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 W27: Superconductivity:Heavy Fermions |
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Sponsoring Units: DCMP Chair: Kalyan Sasmal, Department of Physics, University of California, San Diego. Room: Room 219 |
Thursday, March 9, 2023 3:00PM - 3:12PM |
W27.00001: Fermi surface study of the putative spin-triplet superconductor UTe2 Alexander G Eaton, Zheyu Wu, Alexander J Hickey, Theodore I Weinberger, Michal Valiska The unconventional superconductor UTe2 exhibits numerous properties indicative of spin-triplet pairing, including an upper critical field far in excess of the Pauli paramagnetic limit, and re-entrant superconductivity at high magnetic fields > 40 T. However, a detailed understanding of the material's Fermi surface remains a key open question hampering efforts to attain a more detailed theoretical picture of the microscopic pairing mechanism(s) at play. |
Thursday, March 9, 2023 3:12PM - 3:24PM |
W27.00002: Brief overview of exotic Chiral Spin-triplet Correlated Topological Superconductor UTe2: Synthesis, Structure, Physical and Magnetic properties. Kalyan Sasmal, Chunruo Duan, Andrey Podlesnyak, Jian-Xin Zhu, Qimiao Si, Pengcheng Dai, Brian Maple Topological superconductivity has attracted great interest in condensed matter physics because of its potential applications in quantum computing. Spin-triplet superconductors are one promising class that can host the topological excitations and Majorana fermions relevant for quantum computation, but the experimental realizations are very few for intrinsic spin-triplet superconductors in ambient solids Candidates (e.g. UCoGe, UPt3, Sr2Ru04). Heavy fermion paramagnet UTe2 have orthorhombic structure , space group Immm and is related to known ferromagnetic superconductors such as UGe2, URhGe, and UCoGe.The huge upper critical field of UTe2 exceeding the Paul limit for all field directions suggests of having the spin-triplet state. Spin-triplet pairing is usually mediated by ferromagnetic spin fluctuations. UTe2 is a candidate for novel chiral spin-triplet odd parity superconductivity with Tc=1.7 K near a ferromagnetic instability, although it also has antiferromagnetic spin fluctuations. The large specific heat jump at Tc=1.7 K indicates a strong coupling superconductor. The normal state of UTe2 holds Kondo like heavy-fermion physics, strong magnetic fluctuations, anomalous low-temperature phases and quantum-critical behavior. Superconductivity in UTe2 dramatically differs from conventional superconductivity that spontaneously break time-reversal symmetry, the intertwined order and having nodes that are not dictated by symmetry - but are topologically protected with multiple distinct superconducting phases in the pressure-field space, as well as exotic magnetic field-boosted reentrant phases. Unusual superconducting properties seem to be driven by antiferromagnetic spin fluctuations. So, antiferromagnetic spin fluctuations may also induce spin-triplet pairing or that electron pairing in UTe2 has a spin-singlet component. I will discuss underlying crystal structure, normal and superconducting state properties of UTe2 - and their relations to the electronic band structure and magnetic correlations. |
Thursday, March 9, 2023 3:24PM - 3:36PM |
W27.00003: Fully gapped pairing state in spin-triplet superconductor UTe2 Shota Suetsugu, Masaki Shimomura, Masashi Kamimura, Tomoya Asaba, Hiroto Asaeda, Yuki Kosuge, Yuichi Kasahara, Hironori Sakai, Petr Opletal, Yoshifumi Tokiwa, Yoshinori Haga, Yuji Matsuda Spin-triplet superconductors provide an ideal platform for realizing topological superconductivity with emergent Majorana quasiparticles. The promising candidate is the recently discovered superconductor UTe2. However, the symmetry of the superconducting order parameter remains highly controversial. Here we investigate the superconducting gap structure by the thermal conductivity of ultra-clean UTe2 single crystals with an extremely high residual resistivity ratio over 200. In zero field, the residual thermal conductivity κ/T (T → 0) vanishes, indicating the absence of line nodes. In stark contrast to previous results of thermal conductivity and penetration depth, the thermal conductivity in magnetic fields H in zero temperature limit is vanishingly small for both H//a and H//c up to 60% of upper critical fields. These results provide evidence for the absence of the point nodes, i.e. fully gapped superconductivity. Provided that Fermi surface is present along the c axis direction, the superconducting order parameter most likely belongs to the Au representation, reminiscent of the B phase of superfluid 3He. These findings suggest that UTe2 is a long-sought three-dimensional (3D) strong topological superconductor characterized by a nontrivial 3D winding number, hosting helical Majorana surface states on any plane. |
Thursday, March 9, 2023 3:36PM - 3:48PM |
