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 Q43: Novel Topological SuperconductorsFocus
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Sponsoring Units: DMP Chair: Sean Thomas, Los Alamos National Laboratory Room: Room 317 |
Wednesday, March 8, 2023 3:00PM - 3:36PM |
Q43.00001: Axial Higgs Mode from Quantum Geometry and a Charge Density Wave Invited Speaker: Kenneth S Burch The observation of the Higgs boson solidified the standard model of particle physics. However, explanations of anomalies (e.g., dark matter) rely on further symmetry breaking, calling for a yet-to-be-discovered axial Higgs mode. In condensed matter, the Higgs mode has been observed in magnetic, superconducting, and charge density wave systems (CDW), and is typically assumed to have a scalar representation. Uncovering the vector properties of a low energy mode is extremely challenging, requiring going beyond typical spectroscopic or scattering techniques to reveal the hidden aspects of their wavefunctions. Here, we discover an unconventional axial Higgs mode of the charge density wave in the GdTe3. The Axial Higgs mode is revealed using the interference of excitation quantum pathways in Raman scattering. I will discuss how the Axial Higgs mode emerges from the combination of the quantum geometry of the Fermi surface and the charge density wave, opening opportunities for new topological-correlated states in 2D systems. Furthermore, this technique can be extended to detect novel topological orders in other CDW and superconducting systems. |
Wednesday, March 8, 2023 3:36PM - 3:48PM |
Q43.00002: Topological Kondo Superconductors Yung-Yeh Chang, Khoe v Nguyen, Kuang-Lung Chen, Chung-Hou Chung Spin-triplet p-wave superconductors are promising candidates for topological superconductors. They have been proposed in various heterostructures where a strong spin-orbit interacting materials is coupled to a conventional s-wave superconductor by proximity effect. However, topological superconductors existing in nature and driven by strong electron correlations is yet to be studied. Here we propose a realization of such system in a class of Kondo lattice materials without proximity effect. Therein, the odd-parity Kondo hybridization mediates ferromagnetic spin-spin coupling and leads to spin-triplet resonant-valence-bond (t-RVB) pairing between local moments. Spin-triplet p ± ip′-wave topological superconductivity is reached when Kondo effect co-exists with t-RVB. We identify the topological nature by the non-trivial topological invariant and the Majorana fermions at edges. Experimental implications of our results on the U -based ferromagnetic heavy-electron superconductors with Kondo correlations, in particular UTe2, is discussed |
Wednesday, March 8, 2023 3:48PM - 4:00PM |
Q43.00003: Grain boundary band structure engineering in a topological superconductor Morten Amundsen, Vladimir Juricic Ubiquitous in all crystalline materials is the presence of grains, within which the crystal lattice is oriented in a certain direction. Neighboring grains do not necessarily align, giving rise to a lattice mismatch at their interface, also known as a grain boundary. This extended lattice defect can consist of an array of edge dislocations, which in topologically non-trivial materials can, in turn, yield bands for momenta along the grain boundary. |
Wednesday, March 8, 2023 4:00PM - 4:12PM |
Q43.00004: Superconductivity in Few-Layer Topological Superconductor Candidate (Sn1-xInx)Bi2Te4 Jack Barlow, Dmitry Ovchinnikov, Chaowei Hu, Jiaqi Cai, Zhaoyu Liu, Jiun-Haw Chu, David H Cobden, Jiaqiang Yan, Michael A McGuire, Xiaodong Xu The combination of a superconducting state with a non-trivial topology of band structures may lead to emerging topological superconductivity. The electronic states of such materials are characterized by the coexistence of bulk supercurrents mediated by Cooper pairs and topologically protected boundary modes. One of the approaches to developing topological superconductors is introducing superconducting components (such as Sn1-xInxTe) into the parent compound lattice of a topological insulator (such as Bi2Te3). In this talk, I will describe our progress in measuring and understanding the superconducting and normal states of the topological superconductor candidate (Sn0.5In0.5)Bi2Te4. In bulk, this material is a layered superconductor with a critical temperature of ~1.5 K, which could be further tuned by material composition. I will demonstrate that superconductivity persists down to the few-layer limit, with a critical temperature comparable to the bulk. I will next discuss critical current measurements in this compound in the superconducting state, as well as non-linear transport measurements above the critical temperature. |
Wednesday, March 8, 2023 4:12PM - 4:24PM |
