Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session X49: Superconductors with Magnetic or Spin-Orbit interactions |
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Sponsoring Units: DCMP Chair: Oleh Matvyeyev, Georgetown University Room: Mile High Ballroom 1B |
Friday, March 6, 2020 11:15AM - 11:27AM |
X49.00001: Phase Diagram of Spin Triplet Superconductor UTe2 Under Pressure and Magnetic Field Wen-Chen Lin, Daniel J Campbell, David E Graf, Sheng Ran, Nicholas Butch, Johnpierre Paglione The heavy fermion superconductor UTe2 has recently drawn much attention due to several exotic properties. It exhibits two reentrant superconducting states under extremely high magnetic fields that appear correlated with ferromagnetic interactions [1-2], and has been proposed as a candidate three-dimensional topological superconductor [3-4]. Here, we report details of the field-temperature-pressure phase diagram of UTe2 under pressures up to 18.8kbar and high magnetic fields. Electrical resistivity and tunnel diode oscillator (TDO) measurements were performed under external magnetic field along the crystallographic b axis (hard axis), revealing a systematic progression of the superconducting and field-polarized phases that have relations to those observed at ambient pressure [2][5]. We will discuss our observations and their relevance on the interplay between ferromagnetism and superconductivity in this rich system. |
Friday, March 6, 2020 11:27AM - 11:39AM |
X49.00002: Anomalous heat capacity of spin triplet superconductor UTe2 Ian Hayes, Tristin Metz, Yun Suk Eo, Sheng Ran, Nicholas Butch, Johnpierre Paglione The recently discovered superconducting state in uranium ditelluride is a playground of exotic phenomena, including field-reentrant superconductivity up to sixty tesla and spin-triplet pairing.[1, 2] In addition this system shows a large residual density of states at zero temperature, suggesting that about half of the electrons fail to condense, and an apparent violation of entropy balance across the superconducting transition.[1, 3] This talk will present milikelvin specific heat data on UTe2 as a function of magnetic field applied along multiple crystallographic axes. The specific heat shows an upturn at the lowest temperatures. The form of the upturn in temperature and its evolution in magnetic field suggest that it has its origin in critical ferromagnetic fluctuations, supporting the idea that UTe2 is the paramagnetic end member of the series of uranium-based ferromagnetic superconductors. Furthermore, subtracting this upturn restores entropy balance to the superconducting transition. The talk will conclude with a discussion of the implications of these observations for the triplet pairing scenario. |
Friday, March 6, 2020 11:39AM - 11:51AM |
X49.00003: NMR Study of the Spin-triplet Superconductor UTe2 Qing-Ping Ding, Sheng Ran, Nicholas Butch, Yuji Furukawa Recently, spin-triplet superconductivity has been discovered in nearly ferromagnetic (FM) heavy fermion UTe2 [1]. Here, we report the 125Te nuclear magnetic resonance (NMR) studies of UTe2 in both the normal and superconducting (SC) states. The magnetic fluctuations in the normal state, and the SC gap information in the SC state has been revealed. We will also discuss the relationship between FM spin fluctuations and superconductivity in UTe2. |
Friday, March 6, 2020 11:51AM - 12:03PM |
X49.00004: The electronic fluid in cuprate superconductors and NMR Juergen Haase Nuclear magnetic resonance (NMR) is a powerful technique to explore quantum fluids in solids. Recently it was found that a number of early conclusions derived with NMR about the cuprates were flawed, as is easily seen from an overview of all cuprate planar copper shifts [1] and relaxation data [2,3]. For example, there is no evidence for special electronic spin fluctuations [2,3], and, the uniform magnetic response above Tc shows hitherto unknown behaviour [1,2]. The latter implies a large spin shift below Tc for one direction of the external magnetic field, while the nuclear relaxation ceases completely for all cuprates [3]. This must have consequences for the pairing. To shed more light on this peculiar behaviour, we discuss data for other nuclei and their relation to the local charge symmetry, which sustains the existence of this unusual spin shift. |
Friday, March 6, 2020 12:03PM - 12:15PM |
