Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session Z23: 2D Materials: Optical and Electronic Properties |
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Sponsoring Units: DCMP Chair: Huan Jiang, University of Louisville Room: Room 215 |
Friday, March 10, 2023 11:30AM - 11:42AM |
Z23.00001: Understanding Low Structural Relaxation in Phase-Change Chalcogenide Superlattices Xiangjin Wu, Asir Intisar Khan, Kangsik Kim, Zonghoon Lee, H.-S. Philip Wong, Eric Pop Chalcogenides such as Ge2Sb2Te5 (GST) undergo reversible changes between their low-resistance crystalline phase and high-resistance amorphous phase, induced by Joule heating. However, structural relaxation of their amorphous phase leads to unstable electrical resistance over time, known as resistance drift in phase-change memory (PCM), placing fundamental limits on such data storage [1]. |
Friday, March 10, 2023 11:42AM - 11:54AM |
Z23.00002: Synthesis of quantum emitting structures by Nd3+ ion insertion into van der Waals materials. Muzzakkir Amin, Bruce Barrios, Uriel Silva, Tianfei Zhang, Michael Scheibner Quantum emitters in 2D materials are promising systems for next generation room temperature quantum technology. Here we report on our efforts to synthesize quantum emitting structures via ion insertions of Nd3+ into transition metal dichalcogenides. Neodymium ions are ideal emitters for this task because of their unfilled 4f orbitals, which can be optically pumped and are shielded by 5s and 5p orbitals. This orbital structure makes Nd3+ ions interact weakly with their surroundings. We use an electrochemical approach to insert Nd3+ ions and measure their photoluminescence. By controlling the synthesis parameters like voltage, solution concentration and reaction time we optimize the ion density with the aim to create individual quantum emitters in few-layer transition metal dichalcogenides. |
Friday, March 10, 2023 11:54AM - 12:06PM |
Z23.00003: Optoelectronic Properties of Captured Nd3+ in Transition Metal Dichalcogenides Bruce Barrios, Muzzakkir Amin, Tianfei Zhang, Uriel Silva, Michael Scheibner Semiconductor quantum systems suitable for room temperature quantum technology have thus far remained elusive. Compared to natural atomic systems, atom-like semiconductor nanostructures exhibit reduced electron confinement, making their quantum states prone to thermal perturbations. Rare-earth ions, such as neodymium (Nd3+), inserted in transition metal dichalcogenides may offer a novel solution. Due to their electronic orbital structure rare-earth ions are known to exhibit optical transitions that are weakly affected by the host material surrounding them. MoS2 treated electro-chemically with NdCl3 exhibits photoluminescence signatures within its bandgap that are attributed to the optical transitions of Nd3+. The spectral responses obtained from high and low concentration exfoliated layers of MoS2:Nd3+ are being discussed and compared to those of standard solid state quantum emitters such as self-assembled quantum dots. |
Friday, March 10, 2023 12:06PM - 12:18PM |
Z23.00004: Elementary Excitations in Monolayer Defect Lattices Ali Ghorashi, Nicholas Rivera, Bowen Shi, Marin Soljacic, Ravishankar Sundararaman, John D Joannopoulos, Efthimios Kaxiras Expanding the repertoire of two dimensional materials is of fundamental importance for the viability of optoelectronic and plasmonic properties beyond those achievable by canonical low dimensional materials such as graphene. Herein, we explore the landscape of carbon substitutional defects in hexagonal boron nitride and explicate their electronic, phononic, and plasmonic properties through the use of Density Functional Theory. We report the structural stability of our candidate materials, their band structures as a function of electronic doping, as well as their TM polarized plasmonic dispersions, confinements, and losses. We show that a simple analytical model explains doping induced changes in the spectra of optical excitations in our materials to a high level of accuracy. Our work also indicates that this new class of plasmonic materials allows for tunable plasmonic excitations in the infrared with confinements that exceed those of graphene plasmons by more than an order of magnitude and which maintain comparatively low losses. We envision that our study of this class of materials will open the door for studies of artificially designed two dimensional materials beyond the currently available landscape. |
Friday, March 10, 2023 12:18PM - 12:30PM |