Q43.00005: Thermodynamic and electrical transport properties of UTe2 under uniaxial stress Clement Girod, Callum R Stevens, Andrew Huxley, Eric D Bauer, Frederico B Santos, Joe D Thompson, Rafael M Fernandes, Jian-Xin Zhu, Filip Ronning, Priscila Rosa, Sean Thomas Despite intense experimental efforts, the nature of the unconventional superconducting order parameter of UTe2 remains elusive. This puzzle stems from reports of either a single or a double superconducting transition at ambient pressure as well as a complex pressure-temperature phase diagram. To address this issue, we measured the heat capacity and electrical resistivity of UTe2 under compressive uniaxial stress applied along different crystallographic directions. We find that the critical temperature Tc of the single observed bulk superconducting transition decreases with stress applied along [100] and [110] but increases with stress along [001]. Aside from its effect on Tc, c-axis stress leads to a significant piezoresistivity. Importantly, an in-plane shear stress σxy does not induce any observable splitting of the superconducting transition over a stress range of σxy ≈ 0.17 GPa. This result suggests that the superconducting order parameter of UTe2 may be single component at ambient pressure. |
Wednesday, March 8, 2023 4:24PM - 4:36PM |
Q43.00006: Searching for ideal topological crystalline insulators and topological superconductors in Pb-Sn-In-Te system Genda Gu The discovery of 3D topological insulator materials and topological superconductor open up a new research field in the condensed matter physics. In order to search for the topological superconductor, we have grown a large number of the single crystals of Pb-system ( Pb-Sn-In-Te) topological crystalline insulator and their topological superconductor . We have measured the physical properties on these single crystals by various techniques. We have studied the effect of crystal growth condition, impurity and composition on the bulk electrical conductivity of these single crystals. We try to find out which composition and crystal growth condition is the best for the ideal topological insulator, topological crystalline insulator and topological superconductor. We have got the bulk topological superconductor with Tc=5K. |
Wednesday, March 8, 2023 4:36PM - 4:48PM |
Q43.00007: A mechanism for time-reversal broken superconductivity in UTe2 Tamaghna Hazra, Pavel Volkov An important open puzzle in the superconductivity of UTe2 is the emergence of time-reversal breaking superconductivity from a non-magnetic normal state. Breaking time-reversal symmetry in a homogenous sample with a single superconducting transition requires the existence of two degenerate superconducting order parameters, which is not natural for the orthorhombic UTe2. |
Wednesday, March 8, 2023 4:48PM - 5:00PM |
Q43.00008: Evaluation of two-component superconductivity in Sr2RuO4 through measurements under uniaxial stress Clifford W Hicks Sr2RuO4 is a famous candidate for two-component superconductivity. In this talk, I will present three contradictions in the evidence on the superconducting order parameter, that have come to light through uniaxial stress measurements. (1) Muon spin rotation measurements show clear stress-induced splitting between the critical temperature and the onset of enhanced muon spin relaxation, following qualitative expectations for two-component order, but no signature of this second transition is resolved in heat capacity under uniaxial stress. (2) Although in-plane uniaxial stress drives a strong increase in the critical temperature, compression along the c-axis suppresses Tc, even though the enhancement in the density of states should be stronger. (3) There is a jump in the shear elastic modulus at Tc, consistent with two-component order, but no corresponding cusp is resolved in the dependence of Tc on uniaxial stress applied along a <110> crystal axis. |
Wednesday, March 8, 2023 5:00PM - 5:12PM |
Q43.00009: Unconventional periodicities of the Little-Parks effect observed in a topological superconductor Yufan Li, Xiaoying Xu, Shu-Ping Lee, Chia-Ling Chien The most distinctive feature of superconductivity is the presence of the complex-valued many-particle wave function that sustains phase coherence over macroscopic distances. One of its experimental manifestations is the fluxoid quantization in a superconducting ring. The single-value nature of the wave function dictates a universal phase change of 2π for any closed path around the ring. As a result, the fluxoid can only take on quantized values in integer steps of Φ0=h/2e, where h is the Planck constant and the denominator of 2e is the signature of electron pairing, which is evidenced by a number of macroscopic quantum phenomena, such as the Little-Parks effect and the Josephson effect, where the critical temperature or the critical current oscillates with the periodicity of Φ0 as has been observed in numerous polycrystalline and epitaixal rings of singlet superconductors of s-wave (e.g., Nb) and d-wave (e.g., cuprates). Here we report the observation of novel Little-Parks oscillation periodicities of 2Φ0, 3Φ0 and 4Φ0, in addition to the conventional Φ0, in mesoscopic rings of epitaxial β-Bi2Pd, a topological triplet superconductor. These unexpected new findings suggest new physics to account for the novel quantizations. |
Wednesday, March 8, 2023 5:12PM - 5:24PM |
