arXiv subjects

David Pines

Publications and source records attributed to David Pines.

At least 19 recordsLinked to original sources

arXiv2017

Quantum critical scaling and fluctuations in Kondo lattice materials

We propose a new phenomenological framework for three classes of Kondo lattice materials that incorporates the interplay between the fluctuations associated with the antiferromagnetic quantum critical point and those produced by the hybridization quantum critical point that marks the end of local moment behavior. We show that these fluctuations give rise to two distinct regions of quantum critical scaling: hybridization fluctuations are responsible for the logarithmic scaling in the density of states of the heavy electron Kondo liquid that emerges below the coherence temperature T*; while the unconventional power law scaling in the resistivity that emerges at lower temperatures below T_QC may reflect the combined effects of hybridization and antiferromagnetic quantum critical fluctuations. Our framework is supported by experimental measurements on CeCoIn5, CeRhIn5 and other heavy electron materials.

cond-mat.str-el↗

arXiv2016

Nonlinear interglitch dynamics, the braking index of the Vela pulsar and the time to the next glitch

The inter-glitch timing of the Vela pulsar is characterized by a constant second derivative of the rotation rate. This takes over after the post-glitch exponential relaxation, and is completed at about the time of the next glitch. The vortex creep model explains the second derivatives in terms of non-linear response to the glitch. We present inter-glitch timing fits to the present sample covering 16 large glitches, taking into account the possibility that in some glitches part of the step in spin-down rate may involve a "persistent shift", as observed in the Crab pulsar. Modifying the expression for the time between glitches with this hypothesis leads to better agreement with the observed inter-glitch time intervals. We extrapolate the inter-glitch model fits to obtain spin-down rates just prior to each glitch, and use these to calculate the braking index n = 2.81 +/- 0.12. The next glitch should occur around Dec. 22, 2017 +/- 197 days if no persistent shift is involved, but could occur as early as July 27, 2016 +/- 152 days if the 2013 glitch gave rise to a typical Vela persistent shift. Note added: Literally while we were submitting the first version of this paper, on Dec. 12, 2016, we saw ATel # 9847 announcing a Vela pulsar glitch which has arrived 138 days after our prediction with a persistent shift, within the 1 sigma uncertainty of 152 days.

astro-ph.HE↗

arXiv2016

Emergent Behavior in Strongly Correlated Electron Systems

I describe early work on strongly correlated electron systems [SCES] from the perspective of a theoretical physicist who, while a participant in their reductionist top- down beginnings, is now part of the paradigm change to a bottom-up "emergent" approach with its focus on using phenomenology to find the organizing principles responsible for their emergent behavior disclosed by experiment---and only then constructing microscopic models that incorporate these. After considering the organizing principles responsible for the emergence of plasmons, quasiparticles, and conventional superconductivity in SCES, I consider their application to three of SCES's sister systems, the helium liquids, nuclei, and the nuclear matter found in neutron stars. I note some recent applications of the random phase approximation and examine briefly the role that paradigm change is playing in two central problems in our field: understanding the emergence and subsequent behavior of heavy electrons in Kondo lattice materials; and finding the mechanism for the unconventional superconductivity found in heavy electron, organic, cuprate, and iron-based materials.

cond-mat.str-el↗

arXiv2016

Toward a New Microscopic Framework for Kondo Lattice Materials

Understanding the emergence and subsequent behavior of heavy electrons in Kondo lattice materials is one of the grand challenges in condensed matter physics. In this perspective we review the progress that has been made during the past decade and suggest some directions for future research. Our focus will be on developing a new microscopic framework that incorporates the basic concepts that emerge from a phenomenological description of the key experimental findings.