X49.00005: Identify the Chiral Superconductivity in 4Hb-TaS2 through Magnetic-Spectral Responses Xuejian Gao, Kam Tuen Law, Patrick A Lee Chiral superconductivity, which breaks time-reversal symmetry spontaneously, is an alternative ingredient to cook up a topological superconductor holding the Majorana fermions that can be used to perform fault-tolerant quantum computation. A recent experiment [1] showed signatures of time-reversal symmetry breaking in superconducting 4Hb-TaS2 which abruptly appeared at the critical temperature Tc, implying possibility for the existence of chiral superconductivity. Through group theory analysis, we argue that only a chiral and a non-chiral superconducting states are allowed by the crystalline symmetry and strong Ising-type spin-orbital coupling in 4Hb-TaS2, both of which are mixed singlet-triplet states. It is further shown that the non-chiral superconducting state is more susceptible to an in-plane magnetic field and can be magnetically driven to a nodal superconducting phase, while the chiral one does not share this property. According to their different magnetic-spectral responses, an experimentally feasible way concerning the measurement of specific heat is proposed to identify the chiral superconductivity from the non-chiral one for this particular material. |
Friday, March 6, 2020 12:15PM - 12:27PM |
X49.00006: Mixed-parity superconductivity near Lifshitz transitions in strongly spin-orbit-coupled metals Matthew Trott, Christopher Hooley We consider a strongly spin-orbit-coupled metal, one of whose Fermi surfaces is close to a Lifshitz (topological) transition. Via a renormalization group analysis of the square-lattice Hubbard model with strong Rashba spin-orbit coupling, we show that such a metal is generically unstable to the formation of mixed-parity superconductivity with a helical triplet component. |
Friday, March 6, 2020 12:27PM - 12:39PM |
X49.00007: Superconductivity mediated by ferroelectric fluctuations: anisotropic gap structure and possible application to SrTiO3 Maria Navarro Gastiasoro, Thais Victa Trevisan, Rafael Fernandes SrTiO3 is a semiconducting oxide that undergoes a phase transition to a superconducting state upon electron doping. Although such superconducting phase was first observed more than 50 years ago, its nature and origin remain an unsettled puzzle. Interestingly, recent experimental and theoretical works suggest an interplay between ferroelectricity and superconductivity in this material. Motivated by these studies, we study superconductivity mediated by odd-parity ferroelectric modes. We consider a Rashba-like coupling between the electrons and the ferroelectric fluctuations, which is possible due to the presence of spin-orbit coupling. We derive the effective pairing interaction and solve the resulting linearized gap equation away from quantum criticality. We find that the effective coupling, which is attractive in the singlet channel, is dominated by the soft transverse optical mode. Moreover, the superconducting gap is shown to develop an anisotropy that grows as the system approaches the ferroelectric phase. Finally, we discuss the competition with other even-parity superconducting channels and the possible application of our results to SrTiO3. |
Friday, March 6, 2020 12:39PM - 12:51PM |
X49.00008: Enhancement of superconductivity mediated by antiferromagnetic squeezed magnons Eirik Erlandsen, Akashdeep Kamra, Arne Brataas, Asle Sudbo We theoretically investigate magnon-mediated superconductivity in a heterostructure consisting of a normal metal and a two-sublattice antiferromagnetic insulator. The attractive electron-electron pairing interaction is caused by an interfacial exchange coupling with magnons residing in the antiferromagnet, resulting in p-wave, spin-triplet superconductivity in the normal metal. Our main finding is that one may significantly enhance the superconducting critical temperature by coupling the normal metal to only one of the two antiferromagnetic sublattices employing, for example, an uncompensated interface. Employing realistic material parameters, the critical temperature increases from vanishingly small values to significantly larger values than 1 K as the interfacial coupling becomes strongly sublattice-asymmetric. We provide a general physical picture of this enhancement mechanism based on the notion of squeezed bosonic eigenmodes. |
Friday, March 6, 2020 12:51PM - 1:03PM |
