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 N44: Topological Superconductivity: Proximity and Interface Effects and Low-dimensional SystemsFocus
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Sponsoring Units: DMP Chair: Srijit Goswami; Lia Krusin-Elbaum Room: Room 316 |
Wednesday, March 8, 2023 11:30AM - 12:06PM |
N44.00001: Superconducting proximity effect in the presence of a magnetic texture Invited Speaker: Takis Kontos In this talk, I will describe how one can shape unconventional superconductivity using magnetically textured materials and the proximity effect. I will discuss in particular how superconducting correlations are modified when they are induced in a 1D system - a carbon nanotube - with a magnetic texture or in a chiral antiferromagnet such as Mn3Ge. The connections to topologically protected quantum computation will also be discussed. |
Wednesday, March 8, 2023 12:06PM - 12:18PM |
N44.00002: Scrutinizing a superconductor-topological insulator interface as a platform for topological superconductivity Philipp Ruessmann, Stefan Blügel Interfacing a topological insulator (TI) with an s-wave superconductor (SC) is a promising material platform that offers the possibility to realize a topological superconductor through which Majorana-based topologically protected qubits can be engineered. In our computational study of the prototypical SC/TI interface between Nb and Bi2Te3, we identify the benefits and possible bottlenecks of this potential Majorana material platform. Bringing Nb in contact with the TI film induces charge doping from the SC to the TI, which shifts the Fermi level into the TI conduction band. For thick TI films, this results in band bending leading to the population of trivial TI quantum-well states at the interface. In the superconducting state, we uncover that the topological surface state experiences a sizable superconducting gap-opening at the SC/TI interface, which is furthermore robust against fluctuations of the Fermi energy. We also show that the trivial interface state is only marginally proximitized, potentially obstructing the realization of Majorana-based qubits in this material platform. |
Wednesday, March 8, 2023 12:18PM - 12:30PM |
N44.00003: Dominant scattering mechanisms in InSbAs quantum wells: a promising platform for topological superconductivity Sara Metti, Candice Thomas, Di Xiao, Michael J Manfra The two-dimensional electron gas (2DEG) confined in InSb1−xAsx quantum wells is a promising platform to explore topological superconductivity when coupled to a s-wave superconductor due to its higher effective g-factor and stronger spin-orbit coupling compared to commonly used binary InSb and InAs. Stable mesoscopic device operation and low disorder are two desired properties needed for the exploration of topological superconductivity. We report on material quality and dominant scattering mechanisms in a series of 30 nm quantum wells with arsenic mole fractions of x = 0.05, 0.13, and 0.19. Peak mobility at a density of ∼ 2.5 × 1011 cm−2 is 2.4, 2.0 and 1.4 × 105 cm−2/Vs respectively. For samples with x = 0.13 and 0.19, we find a weak dependence of mobility on 2DEG density, suggesting that short-range scattering limits mobility at arsenic concentrations above ∼ x=0.1. The data indicate that alloy disorder is the main source of short-range scattering; an alloy scattering rate of τalloy = 45 nm−1 per % As is extracted. This parameter is important for considerations of impact of disorder on induced superconductivity. We also present data on mesoscopic devices, including analysis of charge noise, drift, and hysteresis at T=0.3K. |
Wednesday, March 8, 2023 12:30PM - 12:42PM |
N44.00004: Monolayer superconductivity and tunable topological electronic structure at the Fe(Te,Se)/Bi2Te3 heterojunction Robert G Moore, Xiong Yao, Yun-Yi Pai, Michael Chilcote, Hu Miao, Satoshi Okamoto, Seongshik Oh, Matthew Brahlek The interface between two-dimensional topological Dirac states and an s-wave superconductor is expected to support Majorana bound states that can be used for quantum computing applications. Realizing these novel states of matter and their applications requires control over superconductivity and spin-orbit coupling to achieve spin-momentum locked topological surface states which are simultaneously superconducting. Here we investigate superconductivity in FeTe1-xSex grown on Bi2Te3 by molecular beam epitaxy and present the interfacial spin and electronic structure with photoemission spectroscopy. We will show how superconductivity exists at the FeTe1-xSex monolayer limit and describe how to systematically tune the interfacial topological and superconducting electronic structure through control over film growth conditions. We will describe how reducing Se doping not only reduces disorder from chemical inhomogeneities but improves the spin-momentum locking of the interfacial topological states. We will discuss how this platform can be optimized to advance efforts in Majorana interrogation and potential applications. |
Wednesday, March 8, 2023 12:42PM - 12:54PM |
