Anisotropic Weyl Fermions from the Quasiparticle Excitation Spectrum of a 3D Fulde-Ferrell Superfluid

Xu, Yong; Chu, Rui Lin; Zhang, Chuanwei

doi:10.1103/physrevlett.112.136402

Cited by 68 publications

(92 citation statements)

References 62 publications

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“…Hence the transition from the gapped to the gapless region in this case also represents a transition from a topologically trivial to a topologically nontrivial quantum phase. For finite h x , by contrast, the gapless region features a nodal surface in momentum space on which the single particle excitation gap vanishes [17,18,56]. An example of such a nodal surface is plotted in Fig.…”

Section: Zero-temperature Propertiesmentioning

confidence: 99%

Thermodynamic properties of Rashba spin-orbit-coupled Fermi gas

Zheng

Zou

et al. 2014

Phys. Rev. A

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We investigate the thermodynamic properties of a superfluid Fermi gas subject to Rashba spinorbit coupling and effective Zeeman field. We adopt a T-matrix scheme that takes beyond-meanfield effects, which are important for strongly interacting systems, into account. We focus on the calculation of two important quantities: the superfluid transition temperature and the isothermal compressibility. Our calculation shows very distinct influences of the out-of-plane and the in-plane Zeeman fields on the Fermi gas. We also confirm that the in-plane Zeeman field induces a FuldeFerrell superfluid below the critical temperature and an exotic finite-momentum pseudo-gap phase above the critical temperature.

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Section: Zero-temperature Propertiesmentioning

confidence: 99%

Thermodynamic properties of Rashba spin-orbit-coupled Fermi gas

Zheng

Zou

et al. 2014

Phys. Rev. A

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“…However, there is still no compelling experimental evidence for the observation of one. In the field of ultracold atoms, this phase was predicted to appear in spinorbit coupled Fermi gases [14,15]. This line of active research awaits for the future experimental breakthrough of synthesizing higher dimensional artificial spin-orbit coupling with controlled heating [16].…”

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confidence: 99%

“…However, in other regions k z > k C + or k z < k C − , the topological charge vanishes. These two gapless points k C ± are Weyl nodes, defining the corresponding topological transitions in the momentum space [7,15]. Close to the Weyl nodes, the Hamiltonian takes the form of 2 × 2 Hamiltonian of a chiral Weyl fermion [38].…”

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confidence: 99%

Weyl Superfluidity in a Three-Dimensional Dipolar Fermi Gas

Liu

Yin

et al. 2015

Phys. Rev. Lett.

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Weyl superconductivity or superfluidity, a fascinating topological state of matter, features novel phenomena such as emergent Weyl fermionic excitations and anomalies. Here we report that an anisotropic Weyl superfluid state can arise as a low temperature stable phase in a 3D dipolar Fermi gas. A crucial ingredient of our model is a direction-dependent two-body effective attraction generated by a rotating external field. Experimental signatures are predicted for cold gases in radio-frequency spectroscopy. The finite temperature phase diagram of this system is studied and the transition temperature of the Weyl superfluidity is found to be within the experimental scope for atomic dipolar Fermi gases.Weyl superfluids or semimetals represent recent developments in generalizing topological phases from gapped to gapless systems (e.g., from topological insulators to semimetals), in condensed matter physics [1,2]. These Weyl states are characterized by the presence of two (or more) gapless Weyl points, which are topologically protected against small perturbations. The Weyl nodes lead to a variety of fascinating phenomena such as unusual surface states [3,4], Hall effects [5,6], and other transport features [7,8]. Finding electronic materials supporting Weyl states has attracted considerable interests [9]. There are many proposed potential candidate materials, such as the pyrochlore iridates [3], topological insulator multilayer structures [7,[10][11][12], as well as certain quasicrystals [13]. However, there is still no compelling experimental evidence for the observation of one. In the field of ultracold atoms, this phase was predicted to appear in spinorbit coupled Fermi gases [14,15]. This line of active research awaits for the future experimental breakthrough of synthesizing higher dimensional artificial spin-orbit coupling with controlled heating [16]. After all, the search for Weyl superconductors remains an open problem for both electronic and ultracold atomic systems.In this letter, we report the emergence of Weyl superfluidity in a 3D single-component dipolar Fermi gas with an effective attraction engineered by a rotating external field. Recently, degenerate dipolar Fermi gases witnessed rapid developments in both magnetic dipolar atoms (such as 167 Er [17,18] and 161 Dy [19,20] atoms) and polar molecules [21,22], stimulating tremendous interests in dipolar effects in many-body phases. The effects of the anisotropic dipolar interaction on the fermion many-body physics have been extensively investigated [23]. In particular, this provides the possibility of superfluid pairing between dipolar Fermi atoms in spinless or multicomponent systems [24][25][26][27] at low temperatures. For dipoles aligned parallel to the z direction, a p-wave superfluid state with the dominant p z symmetry was studied in a three-dimensional dipolar Fermi gas [28] and the competition between this superfluidity and nematic charge-density-wave (CDW) was also discussed [29]. For a dipolar Fermi gas confined in a 2D plane, superfluid states o...

