OSTI.GOV Journal Article: Observation of electron states of small period artificial graphene in nano-patterned GaAs quantum wells
Title: Observation of electron states of small period artificial graphene in nano-patterned GaAs quantum wells
Engineered honeycomb lattices, called artificial graphene (AG), are tunable platforms for the study of novel electronic states related to Dirac physics. Here in this work, we report the achievement of electronic bands of the honeycomb topology with the period as low as 40 nm on the nano-patterned modulation-doped AlGaAs/GaAs quantum wells. Resonant inelastic light scattering spectra reveal peaks which are interpreted as combined electronic transitions between subbands of the quantum well confinement with a change in the AG band index. Spectra lineshapes are explained by joint density of states obtained from the calculated AG electron band structures. These results provide a basis for further advancements in AG physics.
Wang, Sheng [1];
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Scarabelli, Diego [1]; Kuznetsova, Yuliya Y. [2]; Wind, Shalom J. [1]; Pinczuk, Aron [3]; Pellegrini, Vittorio [4]; Manfra, Michael J. [5]; Gardner, Geoff C. [6]; Pfeiffer, Loren N. [7]; West, Ken W. [7]
Columbia Univ., New York, NY (United States). Dept. of Applied Physics and Applied Mathematics
Columbia Univ., New York, NY (United States). Dept. of Physics
Columbia Univ., New York, NY (United States). Dept. of Applied Physics and Applied Mathematics, and Dept. of Physics
Istituto Italiano di Tecnologia, Genova (Italy). Graphene Lab.; Istituto Nanoscienze-CNR and Scuola Normale Superiore, Pisa (Italy). National Enterprise for nanoScience and nanoTechnology (NEST)
Purdue Univ., West Lafayette, IN (United States). Birck Nanotechnology Center, Dept. of Physics and Astronomy, School of Materials Engineering and School of Electrical and Computer Engineering
Purdue Univ., West Lafayette, IN (United States). Birck Nanotechnology Center, School of Materials Engineering
Princeton Univ., NJ (United States). Dept. of Electrical Engineering
Columbia Univ., New York, NY (United States)
USDOE; National Science Foundation (NSF); Italian Ministry of Research (MIUR); European Union (EU). European Graphene Flagship
SC0010695; SC0006671
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS
Wang, Sheng, Scarabelli, Diego, Kuznetsova, Yuliya Y., Wind, Shalom J., Pinczuk, Aron, Pellegrini, Vittorio, Manfra, Michael J., Gardner, Geoff C., Pfeiffer, Loren N., and West, Ken W. Observation of electron states of small period artificial graphene in nano-patterned GaAs quantum wells. United States: N. p., 2016. Web. doi:10.1063/1.4962461.
Wang, Sheng, Scarabelli, Diego, Kuznetsova, Yuliya Y., Wind, Shalom J., Pinczuk, Aron, Pellegrini, Vittorio, Manfra, Michael J., Gardner, Geoff C., Pfeiffer, Loren N., & West, Ken W. Observation of electron states of small period artificial graphene in nano-patterned GaAs quantum wells. United States. https://doi.org/10.1063/1.4962461
Wang, Sheng, Scarabelli, Diego, Kuznetsova, Yuliya Y., Wind, Shalom J., Pinczuk, Aron, Pellegrini, Vittorio, Manfra, Michael J., Gardner, Geoff C., Pfeiffer, Loren N., and West, Ken W. Mon . "Observation of electron states of small period artificial graphene in nano-patterned GaAs quantum wells". United States. https://doi.org/10.1063/1.4962461. https://www.osti.gov/servlets/purl/1467886.
