Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session P56: Uranium-Based Superconductors, Hidden Order, and Related Phases |
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Sponsoring Units: DCMP Chair: Firoza Kabir, Univ of Central Florida Room: Mile High Ballroom 2C |
Wednesday, March 4, 2020 2:30PM - 2:42PM |
P56.00001: Polar Kerr effect measurements of UTe2 using Sagnac interferometry. Di Wei, Jian Zhang, Sheng Ran, Johnpierre Paglione, Nicholas Butch, Aharon Kapitulnik The heavy fermion compound UTe2 was recently found to superconduct with TC = 1.6K, showing paramagnetic behavior and closely resembling the family of uranium based ferromagnetic superconductors [Ran et al., Science, 2019]. This initial study presented strong evidence of spin-triplet superconductivity, likely mediated by ferromagnetic fluctuations, which have been shown to occur below TC in μSR experiments [Sundar et al., arXiv, 2019]. Additionally, a recent scanning tunneling microscopy experiment claims signatures of chiral modes inside of the superconducting gap, raising the possibility of topological superconductivity [Jiao et al., arXiv, 2019]. A direct measurement of possible time-reversal symmetry (TRS) breaking effects in this system can provide insight on the exact order parameter of UTe2, as well as evidence for the possible topological nature of the system. We present measurements of the polar Kerr effect using Sagnac interferometry in search for a possible TRS breaking state, and to examine ferromagnetic fluctuations in the Meissner and vortex states of this material. |
Wednesday, March 4, 2020 2:42PM - 2:54PM |
P56.00002: Electrodynamic response of the unconventional superconductor UTe2 Sirak Mekonen, David Barbalas, Dipanjan Chaudhuri, Sheng Ran, Wesley T Fuhrman, Nicholas Butch, Peter Armitage Evidence was recently reported that UTe2 is a nonunitary spin-triplet superconductivity, whch features a high (for this material family) transition temperature of 1.6 K and a remarkably large and anisotropic upper critical field exceeding 40 T. Here we report results of measurements on the electrodynamic response of this compound down to low frequencies and temperatures. We investigate the finite frequency response of this system and search for evidence for the ferromagnetic flucutuations that have been seen in the optical response of other exotic superconductors close to ferromagnetism. |
Wednesday, March 4, 2020 2:54PM - 3:06PM |
P56.00003: Electronic structure of ferromagnetic superconductor UGe2 in comparison to UTe2 Jonathan Denlinger, James W Allen, A. D. Huxley, Jacques Flouquet The newly discovered spin-triplet superconductor UTe2 [1] has a strong suggestive relationship to the family of ferromagnetic superconductors UGe2, URhGe and UCoGe. Here we update studies [2] of the electronic bandstructure of UGe2, experimentally measured by angle-resolved photoemission (ARPES) near the U 5d-5f resonance, with comparisons to DFT calculations of ThGe2 decomposed into subunit building block structures. A signature imprint of a 2D diagonal square-net plane of Ge atoms on the formation of large diamond-shaped Fermi surface contours is shown to agree well with ARPES and with dHvA orbit sizes. Similar theoretical decomposition of the UTe2 structure into zig-zag U-Te chains and a plane of Te linear chains with strong p-orbital bonding-antibonding splitting identifies the origins of the underlying orthogonal quasi-1D band structures near the Fermi level, in agreement with recent ARPES measurements [3]. |
Wednesday, March 4, 2020 3:06PM - 3:18PM |
P56.00004: Systematics of uranium-based superconducting materials. Eteri Svanidze A large number of uranium-based materials are exotic – they show complex magnetic orders, coexistence of superconductivity with magnetism, enhanced effective electron masses, quantum critical behavior, and topological states. All of these peculiar phenomena are thought to arise from electrons’ dual nature, which is also believed to lie at the origin of high-temperature superconductivity. Among unconventional uranium-based systems, the most intriguing are in fact superconductors – UBe13, URu2Si2, and UPt3 [1-3]. In this talk, I will provide a brief historic overview of superconductivity in uranium-based compounds, and address several pertinent questions [4]: Is superconductivity in uranium-based materials always unconventional? Why are superconducting temperatures in uranium-based compounds so low, compared to other compounds, based on actinide or lanthanide elements? Is there a way to pinpoint crystallographic motifs, which are favorable for the emergence of superconducting state? |
