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 N23: Electronic structure of topological materials (photoemission, etc.)-I |
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Sponsoring Units: DCMP Chair: Azel Murzabekova, University of Illinois at Urbana-Champaign Room: Room 215 |
Wednesday, March 8, 2023 11:30AM - 11:42AM |
N23.00001: Material Lattice Design of 3D Flat Bands Joshua Wakefield, Paul M Neves, Shiang Fang, Ryan McTigue, Shu Yang Frank Zhao, David E Graf, Jessica L McChesney, Tej Lamichhane, Mingda Li, Takehito Suzuki, Joseph G Checkelsky The realization of bulk flat bands owing to destructive hopping of model lattice systems is a promising route that can be expected to lead to exotic correlated and topological phenomena. However, most current experimental work is limited to twisted moiré heterostructures and 2D toy model systems such as Kagome materials. In bulk materials a 2D sublattice pattern can only guarantee band flatness in the 3D dimension via a generic lack of hopping weights rather than the deconstructive interference of the wavefunction that guarantees the band flatness within the 2D plane. We here discuss material structures for 3D hopping networks that become topological upon inclusion of spin orbit coupling. We demonstrate different origins for band flatness and their potential electronic signatures. |
Wednesday, March 8, 2023 11:42AM - 11:54AM |
N23.00002: Observation of Flat Bands and Dirac Cones in Epitaxial CoSn Thin Films Shuyu Cheng, Nrisimha Murty Madugula, Wenyi Zhou, Alexander J Bishop, Igor Lyalin, Christopher Jozwiak, Aaron Bostwick, Eli Rotenberg, Roland K Kawakami Materials with dispersionless flat bands in momentum space are ideal for studying strongly correlated electronic states. Kagome-structured CoSn has been recognized as one of the materials hosting flat bands several hundred meV below Fermi level. A promising future direction is to grow the thin films and fabricate the devices which allow the tuning of flat bands towards Fermi level. However, most of the reported epitaxial CoSn thin films were grown on metallic buffer layers so far, which may not allow the tuning of flat bands through voltage gating. In this work, we synthesized CoSn thin films on insulating substrates by molecular beam epitaxy. The structure of the sample was confirmed by reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD). The flat bands and Dirac cones were observed using angle-resolved photoemission spectroscopy (ARPES). The transport properties of the CoSn thin films were also studied. This work paves the way towards device fabrication and fine tuning of band filling to promote flat band related phenomena for future studies. |
Wednesday, March 8, 2023 11:54AM - 12:06PM |
N23.00003: Electronic topology-driven helicoid arc van Hove singularities in tunable chiral fermion conductors Tyler A Cochran, Daniel S Sanchez, Ilya Belopolski, Zijia Cheng, Xian Yang, Xitong Xu, Kaustuv Manna, Chandra Shekhar, Jiaxin Yin, Horst Borrmann, Jonathan D Denlinger, Vladimir N Strocov, Weiwei Xie, Claudia Felser, Shuang Jia, Guoqing Chang, Zahid M Hasan The classification scheme of electronic phases uses two prominent paradigms: correlations and topology. Electron correlations give rise to superconductivity and charge density waves, while the quantum geometric Berry phase gives rise to electronic topology. The intersection of these two paradigms has initiated an effort to discover electronic instabilities at or near the Fermi level of topological materials. Here, we identify the electronic topology of chiral fermions as the driving mechanism for creating van Hove singularities that host electronic instabilities in the surface band structure. We observe that the chiral fermion conductors RhSi and CoSi possess two types of helicoid arc van Hove singularities that we call type-I and type-II. In RhSi, the type-I variety drives a switching of the connectivity of the helicoid arcs at different energies. In CoSi, we measure a type-II intra-helicoid arc van Hove singularity near the Fermi level. Chemical engineering methods are able to tune the energy of these singularities. Finally, electronic susceptibility calculations allow us to visualize the dominant Fermi surface nesting vectors of the helicoid arc singularities, consistent with recent observations of surface charge density wave ordering in CoSi. This suggests a connection between helicoid arc singularities and surface charge density waves. |