cond-mat.str-el↗

arXiv2014

The Emergence of Superconductivity in Heavy Electron Materials

Although the pairing glue for the attractive quasiparticle interaction responsible for unconventional superconductivity in heavy electron materials has been identified as the spin fluctuations that arise from their proximity to a magnetic quantum critical point, there has been no model to describe their superconducting transition at Tc that is comparable to that found by Bardeen, Cooper, and Schrieffer (BCS) for conventional superconductors where phonons provide the pairing glue. Here we propose a phenomenological BCS-like expression for Tc in heavy electron materials, that is based on the unusual properties of the heavy electron normal state from which superconductivity emerges, and a simple model for the effective range and strength of the spin-fluctuation-induced quasiparticle interaction. We show that it provides both a physical explanation and the first quantitative understanding of the pressure-induced variation of Tc in the "hydrogen atoms" of unconventional superconductivity, CeCoIn5 and CeRhIn5, and predicts scaling behavior and a dome-like structure for Tc in all heavy electron quantum critical superconductors.

cond-mat.supr-con↗

arXiv2014

Quantum critical scaling and superconductivity in heavy electron materials

We use the two fluid model to determine the conditions under which the nuclear spin-lattice lattice relaxation rate, $T_1$, of candidate heavy quantum critical superconductors can exhibit scaling behavior and find that it can occur if and only if their "hidden" quantum critical spin fluctuations give rise to a temperature-independent intrinsic heavy electron spin-lattice relaxation rate. The resulting scaling of $T_1$ with the strength of the heavy electron component and the coherence temperature, $T^*$, provides a simple test for their presence at pressures at which the superconducting transition temperature, $T_c$, is maximum and is proportional to $T^*$. These findings support the previously noted partial scaling of the spin-lattice relaxation rate with $T_c$ in a number of important heavy electron materials and provide additional evidence that in these materials their optimal superconductivity originates in the quantum critical spin fluctuations associated with a nearby phase transition from partially localized to fully itinerant quasiparticles.

cond-mat.supr-con↗

arXiv2014

Quantum critical behavior in heavy electron materials

Quantum critical behavior in heavy electron materials is typically brought about by changes in pressure or magnetic field. In this communication, we develop a simple unified model for the combined influence of pressure and magnetic field on the effectiveness of the hybridization that plays a central role in the two-fluid description of heavy electron emergence. We show that it leads to quantum critical and delocalization lines that accord well with those measured for CeCoIn5, yields a quantitative explanation of the field and pressure induced changes in antiferromagnetic ordering and quantum critical behavior measured for YbRh2Si2, and provides a valuable framework for describing the role of magnetic fields in bringing about quantum critical behavior in other heavy electron materials.

cond-mat.str-el↗

arXiv2013

Finding New Superconductors: The Spin-Fluctuation Gateway to High Tc and Possible Room Temperature Superconductivity

We propose an experiment-based strategy for finding new high transition temperature superconductors that is based on the well-established spin fluctuation magnetic gateway to superconductivity in which the attractive quasiparticle interaction needed for superconductivity comes from their coupling to dynamical spin fluctuations originating in the proximity of the material to an antiferromagnetic state. We show how lessons learned by combining the results of almost three decades of intensive experimental and theoretical study of the cuprates with those found in the decade-long study of a strikingly similar family of unconventional heavy electron superconductors, the 115 materials, can prove helpful in carrying out that search. We conclude that since Tc in these materials scales approximately with the strength of the interaction, J, between the nearest neighbor local moments in their parent antiferromagnetic state, there may not be a magnetic ceiling that would prevent one from discovering a room temperature superconductor.

cond-mat.supr-con↗

arXiv2012

Emergent states in heavy electron materials

We obtain the conditions necessary for the emergence of various low temperature ordered states (local moment antiferromagnetism, unconventional superconductivity, quantum criticality, and Landau Fermi liquid behavior) in Kondo lattice materials by extending the two-fluid phenomenological theory of heavy electron behavior to incorporate the concept of hybridization effectiveness. We use this expanded framework to present a new phase digram and consistent physical explanation and quantitative description of measured emergent behaviors such as the pressure variation of the onset of local moment antiferromagnetic ordering at T_N, the magnitude of the ordered moment, the growth of superconductivity within that ordered state, the location of a quantum critical point, and of a delocalization line in the pressure/temperature phase diagram at which local moments have disappeared and the heavy electron Fermi surface has grown to its maximum size. We apply our model to CeRhIn_5 and a number of other heavy electron materials and find good agreement with experiment.

