Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session R54: Fe-Based Superconductors: Superconducting PropertiesFocus Live
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Sponsoring Units: DMP Chair: Elena Gati, Ames Lab |
Thursday, March 18, 2021 8:00AM - 8:12AM Live |
R54.00001: Superconductivity and phonon self-energy effects in Fe1+yTe0.6Se0.4 Shangfei Wu, Alexander C Lee, Girsh Blumberg, Avior Almoalem, Irena Feldman, Amit Kanigel The measurement of superconducting gaps on different Fermi surface pockets is essential for elucidating the pairing mechanism in multi-band superconductors. The inelastic light scattering, or Raman spectroscopy, has been proven to be the best bulk probe to study the Cooper pair breaking excitations. Here, we present polarization-resolved Raman spectroscopic study of the multi-band superconductor Fe1+yTe0.6Se0.4 with Tc=14K. Deep in the superconducting state, we detect a pair-breaking excitation at 45 cm-1 ( 5.6 meV) in the non-symmetric channel, consistent with twice of the gap energy (3meV) on the hole-like Fermi pocket with dxz/dyz character around Γ point revealed by ARPES [1]. We also analyze the superconductivity induced phonon self-energy effects for the B1g(Fe) phonon and estimate the electron-phonon coupling constant λΓ ≈ 0.026, which is insufficient to explain the superconducting paring in Fe1+yTe0.6Se0.4 [2]. |
Thursday, March 18, 2021 8:12AM - 8:24AM Live |
R54.00002: Low-energy-plasmon enhanced High-transition-temperature superconductivity in monolayered FeSe on SrTiO3 Tong Wei, Zhenyu Zhang It was observed nearly a decade ago that the superconducting transition temperature (Tc) of a monolayered FeSe grown on SrTiO3 can be drastically enhanced from that of bulk FeSe, yet the likely microscopic mechanisms involved are still under active debate. Here we reveal the vital role of the interfacial optical plasmon mode in mediating electron pairing, which so far has been overlooked for this unique system. The low-energy nature of the plasmon known to be comparable to the energy of the interfacial phonon mode is a direct consequence of the low carrier density, demanding the electron-phonon and electron-plasmon couplings to be treated on equal footing. Our detailed analysis within a generalized Eliashberg formalism shows that, whereas the electron-phonon or electron-plasmon coupling alone could only yield a low Tc of a few K, the constructive interplay of the two is able to enhance the Tc by one order of magnitude, to the experimentally observed range. Our theory also predicts a characteristic dependence of Tc on the plasmon frequency, and is expected to find broader applicability in related superconducting systems. |
Thursday, March 18, 2021 8:24AM - 8:36AM Live |
R54.00003: Retention of metastable superconductivity in FeSe up to 24 K at ambient by pressure quenching Liangzi Deng, Trevor Bontke, Rabin Dahal, Bin Gao, Zheng Wu, Melissa Gooch, Tong Chen, Pengcheng Dai, Ching W Chu High pressure has been shown to be an effective route to achieving high temperature superconductivity. This is exemplified by the current record high Tcs at 164 K in the cuprate HgBa2Ca2Cu3O8+δ under ~31 GPa and at 287 K in C-S-H under ~ 267 GPa. These impressive record high Tcs are significant not only scientifically, but also technologically. Should these superconducting (sc) states under high pressures be retained at ambient, their impacts on technology would be profound and limited only by the imagination. We have chosen the sc FeSe and non-sc Cu-doped FeSe as model compounds to test this possibility. We have succeeded in retaining the high-pressure sc phase with a Tc up to 24 K upon the complete removal of pressure at 77 K following a specific thermodynamic path. A high-pressure non-sc phase of FeSe was also retained and proved to be stable up to room temperature. Detailed results will be presented and discussed. |
Thursday, March 18, 2021 8:36AM - 8:48AM Live |
R54.00004: Tuning stoichiometry and its impact on superconductivity of monolayer and multilayer FeSe on SrTiO3 Chong Liu, Ke Zou Monolayer FeSe on SrTiO3 has a greatly enhanced superconducting Tc compared with the bulk FeSe, but long-time annealing was required to achieve the superconductivity. We grow 1-unit-cell to 5-unit-cell thick FeSe films on SrTiO3 and deposit small amounts of additional Fe onto the as-grown films. We find that adding Fe atoms induces superconductivity with high Tc without the anneal process, indicating that the as-grown FeSe films possess Fe vacancies. In the 5-unit-cell sample, we tune the reconstruction and stoichiometry by alternating deposition of Se and Fe and switch the FeSe multilayer between an Fe-vacancy phase and the superconducting phase. We offer an easy and time-saving treatment method compared to the many hours of annealing. This research unveils the essence of the anneal is to improve the stoichiometry, which is crucial for the properties of FeSe on SrTiO3. |
