TOPICAL REVIEW: Charge and spin-density-wave superconductors (original) (raw)
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Charge-and spin-density-wave superconductors
2001
Abstract This review deals with the properties of superconductors with competing electron spectrum instabilities, namely, charge-density waves (CDWs) and spin-density waves (SDWs). The underlying reasons of the electron spectrum instability may be either Fermi surface nesting or the existence of Van Hove saddle points for lower dimensionalities. CDW superconductors include layered dichalcogenides, NbSe3, and compounds with the A15 and C15 structures among others.
Charge- and spin-density-wave superconductors. Topical review:
Superconding Scence and Technology, 2001
This review deals with the properties of superconductors with competing electron spectrum instabilities, namely, charge-density waves (CDWs) and spin-density waves (SDWs). The underlying reasons of the electron spectrum instability may be either Fermi surface nesting or the existence of Van Hove saddle points for lower dimensionalities. CDW superconductors include layered dichalcogenides, NbSe 3 , and compounds with the A15 and C15 structures among others. There is much evidence to show that high-T c oxides may also belong to this group of materials. The SDW superconductors include URu 2 Si 2 and related heavy-fermion compounds, Cr-Re alloys and organic superconductors. We review the experimental evidence for CDW and SDW instabilities in a wide range of different superconductors, and assess the competition between these instabilities of the Fermi surface and the superconducting gap. Issues concerning the superconducting order parameter symmetry are also touched upon. The accent is put on establishing a universal framework for further theoretical discussions and experimental investigations based on an extensive list of available and up-to-date references. Corresponding authors. become a so-called 'ideal conductor' with a zero resistance, rather than a true superconductor exhibiting the Meissner and Josephson effects . It is remarkable that the concept of the electron spectrum energy gap in the superconducting state had also been proposed by Bardeen [12] almost simultaneously with Fröhlich and before the full microscopic Bardeen-Cooper-Schrieffer (BCS) theory was developed .
Physics Reports-review Section of Physics Letters, 2002
This review is an up-to-date snapshot of the current situation in studies of materials with competing electron spectrum instabilities, namely Cooper pairing, on the one hand, and charge-density waves (CDWs) or spin-density waves (SDWs), on the other. The CDW- or SDW-driven instabilities in electron spectra with reduced dimensionalities may result from either the Fermi surface (FS) nesting or the existence of the Van Hove saddle points and lead to the appearance of the Peierls (excitonic) gap on parts of the FS (partial gapping). CDW superconductors include layered dichalcogenides, NbSe3, some organic substances and compounds with A15 and C15 structures among others. A large body of data is presented which may be considered as an evidence that high-Tc oxides also belong to this class of materials. In particular, an interpretation is given for the pseudogap phenomena in cuprates as having the CDW origin. The SDW superconductors include heavy-fermion compounds and UPd2Al3, Cr–Re alloys and a number of organic superconductors. We discuss the experimental information on the existence of CDW and SDW instabilities in a wide range of different superconductors, and assess their contention with the Cooper pairing on the Fermi surface. The main emphasis is placed on the properties of the existing substances with the interplay between superconductivity and CDW- or SDW-waves rather than on theoretically analyzing the possibility of such mixed phases in the framework of idealized microscopic theoretical models. The problem of symmetry for relevant order parameters is also touched upon. The theoretical description of the partially gapped CDW and SDW superconductors is presented based mostly on the phenomenological Bilbro–McMillan model. Various thermodynamical and electrodynamical properties are analyzed in this framework. Much emphasis is given to the nonstationary Josephson effect in tunnel junctions involving CDW or SDW superconductors. A comparison is carried out with the experiment, with special attention paid to high-Tc oxides.
Superconductors with charge- and spin-density waves: theory and experiment (Review)
Low Temperature Physics, 2000
The properties of existing superconductors with ejectron spectrum instabilities, namely chargedensity waves ͑CDWs͒ and spin-density waves ͑SDWs͒, are reviewed. In such substances the superconducting gap exists over the whole Fermi surface, whereas the dielectric gap emerges only on its nested sections. In particular, CDW superconductors include layered dichalcogenides, NbSe 3 , compounds with the A15 and C15 structures, etc. There is a lot of evidence that high-T c oxides also belong to this group of materials. SDW superconductors include, e.g., URu 2 Si 2 and related heavy-fermion compounds, Cr-Re alloys and organic superconductors. The theoretical description given in this review is based mostly on the Bilbro-McMillan model of the partially dielectrized metal. Various thermodynamic and electrodynamic properties are calculated in the framework of this model. The main subject of the review is the nonstationary Josephson effect in tunnel junctions involving CDW or SDW superconductors. A new effect of symmetry breaking in symmetrical tunnel junctions is predicted by the authors. A comparison with experiment is given.
