High Critical Temperature Superconductors Research Articles

Effect of the Post‐Annealing Temperature on the Interfacial Reaction Between a High TC Superconductor and Topological Insulator

AbstractThis work reports the formation of a heterojunction composed of Tl2Ba2CaCu2O8 (Tl‐2212) and Bi2Se3 as the high critical temperature superconductor and topological insulator, respectively. The Bi2Se3 film is deposited on the Tl‐2212 by a chemical mechanical polishing process. Due to the rough surface of Tl‐2212, the treated Tl‐2212 is then subjected to post‐annealing at various temperatures. This temperature does not affect the formation of the interfacial layer at the heterojunction; however, an improved layered crystal structure of the Bi2Se3 film is observed at 500 °C. The in‐depth profile of the relative atomic concentration indicates the diffusion of Cu and Tl into the Bi2Se3 film with the Ba diffusion being closer to the interfacial layer. At 500 °C, Cu atoms are more actively diffused into the Bi2Se3 film, thus blocking Tl diffusion, and improving the layered crystal structure of the film. The density functional theory calculations reveal that the lowest formation energy of the Cu vacancy is when Bi2Se3 is in contact with Tl‐2212, which results in the diffusion of Cu atoms from Tl‐2212, thus transforming the interstitial Cu atoms into the film. These atoms have an n‐type doping effect and prefer intercalating at a vdW gap deep inside the layered Bi2Se3.

Metal-bonded perovskite lead hydride with phonon-mediated superconductivity exceeding 46 K under ambient pressure

In the search for high-temperature superconductivity in hydrides, a plethora of multi-hydrogen superconductors have been theoretically predicted, and some have been synthesized experimentally under ultrahigh pressures of several hundred GPa. However, the impracticality of these high-pressure methods has been a persistent issue. In response, we propose a new approach to achieve high-temperature superconductivity under ambient pressure by implanting hydrogen into lead to create a stable few-hydrogen binary perovskite, Pb4H. This approach diverges from the popular design methodology of multi-hydrogen covalent high critical temperature (Tc ) superconductors under ultrahigh pressure. By solving the anisotropic Migdal–Eliashberg equations, we demonstrate that perovskite Pb4H presents a phonon-mediated superconductivity exceeding 46 K with inclusion of spin–orbit coupling, which is six times higher than that of bulk Pb (7.22 K) and comparable to that of MgB2, the highest Tc achieved experimentally at ambient pressure under the Bardeen, Cooper, and Schrieffer framework. The high Tc can be attributed to the strong electron–phonon coupling strength of 2.45, which arises from hydrogen implantation in lead that induces several high-frequency optical phonon modes with a relatively large phonon linewidth resulting from H atom vibration. The metallic-bonding in perovskite Pb4H not only improves the structural stability but also guarantees better ductility than the widely investigated multi-hydrogen, iron-based and cuprate superconductors. These results suggest that there is potential for the exploration of new high-temperature superconductors under ambient pressure and may reignite interest in their experimental synthesis in the near future.

Superconductivity and strongly correlated materials in Bariloche

In June 1986, the news on the discovery of high critical temperature superconductivity at IBM, Switzerland, by the physicists Bednorz and Müller, reached the laboratories at the Bariloche Atomic Center in the Argentine Patagonia. The expertise in experimental techniques at low temperatures led by Paco de la Cruz and his team and also in crystal growth led by Daniel Esparza and his group, were important to reproduce the results in a question of a few months. This discovery produced enormous enthusiasm in the community and incentivized research in these materials in other laboratories and theoretical groups at the Bariloche Atomic Center, which had already a vast experience and trajectory in materials science. In this paper I will delve on how this striking discovery fostered theoretical and experimental research in Bariloche which lasts until today.

Design Rules for Resistors, Capacitors and Inductors Fabricated From Single Layer Y-Ba-Cu-O Thin Films With Focused Helium Ion Beam Irradiation

Yttrium barium copper oxide (YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-<inline-formula><tex-math notation="LaTeX">$\delta$</tex-math></inline-formula></sub> or YBCO) Josephson junctions fabricated using focused helium gas field ion sources show great promise for high transition temperature superconducting electronics. A unique feature of this technology is that it can also be utilized for the fabrication of resistors, capacitors and inductors in the same material and process step. The key to this method is that the electrical resistivity of high critical temperature superconductors is very sensitive to ion irradiation. The ions introduce disorder into the material which causes it to undergo a metal-to-insulator transition. By carefully controlling the position of the beam and ion dose delivered to the material, insulating pathways and reduced critical temperature metallic regions can be fabricated to construct the aforementioned passive components. We have prepared this manuscript to serve as a guide for circuit designers utilizing this process. We discuss the capabilities and limitations of helium ion beam lithographic patterning of YBCO and estimate the practical ranges of the values that can be obtained for resistors, capacitors and inductors in single layer thin films. Estimates are provided for two processes: one with the highest resolution with the smallest beam diameter (0.5 nm) and another based on the highest source current (100 pA) for fastest write time.

