Gururaj Naik

• PhD
• Professor (Assistant) at Rice University

It is not currently possible for an infrared camera to see through a hot window. The window’s own blinding thermal emission prevents objects on the other side from being imaged. Here, we demonstrate a path to overcoming this challenge by coating a hot window with an asymmetrically emitting infrared metasurface whose specially engineered imaginary i...

High‐index dielectrics or Super‐Mossian materials are essential for emerging nanophotonic applications. Several transition metal dichalcogenides (TMDCs) are promising as super‐Mossian dielectric materials. Molybdenum disulfide (MoS2) is an outstanding super‐Mossian TMDC exceeding Moss' rule prediction of its refractive index by nearly 40%. This hig...

Exceptional point (EP)-based optical sensors exhibit exceptional sensitivity but poor detectivity due to their acute sensitivity to perturbations, such as noise. When the optical budget is limited, as in applications on mobile platforms, high detectivity might be equally important as high sensitivity. In such scenarios, off-EP sensing is advantageo...

Exceptional point (EP)-based optical sensors exhibit exceptional sensitivity but poor detectivity. Slightly off EP operation boosts detectivity without much loss in sensitivity. We experimentally demonstrate a high-detectivity-off-EP plasmonic-photonic hybrid sensor for anti-mouse IgG protein.

Resonators are at the core of optical sensors enhancing light–analyte interaction and leading to higher sensitivities. Maximizing the sensitivity is an obvious objective function for the resonator design. However, high sensitivity does not guarantee sufficient detectivity. When the optical energy budget is limited, as in sensors on mobile platforms...

Searching for high-index dielectrics, we identify materials that break the index upper bound set by Moss’ rule. We highlight the promise of such super-Mossian materials by demonstrating nanophotonic devices made of FeS 2 and MoS 2 .

Plasmonic sensors exhibit high sensitivity due to enhanced local fields. But, their detectivity is poor because of their poor Q-factors. Using a plasmonic BIC, we experimentally demonstrate enhanced Q-factors in a plasmonic antimouse IgG sensor.

Selective thermal emitters can boost the efficiency of heat-to-electricity conversion in thermophotovoltaic systems only if their spectral selectivity is high. We demonstrate a non-Hermitian metasurface-based selective emitter operating at 1200 K in a GaSb-thermophotovoltaic cell.

Non-Hermitian optics provides a unique platform to take advantage of absorption losses in materials and control radiative properties. We demonstrate a non-Hermitian metasurface that exhibit directional suppression of thermal radiation while maintaining transmission in mid-infrared.

High refractive index dielectrics enable nanoscale integration of optical components with practically no absorption loss. Hence, high index dielectrics are promising for many emerging applications in nanophotonics. However, the lack of a complete library of high index dielectric materials poses a significant challenge to understanding the full pote...

The synergy between topology and non-Hermiticity in photonics holds immense potential for next-generation optical devices that are robust against defects. However, most demonstrations of non-Hermitian and topological photonics have been limited to super-wavelength scales due to increased radiative losses at the deep-subwavelength scale. By carefull...

We demonstrate a dynamically tunable plasmonic metasurface enabled by light-tunable optical constants of a quantum material - 1T-TaS 2 . We observe a relative reflectance change of 10% under low-intensity incoherent illumination.

We exploit strong chromatic dispersion of metasurfaces by combining it with computational imaging to enable compact, single-shot, large field-of-view, and passive 3D imaging. We employ a dielectric metasurface with interleaved RGB meta-elements in this demonstration.

Aligned carbon nanotube films make an excellent hyperbolic material platform in the infrared. Here, we experimentally demonstrate the presence of high- k modes in aligned carbon nanotube films and outcouple them to free-space via gratings.

The synergy between topology and non-Hermiticity in photonics holds potential for optical devices that are robust against defects. We demonstrate a non-Hermitian plasmonic-dielectric metasurface in the visible with non-trivial topology.

The c-axis permittivity of 1T-TaS 2 – a quasi-2D charge-density-wave material – changes upon illumination due to light-induced reorganization of CDW stacking. Here we probe the mechanism of this reorganization and find a nucleation mechanism at work.

1T-TaS2 is a 2D quantum material supporting charge density waves (CDWs) at room temperature. The strong correlations in this material make its electrical properties extremely sensitive to external stimuli such as an electrical bias and illumination. Recently, we demonstrated that the optical properties of this material also considerably change with...

Light is a powerful tool in sculpting the energy landscape of strong correlations. For example, low-intensity incoherent light is sufficient to change the way charge density wave (CDW) domains stack across layers of 1T-TaS2. The change in stacking type manifests in a large change in optical properties of 1T-TaS2 at room temperature. Much remains un...