Superconductors with charge- and spin-density waves: theory and experiment (Review article)
Low Temp. Phys., 2000
The properties of existing superconductors with ejectron spectrum instabilities, namely chargedensity waves ͑CDWs͒ and spin-density waves ͑SDWs͒, are reviewed. In such substances the superconducting gap exists over the whole Fermi surface, whereas the dielectric gap emerges only on its nested sections. In particular, CDW superconductors include layered dichalcogenides, NbSe 3 , compounds with the A15 and C15 structures, etc. There is a lot of evidence that high-T c oxides also belong to this group of materials. SDW superconductors include, e.g., URu 2 Si 2 and related heavy-fermion compounds, Cr-Re alloys and organic superconductors. The theoretical description given in this review is based mostly on the Bilbro-McMillan model of the partially dielectrized metal. Various thermodynamic and electrodynamic properties are calculated in the framework of this model. The main subject of the review is the nonstationary Josephson effect in tunnel junctions involving CDW or SDW superconductors. A new effect of symmetry breaking in symmetrical tunnel junctions is predicted by the authors. A comparison with experiment is given.
d-wave superconductivity near charge instabilities
Physical Review B, 1996
We investigate the symmetry of the superconducting order parameter in the proximity of a phase-separation or of an incommensurate charge-density-wave instability. The attractive effective interaction at small or intermediate transferred momenta is singular near the instability. This strongly q-dependent interaction, together with a residual local repulsion between the quasiparticles and an enhanced density of states for band structures appropriate for the high temperature superconducting oxides, strongly favors the formation of d-wave superconductivity. The relative stability with respect to superconductivity in the s-wave channel is discussed in detail, finding this latter hardly realized in the above conditions. The superconducting temperature is mostly determined by the closeness to the quantum critical point associated to the charge instability and displays a stronger dependence on doping with respect to the simple proximity to a Van Hove singularity. The relevance of this scenario and the generic agreement of the resulting phase diagram with the properties displayed by high temperature superconducting oxides is discussed.
Symmetry, 2011
A review of the theory describing the coexistence between d-wave superconductivity and s-wave charge-density-waves (CDWs) is presented. The CDW gapping is identified with pseudogapping observed in high-T c oxides. According to the cuprate specificity, the analysis is carried out for the two-dimensional geometry of the Fermi surface (FS). Phase diagrams on the σ 0 − α plane-here, σ 0 is the ratio between the energy gaps in the parent pure CDW and superconducting states, and the quantity 2α is connected with the degree of dielectric (CDW) FS gapping-were obtained for various possible configurations of the order parameters in the momentum space. Relevant tunnel and photoemission experimental data for high-T c oxides are compared with theoretical predictions. A brief review of the results obtained earlier for the coexistence between s-wave superconductivity and CDWs is also given. Symmetry 2011, 3 700 Classification: PACS 74.20.-z; 74.20.Rp; 71.45.Lr; 74.72.-h
2011
A review of the theory describing the coexistence between d-wave superconductivity and s-wave charge-density-waves (CDWs) is presented. The CDW gapping is identified with pseudogapping observed in high-T c oxides. According to the cuprate specificity, the analysis is carried out for the two-dimensional geometry of the Fermi surface (FS). Phase diagrams on the σ 0 − α plane-here, σ 0 is the ratio between the energy gaps in the parent pure CDW and superconducting states, and the quantity 2α is connected with the degree of dielectric (CDW) FS gapping-were obtained for various possible configurations of the order parameters in the momentum space. Relevant tunnel and photoemission experimental data for high-T c oxides are compared with theoretical predictions. A brief review of the results obtained earlier for the coexistence between s-wave superconductivity and CDWs is also given.
Charge-4e superconductivity from pair-density-wave order in certain high-temperature superconductors
Nature Physics, 2009
A number of spectacular experimental anomalies 1,2 have recently been discovered in certain cuprates, notably La 2−x Ba x CuO 4 and La 1.6−x Nd 0.4 Sr x CuO 4 , which exhibit unidirectional spin and charge order (known as "stripe order"). We have recently proposed to interpret these observations as evidence for a novel "striped superconducting" state, in which the superconducting order parameter is modulated in space, such that its average is precisely zero. Here, we show that thermal melting of the striped superconducting state can lead to a number of unusual phases, of which the most novel is a charge 4e superconducting state, with a corresponding fractional flux quantum hc/4e. These are never-before observed states of matter, and ones, moreover, that cannot arise from the conventional Bardeen-Cooper-Schrieffer (BCS) mechanism. Thus, direct confirmation of their existence, even in a small subset of the cuprates, could have much broader implications for our understanding of high temperature superconductivity. We propose experiments to observe fractional flux quantization, which thereby could confirm the existence of these states.