Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session N57: Electronic and Optical Properties of Quantum DotsRecordings Available
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Chair: Zhujing Xu, Purdue University Room: Hyatt Regency Hotel -Clark |
Wednesday, March 16, 2022 11:30AM - 11:42AM |
N57.00001: Entropy measurement of a strongly correlated quantum dot Tim J Child, Owen I Sheekey, Silvia Lüscher, Saeed Fallahi, Geoffrey C Gardner, Michael J Manfra, Yaakov Kleeorin, Yigal Meir, Joshua Folk The spin 1/2 entropy of electrons trapped in a quantum dot has previously been measured with great accuracy, but the protocol used for that measurement is valid only within a restrictive set of conditions. Here, we present a novel entropy measurement protocol that is universal for arbitrary mesoscopic circuits and the application of this new approach to measure the entropy of a quantum dot hybridized with a reservoir. The experimental results are compared to numerical renormalization group calculations and demonstrate a clear modification to the entropy due to Kondo correlations. For the largest couplings investigated in this work, NRG predicts a suppression of spin entropy due to the formation of a Kondo singlet. This suppression is not observed in the experiment, perhaps indicating dephasing of the Kondo singlet by the charge sensor. |
Wednesday, March 16, 2022 11:42AM - 11:54AM |
N57.00002: Electron localization in double quantum dots: ideal and realistic confinements Abdennaceur Karoui, Tanja Zatezalo, Igor Filikhin, Branislav Vlahovic The two-level system theory is applicable for various quantum systems, such as bi-atomic molecules or double quantum dots (DQDs). The electron confinement in DQD is studied in different physical aspects. In this work, we discuss the electron localization in DQD in relation to symmetry breaking. Recently, we have shown [1] that the spectral distribution of electron localizations in DQDs strongly depends on the symmetry of the quantum dot confinements. The ideal symmetry means that the QD geometry and other physical parameters of the electron confinement in each QD are the same, but ideal DQD system cannot be experimentally produced. We modeled numerically both cases of confinement in InAs/GaAs DQD using single sub-band effective mass approach. Our model includes an effective potential, simulating the strain in the heterostructure, in the Schrödinger equation, which is solved by finite element method. The spectral distributions of localized/delocalized states are calculated. We show the effect of the realistic confinement on the electron localization in DQD in relation to the geometry and material mixing of the left/right symmetry violation. We also show that the electron localization in ideal DQD is unstable for any symmetry violation. The results lend themselves to discuss the widely used concept of "quantum dot molecules". |
Wednesday, March 16, 2022 11:54AM - 12:06PM |
N57.00003: Theory of tunable embedded quantum dots in solid-state matrices Tongtong Liu, Thanh Nguyen, Mingda Li Multiple embedded quantum dot system is a highly tunable hybrid platform with a variety of phenomena. Experiments have shown a slight amount of embedded quantum dots leads to superior performance in conductivity, thermoelectricity, and optical properties, far beyond what is achievable through chemical doping. However, the fundamental theory of embedded quantum dots is missing, which constrains material design efforts to trial-and-error approaches. In this work, we provide a theoretical foundation that predicts electrical and optical properties, such as conductivity and photoluminescence spectra, in embedded quantum dots, and propose methods to tune these properties in a large range with external light and magnetic fields. Our theory is based on Green's function calculation and discusses multiple competing terms that co-exist in the system, including the energy spacing of multi-level quantum dots, the randomness of embedded quantum dots' positions, the on-site Coulomb interaction which leads to Kondo effects, and the Hund's coupling. We show novel phenomena, such as Anderson localization, Coulomb blockade, and singlet-triplet transition of quantum dot inner states, can appear and be controlled by external fields. |
Wednesday, March 16, 2022 12:06PM - 12:18PM |
