CR - 9th International Conference
Science and Engineering of Novel Superconductors
ABSTRACTS
CR-2:IL01 Nodal Multigap Superconductivity in the Iron-based Compound RbCa2Fe4As4F2
D. Daghero1, D. Torsello1, 2, E. Piatti1, G.A. Ummarino1, 3, X. Yi4, X. Xing4, Z. Shi4, G. Ghigo1, 2, 1Department of Applied Science and Technology, Politecnico di Torino, Torino, Italy; 2Istituto Nazionale di Fisica Nucleare, Sezione di Torino, Torino, Italy; 3National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moskva, Russia; 4School of Physics, Southeast University, Nanjing, China
The 12442 iron-based superconductors (IBS) are the ideal playground for investigating the connection between the coupling mechanism, the shape of the Fermi surface (FS), and the symmetry of the superconducting gap(s). Their FS, with very small electron pockets at the M point of the Brillouin zone, makes them similar to compounds like KFe2As2 and KFe2Se2, in which the electron (hole) bands disappear and a nodal behavior emerges. The gap symmetry of 12442 compounds is highly debated, with various evidence either in favor or against the existence of a d-wave gap (possibly coexisting with a fully gapped state on different bands). Motivated by these results, we studied the gap symmetry of RbCa2(Fe_(1-x)Ni_(x))4As4F2 single crystals at different Ni contents by using a combination of directional point-contact Andreev-reflection spectroscopy (PCARS) and a coplanar waveguide resonator (CPWR) technique. The shape of the PCARS spectra and the temperature dependence of the superfluid density were very well fitted by a model with two nodal, possibly d-wave gaps (compatible with the Fermiology and symmetry of the system) yielding gap amplitudes in very good agreement. The persistence of nodes upon Ni doping up to 5% suggests that these nodes might be symmetry-imposed rather than accidental.
CR-2:IL02 Murunskite - Interpolation Compound between Cuprates and Pnictides
D. TOLJ1, T. Ivšić1, I. Živković1, K. Semeniuk1, E. Martino1, A. Akrap2,
P. Reddy3, B. Klebel-Knobloch4, I. Lončarić5, L. Forró1, N. Barišić4, 3, H. Ronnow1, D.K. Sunko3, 1EPFL, Lausanne, Switzerland; 2University of Fribourg, Switzerland; 3University of Zagreb, Croatia; 4TU Wien, Austria; 5Rudjer Boskovic Institute, Croatia
Exploring novel materials as the candidates for unconventional superconductors can help to understand the mechanism of this exotic phenomenon but also lead to synthesis of compounds with important technological applications. The main compound of interest is murunskite (K2FeCu3S4), a material isostructural to iron-based superconductors. I will discuss the synthesis methods and measurements of structural, electronic and magnetic properties. The current study shows that murunskite is a Mott insulator with sulfur orbitals partially open and electronically active, similar to oxygen orbitals in cuprates. Theoretical calculations combined with ARPES measurements indicate the conduction band is cuprate-like while the valence band is pnictide-like, positioning murunskite as an interpolation compound.
