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 Y47: Superconductivity: Fluctuation -Thermodynamic and Nonequilibrium phenomenaLive
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Sponsoring Units: DCMP Chair: Christian Wolowiec, University of California, San Diego |
Friday, March 19, 2021 11:30AM - 11:42AM Live |
Y47.00001: Theory of the nonlinear susceptibility of layered superconductors: application to strontium ruthenate Fei Chen, Damjan Pelc, Martin Greven, Rafael Fernandes Probing superconducting fluctuations (SF) in unconventional superconductors is essential to elucidate their nature. Much work has been done to elucidate the contributions from SF to the conductivity and the linear susceptibility. Disentangling them from normal state contributions can be challenging. An alternative that has been recently explored is to measure the nonlinear susceptibility via third-order magnetic response, which is believed to be dominated by SF above Tc. Here, we present a phenomenological theoretical model for the nonlinear susceptibility of layered superconductors. Our model, based on the Lawrence-Doniach functional, predicts power-law behaviors in distinct temperature and magnetic field regimes. Comparison with data from conventional BCS superconductors reveals an excellent agreement between theory and experiment. The same does not happen, however, for oxide superconductors, such as the strontium ruthenate Sr2RuO4 [D Pelc et al., Nat. Commun. 10, 2729 (2019)]. We show that inclusion of disorder can capture some of the experimental features. Finally, we discuss the limitations and possible extensions of our model. |
Friday, March 19, 2021 11:42AM - 11:54AM Live |
Y47.00002: Optical excitation of the Higgs mode in superconductors Matteo Bellitti, Christopher Laumann, Boris Spivak We consider the dynamical excitation of the Higgs/amplitude mode in superconductors by quasiparticle avalanche following optical excitation. We comment on the efficiency of this approach for investigation of the amplitude mode in various physical regimes. |
Friday, March 19, 2021 11:54AM - 12:06PM Live |
Y47.00003: Non-BCS Type Enhancement of Superconductivity from Long-Range Photon Fluctuations AHANA CHAKRABORTY, Francesco Piazza Recently, the possibility of inducing superconductivity for electrons in two dimensional materials has been proposed via cavity-mediated pairing. The cavity-mediated electron-electron interactions are long range, which has two main effects: firstly, within the standard BCS-type pairing mediated by adiabatic photons, the superconducting critical temperature depends polynomially on the coupling strength, instead of the exponential dependence; secondly, as we show here, the effect of photon fluctuations is significantly enhanced. These mediate novel non-BCS-type pairing processes, via non-adiabatic photons, which are not sensitive to the electron occupation but rather to the electron dispersion and lifetime at the Fermi surface. Therefore, while the leading temperature dependence of BCS pairing comes from the smoothening of the Fermi-Dirac distribution, the temperature dependence of the fluctuation-induced pairing comes from the electron lifetime. For realistic parameters, also including cavity loss, this results into a critical temperature which can be more than one order of magnitude larger than the BCS prediction. Moreover, a finite average number photons (by incoherently pumping the cavity) adds to the fluctuations and leads to a further enhancement of superconductivity. |
Friday, March 19, 2021 12:06PM - 12:18PM Live |
Y47.00004: Quantum criticality inside the field-induced metallic state in an amorphous superconducting thin film Koichiro Ienaga, Taiko Hayashi, Yutaka Tamoto, Shin-ichi Kaneko, Satoshi Okuma
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Friday, March 19, 2021 12:18PM - 12:30PM Live |
Y47.00005: Sample Rotation as a New Method for Identifying the FFLO State in λ-(BETS)2GaCl4 Brett Laramee, Raju Ghimire, Alireza Alipour, Calvin Bales, William A Coniglio, Charles C Agosta, John A Schlueter, Akiko Kobayashi The FFLO state is a state of inhomogeneous superconductivity that exists at high magnetic fields. In specific crystals, the limit, Hp, where Cooper pairs begin to break due to paramagnetic effects is reached before the ultimate critical field, Hc2. We will present rf penetration depth measurements on the quasi-2D organic superconductor λ-(BETS)2GaCl4 (BETS) using a tunnel diode oscillator. The quasi-2D structure of BETS makes features such as Hc2, the FFLO transition, and vortex effects like the lock-in effect highly sensitive to the angle that the conduction planes make with the applied field. By rotating the sample in a constant external magnetic field, we can locate points on the FFLO phase line that are not easily identifiable via traditional field sweeps, and will use these data to show a Field—Angle FFLO phase diagram at very low temperature (60mK). Using this new identification technique to supplement existing field sweep data, we have started to construct a full 3D Field—Angle—Temperature phase diagram of the FFLO state. |