Wednesday, March 4, 2020 3:18PM - 3:30PM |
P56.00005: Revealing the intrinsic properties of the heavy-fermion superconductor UBe13 Primoz Kozelj, Ulrike Stockert, Markus Koenig, Andreas Leithe-Jasper, Yuri Grin, Elena Hassinger, Eteri Svanidze Even though UBe13 was one of the first reported heavy-fermion superconductors, it continues to receive a considerable amount of attention due to its unconventional ground state [1 - 3]. While single crystals of UBe13, grown out of Al flux, have been available early on [1], it was recently shown that their physical properties are highly affected by the Al incorporation into the lattice [4]. Even though the amount of Al atoms in the UBe13 structure is rather small (< 1 - 2 at. %), it leads to dramatic changes in the physical properties. Our work provides a novel way in which polycrystalline samples of UBe13 can be studied. These samples, which are inherently free of Al inclusions, provide a comprehensive examination of the inherent crystallographic defects both at the atomic- and the micro-scale. We show that these defects have a rather strong influence on the critical temperature Tc, the Sommerfeld coefficient γ, and the size of the specific heat anomaly. |
Wednesday, March 4, 2020 3:30PM - 3:42PM |
P56.00006: Aluminium impurities in single crystals of the heavy-fermion superconductor UBe13 Andreas Leithe-Jasper, Alfred Amon, Eteri Svanidze, Paul Simon, Matej Bobnar, Iryna Zelenina, Marcel Naumann, Primoz Kozelj, Elena Hassinger, Yuri Grin We studied the influence of Al incorporation on the heavy fermion superconductor UBe13 to explain the sample dependence of physical properties. Al which substitutes Be in the crystal structure of flux-grown UBe13 single crystals can be detected by combining X-ray diffraction, nuclear magnetic resonance and X-ray spectroscopy. The minute amounts of Al (1-2 at. %) in the structure are located by atomic resolution transmission electron microscopy. Specific heat measurements complement this study and reveal strong influence of the incorporated Al on the physical properties of UBe13. |
Wednesday, March 4, 2020 3:42PM - 3:54PM |
P56.00007: Generalized Spin Fluctuation Feedback in Heavy Fermion Superconductors Adil Amin, Daniel Agterberg Experiments reveal that the superconductors UPt3, PrOs4Sb12 and U1-xThxBe13 undergo two superconducting transitions in the absence of an applied magnetic field. The prevalence of these multiple transitions suggests a common underlying mechanism. A natural candidate theory which accounts for these two transitions is the existence of a small symmetry breaking field, however such a field has not been observed in PrOs4Sb12 or U1-xThxBe13 and has been called into question for UPt3. Motivated by arguments originally developed for superfluid 3He we propose that a generalized spin fluctuation feedback effect is responsible for these two transitions. In this talk, we show that a phenomenological theory which couples spin fluctuations to superfluidity correctly predicts that a high temperature broken time-reversal superfluid 3He phase can emerge as a consequence. This phenomenological approach is then applied to these three superconductors revealing that this naturally leads to a high-temperature time-reversal invariant nematic superconducting phase, which can be followed by a second transition into a broken time-reversal symmetry phase, as observed. |
Wednesday, March 4, 2020 3:54PM - 4:06PM |