N57.00004: A quantum dot pump coupled with a single quantum Hall edge channel Wanki Park, Sung Un Cho, Myung-Ho Bae, H.-S. Sim Development of single-electron sources is a crucial step towards a fermion version of quantum optics and a solid-state quantum processing. Further development of single-electron sources is desired, since existing sources do not cover the emission energy range of 1 – 60 meV. We theoretically and experimentally propose a new type of a single-electron source, which is composed of an interacting quantum dot and a single lead. As the quantum dot is coupled to the single lead (a chiral quantum Hall edge), electron-hole pairs are pumped by AC modulation of the quantum dot. The energy of pumped electrons can be 10 - 60 meV with help of the charging energy in the quantum dot while the hole energy is near the Fermi energy. Utilizing the energy separation, the electron and the hole of a pumped pair are spatially split by applying a tunable-potential barrier located on the path of the pumped pair. We theoretically describe the pumping mechanism using a master equation. We find that the single-electron generation resulting from the pumping and splitting of the electron-hole pairs is identified by characteristic triangular shape regions in the pump map. Our single-electron source is experimentally realized, and the obtained pump map is in good agreement with the theoretical result. |
Wednesday, March 16, 2022 12:18PM - 12:30PM |
N57.00005: Exotic quantum critical point in a two-site charge Kondo circuit Winston Pouse, Lucas Peeters, Connie L Hsueh, Ulf Gennser, Antonella Cavanna, Marc A Kastner, Andrew K Mitchell, David Goldhaber-Gordon A central feature of heavy fermion materials, the emergence of coherence in a magnetic lattice collectively screened by a surrounding sea of mobile electrons, has yet to be realized in a simple model. We here experimentally implement a tunable nanoelectronic circuit comprising two quantum islands, each of whose charge state acts like a local spin that can be screened via a Kondo interaction. Coupling these two islands together realizes a novel model which captures the essence of competition between local and collective screening of magnetic moments, a variant of the prototypical two-impurity Kondo model. We tune our device to a quantum critical point and show experimentally that the dependence of conductance on deviation from this point matches non-trivial universal predictions from numerical renormalization group calculations. This work is a necessary first step in scaling up such circuits from individual sites to networks or lattices. |
Wednesday, March 16, 2022 12:30PM - 12:42PM |
N57.00006: Spectroscopy of the local density-of-states in nanowires using integrated quantum dot Christian Schonenberger, Frederick Thomas, Malin Nilsson, Carlo Ciaccia, Christian Juenger, Francesca Rossi, Valentina Zannier, Lucia Sorba, Andreas Baumgartner In a quantum dot (QD) an energy eigenstate can be shifted in energy with the aid of a gate voltage. It, hence, can serve as an ideal tunable spectrometer that measure the local density-of-states (DOS) as a function of energy of the electron systems to which it is attached. Semiconducting nanowires (NWs) have become popular quasi-one-dimensional (1d) systems in, for example, studies of the emergence of Majorana-like features in NWs proximitized by a superconductor (SC). Here we report on spectroscopic measurements using a QD integrated directly into the NW during the epitaxial growth as an energetically and spatially well-defined tunnel probe to perform dI/dV spectroscopy of discrete bound states in the NW lead segments. We will focus here on InAs NWs not covered by a SC with InP tunnel barriers and pure InAs lead segments that connect the QD to metallic source and drain contacts. Due to the 1d nature of the lead segments and the non-ideal coupling of the NW to source and drain, strong DOS features appear in the lead segments themselves. These are usually difficult to distinguish from the DOS features of the QD itself. By tuning a side-gate in close proximity of one of the lead segments, we can distinguish transport features related to the modulation in the lead DOS and to excited states in the QD. We implement a non-interacting capacitance model and derive expressions for the slopes of QD and lead resonances that appear in two-dimensional spectroscopy plots of dI/dV as a function of source-drain bias and gate voltage. |
Wednesday, March 16, 2022 12:42PM - 12:54PM |
N57.00007: Entropy measurement of a double quantum dot Owen I Sheekey, Tim J Child, Silvia Lüscher, Saeed Fallahi, Geoffrey C Gardner, Michael J Manfra, Yaakov Kleeorin, Yigal Meir, Joshua Folk Double quantum dots (DQD) offer a convenient platform for the realization and measurement of complex, experimentally tunable Hamiltonians. The electronic entropy, S, is an appealing metric to probe such Hamiltonians experimentally, as it is directly related to the degrees of freedom d of the ground state of electrons in the system, S = kblnd. Here we present measurements of S for a system of two capacitively coupled lateral quantum dots (QD), investigating how entropy changes throughout the (0,1)↔(1,0) transition region of the stability diagram, where inter-dot Coulomb effects increase the gap to the (1,1) charge state. Although the measurements are sensitive primarily to the charge of one of the two dots, S reflects the system as a whole, which is strongly modified by coupling between the dots and to a thermal reservoir. Looked at from a different perspective, our measurement can be understood as a demonstration of the use of one QD as entropy sensor for a second quantum system, an important advance for experiments where the thermodynamics of the system of interest may be hard to probe directly. |
