arXiv subjects

Dimitri N. Basov

Publications and source records attributed to Dimitri N. Basov.

9 recordsLinked to original sources

arXiv2026

Quantitative infrared nanoscopy: Probe-cavity eigenmodes and nano-gap polaritons for strongly coupled nanoscale optics

Optical nanoscopies including near-field optical microscopy and spectroscopy circumvent the diffraction limit of conventional optics thanks to the nanoscale light focus emerging at the apex of a sharp irradiated probe. However, while strong optical coupling between the apex and its dielectric environment affords both enhanced nanoscopic measurement sensitivity and potentially ultra-strong fields within a nano-gap cavity, the conditions for this coupling remain poorly quantified by prevailing analytic models. Here we present a robust formalism of probe-cavity eigenmodes that fully describes how mutual near-field interactions between probe and environment produce a composite response to external fields qualitatively distinct from that of its distinct components. This "EigenProbe" model identifies the fundamental excitations of realistic optical nanoscopies as nano-gap polaritons, which provide an elegant basis to accurately predict near-field microscopy and spectroscopy experiments especially when probe-sample interactions are non-perturbative. Through comparison to carefully controlled nanoscopies of polar phonons and molecular vibrations alike, we show how nano-gap polaritons are both realized and utilized for reliable and rapid "inversion" of local optical constants. This advance demands both a careful understanding of the probe response through quantitative calibration, and our efficient semi-analytic description of cavity eigenmode scattering at the probe apex. Our EigenProbe formalism sets the stage for maturing diverse and proliferating optical nanoscopies into precision metrologies of nano-scale optical environments, and guides future use of nano-gap cavities to manipulate local excitations of quantum materials and to achieve strong coupling over photonic emitters.

physics.optics↗

arXiv2019

Photo-enhanced metastable c-axis electrodynamics in stripe ordered cuprate La$_{1.885}$Ba$_{0.115}$CuO$_{4}$

Quantum materials are amenable to non-equilibrium manipulation with light, enabling modification and control of macroscopic properties. Light-based augmentation of superconductivity is particularly intriguing. Copper-oxide superconductors exhibit complex interplay between spin order, charge order and superconductivity, offering the prospect of enhanced coherence by altering the balance between competing orders. We utilize terahertz time domain spectroscopy to monitor the c-axis Josephson Plasma Resonance (JPR) in La$_{2-x}$Ba$_{x}$CuO$_{4}$ (x = 0.115) as a direct probe of superconductivity dynamics following excitation with near infrared pulses. Starting from the superconducting state, c-axis polarized excitation with a fluence of 100 $μ$J/cm2 results in an increase of the far-infrared spectral weight by more than an order of magnitude as evidenced by a blueshift of the JPR, interpreted as resulting from non-thermal collapse of the charge order. The photo-induced signal persists well beyond our measurement window of 300 ps and exhibits signatures of spatial inhomogeneity. The electrodynamic response of this new metastable state is consistent with enhanced superconducting fluctuations. Our results reveal that La$_{2-x}$Ba$_{x}$CuO$_{4}$ is highly sensitive to non-equilibrium excitation over a wide fluence range, providing an unambiguous example of photo-induced modification of order-parameter competition.

cond-mat.supr-con↗

arXiv2017

Mechanical detection and imaging of hyperbolic phonon polaritons in hexagonal Boron Nitride

Mid-infrared nano-imaging and spectroscopy of two-dimensional (2D) materials have been limited so far to scattering-type Scanning Near-field Optical Microscopy (s-NSOM) experiments where light from the sample is scattered by a metallic-coated Atomic Force Microscope (AFM) tip interacting with the material at the nanoscale. These experiments have recently allowed imaging of plasmon polaritons in graphene as well as hyperbolic phonon polaritons (HP2) in hexagonal Boron Nitride (hBN). Here we show that the high mechanical sensitivity of an AFM cantilever can be exploited for imaging hyperbolic phonon polaritons in hBN. In our imaging process, the lattice vibrations of hBN micrometer-sized flakes are locally enhanced by the launched phonon polaritons. These enhanced vibrations are coupled to the AFM tip in contact to the sample surface and recorded during scanning. Imaging resolution better than λ/20 is showed, comparable to the best resolution in s-NSOM. Importantly, this detection mechanism is free from light background and it is in fact the first photon-less detection of phonon polaritons.

