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 C49: Fundamental Problems in Strongly Correlated U-Based MaterialsInvited Live
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Sponsoring Units: DCMP Chair: Eteri Svanidze, MPI Chemical Physics of Solids |
Monday, March 15, 2021 3:00PM - 3:36PM Live |
C49.00001: Tuning the electronic state in uranium based strongly correlated electron materials Invited Speaker: Ryan Baumbach Uranium based materials with the ThCr2Si2-type (and related) structure have attracted sustained attention as reservoirs for strongly correlated electron physics and novel ordered states. This includes hidden order and superconductivity in URu2Si2 [1], charge ordering in UPt2Si2 [2], a structural instability in UCr2Si2 [3], and complex magnetism in other examples. Substantial attention has been devoted to understanding what factors lead to these different behaviors, where it has become evident that (i) the hybridization between the f- and conduction electron states is of particular importance and (ii) tuning studies that separately control the unit cell volume and electronic composition are useful for unravelling what factors lead to specific phenomena. In particular, several unifying trends have emerged from a focus on URu2Si2. For example, chemical substitution that qualitatively adds electrons (Si → P and Ru → Rh) produces phase diagrams with shared features, including that hidden order is rapidly destroyed even as the underlying Kondo lattice is preserved. Complex magnetism eventually emerges at large substitutions. In contrast, the removal of electrons (Ru → Re) tends to stabilize ferromagnetism. In this talk we will present results for several chemical substitution studies in URu2Si2, with a focus on bulk thermodynamic and electrical transport measurements and the influence of high magnetic fields and applied pressure. The results from these measurements will be compared to earlier studies and prospects for understanding what factors differentiate regions in the broader U-based ThCr2Si2 family electronic phase diagram will be discussed. |
Monday, March 15, 2021 3:36PM - 4:12PM Live |
C49.00002: Identifying multi-component superconductivity with resonant ultrasound spectroscopyIdentifying multi-component superconductivity with resonant ultrasound spectroscopy Invited Speaker: Brad Ramshaw Superconductors can break time-reversal symmetry (TRS) when their order parameter has two degenerate components, or “representations”—perhaps the most famous example of this is the px+ipy state. Most experiments that investigate TRS-breaking superconductivity look for signatures of magnetism—very few experiments are capable of determining the order parameter degeneracy directly. A discontinuity in a shear elastic modulus at Tc is one of the few direct experimental test for two-component superconductivity, and recent advances in resonant ultrasound spectroscopy (RUS) have allowed us to measure the entire elastic tensor with high precision and at low temperature. Using RUS we have discovered that Sr2RuO4 has a two-component order parameter, even though recent NMR measurements rule out the px+ipy state. This suggests an unconventional {dxz, dyz} order parameter, or perhaps even the accidental degeneracy of dx2-y2 and gxy(x2-y2). We have also investigated the proposed TRS-breaking superconductor UTe2, where heat capacity measurements find two superconducting transitions that suggest two nearly-degenerate order parameters. |
Monday, March 15, 2021 4:12PM - 4:48PM Live |
C49.00003: Topology and Correlations in Actinide Materials Invited Speaker: Filip Ronning 5f-electrons possess both strong electronic correlations and strong spin orbit coupling. This combination suggests that actinides are ideal for discovering new topologically non-trivial phases, which arise as a consequence of strong electronic correlations. For instance, some of the most promising candidates to host majorana modes in a bulk topological superconductor exist in actinides such as UTe2. Similarly, topological insulators with large bulk gaps and renormalized surface states are proposed to exist in materials such as PuB4. In this talk we also highlight the potential for topological effects and correlated states using the metallic ferromagnet UCo0.8Ru0.2Al. Our calculations reveal 148 Weyl nodes and two nodal lines that exist within 60 meV of the Fermi level. Within that context, perhaps it is not surprising that we find an anomalous Nernst effect, which gives rise to a colossal Peltier coefficient, αxy = 18 A/Km, more than four times larger than that found in Co2MnGa. Using U3Ru4Al12 and field angle rotation studies we illustrate that the Berry curvature is highly tunable in these actinide materials. These examples illustrate that exploring the actinide road for new states in topologically non-trivial correlated matter is a promising path. |
Monday, March 15, 2021 4:48PM - 5:24PM Live |
C49.00004: The dual nature of f electrons in the UM2Si2 family with M=Fe, Pd, Ru, and Ni studied with x-ray spectroscopy Invited Speaker: Andrea Severing 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) experiments at the U O4,5 edge of UM2Si2 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 [1]; UPd2Si2 and UNi2Si2 are antiferromagnets with TN well above 100 K and sizeable ordered magnetic moments [2]. |
Monday, March 15, 2021 5:24PM - 6:00PM Live |
C49.00005: The spin-triplet topological superconductor UTe2 Invited Speaker: Nicholas Butch Spin triplet superconductivity is found below 1.6 K in the correlated electron compound UTe2. This state features remarkably anisotropic and large upper critical field values, exceeding 35 T. At even higher magnetic fields, an unprecedented reentrant superconducting phase is stabilized, between 40 T and 65 T. Superconductivity coexists with strong magnetic fluctuations but unlike known uranium-based superconductors, UTe2 shows no evidence of long-range magnetism. However, the superconducting state spontaneously breaks time-reversal symmetry and supports chiral surface states. |
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