Phenomenological Theory of Ferromagnetic Superconductivity

Machida, Kazushige; Ohmi, Tetsuo

doi:10.1103/physrevlett.86.850

Cited by 158 publications

(209 citation statements)

References 21 publications

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“…Triplet superconductivity is a rather unusual phenomenon. In our opinion, it has been firmly established in the heavy fermion superconductor UPt 3 [21] and most likely exists in the Sr 2 RuO 4 [22,23] and ferromagnetic superconductors [24].…”

Section: Phenomenological Approach To the Possible Existence Of A Trimentioning

confidence: 99%

Possible triplet superconductivity in the quasi-one-dimensional conductor Li0.9Mo6O17

Lebed

Sepper

2013

Phys. Rev. B

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Section: Phenomenological Approach To the Possible Existence Of A Trimentioning

confidence: 99%

Possible triplet superconductivity in the quasi-one-dimensional conductor Li0.9Mo6O17

Lebed

Sepper

2013

Phys. Rev. B

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“…The most likely explanation for the appearance of superconductivity in these weak itinerant ferromagnets is that the superconducting state is mediated by ferromagnetic spin fluctuations, giving rise to Cooper pairs with parallel spins (Sϭ1). [7][8][9][10] This type of pairing is relatively insensitive to a local magnetic field and can therefore coexist with ferromagnetic order. The pressure-dependent experiments on UGe 2 and ZrZn 2 suggest that in these systems superconductivity emerges near a ferromagnetic quantum critical point, i.e., when the ferromagnetic transition temperature is tuned to T C ϭ0.…”

Section: Introductionmentioning

confidence: 99%

Dilatometry study of the ferromagnetic order in single-crystalline URhGe

et al. 2003

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Thermal expansion measurements have been carried out on single-crystalline URhGe in the temperature range from 2 to 200 K. At the ferromagnetic transition ͑Curie temperature T C ϭ9.7 K), the coefficients of linear thermal expansion along the three principal orthorhombic axes all exhibit pronounced positive peaks. This implies that the uniaxial pressure dependencies of the Curie temperature, determined by the Ehrenfest relation, are all positive. Consequently, the calculated hydrostatic pressure dependence dT C /dp is positive and amounts to 0.12 K/kbar. In addition, the effective Grüneisen parameter was determined. The low-temperature electronic Grüneisen parameter ⌫ sf ϭ 14 indicates an enhanced volume dependence of the ferromagnetic spin fluctuations at low temperatures. Moreover, the volume dependencies of the energy scales for ferromagnetic order and ferromagnetic spin fluctuations were found to be identical.

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“…It has already been successfully employed to describe various phase transitions [13] and to explain the phase diagram [14,15] of the above-mentioned SC ferromagnets, and also has ever been applied to spinor Bose gases [16,17]. Although phenomenological theory only produces qualitative results, it leads to deep insight into the nature of the associated phenomenon.…”

mentioning

confidence: 99%

“…As we predict above, the spin waves in two components should be coupled into one mixed mode (the coherent mode). It is suggested that the strong internal field in SC ferromagnets stabilize a nonunitary triplet state [13], which means that Cooper pairs carry a net magnetization m = 0. This case is equivalent to the polarization of the FM spinor Bose condensate, and thus the system consists of two coexisting ferromagnetic phases.…”

mentioning

confidence: 99%

Spin waves in ferromagnetically coupled spinor Bose gases

Bongs

Sengstock

2004

Phys. Rev. A

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It is shown that the ferromagnetic transition takes place always above Bose-Einstein condensation in ferromagnetically coupled spinor Bose gases. We describe the Bose ferromagnet within GinzburgLandau theory by a "two-fluid" model below Bose-Einstein condensation. Both the Bose condensate and the normal phase are spontaneously magnetized. As a main result we show that spin waves in the two fluids are coupled together so as to produce only one mixed spin-wave mode in the coexisting state. The long wavelength spectrum is quadratic in the wave vector k, consistent with usual ferromagnetism theory, and the spin-wave stiffness coefficient cs includes contributions from both the two phases, implying the "two-fluid" feature of the system. cs can show a sharp bend at the Bose-Einstein condensation temperature.PACS numbers: 03.75. Mn, 05.30.Jp, 74.20.De, 75.30.Ds Ferromagnetism belongs to the oldest phenomena in condensed matters and it is attracting continuous research interest till today [1], sparked by discoveries of new materials or new phenomena in this field. Most ferromagnets being studied so far are composed of fermionic particles. The recent experimental success of optical confining ultracold atomic Bose gases [2,3] provides possibilities to realize a new kind of ferromagnet, the Bose ferromagnet. A promising example might be the gas of F = 1 87 Rb atoms. It has been predicted in theory [4] and confirmed by experiments [5,6] that the hyperfine spin-spin interaction in this Bose gas is ferromagnetic.In dilute atomic gases, interatomic forces are rather weak, with the effective s-wave scattering length being typically of the order 100a B where a B is the Bohr radius. The spin-dependent interaction is even 1 or 2 orders of magnitude smaller [4]. One may question whether the ferromagnetic (FM) transition induced by such a weak FM coupling could be observed in experiments. Recently, it was already shown that the FM transition in Bose gases takes place always above Bose-Einstein condensation (BEC), regardless of the value of the FM coupling [7]. It means that Bose gases can exhibit ferromagnetism at relatively high temperatures in comparison to the energy scale of the FM coupling. Below BEC, the FM Bose gas becomes a "two-fluid" system: the polarized Bose condensate coexisting with the magnetized normal gas. This is a unique feature in the Bose ferromagnet.Accompanying the FM transition, spin waves appear in the ferromagnet as a Goldstone mode. In conventional ferromagnets, both insulating and metallic, the spin-wave excitations are gapless at wave vector k = 0 and the long wavelength dispersion relation is quadratic in k, ω s = c s k 2 , with the spin-wave stiffness coefficient c s proportional to the strength of the FM coupling [1]. It is a rather interesting problem how the spin wave manifests itself in the Bose ferromagnet, especially considering the "two-fluid" feature of the system. In this letter, we shall examine the phase diagram and spin waves in the Bose ferromagnet phenomenologically and show how spin w...

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Phenomenological Theory of Ferromagnetic Superconductivity

Cited by 158 publications

References 21 publications

Possible triplet superconductivity in the quasi-one-dimensional conductor Li0.9Mo6O17

Possible triplet superconductivity in the quasi-one-dimensional conductor Li0.9Mo6O17

Dilatometry study of the ferromagnetic order in single-crystalline URhGe

Spin waves in ferromagnetically coupled spinor Bose gases

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