N44.00005: Effects of the superconducting film edge and surface roughness on the topological superconductivity of planar semiconductor-superconductor Josephson junctions Purna P Paudel, Tudor D Stanescu Planar Josephson junctions have been intensely investigated in recent years as a promising platform for topological superconductivity and Majorana zero modes. The vast majority of the theoretical studies involve pristine systems characterized, in particular, by a proximity-induced pairing potential (typically introduced “by hand”) that is constant throughout the proximitized regions separated by a junction of constant width. On the other hand, it is known that disorder (in the superconductor) plays a crucial role in inducing robust superconductivity and suppressing the dramatic dependence on the film thickness associated with Fermi surface mismatch. In turn, disorder (in the superconductor) may affect the low-energy properties of the hybrid structure. Furthermore, the junction width is expected to exhibit variations generated by imperfect patterning (i.e., etching of the superconducting film), which also impacts the low-energy physics. In this work, we investigate the effect of the superconducting film edge and surface roughness on the topological superconductivity of planar Josephson junctions based on a numerical analysis of a microscopic effective model of the hybrid structure. We provide semi-quantitative estimates of the edge roughness (i.e., variations of the effective junction width) and surface roughness (i.e., variations of the effective superconducting film thickness) consistent with the presence of a topological superconducting phase that supports Majorana zero modes. |
Wednesday, March 8, 2023 12:54PM - 1:06PM |
N44.00006: Flux-Tunable Hybridization in a Double Quantum Dot Interferometer Christian G Prosko, Ivan Kulesh, Michael Chan, Lin Han, Di Xiao, Candice Thomas, Michael J Manfra, Leo P Kouwenhoven, Srijit Goswami, Filip K Malinowski Tuning the hybridization between fermionic modes with magnetic flux to distinguish parity states is crucial for topological quantum computation [1,2]. We demonstrate tuning of the tunnel coupling between two such modes with flux, implemented in a phase-coherent loop comprising two quantum dots in an InSbAs two-dimensional electron gas. Using reflectometry at radio frequencies on the dots’ plunger gate electrodes, we extract the inter-dot tunnel coupling as a function of flux through the loop, observing oscillations of the coupling with a periodicity of a flux quantum across numerous inter-dot charge transitions. This is found to be consistent with reflectometry measurements of the Aharonov-Bohm effect in the open loop measured with the tunnel barriers lowered. Next, in different tunnel coupling regimes we benchmark the contrast of these hybridization oscillations, observing that they vary depending on the modes involved, but are generally not suppressed at their minima. These results establish the feasibility and contrast limitations of conducting parity readout of hybrid qubits with tunnel couplings tuned by flux. |
Wednesday, March 8, 2023 1:06PM - 1:18PM |
N44.00007: Cooper pair splitting in a two-dimensional electron gas I: Probing virtual processes Qingzhen Wang, Sebastiaan ten Haaf, Ivan Kulesh, Di Xiao, Candice Thomas, Michael J Manfra, Srijit Goswami Cooper pair splitting (CPS) has been studied extensively in semiconductor-superconductor hybrids. However, it has thus far been challenging to isolate CPS from other local and non-local processes, such as local Andreev reflection and elastic co-tunnelling (ECT). Recent studies in hybrid nanowires [1] demonstrate that these challenges can be overcome to achieve highly efficient Cooper pair splitting. Here we present the first demonstration of CPS in a semiconductor two-dimensional electron gas. By coupling two quantum dots to the hybrid section via extended Andreev bound states, and operating the dots as charge filters, we achieve a CPS efficiency up to 95% , on par with the highest reported values. Using the two spin-degenerate, single-orbital dot levels, we observe specific spin blockades that are strongly dependent on the applied bias polarities and the nature of the underlying non-local virtual processes. |
Wednesday, March 8, 2023 1:18PM - 1:30PM |
N44.00008: Cooper pair splitting in a two-dimensional electron gas II: Spin-resolved measurements Sebastiaan ten Haaf, Qingzhen Wang, Ivan Kulesh, Candice Thomas, Michael J Manfra, Di Xiao, Srijit Goswami Information about the spin of electrons forming a Cooper pair, can be accessed by coupling spin-polarized quantum dots via a superconductor. Here, we study Cooper pair splitting (CPS) in a semiconductor two-dimensional electron gas, where two quantum dots are coupled via extended Andreev bound states. By applying an external magnetic field, the spin degeneracy of the quantum dot orbitals is lifted, allowing us to use them as bipolar spin filters. The specific spin involved in either elastic co-tunnelling (ECT) or CPS can then be resolved. With the magnetic field aligned along the spin-orbit field, we show that only equal-spin ECT and opposite-spin CPS is allowed to take place. However, upon applying the field perpendicular to the spin-orbit field, ECT and CPS currents arise for all spin combinations. Notably by rotating between these angles, we smoothly transition from fully singlet CPS to having an equal singlet and triplet CPS component. |
Wednesday, March 8, 2023 1:30PM - 1:42PM |