Light-matter interaction in quantum materials presents opportunities for discovery. We observe a low-intensity light-induced phase transition in 1T-TaS 2 , a quasi-2D material supporting charge-density-waves (CDW). We find that the CDW domains stack differently upon illumination.

Strongly correlated materials possess a complex energy landscape and host many interesting physical phenomena, including charge density waves (CDWs). CDWs have been observed and extensively studied in many materials since their first discovery in 1972. Yet, they present ample opportunities for discovery. Here, we report a large tun-ability in the o...

Strongly correlated materials possess a complex energy landscape and host many interesting physical phenomena, including charge density waves (CDWs). CDWs have been observed and extensively studied in many materials since their first discovery in 1972. Yet, they present ample opportunities for discovery. Here, we report a large tunability in the op...

Single-walled carbon nanotubes (SWCNTs) exhibit many unique properties arising from their quantum confinement. However, the lack of a controllable large-scale alignment procedure had limited the exploration of their unique properties. Our recent work has overcome this problem by demonstrating a vacuum-filtration based technique to align SWCNTs on w...

Though thermophotovoltaic (TPV) systems have been studied for many decades, the demonstrated conversion efficiencies have remained far lower than the theoretical maximum. Here, in this work, we investigate the reason for low efficiency, especially in TPV systems employing selective thermal emitters, and determine design pathways toward high efficie...

We present a nanophotonic device capable of displaying non-trivial topology in thermal emission. By coupling the horizontal and vertical modes of two resonators with large loss asymmetry, exceptional lines are observed in parameter space.

Photorefractive optical properties of a strongly-correlated material, 1T-TaS2 allows many nonlinear nanophotonic devices. Here, we present optical limiters using 1T- TaS 2 .

The remarkable flexibility, stable chemical structure, and extraordinary thermal, electrical, and optical properties of carbon nanotubes (CNTs) are promising for a variety of applications in flexible and/or high-temperature electronics, optoelectronics, and thermoelectrics, including wearables, refractory photonics, and waste heat harvesting. Howev...

All open systems that exchange energy with their environment are non‐Hermitian. Thermal emitters are open systems that can benefit from the rich set of physical phenomena enabled by their non‐Hermitian description. Using phase, symmetry, chirality, and topology, thermal radiation from hot surfaces can be unconventionally engineered to generate ligh...

Refractory nanophotonics, or nanophotonics at high temperatures, can revolutionize many applications, including data storage and waste heat recovery. In particular, nanophotonic devices made from hyperbolic materials are promising due to their nearly infinite photonic density of states (PDOS). However, it is challenging to achieve a prominent PDOS...

Electrically tunable optical properties have been demonstrated in many solid-state materials such as semiconductors, transparent conductive oxides and graphene. However, their tunability is limited in the visible range due to the requirement of extremely large charge build-up or high capacitive fields. Here, we propose strongly correlated materials...

We demonstrate intensity dependent optical response in the visible for a strongly correlated material, 1T-TaS2. Using this tunable material, we show the intensity-dependent diffraction of a meta-grating device useful for imaging, display and sensing technologies.

We experimentally demonstrate non-Hermitian physics of thermal emitters by coupling a plasmonic resonator with high losses to a bound-state-in-continuum dielectric resonator with low losses. Our thermal emitter exhibits passive P T-symmetry while operating at 700°C.

Thermophotovoltaic conversion is a promising solid-state heat-to-electricity conversion technology. However, its current efficiency is poor. Optimizing the properties of selective thermal emitter is the key to higher efficiency and our analysis shows that 70% of Carnot efficiency is achievable by an optimum emitter design.

We experimentally demonstrate passive P J -symmetry in thermal emission at 700 °C using a hybrid plasmonic-photonic selective thermal emitter. Additionally, we demonstrate the effect of internal oscillator phase on far-field thermal emission.

We demonstrate a large photo-refractive effect in 1T-TaS2 in the visible at low intensity white light excitation. By using this optical tunability, we demonstrate tunable meta-gratings for nanophotonics applications.

Noble metal nanoparticles support localized surface plasmon resonances (LSPRs), which are light-driven oscillations of free electrons. Thanks to their strong dependence on the metal’s electron density, these resonances can be used to optically probe the equilibration of photogenerated charge carriers at metal/semiconductor interfaces, a process of...

Selective emitters limit thermal radiation to a narrow spectral band enabling applications including energy conversion and sensing. While applications demand high spectral selectivity, the materials used for selective emitters limit the ultimate selectivity. At high temperatures (>600 K), the optical properties of materials degrade, resulting in po...

