Fluctuation-induced pair density wave in itinerant ferromagnets

Conduit, Gareth; Pedder, Christopher J.; Green, Andrew G.

doi:10.1103/physrevb.87.121112

Cited by 20 publications

(44 citation statements)

References 47 publications

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“…In essence this describes a reduction in zero-point energy upon the formation of Cooper pairs. One must think a little to recover the same effects in the fermionic quantum order-by-disorder approach [37]. The central idea is to calculate a generating function for the new type of order.…”

Section: Superconductivity and Nematic Ordermentioning

confidence: 99%

“…A trick [37] may be used to calculate the GinzburgLandau function for continuous transitions: Adding and subtracting a term k ∆θ k c † k,↑ c † −k,↑ + c.c to the Hamiltonian. Diagonalising the quadratic parts of the Hamiltonian alongside the added ∆c † c † -term and treating the remaining terms alongside the subtracted ∆c † c † -term perturbatively, recovers the result of adding a source followed by Legendre transformation up to quadratic order.…”

Section: Superconductivity and Nematic Ordermentioning

confidence: 99%

“…Indeed, the additional fluctuation corrections resulting from the inclusion of superconducting order (see Ref. [37] where these results are obtained as outlined in Section III C), are essentially the modfications to the density functional used for ab initio calculations of electronically mediated superconductivity in Refs. [96,97].…”

Section: A Qobd Vs Dft Dmft and Kadanoff-baymmentioning

confidence: 99%

See 2 more Smart Citations

Quantum Order-by-Disorder in Strongly Correlated Metals

Green

Conduit

Krüger

2018

Annu. Rev. Condens. Matter Phys.

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Entropic forces in classical many-body systems, e.g. colloidal suspensions, can lead to the formation of new phases. Quantum fluctuations can have similar effects: spin fluctuations drive the superfluidity of Helium-3 and a similar mechanism operating in metals can give rise to superconductivity. It is conventional to discuss the latter in terms of the forces induced by the quantum fluctuations. However, focusing directly upon the free energy provides a useful alternative perspective in the classical case and can also be applied to study quantum fluctuations. Villain first developed this approach for insulating magnets and coined the term order-by-disorder to describe the observed effect. We discuss the application of this idea to metallic systems, recent progress made in doing so, and the broader prospects for the future. CONTENTS

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Section: Superconductivity and Nematic Ordermentioning

confidence: 99%

Section: Superconductivity and Nematic Ordermentioning

confidence: 99%

Section: A Qobd Vs Dft Dmft and Kadanoff-baymmentioning

confidence: 99%

See 1 more Smart Citation

Quantum Order-by-Disorder in Strongly Correlated Metals

Green

Conduit

Krüger

2018

Annu. Rev. Condens. Matter Phys.

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“…Details and other discussion on the KL mechanism and its application to p−wave superconductivity in systems with strong ferromagnetic fluctuations can be found in Refs. [28,29,31,44,45,46,47,48,49,50]. The rest of these lecture notes will be devoted to discussion of superconductivity in lattice models, where k F is generally not small and rotational symmetry is broken.…”

Section: Kohn-luttinger Mechanismmentioning

confidence: 99%

Superconductivity from repulsive interaction

Maiti¹,

Chubukov²

2014

Novel Superfluids

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Abstract. The BCS theory of superconductivity named electron-phonon interaction as a glue that overcomes Coulomb repulsion and binds fermions into pairs which then condense and super-conduct. We review recent and not so recent works aiming to understand whether a nominally repulsive Coulomb interaction can by itself give rise to a superconductivity. We first discuss a generic scenario of the pairing by electron-electron interaction, put forward by Kohn and Luttinger back in 1965, and then turn to modern studies of the electronic mechanism of superconductivity in the lattice models for the cuprates, the Fe-pnictides, and the doped graphene. We show that the pairing in all three classes of materials can be viewed as lattice version of Kohn-Luttinger physics, despite that the pairing symmetries are different. We discuss under what conditions the pairing occurs and rationalize the need to do parquet renormalization-group analysis. We also discuss the interplay between superconductivity and density-wave instabilities.

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“…Because of this interplay between low-energy quantum fluctuations, metallic FMs are very susceptible towards the formation of incommensurate magnetic [17], spin nematic [14] or modulated superconducting states [18]. This spatial modulation is associated with deformations of the Fermi surface that enhance the phase space for low energy particle-hole fluctuations.…”

mentioning

confidence: 99%

Fluctuation-Driven Magnetic Hard-Axis Ordering in Metallic Ferromagnets

2014

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We investigate the interplay of quantum fluctuations and magnetic anisotropies in metallic ferromagnets. Our central result is that fluctuations close to a quantum critical point can drive the moments to point along a magnetic hard axis. As a proof of concept, we show this behavior explicitly for a generic two-band model with local Coulomb and Hund's interactions, and a spin-orbit-induced easy plane anisotropy. The phase diagram is calculated within the fermionic quantum order-bydisorder approach, which is based on a self-consistent free energy expansion around a magnetically ordered state with unspecified orientation. Quantum fluctuations render the transition of the easyplane ferromagnet first-order below a tricritical point. At even lower temperatures, directionally dependent transverse fluctuations dominate the magnetic anisotropy and the moments flip to lie along the magnetic hard axis. We discuss our findings in the context of recent experiments that show this unusual ordering along the magnetic hard direction.PACS numbers: 74.40. Kb, 75.50.Cc, 75.30.Gw, 75.70.Tj Fluctuations near to quantum critical points in itinerant ferromagnets (FMs) can have drastic and often surprising effects. They generically render a priori continuous phase transitions first order at low temperatures [1][2][3][4][5]. In many systems, quantum phase transitions are preempted by the formation of superconducting [5][6][7], modulated magnetic [8], or unusual spin-glass phases [9,10]. Other metallic FMs show an unexpected ordering along the magnetic hard axis [11,12].It is well understood that the first-order behavior arrises from the coupling of the magnetic order parameter to soft electronic particle-hole fluctuations, giving rise to non-analytic terms in the free energy [13][14][15][16]. Because of this interplay between low-energy quantum fluctuations, metallic FMs are very susceptible towards the formation of incommensurate magnetic [17], spin nematic [14] or modulated superconducting states [18]. This spatial modulation is associated with deformations of the Fermi surface that enhance the phase space for low energy particle-hole fluctuations. The phase reconstruction can therefore be viewed as a fermionic quantum orderby-disorder effect, which can be studied systematically by self-consistently calculating fluctuations around a whole class of possible broken-symmetry states [19][20][21].The coupling to electronic quantum fluctuations can also have counter-intuitive effects upon the direction of the magnetic order parameter. A notable example is the partially ordered phase of the helimagnet MnSi, in which the spiral ordering vector rotates away from the lattice favored directions [22,23]. Similar effects are possible in homogenous itinerant FMs. This is suggested by recent experiments that show unusual ordering of magnetic moments along hard magnetic directions [11,12].The first example is YbRh 2 Si 2 , which is a prototypical system for studying antiferromagnetic quantum criticality, but exhibits strong FM fluctuations [24]. In...

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Fluctuation-induced pair density wave in itinerant ferromagnets

Cited by 20 publications

References 47 publications

Quantum Order-by-Disorder in Strongly Correlated Metals

Quantum Order-by-Disorder in Strongly Correlated Metals

Superconductivity from repulsive interaction

Fluctuation-Driven Magnetic Hard-Axis Ordering in Metallic Ferromagnets

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