cond-mat.mtrl-sci↗

arXiv2016

Tunable plasmonic reflection by bound 1D electron states in a 2D Dirac metal

We show that surface plasmons of a two-dimensional Dirac metal such as graphene can be reflected by line-like perturbations hosting one-dimensional electron states. The reflection originates from a strong enhancement of the local optical conductivity caused by optical transitions involving these bound states. We propose that the bound states can be systematically created, controlled, and liquidated by an ultranarrow electrostatic gate. Using infrared nanoimaging, we obtain experimental evidence for the locally enhanced conductivity of graphene induced by a carbon nanotube gate, which supports this theoretical concept.

cond-mat.mes-hall↗

arXiv2011

Infrared nanoscopy of Dirac plasmons at the graphene-SiO2 interface

We report on infrared (IR) nanoscopy of 2D plasmon excitations of Dirac fermions in graphene. This is achieved by confining mid-IR radiation at the apex of a nanoscale tip: an approach yielding two orders of magnitude increase in the value of in-plane component of incident wavevector q compared to free space propagation. At these high wavevectors, the Dirac plasmon is found to dramatically enhance the near-field interaction with mid-IR surface phonons of SiO2 substrate. Our data augmented by detailed modeling establish graphene as a new medium supporting plasmonic effects that can be controlled by gate voltage.

cond-mat.mes-hall↗

arXiv2011

Near-field spectroscopy of silicon dioxide thin films

We analyze the results of scanning near-field infrared spectroscopy performed on thin films of a-SiO2 on Si substrate. The measured near-field signal exhibits surface-phonon resonances whose strength has a strong thickness dependence in the range from 2 to 300 {nm}. These observations are compared with calculations in which the tip of the near-field infrared spectrometer is modeled either as a point dipole or an elongated spheroid. The latter model accounts for the antenna effect of the tip and gives a better agreement with the experiment. Possible applications of the near-field technique for depth profiling of layered nanostructures are discussed.

cond-mat.mes-hall↗

arXiv2011

Current oscillations in Vanadium Dioxide: evidence for electrically triggered percolation avalanches

In this work, we experimentally and theoretically explore voltage controlled oscillations occurring in micro-beams of vanadium dioxide. These oscillations are a result of the reversible insulator to metal phase transition in vanadium dioxide. Examining the structure of the observed oscillations in detail, we propose a modified percolative-avalanche model which allows for voltage-triggering. This model captures the periodicity and waveshape of the oscillations as well as several other key features. Importantly, our modeling shows that while temperature plays a critical role in the vanadium dioxide phase transition, electrically induced heating cannot act as the primary instigator of the oscillations in this configuration. This realization leads us to identify electric field as the most likely candidate for driving the phase transition.

cond-mat.mes-hall↗

arXiv2011

Infrared signatures of high carrier densities induced in semiconducting poly(3-hexylthiophene) by fluorinated organosilane molecules

We report on infrared (IR) absorption and dc electrical measurements of thin films of poly(3-hexylthiophene) (P3HT) that have been modified by a fluoroalkyl trichlorosilane (FTS). Spectra for FTS-treated films were compared to data for electrostatically-doped P3HT in an organic field-effect transistor (OFET). The appearance of a prominent polaron band in mid-IR absorption data for FTS-treated P3HT supports the assertion of hole doping via a charge-transfer process between FTS molecules and P3HT. In highly-doped films with a significantly enhanced polaron band, we find a monotonic Drude-like absorption in the far-IR, signifying delocalized states. Utilizing a simple capacitor model of an OFET, we extracted a carrier density for FTS-treated P3HT from the spectroscopic data. With carrier densities reaching 10$^{14}$ holes/cm$^2$, our results demonstrate that FTS doping provides a unique way to study the metal-insulator transition in polythiophenes.

cond-mat.mtrl-sci↗

arXiv2011

Electrodynamics of Correlated Electron Materials

We review studies of the electromagnetic response of various classes of correlated electron materials including transition metal oxides, organic and molecular conductors, intermetallic compounds with $d$- and $f$-electrons as well as magnetic semiconductors. Optical inquiry into correlations in all these diverse systems is enabled by experimental access to the fundamental characteristics of an ensemble of electrons including their self-energy and kinetic energy. Steady-state spectroscopy carried out over a broad range of frequencies from microwaves to UV light and fast optics time-resolved techniques provide complimentary prospectives on correlations. Because the theoretical understanding of strong correlations is still evolving, the review is focused on the analysis of the universal trends that are emerging out of a large body of experimental data augmented where possible with insights from numerical studies.

cond-mat.str-el↗