Evidence for a New Phase of Solid<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">He</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>

Osheroff, D. D.; Richardson, Robert C.; Lee, D. M.

doi:10.1103/physrevlett.28.885

Cited by 588 publications

(367 citation statements)

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“…As a result the quasiparticle spectrum has a gap, which leads to well-known experimental consequences. A variety of materials: 3 He [3], UBe 13 [4], UPt 3 [5], high T c materials [6], and Sr 2 RuO 4 [7], have been discovered that potentially break the G ⊗ R symmetry of the normal state. A well known example is A-phase of 3 He [3] which is not rotationally or time reversal invariant (note that the B phase of 3 He is both rotation and time reversal invariant).…”

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confidence: 99%

“…A variety of materials: 3 He [3], UBe 13 [4], UPt 3 [5], high T c materials [6], and Sr 2 RuO 4 [7], have been discovered that potentially break the G ⊗ R symmetry of the normal state. A well known example is A-phase of 3 He [3] which is not rotationally or time reversal invariant (note that the B phase of 3 He is both rotation and time reversal invariant). Such non s-wave superconductors are usually expected to have a gapless excitation spectrum and arise when the interaction itself depends upon the superconducting ground state (in the case of 3 He the BCS ground state is the B phase and the spin fluctuation feedback effect is required to stabilize the A phase [8]).…”

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confidence: 99%

“…A well known example is A-phase of 3 He [3] which is not rotationally or time reversal invariant (note that the B phase of 3 He is both rotation and time reversal invariant). Such non s-wave superconductors are usually expected to have a gapless excitation spectrum and arise when the interaction itself depends upon the superconducting ground state (in the case of 3 He the BCS ground state is the B phase and the spin fluctuation feedback effect is required to stabilize the A phase [8]). All the possible symmetry classes of the superconducting state in crystalline materials were enumerated in Ref.…”

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Conventional mechanisms for exotic superconductivity

1999

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We consider the pairing state due to the usual BCS mechanism in substances of cubic and hexagonal symmetry where the Fermi surface forms pockets around several points of high symmetry. We find that the symmetry imposed on the multiple pocket positions could give rise to a multidimensional nontrivial superconducting order parameter. The time reversal symmetry in the pairing state is broken. We suggest several candidate substances where such ordering may appear, and discuss means by which such a phase may be identified.Most conventional superconductors are described very well by the BCS theory [1]. The electron-phonon interaction mediates an attraction between electrons that is stronger than the Coulomb repulsion. This gives rise to the Cooper instability of the normal state leading to the appearance of a condensate of pairs. The order parameter (the anomalous function F [2]) in this case belongs to the "s-wave" type, i.e., it is invariant with respect to the transformations of G ⊗ R, where G is the crystal point group and R is time reversal operation. As a result the quasiparticle spectrum has a gap, which leads to well-known experimental consequences. We show below that exotic superconductivity can be a much more common phenomenon and does not require unusual mechanisms. The electron-phonon and Coulomb interactions are enough to give rise to an multidimensional order parameter which would have lower symmetry than the normal state -including the breaking of timereversal invariance. The effects we consider are possible in metals with several pockets which are centered at or around some symmetry points of the Brillouin Zone (BZ). A BCS approximation generalized to the the multi-band case (see, e.g., [12]) will be used. The new point here is that since the form of the interaction parameters describing the two electron scattering on and between the different pockets of the Fermi surface (FS) is fixed by symmetry, the resulting superconducting state need not be s-wave. Below we consider three cases in detail: a) three FS pockets centered about the X-points of a simple cubic lattice; b) three FS pockets at the M-points of the hexagonal lattice; c) four FS pockets at the L-points in the face-centered cubic lattice. A complete analysis of all other high symmetry points is possible, and will be published elsewhere [13].We emphasize that this FS structure is not unusual. Indeed, superconductivity with pockets as in case (a) and T c ∼ 0.1K is found in