Thursday, March 18, 2021 8:48AM - 9:00AM Live |
R54.00005: Design and discovery of CaKRu4P4: a new member of the generalized 1144 structure. Mingyu Xu, Olena Palasyuk, Sergey Budko, Boqun Song, Kai-Ming Ho, Paul C Canfield AeAFe4As4 (Ae=Ca, Sr; A=K, Rb, Cs) compounds were discovered as a new structural type [1] which has alternate stacking of the Ae and A layers. The AeAFe4As4 structure is stabilized by the combination of large Δc (= cA122-cAe122) and small Δa (= aA122-aAe122), where a and c are lattice parameters of the AFe2As2 and AeFe2As2 parent structures. In this presentation this idea was extended to similar, phosphorus-based 122 compounds with large Δc and small Δa values, in particular CaKRu4P4, whose stability was recently predicted by first principle calculations [2]. We synthesize polycrystalline CaKRu4P4 by solid state reaction of CaRu2P2 and KRu2P2. The crystallographic structure and physical properties of CaKRu4P4 will be presented. |
Thursday, March 18, 2021 9:00AM - 9:12AM Live |
R54.00006: Interplay between spin-vortex crystal magnetic order and superconductivity in transition-metal doped CaKFe4As4 John M. Wilde, Wei Tian, Mingyu Xu, Bing Li, Benjamin G. Ueland, Anna E. Böhmer, William Meier, Sergey L. Bud'ko, Alan I. Goldman, Robert J. McQueeney, Paul C. Canfield, Andreas Kreyssig CaKFe4As4 is an iron arsenide superconductor in which partial substitution of Fe by a transition metal shifts the ground state from superconducting to antiferromagnetically (AFM) ordered. Employing single-crystal neutron diffraction data we show that the AFM order is a non-collinear, commensurate structure with a hedgehog spin-vortex crystal (SVC) arrangement within the Fe planes and a simple AFM stacking perpendicular to them. The long-range SVC order coexists with superconductivity, however, the interplay of both phenomena depends on the kind of transition-metal doping: For electron-doping by Ni, a gradual suppression of the ordered magnetic moment is observed with decreasing temperature below the superconducting transition temperature. For hole-doping by Mn, the ordered magnetic moment increases smoothly with decreasing temperature and superconductivity seem not to influence the magnetic order. |
Thursday, March 18, 2021 9:12AM - 9:24AM Live |
R54.00007: Tuning London penetreation depth anisotropy with Disorder in the CaKFe4As4 Superconductor Daniele Torsello, Jonas Bekaert, Giovanni Ummarino, Laura Gozzelino, Roberto Gerbaldo, Makariy Tanatar, Paul C Canfield, Ruslan Prozorov, Gianluca Ghigo We report on the anisotropic behavior of the London penetration depth of CaK(Fe1−xNix)4As4 (CaK1144), discussing how it relates to its electronic structure and how it can be tuned by disorder to match specific requirements for applications. |
Thursday, March 18, 2021 9:24AM - 9:36AM Live |
R54.00008: Heat transport study of KFe2As2 in precisely oriented magnetic field. Effect of controlled disorder Makariy Tanatar, Tristin Metz, Erik I Timmons, Yong Liu, T. A. Lograsso, Xiangfeng Wang, Marcin Konczykowski, olivier cavani, Kirill Samokhin, Ruslan Prozorov, Johnpierre Paglione A systematic evolution of thermal conductivity in magnetic fields parallel to [001] crystallographic axis (orbital upper critical field, Hc2) and parallel to [100] direction (Pauli limited Hc2) was studied in nodal superconductor KFe2As2. Low-temperature irradiation with relativistic 2.5 MeV electrons was used to shift from clean to dirty limit. The dirty limit response in the Zeeman case is in qualitative agreement with the predictions for linear quasi-particle density increase with magnetic field and continuous transition at Hc2, as opposite to the 1st-order transition in the clean limit. |
Thursday, March 18, 2021 9:36AM - 9:48AM Live |
R54.00009: Local and Global measurements of London Penetration Depth in Inhomogeneous Superconductors Kamal Joshi, William S. Setterberg, Naufer M Nusran, Sunil Ghimire, Kyuil Cho, Makariy Tanatar, Sergey Budko, Paul C Canfield, Ruslan Prozorov An important parameter, the London penetration depth (LPD), in superconductors can be estimated from the global (whole sample) response [1] or measuring the first critical field locally near the surface [2]. We compare LPD from the global tunnel diode resonator (TDR) technique [1] with the local values obtained by using NV-centers in diamond optical magnetometry [2]. We deliberately chose a crystal of Ba(Fe1-xCox)2As2 pnictide superconductor that looks like an old book under an electron microscope, revealing a peculiar planar stack-like structure. We also examined a standard single crystal of YBa2Cu3O7-δ. While the temperature dependence of LPD is the same between TDR and NV-centers magnetometry, the absolute values differ by a factor of two in FeCo122, but are practically the same in YBCO. We model this situation numerically by finite-element method solving the London equations for our particular sample geometry and find unobvious behavior apparently due to the non-local long-range electromagnetic behavior of the finite-sized superconductor in an external field. |
