Kondo Effect in High-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>T</mml:mi></mml:mrow><mml:mrow><mml:mi>c</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>Cuprates

Nagaosa, Naoto; Lee, Patrick A.

doi:10.1103/physrevlett.79.3755

Cited by 49 publications

(49 citation statements)

References 28 publications

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“…However, E ± differs from the normal state spectrum E N ± by the appearance of the term −(x pc ∆/x) 2 in Eq. (10). Close to the node this term is small so that qualitatively the spectrum develops from the normal state in a BCS fashion, as shown in Fig.…”

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Theory of Quasiparticles in the Underdoped High-TcSuperconducting State

1998

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The microscopic theory of superconducting (SC) state in the SU (2) slave-boson model is developed. We show how the pseudogap and Fermi surface (FS) segments in the normal state develop into a d-wave gap in the superconducting state. Even though the superfluid density is of order x (the doping concentration), the physical properties of the low lying quasiparticles are found to resemble those in BCS theory. Thus the microscopic theory lay the foundation for our earlier phenomenological discussion of the unusual SC properties in the underdoped cuprates.

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Theory of Quasiparticles in the Underdoped High-TcSuperconducting State

1998

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“…A long-standing problem in heavy fermion physics concerns the very small magnetic moments which have been observed in several materials [1,2] and may be related to grain boundaries and other structural defects [3][4][5]. In a colossal magnetoresistance material, magnetic order was observed to be enhanced near grain boundaries.[6] A related issue is the magnetism induced in high temperature superconductors by apparently non-magnetic substituents such as Zn [7], which have been interpreted [8,9] as spin droplets induced in a nearly critical system (although other interpretations exist also [10]). Nucleation of regions of charge density wave order around defect sites on the surface of a 'correlated' material was reported by [11].…”

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“…[6] A related issue is the magnetism induced in high temperature superconductors by apparently non-magnetic substituents such as Zn [7], which have been interpreted [8,9] as spin droplets induced in a nearly critical system (although other interpretations exist also [10]). Nucleation of regions of charge density wave order around defect sites on the surface of a 'correlated' material was reported by [11].…”

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Local Defect in Metallic Quantum Critical Systems

2001

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We present a theory of a single point, line or plane defect coupling to the square of the order parameter in a metallic system near a quantum critical point at or above its upper critical dimension. At criticality, a spin droplet is nucleated around the defect with droplet core size determined by the strength of the defect potential. Outside the core a universal slowly decaying tail of the droplet is found, leading to many dissipative channels coupling to the droplet and to a complete suppression of quantum tunneling. We propose an NMR experiment to measure the impurity-induced changes in the local spin susceptibility. 75.10.Jm,75.10.Nr,75.70.Kw,76.30.Da The behavior of 'droplets' of local order in a nonordered background is an issue of wide relevance in condensed matter physics. One particularly interesting subclass of problems concerns 'droplets' induced by defects in nearly critical systems. A long-standing problem in heavy fermion physics concerns the very small magnetic moments which have been observed in several materials [1,2] and may be related to grain boundaries and other structural defects [3][4][5]. In a colossal magnetoresistance material, magnetic order was observed to be enhanced near grain boundaries.[6] A related issue is the magnetism induced in high temperature superconductors by apparently non-magnetic substituents such as Zn [7], which have been interpreted [8,9] as spin droplets induced in a nearly critical system (although other interpretations exist also [10]). Nucleation of regions of charge density wave order around defect sites on the surface of a 'correlated' material was reported by [11]. 'Quantum Griffiths' effects and 'Kondo disorder' are presently of intense interest. [12][13][14][15]. The problem bears on the fundamental issue of the Kondo effect near a quantum critical point [16]. Finally, recording of information involves the polarization of small domains, whose long time dynamics and stability are of great importance.This Letter presents the theory of the local polarization ('droplet') induced by a single defect in an otherwise nondisordered system which is near a quantum critical point at or above it upper critical dimension, d u . These restrictions allow a controlled theoretical treatment and apply to a wide range of systems including metallic magnets in dimensions d = 2, 3 [17,18] and "quantum paraelectric" (i.e. nearly ferroelectric) systems in d = 3 [19]. We study defects which couple to the square of the order parameter, i.e. change the 'local T c ', and thus create small regions where order is more favored than in the pure system. We address three questions: under which circumstances does the defect create a 'droplet', a region about the defect in which the order parameter is non-vanishing (at least on short time scales)? What is the size and general properties of the droplet? What are the relevant fluctuations? Our work is complementary to that of Vojta and Sachdev [20], who studied a linear coupling of the defect to the order parameter in a quantum critical system...