W27.00004: Electronic Structure of Unconventional Superconductor YFe2Ge2 studied by ARPES Rafal Kurleto, Cheng-Hsun Wu, Dushyant M Narayan, Bryan S Berggren, Peipei Hao, Amanda Shackelford, Makoto Hashimoto, Donghui Lu, Jiasheng Chen, Friedrich M Grosche, Swagata Acharya, Mark van Schilfgaarde, Daniel S Dessau YFe2Ge2 is a new unconventional superconductor with a critical temperature equal to 1.8 K [1]. Enhanced value of the Sommerfeld coefficient (γ = 100 mJ/mole K2) suggests significance of electron correlations in this material. Departure from the Fermi liquid behavior is visible in temperature dependency of electrical resistivity which follows a power law: ρ∼T3/2. These facts, together with a presence of large fluctuating moments in paramagnetic phase (μFe ≈ 1 μB), suggest that YFe2Ge2 is as quantum critical metal governed by Hund’s coupling. |
Thursday, March 9, 2023 3:48PM - 4:00PM |
W27.00005: Ultrasound Studies on the Unconventional Superconductor UTe2 Florian Theuss, Gael Grissonnanche, Avi Shragai, Ian M Hayes, Shanta Saha, Nicholas P Butch, Johnpierre Paglione, Sheng Ran, Brad J Ramshaw The unconventional spin-triplet superconductor UTe2 has fascinated the condensed matter community since its discovery in 2019. Many intriguing properties like a giant upper critical field, unconventional magnetism, field-reinforced and reentrant superconductivity, and multiple superconducting phases under pressure have been discovered in the meantime. However, even the zero field and ambient pressure superconducting ground state is not yet understood. Investigations into this part of the phase diagram are complicated, since exact details vary significantly between different samples. For example, samples exist with a single superconducting transition at ambient pressure, but also with two successive transitions, similar to the experiments under hydrostatic pressure. We measure the full elastic tensor of both one and two transition samples using resonant ultrasound spectroscopy to study the symmetry of the superconducting order parameter, as well as to determine possible origins of this stark sample dependence. We find discontinuities at Tc in all compressional moduli, with an especially large jump in c33, implying a particular sensitivity of superconductivity to deformations along the c axis. |
Thursday, March 9, 2023 4:00PM - 4:12PM |
W27.00006: Thermodynamic evidence for the anisotropic field-induced change of the superconducting order parameter in the chiral superconductor candidate UTe2. Andrew J Woods, Sangyun Lee, Priscila Rosa, Sean Thomas, Eric D Bauer, Shizeng Lin, Roman Movshovich UTe2 is an unconventional superconductor widely believed to host a spin-triplet ground state. We present measurements of the specific heat C(H, T) of a high-quality single crystal sample of UTe2 at low temperature (70 mK < T < 2 K) and with magnetic fields to 12 T applied along the three principal crystallographic axes. |
Thursday, March 9, 2023 4:12PM - 4:24PM |
W27.00007: Axis-resolved electrodynamic properties and low energy excitations of UTe2 Arthur L Carlton-Jones, Braden Larsen, Alonso Suarez, Yun-Suk Eo, Ian M Hayes, Shanta Saha, Johnpierre Paglione, Nicholas P Butch, Peter Y Zavalij, Steven M Anlage The complex surface impedance of a superconductor provides many insights into its properties, such as the pairing mechanism, super- and normal-fluid responses, Fermi surface, and possibly its topological properties. We explore the surface impedance of UTe2 single crystals as a function of temperature using resonant cavity measurements for a variety of microwave-frequency modes. We determine a composite surface impedance for each mode using resonance data combined with the independently measured normal state dc resistivity tensor. We are able to determine the combination of crystallographic directions excited in each mode using the anisotropy of the resistivity. Studying several modes yields the surface impedance corresponding to each axis. We find approximately a T2 power-law dependence for the magnetic penetration depth in both the a- and c-directions, which is inconsistent with a single pair of point nodes on the Fermi surface. We find the zero temperature penetration depth to be largest for the c-direction, which is consistent with current understanding of the Fermi surface shape. The surface resistance demonstrates a relatively large residual loss at zero temperature, and the c-direction is the most lossy. We compare to theoretical expectations of the electrodynamic properties of topological superconductors. |
Thursday, March 9, 2023 4:24PM - 4:36PM |
W27.00008: Detection of a Pair Density Wave State in UTe2 Qiangqiang Gu, Joseph Carroll, Shuqiu Wang, Sheng Ran, Christopher Broyles, Hasan Siddiquee, Nicholas P Butch, Shanta Saha, Johnpierre Paglione, Seamus Davis, Xiaolong Liu UTe2 is a promising candidate material to embody bulk topological superconductivity due to spin-triplet pairing. Moreover, the newly discovered CDW state coexisting with superconductivity in UTe2 motivates the exciting prospect that a PDW state may occur. To search for a PDW in UTe2, we visualize the pairing energy-gap with μV-scale energy resolution made possible by superconductive STM tips at subkelvin temperatures. We detect three PDWs, each with gap modulations circa 10 μeV and at incommensurate wavevectors that are indistinguishable from the wavevectors of the prevenient CDW, but with a π spatial-phase difference. From these observations and given UTe2 as a spin-triplet superconductor, this PDW may presage spin-triplet pair density wave physics. |
