Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session A61: Superconductivity: U Based & Other SC MaterialsRecordings Available
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Sponsoring Units: DCMP Chair: Vera Smolyaninova, Towson University Room: Hyatt Regency Hotel -Field |
Monday, March 14, 2022 8:00AM - 8:12AM |
A61.00001: Determining UTe2surface impedance through microwave resonance measurements Arthur L Carlton-Jones, Steven M Anlage The complex surface impedance of a superconductor provides many insights into its properties, such as the pairing mechanism, super- and normal-fluid responses, and possibly it’s topological properties. We explore the surface impedance of UTe2 single crystals as a function of temperature using resonant cavity measurements for a variety of microwave-frequency modes. By determining the resonant frequency and quality factor over a range of temperatures, we reconstruct the surface impedance of the sample. We match the behavior of the resistance and reactance in the normal state to their expected behavior, determined by the normal state resistivity. Since UTe2 is anisotropic, we take a linear combination of the losses corresponding to each crystallographic direction to do this fitting. Through this method, the anisotropic nature of UTe2 allows us to determine the combination of crystallographic directions excited in each resonant mode. We present the results of the anisotropic surface impedance temperature dependence in the superconducting and normal states, and relate the results to topics of current interest in this unique material. |
Monday, March 14, 2022 8:12AM - 8:24AM |
A61.00002: Phenomenological theory of re-entrant superconductivity in UTe2 Yue YU, Srinivas Raghu We analyze the re-entrant superconductivity in UTe2 within the framework of the phenomenological theory. Our analysis is based on the resistivity data, under the magnetic field along the b-axis. We compare the Pauli-limited and orbital-limited suppression of the magnetic field. We will highlight the connection of our work with the Kerr effect measurement. |
Monday, March 14, 2022 8:24AM - 8:36AM |
A61.00003: Effect of Synthesis Conditions on Superconducting of Uranium Ditelluride Corey Frank, Ian M Hayes, Shanta Saha, Johnpierre Paglione, Nicholas Butch Uranium ditelluride was recently identified as a candidate spin triplet superconductor, however this discovery has come with some controversy surrounding the nature of the superconducting transition. Much of the confusion between properties reported by different laboratories can be attributed to the sensitivity UTe2 shows to synthetic conditions, with different approaches leading to wildly different superconducting transition temperatures, or even full suppression of desirable properties. In this talk I will summarize the effects that preparation technique has on the superconducting properties of UTe2. |
Monday, March 14, 2022 8:36AM - 8:48AM |
A61.00004: Superfluid density ρS/ρ=Λ/ΛT [London] and specific heat ratio CS/CN 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)] with a finite pairing interaction energy range Td to have a finite transition temperature Tc [Nam, Phys. Lett. A193, 111 (1994); (E) ibid A197, 458 (1995)], we present novel results: ρS/ρ[T=0]= tanh(G/2) =1-ρN/ρ, G= Σj (2/wj)tan-1(z/wj), wj=(π/2)j (odd integer), z=Td/2Tc, 1/G=N(0)V [the density of states/spin at a reference energy times the BCS pairing interaction energy]; CS/CN[T=0]=R(z) =(χS/χN) [12(z/π)2 + (1+2z)/(1+tanhz)], χS/χN =1-tanhz [spin susceptibility at T=0]; R(1.4)=0.496 may account for the data 0.5 in UTe2 [Ran et al, Science, 365, 684 (2019)]; R(BCS)=0; CS/CN[T=Tc]-1=d(z) =(6/π2) tanhz/[h(z)+(z-tanhz)/2z2], h(z)=Σj wj-3 tan-1(z/wj); d(z>>1) =12/7ζ(3) [BCS]; d(z<<1) =18/π2 [Nam, APSMAR21, M47.12]; Free energy difference (FN-FS)[T=0]= N(0)Δ2 tanhG/[1+tanhG], Δ=Td/sinhG. Superconducting state is a miscible liquid state with both ρS and ρN. Superconductors are multiconnected [Nam, Phys. Lett. A198, 447 (1995)]. |
Monday, March 14, 2022 8:48AM - 9:00AM |
A61.00005: Scanning tunneling microscope study of the unconventional superconducting state in UTe2 Yuwen Hu, Yen-Chen Tsui, Hao Ding, Priscila Rosa, Ali Yazdani Superconductivity in UTe2 (Tc = 1.6 - 2 K) with extremely high upper critical field, far exceeding the Pauli limit, as well as its re-entrant behavior at even higher magnetic field is a subject of great recent interest. It has been proposed that the superconducting state in UTe2 has a triplet chiral p-wave pairing symmetry with a non-unitary order parameter. Here we use a dilution refrigerator scanning tunneling microscope (STM) to measure the spatial variation of the superconducting gap on both (001) and (011) surfaces of UTe2 cleaved in ultra-high vacuum. We observe in-gap states on step edges and defects, similar to those reported previously [1], which implies that the pairing symmetry in UTe2 is likely not s-wave. We also probe the response of superconducting state to adatoms defects deposited on the UTe2 surface resolving Yu-Shiba-Rusinov (YSR) states near individual impurities. Similarly to the in-gap states near step edges, the YSR states show abnormally asymmetric spatial distribution, which may shed new light to the unconventional pairing symmetry in this system. Finally, we have explored imaging the local density of states in a magnetic field to the UTe2 sample to probe its vortex lattice. |