Many important applications of nanometer-scale metallic complexes arise from the light-induced, near-field interactions between their component structures. Here we examine the near-field interactions in bimetallic Al-Au plasmonic nanodisk heterodimers, where the coupling between the primitive plasmons of nanostructures composed of two different met...

Chameleons are masters of light, expertly changing their color, pattern, and reflectivity in response to their environment. Engineered materials that share this tunability can be transformative, enabling active camouflage, tunable holograms, and novel colorimetric medical sensors. While progress has been made in creating artificial chameleon skin,...

Manipulating the frequency of electromagnetic waves forms the core of many modern technologies, ranging from imaging and spectroscopy to radio and optical communication. The process of converting photons from higher to lower energy is easily accomplished and technologically widespread. However, upconversion - the process of converting lower-energy...

The refractory metal titanium nitride is promising for high-temperature nanophotonic and plasmonic applications, but its optical properties have not been studied at temperatures exceeding 400 °C. Here, we perform in-situ high-temperature ellipsometry to quantify the permittivity of TiN films from room temperature to 1258 °C. We find that the materi...

Radiation patterns and the resonance wavelength of a plasmonic antenna are significantly influenced by its local environment, particularly its substrate. Here, we experimentally explore the role of dispersive substrates, such as aluminum- or gallium-doped zinc oxide in the near infrared and 4H-silicon carbide in the mid-infrared, upon Au plasmonic...

CMOS-compatible fabrication of plasmonicmaterials and devices will accelerate the development of integrated nanophotonics for information processing applications. Using low-temperature plasma-enhanced atomic layer deposition (PEALD), we develop a recipe for fully CMOS-compatible titanium nitride (TiN) that is plasmonic in the visible and near infra...

We experimentally demonstrate a new photon upconversion technique based on hot-carriers in plasmonic systems. We show that silver nanostructures on GaN/InGaN multiquantum well can upconvert ~2.48 eV photons to 2.82 eV photons via a linear process.

We report the first visible/NIR darkfield scattering spectroscopy measurements of single TiN nanostructures. We grow these fully CMOS-compatible nanoantennas via low-temperature atomic layer deposition and characterize and correlate their optical and material properties.

From the photoinduced transport of energy that accompanies photosynthesis to the transcontinental transmission of optical data that enable the Internet, our world relies and thrives on optical signals. To highlight the importance of optics to society, the United Nations designated 2015 as The International Year of Light and Light-based Technologies...

The broadband complex conductivities of transparent conducting oxides (TCO), namely, aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO) and tin-doped indium oxide (ITO), were investigated by using THz-TDS from 0.5 to 18 THz. The complex conductivities were accurately calculated using a thin film extraction algorithm and analyzed in ter...

The broadband complex conductivities of transparent conducting oxides (TCO), namely aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO) and tin-doped indium oxide (ITO), were investigated by terahertz time domain spectroscopy (THz-TDS) in the frequency range from 0.5 to 18 THz using air plasma techniques, supplemented by the photoconduc...

Since the 1960s, researchers exploring the potential of artificially structured materials for applications in quantum electronic devices and nanophotonics have sought combinations of metals and semiconductors that could be integrated on the nanoscale to make epitaxial superlattices with atomically-sharp interfaces. Incompatibility and mismatch in t...

We propose a novel scheme of photon upconversion based on harnessing the energy of plasmonic hot carriers. Low-energy photons excite hot electrons and hot holes in a plasmonic nanoparticle, which are then injected into an adjacent semiconductor quantum well where they radiatively recombine to emit a photon of higher energy. We theoretically study t...

This chapter is an overview of the recent progress in the search for alternative plasmonic materials. The efficiency of plasmonic and optical metamaterial devices depends on the geometry and optical properties of the constituent materials. Usually, geometry optimization is performed to design efficient devices and obtain the required functionality....

Alternative plasmonic materials can withstand extreme temperatures, opening new frontiers in energy-harvesting applications. A metamaterial based on titanium nitride, described by J. G. Guan, A. V. Kildishev, and co-workers on page 7959, efficiently converts sunlight into heat, achieving temperatures greater than 1000 °C and it re-radiates this ene...

Epitaxial nitride rocksalt metal/semiconductor superlattices are emerging as a novel class of artificially structured materials that have generated significant interest in recent years for their potential application in plasmonic and thermoelectric devices. Though most nitride metals are rocksalt, nitride semiconductors in general have hexagonal cr...

