction parameter and Rindler acceleration parameter for fixed values of a cosmological constant. In this study, we examine the stability of black holes in the presence of thermal fluctuations. We find that when the correction parameter is positive, small-sized black holes remain stable, while large-sized ones become unstable. Conversely, when the correction parameter is negative, both small and large black holes exhibit instability. Additionally, we demonstrate that the first law of thermodynamics remains valid even in the presence of thermal fluctuations.

gr-qc↗

arXiv2023

Weak Deflection Angle, Greybody Bound and Shadow for Charged Massive BTZ Black Hole

We provide a discussion on a light ray in a charged black hole solution in massive gravity. To serve the purpose, we exploit the optical geometry of the black hole solution and find the Gaussian curvature in weak gravitational lensing. Furthermore, we discuss the deflection angle of the light ray in both plasma and non-plasma mediums using the Gauss-Bonnet theorem on the black hole. We also analyze the Regge--Wheeler equation and derive rigorous bounds on the greybody factors of linearly charged massive BTZ black hole. We also study the shadow or silhouette generated by charged massive BTZ black holes. The effects of charge and cosmological constant on the radius of the shadow are also discussed.

gr-qc↗

arXiv2022

Geodesic Motions near an improved Schwarzschild black hole

In this paper, we studied the geodesics of timelike and null like particles near an improved Schwarzschild black hole. The lapse function has been plotted and was found that only one horizon is possible. The equation of motion and effective potential of test particle have been calculated. This equation has an importance in studying the radial free fall and in studying the stability of radial orbits (trajectories). The energy and angular momentum have also been calculated to analysis the cicrular motion and stability of circular orbits. Moreover, Innermost stable circular orbit radius has determined. To get a deeper insight of the nature of these trajectories, we have studied the timelike and null geodesics with the help of the dynamical systems approach. This analysis help us to determine the stability as well as fixed point of phase space trajectories.

gr-qc↗

arXiv2022

Shadow of the $5D$ Reissner-Nordström AdS Black Hole

We discuss the shadow cast by the charged Reissner-Nordström (RN) AdS black hole. With the help of Killing equation and Hamilton-Jacobi equation, we calculate the geodesic equations for null particle. With the help of geodesics of null particle, we then determine the celestial coordinates ($α$, $β$) and the shadow radius of the RN AdS black hole. We present a graphical analysis of the black hole shadow and find that shadow is a perfectly dark circle. The impacts of charge and cosmological constant of the RN AdS black hole on the radius of shadow are also presented. In this connection, radius of the shadow is a decreasing function of the charge. Furthermore, we study the effects of plasma medium on the RN AdS black hole shadow. Here, we find that radius of circular shadow increases with increasing plasma parameter. In addition, we also discuss the energy emission rate of RN AdS black hole. The effects of parameters like charge, cosmological constant and plasma parameter on energy emission rate are analyzed graphically.

gr-qc↗