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 UTe_{2}_{}surface impedance through microwave resonance measurements Arthur L CarltonJones, Steven M Anlage The complex surface impedance of a superconductor provides many insights into its properties, such as the pairing mechanism, super and normalfluid responses, and possibly it’s topological properties. We explore the surface impedance of UTe_{2} single crystals as a function of temperature using resonant cavity measurements for a variety of microwavefrequency 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 UTe_{2} 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 UTe_{2}_{ }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 reentrant superconductivity in UTe_{2} Yue YU, Srinivas Raghu We analyze the reentrant superconductivity in UTe_{2} within the framework of the phenomenological theory. Our analysis is based on the resistivity data, under the magnetic field along the baxis. We compare the Paulilimited and orbitallimited 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 UTe_{2} 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 UTe_{2}. 
Monday, March 14, 2022 8:36AM  8:48AM 
A61.00004: Superfluid density ρ_{S}/ρ=Λ/Λ_{T} [London] and specific heat ratio C_{S}/C_{N} in a superconductor SangBoo 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: ρ_{S}/ρ[T=0]= tanh(G/2) =1ρ_{N}/ρ, G= Σ_{j }(2/w_{j})tan^{1}(z/w_{j}), w_{j}=(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]; C_{S}/C_{N}[T=0]=R(z) =(χ_{S}/χ_{N}) [12(z/π)^{2} + (1+2z)/(1+tanhz)], χ_{S}/χ_{N }=1tanhz [spin susceptibility at T=0]; R(1.4)=0.496 may account for the data 0.5 in UTe_{2} [Ran et al, Science, 365, 684 (2019)]; R(BCS)=0; C_{S}/C_{N}[T=Tc]1=d(z) =(6/π^{2}) tanhz/[h(z)+(ztanhz)/2z^{2}], h(z)=Σ_{j} w_{j}^{3} tan^{1}(z/w_{j}); d(z>>1) =12/7ζ(3) [BCS]; d(z<<1) =18/π^{2} [Nam, APSMAR21, M47.12]; Free energy difference (F_{N}F_{S})[T=0]= N(0)Δ^{2 }tanhG/[1+tanhG], Δ=Td/sinhG. Superconducting state is a miscible liquid state with both ρ_{S} and ρ_{N}. 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 UTe_{2} Yuwen Hu, YenChen Tsui, Hao Ding, Priscila Rosa, Ali Yazdani Superconductivity in UTe_{2} (T_{c }= 1.6  2 K) with extremely high upper critical field, far exceeding the Pauli limit, as well as its reentrant behavior at even higher magnetic field is a subject of great recent interest. It has been proposed that the superconducting state in UTe_{2} has a triplet chiral pwave pairing symmetry with a nonunitary 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 UTe_{2} cleaved in ultrahigh vacuum. We observe ingap states on step edges and defects, similar to those reported previously [1], which implies that the pairing symmetry in UTe_{2} is likely not swave. We also probe the response of superconducting state to adatoms defects deposited on the UTe_{2} surface resolving YuShibaRusinov (YSR) states near individual impurities. Similarly to the ingap 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 UTe_{2 }sample to probe its vortex lattice. 
Monday, March 14, 2022 9:00AM  9:12AM 
A61.00006: Topology change of the Landau Fermi surface in CeCoIn_{5}. Sangyun Lee, Duk Y Kim, Andrew J Woods, Eric D Bauer, Filip Ronning, Shizeng Lin, Roman Movshovich The highfield/low temperature state of CeCoIn_{5} (socalled Qphase) is an intertwined d_{x2y2}wave superconducting order, a pwave superconducting pair density wave (PDW), and a magnetically ordered spindensitywave (SDW) [1]. When magnetic field is oriented within the ab plane, the SDW ordering wave vector Q_{SDW }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 electronbeam 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 Ubased ferromagnetic superconducting compounds UGe_{2}, UCoGe, URhGe, and UTe_{2}. 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, BohmJung Yang, Hongchul Choi UTe2 poses a promising platform of the paramagnetic end member among the Uraniumbased superconductor where spintriplet pairing superconductivity arises from ferromagnetic fluctuation. Here, we report a theoretical calculation to predict a correlationdriven 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 nontrivial 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 CeCoIn_{5} 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, sublatticespecific scattering interference patterns generated by OO, which we predict to be strongly enhanced in the latter phase. Sublatticeresolved QPI visualization in superconducting CeCoIn_{5} 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 symmetrypreserving orbital order in superconductors. 
