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 K22: Superconductivity: Competing Phases-II |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Kalyan Sasmal, Department of Physics, University of California, San Diego. Room: Room 214 |
Tuesday, March 7, 2023 3:00PM - 3:12PM |
K22.00001: Zeeman effects on Yu-Shiba-Rusinov states Tadashi Machida A magnetic impurity in a superconductor locally disrupts the superconductivity due to the exchange interaction (J) between the spins of the impurity and an itinerant electron, forming so-called Yu-Shiba-Rusinov (YSR) bound states. Upon increasing J, the YSR state undergoes a quantum phase transition from the free-spin to the screened-spin ground states. Although vigorous STM experiments have been done to distinguish these two states [1,2], an unambiguous way has not yet been established. Here we demonstrate that these two ground states exhibit distinct Zeeman effects. By using ultra-low temperature STM [3], we investigated a tunneling junction between Cu(111) surface and a superconducting niobium tip decorated by a single Fe atom. Depending on the condition of the Fe adsorbate, the YSR state either splits or shifts, signifying the screened-spin or free-spin ground states, respectively [4]. We also confirmed the complete spin polarization of these YSR states by comparing the spectra on a bare Cu(111) surface and on a single Fe adatom on Cu(111). These findings make it possible to discriminate the two different YSR states and pave the way for high-resolution spin-polarized spectroscopy [5]. |
Tuesday, March 7, 2023 3:12PM - 3:24PM |
K22.00002: Theoretical analysis of anisotropic upper critical field in nodal-line semimetals Junya Endo, Hiroyasu Matsuura, Masao Ogata Nodal-line semimetals are semimetals in which a one-dimensional band intersection called a nodal-line exists due to a continuous series of band intersections. Some experiments have shown that the upper critical fields of superconductivities in nodal-line semimetals have unique behaviors. For example, PbTaSe2 and SnTaS2 are proposed to be nodal-line semimetals and show peculiar temperature dependence and anisotropy of the upper critical field. |
Tuesday, March 7, 2023 3:24PM - 3:36PM |
K22.00003: High magnetic field superconductivity in a two-band superconductor Tancredi Salamone, Henning G Hugdal, Sol H Jacobsen, Morten Amundsen The simultaneous presence of superconductivity and magnetism is of great interest for the field of superconducting spintronics. Multiband superconductors can support high critical fields, and together with their high critical temperatures this makes them particularly favourable. Several recent experiments indicate critical fields exceeding theoretical predictions (see, e.g., Nature Phys 12, 139-143 (2016), Sci Rep 7, 45943 (2017), Nature 595, 526-531 (2021), arXiv:2204.12606 (2022)). Moreover, multiple theoretical works have investigated possible principles allowing for this violation (Nature Phys 12, 139 (2016), PRB 98, 144509 (2018), PRB 105, L060501 (2022)). However, an underlying general mechanism is not established. |
Tuesday, March 7, 2023 3:36PM - 3:48PM |
K22.00004: On the ``naturalness'' of $d+ig$ superconductivity in Sr$_2$RuO$_4$ Andrew C Yuan, Erez Berg, Steven A Kivelson Many seemingly contradictory experimental findings concerning the superconducting state in Sr$_2$RuO$_4$ can be accounted for on the basis of a conjectured accidental degeneracy between two patterns of pairing that are unrelated to each other under the $(D_{4h})$ symmetry of the crystal: a $d_{x^2-y^2}$-wave $(B_{1g})$ and a $g_{xy(x^2-y^2)}$-wave $(A_{2g})$ superconducting state. In this paper, we propose a generic multi-band model in which the $g$-wave pairing involving the $xz$ and $yz$ orbitals arises from second-nearest-neighbor interactions. Even if time-reversal symmetry is broken - as in a $d+ig$ state - the superconductor remains gapless with a Bogoliubov Fermi surface that approximates a (vertical) line node. The model gives rise to a strain-dependent splitting between the critical temperature $T_c$ and the time-reversal symmetry-breaking temperature $T_ ext{trsb}$ that is qualitatively similar to some of the experimental observations in Sr$_2$RuO$_4$. |
Tuesday, March 7, 2023 3:48PM - 4:00PM |
K22.00005: Pairing of Anomalous Pseudospin Han Gyeol Suh, Daniel F Agterberg, Philip Brydon, TATSUYA SHISHIDOU, Michael Weinert, Yue YU In non-centrosymmetric materials, the resultant generalized Rashba spin-orbit coupling leads to novel behavior of superconductivity, allowing, for example, critical fields exceeding the Pauli field for singlet-superconductors, singlet-triplet mixing, and symmetry-dictated finite momentum pairing states. In locally non-centrosymmetric materials, generalizations of this novel behavior appear even when inversion symmetry is present, provided the spin-orbit coupling is sufficiently strong. Here we further generalize this through the introduction of anomalous pseudospin, which reveals that spin-orbit coupling dominates in materials with inversion symmetry, even without inversion-related sectors in the crystal structure. We classify all TRIM on momentum planes that allow anomalous pseudospin and highlight the resultant superconducting properties for Fermi surfaces near these momentum planes. We show how the superconducting pairing of anomalous pseudospin allows for an unusual response to magnetic fields and gives rise to a novel manifestation of nodal excitations. |
