Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session M57: Properties of Nanostructures and NanowiresRecordings Available
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Sponsoring Units: DCMP Chair: Hung-Yu Yang, Boston College Room: Hyatt Regency Hotel -Clark |
Wednesday, March 16, 2022 8:00AM - 8:12AM |
M57.00001: Vernier Spectrum and Valley Polarization Control in Carbon Nanotube Quantum Dots Jameson G Berg, Neda Lotfizadeh, Wade De Gottardi, Mitchell J Senger, Dublin Nichols, Ethan D Minot, Vikram V Deshpande Dirac cones can tilt or warp due to spin-orbit or lattice interaction resulting in asymmetric velocities for left- and right-moving electrons. In carbon nanotubes, this effect has manifested in a secondary quantum interference on top of the Fabry-Perot interference [1,2]. In finite-sized systems such as quantum dots, this effect is predicted [3] to result in unequally spaced energy levels for left/right movers or K/K’ valley electrons leading to accidental degeneracies and a Vernier spectrum. In this work, we present the Vernier-like spectrum seen in Coulomb blockade measurements of ultraclean suspended carbon nanotubes. Four-fold shell filling on a slowly oscillating background conductance versus gate voltage is seen to be interrupted periodically to add two additional electrons. We present a theoretical model to describe such behavior in the conductance of finite-sized nanotubes that lifts the four-fold degeneracy and gives rise to the Vernier-like spectrum. The model also shows that valley-polarized energy levels are available at specific gate voltages, and the degree of polarization can be tuned by gate voltage. Our work showcases the continued surprises revealed by quantum transport in ultraclean carbon nanotubes. |
Wednesday, March 16, 2022 8:12AM - 8:24AM |
M57.00002: NMR Studies of NiTi Strain-Glass Rui Li, Daniel Salas, Woohyun Cho, Ibrahim Karaman, Joseph H Ross We have studied Ni50+xTi50-x materials using 47Ti and 49Ti NMR, at temperatures up to 400 K. Measured compositions range from x = 0.1 featuring a martensitic transformation, to x = 1.2 exhibiting a strain glass transformation, which is believed to involve freezing of dynamical ferroelastic nanodomains. In the high-temperature phase we find a small enhancement of the NMR Knight shift for the strain glass composition, an indication of an enhanced electronic density of states at EF. For x = 0.1, the line shape changes observed across the austenite to martensite transformation (B2 to B19') are consistent with previous reports, and include a very small change of the Knight shift, along with an enhancement of the electric field gradients (EFGs) in the locally distorted B19' phase. The strain glass exhibits a significantly larger reduction in Knight shift at the freezing transformation near 180 K, along with a large increase in EFG in the frozen strain glass, corresponding to the anisotropic atomic arrangement within the frozen strain glass. These results are analyzed according to the reduced metallic behavior of the strain glass, and the local dynamics above the strain glass transition, and compared to the proposed R-phase structure for this system. |
Wednesday, March 16, 2022 8:24AM - 8:36AM |
M57.00003: Superfluidity of a two-component Bose gas of dipolar excitons in a double layer of gapped hexagonal alpha-T3 Oleg L Berman, Gabriel P Martins, Godfrey A Gumbs, Paula Fekete We present the conditions for Bose-Einstein condensation and superfluidity of a two-component weakly interacting Bose gas of dipolar excitons, formed by electron-hole pairs in spatially separated gapped hexagonal alpha-T3 (GHAT3) layers. An applied magnetic field to this pseudospin-1 monolayer system results in a Zeeman-type splitting of the energy subbands. This dispersion relation consists of three bands: conductivity (CB), intermediate (IB) and valence bands (VB). We consider two types of dipolar excitons in double-layer of GHAT3: (a) “A excitons,” which are bound states of electrons in CB and holes in IB and (b) “B excitons,” which are bound states of electrons in CB and holes in VB. The binding energy of A and B dipolar excitons is calculated. For a two-component weakly interacting Bose gas of dipolar excitons in a GHAT3 double layer, we obtain the energy dispersion of collective excitations, two sound velocities for two branches of the collective excitation spectrum, the superfluid density, and the mean-field critical temperature Tc for superfluidity. We found the optimal ranges for the hoping parameter alpha, the gap in the single particle spectrum, the interlayer separation that correspond to higher exciton binding energy, higher Tc, lower critical concentrations of A and B excitons. |
Wednesday, March 16, 2022 8:36AM - 8:48AM |
