Bulletin of the American Physical Society
APS March Meeting 2024
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session Y16: Other Superconductors, MgB2, Complex Compounds, Organics, etc. I |
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Sponsoring Units: DCMP Chair: Komalavalli Thirunavukkuarasu, Florida A&M University Room: M100G |
Friday, March 8, 2024 8:00AM - 8:12AM |
Y16.00001: Identification of Bosonic Quantum States in a Finite Momentum Superconductor Charles C Agosta, Brett Laramee, Raju Ghimire, Logan Bishop-Van Horn, Calvin C Bales, David E Graf, William A Coniglio, John A Schlueter, Akiko Kobayashi In most superconductors Cooper pairs have zero momentum, but it is possible in a quasi two dimensional material to create Cooper pairs that have finite momentum. When subjected to a small magnetic field, finite momentum Cooper pairs, which are bosons, can form a novel type of Landau level that consists of bosons rather than fermions.1 We have studied highly two dimensional organic superconductors in a magnetic field oriented very close to parallel to the conducting planes. In this orientation, the material falls into an inhomogeneous superconducting state, caused by finite momentum Cooper pairs, called the FFLO state, named after the authors (Fulde, Ferrell, Larkin, Ovchinnikov) who predicted it. By tilting the sample to small angles from perfectly parallel, a small magnetic field is produced perpendicular to the layers while preserving the superconducting state, creating Landau levels. As the transverse field increases, the highest occupied bosonic Landau level decreases until all the bosons (Cooper pairs) are in the n = 0 state, which corresponds to the common Abrikosov vortex lattice. Bosonic quantum systems with n > 0 are rare. By accurately rotating our samples in constant magnetic fields between 8 and 25 tesla, and measuring the penetration depth with a tunnel diode oscillator, we have identified transitions between bosonic Landau levels. We will compare our measurements to calculations where we numerically solved for the phase diagrams of these materials. |
Friday, March 8, 2024 8:12AM - 8:24AM |
Y16.00002: Superconducting Coupling in High-Tc Hydrides Fedor F Balakirev, Gregory Alexander Smith, Boris A Maiorov, Vasily Minkov, Fengmin Du, Panpan P Kong, Alexander P Drozdov, Mikhail Eremets Materials with desired structure and physical properties such as near-room temperature superconductivity can be fabricated under pressure in the megabar range. By leveraging the advances in the diamond anvil pressure cell and pulsed magnetic field technologies we are able to characterize the superconducting order and the vortex matter in hydrogen-rich high temperature superconductors. We will discuss the direct probes of the superconducting gap and the evidence of the multi-band nature of the underlying ground state. |
Friday, March 8, 2024 8:24AM - 8:36AM |
Y16.00003: Superconductivity of transition-metal-based superconductors Sc6MTe2( M= Fe, Co, Ni): Ab initio study on electron-phonon coupling, rattling modes, and anharmonic effects. Ming-Chun Jiang, Ryota Masuki, Atsusi Togo, Guang-Yu Guo, Ryotaro Arita In recent experiments by Y. Shinoda et al., J. Phys. Soc. Japan 92, 103701 (2023), the superconductivity of a new family of materials, Sc6MTe2 (M= 3d, 4d, 5d elements), has been observed. In this study, we employ density functional perturbation theory and self-consistent phonon theory to investigate the role of electron-phonon coupling in Sc6MTe2 (M= Fe, Co, Ni). Our predicted transition temperatures, importantly, reproduce the chemical trend. We attribute superconductivity to the electronegativity difference between Sc and the M element, which suppresses the magnetism of Fe, Co, and Ni, possibly influencing the spin fluctuations in Sc, avoiding the suppression of the superconductivity. In the M = Fe and Co cases, we observe rattling phonon modes contributing to strong electron-phonon coupling. We also find imaginary modes for M = Fe due to anharmonicity. Interestingly, renormalized phonon bands yield a significant plateau in the Eliashberg spectral function, enhancing superconductivity. Our findings propose a novel material design strategy for phonon-mediated superconductors with d-elements, combining non-superconducting and magnetic elements. This study also underscores the role of rattling modes and anharmonicity in electron-phonon interactions and, consequently, superconductivity. |