Wednesday, March 8, 2023 12:06PM - 12:18PM |
N23.00004: Manipulating electronic structure via vacancies and uniaxial stress. Na Hyun Jo, Omar A Ashour, Zhixue Shu, Christopher Jozwiak, Aaron Bostwick, Sae Hee Ryu, Tai Kong, Sinead M Griffin, Eli Rotenberg A fundamental issue in condensed matter physics is the influence of lattice distortion on the electronic structure, which determines physical properties. The lattice is commonly tuned through chemical doping or the application of mechanical stress. Unlike mechanical stress, chemical doping can raise more complications such as impurities, charge count, and local variations. Therefore, it is unclear whether the effects of chemical doping are mainly governed by lattice changes. Here we studied the modification of electronic structure through Te vacancies and uniaxial stress using angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT). The results indicate that the appearance or disappearance of primary features in electronic structure due to Te vacancies is reproducible with applied uniaxial stress. Furthermore, DFT calculations imply that these changes in electronic structure are related to the topological phase transition. This suggests various physical properties that show different behavior depending on vacancy concentrations can be manipulated via in-situ uniaxial stress control. |
Wednesday, March 8, 2023 12:18PM - 12:30PM |
N23.00005: Anharmonic treatment of the charge-density wave in the kagome-metal CsV3Sb5. Martin Gutierrez-Amigo After three years since the discovery of the AV3Sb5 (A=Cs,Rb,K) kagome-metals [1], the structure and origin of the charge-density wave (CDW) state still remain elusive. Since the high-symmetry structures stabilized around 90 K are unstable in the harmonic approximation, strong anharmonicity has to be a major ingredient in these systems and advocates for a more detailed analysis. |
Wednesday, March 8, 2023 12:30PM - 12:42PM |
N23.00006: Unremovable linked nodal structures in stacked bilayer graphene with Kekulé texture Chiranjit Mondal Linking structure is a new concept characterizing topological semimetals, which indicates the interweaving of the gap closing nodes at the Fermi energy (EF) with other nodes below EF. As the number of linked nodes can be changed only via pair-creation or pair-annihilation, a linked node is more stable and robust than ordinary nodes without linking. |
Wednesday, March 8, 2023 12:42PM - 12:54PM |
N23.00007: Spectroscopic evidence of flat bands in breathing kagome semiconductor Nb3I8 Madhab Neupane, Sabin Regmi, Tharindu Warnakulasooriya Fernando, Yuzhou Zhao, Anup Pradhan Sakhya, Gyanendra Dhakal, Iftakhar Bin Elius, Hector Vazquez, Jonathan D Denlinger, Jihui Yang, Jiun-Haw Chu, Xiaodong Xu, Ting Cao Kagome materials have become solid grounds to study the interplay among geometry, topology, correlation, and magnetism. Recently, semiconductors Nb3X8 (X = Cl, Br, I) |
Wednesday, March 8, 2023 12:54PM - 1:06PM |
N23.00008: Quantum Oscillations of YV6Sn6 and GdV6Sn6 Elliott W Rosenberg, Jonathan M DeStefano, David E Graf, Jiun-Haw Chu Recently, materials containing kagome lattices have gained attention due to the appearance of Dirac points, van Hove singularities and geometrically driven flat bands in their resulting band structures. In particular, members of the RV6Sn6 (R=rare earth) subset of these materials form with pristine vanadium kagome lattices, analogous to those in the kagome based superconductor AV3Sb5 family, and they offer an experimental landscape to investigate the interplay of rare earth magnetism with kagome band structures. Here we present the characterization of the Fermi surfaces of both the non-magnetic member YV6Sn6, as well as the ferromagnetic GdV6Sn6, through quantum oscillations in torque magnetometry in fields up to 41.5T and temperatures down to 0.3K. The temperature and angle dependences of oscillation frequencies for YV6Sn6 reveal the existence of a relatively large 2D pocket (~1/2 of the area of the Brillouin Zone) with an effective mass of m*=2.5me, as well as small pockets (~20T) with light effective masses, approaching the quantum limit at around 25T. Similar features but with different sizes and effective masses are seen in GdV6Sn6, illustrating the effect of local moment magnetism on the kagome band structure. |