Wednesday, March 16, 2022 12:54PM - 1:06PM |
N57.00008: Smartphone-based Fingerprint Extraction from Quantum Dot Optical Physically Unclonable Functions Elliott M Ball, Kieran Longmate, Joonas Majaniemi, Daniel Abreu, Angelo Lamantia, Robert J Young Physically Unclonable Functions are physical systems that can be interrogated in such a way that they exhibit some unique and readable response due to properties intrinsic to the system, allowing for their use as security devices for authentication. That quantum dots emit light at fine-tunable wavelengths as a non-linear response to stimulation via incident light allows us to make use of them in PUF devices. We use CuInS/ZnS colloidal quantum dots deposited on a surface in order to create a unique, impossible to forge optical emission pattern, and capture its response to incident light to use as source information for fingerprint extraction. Using only a smartphone to challenge the quantum dot PUF with its built-in flash, and using its built-in camera to capture the emission pattern, we successfully demonstrate the extraction of fingerprints from quantum dot PUFs via the use of two algorithms. |
Wednesday, March 16, 2022 1:06PM - 1:18PM |
N57.00009: Hexagonal Boron Nitride Substrates for High-Performance Quantum Dot Light-Emitting Devices Yuanpeng Wu, Yixin Xiao, Boyu Wang, Ping Wang, Kai Sun, Woncheol Lee, Emmanouil Kioupakis, Zetian Mi Semiconductor quantum dots (QDs) have potential applications in the field of integrated quantum optics including quantum-computing, quantum key distribution and secure data transmission. Charge carrier dynamics and radiative recombination process within QDs are highly dependent on the crystallinity and defects within the supporting substrates as well as the interface. We show that this dependence can be potentially lifted through van der Waals bonded QD/two-dimensional hexagonal boron nitride (hBN) heterostructures. Epitaxy of wetting layer free GaN QDs on layered hBN and morphology control were successfully demonstrated, wherein the GaN QDs are free of threading dislocations and stacking faults. Unlike QDs covalently bonded to substrate, multiple crystallographic orientations were observed in QDs bonded through van der Waals interactions. Moreover, unexpected efficient radiative recombination process was obtained from GaN QDs on hBN with the photoluminescence emission intensity significantly stronger compared with QDs synthesized on AlN and Si substrates while the QD density on hBN is 1-2 orders of magnitude lower. This work provides a new strategy for synthesizing high quality QDs structure which can enable next-generation high performance optoelectronic and quantum devices. |
Wednesday, March 16, 2022 1:18PM - 1:30PM |
N57.00010: Towards tunable quantum criticality in InAs quantum wells: Quantum point contacts and other quantum circuit building blocks Connie L Hsueh, Praveen Sriram, Tiantian Wang, Candice Thomas, Marc A Kastner, Geoff Gardner, Michael J Manfra, David Goldhaber-Gordon The intrinsic surface Fermi level pinning in InAs allows for submicron, non-annealed Ohmic contacts—in contrast to GaAs/AlGaAs—providing an avenue for miniaturizing charge Kondo devices recently studied in GaAs[1, 2]. We demonstrate quantum point contacts in a high-mobility (106 cm2/Vs) buried InAs quantum well grown on a lattice-mismatched InP substrate. We additionally report on the measured g-factors, observing a many-body exchange enhancement of the out-of-plane g-factor. Despite the substrate-induced strain which is expected to produce dislocations, these gate-defined QPCs are of remarkable cleanliness and stability compared to previous demonstrations in similar heterostructures, and they offer exciting potential as building blocks for electron quantum optics and quantum simulation in InAs-based platforms. |
Wednesday, March 16, 2022 1:30PM - 1:42PM |
