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 TT07: V: Superconductivity I |
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Sponsoring Units: DCMP Chair: Makariy Tanatar, Ames Laboratory/Iowa State University Room: Virtual Room 7 |
Tuesday, March 21, 2023 3:30PM - 3:42PM |
TT07.00001: Controllable critical Josephson current and 0-π transition in superconductor-insulator-superconductor heterostructures. Giorgos Livanas The intriguing electromagnetic properties of superconductors have led to the development of novel electronic devices which minimize energy dissipation, such as the energy-efficient rapid flux quantum logic devices. However, their broad implementation in classical computing setups is hindered by the absence of compatible memory units. To date, several variations of magnetic Josephson junctions have been proposed which, however, exhibit high switching time. |
Tuesday, March 21, 2023 3:42PM - 3:54PM |
TT07.00002: Magnetic critical field Hc and spin polarization energy limit field Hp in a superconductor Sang-Boo Nam By the BCS framework [Bardeen, Cooper and Schrieffer, Phys. Rev., 108, 1175 (1957); Nam, Phys. Rev., 156, 470 (1967)], we present novel results, at zero temperature, Hc(x) = [4πN(0)]1/22Δ/(1+x), Hc(1) = Hc(BCS) and Hp(x) = 21/22Δ/(1+x)(gμB), Hp(1) = Hp(CC) [Chandrasekhar, Appl. Phys. Lett., 1, 7 (1962); Clogston, Phys. Rev. Lett., 9, 266 (1962)], with the superfluid density x = ρs/ρ = tanh(G/2) [Nam, APSMAR22/A61.4 (2022), Phys. Rev. B3, 2946 (1971)], G= [1/N(0)V] [Nam, Phys. Lett. A193, 111 (1994); (E) ibid A197, 458 (1995)] = Σj (2/wj)tan-1(z/wj), wj=(π/2)j (odd integer), z=Td/2Tc, Δ/2Tc = A(z) = z/sinhG, where N(0), V, and Td are the density of states/spin at a reference energy, the BCS interaction energy, and the pairing interaction energy range (the cut-off energy), respectively. A(z>>1) (BCS) =0.88 and A(z<<1) = 1. The upper value [Hp(x)/Tc] =[2/0.88] [Hp(CC)/Tc]. For UTe2, Tc = 1.6K, Hp(0.53) is found to be 4.5T contrast to 3T = Hp(CC) by Ran et al, Science, 365, 684 (2019). Superconducting state [x<1] is a miscible liquid state with both ρs and ρn. Superconductors are multiconnected [Nam, Phys. Lett. A198, 447 (1995)]. |
Tuesday, March 21, 2023 3:54PM - 4:06PM |
TT07.00003: Dynamical structural instability and its implication on the physical properties of infinite-layer nickelates Chengliang Xia, Jiaxuan Wu, Yue Chen, Hanghui Chen We use first-principles calculations to find that in infinite-layer nickelates RNiO2, the widely studied tetragonal P4/mmm structure is only dynamically stable for early lanthanide elements R = La-Sm. For late lanthanide elements R = Eu-Lu, an imaginary phonon frequency appears at A = (π,π,π) point. For those infinite-layer nickelates, condensation of this phonon mode into the P4/mmm structure leads to a more energetically favorable I4/mcm structure that is characterized by an out-of-phase rotation of "NiO4 square". Special attention is given to two borderline cases: PmNiO2 and SmNiO2, in which both the P4/mmm structure and the I4/mcm structure are local minimums, and the energy difference between the two structures can be fine-tuned by epitaxial strain. Compared to the P4/mmm structure, RNiO2 in the I4/mcm structure has a substantially reduced Ni dx2-y2 bandwidth, a smaller Ni d occupancy, a "cleaner" Fermi surface with a lanthanide-d-derived electron pocket suppressed at Γ point, and a decreased critical UNi to stabilize long-range antiferromagnetic ordering. All these features imply enhanced correlation effects and favor Mott physics. Our work reveals the importance of structure-property relation in infinite-layer nickelates, in particular the spontaneous "NiO4 square" rotation provides a tuning knob to render RNiO2 in the I4/mcm structure a closer analogy to superconducting infinite-layer cuprates. |
Tuesday, March 21, 2023 4:06PM - 4:18PM |
TT07.00004: Investigating the crystal structure and superconductivity of ErBa2-xSrxCu3O7-δ Anushika K Athauda, Faith Guy, Mitchel Meyer, Sharon S Philip, Despina A Louca ErBa2-xSrxCu3O7-y is a novel material having an orthorhombic structure (Pmmm space group) similar to the YBa2Cu3O7 ceramic superconductors. The samples of ErBa2-xSrxCu3O7-y are prepared using solid state reaction method systematically to optimize the sintering parameters on the phase formation. Strontium, having a smaller ionic radius than barium, expected to apply chemical pressure on the unit cell upon doping at the barium site. The crystal structure of ErBa2-xSrxCu3O7-y is investigated at different strontium doping levels using x-ray and neutron diffraction as a function of temperature. X-ray diffraction studies show that the Ba site accepted Sr up to doping level of x=1. Superconducting and magnetic properties of the system as a function of doping will also be discussed. |
Tuesday, March 21, 2023 4:18PM - 4:30PM |
TT07.00005: Ab initio Tc screening for ThCr2Si2-type compounds within the BCS theory of superconductivity Kenji Oqmhula, Kenta Hongo, Ryo Maezono, Kousuke Nakano ThCr2Si2-type (122) compounds have been considered promising candidates for BCS-type superconductors (SCs), but most of their superconductivity have yet to be studied experimentally. Based on their ab initio Tc evaluations, we have performed the high-throughput virtual screening from the Inorganic Crystal Structure Database (ICSD): We first ruled out those which include Cr, Mn, Fe, Co, and Ni atoms, because they might show magnetic ordering that hinders superconductivity.Similarly, the f-electron systems were excluded,because they might show non-BCS-type superconductivity that is beyond the ab initio Tc evaluation. Furthermore, dynamically unstable compounds were removed by performing the ab initio phonon simulations. Thus, 68 compounds remained as candidates for BCS-type SCsand then their Tc values were evaluated by the Allen-Dynes formula. For 30 compounds having experimental Tc values, we investigated the correlation between experimental and theoretical Tc values; they correlate well with each other. Among the remaining 38 compounds, we found SrPb2Al2 to have the highest Tc (2.2 K), which is a newly predicted BCS-type SC. We also investigated electronic and phonon band structures as well as the Eliashberg function with mode-resolved electron-phonon coupling constant. Their comparison between SCs and NSCs provides a physical insight into comprehensive understandingof the origin of superconductivity in the 122 compounds, which will be explained in detail in this talk. |