Hyperbolic metamaterials (HMMs) based on metal/dielectric multilayers have garnered attention in recent years due to their extraordinary optical properties emanating from hyperbolic dispersion of isofrequency surfaces. We have developed a new class of epitaxial metal/dielectric superlattice HMMs based on transition-metal nitrides-titanium nitride (...

In this work, a design of ultra-compact plasmonic modulator is proposed and numerically analyzed. The device layout utilizes alternative plasmonic materials such as transparent conducting oxides and titanium nitride which potentially can be applied for CMOS compatible process. The modulation is obtained by varying the carrier concentration of the t...

A planar layout for an ultra-compact plasmonic modulator is proposed and numerically investigated. Our device utilizes potentially CMOS compatible materials and can achieve 3-dB modulation in just 65nm and insertion loss <1dB at telecommunication wavelengths.

In this work we report low-loss insulator-metal-insulator plasmonic interconnects using the CMOS-compatible material titanium nitride. The mode profile shows the characteristic exponential decay of the plasmonic regime, with propagation losses as low as 0.79 dB/mm.

An insulator-metal-insulator plasmonic interconnect using TiN, a CMOS-compatible material, is proposed and investigated experimentally at the telecommunication wavelength of 1.55 µm. The TiN waveguide was shown to obtain propagation losses less than 0.8 dB/mm with a mode size of 9.8 µm on sapphire, which agree well with theoretical predictions. A t...

Significance Plasmonic and metamaterial devices require high-performance material building blocks, both plasmonic and dielectric, to be useful in any real-world application. Here, we develop both plasmonic and dielectric materials that can be grown epitaxially into ultrathin and ultrasmooth layers with sharp interfaces. We show that a superlattice...

We investigate the absorption properties of planar hyperbolic metamaterials (HMMs) consisting of metal-dielectric multilayers, which support propagating plane waves with anomalously large wavevectors and high photonic-density-of-states over a broad bandwidth. An interface formed by depositing indium-tin-oxide nanoparticles on an HMM surface scatter...

Searching for better materials for plasmonic and metamaterial applications is an inverse design problem where theoretical studies are necessary. Using basic models of impurity doping in semiconductors, transparent conducting oxides (TCOs) are identified as low-loss plasmonic materials in the near-infrared wavelength range. A more sophisticated theo...

Titanium nitride is considered a promising alternative plasmonic material and is known to exhibit localized surface plasmon resonances within the near infrared biological transparency window. Here, local heating efficiencies of disk-shaped nanoparticles made of titanium nitride and gold are compared in the visible and near infrared regions numerica...

We propose several planar layouts of ultra-compact plasmonic modulators that utilize alternative plasmonic materials such as transparent conducting oxides and titanium nitride. The modulation is achieved by tuning the carrier concentration in a transparent conducting oxide layer into and out of the plasmon resonance with an applied electric field....

We propose a metamaterial based perfect absorber in the visible region, and investigate the performance of titanium nitride as an alternative plasmonic material. Numerical and experimental results reveal that titanium nitride performs better than gold as a plasmonic absorbing material.

Materials research plays a vital role in transforming breakthrough scientific ideas into next-generation technology. Similar to the way silicon revolutionized the microelectronics industry, the proper materials can greatly impact the field of plasmonics and metamaterials. Currently, research in plasmonics and metamaterials lacks good material build...

We correct an error in figure 6 of our manuscript [Opt. Mater. Exp. 2, 478–489 (2012)] showing the propagation length and confinement width of surface-plasmon-polariton on metal/air interface.

Scandium nitride (ScN) is a rocksalt semiconductor that has attracted significant attention from various researchers for a diverse range of applications. Motivated by the prospect of using its interesting electronic structure for optoelectronic and dilute magnetic semiconductor applications, we present detailed studies of the electronic transport a...

Beyond Silver and Gold: Better material buildingblocks are essential in transforming the novel ideas of plasmonics and metamaterials into technologies of the future, as reviewed by Alexandra Boltasseva and co-workers on page 3264. Devices built from tailored materials offer improved performance and new functionalities with applications in sensing,...

Epitaxially grown TiN/Al0.6Sc0.4N superlattice behaves as a hyperbolic metamaterial (HMM) in the visible range. Since HMMs enhance photonic-density-of-states and reduce lifetime of an emitter, we observed nine times decrease in lifetime of a dye molecule placed close to this HMM.

We investigate the feasibility of titanium nitride (TiN) nanoparticles as local heat sources in the near infrared region, focusing on biological window. Experiments and simulations provide promising results for TiN, which is known to be bio-compatible.

Transparent conductive oxides (TCOs) as substitutes to metals could offer many advantages for low-loss plasmonic and metamaterial (MM) applications in the near infrared (NIR) regime.

