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 A29: UTe2 and Actinide Heavy Fermion Materials |
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Sponsoring Units: DCMP Chair: Ravhi Kumar, University of Illinois at Chicago Room: Room 221 |
Monday, March 6, 2023 8:00AM - 8:12AM |
A29.00001: Thermal transport studies of the superconducting state of uranium ditelluride Ian M Hayes, Tristin E Metz, Yun Suk Eo, Shanta Saha, Corey E Frank, Sheng Ran, Nicholas P Butch, Johnpierre Paglione The superconducting state of uranium ditelluride (UTe2) has become the focus of considerable experimental effort as a testbed for the physics of spin-triplet superconductivity. A key open question it the exact nature of the gap structure, including the type, number, and location of nodes. In this talk I will present data on the thermal conductivity of UTe2 in both the superconducting and normal state for a series of samples with different normal state scattering rates. Then I will discuss the possible locations of point nodes in light of these data, in particular in light of the zero-temperature behavior of the thermal transport for heat applied along each of the three crystal axes in a variety of magnetic field orientations. Finally, I will examine the possible implications of these data for the pairing interaction in UTe2. |
Monday, March 6, 2023 8:12AM - 8:24AM |
A29.00002: The Implications of Recent High Field Measurements on the Phase Diagram of Superconducting Uranium Ditelluride Gicela G Saucedo Salas, Corey E Frank, Sylvia K Lewin, John C Collini, Johnpierre Paglione, Nicholas P Butch Paramagnetic uranium ditelluride (UTe2) was recently identified as candidate for a spin-triplet superconductivity. The upper critical field exceeds the Pauli limit at every field orientation, with superconductivity persisting to a remarkable 10x the Pauli limit for H||b. Even more remarkably, in the field polarized state, a separate high field superconducting phase is found when field is offset about 30 degrees between b and c. Other evidence for a topologically non-trivial superconducting state include a point node gap structure, chiral surface modes that develop within the superconducting gap, and broken time reversal symmetry as indicated by the polar Kerr effect. Finally, I will describe recent high field electrical and magnetic measurements on superconducting UTe2, and discuss them in the context of other topologically nontrivial heavy fermion superconductors. |
Monday, March 6, 2023 8:24AM - 8:36AM |
A29.00003: Exploration of the High Field Properties of Heavy Fermion UTe2 Corey E Frank, Sylvia K Lewin, Gicela G Saucedo Salas, Nicholas P Butch Unconventional superconductivity in uranium ditelluride has elicited a great deal of interest since first reported in 2019. The upper critical field exceeds the Pauli limit in all directions, with superconductivity persisting to up to 34.5 T when H || b, the magnetic hard axis. Above 40 T, when H is tilted approx. 30o in the bc plane, a high field superconducting phase develops, which itself persists to at least 65 T. These remarkable properties indicate UTe2 to be a spin triplet superconductor, wherein one or all of the superconducting phases exhibit a topologically non-trivial wavefunction. Moreover, recent STM investigations into the low field superconducting phase evidenced chiral edge states in the superconducting gap, suggesting UTe2 as a candidate platform for the realization and manipulation of elusive Majorana edge modes. In this talk, I will discuss some of the high field properties of superconducting UTe2, focusing primarily on resistivity measurements at various angular offsets from b. |
Monday, March 6, 2023 8:36AM - 8:48AM |
A29.00004: N-point model for the Hidden Order phase of URu2Si2 Jonathan D Denlinger, Jeongsoo Kang, Lenart Dudy, James W Allen, Lewis A Wray, Andrew Gallagher, Ryan E Baumbach, Nicholas P Butch, M Brian Maple The 5f heavy fermion system of URu2Si2 is famous for an unconventional hidden order (HO) phase transition at T0=17.5K and the various related doping phase diagrams explored to elucidate the nature of this unknown transition. A new model of an extended U 5f saddle-point dispersion at the N-point is proposed for the underlying physics of this 35-year old puzzle. With a 10X DFT energy renormalization suggested by angle resolved photoemission (ARPES) measurements [1], this feature lies only a few meV below EF, and thus is thermally active at T0. ARPES reveals a distinct temperature-dependent evolution of incommensurate 5f nesting hotspots lying along Z-N-Z [1], whose origins are found in electronic susceptibility calculations of intraband q-scattering for thermal occupations in the temperature range of T0. Tuning of the N-point region f-band energetics with chemical doping is proposed to unify our understanding of the various phase diagrams, and ARPES confirms the existence of N-point spectral and dichroic changes for ferromagnetic Re/Ru-substitution, for (001) antiferromagnetic Fe and Os/Ru-substitution, and for (1/2,1/2,1/2) antiferromagnetic P/Si-substitution. |