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“…The significance of the filter functions remains controversial. Other scenarios have focused on the formation of local moments near the Zn impurities [11,12,13]. For instance, if the main effect of nonmagnetic impurities in cuprate superconductors is to locally break spin singlet bonds, the sharp conductance peak has been interpreted as a Kondo resonance [12].…”

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Andreev States near Short-Ranged Pairing Potential Impurities

et al. 2006

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We study Andreev states near atomic scale modulations in the pairing potential in both s-and d-wave superconductors with short coherence lengths. For a moderate reduction of the local gap, the states exist only close to the gap edge. If one allows for local sign changes of the order parameter, however, resonances can occur at energies close to the Fermi level. The local density of states (LDOS) around such pairing potential defects strongly resembles the patterns observed by tunneling measurements around Zn impurities in Bi2Sr2CaCu2O8+x (BSCCO). We discuss how this phase impurity model of the Zn LDOS pattern can be distinguished from other proposals experimentally.PACS numbers: 74.45.+c, 74.62.Dh Motivated by the experimental ability to determine the LDOS with high resolution in both energy and real space using scanning tunneling microscopy (STM), there has recently been a large interest in the perturbations caused by impurities in superconductors. This is because impurities disturb the underlying superconducting state and hence constitute a natural probe of the state in which they are embedded [1]. For magnetic adatoms on the surface of conventional s-wave superconductors such experiments were performed by Yazdani et al [2]. In the superconducting state of BSCCO, STM measurements have provided detailed information about the electronic structure near Ni and Zn impurities [3,4,5]. Near Zn it was found that each impurity generates a sharp conductance peak close to the Fermi level (ω B ∼ −1.5meV). By fixing the bias voltage between the tip and the sample at ω B , the spatial structure of this state can be mapped out: it is strongly localized near the Zn atom with maximum intensity on the impurity site and second largest intensity on the next-nearest neighbor sites.Although there exists a large number of theoretical treatments dealing with the resonant states generated by nonmagnetic impurities in d-wave superconductors, no consensus has been reached on their relevance to experiments [1]. Within the most straightforward scenario where Zn is modelled as a delta-function potential scatterer, low-energy resonant states are generated in the unitary limit where the potential is large compared to all other energy scales of the problem [6]. For realistic bands with particle-hole asymmetry, a particular value of the impurity potential V must be chosen to tune the resonance energy ω B to be close to the Fermi level. Thus, the potential scattering model can reproduce the energetics of the resonant state. However, as is well-known, it produces a low-energy spatial LDOS pattern with a severely suppressed amplitude on the impurity site, in contrast to experimental results on Zn [5]. Physically, this is clear since a large on-site potential V penalizes any substantial amplitude of the impurity-state wavefunction on the impurity site. In fact, within this model the largest intensity is found on the nearest neighbor site to the impurity.These properties of the delta-function potential scatterer are shown in Fig.1. The discrepanc...

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Kondo Effect in High-TcCuprates

Cited by 49 publications

References 28 publications

Theory of Quasiparticles in the Underdoped High-TcSuperconducting State

Theory of Quasiparticles in the Underdoped High-TcSuperconducting State

Local Defect in Metallic Quantum Critical Systems

Andreev States near Short-Ranged Pairing Potential Impurities

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