Monday, March 14, 2022 9:00AM - 9:12AM |
A61.00006: Topology change of the Landau Fermi surface in CeCoIn5. Sangyun Lee, Duk Y Kim, Andrew J Woods, Eric D Bauer, Filip Ronning, Shizeng Lin, Roman Movshovich The high-field/low temperature state of CeCoIn5 (so-called Q-phase) is an intertwined dx2-y2-wave superconducting order, a p-wave superconducting pair density wave (PDW), and a magnetically ordered spin-density-wave (SDW) [1]. When magnetic field is oriented within the a-b plane, the SDW ordering wave vector QSDW lies in one of the nodal directions of the |
Monday, March 14, 2022 9:12AM - 9:24AM |
A61.00007: Insight into the metallurgy of UCoGe by electron-beam zone refining crystal growth Keenan Avers, Man D Nguyen, John W Scott, William P Halperin, Andrew Zimmerman, Sean Thomas, Joe D Thompson, Priscila Rosa New insights into the phenomena of superconductivity have been enabled by the recently discovered U-based ferromagnetic superconducting compounds UGe2, UCoGe, URhGe, and UTe2. Sample quality in these compounds has proven to be a challenge for achieving a maximal superconducting transition temperature. |
Monday, March 14, 2022 9:24AM - 9:36AM |
A61.00008: Correlated normal state and topological superconductivity in UTe2 Seung Hun Lee, Bohm-Jung Yang, Hongchul Choi UTe2 poses a promising platform of the paramagnetic end member among the Uranium-based superconductor where spin-triplet pairing superconductivity arises from ferromagnetic fluctuation. Here, we report a theoretical calculation to predict a correlation-driven large Fermi surface (FS) in UTe2, which has a geometry different from those predicted by the previous theoretical studies. The geometry of the FS indicates a robust non-trivial topology of the superconducting state that hosts a Majonara fermion within the weak coupling theory. We also solve the linearized Eliashberg equations in the random phase approximation level considering ferromagnetic spin fluctuation and find the possible superconducting ground state. |
Monday, March 14, 2022 9:36AM - 9:48AM |
A61.00009: Scattering Interference Signature of Hidden Orbital Orderin Superconducting CeCoIn5 Weijiong Chen, Clara Neerup Breiø, Freek Massee, Cedomir Petrovic, JC S Davis, Peter J Hirschfeld, Milan P Allan, Brian M Andersen, Andreas Kreisel Visualizing orbital degrees of freedom and orders is a new challenge in scanned microscopy. Some types of orbital order(OO) are virtually imperceptible because they do not reduce the overall crystal symmetry. Recently, however, direct visualization of quasiparticle scattering interference(QPI) has become a powerful technique for detecting OO states[1,2]. Hence, we model the QPI of (π,π) OO in both normal and superconductive phases and find distinct, sublattice-specific scattering interference patterns generated by OO, which we predict to be strongly enhanced in the latter phase. Sublattice-resolved QPI visualization in superconducting CeCoIn5 then reveals two orthogonal QPI signatures at impurity atoms, with each QPI pattern specific to one sublattice. This discovery implies that QPI is a powerful technique to detect the hidden global symmetry-preserving orbital order in superconductors. |
Monday, March 14, 2022 9:48AM - 10:00AM |
A61.00010: Mapping the superconducting phase of UTe2 under uniaxial stress Clement Girod, Priscila Rosa, Eric D Bauer, Joe D Thompson, Andrew Huxley, Callum Stevens, Filip Ronning, Sean Thomas The recently discovered uranium-based unconventional superconductor UTe2 has attracted attention as a promising candidate for spin-triplet pairing and topological superconductivity. Among its numerous peculiarities, UTe2 hosts different superconducting phases as a function of applied hydrostatic pressure and magnetic fields. For hydrostatic pressures exceeding 0.3 GPa, UTe2 exhibits two superconducting transitions that have opposite pressure dependence. At zero field and ambient pressure, UTe2 crystals with an optimal superconducting transition temperature, Tc = 2 K, host a single thermodynamic superconducting transition. Some reports, however, argue that a multi-component order parameter exists even at ambient pressure. Due to its orthorhombic structure symmetry, any multi-component order parameter should lead to two non-degenerate superconducting transitions in UTe2. The reason multiple transitions are not observed below P = 0.3 GPa in the highest quality crystals remains unknown, as does the sudden emergence of two transitions at P = 0.3 GPa. Here, we investigate the uniaxial stress dependence of the low temperature specific heat and electrical resistivity of UTe2 along different crystallographic directions to better understand the pressure-temperature phase diagram of UTe2. |
Monday, March 14, 2022 10:00AM - 10:12AM |