Monday, March 6, 2023 8:48AM - 9:00AM |
A29.00005: Transport properties of strongly correlated compounds AnPd3 (An = Pu, Np) Krzysztof Gofryk, Jean-Christoph Griveau, James L Smith Actinides are characterized by the coexistence of localized and itinerant (delocalized) 5f-states near the Fermi energy. This dual nature of the 5f electrons leads to many exotic phenomena that are observed in these strongly correlated materials, spanning magnetic ordering, heavy-fermion ground state, unconventional superconductivity, and/or a "non-Fermi liquid" state. The unusual transport properties of the strongly correlated electron systems are related to the formation, near the Fermi level, of a narrow band with a large density of states. Therefore, the Seebeck coefficient in these materials, being proportional to the density of states at the Fermi level, often reaches large values and shows the characteristic temperature dependence [Phys. Rev. B 94, 195117 (2016)]. To explore the influence of electronic correlations on the transport properties in the AnPd3 system, here we present low-temperature electrical resistivity and Seebeck coefficient measurements of NpPd3 and PuPd3 intermetallics. We show that the electrical resistivity shows characteristic behavior of systems with Kondo interactions. The magnitude and overall temperature dependence of the thermoelectric power of NpPd3 and PuPd3 are characteristic of 4f- and 5f-electron strongly correlated materials. For cubic NpPd3 a sharp transition and change of sign in S(T) at the Néel temperature indicate a first-order nature of the magnetic transition, probably accompanied by a large change in the Fermi surface topology. We have also estimated the power factor (S2/ρ) of these materials. |
Monday, March 6, 2023 9:00AM - 9:12AM |
A29.00006: Probing the field-polarized state of UTe2 Sylvia K Lewin, Corey E Frank, Sheng Ran, John Singleton, Laurel E Winter, Nicholas P Butch With field along the b axis of uranium ditelluride (UTe2), the system undergoes a metamagnetic transition at approximately 35 T. When field is tilted roughly 30 degrees from the b axis in the bc plane, an extremely high-field superconducting phase exists above the metamagnetic transition. Characterizing the field-polarized state of UTe2 is an important step in understanding the superconducting state that it hosts. In this talk, I will share the results of recent pulsed-field measurements in which we explored how the metamagnetic transition evolves as applied field is tilted away from the b axis. I will discuss what these results can tell us about the field-polarized state of UTe2. |
Monday, March 6, 2023 9:12AM - 9:24AM |
A29.00007: Identifying f-electron valence and correlations in UTe2 with O-edge resonant inelastic X-ray scattering Shouzheng Liu, Yishuai Xu, Erica Kotta, Lin Miao, Sheng Ran, Johnpierre Paglione, Nicholas P Butch, Jonathan D Denlinger, Yi-De Chuang, L. Andrew Wray The recent discovery of spin-triplet superconductivity emerging from a non-magnetic parent state in UTe2 has stimulated great interest in the underlying mechanism of Cooper pairing. For the electron configuration of uranium in UTe2, there is an active debate between 5f26d1-based models with singlet crystal field states versus 5f3-based models that predict atomic Kramers doublets and much greater 5f itinerancy. I will present resonant inelastic X-ray scattering (RIXS) and X-ray absorption spectroscopy (XAS) measurements, comparing with our atomic multiplet-based modeling. The XAS and RIXS data are found to agree strongly with predictions for a 5f26d1-like valence electron configuration with weak intra-dimer magnetic correlations, and provide a new context for interpreting recent investigations of the electronic structure and superconducting pairing mechanism. |
Monday, March 6, 2023 9:24AM - 9:36AM |
