arXiv subjects

Anjaly Rajendran

Publications and source records attributed to Anjaly Rajendran.

5 recordsLinked to original sources

arXiv2023

In-plane anisotropy in biaxial ReS2 crystals probed by nano-optical imaging of waveguide modes

Near-field imaging has emerged as a reliable probe of the dielectric function of van der Waals crystals. In principle, analyzing the propagation patterns of subwavelength waveguide modes (WMs) allows for extraction of the full dielectric tensor. Yet previous studies have mostly been restricted to high-symmetry materials or narrowband probing. Here, we resolve in-plane anisotropic WMs in thin rhenium disulfide (ReS2) crystals across a wide range of near-infrared frequencies. By tracing the evolution of these modes as a function of crystallographic direction, polarization of the electric field and sample thickness, we have determined the anisotropic dielectric tensor including the elusive out-of-plane response. The excitonic absorption at ~1.5 eV manifests itself as a clear backbending feature in the WM dispersion and a reduction of the quality factors as fully supported by numerical calculations. Our results extend the sensitivity of near-field microscopy towards biaxial anisotropy and provide key insights into the optoelectronic properties of ReS2.

physics.optics↗

arXiv2022

Atomically imprinted graphene plasmonic cavities

Plasmon polaritons in van der Waals (vdW) materials hold promise for next-generation photonics. The ability to deterministically imprint spatial patterns of high carrier density in cavities and circuitry with nanoscale features underlies future progress in nonlinear nanophotonics and strong light-matter interactions. Here, we demonstrate a general strategy to atomically imprint low-loss graphene plasmonic structures using oxidation-activated charge transfer (OCT). We cover graphene with a monolayer of WSe$_2$, which is subsequently oxidized into high work-function WOx to activate charge transfer. Nano-infrared imaging reveals low-loss plasmon polaritons at the WOx/graphene interface. We insert WSe$_2$ spacers to precisely control the OCT-induced carrier density and achieve a near-intrinsic quality factor of plasmons. Finally, we imprint canonical plasmonic cavities exhibiting laterally abrupt doping profiles with single-digit nanoscale precision via programmable OCT. Specifically, we demonstrate technologically appealing but elusive plasmonic whispering-gallery resonators based on free-standing graphene encapsulated in WOx. Our results open avenues for novel quantum photonic architectures incorporating two-dimensional materials.

physics.optics↗

arXiv2022

Unzipping hBN with ultrashort mid-infrared pulses

Manipulating the nanostructure of materials is critical for numerous applications in electronics, magnetics, and photonics. However, conventional methods such as lithography and laser-writing require cleanroom facilities or leave residue. Here, we describe a new approach to create atomically sharp line defects in hexagonal boron nitride (hBN) at room temperature by direct optical phonon excitation in the mid-infrared (mid-IR). We term this phenomenon "unzipping" to describe the rapid formation and growth of a <30-nm-wide crack from a point within the laser-driven region. The formation of these features is attributed to large atomic displacements and high local bond strain from driving the crystal at a natural resonance. This process is distinguished by (i) occurring only under resonant phonon excitation, (ii) producing highly sub-wavelength features, and (iii) sensitivity to crystal orientation and pump laser polarization. Its cleanliness, directionality, and sharpness enable applications in in-situ flake cleaving and phonon-wave-coupling via free space optical excitation.

cond-mat.mtrl-sci↗

arXiv2022

Miniaturizing transmon qubits using van der Waals materials

Quantum computers can potentially achieve an exponential speedup versus classical computers on certain computational tasks, as recently demonstrated in systems of superconducting qubits. However, these qubits have large footprints due to their large capacitor electrodes needed to suppress losses by avoiding dielectric materials. This tactic hinders scaling by increasing parasitic coupling among circuit components, degrading individual qubit addressability, and limiting the spatial density of qubits. Here, we take advantage of the unique properties of the van der Waals (vdW) materials to reduce the qubit area by a factor of $>1000$ while preserving the required capacitance without increasing substantial loss. Our qubits combine conventional aluminum-based Josephson junctions with parallel-plate capacitors composed of crystalline layers of superconducting niobium diselenide (NbSe$_2$) and insulating hexagonal-boron nitride (hBN). We measure a vdW transmon $T_1$ relaxation time of 1.06 $μ$s, which demonstrates a path to achieve high-qubit-density quantum processors with long coherence times, and illustrates the broad utility of layered heterostructures in low-loss, high-coherence quantum devices.

quant-ph↗

arXiv2021

Making high-quality quantum microwave devices with van der Waals superconductors

Ultra low-loss microwave materials are crucial for enhancing quantum coherence and scalability of superconducting qubits. Van der Waals (vdW) heterostructure is an attractive platform for quantum devices due to the single-crystal structure of the constituent two-dimensional (2D) layered materials and the lack of dangling bonds at their atomically sharp interfaces. However, new fabrication and characterization techniques are required to determine whether these structures can achieve low loss in the microwave regime. Here we report the fabrication of superconducting microwave resonators using NbSe$_2$ that achieve a quality factor $Q > 10^5$. This value sets an upper bound that corresponds to a resistance of $\leq 192 μΩ$ when considering the additional loss introduced by integrating NbSe$_2$ into a standard transmon circuit. This work demonstrates the compatibility of 2D layered materials with high-quality microwave quantum devices.

cond-mat.supr-con↗