M57.00004: Template-defined In(Ga)As Nanowires Kristopher Cerveny, Dominik M Zumbuhl, Didem Dede, Mohammad Samani, Anna Fontcuberta i Morral, Valerio Piazza, Lincoln J Lauhon, Chunyi Huang Templated semiconductor nanowires with strong spin-orbit interaction (SOI) are a scalable and versatile platform [1] to create and study novel quantum states of matter, such as helical states and spin helices and Majorana fermions. Modulation doping is a well-established technique to enhance mobility and control carrier concentration. Here, we report recent results on In(Ga)As nanowires with remote doping in the GaAs nanomembrane template grown via molecular beam epitaxy in a selective area growth approach [2], improving on a bulk-doping approach. This process gives major improvements in mean free path and SOI, which are illustrated in magnetoconductance measurements revealing weak anti-localization behavior across nanowire Y-junctions. With a wrap-around top gate, the density can be tuned down to full depletion without applying an electric field. However, it would be important to control the Rashba SOI with an electric field, which could be generated with a split gate. To implement this on a tall and thin membrane with large aspect ratio is challenging. Here, we employ multiple angle evaporation combined with atomic layer deposition of dielectric layers of HfO2 to create a split gate wrapped around the membrane and nanowire. |
Wednesday, March 16, 2022 8:48AM - 9:00AM |
M57.00005: Reduction of Fabrication-Related Disorder in InSb Nanowire Devices Using 2D Techniques and Materials Colin J Riggert, Garett D Reichenbach, Sasa Gazibegovic, Ghada Badawy, Diana Car, Paul A Crowell, Erik P. A. M. Bakkers, Vlad S Pribiag Majorana zero modes (MZMs) are a promising candidate for quantum computation due to their non-Abelian braiding and topological protection against perturbation, and InSb nanowires are one of the most promising platforms for their realization. Recent theoretical works, however, have highlighted disorder as a considerable obstacle for MZM observation in such nanowires. Consequently, much effort is being made to reduce material disorder introduced in the nanowire growth process. As a parallel effort in device improvement, we adopt, adapt, and apply techniques used in the study of 2D Van der Waals heterostructures to the fabrication process of nanowire devices, and explore the impact of these techniques on fabrication-related disorder. |
Wednesday, March 16, 2022 9:00AM - 9:12AM |
M57.00006: Observation of magnetic-field-induced optical vortex-antivortex pair Dongha Kim, Min-Kyo Seo Optical vortices, topological textures in electromagnetic waves, received significant attention in high-dimensional communication and optical manipulations. Unlike the topological textures in other physical systems, optical vortices have been considered passive field distribution, non-interactive to the external stimulus. This work demonstrated magnetic field-induced generation and manipulation of optical vortex-antivortex pair in a gradient-thickness optical cavity (GTOC). GTOC consists of Al/SiO2/Ni/SiO2 quad-layer with two-dimensional thickness variation in the top and bottom SiO2 layers. In the generalized parameter space with thicknesses of SiO2 layers, GTOC reveals a non-trivial topological phase in the specific ranges of Ni layer thicknesses, generating optical vortex-antivortex pair in reflected light. The magneto-optic effect enables the control of an effective thickness change in the Ni layer which is the control parameter of the topological phases. In the experiment, we confirmed the existence of the non-trivial topological phase of GTOC by the bijection of synthetic dimension into real space. We demonstrated magnetically-induced generation and manipulation of the optical vortex-antivortex pair based on the topological phase transition of GTOC. |
Wednesday, March 16, 2022 9:12AM - 9:24AM |
M57.00007: Magnetotransport properties of LaAlO3/SrTiO3-based ultradense two-dimensional nanowire networks Ranjani Ramachandran, Aditi Nethwewala, Patrick R Irvin, Jeremy Levy, Hyungwoo Lee, Jung-Woo Lee, Chang-Beom Eom Conductive AFM lithography can be used to form various conductive nanostructures in the 2D electron system formed at the interface of LaAlO3/SrTiO3. Previous studies on quasi-2D structures, such as waveguide 'nanocrosses', indicate that the electron transport is strongly influenced by ferroelastic domain structure, which in turn depends on the angle between the nanocross and the crystallographic direction. Here we characterize a dense network of nanocrosses or 2D nanowire networks, and probe the magnetotransport properties as a function of the angle of orientation of the nanowire network with the crystallographic direction. Such families of 2D networks of nanowires and/or waveguides, if sufficiently well understood, can be regarded as a possible platform for 2D quantum simulation. |
Wednesday, March 16, 2022 9:24AM - 9:36AM |