Q43.00010: Investigating the crystal field ground state and the limits of superconductivity in UTe2 Priscila Rosa, Ashley Weiland, Mitchell Bordelon, Filip Ronning, Joe D Thompson, Eric D Bauer, Sean Thomas Spin-triplet bulk superconductors are a promising route to topological superconductivity, and UTe2 is a recently discovered contender. The superconducting properties of UTe2, however, vary substantially as a function of the synthetic route, and even nonsuperconducting single crystals have been reported. To understand the driving mechanism suppressing superconductivity, we investigate UTe2 single crystals grown close to the nonsuperconducting boundary (growth temperature ~ 710 oC) through a combination of thermodynamic and x-ray diffraction measurements. Specific heat measurements reveal a sharp decrease in the superconducting volume and a concomitant increase in the residual specific heat coefficient near the nonsuperconducting boundary. Notably, these crystals are inhomogeneous and show an apparent double transition in specific heat measurements, similar to |
Wednesday, March 8, 2023 5:24PM - 5:36PM |
Q43.00011: Dirac lines and loop at the Fermi level in the time-reversal symmetry breaking superconductor LaNiGa2 Valentin Taufour, Jackson R Badger, Yundi Quan, Matthew C Staab, Shuntaro Sumita, Antonio Rossi, Kasey P Devlin, Kelly Neubauer, Daniel S Shulman, James C Fettinger, Peter Klavins, Susan M Kauzlarich, Dai Aoki, Inna M Vishik, Warren E Pickett Unconventional superconductors have Cooper pairs with lower symmetries than in conventional superconductors. In most unconventional superconductors, the additional symmetry breaking occurs in relation to typical ingredients such as strongly correlated Fermi liquid phases, magnetic fluctuations, or strong spin-orbit coupling in noncentrosymmetric structures. In this presentation [J. R. Badger et al. Communications Physics 5, 22 (2022)] [Y. Quan et al. Phys. Rev. B 105,064517 (2022)], I will show that the time-reversal symmetry breaking in the superconductor LaNiGa2 is enabled by its previously unknown topological electronic band structure, with Dirac lines and a Dirac loop at the Fermi level. Two symmetry related Dirac points even remain degenerate under spin-orbit coupling. These unique topological features enable an unconventional superconducting gap in which time-reversal symmetry can be broken in the absence of other typical ingredients. Our findings provide a route to identify a new type of unconventional superconductors based on nonsymmorphic symmetries and will enable future discoveries of topological crystalline superconductors. |
Wednesday, March 8, 2023 5:36PM - 5:48PM |
Q43.00012: Towards an understanding of the intrinsic properties in UTe2 Sean Thomas, Callum R Stevens, Ashley Weiland, Filip Ronning, Eric D Bauer, Joe D Thompson, Andrew Huxley, Priscila Rosa UTe2 has attracted much recent interest as a possible spin-triplet topological superconductor. With improvements in sample quality [1, 2], it has become increasingly important to understand which properties of UTe2 are intrinsic and which arise from disorder or impurities. Here, we show via thermal expansion and specific heat measurements that the double transition in some UTe2 samples arises from sample inhomogeneity [3]. We will also discuss how growing under optimal conditions reliably results in single crystals with both a higher Tc and a single transition [1]. Pressure studies on these improved crystals reveal that the single transition splits into two transitions near 0.3 GPa. For crystals that show a double transition at ambient pressure, we observe a double transition at all superconducting transitions in the phase diagram [4]. This provides further support that the double transition arises from sample inhomogeneity. Finally, we note a correspondence between the residual gamma in specific heat and the superconducting transition temperature, indicating that the residual gamma is likely arising from impurities [3, 5, 6]. |
Wednesday, March 8, 2023 5:48PM - 6:00PM |
Q43.00013: Electronic Structure and Pairing Instability of Heavy-Fermion Superconductor UTe2 Jian-Xin Zhu, Christopher A Lane, Bo Gyu Jang, Filip Ronning, Qimiao Si Spin-triplet superconductors are of extensive current interest because they are promising candidates to host topological states and Majorana fermions for quantum computation. The uranium-based heavy-fermion superconductor UTe2 has recently been argued as a spin-triplet superconductor. However, the nature of the pairing state remains one of the most outstanding issues. Recent observations of antiferromagnetic fluctuations by neutron scattering are at odds with the notion of spin-triplet superconductivity driven by ferromagnetic interactions. In this work, we focus on some salient features of the electronic structure and magnetic properties of the system. In particular, the role of U-5f electron correlations in determining the nature of normal state and magnetic interactions will be elucidated within first-principles approaches. We will also discuss the superconducting pairing instability via a first-principles strongly correlated electron theoretical treatment, and its relationship to the underlying magnetic fluctuations. |
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