Friday, March 8, 2024 8:36AM - 8:48AM |
Y16.00004: Implications of the electron-phonon coupling in CuPb9(PO4)6O for superconductivity: an ab initio study Hari Paudyal, Michael E Flatté, Durga Paudyal We report ab initio calculations of the electronic and vibrational properties in CuPb9(PO4)6O, including the electron-phonon coupling strength via strong-coupling Migdal-Eliashberg theory. We verify the presence of appealing flat electronic bands near the Fermi level, a strong hybridization between the Cu 3d and O 2p states, and soft low-energy phonons, which can suggest high-temperature superconducting behavior. However, the electron-phonon coupling strength appears insufficient to overcome the Coulomb repulsion between an electron pair and thus does not support high-temperature superconductivity in CuPb9(PO4)6O via the conventional electron-phonon Migdal-Eliashberg mechanism. Even neglecting Coulomb repulsion of the electron pair we find this electron-phonon coupling suggests a superconducting transition temperature less than 2 K. |
Friday, March 8, 2024 8:48AM - 9:00AM |
Y16.00005: Artificial non-magnetic disorder effect and devastation to the FFLO phase in layered organic superconductor κ-(BEDT-TTF)2Cu(NCS)2 Shiori Sugiura, Shusaku Imajo, Koichi Kindo, Takahiko Sasaki The exotic superconductivity beyond the well-established BCS theory has attracted substantial attention in both applied and fundamental research across various scientific disciplines. Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconductivity is known as one of the unconventional superconducting states, which can be stabilized even above the Pauli limit. In these days, the FFLO state has found a place in numerous textbooks as a non-zero center-of-mass momentum pairing state with spatial modulation in real space. However, some crucial characteristics of the FFLO state remain experimentally elusive, such as direct observation of spatial modulation and the vulnerability to non-magnetic disorders, due to the experimental difficulties. |
Friday, March 8, 2024 9:00AM - 9:12AM |
Y16.00006: Failed superconducting transitions in organic charge transfer salts κ-[(BEDT-TTF)1-x(BEDT-STF)x]2Cu2(CN)3 Yuxin Wang, Dragana Popovic, Yohei Saito, Martin Dressel, Andrej Pustogow, Atsushi Kawamoto Previous measurements of transport and magnetism at ambient pressure and temperatures (T) above 1 K indicated onset of superconductivity on the charge transfer salt κ-[(BEDT-TTF)1-x (BEDT-STF)x] 2Cu2(CN)3 (abbr. κ-(STF) x) near x=0.11. In this study, we perform dc transport measurements at ambient pressure on κ-(STF)0.11 and κ-(STF)0.12 in magnetic fields (H) up to 18 T and temperatures (T) down to 20 mK. In zero magnetic field, despite a sharp drop of temperature-dependent resistivity due to the onset of superconducting fluctuations, the measured and the 0 K-extrapolated resistivities clearly remain finite. In finite fields, positive magnetoresistance and the associated scaling analysis indicate an underlying quantum “superconductor”-metal transition. In the high-field normal state, the resistivity exhibits a logarithmic temperature dependence, consistent with the Altshuler-Aronov effect. Surprisingly, universal conductance fluctuations (UCFs) are observed in these two macroscopic samples. Both phenomena indicate that the high-field normal state is metallic. Possible interpretations of the incomplete superconducting transitions and UCFs in macroscopic systems, and comparisons with “failed superconductors” will be discussed. |
Friday, March 8, 2024 9:12AM - 9:24AM |
Y16.00007: Large critical fields in superconducting Ti4Ir2O from anomalous pseudospin Hao Wu, TATSUYA SHISHIDOU, Michael Weinert, Daniel Agterberg The recently synthesized superconductor Ti4Ir2O was reported to exhibit a large upper critical field that strongly violates the Pauli paramagnetic limit. This is puzzling since this material is cubic and preserves inversion symmetry, so spin-orbit coupling is not expected to qualitatively change the usual superconducting paramagnetic response. Here, combining density functional theory calculations and analytic kp theories, we reveal that an anomalous spin-orbit driven Kramers degenerate pseudospin provides a natural explanation for the observations. Our results provide new insight into the role of spin-orbit coupling in non-symmorphic materials. |
