Session W12: Optical/Laser and High Frequency Devices and Applications Including Optoelectronics and Photonics

Enhanced amplitude modulation of a terahertz complementary vanadium dioxide metamaterial

Vanadium dioxide (VO₂) is a dynamic quantum material that undergoes an insulator-to-metal transition (IMT) at ~340K. Integration with metamaterials yields enhanced manipulation and control of terahertz radiation which enables, as but two examples, signal modulation and tunable absorption. We introduce a complementary split ring resonator (CSRR) array integrated with a VO₂ film that provides greatly increased transmission modulation at terahertz (THz) frequencies in comparison to either bare VO₂ films or conventional split ring resonator arrays integrated with VO₂. The amplitude modulation at ~0.5 THz is increased from 0.42 for the bare VO₂ film to 0.68 for the metamaterial composite, corresponding to a 62.4% enhancement. Moreover, temperature dependent transmission measurements reveal a redshift of the resonant frequency upon traversing the IMT. Maxwell-Wagner modeling suggests that the origin of this redshift arises from a percolation induced permittivity increase in VO₂ during the IMT. Our work provides a route to obtain dynamic enhancement and dielectric sensitivity that facilitates the development of tunable devices and provides a simple and effective means to investigate the local electrodynamic properties of quantum materials.   

Molecular Beam Epitaxy Growth of Ferromagnetic MnSb on InGaSb: Characterization of Orientation, Interfaces, and Magnetic Properties

Ferromagnets compatible with high spin-orbit coupling III-V semiconductors (InAs, InSb) can be used for spin injection, breaking the spin degeneracy in 1D nanowire systems with the potential for creating Majorana Zero Modes.¹ The transition metal monopnictide MnSb is a hexagonal ferromagnet with a high Curie temperature and is the most Sb-rich binary phase, suggesting high thermodynamic stability in contact with InGaSb. Although MnSb has been grown on III-V substrates, here a new growth orientation has been observed with the c-axis perpendicular to the growth plane. In-situ reflection high-energy electron diffraction and ex-situ high resolution X-ray diffraction were used to determine that the films are oriented as (10-10)[0001][-12-10] MnSb||(001)[1-10][110] InGaSb. Superconducting quantum interference device (SQUID) magnetometry was used to determine that the magnetic easy axis lies along the c axis of the MnSb, while the hard axis lies in the basal plane. Transmission electron microscopy confirmed the growth techniques presented allow us to grow MnSb on a high spin-orbit coupling III-V ternary semiconductor with a relatively abrupt interface, in comparison to MnSb films grown on InGaAs.<sup>2

1</sup>Nano Lett. 20, 3232 (2020).

²J. Cryst. Growth, 498, 391 (2018).   

Chiral Quantum Light Emitters in 2D Semiconductor/Magnet Heterostructures

Quantum light emitters (QEs)  are essential components for photonic quantum technology. The well-defined chirality of them is required to realize complex quantum networks. However, such chiral quantum light signature can only be established via applying a high external magnetic field or integrating with photonic or meta-cavities. Recent studies demonstrated the site-control 0D-confined QEs in monolayer transition-metal dichalcogenides (TMDCs) semiconductors through localized strain engineering make them ideal candidates for coupling with other structures. Here we present highly chiral single photons generated from QEs in monolayer TMDCs and van der Waal antiferromagnetic (AFM) insulator heterostructures at zero external magnetic field. These QEs are created by using a blunt scanning probe microscope to deform the heterostructures with near-unity spontaneous circular polarization and single-photon purity as high as 0.15. This deterministic approach enables the practical integration of solid-state highly chiral single photon QEs for future quantum information and communication application.   

Impact ionization-induced bistability in cryogenic CMOS transistors for capacitorless memory applications

Cryogenic operation of complementary metal oxide semiconductor (CMOS) silicon transistors is crucial for quantum information science. We report bistability and dramatic hysteretic loops that are observed in the drain current as a function of gate voltage characteristics I_D(V_G) of 180 nm, foundry fabricated, CMOS transistors operated at low temperatures (T<30 K). The hysteretic loops – which have a >10⁷ ratio of high to low drain current states at the same V_G – can be used for a capacitorless single-transistor memory at cryogenic temperatures. The bistable behavior occurs when the transistors are operated at voltages exceeding 1.3 V at cryogenic temperatures and can be obtained from both n-type and p-type transistor polarities. The device bistability arises from impact ionization charging of the transistor body, which leads to effective back-gating of the inversion channel. This physical mechanism was verified by independent measurements of the body potential where voltages as large as ≈1 V are seen. The retention time at cryogenic temperatures is many minutes, sufficiently long to provide effectively nonvolatile memory on the time scales predicted for quantum computation controlled and read out by CMOS circuitry.   

