Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session G66: Discovery of New Spin-Triplet Superconductivity in Nearly Ferromagnetic UTe2Invited
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Sponsoring Units: DCMP Chair: Johnpierre Paglione, University of Maryland, College Park Room: Four Seasons 1 |
Tuesday, March 3, 2020 11:15AM - 11:51AM |
G66.00001: Spin-triplet superconducting state in the nearly ferromagnetic compound UTe2 Invited Speaker: Sheng Ran Our recent discovery of the novel spin-triplet superconductivity in UTe2 [1] has inspired a lot of interests in the community. Superconducting state of UTe2 closely resembles that of ferromagnetic superconductors, but the normal state is paramagnetic with no indication of magnetic ordering. Unusual properties of Hc2, NMR Knight shift, and specific heat strongly indicate that the superconductivity in UTe2 is carried by spin-triplet pairs. Even more striking, superconductivity reenters in the magnetic field of 45 tesla and persists up to 65 tesla, reflect a new kind of exotic superconductivity rooted in magnetic fluctuations and quantum dimensionality [2]. Application of pressure reveals a two-fold enhancement of this unusual superconductivity, which is closely related to the suppression of Kondo coherence [3]. In this talk, I will review our recent results on UTe2. |
Tuesday, March 3, 2020 11:51AM - 12:27PM |
G66.00002: Field- and pressure-induced phenomena in novel spin-triplet superconductor UTe2 Invited Speaker: Dai Aoki We present our recent results on the novel spin-triplet superconductor UTe2, which is at the verge of the ferromagnetic order. The huge upper critical field exceeding the Pauli limit indicates the spin-triplet state. For the field along b-axis, the field reentrant superconductivity is observed up to Hm~35T, where the first order metamagnetic transition occurs. The field reentrant superconductivity in UTe2 is similar to that observed in ferromagnetic superconductors, namely URhGe and UCoGe. Applying the pressure in UTe2, the superconducting transition temperature splits and the mulitple superconducting phase is detected in the AC calorimetry measurements. We overview the results on UTe2 comparing with ferromagnetic superconductors, and show our perspective. This work was done in collaboration with G. Knebel, A. Pourret, J.P. Brison, D. Braithwaite, Q. Niu, M. Valiska, J. Flouquet, A. Nakamura, F. Honda, Y. Homma, D.X,Li, Y. Shimizu, Y. J. Sato, A. Miyake, S. Imajo, S. Kohama, M. Tokunaga, H. Harima, W. Knafo, I. Sheikin, C. Paulsen, Y. Tokunaga, S. Kambe, H. Sakai, S. Fujimori, K. Ishida, G. Nakamine, S. Kitagawa. |
Tuesday, March 3, 2020 12:27PM - 1:03PM |
G66.00003: Point Node Gap Structure of Spin-Triplet Superconductor UTe2 Invited Speaker: Tristin Metz Low-temperature electrical and thermal transport, magnetic penetration depth, and heat capacity measurements were performed on single crystals of the actinide superconductor UTe2 (Tc=1.6K) to determine the structure of the superconducting energy gap. Heat transport measurements performed with currents directed along both crystallographic a- and b-axes reveal a vanishingly small residual fermionic component of the thermal conductivity. The magnetic field dependence of the residual term follows a quasi-linear increase consistent with the presence of nodal quasiparticles, rising rapidly toward the a-axis upper critical field where the Wiedemann-Franz (WF) law is recovered. Together with a quadratic temperature dependence of the magnetic penetration depth up to T/Tc= 0.3, these measurements provide evidence for an unconventional spin-triplet superconducting order parameter with point nodes positioned along the crystallographic a-axis. Millikelvin specific heat measurements reveal an upturn below 300 mK that is well described by a divergent quantum-critical contribution to the density of states (DOS). Modeling this contribution with a T-1/3 power law allows restoration of the full entropy balance in the superconducting state and reveals a perfect T3 power law for the electronic DOS below Tc which is consistent with the point nodal gap structure determined by thermal conductivity and penetration depth measurements. |
Tuesday, March 3, 2020 1:03PM - 1:39PM |
G66.00004: Electronic band structure of triplet superconductor UTe2 from angle resolved photoemission spectroscopy Invited Speaker: L. Andrew Wray The compound UTe2 has recently been shown to realize spin triplet superconductivity from a non-magnetic normal state. This has sparked intense research activity, including theoretical analyses that suggest the superconducting order parameter to be topologically nontrivial. However, the underlying electronic band structure is a critical factor for these analyses, and remains poorly understood. I will present high resolution angle resolved photoemission (ARPES) measurements covering multiple planes in the 3D Brillouin zone of UTe2, revealing distinct Fermi pockets from two light electron bands and one heavy band. Electronic symmetries and many-body ordering instabilities will be discussed in comparison with numerical simulations. |
Tuesday, March 3, 2020 1:39PM - 2:15PM |
G66.00005: Coexistence of ferromagnetic fluctuations and superconductivity in the actinide superconductor UTe2 Invited Speaker: Jeff Sonier We report low-temperature muon spin relaxation/rotation (μSR) measurements on single crystals of the actinide superconductor UTe2. Below 5 K, we observe a continuous slowing down of magnetic fluctuations that persists into the superconducting state, but find no evidence of long-range or local magnetic order down to millikelvin temperatures. The temperature dependence of the dynamic relaxation rate is consistent with spin fluctuations for a three-dimensional weak itinerant ferromagnetic metal, and suggests UTe2 is close to a ferromagnetic quantum critical point. Our μSR results also indicate that the superconductivity coexists with the magnetic fluctuations and similar to other actinide-based superconductors, UTe2 has a very low superfluid density. |
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