cond-mat.str-el↗

arXiv2009

Magnetic excitations in Kondo liquid: Superconductivity and Hidden Magnetic Quantum Critical Fluctuations

We report Knight shift experiments on the superconducting heavy electron material CeCoIn$_5$ that allow one to track with some precision the behavior of the heavy electron Kondo liquid in the superconducting state with results in agreement with BCS theory. An analysis of the $^{115}$In nuclear quadrupole resonance (NQR) spin-lattice relaxation rate $T_1^{-1}$ measurements under pressure reveals the presence of 2d magnetic quantum critical fluctuations in the heavy electron component that are a promising candidate for the pairing mechanism in this material. Our results are consistent with an antiferromagnetic quantum critical point (QCP) located at slightly negative pressure in CeCoIn$_5$ and provide additional evidence for significant similarities between the heavy electron materials and the high $T_c$ cuprates.

cond-mat.str-el↗

arXiv2009

Universal Behavior and the Two-component Character of Magnetically Underdoped Cuprate Superconductors

We present a detailed review of scaling behavior in the magnetically underdoped cuprate superconductors (hole dopings less than 0.20) and show that it reflects the presence of two coupled components throughout this doping regime: a non-Landau Fermi liquid and a spin liquid whose behavior maps onto the theoretical Monte Carlo calculations of the 2D Heisenberg model of localized Cu spins for most of its temperature domain. We use this mapping to extract the doping dependence of the strength, $f(x)$ of the spin liquid component and the effective interaction, J_eff(x) between the remnant localized spins that compose it; we find both decrease linearly with x as the doping level increases. We discuss the physical origin of pseudogap behavior and conclude that it is consistent with scenarios in which the both the large energy gaps found in the normal state and their subsequent superconductivity are brought about by the coupling between the Fermi liquid quasiparticles and the spin liquid excitations, and that differences in this coupling between the 1-2-3 and 2-1-4 materials can explain the measured differences in their superconducting transition temperatures and other properties.

cond-mat.supr-con↗

arXiv2007

Universal Behavior in Heavy Electron Materials

We present our finding that an especially simple scaling expression describes the formation of a new state of quantum matter, the Kondo Fermi liquid (KL) in heavy electron materials. Emerging at $T^*$ as a result of the collective coherent hybridization of localized f electrons and conduction electrons, the KL possesses a non-Landau density of states varying as $(1-T/T^*)^{3/2}[1+\ln(T^*/T)]$. We show that four independent experimental probes verify this scaling behavior and that for CeIrIn$_5$ the KL state density is in excellent agreement with the recent microscopic calculations of hybridization in this material by Shim, Haule, and Kotliar.

cond-mat.str-el↗

arXiv2006

Phenomenological model of protected behavior in the cuprate superconductors

By extending previous work on the scaling of low frequency magnetic properties of the 2-1-4 cuprates to the 1-2-3 materials, we arrive at a consistent phenomenological description of protected behavior in the pseudogap state of the magnetically underdoped cuprates. Between zero hole doping and a doping level of $\sim 0.22$ it reflects the presence of a mixture of an insulating spin liquid that produces the measured magnetic scaling behavior and a Fermi liquid that becomes superconducting for doping levels $x>0.06$. Our analysis suggests the existence of two quantum critical points, at doping levels, $x \sim 0.05$ and $x \sim 0.22$, and that d-wave superconductivity in the pseudogap region arises from quasiparticle-spin liquid interaction, i.e. magnetic interactions between quasiparticles in the Fermi liquid induced by their coupling to the spin liquid excitations.

cond-mat.str-el↗

arXiv2004

Pseudogap Behavior in Underdoped Cuprates

I review some of the experimental evidence and theoretical arguments that suggest that pseudogap matter is a new form of matter that coexists with coherent electron matter in the normal state and with superconducting matter below the superconducting transition temperature. I describe work in progress on a phenomenological two-fluid description of the evolution of pseudogap behavior that offers an explanation for the unexpectedly simple scaling behavior for the uniform magnetic susceptibility found in the underdoped cuprates and use this to propose a physical picture of the underdoped cuprates and to estimate the fraction of quasiparticles that become superconducting in underdoped superconductors.