Tuesday, March 7, 2023 4:00PM - 4:12PM |
K22.00006: Pseudospin in LaO1/2F1/2BiX2 (X=S,Se) TATSUYA SHISHIDOU, Han Gyeol Suh, Yue YU, Philip Brydon, Daniel F Agterberg, Michael Weinert The layered material Re(O,F)Bi(S,Se)2 has drawn attention for its superconductivity. In addition to experiments that suggest unconventional superconductivity [1,2], an upper critical field (Hc2) considerably surpassing the Pauli limit has been found for in-plane fields [3,4]. In this talk, we will discuss the electronic valence bands and their spin states in LaO1/2F1/2BiX2 from DFT calculations and symmetry-based model analyses. A mechanism that accounts for the high Hc2 will also be presented. |
Tuesday, March 7, 2023 4:12PM - 4:24PM |
K22.00007: Signatures of the order parameter of a superconducting adatom layer in quasiparticle interference patterns Benjamin A Levitan, Jonathan Eid, Tami Pereg-Barnea Superconductivity has been observed in a 2D triangular lattice of Sn adatoms deposited on a Si (111) surface. As with any novel superconductor, identifying the symmetry of the superconducting order parameter is of the utmost importance, in order to shed light on the underlying pairing mechanism. To that end, we calculate the quasiparticle interference (QPI) patterns which would result from several putative order parameters, for scattering from charge disorder (impurities) and order parameter disorder (vortices). These patterns can be obtained experimentally as the Fourier transform of the real-space local density of states, measured by scanning tunneling spectroscopy. By performing the experiment in a varying magnetic field, the relative contributions to the QPI pattern from charge scattering and vortex scattering can be tuned. We show that characteristic differences between the charge and vortex scattering signals, at particular momentum transfers, can be used to distinguish between order parameters with different angular momenta. |
Tuesday, March 7, 2023 4:24PM - 4:36PM Author not Attending |
K22.00008: Fragmented Cooper Pair Condensation in Striped Superconductors Alexander Wietek Condensation of bosons in Bose-Einstein condensates or Cooper pairs in superconductors refers to a macroscopic occupation of a few single- or two-particle states. A condensate is called "fragmented" if not a single, but multiple states are macroscopically occupied. While fragmentation is known to occur in particular Bose-Einstein condensates, we propose that fragmentation naturally takes place in striped superconductors. To this end, we investigate the nature of the superconducting ground state realized in the two-dimensional t−t′−J model. In the presence of charge density modulations, the condensate is shown to be fragmented and composed of partial condensates located on the stripes. The fragments of the condensates hybridize to form an extended macroscopic wave function across the system. The results are obtained from evaluating the singlet-pairing two-particle density matrix of the ground state on finite cylinders computed via the density matrix renormalization group method. Our results shed light on the intricate relation between stripe order and superconductivity in systems of strongly correlated electrons. |
Tuesday, March 7, 2023 4:36PM - 4:48PM |
K22.00009: Hybrid s-wave superconductivity in CrB2 Sananda Biswas, Andreas Kreisel, Adrian Valadkhani, Matteo Dûrrnagel, Tilman Schwemmer, Ronny Thomale, Roser Valenti, Igor I Mazin In a metal with multiple Fermi pockets, the formation of s-wave superconductivity can both be conventional due to electron-phonon coupling or unconventional due to spin fluctuations. We analyze the hexagonal diboride CrB2 which is found to be an itinerant antiferromagnet at ambient conditions and turn superconducting upon increasing pressure. While the high pressure behavior of Tc suggests conventional s-wave pairing, we find that spin fluctuations mediating unconventional s-wave pairing form a significant contribution in the vicinity of the antiferromagnetic dome. As the symmetry class of the s-wave state is independent of its underlying mechanism, we argue that CrB2 is a realization of a hybrid s-wave superconductor where unconventional and conventional s-wave mechanisms team up to form a joint superconducting dome. |
Tuesday, March 7, 2023 4:48PM - 5:00PM Author not Attending |