title = {Observation of electron states of small period artificial graphene in nano-patterned GaAs quantum wells},
author = {Wang, Sheng and Scarabelli, Diego and Kuznetsova, Yuliya Y. and Wind, Shalom J. and Pinczuk, Aron and Pellegrini, Vittorio and Manfra, Michael J. and Gardner, Geoff C. and Pfeiffer, Loren N. and West, Ken W.},
abstractNote = {Engineered honeycomb lattices, called artificial graphene (AG), are tunable platforms for the study of novel electronic states related to Dirac physics. Here in this work, we report the achievement of electronic bands of the honeycomb topology with the period as low as 40 nm on the nano-patterned modulation-doped AlGaAs/GaAs quantum wells. Resonant inelastic light scattering spectra reveal peaks which are interpreted as combined electronic transitions between subbands of the quantum well confinement with a change in the AG band index. Spectra lineshapes are explained by joint density of states obtained from the calculated AG electron band structures. These results provide a basis for further advancements in AG physics.},
doi = {10.1063/1.4962461},
url = {https://www.osti.gov/biblio/1467886}, journal = {Applied Physics Letters},
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Award Period: September 1st, 2013 through February 15th, 2017 Submitted to the USDOE Office of Basic Energy Sciences By Aron Pinczuk and Shalom J. Wind Department of Applied Physics and Applied Mathematics Columbia University New York, NY 10027 January 2017 Award # DE-SC0010695 ABSTRACT Research in this project seeks to design, create and study a class of tunable artificial quantum structures in order to extend the range and scope of new and exciting physical phenomena and to explore the potential for new applications. Advanced nanofabrication was used to create an external potential landscape that acts as a lattice of confinementmore » sites for electrons (and/or holes) in a two-dimensional electron gas in a high perfection semiconductor in such a manner that quantum interactions between different sites dictate the significant physics. Our current focus is on 'artificial graphene' (AG) in which a set of quantum dots (or sites) are patterned in a honeycomb lattice. The combination of leading edge nanofabrication with ultra-pure semiconductor materials in this project extends the frontier for small period, low-disorder AG systems, enabling the exploration of graphene physics in a semiconductor platform. TECHNICAL DESCRIPTION Contemporary condensed matter science has entered an era of discovery of new low-dimensional materials, such as graphene and other atomically thin materials, that exhibit exciting new physical phenomena that were previously inaccessible. Concurrent with the discovery and development of these new materials are impressive advancements in nanofabrication, which offer an ever-expanding toolbox for creating a myriad of high quality patterns at nanoscale dimensions. This project started about four years ago. Among its major achievements are the realizations of very small period artificial lattices with honeycomb topology in GaAs quantum wells. In our most recent work the periods of the 'artificial graphene' (AG) lattices extend down to 40 nm. These small periods are about three times smaller than previously reported in GaAs quantum wells. This milestone establishes a new state-of-the-art in fields of research and nanofabrication. In experiments using optical scattering methods we uncovered evidence that free electrons in the small period AG lattices display novel features that arise from the symmetry of the honeycomb lattice. These achievements create semiconductor platforms for explorations of novel states and effects that offer opportunities to create quasiparticles with tunable character. The quest for the discovery of novel quantum physics by nanofabrication of 'artificial structures' in semiconductor quantum structures overlaps with the development of quantum simulators. Nanopatterns were created at Columbia University by the group of co-PI Shalom Wind using a 100keV e-beam nanolithography instrument (along with associated processing) that is part of the Columbia Nano Initiative. Optical experiments were carried out in the group of PI Aron Pinczuk. GaAs/AlGaAs quantum wells(QWs) of world-class perfection that serve as electron hosts are the starting material grown by molecular beam epitaxy (MBE) by our partners Dr. Loren Pfeiffer (Princeton Univ.) and Prof. Michael Manfra (Purdue Univ.). The inductively coupled plasma reactive ion etching (ICP-RIE) was carried out at the PRISM Micro/Nano Fabrication Laboratory of Princeton University. Dr. Vittorio Pellegrini (Istituto Italiano di Tecnologia, Genoa, Italy) has contributed critical insight on this research. Two graduate students in this project Sheng Wang and Diego Scarabelli, graduated in the summer/fall of 2016. Dr. Yuliya Kuznetsova has been a postdoc in the group. The current work is led by Dr. Lingjie Du, a postdoctoral scientist that joined the