CR-3:IL03 Tuning Quantum Phases in Transition Metal Dichalcogenides via Ionic Liquid Gating-induced Protonation
E. PIATTI, J. Montagna Bozzone, D. Daghero, R.S. Gonnelli, Department of Applied Science and Technology, Politecnico di Torino, Torino, Italy; G. Lamura, M. Meinero, Dipartimento di Fisica, Università di Genova, Genova, Italy; S. Roddaro, Istituto Nanoscienze-CNR, NEST and Scuola Normale Superiore, Pisa, Italy; D. De Fazio, ICFO-The Institute of Photonic Sciences, Castelldefels, Spain; G. Profeta, Department of Physical and Chemical Sciences, University of L’Aquila, L’Aquila, Italy; G. Prando, P. Carretta, Dipartimento di Fisica, Università di Pavia, Pavia, Italy
Ion injection in crystalline materials – such as injection of H+, Li+, or O2- species – has historically allowed to profoundly change their electrical, optical, and magnetic properties, sparking interest both on the fundamental level and in applications such as batteries, fuel cells and smart windows. Recently, a novel method to induce and stabilize hydrogen-rich phases at room pressure was introduced, where the strong electric field at a polarized solid-electrolyte interface dissociates the water molecules in the electrolyte and drives H+ ions into the material. An efficient control over the superconducting (SC) phase was demonstrated by using this ionic liquid gating-induced protonation (ILP) in several different materials, including iron-based superconductors of the 11 family, ZrNCl, and the transition metal dichalcogenide (TMD) TaS2. In this invited talk, I will discuss how ILP allowed us to control two quantum phases – SC and charge density wave (CDW) – in archetypal TMDs TiSe2 and MoS2. By combining low-temperature magnetotransport, XRD, NMR, μSR and Raman measurements, we show how upon ILP the intrinsic CDW phase of TiSe2 can be suppressed in favor of a SC phase, whereas a metallic state can be induced in MoS2 which undergoes a CDW reconstruction at low temperature.
CR-3:IL05 Proximity Induced Superconductivity in Monolayer MoS2
M. IAVARONE1, D.J. Trainer1, B. Wang2, F. Bobba1, 3, N. Samuelson4, X. Xi1, J. Zasadzinnski4, J. Nieminen5, A. Bansil2, 1Physics Department, Temple University, Philadelphia, PA, USA; 2Physics Department, Northeastern University, Boston, MA, USA; 3Physics Department, University of Salerno, Fisciano (SA), Italy; 4Physics Department, Illinois Institute of Technology, Chicago, IL, USA; 5Computational Physics Laboratory, Tampere University, Tampere, Finland
Molybdenum disulfide (MoS2) has emerged as a prototypical material among the 2D transition metal dichalcogenides for its stability, low cost and unique electronic, optical and mechanical properties. Its electronic properties can be tuned using different control parameters. This great sensitivity presents an opportunity to functionalize its properties through defect engineering, strain or by proximity to another material. We use high resolution low temperature STM/STS to study the local electronic properties of monolayer MoS2 and the proximity induced superconductivity in monolayer MoS2 placed on top of a Pb thin-film. We find a coherence peak amplitude modulated spatially on the surface of MoS2. Our study indicates that the local modulation of induced superconductivity in MoS2 could be controlled via geometrical tuning. This study suggests that heterostructures based on MoS2 offer a viable possibility to tune its electronic properties and open unprecedented possibilities of combining them for technological use.
CR-3:IL06 Charge Correlations and Charge Fluctuations in Cuprate Superconductors
W. TABIS, AGH University of Science and Technology in Krakow, Poland & Vienna University of Technology, Austria
A major difficulty in understanding cuprate superconductors is the presence of strong correlations which give rise to the rich phase diagrams of these systems. Besides the tendency to spin ordering, cuprates display various charge ordering phenomena. Synchrotron X-ray scattering techniques are very powerful to explore such correlations. I will discuss the charge density wave (CDW) order, which was demonstrated to be intrinsic to cuprates. This modulation is observed in the intermediate carrier concentration range, below the optimal doping. While resonant X-ray scattering allowed us to establish the doping-temperature range of the static CDW order in HgBa2CuO4+d,[1] resonant inelastic X-ray scattering enabled the discovery of the short-range CDW fluctuations at temperatures exceeding the onset of the static correlations.[2] Such coexistence of static and dynamic CDW correlations is consistent with theoretical predictions.[3]
1. W. Tabis et al., Nat. Commun. 5:5875 (2014)
2. W. Tabis et al., Phys. Rev. B 96:134510 (2017)
3. S. Caprara et al., Phys. Rev. B 95:224511 (2017)
CR-3:IL08 Ultranodal Pair State in FeSe1-xSx Superconductors
Takasada Shibauchi, Department of Advanced Materials Science, University of Tokyo, Kashiwa, Japan
The FeSe1-xSx superconductors involving non-magnetic nematic phase and its quantum criticality provide a unique platform to investigate the relationship between nematicity and superconductivity [1]. It has been shown that across the nematic quantum critical point, the superconducting properties change drastically [2,3], and the non-nematic tetragonal FeSe1-xSx (x>0.17) exhibits substantial low-energy states despite the high-quality of crystals. Here we report the muon spin rotation (µSR) measurements on FeSe1-xSx (x=0, 0.20, 0.22), which show the spontaneous internal field below the superconducting transition temperature Tc, providing strong evidence for time-reversal breaking (TRSB) state in bulk FeSe1-xSx [4]. We also find that the superfluid density in the tetragonal crystals is suppressed from the expected value, indicating the presence of non-superconducting carriers. These results in FeSe1-xSx are consistent with the recently proposed topological phase transition to a novel ultranodal pair state with Bogoliubov Fermi surface [5].