Friday, March 19, 2021 12:30PM - 12:42PM Live |
Y47.00006: Ab initio study of possible metastable occupation of tetrahedral sites in Palladium Hydride compounds Antonella Meninno, Ion Errea Palladium hydrides are one of the rare examples of superconducting hydrides at ambient pressure. Even if their critical temperature is around 10 K, they are fascinating superconductors because of their inverse isotope effect: the palladium compound has a larger critical temperature than the hydrogen compound, in clear contradiction with standard electron-phonon superconductors. As shown by Errea et al. [1], this anomalous behavior is induced by the large anharmonicity of the hydrogen vibrations in the octahedral sites they occupy. |
Friday, March 19, 2021 12:42PM - 12:54PM Live |
Y47.00007: Strain as a Tuning Parameter of the Superconducting Transition in Nb-doped SrTiO3 Craig Topping, Mari Cole, Soumendra Panja, Andreas Rost The perovskite semiconductor SrTiO3 is a quantum paraelectric tunable towards a ferroelectric transition by either 18O substitution [1] or strain [2] via a quantum critical phase transition and shows a superconducting dome when doped by n-type carriers (Nb or O-deficiency) [3]. The interplay of superconductivity with the unconventional dielectric properties due to the ferroelectric quantum phase transition is a longstanding question [4]. Recent experiments showed that strain can tune TC [5]. Here we will report on magnetotransport studies on strained single crystals of SrTi1-xNbxO3 in the underdoped, optimally doped and overdoped regimes with a superconducting dome with tensile strain observed when underdoped. This is discussed in relation to the ferroelectric quantum phase transition. |
Friday, March 19, 2021 12:54PM - 1:06PM Live |
Y47.00008: Phase Diagram of Ternary Carbon-Sulfur-Hydrogen System up to 300 GPa Reetam Paul, Suxing Hu, Valentin Karasiev, Ranga P Dias The recent discovery of a room-temperature superconductor[1] with Tc = 287.7±1.2 K at high pressures (267±10 GPa) in carbonaceous sulfur hydride has demonstrated the necessity of analyzing the phase diagrams of such ternary C-S-H systems. The stoichiometry and the electronic properties of this material are now an open question. Using evolutionary algorithms and density functional theory (DFT) calculations, we explore the phase diagram of this system. We report the candidate for the low-pressure phase III prior to metallization at ~60 GPa as C2S2H10, using comparisons of the Raman modes from calculations vis-à-vis experiments. Due to the limit of chemical accuracy of DFT being ~50 meV, it is almost impossible to discern the candidate structures among a host of structures purely from free-energy comparisons. We present a phase diagram spanning from 30 to 300 GPa derived from pure thermodynamic considerations, inclusive of the zero-point effect which is significant because of the presence of hydrogen. Possible superconducting phase(s) will be discussed. |
Friday, March 19, 2021 1:06PM - 1:18PM Live |
Y47.00009: Retention of high-pressure-induced superconducting and non-superconducting phases in solids at ambient Paul C. W. Chu, Liangzi Deng, Zheng Wu, Trevor Bontke, Shuyuan Huyan, Melissa Gooch, Rabin Dahal, Bin Gao, Tong Chen, Pengcheng Dai To raise the Tc has been one of the main driving forces in the extensive high temperature superconductivity research for more than three decades. Record Tcs have been set for different compound systems, e.g. 164 K for the cuprates and 287 K for the C-S-H hydrides. Unfortunately, all of these are achieved under pressures, i.e. ~31 GPa for the former and 267 GPa for the latter, posing a serious obstacle for applications. To remove the obstacle, we have investigated means to retain at ambient the high-pressure phases by taking advantage of the energy barriers between different phases in solids through pressure quench at 77 K. We shall report our success in retaining at ambient the following pressure-induced phases: superconducting (sc) phases II at ~5-20 GPa and IV at ~22-62 GPa in non-sc Sb I single crystals; sc phases III at ~2.4-7 GPa and V at ~7-12 GPa in non-sc Bi I single crystals, sc tetragonal FeSe at ~2-7.5 GPa and non-sc hexagonal FeSe above ~8 GPa in sc orthogonal FeSe single crystals; and sc tetragonal Cu-doped FeSe at ~4-6 GPa in non-sc orthogonal Cu-doped FeSe single crystals. The thermal stability of each of these phases has also been determined. |
Friday, March 19, 2021 1:18PM - 1:30PM Live |