Direct evidence of high Tc superconductivity in glossy carbon films

Recent achievements and predictions in the field of intrinsic superconductivity in column IV-based covalent semiconductors and the nature of coupling, which determines the prospects for higher transition temperatures as well as the influence of disorder, are debated issues that can determine the future of the field. With this context, here we report the experimental findings of intrinsic superconductivity in glossy carbon (GC) films. These films are one of the forms of carbon materials obtained by pyrolysis of Pongamia glabra oil under high pressure and temperature. A zero-resistance state for films was observed at a critical Zero Resistance temperature of 134 K. Such relatively high superconducting critical temperature of films puts it among the superconductors with the strongest pairing strength between electrons and therefore an ideal material for investigations of high critical temperature superconductors.

Tunable properties of the defect mode of a ternary photonic crystal with a high T C superconductor and semiconductor layers

Abstract The tuning of a defect mode in a photonic crystal (PC) is of high significance for filter and sensor applications. We here investigate the tuning of the defect mode of a defective ternary PC with a semiconductor and high critical-temperature superconductor layers. A ternary photonic crystal with the heterostructure (semiconductor/superconductor/dielectric) is assumed. The transfer matrix method is employed to investigate the transmission of transverse electric waves. The refractive indices of the semiconductor and superconductor layers can be tuned by changing the operating temperature and the hydrostatic pressure. The defect mode and transmission properties can be controlled by using the hydrostatic pressure, operating temperature, frequency and thicknesses of the heterostructure layers. The analysis is performed in the frequency range of 20–65 THz. The proposed structure can be utilized as a biosensor and a narrowband transmission peaks filter.

Josephson junction based on high critical-temperature superconductors: analysis, microcontroller implementation, and suppression of coexisting and chaotic attractors

Josephson junction based on high critical-temperature superconductors: analysis, microcontroller implementation, and suppression of coexisting and chaotic attractors

Very Low-Noise Figure HTSC RF Front-End

A very low noise figure radio frequency (RF) front-end for the cellular realm is presented. The front-end is composed of two planar YBCO high critical temperature superconductor (HTSC) bandpass filters (BPFs) and a low temperature, low noise amplifier. Using advanced HTSC growth techniques, 8-pole hairpin BPFs are implemented in a YBCO thin film grown on both sides of a sapphire substrate. The front-end is designed and implemented based on the optimal configuration of the filters derived from advanced electromagnetic simulations. Measured performance at 77 K shows a high-frequency response and very low losses, with an insertion loss of 0.15 dB and a rejection ratio of −93 dBc. The integration of HTSC filters with the low noise amplifier results in a system with superior performance, with a low noise figure of around 0.5 dB. Low insertion loss and the compact dimensions of the filter, along with low total system noise, make the designed superconducting RF front-end highly attractive for radio receivers.

Computational materials discovery for lanthanide hydrides at high pressure for high temperature superconductivity

Hydrogen-rich superhydrides are believed to be very promising high critical temperature (high ${T}_{c}$) superconductors, with experimentally observed critical temperatures near room temperature, as shown in recently discovered lanthanide superhydrides at very high pressures, e.g., ${\mathrm{LaH}}_{10}$ at 170 GPa and ${\mathrm{CeH}}_{9}$ at 150 GPa. With the motivation of discovering new hydrogen-rich high ${T}_{c}$ superconductors at the lowest possible pressure, quantitative theoretical predictions are needed. In these promising compounds, superconductivity is mediated by the highly energetic lattice vibrations associated with hydrogen and their interplay with the electronic structure, requiring fine descriptions of the electronic properties, notoriously challenging for correlated $f$ systems. In this paper, we propose a first-principles calculation platform with the inclusion of many-body corrections to evaluate the detailed physical properties of the Ce-H system and to understand the structure, stability, and superconductivity of ${\mathrm{CeH}}_{9}$ at high pressure. We report how the calculation of ${T}_{c}$ is affected by the hierarchy of many-body corrections and obtain a compelling increase in ${T}_{c}$ at the highest level of theory, which goes in the direction of experimental observations. Our findings shed significant light on the search for superhydrides in close similarity with atomic hydrogen within a feasible pressure range. We provide a practical platform to further investigate and understand conventional superconductivity in hydrogen-rich superhydrides.