Z23.00005: Probing photo-induced CDW melting in 1T-TiSe2 using elastic neutron scattering Sharon S Philip, Despina A Louca Quasi-two-dimensional Mott insulating material 1T-TiSe2 has long been investigated as it exhibits a wide range of exotic phenomena including a charge density wave (CDW), Bose-Einstein exciton condensation, a gyrotropic electronic order, and superconductivity in the vicinity of the CDW phase. It undergoes a structural phase transition at ~200K as it transforms into a commensurate CDW state with a periodic lattice distortion expanding the unit cell into a 2 × 2 × 2 superlattice that lowers the crystal symmetry from an undistorted P-3m1 symmetry to P-3c1 symmetry. Neutron diffraction experiments on 1T-TiSe2 reveals half-integer superlattice peaks that can be indexed by a 2 x 2 x 2 periodic lattice distortion. Local structure analysis showed splitting of the Ti-Se bonds due to displacements of Ti in the CDW phase which suggested that a Jahn-Teller like mechanism is most likely key to the CDW instability and the Ti atom displacements can be described by a breathing mode model. Studies thus far have focused on the electronic properties, and little is known of the effects on the lattice and phonons in the presence of strong electron-phonon coupling. Given the strong coupling of the CDW to the lattice, we study the photo-excitation of the crystal leading to interesting structural characteristics that have not been directly probed so far. Using elastic and inelastic neutron scattering, we investigate the structural features and dynamics associated with the CDW transition under photo-excitation. |
Friday, March 10, 2023 12:30PM - 12:42PM |
Z23.00006: Material Design of TMD Superlattices Alan Chen, Aravind Devarakonda, Joshua Wakefield, Caolan John, Jingxu Zheng, Shiang Fang, David C Bell, Takehito Suzuki, Joseph G Checkelsky Transition metal dichalcogenides (TMDs) are a family of van der Waals materials that possess numerous correlated phases of matter. A common way of studying these phases is via exfoliation and careful assembly of 2D heterostructures, a process that is delicate and prone to disorder. Such studies have recently been extended to natural superlattice structures, which combine TMD layers with partner spacer layers in natural crystals. Here we discuss the development of such structures in which the electronic transport can be quenched, toward the study of new types of superlattice materials beyond the currently known superconducting variants. |
Friday, March 10, 2023 12:42PM - 12:54PM |
Z23.00007: Vortexable Chern bands and Fractional Chern insulators in Twisted Graphene Systems Patrick J Ledwith, Ashvin Vishwanath, Daniel E Parker Fractional Chern insulators realize the remarkable physics of the fractional quantum Hall effect (FQHE) in crystalline systems with Chern bands. The lowest Landau level (LLL) is known to host the FQHE, but not all Chern bands are suitable for realizing fractional Chern insulators (FCI). Previous approaches to stabilizing FCIs focused on mimicking the LLL through momentum-space criteria. Here instead we take a real-space perspective by introducing the notion of vortexability. Vortexable Chern bands admit a fixed operator that introduces vortices into any band wavefunction while keeping the state entirely within the same band. Vortexable bands admit trial wavefunctions for FCI states, akin to Laughlin states. In the absence of dispersion and for sufficiently short ranged interactions, these FCI states are the ground state — independent of the distribution of Berry curvature. Vortexable bands are much more general than the LLL, and we showcase a recipe for constructing them. We exhibit diverse examples in twisted graphene-based systems with or without magnetic field, and with any Chern number. We will discuss the recent observation of fractional Chern insulators in twisted bilayer graphene in this context. Vortexable bands have a close relationship with momentum-space band geometry that clarifies and expands standard approaches as discussed in a companion talk. |
Friday, March 10, 2023 12:54PM - 1:06PM |
Z23.00008: Vortexable bands: A unifying perspective on band geometry Daniel E Parker, Patrick J Ledwith, Ashvin Vishwanath Vortexable bands provide a unifying real-space perspective on quantum geometry. We define a band as vortexable if, roughly, one can choose complex coordinates on the plane so that multiplying the band by that coordinate operator does not cause interband transitions. A companion talk shows how vortexable bands are ideal for fractional Chern insulators and other many-body consequences. When this real-space concept is expressed in momentum space, it becomes a statement about the quantum geometry of the system. The subset of ``special" vortexable bands is shown to be equivalent to the momentum space ``trace condition" or ``ideal band condition." Alternatively, one can always choose a gauge so that the periodic Bloch wavefunctions of special vortexable bands are holomorphic in the Brillouin zone --- a powerful result linking to holomorphic geometry. We provide a number of examples of vortexable bands derived from chiral graphene and its variants with internal strain and moire potentials. ``General" vortexable bands, however, lie beyond the trace condition. We show the point of failure is the definition of periodic Bloch wavefunctions in terms of the laboratory coordinates, and introduce a modified momentum space measure that can detect any vortexable bands. Moreover, this measure quantifies deviations from vortexability, which can be applied to generic Chern bands to identify promising FCI platforms in moire systems. |