N44.00009: Cooper pair splitting in a two-dimensional electron gas III: Flux-control Ivan Kulesh, Christian G Prosko, Qingzhen Wang, Sebastiaan ten Haaf, Candice Thomas, Di Xiao, Michael J Manfra, Srijit Goswami We study CPS in a three-terminal device implemented in an InSbAs two-dimensional electron gas. The device consists of two quantum dots coupled via a Josephson junction (JJ). The dots act as charge and energy filters and allow us to select between two non-local processes: CPS or elastic co-tunnelling (ECT). The junction is embedded in a superconducting loop, thus allowing us to control the phase difference across the JJ with an applied flux. Tuning the device in the CPS-only allowed regime, we demonstrate that the non-local current depends periodically on the flux through the loop. The periodicity is consistent with the flux-dependent modulation of the Andreev bound state (ABS) energy, extracted from tunnelling spectroscopy measurements. This work demonstrates that the CPS amplitude is directly linked to virtual processes mediated by ABSs. Moreover, such a device could be used a flux-controlled source of entangled electrons. |
Wednesday, March 8, 2023 1:42PM - 1:54PM |
N44.00010: Quantum sensing with highly transparent Al-InAs planar Josephson junctions William F Schiela, Melissa E Mikalsen, Ido Levy, William M Strickland, Javad Shabani Josephson junctions of superconducting epitaxial aluminum on quantum wells of semiconducting indium arsenide with large spin-orbit coupling have been proposed to exhibit topological superconductivity. The topological state is stabilized at a phase difference of π where the current-phase relation of a transparent junction becomes highly sensitive to changes in magnetic flux. We fabricate planar junctions embedded in a SQUID geometry, enabling phase-sensitive measurements. We study the current-phase relation and tunneling spectrum of the junction as a function of in-plane Zeeman field and gate voltage. We further explore the integration of remote flux lines to bias the junction to a phase difference of π, where the magnetometric sensitivity of the device is significantly enhanced. |
Wednesday, March 8, 2023 1:54PM - 2:06PM |
N44.00011: Moiré superlattices and high-temperature surface superconductivity in the topological insulator Sb2Te3 Afrin Nahar Tamanna, Entela Buzi, Haiming Deng, Kyungwha Park, Jennifer Cano, Lia Krusin-Elbaum Moiré superlattices formed by a relative twisting of abutting 2D layers can strongly impact the local electronic band structure in a variety of materials, inducing van Hove singularities, band gaps, minibands, and the recently discovered remarkable occurrence of superconductivity at Tc ~ 1.7 K in the magic-angle twisted bilayer graphene. In the vicinity of the magic angle, the periodic moiré potentials flatten the electronic bands, with electron correlations becoming strongly enhanced. Thus far only limited studies exist for moiré superlattices formed in 3D topological insulators (TIs), and the theoretical prediction [1] of moiré-induced high-Tc superconductivity in a 3D TI has not been experimentally confirmed. We have previously shown that a 2D superconductivity can be realized in a 3D TI Sb2Te3 [2], where the superconducting condensate emerges in surface Dirac puddles at a very high temperature of 55-60 K. Here, we demonstrate the existence of complex moiré-type superlattices in the thin exfoliated layers of this surface-superconducting Sb2Te3. The analysis of high-resolution transmission electron microscopy reveals a distribution of puddle sizes consistent with the ac susceptibility and scanning tunneling spectroscopy, and a skewed distribution of twist angle θ corresponding to hexagonal (θ ≤ 3°) and striped (θ ≥ 3°) moiré patterns. We corroborate our findings by density functional theory (DFT) calculations and discuss the association with high-Tc. |
Wednesday, March 8, 2023 2:06PM - 2:18PM |
N44.00012: Coexistence of bulk-nodal and surface-nodeless Cooper pairings in a superconducting topological material. Xian Yang, Yigui Zhong, Sougata Mardanya, Tyler A Cochran, Ramakanta Chapai, Akifumi Mine, Junyi Zhang, Jaime Sánchez-Barriga, Zijia Cheng, Oliver J Clark, Jiaxin Yin, Guangming Cheng, Nan Yao, Rongying Jin, Tay-Rong Chang, Shik Shin, Kozo Okazaki, Zahid M Hasan The interplay of nontrivial topology and superconductivity in condensed matter physics gives rise to exotic phenomena. However, materials are extremely rare where it is possible to explore the full details of the superconducting pairing. Here, we investigate the momentum dependence of the superconducting gap distribution in a novel Dirac material. Using high resolution, low temperature photoemission spectroscopy, we establish it as a spin-orbit coupled Dirac semimetal with the topological Fermi arc crossing the Fermi level on the (010) surface. This spin-textured surface state exhibits a fully gapped superconducting Cooper pairing structure below ~ 4.5 K. Moreover, we find a node in the bulk near the Brillouin zone boundary, away from the topological Fermi arc. These observations not only demonstrate the band resolved electronic correlation between topological Fermi arc states and the way it induces Cooper pairing, but also provide a rare case where surface and bulk states host a coexistence of nodeless and nodal gap structures enforced by spin-orbit coupling. |
Wednesday, March 8, 2023 2:18PM - 2:30PM |
N44.00013: Dependence of topological signatures to junction geometry in planar Josephson junctions PENG YU, Neda Lotfizadeh, William F Schiela, Bassel H Elfeky, Mehdi Hatefipour, William M Strickland, Ido Levy, Mohammad Farzaneh, Javad Shabani
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