arXiv subjects

Debraj Bose

Publications and source records attributed to Debraj Bose.

4 recordsLinked to original sources

arXiv2026

The Interplay of Thermal Melting and Pump Driven Melting of Charge Order: A Two-Temperature Study of the Holstein Model

Charge order driven by electron-phonon coupling is well understood at equilibrium but pump-probe experiments raise a new question: how does this order melt and recover after strong photoexcitation? A pump pulse promotes carriers across the charge-order gap and creates a nonequilibrium high-energy electronic population. In a closed system the subsequent dynamics is constrained by energy conservation. In an `open system' - where the system is coupled to a thermal bath at some temperature $T_{\rm bath}$ - there are new fluctuation and dissipation processes at play. One can attempt a computational scheme that incorporates coupling of electrons to a laser pump, the coupling of system phonons to a thermal bath, and the Holstein interaction that couples electrons and phonons. We attempt an approximation where the pump induced electronic excitations are modeled by a slowly time varying `electron temperature', $T_{\rm el}(t)$, indicative of a quasi-equilibrium electronic state. We solve the problem for different combinations of $T_{\rm el}$ and $T_{\rm bath}$, probing the order parameter dynamics, the static properties and excitations in the long time `quasi steady state', and establish a `phase diagram' in terms of bath temperature and electron temperature.

cond-mat.str-el↗

arXiv2026

Electron and phonon spectrum in a metallic nanohybrid

Recent experiments on metallic nanohybrids have revealed unusually strong electron-phonon effects emerging from nanoscale interfaces, despite the weak coupling character of the constituent bulk materials. Motivated by these observations, we investigate the electronic and lattice spectral properties of an inhomogeneous electron phonon system in which strong coupling is confined to interfacial regions embedded in a weakly coupled metallic background. Using a real-space formulation of the Holstein model combined with Langevin dynamics for lattice equilibration, we compute both electronic and phonon spectral functions in the presence of spatially varying coupling. We find that increasing the fraction of interfacial sites leads to a pronounced broadening of electronic spectral features, reflecting enhanced quasiparticle scattering from lattice distortions, but leaves the underlying band dispersion largely intact. Simultaneously, the phonon spectrum exhibits significant softening and damping, originating from strongly distorted interfacial regions. These modifications result in a redistribution of the Eliashberg spectral function toward low frequencies, producing a substantial enhancement of the effective electron-phonon coupling constant. Our results demonstrate that spatial inhomogeneity alone can strongly renormalize both electronic and lattice spectra, and provide a microscopic framework for understanding interface-driven transport and interaction effects in metallic nanohybrids.

cond-mat.str-el↗

arXiv2024

Enormous enhancement of resistivity in nanostructured electron-phonon systems

Recent experiments on nanoclusters of silver (Ag) embedded in a gold (Au) matrix reveal a huge increase in both the zero temperature resistivity and the coefficient of the ``$T$ linear'' thermal resistivity with increasing volume fraction of Ag. A fraction $f \sim 50\%$ of Ag leads to a factor of $20$ increase in the residual resistivity, and a $40$ fold enhancement in the coefficient of linear $T$ resistivity, with respect to Au. Since Au and Ag both have weak electron-phonon coupling we surmise that the huge enhancements arise from a moderately large electron-phonon coupling that may emerge at the Ag-Au interface. We construct nanocluster configurations for varying $f$ in two dimensions, define a Holstein model on it with weak coupling on the `interior' sites and a strong coupling on the interfacial sites, and solve the model through exact diagonalisation based Langevin dynamics. Computing the resistivity, we observe a large $T=0$ increase with $f$ and also a linear $T$ enhancement factor of $\sim 30$. While the enhancement factors are parameter choice dependent, our key qualitative result is that the interface physics is inhomogeneous, with widely varying distortions, and different segments of the interface dictate the residual resistivity and the thermal scattering.

cond-mat.str-el↗

arXiv2022

Nonequilibrium dynamics of suppression, revival, and loss of charge order in a laser pumped electron-phonon system

An electron-phonon system at commensurate filling often displays charge order (CO) in the ground state. Such a system subject to a laser pulse shows a wide variety of behaviour. A weak pulse sets up low amplitude oscillations in the order parameter, with slow decay to a slightly suppressed value. A strong pulse leads to the destruction of the charge order with the order parameter showing rapid, oscillatory, decay to zero. The regime in between, separating the weak pulse CO sustained state from the strong pulse CO destroyed state, shows complex dynamics characterised by multiple, pulse strength dependent, time scales. It involves an initial rapid decay of the order parameter, followed by a low amplitude quiescent state, and the power-law rise to a steady-state over a timescale $\tau_{cr}$. We provide a complete characterisation of the dynamics in this nonequilibrium problem for varying electron-phonon coupling and pulse strength, examine the possibility of an effective "thermal" description of the long time state, and present results on the multiple insulator-metal transitions that show up.

cond-mat.str-el↗