Wednesday, March 8, 2023 1:06PM - 1:18PM |
N23.00009: Electronic band structure of the Co pnictide A(CoX)2 (A=Ca, Eu and X=As, P) probed by ARPES Antonio David Subires Santana, Mikel García Díez, Lorea Sánchez Fernández, Gerardina Carbone, Turgut Yilmaz, Elio Vescovo, Michael Shatruk, Maia Garcia Vergniory, Santiago Blanco-Canosa The pnictide family of transition metals is being widely studied for emergence of new collective quantum states. In the iron-family, the suppression of the antiferromagnet order is accompanied with the emergence of superconductivity [1] and the Ni-based family has been demonstrated to show an electronic liquid nematic ground state [2]. The Co-pnictide family (ACo2X2, A=Ba,Ca,Eu,... X=As,P) has been discussed in the framework of itinerant magnetism of conducting electrons and non-Fermi liquid scenarios. Besides, some of these Co-pnictides have been predicted to be topological Weyl semimetals where the low-energy excitations are Weyl fermions [3]. The experimental observation of these surface states gives an unequivocal proof that a particular compound is a Weyl semimetal [4]. Here, by means of ARPES and DFT, we report the experimental and theoretical band structure of the magnetic Co-pnictide ACo2X2 (A = Ca, Eu and X = As, P). We address the role of the dimensionality, disorder and the possible observation of topological physics. |
Wednesday, March 8, 2023 1:18PM - 1:30PM Author not Attending |
N23.00010: Quantum oscillation study of the kagome superconductor Wei Zhang, Lingfei Wang, Chun Wai Tsang, Xinyou Liu, Jianyu Xie, Wing Chi Yu, Kwing To Lai, Swee Kuan Goh Kagome metals AV3Sb5 (A = K, Rb, Cs) are recently discovered platforms featuring an unusual charge-density-wave (CDW) order and superconductivity. The electronic band structure of a kagome lattice can host both flat bands as well as Dirac-like bands, offering the possibility to stabilize various quantum states. I will present the electronic structure study of CsV3Sb5 via Shubnikov-de Haas quantum oscillations. We unambiguously reveal the existence of new frequencies with large frequencies ranging from ∼2085 T to ∼2717 T in thin flakes when the magnetic field is along the c-axis. These quasi-two-dimensional frequencies correspond to ∼52% to 67% of the CDW-distorted Brillouin zone volume. The Lifshitz-Kosevich analysis further uncovers surprisingly small cyclotron effective masses, of the order of ∼0.1 me, for these frequencies. Consequently, a large number of high-velocity carriers exists in the thin flake of CsV3Sb5. Furthermore, the detected high frequencies cannot be captured by the DFT calculations even with the CDW distortion considered. Our results provide new information for understanding the fermiology of the kagome superconductor AV3Sb5. |
Wednesday, March 8, 2023 1:30PM - 1:42PM |
N23.00011: Topological Proximity Coupling in Pb/Sb Thin-Film Heterostructures Yao Li, Yang-Hao Chan, John W Bowers, Joseph A Hlevyack, Mei-Yin Chou, Tai-Chang Chiang Proximity coupling between topological thin films and ordinary metals can result in the propagation of spin-polarized topological surface states over extended distances. This effect may be utilized to realize the sought-after topological superconductors essential for quantum computing applications. However, suitable candidate systems are rare. Herein, we report a case study of topological proximity coupling in the thin-film heterostructures of Pb, a conventional s-wave superconductor, and Sb, a topological semimetal. By band mappings with angle-resolved photoemission spectroscopy, we show evidence of coherent coupling of Pb and Sb that results in composite quantum well states and emergent surface states at the Pb/vacuum interface consistent with the surface state propagation scenario. The spin texture and spatial charge distribution of the emergent states are investigated by first-principles theoretical calculations. Our results demonstrate the rich possibilities of emergent physics in metal/topological thin film heterostructures and establish Pb/Sb as a topological superconductor candidate. |