Thursday, March 18, 2021 9:48AM - 10:00AM Live |
R54.00010: Vortex-Nernst and Diamagnetism in Iron-based Superconductor Fe1+yTe1-xSex Dechen Zhang, Lu Chen, Ziji Xiang, Jiaxin Yin, Kuan-Wen Chen, Guoxin Zheng, Genda Gu, Lu Li Nernst effect and torque magnetometry experiments have provided direct evidence for phase-coherence scenario in an iron-based superconductor Fe1+yTe1-xSex. The Nernst experiment, which measures the transverse electric field when applying a longitudinal temperature gradient and a perpendicular magnetic field, can detect vorticity with high sensitivity. Fe1+yTe1-xSex with different iron concentration has distinctly different critical temperature Tc, while their vortex-Nernst signal eN extends to a higher temperature Tonset and remains robust to fields of 13T. The fluctuation diamagnetic signal resolved by high-resolution torque magnetometry also onsets at temperature higher than Tc, and it scales similarly with the vortex-Nernst signal for the same sample. The results support the transition at Tc is caused by the loss of phase-rigidity of Cooper pairs. |
Thursday, March 18, 2021 10:00AM - 10:12AM Live |
R54.00011: Superfluid Stiffness of Systems with Bogoliubov Fermi Surfaces Yifu Cao, Chandan Setty, Andreas Kreisel, Shinibali Bhattacharyya, Peter Hirschfeld Bogoliubov Fermi surfaces are topologically protected regions of zero energy excitations in a superconductor whose dimension equals that of the underlying normal state Fermi surface. Hamiltonians exhibiting this "ultranodal" phase are regarded as unphysical if superfluid stiffness is negative. In this work we show that superfluid stiffness is positive within large areas of the parameter space of our previously proposed model Hamiltonian, confirming that the proposed model has stable ultranodal phase. We further investigate the the free energy expansion beyond Gaussian levell, and investigate the possibility that the instability in the case of negative stiffness can be to pair density wave order. |
Thursday, March 18, 2021 10:12AM - 10:48AM Live |
R54.00012: Evidence for FFLO superconducting states in the BCS-BEC crossover superconductor FeSe Invited Speaker: Shigeru Kasahara The iron-chalcogenide FeSe is argued as a strong candidate superconductor located in the crossover regime between the weakly coupled BCS and the strongly coupled BEC limits [1,2]. Its extremely small and shallow Fermi pockets, large superconducting gap, and consequently a large Maki parameter suggest that FeSe offers an ideal platform to study the potential Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state, in which a new pairing (k, -k+q) with nonzero q is formed. Here, we present several pieces of evidence for the emergence of distinct high-field superconducting phases in FeSe. For H || ab, our state-of-the-art high-field thermal transport up to 33 T shows a discontinuous downward jump within the superconducting state, indicating a first-order phase transition to a distinct high-field superconducting phase [3]. For H || c, the presence of a high-field phase is shown by an anomalous kink of the heat capacity, which occurs well below the irreversibility field. We attribute these high-field superconducting phases to the FFLO superconducting states. We also point out the importance of the multi-band nature and the orbital dependent pairing for the formation of the FFLO phase in FeSe. |
Thursday, March 18, 2021 10:48AM - 11:00AM On Demand |
R54.00013: Pressure-Induced Superconductivity in EuxCa1-xFe2As2 Single Crystals Keshav Shrestha, Liangzi Deng, Kui Zhao, Ben I Jawdat, Bing Lv, Bernd Lorenz, Ching W Chu We have carried out systematic electrical transport and magnetic properties of EuxCa1-xFe2As2 (ECFA) single crystals. The resistance shows a clear anomaly due to the spin-density wave (SDW) at TSDW ~ (165-190 K) and it varies systematically with the doping level (x). There exists another transition at low-temperature TN ~ (15-20 K) due to the antiferromagnetic order of Eu2+ spins. TN also shows a systematic dependence with x. At ambient pressure, none of the ECFA samples show superconducting properties. Therefore, we have used a high-pressure technique to induce superconductivity, and superconductivity with Tc ~ 19 K is induced under ~19 kbar applied pressure. The pressure dependence of Tc and pressure-temperature phase diagram will be discussed. |
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