P56.00008: Magnetic Field Dependent Low-Temperature Specific Heat in UCo1-xFexGe Sangyun Lee, Eric Bauer, Filip Ronning, Roman Movshovich We have investigated low-temperature specific heat of UCo1-xFexGe with x spanning a narrow region around the concentration x=0.23 of the purported Ferromagnetic Quantum Critical point (FM QCP), at temperatures from 60 mK to 2 K and in magnetic field up to 9 T. All investigated samples show a rise in specific heat at low temperature when external field is applied, interpreted as being due to the Co nuclear Schottky anomaly, as the magnitude of the low temperature anomaly scales with the Co content. The Schottky anomaly is absent when the external field is zero, and x is close to 0.23, indicating paramagnetic ground state in these samples. The shallow rise of the Sommerfeld coefficient γ= C/T with decreasing temperature for x=0.22 and x=0.23 samples is consistent with previously reported higher temperature specific heat data, which were interpreted as an evidence of an FM QCP. In this talk, we discuss about quantum criticality of UCo1-xFexGe system. |
Wednesday, March 4, 2020 4:06PM - 4:18PM |
P56.00009: Quantum phase transition and superconductivity in ferromagnetic heavy-fermion systems Haoyu Hu, Ang Cai, Qimiao Si Ferromagnetic Kondo lattice systems have been shown to display the phenomenon of Kondo destruction [1], raising the prospect of quantum criticality in ferromagnetic heavy fermion systems in parallel with their antiferromagnetic counterparts [2]. The issue becomes particularly pressing given the recent developments on UTe2. This system shows strong evidence for spin-triplet superconducting pairing and indications of quantum criticality in the normal state [3,4]. In this work, we study a periodic Anderson model with ferromagnetic RKKY interactions. We treat the model within the extended dynamical mean-field theory [5] and solve the self-consistency equations with the continuous-time quantum Monte Carlo method [6]. We present the results on the underlying quantum phase transition and the superconducting pairing correlations, showing that the system has a strong tendency to triplet pairing. |
Wednesday, March 4, 2020 4:18PM - 4:30PM |
P56.00010: Angle Dependence of the Field-Induced Phases in UPt2Si2 Greta Chappell, David E Graf, Kaya Wei, You Lai, William Nelson, Benny Schundelmier, Chris Mann, Ryan Baumbach The low temperature antiferromagnet (TN = 32 K) UPt2Si2 exhibits complex magnetic field-induced phases. Previous studies have established magnetic phase diagrams for applied fields along the a- and c-axes and suggest that the metamagnetic phase transitions (PT) may be associated with an evolution of the Fermi surface [1,2]. Here, we examine the PT angle dependence with RF skin depth and torque magnetometry experiments at temperatures T < 1 K and in fields H < 45 T. We find that AFMI → III evolves with nearly 1/cosθ dependence, III → V is hysteretic and nearly angle independent, and an additional PT in region V that also follows a 1/cosθ dependence. We shall discuss these results and the implications for the metamagnetism in UPt2Si2 and similar uranium-based materials. |
Wednesday, March 4, 2020 4:30PM - 4:42PM |
P56.00011: Field induced phases in UCr2Si2 You Lai, Jonas Diaz, Greta Chappell, Philip Moll, Ryan Baumbach, Ross McDonald In the broader family of (Ln-An)Cr2Si2 (Ln = lanthanide and An = actinide), UCr2Si2 is unique, where the system undergoes a structural (tetragonal to monoclinic) and antiferromagnetic phase transitions at TS = 210 K and TN = 27 K, respectively, and the U ions carry a magnetic moment. Here, we present an extensive study of the behavior in high magnetic fields. We have performed pulsed field torque magnetometry and resistivity measurements on single crystalline samples UCr2Si2 grown first time by molten flux method. Along the crystallographic c axis, at low temperatures, we find a metamagnetic-like transition in fields of the order 10 T, possibly indicating a first-order transition, the field induced phase transition moves to higher field and reaches maximum while the field is along the <101> diagonal of the tetragonal lattice. From our analysis of the data we can distinguish new high-field phases above the AFM ground state, which indicate the UCr2Si2 is possibly similar to what is seen for URu2Si2 and UPt2Si2, where the emergence of these new phase is due to the Fermi surface effects. |
Wednesday, March 4, 2020 4:42PM - 4:54PM |