Graphene based pH sensing with extremely high sensitivity

Field-effect transistors (FETs) are versatile tools for measuring numerous biomarkers. We demonstrate that their measurement sensitivity and resolution can be improved by using new materials and device designs. Here, we report on the sensitivity and noise performance of dual-gated graphene FETs. As an example, when measuring pH, the devices exhibit a sensitivity of up to 30 V for a unit change in pH, ≈ 500-fold greater than the Nernst value at room temperature, and a noise limited resolution of 2x10^-4 in the biomedically relevant bandwidth between 0.1 Hz to 10 Hz. The results represent a factor of 2 improvement over previously reported values using dual-gate MoS₂ FETs. This exceptional performance arises from a highly asymmetric dual-gate design that utilizes an ionic liquid top-gate dielectric. The high top-gate capacitance when coupled with the large intrinsic quantum capacitance (≈ 15 µC/cm²) of graphene enables a top-gate to back-gate coupling ratio of ≈ 500. The higher sensitivity, combined with improved resolution make graphene dual-gated FETs powerful tools for field monitoring of pH with applications in biomedical research and technology.

Towards millimeter-wave standards for dielectrics and loss tangent

In this talk, I will introduce the National Institute of Standards and Technology’s (NIST) microwave materials program. I will introduce our new effort to develop traceable mmWave standard reference materials. I will discuss how this new standard will impact on-wafer calibration standards, traceable power, phase and impedance. I plan to briefly discuss cavity perturbation theory, which is a method that’s easy and inexpensive to do. Having introduced NIST’s goals, I will provide a list of essential equipment needed to perform the on-wafer calibrations. After laying out our program at NIST and some of our recent accomplishments, I want to open the conversation and answer your questions about microwave measurements.   

Plasmonic Color Printing with Semicontinuous Silver Films and Modeling of Inhomogeneous Broadening

Among many kinds of plasmonic structures, semicontinuous metal films (SMF), which are randomly distributed metal nanoparticles at the near-percolation regime, can generate sub-wavelength, fade-free, and environment-friendly plasmonic colors. SMFs comprise of random, fractal-type island films with nanoparticles which resonate at different wavelengths. Such structures can confine light at the nanoscale under illumination and result in an enhancement of the local electromagnetic field. Laser illumination reshapes the metal nanoparticles through thermally induced changes allowing for vibrant colors due to spectral modification. In this work, we have an asymmetric Fabry-Pérot plasmonic structure comprising of semicontinuous metal films deposited on a metallic (Ag) mirror with a thick dielectric (SiO₂) to utilize the multiple-beam interference and observe colors in the reflection mode. The absorption of SMF exhibits inhomogeneous broadening and hence was fitted with Lorentz-convoluted models where the statistics of the nanoparticles is accounted for with a probability distribution. In order to implement such dispersion in frequency/time domain solvers we developed a time-domain compatible analytical approximation based on our generalized dispersive material (GDM) model framework.   

Inverse-Designed Nonlinear Photonics in 4H-SiC

We optimized and fabricated inverse-designed nano-resonators in 4H-Silicon-Carbide-on-Insulator to take advantage of the material's large nonlinear optical coefficients and low waveguide loss. We characterize high quality factors of the nano-resonators and observe nonlinear frequency conversion. Such nonlinear frequency generation has a wide range of important applications, from chip-scale optical parametric oscillator lasers to quantum frequency conversion of solid-state spin qubits.    

Withdrawn

Recently, we have demonstrated novel lasers which exploit the topological properties of the photonic band structure to control the scaling and emission profile of semiconductor lasers. Among them are topological lasers based on the quantum-hall and valley-hall effects. These laser cavities rely on feedback from edge-modes that are robust to disorders and can produce vortex beams with orbital angular momentum. We also developed the first bound state in the continuum (BIC) laser which can minimize the threshold for small cavities and investigated their viability for electrical injection. Due to the properties of this topological singularity, lasers operating at BIC modes can be optimized for both small and large scale apertures. In this talk, we will focus on the scaling of photonic crystal lasers with increasing cavity size. The influence of the symmetry of the modes and the coupling between Bloch bands on the lasing response will also be discussed. Finally, we conclude by introducing a scheme that can improve the threshold gain difference between the fundamental and higher-order modes and enable single-mode lasing in large-scale photonic crystal lasers.   