M57.00008: Mesoscale Fabrication of the Thin-filmed Strange Metal Sr3Ru2O7 Dale T Lowder, Liyang Chen, Douglas Natelson, Jihwan Jeong, Jinkwon Kim, Tae W Noh In the bulk,Sr3Ru2O7(SRO327) exhibits a strange metal phase in the presence of a field-tuned quantum critical point. One avenue of study of such non-Fermi liquids is electronic transport and spectroscopy at the mesoscopic scale ( i.e. shot noise and tunneling density of states measurements). However, these techniques require the fabrication of mesoscopic devices, typically based on thin films of the starting material. While recent progress has been made in the growth of SRO327 films, SRO327’s chemical and structural sensitivity bring in problems in the fabrication of the nanostructures required. Standard techniques like e-beam lithography (EBL) can damage the SRO327 films at the high column voltages, required for nanoscale resolution. Most etchants drastically damage and change the properties of SRO327 as well. We describe recent progress in the use of focused ion beam (FIB) patterning of this material, and transport properties of the resulting constrictions. Outlining the desired structure with a FIB allows one to achieve the nanoscale resolution to fabricate required nanostructures while avoiding heavy damage to the SRO327 films. |
Wednesday, March 16, 2022 9:36AM - 9:48AM |
M57.00009: Electrical measurement of real-time ion migration dynamics in one-dimensional organic metal-halides Zhenqi Hua, Azza Ben, Tianhan Liu, Hanwei Gao, Biwu Ma, Peng Xiong Organic metal-halide perovskites have shown many superior properties amenable to optoelectronic applications, however, the realization of these potentials has been hampered by their environmental and electronic instabilities. The low-dimensional versions of these materials have been shown to exhibit enhanced chemical stability due to their unique molecular structures. However, the charge transport properties of these materials, particularly their electronic stability with respect to ion migration, have yet to be systematically investigated. Here, we report on electrical measurements of real-time ion dynamics in the 1D hybrid metal-halide (R-MBA)PbI3. The four-terminal (4T) I-V curves exhibit a number of reproducible features indicative of common ion dynamics, including negative differential resistance, nonlinearity, and hysteresis that depend on the rate and direction of the current sweep. Measurements of the time-dependent voltage at constant current evidence an exponential dynamic of a time constant of ~ 2 s for the ion migration current. Moreover, all the unusual features in the I-V’s can be quantitatively modeled based on this single ion dynamic, which shows marked enhancement under photo illumination. Our observations are consistent with the photo-activation of mobile ions and field-assisted ion migration. They provide valuable new insights into the hysteresis in halide perovskite solar cells and the general dynamics of ion migration in these materials. |
Wednesday, March 16, 2022 9:48AM - 10:00AM |
M57.00010: Photoresponse in low dimensional metals Talip Serkan Kasirga, Mohammadali Razeghi, Ugur Basci Photothermal or photovoltaic processes in a material leads to an electrical response. Typically, semiconductors and their devices produce a significant photoresponse and has been investigated widely. Photoreponse from metals on the other hand, is rare in a few cases where optical absorption leads to a bolometric response. Here, we will show that the photoresponse from the nanostructured metals is more ubiquitous than predicted before. We demonstrate that a single nanowire and networked formed by them exhibits a significant photoresponse thanks to the plasmon assisted bolometric effect. The responsivity is as large as silicon pn junctions at moderate laser intensities. We will also show that there are other such metallic nanostructures that exhibit similar photoresponse and they can be used in detection of certain molecules selectively. |
Wednesday, March 16, 2022 10:00AM - 10:12AM |
M57.00011: Characterization of metal contacts to Ta2Ni3Se8 semiconducting nanowires Abin Joshy, Nirasha Thilakaratne, Fei Wang, Jiang Wei The 1D nanostructure of ternary transition metal chalcogenides M2X3Y8 (M= Ta, Nb; X= Ni, Pd, Pt; Y= S, Se) have been found to exhibit remarkable electronic and optoelectronic properties. In this work, single crystals of centimeters long Ta2Ni3Se8 bulk crystals were obtained by optimizing the growth temperature for solid-state growth. Nanowires were prepared from single crystals of Ta2Ni3Se8 by mechanical exfoliation. Field-effect transistors in the back gate geometry had been successfully fabricated. Transport measurements at room temperature revealed that Ta2Ni3Se8 nanowires exhibit n-type semiconducting behavior. Understanding the nature of the contacts is crucial for the study of the intrinsic properties of electronic devices. For charge carriers, barriers are often formed at the metal-semiconductor junction, which affects the charge carrier transport and significantly lowers the transistor performance. We studied the transport behavior of Ta2Ni3Se8 nanowires contacted with different metals. Using a systematic temperature-dependent measurement, we found that electron transport through barriers dominated by thermionic emission. In addition, with a variable-length method, we demonstrate that resistance at each contact and the intrinsic resistivity can be accurately measured. |