[1] T. Shibauchi et al., J. Phys. Soc. Jpn. 89, 102002 (2020).
[2] Y. Sato et al., PNAS 115, 1227-1231 (2018).
[3] T. Hanaguri et al., Sci. Adv. 4, eaar6419 (2018).
[4] K. Matsuura et al.
[5] C. Setty et al., Nat. Commun. 11, 523 (2020).
CR-3:IL10 High-Tc Cuprates - Story of Two Electronic Subsystems
N. Barišić1, 2, 1Institute of Solid State Physics, TU Wien, Wien, Austria; 2Department of Physics, Faculty of Science, University of Zagreb, Zagreb, Croatia
We have performed a thorough experimental study of HgBa2CuO4+δ, which, in many respects, is a model cuprate compound. From the comparison of our measurements with data for other cuprates, we are able to separate universal behavior from compound-specific features. This exercise leads to a series of remarkable findings, the most important of which are that the effective mass and the scattering rate remain essentially unchanged across the phase diagram, and that the scattering rate is dominated by an umklapp process. These novel insights enabled an accurate count of charges across the phase diagram. The electronic system is thus found to consist of 1+p charges, where p corresponds to doping. At low dopings, within the pseudogap regime, exactly one hole is localized per planar copper-oxygen unit. Upon increasing doping and temperature, the hole is gradually delocalized and becomes itinerant. The overall behaviors are consistent with a gradual extension of Fermi arcs to a full Fermi surface, without an essential change of the underlying Fermi surface that encloses 1+p states. Finally, we have established that the itinerant Fermi-liquid holes become superconducting while the localized hole provides the glue.
CR-4:IL02 Room-temperature Superconductivity in Hydrides
S. DI CATALDO, University of Rome "La Sapienza", Rome, Italy
The experimental discovery of high-temperature superconductivity with a Tc of 203 K in sulphur hydride (H3S at a pressure of 150 GPa, in 2014 [1], drew great interest in this class of high-Tc conventional superconductors. Despite the extreme technical challenges presented by experiments at such high pressures, the intense research effort following H3S has led to the discovery of several other superhydrides with even higher Tc’s [2-5], up to a disputed claim of room-temperature superconductivity [6]. In this talk, after introducing the general properties of high-Tc hydrides, I will show how ab-initio calculations contributed to dramatically accelerate experimental discoveries [7]. Then, I will discuss the future perspectives of this research field, where the focus has shifted towards more complex hydrides, with the goal of lowering the stabilization pressure while maintaining a high-Tc [8-10].
