arXiv subjects

Shreya Kumbhakar

Publications and source records attributed to Shreya Kumbhakar.

5 recordsLinked to original sources

arXiv2026

Dynamics of Charge-Density-Wave puddles in 2$H$-NbSe$_2$

Electronic phases in quantum materials are often governed by nanoscale inhomogeneity, where local order develops within spatially confined regions or puddles. A prominent example is an incommensurate charge-density-wave (I-CDW) that comprises locally commensurate domains. In 2$H$-NbSe$_2$, such an I-CDW state persists alongside lattice anharmonicity and superconductivity, raising fundamental questions about the dynamical stabilization of CDW order in puddles. Here, we probe the puddle-dynamics in 2$H$-NbSe$_2$. Raman scattering reveals a strong Fano-coupling between the interlayer shear vibration and the CDW amplitude mode. Time-resolved reflectivity measurement shows a low-frequency ~0.15 THz coherent overdamped oscillation onsetting within the CDW regime at ~17 K, pointing towards a so far unexplored transition. This we identify as a Fano-coupled phonon-CDW hybrid emerging from the collective dynamics of CDW puddles. We establish a framework for capturing intertwinned glassy dynamics with an overdamped oscillatory model. Such dynamics in 2H-NbSe2 highlight how lattice pinning and electronic correlations in layered materials affect the CDW order, which is crucial for the design of novel Van der Waals devices.

cond-mat.str-el↗

arXiv2026

Simplified Silicon Nitride Nanomembrane Circuits for van der Waals Integration

Two-dimensional (2D) materials and van der Waals (vdW) heterostructures provide an exceptional platform for engineering quantum devices, yet realizing their potential requires electrical integration without compromising the pristine properties of atomically thin crystals through conventional nanofabrication. Transferable circuitry addresses this challenge by decoupling circuit fabrication from device assembly, enabling electrical contacting without directly processing the active material. Here, we introduce SiN$_x$ nanomembrane (NMB) circuits realized through a simplified top-down strategy that reduces fabrication complexity, processing steps and specialized tools required by our previous bottom-up approach. As a stringent benchmark of material preservation, we electrically integrate a four-unit-cell-thick, optimally doped Bi$_2$Sr$_{2-x}$La$_x$CuO$_{6+δ}$ (Bi2201) flake and observe a superconducting transition at T$_c^{inf}$~32K, close to the T$_c^{onset}$~34K measured by susceptibility in the parent crystals. The preservation of superconductivity demonstrates electrical integration of fragile layered materials without direct exposure to conventional cleanroom procedures, providing a versatile platform for integrating increasingly complicated vdW heterostructures, moiré materials, and hybrid quantum architectures.

cond-mat.supr-con↗

arXiv2025

Emergent Rashba spin-orbit coupling in bulk gold with buried network of nanoscale interfaces

The Rashba effect, which plays a crucial role in fundamental materials physics and potential spintronics applications, has been engineered in diverse systems, including semiconductor quantum wells, oxide heterostructures, metallic surfaces, topological insulators, ferroelectrics, etc. However, generating it in systems that preserve bulk inversion symmetry (BIS), for example, in bulk metals, has not been possible so far. We demonstrate a unique strategy to introduce and tune Rashba spin-orbit interaction (SOI) to unprecedented magnitudes in inversion-symmetric solids, by incorporating ultra-small silver nanoparticles in bulk gold. The near-identical lattice constants of Ag and Au allowed dense packing of the Ag/Au hetero-interfaces without compromising the global BIS. By varying the density of embedded nanoparticles, we generate Rashba SOI in a bulk metal with a coupling strength of ~15 meV.Angstrom, higher than any known system preserving BIS globally, and up to ~20 times increase in the spin-orbit scattering rate. We argue that the combined effect of charge-transfer at the interfaces and polaronic localization enhances the SOI.

cond-mat.mes-hall↗

arXiv2024

Engineering ultra-strong electron-phonon coupling and nonclassical electron transport in crystalline gold with nanoscale interfaces

Electrical resistivity in good metals, particularly noble metals such as gold (Au), silver (Ag), or copper, increases linearly with temperature ($T$) for $T > Θ_{\mathrm{D}}$, where $Θ_{\mathrm{D}}$ is the Debye temperature. This is because the coupling ($λ$) between the electrons and the lattice vibrations, or phonons, in these metals is rather weak with $λ\sim 0.1-0.2$, and a perturbative analysis suffices to explain the $T$-linear electron-phonon scattering rate. In this work, we outline a new nanostructuring strategy of crystalline Au where this foundational concept of metallic transport breaks down. We show that by embedding a distributed network of ultra-small Ag nanoparticles (AgNPs) of radius $\sim1-2$ nm inside a crystalline Au shell, an unprecedented enhancement in the electron-phonon interaction, with $λ$ as high as $\approx 20$, can be achieved. This is over hundred times that of bare Au or Ag, and ten times larger than any known metal. With increasing AgNP density, the electrical resistivity deviates from $T$-linearity, and approaches a saturation to the Mott-Ioffe-Regel scale $ρ_{\mathrm{MIR}}\sim h a /e^2$ for both disorder ($T\to 0$) and phonon ($T \gg Θ_{\mathrm{D}}$)-dependent components of resistivity (here, $a=0.3$~nm, is the lattice constant of Au). This giant electron-phonon interaction, which we suggest arises from the coulomb interaction-induced coupling of conduction electrons to the localized phonon modes at the buried Au-Ag hetero-interfaces, allows experimental access to a regime of nonclassical metallic transport that has never been probed before.

cond-mat.mes-hall↗

arXiv2019

Observation of excess resistance anomaly at resistive transitions in Ag/Au nanostructures

The resistive transition in nanocomposite films of silver (Ag) nanoclusters of ~ 1 nm diameter embedded in gold (Au) matrix exhibits an anomalous resistance peak at the onset of the transition, even for transition temperatures as high as 260 K. The maximum value of the resistance ranges between ~ 30% - 300% above that of the normal state depending on devices as well as lead configuration within a single device. The excess resistance regime was observed in about 10% of the devices, and extends from ~ 10 - 100 K. Application of magnetic field of 9 T was found to partially suppress the excess resistance. From the critical current behavior, as well as negative differential resistance in the current-voltage characteristics, we discuss the possibility of interacting phase slip centers and alternate physical scenarios that may cause the excess resistance in our system.

cond-mat.supr-con↗