A29.00008: High Pressure Resonant Inelastic X-ray Scattering (RIXS) and Diffraction studies on UTe2 Camilla M Moir, Yuhang Deng, Eric J Lee-Wong, Ravhi Kumar, Changyong Park, Yuming Xiao, Paul Chow, Russell J Hemley, Ryan E Baumbach, M Brian Maple The spin-triplet superconductor UTe2 [1] has quickly become a ‘hot topic’ in condensed matter physics due to the discovery of re-entrant superconductivity at high magnetic fields [2] One area of interest concerning UTe2 and its family of substitutions includes quantum criticality and other phenomena under pressure. Previous studies have found evidence of quantum criticality and spin triplet behavior at pressures up to 2 GPa [3], however the U-valence and structural behavior at high pressures have not yet been fully explored. We have synthesized single crystals of UTe2 by chemical vapor transport (CVT) and characterized them by powder x-ray diffraction (XRD), resistivity, specific heat, magnetization. Here I will present the findings of resonant inelastic x-ray scattering and XRD measurements conducted under high pressures up to 50 GPa. |
Monday, March 6, 2023 9:36AM - 9:48AM |
A29.00009: Dynamic magnetotropic coefficient measurements in UTe2 Amit Nathwani, Valeska Zambra, Muhammad Nauman, Kimberly Modic, Arkady Shekhter, Brad J Ramshaw A class of widely studied strongly-correlated materials are heavy fermion systems. These display a rich array of |
Monday, March 6, 2023 9:48AM - 10:00AM |
A29.00010: Complex magnetism in novel intermetallic compound UAgBi2 Gabriel Silva Freitas, Clement Girod, Pascoal Pagliuso, Joe D Thompson, Sean Thomas, Priscila Rosa In this work, we report the structural and physical properties of the newly synthesized UAgBi2 intermetallic compound. UAgBi2 crystallizes in a tetragonal HfCuSi2-type structure (space group P4/nmm), which presents a stacking arrangement of UBi-Ag-UBi-Bi layers. Magnetic susceptibility (c) and magnetization measurements show clear evidence for a complex magnetic structure and multiple competing exchange interactions that give rise to a cascade of field-induced transitions. Curie-Weiss (CW) fits to c(T) provide an effective magnetic moment of μeff = 3.4 µB/U with an antiferromagnetic CW temperature θCW = -2.5 K for magnetic fields applied along the c axis (magnetic easy axis), and a ferromagnetic θCW = 75 K when the magnetic field is applied parallel to the ab plane. Two antiferromagnetic-like anomalies are observed in c(T) at TN1 = 68 K and TN2 = 65 K only when the magnetic field is applied parallel to the c axis. In addition, a hysteretic anomaly is observed around TM3 = 25 K for both directions of the applied magnetic field. We will discuss specific heat, electrical resistivity, Hall effect, and thermal expansion measurements in light of crystalline electrical field effects and competing magnetic interactions to understand the intricate magnetic ground state of UAgBi2. |
Monday, March 6, 2023 10:00AM - 10:12AM |
A29.00011: Self-irradiation Damage in α-Uranium: an Ab Initio Study Kashi Subedi N Subedi, Roxanne M Tutchton The α phase is a stable isotope of uranium at low temperatures (below 934 K) and has highly asymmetric face-centered orthorhombic structure. Understanding the radiation damage in α-uranium (α-U) is of central importance to modeling the behavior of uranium-based fuels. Threshold displacement energy (TDE) is regarded as one of the fundamental quantities to study the radiation damage in materials. The TDE is used in radiation damage theory within Kinchin-Pease models or NRT equations to estimate the number of displacements per atom over the extended time. It is therefore critical to determine the accurate values of the TDE to quantify the radiation damage. The classical molecular dynamics based on empirical potentials are unable to reliably capture the interatomic forces and fail to model lattice defects and recovery. So, in this work, we use ab initio molecular dynamics (AIMD) to perform primary-knock-on-atom (PKA) simulations in α-U along different crystallographic directions. We then determine the accurate values for the TDE along the studied directions and calculate the average TDE. We also study the evolution of the local structure in α-U for varying PKA energies. |
Monday, March 6, 2023 10:12AM - 10:24AM |