Wednesday, March 8, 2023 1:42PM - 1:54PM |
N23.00012: Optical manipulation of Rashba-split 2-Dimensional Electron Gas tracked by TR-ARPES Fabio Boschini, Matteo Michiardi, Hsiang-Hsi Kung, MengXing Na, Sydney K Dufresne, Giorgio Levy, Sergey Zhadanovich, Arthur K Mills, B. IVERSEN BRUMMERSTEDT, Philip Hofmann, Andrea Damascelli A new promising approach to control the electrons' spin degree of freedom in spintronic devices consists of using optical fields. Optical fields would bolster spin devices' performance, allowing for significantly faster, yet more efficient, spin-logics. To date, research has mainly focused on the optical injection of spin currents through the photogalvanic effect, and little is known about optical control of spin-gates. To explore the possibility of all-optical manipulation of the material's spin properties, we consider the Rashba effect that manifests at semiconductors' interfaces. The Rashba effect has long been a staple in this field due to its superior electrical tunability, which led to the observation of fully spin-dependent phenomena, such as the spin-Hall effect, spin-charge conversion, and spin-torque in semiconductor devices. Here we use of ultrafast optical excitation to manipulate the spin-orbit coupling strength of Rashba states. A 2-dimensional electron gas (2DEG) is engineered at the surface of the topological insulator Bi2Se3. We track the Rashba-induced spin splitting of the 2DEG in energy and momentum via time and angle-resolved photoemission (TR-ARPES), which allows the direct extraction of the SOC strength dynamics. We establish that light-induced photovoltage and charge carrier redistribution can offer an unprecedented route for achieving all optically-driven THz spin-logic. |
Wednesday, March 8, 2023 1:54PM - 2:06PM |
N23.00013: Scanning Tunneling Microscopy of Candidate Majorana States in Josephson Junctions Elinore L McLain, Michael Gottschalk, Reza Loloee, Hande Huang, Guang Yue, Yongxi Ou, Nitin Samarth, Anthony R Richardella, Dale J Van Harlingen, Stuart H Tessmer In this talk we will present progress on scanning tunneling microscopy (STM) and spectroscopy (STS) probes of devices that meet the theoretical requirements to support Majorana Zero Modes (MZMs). We will detail our nanofabrication process to create candidate Majorana systems that are tailored for compatibility with cryogenic STS probing. We will present STM and STS data acquired on Josephson Junctions constructed from superconducting niobium and topological insulator bismuth selenide. Our main target is to probe Josephson vortices in these devices that result from an applied magnetic field. |
Wednesday, March 8, 2023 2:06PM - 2:18PM |
N23.00014: A phase stable hybrid dual comb spectrometer for time-resolved spectroscopy Sutapa Ghosh, Gadi Eisenstein Dual comb spectroscopy (DCS) is a broadband technique offering high resolution and fast data acquisition. We describe a hybrid dual-comb spectrometer comprising a broadband commercial fiber laser and an actively mode-locked semiconductor laser with a tunable and relatively narrow spectrum. We have devised a direct locking method, which leads to high long-term absolute stability (5 x $10^{-12}$ at 1 second). Our hybrid DCS system exhibits a mutual coherence time of roughly 100 seconds, a significant improvement over current schemes. We demonstrate this by performing DCS on rubidium atoms at 313 K with different data integration times. Finally, we used the phase stable DCS system to perform time-resolved measurements, where the resolution is limited only by the laser repetition rate (4 ns) and observed Rabi oscillations of the rubidium atoms at room temperature. The high time resolution is achieved by performing a series of DCS measurements with varying numbers of laser pulses incident on the atoms. The temporal evolution of the population of atoms in the excited state is recovered by suitably combining the measurement data. This is the first demonstration of the DCS method with a few nanosecond resolutions without using pump-probe spectroscopy. |
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