Thursday, March 9, 2023 4:36PM - 4:48PM |
W27.00009: AC magnetic-susceptibility studies on superconducting UTe2 Ajeesh Mukkattu Omanakuttan, Sean Thomas, Joe D Thompson, Boris A Maiorov, Priscila Rosa UTe2 has recently attracted enormous attention as a spin-triplet superconductor candidate. Several intriguing properties have been observed in UTe2, such as multiple pressure-induced superconducting and magnetic phases as well as re-entrant superconductivity under applied magnetic field [1]. Importantly, the superconducting properties of UTe2 at ambient conditions crucially depend on the details of crystal growth. For instance, both the superconducting transition temperature and the residual specific heat coefficient drastically vary among crystals grown in different conditions despite having very similar structural properties [2-4]. Here, we investigate UTe2 samples with a range of values of Tc using ac magnetic-susceptibility measurements, which reveal the vortex dynamics in the superconducting state. We also re-visit the pressure-temperature phase diagram of UTe2 by means of ac magnetic-susceptibility measurements under hydrostatic pressure and investigate pressure-induced superconducting and magnetic phases in the vicinity of the critical pressure. |
Thursday, March 9, 2023 4:48PM - 5:00PM Author not Attending |
W27.00010: Pressure study on heavy fermion superconductor CeRh2As2 Hasan Siddiquee, Christopher Broyles, Zack Rehfuss, Sheng Ran In the recently discovered heavy fermion superconductor CeRh2As2, a phase transition induced by magnetic field has been observed inside the superconducting state, which is proposed to be a transformation from a even-parity to odd-parity superconducting state. The odd-parity superconducting state and its large upper critical field have been explained based on local inversion symmetry breaking and consequent Rashba-like spin-orbit coupling. The normal state of CeRh2As2 exhibit non-Fermi-liquid behavior, indicating that it is close to a quantum critical point. Revealing the quantum critical point via tunning parameters such as chemical substitution and pressure will shed important light on the pairing mechanism of the odd-parity superconducting state. In this talk we will discuss our recent results on the phase diagram of CeRh2As2 under applied pressure. |
Thursday, March 9, 2023 5:00PM - 5:12PM |
W27.00011: Chiral superconductivity in UTe2 via emergent C4 symmetry and spin-orbit coupling Dmitry Chichinadze, Daniel Shaffer |
Thursday, March 9, 2023 5:12PM - 5:24PM |
W27.00012: Multiorbital spin-triplet pairing and spin resonance in the heavy-fermion superconductor UTe2 Lei Chen, Haoyu Hu, Christopher A Lane, Emilian M Nica, Qimiao Si UTe2 is a candidate spin-triplet superconductor. Among the outstanding issues is the nature of the pairing state. A recent surprising discovery is a resonance in the spin excitation spectrum at an antiferromagnetic (AF) wavevector [1], which stands in apparent contrast to the expected ferromagnetic nature. Here [2], we advanced a theoretical resolution to these seemingly contradictory issues by considering a multiorbital spin-triplet pairing constructed from the dimer of U ions in the unit cell. Because it does not commute with the kinetic part of the Hamiltonian, the pairing function contains both intra- and inter- band terms in the band basis. We demonstrate the existence of a spin resonance at the AF wavevector. Our work illustrates how orbital degrees of freedom can enrich the nature and properties of spin-triplet superconductivity in general. |
Thursday, March 9, 2023 5:24PM - 5:36PM |
W27.00013: Triplet Pair Density Waves in UTe2 Julian May-Mann, Eduardo H Fradkin, Anuva Aishwarya, Vidya Madhavan, Laimei Nie It was recently discovered that charge density wave (CDW) order also occurs in the superconducting phase of uranium ditelluride (UTe2). Unexpectedly, in the presence of an external magnetic field, the CDWs are suppressed and disappear above the superconducting upper critical field of UTe2. In this talk, we show that the behavior of the CDWs is explained by the existence of spin-triplet pair-density waves (PDWs) that coexist with the uniform spin-triplet superconductivity of UTe2. The combination of PDWs and uniform superconductivity gives rise to daughter CDWs, and the daughter CDWs inherit the magnetic field sensitivities of the parent PDW and superconducting orders. These results indicate that UTe2 potentially hosts the first known example of a triplet PDW state. |
Thursday, March 9, 2023 5:36PM - 5:48PM |
W27.00014: The low- and high-field superconducting phases of UTe2 Josephine Yu, Srinivas Raghu, Yue YU, Daniel F Agterberg Recent NMR and calorimetric experiments have observed that UTe2 exhibits a transition between two distinct superconducting phases as a function of magnetic field strength for a field applied along the crystalline b-axis. To determine the nature of these phases, we employ microscopic model Hamiltonians inspired by density functional theory. We apply a mean field theory to study the symmetries and properties of these low- and high-field phases. |
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