arXiv subjects

Somsubhra Ghosh

Publications and source records attributed to Somsubhra Ghosh.

9 recordsLinked to original sources

arXiv2025

Destructive Interference induced constraints in Floquet systems

We introduce the paradigm of destructive many-body interference between quantum trajectories as a means to systematically generate prethermal kinetically constrained dynamics in Floquet systems driven at special frequencies. Depending on the processes that are suppressed by interference, the constraint may or may not be associated with an emergent global conservation; the latter kind having no mechanism of generation in time-independent settings. As an example, we construct an one-dimensional interacting spin model exhibiting strong Hilbert space fragmentation with and without dipole moment conservation, depending on the drive frequency. By probing the spatiotemporal profile of the out-of-time-ordered correlator, we show that this model, in particular, has initial states in which quantum information can be spatially localized - a useful feature in the field of quantum technologies. Our paradigm unifies various types of Hilbert space fragmentation that can be realized in driven systems.

cond-mat.str-el↗

arXiv2024

Magnon-Phonon Coupling in Layered Antiferromagnet

We present a fully analytical model of hybridization between magnon, and phonons observed experimentally in magneto-Raman scattering in van der Waals (vdW) antiferromagnets (AFM). Here, the representative material, FePS3, has been shown to be a quasi-two-dimensional-Ising antiferromagnet, with additional features of spin-phonon coupling in the Raman spectra emerging below the Néel temperature (TN) of approximately 120 K. Using magneto-Raman spectroscopy as an optical probe of magnetic structure, we show that one of these Raman-active modes in the magnetically ordered state is a magnon with a frequency of 3.7 THz (~ 122 cm-1). In addition, one magnon band and three phonon bands are coupled via the magneto-elastic coupling evidenced by anti-crossing in the complete spectra. We consider a simple model involving only in-plane nearest neighbor exchange couplings (designed to give rise to a similar magnetic structure) and perpendicular anisotropy in presence of an out-of-plane magnetic field. Exact diagonalization of the Hamiltonian leads to energy bands which show that the interaction term gives rise to avoided crossings between the hybridized magnon and phonon branches. Realizing magnon-phonon coupling in two-dimensional (2D) AFMs is important for the verification of the theoretical predictions on exotic quantum transport phenomena like spin-caloritronics, topological magnonics, etc.

cond-mat.mes-hall↗

arXiv2024

Hilbert space fragmentation imposed real spectrum of non-Hermitian systems

We show that constraints imposed by strong Hilbert space fragmentation (HSF) along with the presence of certain global symmetries can ensure the reality of eigenspectra of non-Hermitian quantum systems; such a reality cannot be guaranteed by global symmetries alone. We demonstrate this insight for two interacting finite chains, namely the fermionic Nelson-Hatano and the Su-Schrieffer-Heeger models, none of which has a $\mathcal{PT}$ symmetry. We show analytically that strong HSF and real spectrum are both consequences of the same dynamical constraints in the limit of large interaction, provided the systems have sufficient global symmetries. We also show that a local equal-time correlation function can detect the many-body exceptional point at a finite critical interaction strength above which the eigenspectrum is real.

cond-mat.str-el↗

arXiv2024

Signatures of fragmentation for periodically driven fermions

We study the possible signatures of prethermal strong Hilbert space fragmentation (HSF) for one-dimensional (1D) fermions subjected to a periodic drive. We extend the results of Phys. Rev. Lett. 130, 120401 (2023) to show the possibility of such fragmentation for a large class of experimentally relevant drive protocols. Moreover, we demonstrate the persistence of HSF when the fermion chain is taken away from half-filling. Both these analysis indicate the robustness of the fragmentation phenomenon reported earlier. We also provide an alternate derivation of the Floquet Hamiltonian of the driven chain which yields insight into the generic nested commutator structure of its higher order terms. Finally, we study the density-density out-of-time-correlators (OTOC) of the driven chain both away and near the special drive frequencies at which its first order Floquet Hamiltonian exhibits fragmentation. We show that these OTOCs, for a chain with open boundary condition, exhibit a distinct periodic unscrambling of information at special drive frequencies; such unscrambling can therefore serve as a marker of prethermal HSF. We provide an approximate analytic explanation of the role of HSF behind such periodic unscrambling and discuss experiments which can detect signatures of strong HSF in such driven chains.