Monday, March 14, 2022 9:48AM  10:00AM 
A61.00010: Mapping the superconducting phase of UTe_{2} under uniaxial stress Clement Girod, Priscila Rosa, Eric D Bauer, Joe D Thompson, Andrew Huxley, Callum Stevens, Filip Ronning, Sean Thomas The recently discovered uraniumbased unconventional superconductor UTe_{2} has attracted attention as a promising candidate for spintriplet pairing and topological superconductivity. Among its numerous peculiarities, UTe_{2} hosts different superconducting phases as a function of applied hydrostatic pressure and magnetic fields. For hydrostatic pressures exceeding 0.3 GPa, UTe_{2} exhibits two superconducting transitions that have opposite pressure dependence. At zero field and ambient pressure, UTe_{2} crystals with an optimal superconducting transition temperature, T_{c} = 2 K, host a single thermodynamic superconducting transition. Some reports, however, argue that a multicomponent order parameter exists even at ambient pressure. Due to its orthorhombic structure symmetry, any multicomponent order parameter should lead to two nondegenerate superconducting transitions in UTe_{2}. 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 UTe_{2} along different crystallographic directions to better understand the pressuretemperature phase diagram of UTe_{2}. 
Monday, March 14, 2022 10:00AM  10:12AM 
A61.00011: Superconductivity observed in the vicinity of Mott insulating states in A_{3}C_{60} 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 C_{60} superconductors, and electronelectron (ee) 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 H_{2}S under high pressure gives the discussion back to the electronphonon (eph) mediated superconductivity for achieving high superconducting critical temperature (high T_{c}). The Fermi surface of A_{3}C_{60} (A=alkali metals: K, Rb, Cs) superconductors with expanded cell (V_{cell}(C_{60}^{3})) provides an intriguing research platform for both ee and eph interactions. However, being different from other unconventional superconductors, electrical transport measurements had been very difficult in expanded A_{3}C_{60} 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 A_{3}C_{60} with expanded V_{cell}(C_{60}^{3}) 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 eph interactions via dynamic Jahn Teller phonons and shows a strong T evolution of ρ(T), which can systematically be observed for A_{3}C_{60} with a variety of cell volume controlled by chemical (stoichiometric composition of A_{3}C_{60}) 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 HeavyFermion Superconductor CeCoIn_{5} Tuson Park, Harim Jang, Anh Hong, Jihyun Kim, Dale J Van Harlingen We report the quasiparticle scattering spectroscopy on the heavyfermion superconductor CeCoIn_{5 }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 T_{g}, indicating a pseudogap with energy ∆_{g}. When subjected to the external pressure, ∆_{g} and T_{g} gradually increase, following the trend of the Kondo coherence temperature (T_{coh}). The Fanoresonance asymmetry in dI/dV, which could be attributed to delocalization of felectrons, persists even at elevated temperatures much higher than T_{coh} and collapses on a single line against the reduced temperature (T/T_{sat}) among different pressures, signifying the onset of Kondo coherence at T_{sat}. The dependence on pressure of ∆_{g} is in sharp contrast to that of superconducting gap ∆_{sc}, but is consistent with T_{coh}, showing that the pseudogap observed in CeCoIn_{5} 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 cesiumdoped C_{60} at ambient pressure. Di Peng, Renshu Wang, Lina Zong, XiaoJia Chen The early discovery of cesiumdoped C_{60} is a superconductor by the applied pressure. Here we report the superconductivity of cesiumdoped C_{60} obtained at ambient pressure from the resistance and magnetization measurements based on the observed zeroresistivity state and Meissner effect. Xray diffraction shows that the new superconductor possesses the primitive cubic with space group of Pa3, 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 A_{g }(2) mode compared with that of the pure C_{60}, providing the charge transfer of 3 electrons per C_{60}. The application of pressure is found to suppress the superconducting critical temperature, which is obviously different to the behavior in early found cesiumdoped C_{60} superconductors with bodycentered cubic A15structured and facecentredcubic structures. Furthermore, the superconducting parameters such as the critical fields, GinzburgLandau 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 rubidiumdoped C_{60} compounds Lina Zong, Di Peng, RenShu Wang, XiaoJia Chen A rubidiumdoped C_{60} superconductor with a critical temperature (T_{c}) of 2223 K synthesized by a wetchemical method is welldefined 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 A_{g}(2) vibrational mode, yielding the charge transfer is less than 3, which puts the new superconductor in the facecentred cubic structure based on the wellestablished 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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