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Conventional mechanisms for exotic superconductivity

1999

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“…Another fundamental issue that arises in the study of superfluidity is the pairing of fermions. While fermionic superfluidity has been extensively investigated in 3D systems [21][22][23], there are open experimental questions in the 2D context. In particular, what is the long-range behavior of spatial coherence of a 2D fermionic superfluid, and can it also be described in the BKT framework like its bosonic counterpart?…”

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Observation of the Berezinskii-Kosterlitz-Thouless Phase Transition in an Ultracold Fermi Gas

et al. 2015

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We experimentally investigate the first-order correlation function of a trapped Fermi gas in the two-dimensional BEC-BCS crossover. We observe a transition to a low-temperature superfluid phase with algebraically decaying correlations. We show that the spatial coherence of the entire trapped system can be characterized by a single temperature-dependent exponent. We find the exponent at the transition to be constant over a wide range of interaction strengths across the crossover. This suggests that the phase transitions in both the bosonic regime and the strongly interacting crossover regime are of Berezinskii-Kosterlitz-Thouless type and lie within the same universality class. On the bosonic side of the crossover, our data are well-described by the quantum Monte Carlo calculations for a Bose gas. In contrast, in the strongly interacting regime, we observe a superfluid phase which is significantly influenced by the fermionic nature of the constituent particles.Long-range coherence is the hallmark of superfluidity and Bose-Einstein condensation [1,2]. The character of spatial coherence in a system and the properties of the corresponding phase transitions are fundamentally influenced by dimensionality. The two-dimensional case is particularly intriguing as for a homogeneous system, true long-range order cannot persist at any finite temperature due to the dominant role of phase fluctuations with large wavelengths [3][4][5]. Although this prevents Bose-Einstein condensation in 2D, a transition to a superfluid phase with quasi-long-range order can still occur, as pointed out by Berezinskii, Kosterlitz, and Thouless (BKT) [6][7][8]. A key prediction of this theory is the scale-invariant behavior of the first-order correlation function g 1 (r), which, in the low-temperature phase, decays algebraically according to g 1 (r) ∝ r −η for large separations r. Importantly, the BKT theory for homogeneous systems predicts a universal value of η c = 1/4 at the critical temperature, accompanied by a universal jump of the superfluid density [9].Several key signatures of BKT physics have been experimentally observed in a variety of systems such as exciton-polariton condensates [10], layered magnets [11,12], liquid 4 He films [13], and trapped Bose gases [14][15][16][17][18][19][20]. Particularly in the context of superfluidity, the universal jump in the superfluid density was measured in thin films of liquid 4 He [13]. More recently, in the pioneering interference experiment with a weakly interacting Bose gas [14], the emergence of quasi-long-range order and the proliferation of vortices were shown.There are still important aspects of superfluidity in two-dimensional systems that remain to be understood, which we aim to elucidate in this work with ultracold atoms. One question is whether the BKT phenomenology can also be extended to systems with nonuniform density. Indeed, if the microscopic symmetries are the same, the general physical picture involving phase fluctuations should be valid also for inhomogeneous systems. However, it ...

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“…Research on the subject then exploded following the unexpected discovery 8 in 1972 of this superfluid at temperatures below 0.003 K. At first, the observations were interpreted as spontaneous nuclear magnetic ordering in solid helium-3, but shortly afterwards, they were correctly identified as the transition to a superfluid 9 . Nuclear magnetic ordering in solid helium-3 was discovered 10 two years later at a temperature of 0.001 K.…”

Section: Years Agomentioning

confidence: 99%

Eighty years of superfluidity

Halperin¹

2018

Nature

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Evidence for a New Phase of SolidHe3

Cited by 588 publications

References 8 publications

Conventional mechanisms for exotic superconductivity

Conventional mechanisms for exotic superconductivity

Observation of the Berezinskii-Kosterlitz-Thouless Phase Transition in an Ultracold Fermi Gas

Eighty years of superfluidity

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