First principles study and reconsideration of the mechanical and dynamic stability of hydrogen-rich compound cI14-CaH6 high critical temperature superconductor under pressure

In this paper, we used the density functional theory based on GGA-PBE approximation, to reconsider the stability of CaH6 in phase cI14, which corresponds to the superconducting state according to some theoretical study. Our motivation for reconsidering is the conflict between an experimental and theoretical result about the stability of CaH6 in the superconducting phase under high stress. The obtained results of the elastic constants at a wide range of pressures indicated the mechanical instability of CaH6 in the cI14 prototype. The phonon spectrum showed positive frequencies at pressures higher than 150 GPa, which correspond to dynamic stability.

Interaction-induced topological phase transition and Majorana edge states in low-dimensional orbital-selective Mott insulators

Topological phases of matter are among the most intriguing research directions in Condensed Matter Physics. It is known that superconductivity induced on a topological insulator’s surface can lead to exotic Majorana modes, the main ingredient of many proposed quantum computation schemes. In this context, the iron-based high critical temperature superconductors are a promising platform to host such an exotic phenomenon in real condensed-matter compounds. The Coulomb interaction is commonly believed to be vital for the magnetic and superconducting properties of these systems. This work bridges these two perspectives and shows that the Coulomb interaction can also drive a canonical superconductor with orbital degrees of freedom into the topological state. Namely, we show that above a critical value of the Hubbard interaction the system simultaneously develops spiral spin order, a highly unusual triplet amplitude in superconductivity, and, remarkably, Majorana fermions at the edges of the system.

Superconductor-insulator transition in space charge doped one unit cell Bi2.1Sr1.9CaCu2O8+x

The superconductor-insulator transition in two dimensions is a prototype continuous quantum phase transition at absolute zero, driven by a parameter other than temperature. Here we reveal this transition in one unit-cell Bi2.1Sr1.9CaCu2O8+x by space charge doping, a field effect electrostatic doping technique. We determine the related critical parameters and develop a reliable way to estimate doping in the nonsuperconducting region, a crucial and central problem in these materials. Finite-size scaling analysis yields a critical doping of 0.057 holes/Cu, a critical resistance of ~6.85 kΩ and a scaling exponent product νz ~ 1.57. These results, together with earlier work in other materials, provide a coherent picture of the superconductor-insulator transition and its bosonic nature in the underdoped regime of emerging superconductivity in high critical temperature superconductors.

Current Status in Building a Compact and Mobile HTS MRI Instrument

Magnetic Resonance Imaging (MRI) is an indispensable tool in monitoring lipid-rich tissues and the musculoskeletal system. It however requires maintaining a huge homogeneous (1 to 7 T) field. That is where superconductors come into play since they are the only feasible way to create such fields. The state-of-the-art technology utilizes low critical temperature superconductors (LTS) which require cooling down to liquid helium temperatures (4.2K). The new generation superconductors, aka the high critical temperature superconductors (HTS), can operate up to relatively elevated temperatures (technically above 100K's). In addition to that, they can withstand larger magnetic field strengths which can theoretically go up to the order of hundred Teslas in magnitude. It is evident that LTS wires of current MRI magnet technology is at their limits and new pursuits such as reaching higher fields and reducing operational/maintenance costs are in the favor of HTS tapes. There is, in fact, another advantage beyond minimization of the cryogenic costs, namely the compactness of the overall system. Utilizing certain auxiliary techniques such as flux pumping and conductive cooling of the tapes, MRI magnets can be reduced in size substantially. That, in turn, enables constructing much smaller thus mobile MRI scanners which can be brought to patients' doorsteps. Here we present the current status of our project aiming to build an HTS MRI machine dedicated to use as a mobile head scanner.

New Application Method of Static-Field Magnetization to Magnetically Levitated Mover System With High T c Superconductors

Application method of static-field magnetization to magnetically levitated mover system with high critical temperature (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) superconductors is discussed. The system is composed of a levitated mover, magnetic rails, a linear induction motor (LIM) and some power supplies. In the paper, static-field magnetization is applied to superconductors in the levitated system from bottom superconductor surfaces. Then, magnetizations in superconductors are tried to control using static-field on superconductor surfaces. That is, magnetic flux density distributions are successfully forced to change to initial flux density distributions.