[1] A. P. Drodzov et al., Nature 525, 73-76 (2015)
[2] A. P. Drodzov et al., Nature 569, 528-531 (2019)
[3] M. Somayazulu et al., Phys. Rev. Lett. 122, 027001 (2019)
[4] P. Kong et al., Nature Communications 12, 5075 (2021)
[5] D. V. Semenok et al., Mat. Today 33, 36-44 (2020)
[6] E. Snider, et al., Nature 586, 373-377 (2020)
[7] A. R. Oganov et al., Nature Reviews Materials 4, 331-348 (2019)
[8] J. Flores-Livas et al., Phys. Rep. 856, 1-78 (2020)
[9] L. Boeri et al., J. Phys. Condens. Matter 34, 18 (2021)
[10] R. Lucrezi et al., arXiv:2112.02131 (2021)
CR-5:IL01 Super-oxidized Phases in Cuprate and Iridate Thin Films
John Wei, Department of Physics, University of Toronto, Canada
Hyperbaric oxygen has long been used to hole-dope and to stabilize super-oxidized phases of cuprates. We extend this superoxygenation technique to YBa2Cu3O7-δ thin films, which are more reactive due to their large surface-to-volume ratio, and to the layered iridate Sr2IrO4, which is difficult to hole-dope by cation substitution. First, epitaxial YBa2Cu3O7-δ thin films grown by pulsed laser-ablated deposition are annealed in up to 700 atm O2 and then characterized by TEM, XRD and XAS. The annealed films show phase conversion to Y2Ba4Cu7O15-δ and Y2Ba4Cu8O16, as well as regions of YBa2Cu5O9-δ and YBa2Cu6O10-δ. Second, epitaxial thin films of Sr2IrO4 are subjected to extended high-pressure annealing and similarly characterized. The post-annealed films show up to 3 order-of-magnitude drop in room temperature resistivity and an evolution towards semi-metallic behaviour. Furthermore, as film thickness is reduced, the annealed films show a structural transformation towards a quasi-cubic phase. Our results demonstrate the potential of using superoxygenation to stabilize exotic phases of transition metal oxides not achievable in bulk form [1].
[1] H. Zhang et al., Phys. Rev. Materials 2, 033803 (2018). Work was supported by NSERC, CFI-OIT and CIFAR.
CR-6:IL01 Energy & Material Efficiency: Liquid Hydrogen & HTS - A Perfect Fit
T. ARNDT, KIT, ITEP, Eggenstein-Leopoldshafen, Germany
Devices based on High-Temperature Superconductors (HTS) offer great technical advantages. A multitude of demonstrators in magnets, motors and generators, transformers, fault current limiters and power lines have shown the outstanding electromagnetic efficiency. However, the cooling effort and technology – very frequently not familiar to the operators – are the main hurdles preventing a wide spread application. The transport of energy is realized by electric power lines or by pipelines for chemical energy vectors (fossil fuels and gases). The need to reduce CO2 emissions has fostered regional strategies to push for Hydrogen (H2) as an energy vector. As the energy density of as-is H2 is quite low, pressurized H2 or liquefied H2(LH2) is considered. Both options require some upfront energy reducing the efficiency of the overall energy chain. However, for LH2 the “free backpack of cold” may be used to replace the cooling systems in HTS applications and thus increasing the overall efficiency of the hydrogen energy chain as well as the efficiency of the electric power applications. In this presentation, we describe the interplay of these approaches and the opportunities in new designs of applications. HTS: the missing efficiency link of bulk transport of LH2 and power applications.
CR-6:IL02 Use of Electromagnetic Potentials for the Modeling of Critical State and AC Losses in Superconducting Wires and Cables
F. Gömöry, M. Solovyov, Institute of Electrical Engineering, Slovak Academy of Sciences, Bratislava, Slovakia
Motivated by a growing demand on precision of theoretical predictions on one side and a rapid growth of numerical computing power on other side, applied superconductivity community faced in two recent decades the problem of transposing the critical state model into mathematical expressions that could be implemented in numerical codes. In our group we adopted the approach proposed by A. M. Campbell, that linked the density of electrical current in superconductor with the vector potential of magnetic field, the quantity favoured in numerical computations with finite elements. This provided straight way for inserting the interaction of magnetic flux with superconductors into commercial codes. We found this approach extremely helpful for tackling several problems. Important advance has been achieved after inserting the electrostatic potential for imposing a transport current into parallel wires, arriving to the nowadays A-V formulation. We show how it can be successfully used in modelling of superconducting coil in axisymmetric two-dimensional approximation, or for the transport of current in superconducting cable, followed by the evaluation of AC loss.