Tuesday, March 21, 2023 4:30PM - 4:42PM |
TT07.00006: Pair-breaking in superconductors with strong spin-orbit coupling Philip Brydon, Daniel F Agterberg, David C Cavanagh We present a general theory for the pair-breaking effect of an arbitrary external perturbation in a multiband superconductor with strong spin-orbit coupling. Our central result is that the pair-breaking can be quantified by a single measure which we dub the "field-fitness function", which incorporates the interplay of the normal-state spin-orbital texture with both the pairing potential and the perturbation. This parameter controls the suppression of the critical temperature and, for the case of an external magnetic field, the magnitude of the Knight shift in the superconducting state. For even-parity superconductors we find that the field-fitness function for an external magnetic field is one, implying maximal pair-breaking consistent with Anderson's theorem. For odd-parity superconductors, in contrast, the field-fitness function reveals a more complicated interplay which can yield counter-intuitive behaviour. We apply our method to the topical case of p-wave pairing in the effective j = 3/2 electronic states of the Luttinger-Kohn model. |
Tuesday, March 21, 2023 4:42PM - 4:54PM |
TT07.00007: Charge and spin correlations in the superconducting state of the two-dimensional Hubbard model with cellular dynamical mean-field theory Giovanni Sordi, Caitlin Walsh, Maxime Charlebois, Patrick Sémon, A.-M. S Tremblay The nature of the superconducting correlations in a doped Mott insulator remains a central question to understand the phenomenology of cuprate high-temperature superconductors. Here we use the two-dimensional Hubbard model with cellular dynamical mean-field theory on a 2x2 plaquette to address the interplay between d-wave superconductivity and Mott physics. We gain insights on the superconducting correlations by studying the probability obtained from the largest diagonal elements of the reduced density matrix of the 2x2 plaquette. We examine the probabilities of the plaquette eigenstates in the superconducting state and in the underlying normal state at finite temperature, and in a wide range of interaction strengths and doping levels. We show that upon condensation, the probability of half-filled singlets increases and of half-filled triplets decreases for all doping levels and all correlation strengths that we have investigated. We show that the reduction of spin fluctuations is reflected by a marked drop of the spin susceptibility upon entering the superconducting state. |
Tuesday, March 21, 2023 4:54PM - 5:06PM |
TT07.00008: The mysterious oddness of strontium ruthenate's superconducting state: Strong electronic correlations, spin-orbit coupling and odd-frequency correlations in multi-orbital systems Olivier Gingras Recent experimental improvements have established key properties of the superconducting order parameter of strontium ruthenate, yet some of those give seemingly different pictures that are challenging to reconcile in a single theory [1, 2]. First reviewing these latest developments, we then present a numerical framework to study potential leading instabilities based on first-principles approaches and strong electronic correlations [3, 4]. The results highlight the importance of spin-orbit coupling in entangling electronic quantum numbers, yielding rich and complex order parameters. They suggest a rare type of order dominated by odd-frequency pairing as a prime candidate, which is also found using frequency-dependent linear response theory within dynamical mean-field theory. We discuss observable signatures in specific heat associated with these leading states and develop a static interpretation of odd-frequency pairings. |
Tuesday, March 21, 2023 5:06PM - 5:18PM |
TT07.00009: Temperature and Density Dependence of the 2D Hubbard Model Entropy at Intermediate to High Temperatures William O Putikka The entropy of the 2D Hubbard Model on a square lattice has a crossover at intermediate temperatures due to the growing importance of strong on-site repulsion as the temperature is lowered. At high temperatures T» U the density derivative of the entropy ∂S/∂n at fixed temperature is zero at half filling, indicating the entropy has a maximum as a function of density at half filling, like the non-interacting tight binding model. For large U as the temperature is reduced there is a sharp temperature where the density dependence of the entropy at half filling goes from a maximum to a local minimum, with ∂S/∂n¦T = ∂μ/∂T¦n = 0 for all temperatures, since μ = U/2 is temperature independent at half filling. The maximum in the entropy as a function of density shifts smoothly on both sides of half filling to n = 2/3 and n = 4/3 at intermediate temperatures below the sharp change in behavior at half filling. The entropy having a maximum as a function of density at n = 2/3 agrees with the high temperature behavior of the t-J model and is an unambiguous sign of strong electronic correlations. |
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