Anisotropic superconductivity in the spin-vortex antiferromagnetic superconductor CaK(Fe0.95Ni0.05)4As4

High critical temperature superconductivity often occurs in systems where an antiferromagnetic order is brought near $T=0K$ by slightly modifying pressure or doping. CaKFe$_4$As$_4$ is a superconducting, stoichiometric iron pnictide compound showing optimal superconducting critical temperature with $T_c$ as large as $38$ K. Doping with Ni induces a decrease in $T_c$ and the onset of spin-vortex antiferromagnetic order, which consists of spins pointing inwards to or outwards from alternating As sites on the diagonals of the in-plane square Fe lattice. Here we study the band structure of CaK(Fe$_{0.95}$Ni$_{0.05}$)$_4$As$_4$ (T$_c$ = 10 K, T$_N$ = 50 K) using quasiparticle interference with a Scanning Tunneling Microscope (STM) and show that the spin-vortex order induces a Fermi surface reconstruction and a fourfold superconducting gap anisotropy.

Strange metal behaviour from charge density fluctuations in cuprates

Besides the mechanism responsible for high critical temperature superconductivity, the grand unresolved issue of the cuprates is the occurrence of a strange metallic state above the so-called pseudogap temperature T*. Even though such state has been successfully described within a phenomenological scheme, the so-called Marginal Fermi-Liquid theory, a microscopic explanation is still missing. However, recent resonant X-ray scattering experiments identified a new class of charge density fluctuations characterized by low characteristic energies and short correlation lengths, which are related to the well-known charge density waves. These fluctuations are present over a wide region of the temperature-vs-doping phase diagram and extend well above T*. Here we investigate the consequences of charge density fluctuations on the electron and transport properties and find that they can explain the strange metal phenomenology. Therefore, charge density fluctuations are likely the long-sought microscopic mechanism underlying the peculiarities of the metallic state of cuprates.

WHAT CAN WE EXPECT FROM THE HIGH TEMPERATURE SUPERCONDUCTORS IN THE NEXT FUTURE?

Thirty years after its discovery, high critical temperature superconductors have confirmed the operation cost saving compared with the low temperature superconductors. Their properties have improved significantly, both in current transport capability and available length. However, their applications are not spread. Why? The main reason is that their cost is not competitive yet. In this review, the reasons behind this situation are analyzed, together with the perspectives for the coming years. Keywords: superconductors, high critical temperature superconductors, superconductor applications, high magnetic fields

Near-room-temperature superconductivity of Mg/Ca substituted metal hexahydride under pressure

A quest for room-temperature superconductors is undergoing rapid innovation due to the continuing proliferation of experimental and theoretical researches on high-pressure physics. Hydrogen-caged metal compounds have been proposed to promote high critical temperature superconductivity at pressures, providing a decent opportunity to investigate related phenomena at experimentally attainable pressures. This breakthrough is attributable to the uplifting key parameters, such as electron-phonon interaction and maximum phonon frequency, once thought to be limited, by utilising high pressures. A large class of metal polyhydrides has been theoretically proposed and experimentally realised to promote near-room-temperature superconductivity under high pressures. In this work, we theoretically reported the near-room-temperature superconductivity in a symmetrically Mg/Ca substituted hexahydride, i.e. Mg0.5Ca0.5H6. We showed that this ternary Mg0.5Ca0.5H6 compound adopts an Im3¯m structure, wherein a metal atom is embedded in a H24 cage, is thermodynamically and dynamically stable at pressures ranging from 200 to 400 GPa. The analyses of the electronic band structure, Fermi surface topologies, phonon dispersion, and spectral function manifest strong support for superconductivity. We obtained λ=2.53 and ωlog=1,400K for our Mg/Ca substituted hexahydride at 200 GPa, exhibiting a near-room-temperature Tc of 288 K, which completely exceeds the calculated Tc of its parent compounds, i.e. MgH6 and CaH6.

Quench propagation in commercial REBCO composite tapes

The Normal Zone Propagation Velocity, NZPV, is a widely studied feature in superconducting composite tapes for its technological implications. The stability features and the NZPV values, in different operative conditions, have been investigated in different second generation high critical temperature superconductor tapes. In particular, we focused our studies on tapes, produced by the manufactures SuNAM© and Superpower©. Experimental procedures on the determination of the NZPV, related problems and peculiarities, have been presented and discussed. Data obtained with our experimental configuration, have been analyzed and compared with a phenomenological model.

Proposal of Magnetically Levitated Mover Using High T c SC Coils

Levitation techniques using high critical temperature ( Tc ) superconductors are based on pinning forces between high Tc superconductors and permanent magnets (PMs). In this paper, new type of magnetically levitated mover based on repulsion forces by induced current between high T c superconducting (SC) coils and PMs is proposed. Induced current in SC coil is different from that in normal copper coil. Thus, the static and dynamic characteristics of both the SC coil and the levitated mover are discussed.