A29.00012: NMR study of spin polarized and superconducting phases of UTe2 in high magnetic fields Riku Yamamoto, Michihiro Hirata, Phurba Sherpa, Joe D Thompson, Filip Ronning, Sean Thomas, Eric D Bauer, Priscila Rosa, Arneil P Reyes, Stuart E Brown The candidate triplet superconductor UTe2 shows a unique interplay of magnetism and superconductivity (SC). Unlike other U-based ferromagnetic superconductors, it does not magnetically order. Superconductivity onsets at TC ~ 2.0 K, coexisting with antiferromagnetic (AFM) fluctuations and a large internal magnetic field (H) distribution. At a high-H of Hm = 35 T, it shows a metamagnetic transition into a fully polarized state for H||b, and for a tilted H orientation (~20-40o from H||b to H||c) above 40 T, an unusual reentrant superconducting state appears within the polarized phase, which suggests a close relationship between SC and magnetism. However, knowledge of local magnetic anisotropy and fluctuations is still lacking. To better understand these high-H polarized and superconducting states, we performed 125Te nuclear magnetic resonance (NMR) experiments in the 125Te-enriched single crystal of UTe2 at field strengths near to, and greater than Hm. We will show our results of static and dynamic spin susceptibility measurements at high H and discuss the microscopic nature of reentrant superconducting phase. We will also analyze the possible relevance, as suggested recently, between the high-H states above Hm and the (low-field) high-pressure states above a critical pressure Pc = 1.5 GPa where magnetically ordered phases, which seem to be AFM, are stabilized. |
Monday, March 6, 2023 10:24AM - 10:36AM |
A29.00013: Characterising the magnetic anisotropy of UTe2 Valeska Zambra, Amit Nathwani, Muhammad NAUMAN, Kimberly Modic, Brad Ramshaw, Arkady Shekhter Unconventional superconductors could play a crucial role in developing topological quantum computing. A potential component for this development are spin-triplet superconductors, which are characterised by electron pairs with an odd wave function in a spin-1 state. Helium-3 is the only known realisation of this state, calling for a search of bulk materials that can host spin-triplet superconductivity. UTe2, a heavy-fermion that superconducts at 1.6 K [1], has emerged as a promising candidate [2]. However, the two zero-field superconducting transitions that have been taken as evidence for a two-component order parameter [3] have recently been related to sample inhomogeneities [4]. |
Monday, March 6, 2023 10:36AM - 10:48AM |
A29.00014: Possible coexistence of antiferromagnetic and ferromagnetic spin fluctuations in UTe2 revealed by 125Te NMR under pressure Devi Vijayan Ambika, Qing-Ping Ding, Khusboo Rana, Corey E Frank, Elizabeth L Green, Sheng Ran, Nicholas P Butch, YUJI FURUKAWA UTe2 is a newly discovered heavy-fermion superconductor proposed to be an end member of the U-based ferromagnetic (FM) superconductors. The spin-triplet superconducting state in UTe2 mediated by FM spin fluctuations has been proposed by muon spin relaxation and nuclear magnetic resonance measurements (NMR). Recently, neutron scattering measurements detected the presence of antiferromagnetic (AFM) spin fluctuations in UTe2. In this study, we carried out 125Te NMR measurements on a single crystal UTe2 to investigate the evolution of magnetic fluctuations in UTe2 under pressure. From the temperature dependence of 125Te spin-lattice relaxation rates, we propose the possible coexistence of AFM and FM spin fluctuations in the system. In addition, owing to the two different Te sites in the compound, the FM spin fluctuations are considered to exist within the ladders, while the AFM spin fluctuations originate from the inter-ladder magnetic coupling. We point out that although the AFM spin fluctuations exist in the system, the FM spin fluctuations in the ladders may play a more important role in the appearance of the spin-triplet superconducting state of UTe2. |
Monday, March 6, 2023 10:48AM - 11:00AM |
A29.00015: Large cluster DCA study of the Mott metal-insulator transition in two dimensions Hanna Terletska, Sergei Iskakov, Thomas A Maier, Emanuel C Gull The problem of the Mott metal-insulator transition (MIT) in the 2D Hubbard model has recently come under renewed scrutiny. In particular, the fate of the Mott MIT in the presence of long-range nonlocal spatial correlations remains unclear. With recent advances in numerical tools, it has been shown that non-local spatial effects are very strong in this system, and neglecting them may dramatically modify the phase diagram of MIT. With high-performance computing and advanced numerical methods, we access large system sizes and low temperatures to perform detailed large cluster calculations of the Mott MIT in 2D Hubbard model using DCA. We observe a very strong cluster size dependence of the phase boundaries of the Mott MIT, consistent with the recent Quantum Monte Carlo results. |
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