K22.00010: Interpretable Machine Learning Surrogate Model for Critical Temperature Prediction of Superconductors Angel Diaz Carral A general theory of superconductivity has been the focus of research over the last decades. Machine learning (ML) approaches based on chemical and structural features have been developed in order to predict both the critical temperature Tc and potential novel candidates. Nevertheless, these models lack interpretability. Either the feature matrix is reduced via mathematical transformations such as SVD/PCA or augmented with statistical feature generation. In this work, we introduce a ML model based only on electronic and structural descriptors derived from the composition formula and the individual elements. We reach an R2 >91% a reduced number of descriptors while keeping the physical meaning of the feature space. In the end, we test our model predicting the Tc of new superconductors. |
Tuesday, March 7, 2023 5:00PM - 5:12PM |
K22.00011: Ambient pressure stabilization of high-pressure superconducting phase of MoB2 by Nb doping Ajinkya C Hire, Shubham Sinha, Jinhyuk Lim, Jung S Kim, Philip M Dee, Laura Fanfarillo, James J Hamlin, Richard G Hennig, Peter Hirschfeld, Gregory R Stewart In the last few years, researchers have discovered many superconductors which are stable only at high pressure. One such high-pressure superconductor is MoB2 which undergoes a structural transformation from R-3m to P6/mmm MgB2-like structure at 60GPa and becomes a superconductor below 32K. We show how Nb doping stabilizes the high-pressure MgB2-like phase, first predicted by theory and then confirmed by experiments. We will present density functional theory calculations that reveal how the MgB2-like phase is stabilized at ambient pressure by phonon entropy and disorder across the NbxMo1-xB2 series. The samples used in the experiments were synthesized by arc-melting the elements. X-ray diffraction on our Nb-doped samples confirmed the presence of an MgB2-like bulk phase in the Nb-doped samples. Our Nb-doped MoB2 samples are superconducting with the highest Tc of 8K and higher critical fields approaching 6T, as seen in our specific heat and high-field electrical resistivity. The doping method utilized in this work might help stabilize other high-pressure superconducting diborides. |
Tuesday, March 7, 2023 5:12PM - 5:24PM |
K22.00012: High Upper Critical Field Anisotropy in an Organic Superconductor with a Wide Anion Layer Brett Laramee, Raju Ghimire, Charles C Agosta, Lee Martin, David E Graf The salt β”-(BEDT-TTF)2[(H2O)(NH4)2Cr(C2O4)3]•18-crown-6 is a layered, quasi-2D organic superconductor that has an extraordinarily wide anion layer compared to other organic crystals, and was predicted to be a possible FFLO state candidate. We will present rf-penetration depth measurements using a tunnel diode oscillator (TDO) taken up to B=28T (DC) and T<100mk at the NHMFL in Tallahassee, FL. When the applied external magnetic field is oriented perpendicular to the conduction planes of the crystal, single frequency Shubnikov-de Haas (SdH) oscillations are observed above 6T. When oriented parallel to the layers, despite prior predictions, no superconductivity is observed above the calculated Clogston-Chandrasekhar paramagnetic limit, Hp, and no FFLO state is observed. We further support this with calculations of the mean free path & superconducting coherence length, among other Fermi surface parameters such as the Dingle temperature, showing the crystal is in the dirty limit. In addition, we will show evidence of bulk-anistropic to Josephson coupled (3D to 2D) dimensional crossover just below Tc. One remarkable takeaway from our data is that the anisotropy ratio of the upper critical fields, Hc2, in the parallel & perpendicular directions is incredibly high, due to a surprisingly small perpendicular Hc2=0.2T. The mechanism causing this abnormally low upper critical field is not yet understood, and future work is needed to understand the impacts of the novel geometry on this material. |
Tuesday, March 7, 2023 5:24PM - 5:36PM |
K22.00013: Superconductivity in the Fibonacci Chain YING WANG The discovery of superconductivity in Al–Zn–Mg quasicrystal paved the way for fractal superconductivity[1]. We consider approximants of the Fibonacci chain, which are periodic structures locally retaining quasiperiodic character inside a large unit cell. For a fixed unit cell size, our model is characterized by the quasiperiodic modulation strength. Superconductivity is introduced by an attractive Hubbard interaction. We apply the Bogoliubov-de Gennes mean field theory for the simulation. We find that sites with similar local environments have order parameters of similar magnitude, regardless of the distance between them. The multifractality of the spectrum results in a rich phase diagram as a function of doping and pairing strength. The superconducting gap is insensitive to fluctuations in the local order parameter. This is a corollary to the fact that the entire length of the quasicrystal has the same critical temperature. The critical temperature increases quadratically with the modulation strength. These findings are of interest to the application of low-dimensional quasicrystals. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700