Y47.00010: Disorder perturbations of topological superconductor surface fluids: Semiclassical geodesic approach Seth Davis, Matthew Foster At the boundary of the simplest type of bulk topological superconductor, electric impurity potentials couple gravitationally to the stress tensor of the surface Majorana cone. While weak disorder is irrelevant near the Dirac point, recent numerics uncovered an unexpected result: the finite energy states form “stacks” of statistically identical, quantum critical wave functions [1]. |
Friday, March 19, 2021 1:30PM - 1:42PM Live |
Y47.00011: Multi-component superconducting pairing and possible vestigial order in half-Heusler compounds Matthias Hecker, Roland Willa, Joerg Schmalian Various members of the half-Heusler family undergo a superconducting transition with a Tc ~1K. |
Friday, March 19, 2021 1:42PM - 1:54PM Live |
Y47.00012: Collective modes in disordered s-wave superconductors Abhisek Samanta, Anirban Das, Nandini Trivedi, Rajdeep Sensarma We investigate the effect of disorder and temperature on the two particle spectral function for s-wave superconductors, focusing on the evolution of the low energy collective Higgs and phase modes. We find that disorder creates a subgap Higgs mode and flattens the Goldstone mode. In the presence of weak disorder, the Higgs mode remains spectrally separated from phase modes for a large range of temperature, thereby making it a possible candidate to observe in energy resolved spectroscopies. |
Friday, March 19, 2021 1:54PM - 2:06PM Live |
Y47.00013: Universal short-range orthorhombic correlations in two cuprate superconductors Damjan Pelc, Richard Spieker, Zachary Anderson, Matthew Krogstad, Nikolaos Biniskos, Nina G Bielinski, Biqiong Yu, Takao Sasagawa, Ludivine Chaviere, Pinder Dosanjh, Ruixing Liang, Douglas A. Bonn, Andrea Damascelli, Yaohua Liu, Raymond Osborn, Martin Greven The high-temperature copper-oxide (cuprate) superconductors have been extensively studied for over thirty years, yet important questions regarding their phase diagram and unconventional superconductivity remain. In particular, the role of inherent structural inhomogeneity is not well understood. We carried out diffuse X-ray and neutron scattering experiments on two cuprates – La2-xSrxCuO4 and Tl2Ba2CuO6+δ – and observed short-range orthorhombic correlations in wide doping and temperature ranges, including compositions that maintain tetragonal average structure at low temperature. The strength of this structural precursor response exhibits exponential temperature scaling. Similar exponential behavior was seen in the superconducting precursor of cuprates [1,2] and other oxides [3]. This points to the relevance of structural inhomogeneity for the emergence of superconductivity and is consistent with a recent phenomenological model for the cuprates [4]. |
Friday, March 19, 2021 2:06PM - 2:18PM Live |
Y47.00014: Superconducting properties near structural instabilities in LaH10 Dan Sun, Vasily S Minkov, Shirin Mozaffari, Stella Chariton, Vitali B. Prakapenka, Mikhail Eremets, Luis Balicas, Fedor F Balakirev The hydride superconductor LaH10 has a Tc ~250 K at 150 GPa. We measured the properties of the superconductor in the pulsed magnetic field, above and below the structure transition at 135 GPa, where a steep Tc jump happens. We established key superconducting quantities of LaH10 under high magnetic fields, including upper critical fields and coherence lengths. We find that the drop in the Femi velocity in LaH10 is consistent with the Brillouin zone changes induced by the structural transition and that there is a correlation between the superconductivity and the structure instability. |
Friday, March 19, 2021 2:18PM - 2:30PM Not Participating |
Y47.00015: Near-filed heat transfer in high-Tc superconductors Raul Esquivel-Sirvent, Shunashi Castillo-López, Giuseppe Pirruccio, Carlos Villarreal Near-field radiative heat transfer (NFRHT) management can be achieved using high-temperature superconductors. In this work, we present a theoretical study of the radiative heat transfer between two YBa_2Cu_3O_6.95 (YBCO) slabs. The radiative heat transfer is calculated using Rytov's theory of fluctuating electrodynamics, while a two-fluid model describes the dielectric function of the superconducting materials. Our main result is the significant suppression of the NFRHT when one or both of the slabs are superconducting, which is explained in terms of the detailed balance of the charge carriers density together with the sudden reduction of the free electron scattering rate. A critical feature affecting the radiative heat transfer between high-temperature superconductors is the large damping of the mid-infrared carriers which screens the surface plasmon excitation. The role of p and s-poalrization for the different cases is also discussed. Our results are for bulk materials and we also show the effect of working with superconducting thin-films. |
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