P56.00012: Spectroscopic investigation of UFe2Si2, URu2Si2, UNi2Si2, and UPd2Si2: from Pauli paramagnetism to antiferromagnetism via the hidden order state. Andrea Severing, Andrea Amorese, Martin Sundermann, Maurits Haverkort, Yingkai Huang, Maria Szlawska, Dariusz Kaczorowski, Ran Sheng, M Brian Maple, Eric Bauer, Andreas Leithe-Jasper, Liu Tjeng We have carried out hard x-ray photoelectron spectroscopy (HAXPES) measurements at the U 4f core level and non-resonant inelastic x-ray scattering (NIXS) at the U O4,5 edge of UT2Si2 compounds that all form in the tetragonal ThCr2Si2 structure but exhibit different ground state properties: UFe2Si2 is a Pauli paramagnet; URu2Si2 is the famous hidden order compound of which the order parameter is still fiercely debated despite 30 years of intense experimental and theoretical studies [1]; UPd2Si2 and UNi2Si2 are antiferromagnets with TN well above 100 K and sizeable ordered magnetic moments [2]. |
Wednesday, March 4, 2020 4:54PM - 5:06PM |
P56.00013: Origin of the gap-like behavior in pure and doped URu2Si2 : A combined study via quasiparticle scattering spectroscopy and resistivity measurements Shengzhi Zhang, Greta Chappell, Ryan Baumbach, Naveen Pouse, M Brian Maple, Laura Greene, Wan Kyu Park Using Quasiparticle scattering spectroscopy (QPS), we track the temperature dependence of the hybridization gap in URu2-xFexSi2 and URu2Si2-xPx (URSP) [1,2,3] in all substitutions, whether the hidden order (HO) appears or not. This poses a challenge to the Fermi surface gapping scenario, due to the absence of drastic changes in the conductance spectra across the HO transition. As an alternative way to explain the gap-like behavior, we adopt a model based on gapped bosonic excitations in the ordered state [4]. With an unusual temperature dependence of their stiffness, the temperature-dependent resistivity can be reproduced well including the jump at the HO transition. The extracted gap increases with increasing Fe-content, which agrees with the behavior of the E1 gap in inelastic neutron scattering under pressure. This implies that the E1 gap might originate from the same gapped bosonic excitations. |
Wednesday, March 4, 2020 5:06PM - 5:18PM |
P56.00014: Structural studies of Fe-doped URu2Si2 near the hidden order transition using X-ray crystallography Xiaolan Sun, John A Mydosh, Naveen Pouse, M Brian Maple, Sangjun Lee, Peter Abbamonte The origin of hidden order (HO) in URu2Si2 has been debated for the past thirty years. An interesting observation in recent years is the phase transition into a large moment antiferromagnetic (LMAF) state under either high pressure or Fe substitution for Ru. We used low-temperature x-ray crystallography to study the structure of URu2Si2, both with and without Fe doping. We observed changes in the intensities of the Bragg peaks suggesting the HO transition is associated with a breaking of spacegroup symmetry not accompanied by a change in lattice parameters. The pattern of atomic displacements changes markedly when crossing into the LMAF phase via Fe doping. No structural superlattice reflections were observed, consistent with past studies. We will discuss how our results constrain the subgroups and physical origin of the HO and LMAF phases. |
Wednesday, March 4, 2020 5:18PM - 5:30PM |
P56.00015: Magnetostriction of URu2-xFexSi2 in High Magnetic Fields Alexander Breindel, Sheng Ran, Naveen Pouse, Inho Jeon, Marcelo Jaime, M Brian Maple URu2Si2 is a compound of great interest due to its hidden order (HO) phase whose order parameter has remained a mystery for more than three decades. It has been discovered that the substitution of Fe for Ru produces a transition from the HO to an antiferromagnetic (AFM), similar to what occurs under the application of pressure. This provides an opportunity to study URu2Si2 in both the HO and AFM phases at atmospheric pressure using experimental techniques that cannot readily be performed under pressure. In that vein, we conducted high field magnetostriction measurements on URu2-xFexSi2. Our results support the findings of other high field measurements on URu2-xFexSi2. However, we do not see a signature of the HO transition in our data, suggesting that our probe is not sensitive to the HO transition. |
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