Friday, March 10, 2023 1:06PM - 1:18PM |
Z23.00009: Far-field controlling of phonon polaritons in biaxial natural hyperbolic van der Waals crystal for molecular sensing Nihar R Sahoo, Saurabh Dixit, ANSHUMAN KUMAR Mid-IR light is spectrally overlapped with the molecular fingerprint region of the electromagnetic spectrum, as many biomolecules exhibit their signature vibrational modes in this regime. Traditional IR spectroscopic methods for sensing present challenges in signal to noise ratio, impairing their sensitivity to trace levels of biomolecules. These signatures are enhanced significantly by coupling of light with charged particles to form quasi-particles referred to as polaritons. This enhancement is possible in the infrared by coupling between molecular vibrations and IR-active polaritonic modes. In this work, we show efficient detection of biomolecules using polaritons supported by in-plane vdW natural hyperbolic material, where the principal components of the dielectric permittivity have opposite signs at the same frequency. These vdW materials support low-loss hyperbolic modes resulting from the formation of phonon polaritons(PhP) which is due to the hybridization of crystal vibrations (phonons) with light. This results in deep sub-wavelength confinement of infrared light, amplifying interactions between light and matter. Nanostructures of such vdW crystals can support localized PhP modes in the far-field, dramatically enhancing coupling between light with the vibrational resonances of a molecule adsorbed on the surface. Due to the enhanced light-matter interaction with the hyperbolic PhPs supported by the vdW nanopatterns, we enhance the sensitivity to the vibrational modes of the biomolecules, enhancing their detection to point-of-care levels. |
Friday, March 10, 2023 1:18PM - 1:30PM |
Z23.00010: Graphene on a dielectric-defined superlattice: A versatile plasmonics platform Yutao Li, Lin Xiong, Minwoo Jung, Carlos Forsythe, Shuai Zhang, Alexander S McLeod, Yinan Dong, Song Liu, Frank Ruta, Casey Li, Suheng Xu, Ran Jing, Kenji Watanabe, Takashi Taniguchi, Michael M Fogler, James H Edgar, Cory R Dean, Dmitri N Basov The Dirac-cone shaped electronics band structure of graphene can be engineered into various geometries by a superlattice potential. Compared to moiré superlattices that happen naturally at a van der Waals interface, dielectric-defined superlattice has the advantage of a wider range of available superlattice pattern symmetries and on-chip tunability of modulation strength. We achieved, experimentally, a similar dielectric-defined superlattice modulation to plasmonic band structure on graphene. An anisotropic plasmonic band gap is opened at mid-infrared frequency, allowing the use of such a device as a tunable plasmonic switch. Furthermore, it has been theoretically predicted that a graphene-1DSL system with ~600nm pitch hosts a plasmonic band gap in the terahertz (THz) regime, and graphene-1DSL with pitch ~75nm can produces Bloch oscillations that may act as a THz emitter. Experimental results on these systems will be reported. |
Friday, March 10, 2023 1:30PM - 1:42PM |
Z23.00011: Anisotropic Electronic Transport in Strain Superlattices in Graphene Preetha Sarkar, Nadya Mason Strain superlattice effects in atomically thin materials such as graphene can lead to novel quantum phenomena and also have applications in the field of bendable electronics. In this research, we generate tensile strain in monolayer graphene by stacking it on a self-assembled array of dielectric nanospheres (NS), thus creating a strain superlattice (SL). Previous [1] two terminal charge transport measurements on these graphene SLs revealed strain-tunable conductance dips associated with SL miniband effects. We now report studies of the Hall effect and non-local transport in these graphene-NS systems. We observe anisotropic transport characteristics and symmetry breaking which may be attributed to the lifting of the valley degeneracy in these systems. |
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