cond-mat.str-el↗

arXiv2023

Anisotropic Magnetodielectric Coupling in Layered Antiferromagnetic FePS$_3$

We report anisotropic magnetodielectric (MD) coupling in layered van der Waals (vdW) antiferromagnetic (AFM) FePS$_3$ (Néel temperature $T_{\mathrm{N}}$ $\sim$ 120K) with perpendicular anisotropy. Above $T_N$, while dielectric response function along \textit{c}-axis shows frequency dependent relaxations, in-plane data is frequency independent and reveals a deviation from phonon-anharmonicity in the ordered state, thereby implying a connection to spin-phonon coupling known to be indicative of onset of magnetic ordering. At low temperature (below 40 K), atypical anomaly in the dielectric constant is corroborated with temperature dependent DC and AC susceptibility. The magnetodielectric response across this anomaly differs significantly for both, in-plane and out-of-plane cases. We have explained this in terms of preferential orientation of magnetic AFM-z alignment, implied by the in-plane structural anisotropy as confirmed by \textit{ab-initio} calculations. Controlling relative strength of magnetodielectric coupling with magnetic anisotropy opens up a strategy for tracking subtle modifications of structure, such as in-plane anisotropy, with potential application to spintronic technologies.

cond-mat.mes-hall↗

arXiv2023

Detecting prethermal Floquet phases of Rydberg atom arrays

We study the prethermal Floquet phases of a two-dimensional (2D) Rydberg atom array on a rectangular lattice in the presence of a periodic drive with large drive amplitude. We derive an analytic, albeit perturbative, Floquet Hamiltonian using Floquet perturbation theory (FPT) which charts out these phases and shows that the transition between them can be accessed by tuning the drive frequency. Using both numerical exact diagonalization on finite-size arrays and analytical first-order Floquet Hamiltonian derived using FPT, we show that these prethermal Floquet phases and the transitions between them can be detected by studying the dynamics of equal-time density-density correlation functions of the Rydberg atoms. Our analysis thus provides a simple way of detecting these phases and associated transitions in this system; such a detection can be achieved in standard experiments which we discuss.

cond-mat.str-el↗

arXiv2022

Prethermal fragmentation in a periodically driven Fermionic chain

We study a Fermionic chain with nearest-neighbor hopping and density-density interactions, where the nearest-neighbor interaction term is driven periodically. We show that such a driven chain exhibits prethermal strong Hilbert space fragmentation (HSF) in the high drive amplitude regime at specific drive frequencies $ω_m^{\ast}$. This constitutes the first realization of HSF for out-of-equilibrium systems. We obtain analytic expressions of $ω_m^{\ast}$ using a Floquet perturbation theory and provide exact numerical computation of entanglement entropy, equal-time correlation functions, and the density autocorrelation of Fermions for finite chains. All of these quantities indicate clear signatures of strong HSF. We study the fate of the HSF as one tunes away from $ω_m^{\ast}$ and discuss the extent of the prethermal regime as a function of the drive amplitude.

cond-mat.str-el↗

arXiv2022

Hinge mode dynamics of periodically driven higher-order Weyl semimetals

We study the stroboscopic dynamics of hinge modes of a second-order topological material modeled by a tight-binding free fermion Hamiltonian on a cubic lattice in the intermediate drive frequency regime for both discrete (square pulse) and continuous (cosine) periodic drive protocols. We analyze the Floquet phases of this system and show that its quasienergy spectrum becomes almost gapless in the large drive amplitude regime at special drive frequencies. Away from these frequencies, the gapped quasienergy spectrum supports weakly dispersing Floquet hinge modes. Near them, these hinge modes penetrate into the bulk and eventually become indistinguishable from the bulk modes. We provide an analytic, albeit perturbative, expression for the Floquet Hamiltonian using Floquet perturbation theory (FPT) which explains this phenomenon and leads to analytic expressions of these special frequencies. We also show that in the large drive amplitude regime, the zero energy hinge modes corresponding to the static tight-binding Hamiltonian display qualitatively different dynamics at these special frequencies. We discuss possible local density of state measurement using a scanning tunneling microscope which can test our theory.

cond-mat.mes-hall↗

arXiv2020

Criticality in Tissue Homeostasis: Models and Experiments

There is considerable theoretical and experimental support to the proposal that tissue homeostasis in the adult skin can be represented as a critical branching process. The homeostatic condition requires that the proliferation rate of the progenitor (P) cells (capable of cell division) is counterbalanced by the loss rate due to the differentiation of a P cell into differentiated (D) cells so that the total number of P cells remains constant. We consider the two-branch and three-branch models of tissue homeostasis to establish homeostasis as a critical phenomenon. It is first shown that some critical branching process theorems correctly predict experimental observations. A number of temporal signatures of the approach to criticality are investigated based on simulation and analytical results. The analogy between a critical branching process and mean-field percolation and sandpile models is invoked to show that the size and lifetime distributions of the populations of P cells have power-law forms. The associated critical exponents have the same magnitudes as in the cases of the mean-field lattice statistical models. The results indicate that tissue homeostasis provides experimental opportunities for testing critical phenomena.

cond-mat.stat-mech↗