X49.00009: Nonlinear optical effects in inversion-symmetry-breaking superconductors Tianrui Xu, Takahiro Morimoto, Joel Moore We study nonlinear optical responses in superconducting systems with inversion (I) symmetry-breaking order parameters. We first show that any superconducting system with I and time-reversal (T) symmetries requires an I-breaking order parameter to support optical transitions between particle-hole pair bands. We then use a 1D toy model of an I-breaking superconductor to numerically calculate linear and nonlinear conductivities, including shift current and second harmonic generations (SHG) responses. We find that the magnitude of the signal is significantly larger in shift current/ SHG response than in the linear response due to the matrix element effect. We also present various scaling behaviors of the SHG signal, which may be relevant to the recent experimental observation of SHG in cuprates[1]. Finally, we confirm the generality of our observations regarding nonlinear responses of I-breaking superconductors, by analyzing other models including a 1D three-band model and 2D square lattice model. |
Friday, March 6, 2020 1:03PM - 1:15PM |
X49.00010: Energy-scale relationship between magnetic excitations and superconductivity in Hg-family of high-Tc cuprates Lichen Wang, Guanhong He, Zichen Yang, Mirian Garcia-Fernandez, Abhishek Nag, Kejin Zhou, Matteo Minola, Matthieu Le Tacon, Bernhard Keimer, Yingying Peng, Yuan Li High-temperature superconductivity in the cuprates is realized upon doping antiferromagnetic parent compounds, in which spin excitations have a band width of a few hundred meV. At such high energies, paramagnons and two-magnon excitations are known to persist well into and beyond the superconducting doping range [1,2,3], but it remains unclear to what extent they contribute to Cooper pairing [4] or how the magnetic and superconducting energy scales are related to each other. We have used resonant inelastic X-ray scattering and Raman scattering to study the first two members of the Hg-family of cuprates, HgBa2CuO4+d and HgBa2CaCu2O6+d, which have nearly identical crystal structure in the charge-reservoir layers but different electronic environment in the quintessential Cu-O layers. We find that the latter compound, which has higher Tc and larger superconducting gap, also has considerably higher magnetic excitation energies. |
Friday, March 6, 2020 1:15PM - 1:27PM |
X49.00011: Hidden Spin-Momentum Texture in High Tc Cuprate Superconductor Chiu-Yun Lin, Kenneth Gotlieb, Maksym Serbyn, Wentao Zhang, Christopher Smallwood, Chris Jozwiak, Zahid Hussain, Ashvin Vishwanath, Alessandra Lanzara Cuprate supercoductor is one of the most well studied compounds. Even so, experiments discover new results after thirty years of intense study by the community. Spin-orbit coupling (SOC) in cuprate superconductors was not a focus of condensed matter research due to the negligible SOC value of the conducting orbitals comparing with the strong electronic correlations and its centrosymmetric crystal structure. However, using spin- and angle-resolved photoemission spectroscopy, we directly probed the spin-momentum entangled texture in Bi2Sr2CaCu2O8+x. The unexpectedly strong spin asymmetry in such globally inversion-symmetric crystal highlights the importance of the local environment that carriers see, meanwhile, poses the intriguing question of how the high-temperature superconducting state emerges in the presence of this nontrivial spin texture. |
Friday, March 6, 2020 1:27PM - 1:39PM |
X49.00012: NCCO: Examining antiferromagnetic hotspots and spin texture comparison with Bi-based cuprates Kayla Currier Recent work on cuprate Bi2212 has revealed a nontrivial spin texture with a rashba-like spin orbit coupling. This texture has been attributed to local inversion symmetry breaking that causes a local electric field within the material. Theory suggests that this property is due to the specific structure of the layers in Bi2212. We examine the spin texture in single-layer electron-doped cuprate NCCO and show how it fits in with the proposed theory. In addition, equilibrium data taken on different dopings of NCCO are compared to recent work showing fermi surface reconstruction. Here we focus on the antiferromagnetic hotspots along the zone boundary. Overall we show part of the picture of how NCCO fits in with the current understanding of cuprates and some of their properties. |
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