Wednesday, March 16, 2022 10:12AM - 10:24AM |
M57.00012: Mechanisms of nanoscroll formation in 2-D transition metal oxides from ab-initio simulations Adway Gupta, Arunima K Singh The study of 2-D transition metal dichacogenides(TMDCs) and their corresponding stable oxides is a growing area of interest due to their promising optoelectronic and thermal properties. In a recent experiment, we have observed the plasma assisted conversion of 2-D TMDCs into 2-D oxides and their subsequent rolling into nanoscrolls. With the goal of assigning a mechanism to this process, we use van der Waals corrected density functional theory simulations to determine the individual driving forces that play a role in nanoscroll formation. We then use the parameters derived from these computations into existing physio-mechanical models that have been developed to study CNTs in the past to find the equilibrium core radii of the nanoscrolls, and compare them to our experiments. We finally conclude by presenting DFT computed properties of the 2-D oxide nanoscrolls in order to unearth their novel properties and potential applications. |
Wednesday, March 16, 2022 10:24AM - 10:36AM |
M57.00013: Electrochemical intercalation of atomically thin 1D van der Waals MoS2 Chinedu E Ekuma, Srinivas Rangarajan, Sina Najmaei, Zhong-Li Liu, Rong Xiang, Madan Dubey, Elsa Reichmanis Electrochemical doping provides a robust means to improve and efficiently control carrier dynamics in materials. Here, we design coaxially wrapped single-layer 2D-based (1D van der Waals) MoS2 with (8,8) chirality index. We exploit the intrinsic hollow structure to engineer new physics through electrochemical intercalation with atoms of Li and zero-valent Cu atoms. Our first-principles modeling based on the hybrid functional show that (8,8) 1D vdW MoS2 is a semiconductor with a bandgap Eg~1.27 eV and work function Φ~5.67 eV. Both the intercalants electrostatically doped the host and showed n-type conductivity, which is consistent with the lowering of the work function ΔΦ~0.78 eV (0.30 eV) in the Li (Cu) doped sample. While zero-valent Cu led to a reduction of Eg~0.43 eV and unpolarized ground state, Li intercalation manifested a magnetic ground state with a magnetic moment μ~0.81 μB. |
Wednesday, March 16, 2022 10:36AM - 10:48AM |
M57.00014: Carbon Nanotube Network P-N Junction Diodes: Exploring the Dark and Light Properties GIDEON OYIBO, Thomas Barrett, Jeffrey L Blackburn, Ji Ung Lee Semiconducting carbon nanotubes are attractive for photovoltaic applications because of their large variation of chiralities, which makes it possible to absorb a broad range of the solar spectrum. Here, we fabricate a network of CNTs and form P-N diodes using buried split gates. We study the intrinsic optical properties of the CNT network without the need for electron or hole acceptor material. We study the diode properties of both monochiral and polychiral networks, including those fashioned into tandem cells. We examine the current-voltage characteristics of these diodes in the dark and find correlations between the key figure of merits, including the diode leakage current and the ideality factor, to different CNT networks. We also examine their optical properties by measuring the photocurrent spectroscopy to gain insights into the dynamics of excitons in a network of CNTs. |
Wednesday, March 16, 2022 10:48AM - 11:00AM |
M57.00015: Addition Spectroscopy of Graphene Nanoribbons Juliana Sebolt, Muqing Yu, Ki-Tae Eom, Chang-Beom Eom, Patrick R Irvin, Jeremy Levy Graphene nanoribbons (GNRs) have unique electronic properties that can potentially be used to develop electron spin-based qubits. The LaAlO3/SrTiO3 (LAO/STO) correlated nanoelectronics platform [1] enables single GNRs to be addressed both optically and electrically. Here we use a LAO/STO-based sketched single electron transistor (SketchSET) [2] to probe the energies at which a single electron is added to a GNR. This addition energy spectrum [3] is expected to be influenced by local electric fields from proximal sketched gates as well as global magnetic fields which can Zeeman split the energy states. This information is complementary to other probes, e.g., THz spectroscopy [4] and STM which also provide detailed information about the electronic structures of these GNR-based spin qubit candidates. |
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