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 CCC05: Fe-Based Superconductor and Strong Correlated SystemFocus
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Chair: Yuan Gao, University of Memphis Room: Virtual Room 5 |
Wednesday, March 22, 2023 3:00PM - 3:36PM |
CCC05.00001: Discrete Caroli-de Gennes-Matricon vortex bound states induced by the incipient and shallow bands in iron based superconductors Invited Speaker: Hai-Hu Wen Due to the spatial confinement to the quasiparticles within a vortex, it was predicted in 1964 by Caroli, de Gennes and Matricon (CdGM) that bound states with energies of (m=±1/2, 3/2, 5/2,,,) should exist within the vortex core. In conventional superconductors, because , these discrete CdGM states are too close to be discernable because the spacing between these energy levers is very small. By doing STM measurements on the surface of FeTe0.55Se0.45, we observed the long sought discrete CdGM bound states[1] which roughly satisfy the theoretically predicted ratio 1:3:5. Furthermore we have observed the discrete CdGM vortex bound states in another iron based superconductor KCa2Fe4As4F2, now they deviate from the widely believed 1:3:5, but more close to 1:2:3. Meanwhile we observed clear Friedel oscillations of the vortex bound states in this system[2]. By solving the BdG equations self-consistently, we found that the order parameter should exhibit a Friedel oscillation on top of a smooth function in the extreme quantum limit T/Tc<<, a natural consequence is that the bound state energies deviate from the ratio of 1:3:5 and Friedel oscillations of the bound states should show up[3]. Our results indicate a quite general feature of shallow and incipient bands in iron based superconductors, and shed new light in understanding the underline superconductivity mechanism. Finally, some bamboo like vortices are observed at the domain walls, showing intriguing physics induced by the shallow band effect. |
Wednesday, March 22, 2023 3:36PM - 4:12PM |
CCC05.00002: Ordered and tunable Majorana-zero-mode lattice in naturally strained LiFeAs Invited Speaker: Hongjun Gao Majorana zero-modes (MZMs) are spatially-localized zero-energy fractional quasiparticles with non-Abelian braiding statistics. They are believed to hold great promise for topological quantum computing. By using low-temperature and strong-magnetic-field scanning tunneling microscopy/spectroscopy, a breakthrough of Majorana zero mode has been firstly achieved in a single material platform of high-Tc iron-based superconductor, FeTe0.55Se0.45. The mechanism of two distinct classes of vortices presented in this system was revealed, which directly tied with the presence or absence of zero-bias peak. We further found the Majorana conductance plateau in vortices. Both the extrinsic instrumental convoluted broadening and the intrinsic quasiparticle poisoning can reduce the conductance plateau value, and when extrinsic instrumental broadening is removed by deconvolution, the plateau nearly reaches a 2e2/h quantized value. Moreover, we confirmed the existence of MZMs in the vortex cores of CaKFe4As4 and LiFeAs. Based on these works mentioned above, most recently, we have successfully achieved the large-scale, highly-ordered and tunable MZM lattice in strained LiFeAs. Notably, more than 90% of the vortices are topological and possess the characteristics of isolated MZMs at the vortex center, forming ordered MZM lattice with the density and the geometry tunable by external magnetic field. With decreasing the spacing of neighboring vortices, the MZMs start to couple with each other. This kind of materials combine the advantages of a simple material, high- Tc, large ratio of Δ/EF and etc. Our results show a great potential of MZMs in the application of topological quantum computations in the future. |
Wednesday, March 22, 2023 4:12PM - 4:24PM |
CCC05.00003: Cavitation instabilities in amorphous solids Umang A Dattani, Smarajit Karmakar, Pinaki Chaudhuri Amorphous solids are known to fail catastrophically. As a result, studying the response of amorphous solids to mechanical deformation is of great interest. Recent experiments suggest that fracture in amorphous solids occurs via nano-scale cavitation. In numerical simulations, the studies of plasticity in amorphous solids typically employ constant-density shear deformation. Upon shear deformation, amorphous solids undergo extensive plasticity via a yielding transition. Under constant-density shear deformation, one usually doesn't observe any significant density inhomogeneities, let alone fracture. To overcome this, we explore the elasto-plastic response of the amorphous solids to athermal quasistatic expansion(AQE) in numerical simulations. We find that under AQE, the solid undergoes a yielding-like transition that leads to formation of cavities in the solid. On further loading, the cavities grow and merge, ultimately resulting in complete fracture of the solid. Via this study, we highlight some similarities & differences between plasticity under shear and plasticity under volume expansion. |
Wednesday, March 22, 2023 4:24PM - 4:36PM |
CCC05.00004: Modulating Optical Properties of TiN/TiNO Thin Films for Photocatalytic Applications Manosi Roy, Abiodun Odusanya, Brooke Smith, Mark A Pfeifer, Darrah Dare, Valentine Craciun, James D Schall, Frank W Wise, Dhananjay Kumar Transition metal oxynitrides (TMON) can open new pathways to develop robust optoelectronic devices for use in photocatalysis and solar energy harvesting. TiN/TiNO thin films grown on sapphire substrates using a pulsed laser deposition (PLD) method in high vacuum conditions. However, some residual oxygen in the PLD chamber allowed both time-independent gas phase oxidation and time-dependent controlled surface oxidation of TiN to TiNO films. The time-dependent surface oxidation was controlled by deposition time, i.e., changing the number of laser pulses impinging on the polycrystalline TiN target. X-ray photoelectron spectroscopy (XPS) investigations revealed higher oxygen content in TiNO films prepared with a larger number of laser pulses (or longer deposition time), which was attributed to the surface diffusion of oxygen to the TiN film lattice. Higher oxygen content also increased the lattice constants of the TiNO films, as predicted by molecular dynamics (MD) simulations. The lattice constant increase was further explained based on a larger electrostatic repulsive force in the vicinity of Ti3+ vacancies and substitutional O atoms. UV-vis measurements demonstrated an asymmetric V-shape variation of the optical bandgap as a function of the number of pulses. The bandgap variations on the left and right arms of the V-curve were attributed to the quantum confinement effect and modification in the band structure due to the hybridization of O2p and N2p energy levels, respectively. Electrochemical catalytic activity experiments also demonstrated strong sensitivity to the number of pulses and oxidation state of the sample, e.g., the highest electrochemical activity was obtained for the lowest-oxidized TiNO sample (and lowest bandgap). This study suggests that the oxidation environment during fabrication and the resulting chemical state of TiN/TiNO thin films play a critical role in modulating the optical properties of the materials and could be tailored to design for applications in clean energy and water-splitting research. |
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