Unconventional high-Tc superconductivity in fullerides Takabayashi, Yasuhiro; Prassides, Kosmas
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
09/2016, Letnik:
374, Številka:
2076
Journal Article
Recenzirano
A3C60 molecular superconductors share a common electronic phase diagram with unconventional high-temperature superconductors such as the cuprates: superconductivity emerges from an antiferromagnetic ...strongly correlated Mott-insulating state upon tuning a parameter such as pressure (bandwidth control) accompanied by a dome-shaped dependence of the critical temperature, Tc. However, unlike atom-based superconductors, the parent state from which superconductivity emerges solely by changing an electronic parameter-the overlap between the outer wave functions of the constituent molecules-is controlled by the C603− molecular electronic structure via the on-molecule Jahn-Teller effect influence of molecular geometry and spin state. Destruction of the parent Mott-Jahn-Teller state through chemical or physical pressurization yields an unconventional Jahn-Teller metal, where quasi-localized and itinerant electron behaviours coexist. Localized features gradually disappear with lattice contraction and conventional Fermi liquid behaviour is recovered. The nature of the underlying (correlated versus weak-coupling Bardeen-Cooper-Schrieffer theory) s-wave superconducting states mirrors the unconventional/conventional metal dichotomy: the highest superconducting critical temperature occurs at the crossover between Jahn-Teller and Fermi liquid metal when the Jahn-Teller distortion melts.
This article is part of the themed issue ‘Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene’.
We use the cumulant Green's functions method (CGFM) to study the single-band Hubbard model. The starting point of the method is to diagonalize a cluster ('seed') containing
correlated sites and ...employ the cumulants calculated from the cluster solution to obtain the full Green's functions for the lattice. All calculations are done directly; no variational or self-consistent process is needed. We benchmark the one-dimensional results for the gap, the double occupancy, and the ground-state energy as functions of the electronic correlation at half-filling and the occupation numbers as functions of the chemical potential obtained from the CGFM against the corresponding results of the thermodynamic Bethe ansatz and the quantum transfer matrix methods. The particle-hole symmetry of the density of states is fulfilled, and the gap, occupation numbers, and ground-state energy tend systematically to the known results as the cluster size increases. We include a straightforward application of the CGFM to simulate the singles occupation of an optical lattice experiment with lithium-6 atoms in an eight-site Fermi-Hubbard chain near half-filling. The method can be applied to any parameter space for one, two, or three-dimensional Hubbard Hamiltonians and extended to other strongly correlated models, like the Anderson Hamiltonian, the
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, Kondo, and Coqblin-Schrieffer models.
In this work, a type-III heterojunction based on a pulsed-laser-deposited vanadium dioxide (VO2) and p-type silicon (p-Si) substrate is realized. The device shows a large self-powered and ...room-temperature photoresponse to IR (950 nm), green (515 nm) and blue (456 nm) LEDs. A short-circuit current (Isc) of ∼3 µA and an open-circuit voltage (Voc) of ∼−120 mV are observed under IR LED illumination. The work function data in literature along with the sign of Voc measurement is used to sketch the energy band diagram of the heterojunction. The temperature-dependent Isc properties of the junction, contrary to conventional photodetectors, show an initial rise and then a sharp transition from maximum (3.5 μA) to almost zero near 337 K, corresponding to a metal-insulator phase transition, paving the way for photodetectors with temperature-tunable photoresponsivity.
We construct a four-leg spin-1/2 t-J type model to simulate a doped two-leg spin-1 antiferromagnetic Heisenberg ladder. Employing renormalized mean-field theory with simple Gutzwiller factors, we ...obtain three degenerate superconducting states with different pairing symmetry. Through improving the Gutzwiller factors, we find that the state C with inter-layer modified d y 2 − z 2 -wave pairing has the lowest energy in a large doping range. Besides, we use the density matrix renormalization group method to solve the model. The negative binding energy reveals the pairing tendency, and the pair-pair correlation functions exhibit a slowly decaying behavior on certain types of bonds. From the pair correlations, we confirm the inter-layer modified d y 2 − z 2 -wave superconducting state as the ground state of the model.
Abstract
The cluster mean-field with density matrix renormalization (CMFT + DMRG) method which combines the simplicity of the mean-field theory and the numerical power of the density-matrix ...renormalization group method is applied to understand the quantum phases of the one-dimensional Bose–Hubbard models. We show that the CMFT + DMRG method is an effective numerical technique with moderate computational resources to determine relevant order parameters and correlation functions of large one-dimensional systems. We apply the CMFT + DMRG for the Bose Hubbard and extended Bose Hubbard models to account for the superfluid, Mott insulator, and density wave phases in these models. Our results are in good agreement with the known phase diagram of these models, demonstrating the efficacy of this method.
The AM4Q8 family of chalcogenide Mott insulator compounds exhibit an electric pulse induced resistive switching that could be used in data storage applications as Mott memories. Depending on the ...applied electric field, this transition is either volatile or non‐volatile. This study demonstrates that the theory established for the volatile transition can be used to understand the non‐volatile transition. It leads to propose a simple model for the SET and RESET transitions. In addition, we show that the alternation of short high voltage multi‐pulses with long low voltage single pulses enables to control the non‐volatile resistive switching and to achieve multi‐level switching. This memristive property opens the way to the use in neuromorphic applications of this new type of resistive switching inherent to Mott insulators.