Friday, March 8, 2024 9:24AM - 9:36AM |
Y16.00008: Two-dimensional Ising superconductivity and charge density wave in three-dimensional bulk 4Hb-TaS2 Fazhi Yang, Heda Zhang, Hechang Lei, Hu Miao The dimensionality of matter significantly influences its quantum properties. In two-dimensional (2D) superconducting transition-metal-dichalcogenides (TMDs) with 1H structure, the in-plane critical magnetic field (Hc2) is substantially larger than the Pauli limit due to the strong Ising spin-orbital coupling. This phenomenon, known as Ising superconductivity, disappears in three-dimension (3D) as the global inversion symmetry restores in the 2H structure. Similarly, a quantum spin liquid state can emerge in the 2D 1T-TaS2 monolayers but vanishes in the 3D counterpart due to interlayer coupling. Using elastic and meV-resolution inelastic X-ray scattering and quantum transport, we show that the 2D Ising superconductivity and CDW emerge in the 3D bulk materials 4Hb-TaS2. The 2D nature of star-of-David CDW phase in 1T layer, combined with the 2D Ising superconductivity in 1H layer, provides a foundation for the potential realization of the Z2 quantum spin liquid state in 4Hb-TaS2. Our findings establish 4Hb-TaS2 as a promising platform for the exploration of exotic 2D quantum phenomena in 3D quantum heterostructures. |
Friday, March 8, 2024 9:36AM - 9:48AM |
Y16.00009: Superconductivity and local structural correlations in Ba1-xKxBiO3 Dayu Zhai, Xing He, Siddharth S Gorregattu, Sylvia L Griffitt, Marin Spaić, Zachary W Anderson, Joseph Joe, Matthew J Krogstad, Raymond Osborn, Suchismita Sarker, Jacob Ruff, Yong Q Cai, Damjan Pelc, Martin Greven Potassium-doped barium bismuthate (Ba1-xKxBiO3) exhibits a maximum superconducting transition temperature (Tc) of just above 30 K and was the first high-Tc oxide to be discovered. Although Ba1-xKxBiO3 is generally thought to be a conventional s-wave superconductor, the pairing mechanism is still under debate, and both electron-phonon coupling and charge-disproportionation effects may play a role. Our recent diffuse x-ray scattering measurements of the local structure, complemented by Monte Carlo modeling, demonstrated that disproportionation is absent in the metallic/superconducting doping regime [1]. Instead, this work revealed nanoscale structural correlations that break inversion symmetry, with profound implications for the electronic physics, including the pairing mechanism. Here we report on our efforts to extend the diffuse scattering measurements to temperatures below Tc and to additional doping levels. We will also describe recent complementary inelastic x-ray scattering experiments aimed at elucidating the observed structural features. |
Friday, March 8, 2024 9:48AM - 10:00AM |
Y16.00010: Exploring the effects of doping on polar order and lattice dynamics in strontium titanate Alex Hallett, John W Harter Strontium titanate is an incipient ferroelectric in which superconductivity emerges at exceptionally low doping levels. Stabilizing the polar phase through strain or chemical substitution has been shown to significantly enhance the superconducting critical temperature, and the polar instability plays a pivotal role in most proposed superconducting pairing mechanisms. To investigate the effects of doping on the nature of the polar order in strontium titanate, we develop a simplified free energy model which includes the degrees of freedom necessary to capture the relevant physics in a doped, biaxially compressively strained system. We simulate the ferroelectric and antiferrodistortive phase transitions using the Monte Carlo method for different doping levels, and comment on the doping dependence of the transition temperatures and the formation of polar nanodomains. The temperature-dependent phonon spectral function is calculated using Langevin dynamics to investigate the lattice dynamics of the doped system. Finally, we calculate the electron phonon coupling constant and place our results in the broader context of proposed pairing mechanisms in strontium titanate. |