cond-mat.str-el↗

arXiv2003

Probing the Kondo Lattice

We present a phenomenological solution of the Kondo lattice that is derived from an analysis of the bulk specific heat and spin susceptibility of the heavy electron superconductor CeCoIn5. We find that below a crossover temperature corresponding to the intersite coupling scale, T* ~ 45 K, the Kondo gas (of non-interacting Kondo impurities) partially condenses into a heavy electron "Kondo" liquid that has a temperature independent Wilson ratio = 2.0. The relative fraction, f, of the "condensed" Kondo liquid component plays the role of an order parameter; it increases linearly with decreasing temperature until it saturates at its low temperature value of 0.9. The resistivity is shown to be simply the product of (1-f) and that of an isolated Kondo impurity. The generality of this result is suggested by the corresponding analysis for Ce1-xLaxCoIn5 and CeIrIn5.

cond-mat.str-el↗

arXiv2002

A Spin Fluctuation Model for D-wave Superconductivity

In this review we demonstrate that superconducting pairing, mediated by the exchange of spin fluctuations, is a viable alternative to conventional phonon-mediated pairing. We discuss in detail the normal state properties, the spin fluctuation induced d-wave pairing and the superconducting behavior of a material near an antiferromagnetic instability, when the dominant interaction between quasiparticles is of electronic origin, and at energies much smaller than the fermionic bandwidth, can be viewed as being due to the emission and absorption of a collective, soft spin degree of freedom. We show that in the vicinity of an antiferromagnetic quantum critical point the system behavior is universal, at least when the effective spin fermion interaction is smaller than the fermionic bandwidth. We further argue that spin-fluctuation exchange yields an attraction and pairing in the $d_{x^{2}-y^{2}}$ channel in agreement with what nearly all researchers now believe is the pairing symmetry in the cuprates. We discuss "fingerprints" of a spin mediated pairing state, chiefly associated with the emergence of the resonance peak in the spin response in a d-wave superconductor and identify these fingerprints in spectroscopic experiments on optimally doped cuprate superconconductors.

cond-mat.str-el↗

arXiv2000

Magnetic Coherence as a Universal Feature of Cuprate Superconductors

Recent inelastic neutron scattering (INS) experiments on La$_{2-x}$Sr$_x$CuO$_4$ have established the existence of a {\it magnetic coherence effect}, i.e., strong frequency and momentum dependent changes of the spin susceptibility, $χ''$, in the superconducting phase. We show, using the spin-fermion model for incommensurate antiferromagnetic spin fluctuations, that the magnetic coherence effect establishes the ability of INS experiments to probe the electronic spectrum of the cuprates, in that the effect arises from the interplay of an incommensurate magnetic response, the form of the underlying Fermi surface, and the opening of the d-wave gap in the fermionic spectrum. In particular, we find that the magnetic coherence effect observed in INS experiments on La$_{2-x}$Sr$_x$CuO$_4$ requires that the Fermi surface be closed around $(π,π)$ up to optimal doping. We present several predictions for the form of the magnetic coherence effect in YBa$_2$Cu$_3$O$_{6+x}$ in which an incommensurate magnetic response has been observed in the superconducting state.

cond-mat.supr-con↗

arXiv2000

Magnetic Coherence in Cuprate Superconductors

Recent inelastic neutron scattering (INS) experiments on La$_{2-x}$Sr$_x$CuO$_4$ observed a {\it magnetic coherence effect}, i.e., strong frequency and momentum dependent changes of the spin susceptibility, $χ''$, in the superconducting phase. We show that this effect is a direct consequence of changes in the damping of incommensurate antiferromagnetic spin fluctuations due to the appearance of a d-wave gap in the fermionic spectrum. Our theoretical results provide a quantitative explanation for the weak momentum dependence of the observed spin-gap. Moreover, we predict {\bf (a)} a Fermi surface in La$_{2-x}$Sr$_x$CuO$_4$ which is closed around $(π,π)$ up to optimal doping, and {\bf (b)} similar changes in $χ''$ for all cuprates with an incommensurate magnetic response.

cond-mat.supr-con↗