Spectral computed tomography for material classification

Photon counting spectral detectors are finding applications in industrial and medical x-ray imaging. We will show novel imaging techniques and material decomposition approaches for classifying and volumetrically separating materials, chemicals and biological contents in a spectral computed tompgraphic imaging system. Our methods use cutting-edge photon counting detectors (PCD) developed in CERN (Medipix3) originally for particle tracking. We show the correction and calibration methods required to use these detectors along with novel algorithms involving Guassian mixture models and multi-step material decomposition developed by our group to separate multiple (upto 6 materials) of various concentrations. The high resolution and low noise from the PCDs combined with novel decomposition algorithms has the potential for applications of these mtheods in an array of industrial and biomedical imaging applications.   

Corundum, bixbyite, and monoclinic alloys of Al2O3 and In2O3

By alloying Al₂O₃ and In₂O₃ with Ga₂O₃ [1-4], material properties such as bandgaps (for optical devices) and lattice constants (to control strain) can be tailored to the requirements of specific device applications, with several demonstrated applications. The design space can be increased by considering InAlO₃ alloys. However, a characterization and understanding the properties of InAlO₃ alloys is still missing. We therefore use density functional theory (DFT) with hybrid functionals to detail the energetics and changes in electronic and structural properties of these alloys. We consider alloys in the bixbyite, corundum, and monoclinic crystal structures. Our results show that the pseudocubic lattice constants for all structures increase linearly as a function of In content, following Vegard’s law. The bandgap decreases nonlinearly, exhibiting stronger bowing in the corundum (b=4.16 eV) and bixbyite structures (b=4.9 eV) than the monoclinic structure (b=1.73 eV). These findings can be used for rational device design.

[1] Appl. Phys. Lett. 119, 042104 (2021)

[2] Appl. Phys. Lett. 116, 232102 (2020)

[3] Appl. Phys. Lett. 112, 242101 (2018)

[4] Phys. Rev. B 92, 085206 (2015)   

Spin dependent charge transfer in MoSe2/hBN/Ni hybrid structures

The manipulation of the spin/valley properties in monolayer transition metal dichalcogenide (TMD) monolayers (MLs) can be achieved thanks to a magnetic layer in close proximity to the TMD ML. We present magneto-photoluminescence measurements in a hybrid 2D semiconductor/ ferromagnetic structure consisting of MoSe₂/hBN/Ni. When the Nickel layer is magnetized, we observe circularly polarized photoluminescence of the trion peak in MoSe₂ monolayer under linearly polarized excitation. This build-up of circular polarization can reach a measured value of about 4% when the magnetization of Ni is saturated perpendicularly to the sample plane, and changes its sign when the magnetization is reversed. The circular polarization decreases when the hBN barrier thickness increases. These results are interpreted in terms of a spin-dependent charge transfer between the MoSe₂ monolayer and the Nickel film. The build-up of circular polarization is observed up to 120 K, mainly limited by the trion emission that vanishes with temperature.   

Fast coherent control of a Nitrogen-Vacancy spin ensemble using a KTaO3 dielectric resonator at cryogenic temperatures

Microwave delivery to samples in a cryogenic environment can pose experimental challenges such as restricting optical access, space constraints and heat generation. Moreover, existing solutions that overcome various experimental restrictions do not necessarily provide a large, homogeneous oscillating magnetic field over macroscopic length-scales, which is required for control of spin ensembles or fast gate operations in scaled-up quantum computing implementations. Here [1] we show fast and coherent control of a negatively charged nitrogen vacancy spin ensemble by taking advantage of the high permittivity of a KTaO₃ dielectric resonator at cryogenic temperatures. We achieve Rabi frequencies of up to 48 MHz, with a total field-to-power conversion factor C_P = 9.7 mT/sqrt(W)(191 MHz_Rabi/sqrt(W)). We use the nitrogen vacancy center spin ensemble to probe the quality factor, the coherent enhancement, and the spatial distribution of the magnetic field inside the diamond sample. The key advantages of the dielectric resonator utilized in this work are: ease of assembly, in-situ tuneability, a high magnetic field conversion efficiency, a low volume footprint, and optical transparency. This makes KTaO₃ dielectric resonators a promising platform for the delivery of microwave fields for the control of spins in various materials at cryogenic temperatures.

[1] Vallabhapurapu, H. H. et al. Fast coherent control of an NV spin ensemble using a KTaO₃ dielectric resonator at cryogenic temperatures. arXiv preprint arXiv:2105.06781 (2021).