The influence of particle shape on plasmonic response and local electric field strength is well documented in metallic nanoparticles. Morphologies such as rods, plates, and octahedra are readily synthesized and exhibit drastically different extinction spectra than spherical particles. Despite this fact, the influence of composition and shape on the...

Transparent conducting oxides (TCO) are emerging as possible alternative constituent materials to replace noble metals such as silver and gold for low-loss plasmonic and metamaterial (MMs) applications in the near infrared (NIR) regime. The optical characteristics of TCOs have been studied to evaluate the functionalities and potential of these mate...

Optical responses of titanium nitride and zirconium nitride are studied in the visible and near-infrared regions for localized surface plasmon applications. Both materials are found to be promising alternatives to noble metals.

The pulsed laser deposited nanocrystalline ZnO films doped by Ga up to six weight percent are studied by X-ray difraction and generalized spectro-ellipsometry. We report substantial atomic structure modification of heavy Ga-doped ZnO resulted and a concentration dependent increase of inter-planar distance. Measured dielectric function spectra show...

Noble metals such as gold and silver are conventionally used as the primary plasmonic building blocks of optical metamaterials. Making subwavelength-scale structural elements from these metals not only seriously limits the optical performance of a device due to high absorption, it also substantially complicates the manufacturing process of nearly a...

We consider methods to define the performance metrics for different plasmonic materials to be used in localized surface plasmon applications. Optical efficiencies are shown to be better indicators of performance as compared to approximations in the quasistatic regime. The near-field intensity efficiency, which is a generalized form of the well-know...

The search for alternative plasmonic materials with improved optical properties, easier fabrication and integration capabilities over those of the traditional materials such as silver and gold could ultimately lead to real-life applications for plasmonics and metamaterials. In this work, we show that titanium nitride could perform as an alternative...

We directly demonstrate an improvement in the radiative decay rate of dye molecules near multilayer hyperbolic metamaterials (HMMs). Our comprehensive study shows a radiative decay rate for rhodamine 800 (Rh800) that is several times higher due to the use of HMM samples as compared to dielectric substrates. This is also the first experimental demon...

Aluminum and gallium doped zinc oxide thin films with negative dielectric permittivity in the near infrared spectral range are grown by pulsed laser deposition. Composite ceramics comprising ZnO and secondary phase Al2O3 or Ga2O3 are employed as targets for laser ablation. Films deposited on glass from dense and small-grained ceramic targets show o...

Metal nitrides as alternatives to metals such as gold could offer many advantages when used as plasmonic material. We show that transition metal nitrides can replace metals providing equally good optical performance for many plasmonic applications.

When heavily doped, semiconductors such as ZnO can exhibit metallic properties thus becoming versatile building blocks for optical metamaterials. Here, we design and fabricate an all-semiconductor metamaterial and demonstrate negative refraction in the near-infrared region.

Several different types of nanodiamonds were characterized in order to find the best sample to be used in further experiments with metamaterials. In this work we present the results of optical analysis of aqueous suspensions containing nanodiamonds, SEM analysis of diamond particles dispersed on silicon substrates and measurements of photoluminesce...

Noble metals such as gold and silver are the primary metallic building blocks of metamaterial devices. Making subwavelength-sized structural elements from these metals seriously limits the optical performance of a device, however, and complicates the manufacturing process of nearly all metamaterial devices in the optical wavelength range. As an alt...

As alternatives to conventional metals, new plasmonic materials offer many advantages in the rapidly growing fields of plasmonics and metamaterials. These advantages include low intrinsic loss, semiconductor-based design, compatibility with standard nanofabrication processes, tunability, and others. Transparent conducting oxides such as Al:ZnO, Ga:...

Recent metamaterial (MM) research faces several problems when using metal-based plasmonic components as building blocks for MMs. The use of conventional metals for MMs is limited by several factors: metals such as gold and silver have high losses in the visible and near-infrared (NIR) ranges and very large negative real permittivity values, and in...

Spontaneous emission patterns of electric and magnetic dipoles on different metallic surfaces and a hyperbolic metamaterial (HMM) surface were simulated using the dyadic Green’s function technique. The theoretical approach was verified by experimental results obtained by measuring angular-dependent emission spectra of europium ions on top of differ...

The performance of metamaterial and transformation-optics devices is limited by losses in their plasmonic components. We show that ceramics (heavily doped-zinc oxide and titanium nitride) could help in overcoming the loss issue in the optical range.

Spontaneous emission patterns of electric and magnetic dipoles on different material surfaces were studied numerically and experimentally. The results show the modified behavior of electric and magnetic dipoles on metallic and HMM surfaces.