N57.00011: Towards tunable quantum criticality in InAs quantum wells: hybrid metal-semiconductor quantum dots for charge Kondo effects Praveen Sriram, Connie L Hsueh, Tiantian Wang, Candice Thomas, Geoffrey C Gardner, Marc A Kastner, Michael J Manfra, David Goldhaber-Gordon Tunable quantum phase transitions based on the multichannel[1] and multi-island[2] charge Kondo effect has provided access to non-Fermi liquid quantum critical points. Work to date has been based on GaAs heterostructures, contacted by few-micron-size annealed metal islands. The large island size has limited studies to electron temperatures of 50 mK and below. The surface Fermi-level pinning in InAs affords direct ohmic contact to non-annealed sub-micron islands with large charging energies (Ec), offering the possibility of measurement over a 10x broader temperature range. We have demonstrated highly transparent interfaces (>99%) between quantum Hall edge states and sub-micron ohmic islands, and clean gate-defined constrictions in an InAs quantum well grown on InP. These building blocks enable the design of hybrid InAs/metal islands -- and arrays of effectively identical islands -- for simulating quantum criticality and gaining insight into Kondo lattice coherence. |
Wednesday, March 16, 2022 1:42PM - 1:54PM |
N57.00012: Lead sulfide/polymer nanocomposite morphological and optical characteristics controlled under metal impurity doping Milad Rasouli, Ali Fatemi, Mahmood Ghoranneviss, Kostya Ostrikov Doping metal impurities is a solution for obtaining new properties for semiconductor nanocomposites. It provides a tool for structural and optical characteristics controlling for the material. PVA/PbS nanoparticles synthesized by chemical bath route in the presence of PVA polymer as colloidal stabilizer Sn and Ag ions injected in material as impurities. Samples investigated by XRD and TEM for morphology and structural studying, which were in agreement with each other. Optical spectroscopy of nanocomposites studied by Uv-Vis (300-900 nm) range absorption spectra and by using tach relation bandgap of samples was measured that was obviously a semiconductor (around 2.3 -2.8 eV). Studying followed by photoluminescence spectroscopy (PL), we saw in this case for both impurities PL quenched by doping. Nonlinear measurements were done by the Z-scan technique with a He-Ne CW laser by 632.8 nm wavelength. For nonlinear refractive index n2 and nonlinear absorption β, self-focusing and saturable absorber attributes were observed respectively. n2 and β were from the order of 10-9 and 10-3 respectively. |
Wednesday, March 16, 2022 1:54PM - 2:06PM |
N57.00013: Quantum Transport of Single-Molecule Junctions when Theory and Experiment Meet. Carlos Sabater, Wynand Dednam, Tamara de Ara, Laura Pastor-Amat, Andrés Martínez Molecular electronic transport experiments performed via Mechanically Controllable Break Junctions (MCBJ) or Scanning Tunneling Microscope on the BJ approach (STM-BJ) don’t provide direct information about the bonding of the molecule at the electrodes. However, to unmask the geometrical configuration acquired by the molecules between the electrodes, a combination of atomistic simulations, ab initio calculations, and electronic transport experiments is required. |
Wednesday, March 16, 2022 2:06PM - 2:18PM |
N57.00014: Proton irradiation effects on GaN nanoscale vacuum electron diodes Keshab R Sapkota, Gyorgy Vizkelethy, George T Wang Vacuum tubes are well known for their resilience under radiation environments, but are bulky, non-integrated, and power hungry. We recently demonstrated high performance, low voltage turn-on GaN nanogap vacuum electron diodes which realize a vacuum electron device architecture on an on-chip GaN-based platform. Here, we present initial studies of radiation effects on the performance and reliability of these devices, focusing on proton irradiation. No significant change on the device performance under a very high dose of radiation exposure, up to 600 MRad, using 2.5 MeV protons was observed. In contrast, prior radiation studies of state of the art GaN PiN diodes show degradation beginning at more than two orders of magnitude lower exposure dose of 2.5 MeV protons. We will present experimental and modeling studies of effect of radiation exposure on the GaN vacuum diode field emission behavior which shed light into potential radiation damage mechanisms for this new class of devices. |
Wednesday, March 16, 2022 2:18PM - 2:30PM |
N57.00015: Electron dressed states in tilted MoS2 Andrii Iurov, Liubov Zhemchuzhna, Godfrey A Gumbs, Danhong Huang We have obtained closed-form analytical expressions for the electron dressed states, or interacting Floquet states, which are generated by the off-resonant coupling between photon and the electrons in T’-MoS_2 (tilted MoS2). We note that T’-MoS2 is one of the most recently discovered two-dimensional lattices which demonstrates spin- and valley-dependent tilted and anisotropic Dirac energy subbands that depend on the external vertical electric field. We have investigated the manner in which all these bands are affected by the off-resonant dressing field of various polarizations. Specifically, linearly polarized light modifies the existing anisotropy of the electronic states and a circularly polarized field results in an alteration of the existing bandgap. We believe that our results are important for applications in band structure Floquet engineering. |
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