A61.00011: Superconductivity observed in the vicinity of Mott insulating states in A3C60 Katsumi Tanigaki, Yuki Matsuda, Satoshi Heguri A similar Mott physics on unconventional superconductors, such as cuprates, Fe pnictides, and organic conductors is now claimed for expanded C60 superconductors, and electron-electron (e-e) interactions are thought to be very important origin of its high Tc superconductivity. On the other hand, the highest superconductivity surpassing the cuprates recently found in H2S under high pressure gives the discussion back to the electron-phonon (e-ph) mediated superconductivity for achieving high superconducting critical temperature (high Tc). The Fermi surface of A3C60 (A=alkali metals: K, Rb, Cs) superconductors with expanded cell (Vcell(C603-)) provides an intriguing research platform for both e-e and e-ph interactions. However, being different from other unconventional superconductors, electrical transport measurements had been very difficult in expanded A3C60 and important scientific discussions have been made based on only limited magnetic and optical probes. Here, we give experimental results that accurate electrical resistivity (ρ(T,P)) can be achieved for a variety A3C60 with expanded Vcell(C603-) near the Mott boundary under various temperature (T) and pressure (P). Electrical transport was carefully measured as a function of T and P, straddling the phase boundary between the Mott insulator and the metallic/superconducting phase. A new phase can be recognized to be located in the middle temperature range. The new phase is interpreted to be generated by e-ph interactions via dynamic Jahn Teller phonons and shows a strong T evolution of ρ(T), which can systematically be observed for A3C60 with a variety of cell volume controlled by chemical (stoichiometric composition of A3C60) and physical pressure. The new electronic phase observed unprecedentedly is considered to have common physics among many materials. |
Monday, March 14, 2022 10:12AM - 10:24AM |
A61.00012: Pseudogap and Kondo Hybridization in the Heavy-Fermion Superconductor CeCoIn5 Tuson Park, Harim Jang, Anh Hong, Jihyun Kim, Dale J Van Harlingen We report the quasi-particle scattering spectroscopy on the heavy-fermion superconductor CeCoIn5 under pressure. In the normal state above the superconducting transition temperature, a dip in differential conductance (dI/dV) is observed below the characteristic temperature of Tg, indicating a pseudogap with energy ∆g. When subjected to the external pressure, ∆g and Tg gradually increase, following the trend of the Kondo coherence temperature (Tcoh). The Fano-resonance asymmetry in dI/dV, which could be attributed to delocalization of f-electrons, persists even at elevated temperatures much higher than Tcoh and collapses on a single line against the reduced temperature (T/Tsat) among different pressures, signifying the onset of Kondo coherence at Tsat. The dependence on pressure of ∆g is in sharp contrast to that of superconducting gap ∆sc, but is consistent with Tcoh, showing that the pseudogap observed in CeCoIn5 is less likely involved in the SC pairing process, but is rather related to Kondo hybridization. |
Monday, March 14, 2022 10:24AM - 10:36AM |
A61.00013: Discovery of superconductivity in cesium-doped C60 at ambient pressure. Di Peng, Renshu Wang, Lina Zong, Xiao-Jia Chen The early discovery of cesium-doped C60 is a superconductor by the applied pressure. Here we report the superconductivity of cesium-doped C60 obtained at ambient pressure from the resistance and magnetization measurements based on the observed zero-resistivity state and Meissner effect. X-ray diffraction shows that the new superconductor possesses the primitive cubic with space group of Pa-3, which is different from the structures reported for superconducting at high pressure. Raman spectroscopy measurements shows the 18 cm-1 downshift to the frequency of Ag (2) mode compared with that of the pure C60, providing the charge transfer of 3 electrons per C60. The application of pressure is found to suppress the superconducting critical temperature, which is obviously different to the behavior in early found cesium-doped C60 superconductors with body-centered cubic A15-structured and face-centred-cubic structures. Furthermore, the superconducting parameters such as the critical fields, Ginzburg-Landau coherence length and London penetration depth of the 21 K superconducting phase are determined for this new superconductor. This discovery provides a new idea for searching these molecules superconductors at ambient pressure. |
Monday, March 14, 2022 10:36AM - 10:48AM Withdrawn |
A61.00014: Superconductivity in nonstoichiometric rubidium-doped C60 compounds Lina Zong, Di Peng, Ren-Shu Wang, Xiao-Jia Chen A rubidium-doped C60 superconductor with a critical temperature (Tc) of 22-23 K synthesized by a wet-chemical method is well-defined from the magnetization and resistivity measurements based on the observations of the Meissner effect and zero resistivity state. Raman scattering measurements show the downshift of 15 cm-1 for the Ag(2) vibrational mode, yielding the charge transfer is less than 3, which puts the new superconductor in the face-centred cubic structure based on the well-established phase diagram for this system. The superconducting parameters, such as the critical current density, the lower and upper critical field, and the derived coherence length and penetration depth, are determined from multiple techniques for this superconductor. |
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