Friday, March 8, 2024 10:00AM - 10:12AM |
Y16.00011: Magnetic Penetration Depth Measurements of Kagome Superconductors AV3Sb5 (A=Cs, K, Rb) Austin R Kaczmarek, Andrea C Salinas, Stephen D Wilson, Katja C Nowack The recently discovered kagome metal series AV3Sb5 (A=Cs, K, Rb) hosts a variety of electronic states, including superconductivity. Key questions about the superconducting phase are what is the structure of the superconducting gap and what is the pairing symmetry. Some features of the superconducting gap, such as the presence of nodes, can be inferred from the temperature dependence of the magnetic penetration depth. The penetration depth in CsV3Sb5 has been determined via several probes [1],[2],[3],[4], but similar measurements on KV3Sb5 and RbV3Sb5 are limited [5],[6], and a careful comparison between the three compounds is lacking. In this work, we use scanning superconducting quantum interference device (SQUID) susceptometry to measure, side by side, the temperature dependence of the magnetic penetration depth of the series of kagome superconductors AV3Sb5 (A=Cs, K, Rb). We will discuss what we can infer about the superconducting gap from these measurements. |
Friday, March 8, 2024 10:12AM - 10:24AM |
Y16.00012: TDO as AMRO; Finding g* in Organic Superconductors with an Untraditional Tunnel Diode Oscillator Technique Brett Laramee, Raju Ghimire, William A Coniglio, David E Graf, Lee Martin, John A Schlueter, Charles C Agosta The renormalized gyromagnetic ratio, g*, which accounts for many-body effects and is also related to Wilson’s ratio, is an important, yet underreported quantity in low-dimensional superconductivity that links magnetic susceptibility to the Sommerfeld coefficient, γ, in electronic specific heat data. In crystals with quantum oscillation orbits from multiple parts of the Fermi surface, amplitude ratios of Shubnikov-de Haas (SdH) oscillations can be fit to the Lifshitz-Kosevich formula to find g*, but this cannot be done in crystals with only one orbit. Alternatively, spin-zeroes, angles where SdH oscillation amplitudes vanish, also define g* and can be found using traditional (tedious) B-Field sweeps or by AMRO techniques. Using a contactless tunnel diode oscillator (TDO) measurement technique, we report g* in multiple Q2D organic superconductors not only from traditional field-dependent data, but we also reproduce previous AMRO data in κ-(ET)2Cu(NCS)2. In the future, we hope to study angular-dependent parameters of Q2D organic superconductors with the TDO as a new, unconventional AMRO-style device. |
Friday, March 8, 2024 10:24AM - 10:36AM |
Y16.00013: Oral: Study on Electronic Structure and Electron-phonon Coupling of Spinel Oxide Superconductor LiTi2O4 Minyinan Lei, Xiaoyang Chen, Xiaoxiao Wang, Haichao Xu, Rui Peng, Donglai Feng, Nan Guo, Zhihui Chen LiTi2O4 is known for its remarkably high critical transition temperature as a spinel superconductor. The spin-orbital fluctuations, the mixed valences, and d-d electron correlations [1-3] may be responsible for many novel behavior of the superconductivity in LiTi2O4. Recent angle-dependent magnetoresistance measurements have unveiled anisotropic magnetoresistance signals in LiTi2O4 thin films below the superconducting transition temperature (Tc). This observation suggests that LiTi2O4 may be a promising candidate for d-wave superconductors [4]. Despite numerous investigations, the superconductivity mechanism of LiTi2O4 has remained Controversial. In our latest study, we have employed in-situ measurements to obtain a comprehensive electronic structure and ultra-low-temperature tunneling spectrum of LiTi2O4. Our findings shed light on the electronic structure, electron-electron correlations, and energy gap structure of LiTi2O4. Furthermore, we have discovered a remarkably strong and anisotropic electron-phonon coupling in this material. These observations provide valuable insights into the superconductivity mechanism of LiTi2O4, suggesting that it exhibits characteristics of a BCS superconductor with an anisotropic electron-phonon coupling strength. |
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