The interfaces between superconductors and other materials have long been established as being an important part in the exploration of new physics to aid in our understanding of superconductivity and ...open us up to new technological advancements. Herein this article we analyse the recent progress made in the understanding of superconductivity at the interfaces involving a wide range of functional materials, mostly looking at two-dimensional (2D) systems.
We start off in the first half of this review by focusing on magnetic and superconductive hybrid heterostructures, as well as the resulting physical phenomena from these systems. The first is a section on vortex and anti-vortex phenomena; the second key area is ferromagnet–superconductor hybrid phenomena with particular interest of magnetic skyrmions, the third is the novel frontier based on 2D magnetic and superconductive interfaces particularly examining Ising superconductivity at these interfaces; the fourth is superconductivity at anti-ferromagnetic interfaces and finally half-metals at superconducting interfaces.
The second half of this review focuses on superconductivity at insulating and other functional interfaces. Examining firstly, Mott insulator interfaces with wide ranging discussions about how such interfaces can enhance our understanding in high-temperature superconductive cuprates and other unconventional superconductor systems such as the nickelates; in the second section the interface of 2D and 3D ferroelectric materials with superconductors with a key emphasis on devices that have been developed to control the superconducting phase; Topological insulators at interfaces with superconductors is the third section; and lastly 2D twisted material interfaces are explored, including the newly discovered magic angle interfaces discovered with graphene and other van Der Waals materials. It is anticipated that this review will lead to further interest in such interfaces to improve our understanding and expose the exotic science behind these interfaces.
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Magnetic and structural properties of double perovskite type bromides Cs2MBr6 (M = Ta, Nb), where Ta4+ (5d1) and Nb4+ (4d1) ions form the face centered cubic lattice, are investigated and compared ...with chlorides Cs2MCl6. Cs2TaBr6 exhibits the effective magnetic moment of 0.24 μB, which is much smaller than the spin only value of a d1 ion, 1.73 μB, and comparable to 0.25 μB in Cs2TaCl6. On the other hand, the effective magnetic moment of Cs2NbBr6 is 0.7 μB and is substantially smaller than 1.0 μB in Cs2NbCl6. On cooling, successive structural and magnetic phase transitions accompanying the release of electronic entropy approximately Rln 4 in total as expected for the Jeff = 3/2 state are observed. The type of the ligand changes the temperature dependence of magnetic susceptibility at low temperature as well as its magnitude. The role of the ligands on the magnetism of Jeff = 3/2 Mott insulators are discussed in the light of metal-ligand hybridization and the electron-lattice coupling.
Vanadium dioxide (VO2), a well-known Mott insulator and a prominent thermochromic material, exhibits an intelligent optical response from the infrared-transparent state to the infrared-blocking state ...below and above its transition temperature, respectively. Despite there have been numerous studies on its synthesis, a few could readily obtain high quality VO2 thin films except on single crystal epitaxial substrates. Its lack of versatility to form onto various substrates while retaining the specific function also needs to be addressed. Here, we present a sputtering method using V2O5 target with in situ annealing to prepare high-quality VO2 thin films on Si and quartz substrates. The results show that pure monoclinic VO2 could be obtained in a narrow range of oxygen flow ratio (from 0 to 0.74%) in Ar/O2 working gas during sputter deposition. The structural evolution was verified by Raman spectroscopy. At the transition temperature, the remarkably large optical transmittance contrasts of ~74% and ~77% were obtained at the incident wavelength of 2.5 and 3 μm, respectively. The luminous transmittance values at room temperature and high temperature were 36.63 and 38.87%, respectively. The measured solar transmittance modulation efficiency (∆Tsol) was 5.87%, which is comparable to or even better than the reported values of VO2 films prepared using sputtering. We also demonstrated the spontaneous response of electrical performance with applying potential and varying temperature. Our results revealed the facile preparation of large area and high-performance thermochromic VO2 thin film on non-epitaxial substrates of Si and quartz which greatly augment its applications in solar-heat managements and optoelectronics.
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•VO2 films are prepared using sputter deposition from V2O5 with in situ annealing.•Sharp semiconductor-to-metal transition is revealed by Raman spectroscopy/mapping.•Remarkably high transmittance contrast of ~74% (λ = 2.5 μm) and ~77% (λ = 3 μm).•The prepared VO2 film provides a promising perspective for thermal management applications.
In this work, we demonstrate abrupt, reversible switching of resistance in 1T-TaS2 using dc and pulsed sources, corresponding to an insulator–metal transition between the insulating Mott and ...equilibrium metallic states. This transition occurs at a constant critical resistivity of 7 mohm-cm regardless of temperature or bias conditions and the transition time is significantly smaller than abrupt transitions by avalanche breakdown in other small gap Mott insulating materials. Furthermore, this critical resistivity corresponds to a carrier density of 4.5 × 1019 cm–3, which compares well with the critical carrier density for the commensurate to nearly commensurate charge density wave transition. These results suggest that the transition is facilitated by a carrier driven collapse of the Mott gap in 1T-TaS2, which results in fast (3 ns) switching.
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