group of the PI on October 15th, 2016. Since the start of this project we have focused primarily on developing protocols towards the fabrication of the artificial lattices and in the implementation of characterization methods to identify the new electron states that are created. A major milestone has been the realization of the Dirac cones that emerge in honeycomb lattices. In the next phases of this project, and as we achieve milestones, we wish to expand our experimental platform so that we will be better positioned to access emergent novel quantum behavior and phases of electrons in artificial lattices designed and fabricated with 'exquisite' precision. The AG lattices with greatly reduced disorder from nano-processing that we have already created demonstrate that we are poised for the next stage exploration of graphene physics and applications in semiconductor quantum structures.« less
Journal Article Du, Lingjie ; Wang, Sheng ; Scarabelli, Diego ; ... - Nature Communications
The interplay between electron–electron interactions and the honeycomb topology is expected to produce exotic quantum phenomena and find applications in advanced devices. Semiconductor-based artificial graphene (AG) is an ideal system for these studies that combines high-mobility electron gases with AG topology. However, to date, low-disorder conditions that reveal the interplay of electron–electron interaction with AG symmetry have not been achieved. Here, we report the creation of low-disorder AG that preserves the near-perfection of the pristine electron layer by fabricating small period triangular antidot lattices on high-quality quantum wells. Resonant inelastic light scattering spectra show collective spin-exciton modes at the M-point'smore » nearly flatband saddle-point singularity in the density of states. The observed Coulomb exchange interaction energies are comparable to the gap of Dirac bands at the M-point, demonstrating interplay between quasiparticle interactions and the AG potential. The saddle-point exciton energies are in the terahertz range, making low-disorder AG suitable for contemporary optoelectronic applications.« less
Intersubband stimulated emission in GaAs/AlGaAs quantum wells: Pump-probe experiments using a two-color free-electron laser
Journal Article Gauthier-Lafaye, O ; Sauvage, S ; Boucaud, P ; ... - Applied Physics Letters
Intersubband stimulated emission under optical pumping has been observed in the conduction band of GaAs{endash}AlGaAs quantum wells. The asymmetric coupled quantum wells which exhibit three conduction bound levels are designed to exhibit population inversion under optical pumping. An optical excitation at {lambda}=9.2{mu}m is used to bleach the absorption between the ground and second excited subband. The population inversion between excited subbands is pumped and probed on a picosecond time scale by a tunable two-color free-electron laser. The stimulated amplification is studied at low temperature in infrared waveguides as a function of the waveguide length and of the probe wavelength. Amore » stimulated gain {approx}80cm{sup {minus}1} is measured at 12.5 {mu}m in agreement with calculations. {copyright} {ital 1997 American Institute of Physics.}« less
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Journal Article Glembocki, O J ; Shanabrook, B V ; Bottka, N ; ... - Appl. Phys. Lett.; (United States)
The optical modulation technique of photoreflectance (PR) has been applied to characterize the interband transitions in GaAs/AlGaAs multiple quantum wells (MQW) and modulation-doped heterojunctions at room temperature. The spectra of the MQW show derivative-like reflectance features due to allowed interband transitions from heavy and light hole subbands to conduction subbands, and the E0(Gamma/8,v/ to Gamma/6,c/) transitions of the AlGaAs layers. The data are consistent with a square well calculation using a conduction-band offset of 60 percent of the band-gap discontinuity. For modulation-doped heterojunctions, a correlation is observed between a PR feature approximately 18 meV above the GaAs fundamental gap andmore » the presence of a two-dimensional electron gas. 14 references.« less
https://doi.org/10.1063/1.95784
Terahertz emission and photoconductivity in n-type GaAs/AlGaAs quantum wells: the role of resonant impurity states
Journal Article Firsov, D. A., E-mail: dmfir@rphf.spbstu.ru ; Shalygin, V A ; Panevin, V Yu ; ... - Semiconductors
Terahertz emission spectra in a longitudinal electric field and lateral photoconductivity spectra under terahertz illumination have been studied in structures with GaAs/AlGaAs quantum wells (QWs). It is shown that the spectra contain features associated with electron transitions involving resonant impurity states related to the second quantum-well subband. Calculations of the energy spectrum of impurity states and matrix elements of optical transitions made by taking into account various positions of the impurity relative to the QW center confirm the assumptions made.