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“…We obtain a rich phase diagram in the gapless region of 3D FF superfluids, where not only the featureless Weyl points [19][20][21][22][23][24][25][26][27][28] but also the structured Weyl points emerge. Note that the featureless Weyl points have been well studied in SOC FF superfluids [24], and here we focus only on the novel structured Weyl points. (iii) We also discuss how the structured Weyl points can be detected in experiments by measuring spectral densities in photoemission spectroscopy that has already been utilized in degenerate Fermi gases [42].…”

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confidence: 99%

“…In contrast to traditional fully gapped superfluids, the Weyl superfluids bear doubly degenerate nodes pinned to zero energy, around which the quasiparticle energies disperse linearly in all directions. Most recently, the existence of such Weyl nodes has also been generalized to various coldatom superfluids and solid-state superconductors [19][20][21][22][23][24][25][26][27][28].…”

mentioning

confidence: 99%

Structured Weyl Points in Spin-Orbit Coupled Fermionic Superfluids

Xu¹,

Zhang²,

Zhang³

2015

Phys. Rev. Lett.

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298

233

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We demonstrate that a Weyl point, widely examined in 3D Weyl semimetals and superfluids, can develop a pair of non-degenerate gapless spheres. Such a bouquet of two spheres is characterized by three distinct topological invariants of manifolds with full energy gaps, i.e., the Chern number of a 0D point inside one developed sphere, the winding number of a 1D loop around the original Weyl point, and the Chern number of a 2D surface enclosing the whole bouquet. We show that such structured Weyl points can be realized in the superfluid quasiparticle spectrum of a 3D degenerate Fermi gas subject to spin-orbit couplings and Zeeman fields, which supports Fulde-Ferrell superfluids as the ground state. [17,18]. A Weyl point can also be regarded as a monopole in 3D momentum space that exhibits an integer topological charge, i.e., the quantized first Chern number of a surface enclosing the singularity. Weyl points were also suggested to exist in the quasiparticle spectrum of superfluid 3 He A phase [2]. In contrast to traditional fully gapped superfluids, the Weyl superfluids bear doubly degenerate nodes pinned to zero energy, around which the quasiparticle energies disperse linearly in all directions. Most recently, the existence of such Weyl nodes has also been generalized to various coldatom superfluids and solid-state superconductors [19][20][21][22][23][24][25][26][27][28].In this Letter, we investigate whether a Weyl point can develop a nontrivial structure at zero energy and whether there exist any topological property protecting the developed structure. (i) We first consider a toy model to examine the possibility for a Weyl point to develop a gapless structure. Mathematically, the structured Weyl point can be viewed as a bouquet of two spheres (or wedge of two spheres) [29], which is a new class of topological state that has not been explored previously. Amazingly, the zero-energy bouquet is characterized by three distinct topological invariants: the first Chern number of a surface enclosing the whole bouquet, the zeroth Chern numbers of the interiors of the two spheres, and the winding number of a loop enclosing the touching point in the plane of symmetry. (ii) We further show that the structured Weyl points can be physically realized in the quasiparticle excitation spectrum of a 3D spin-orbit-coupled (SOC) fermionic cold-atom superfluid with the FuldeFerrell (FF) ground state. FF superfluids [30][31][32][33][34][35][36][37][38][39][40][41] have been studied recently in SOC degenerate Fermi gases subject to Zeeman fields, which yield asymmetries of the Fermi surface and induce the FF Cooper pairing with nonzero total momenta. We obtain a rich phase diagram in the gapless region of 3D FF superfluids, where not only the featureless Weyl points [19][20][21][22][23][24][25][26][27][28] but also the structured Weyl points emerge. Note that the featureless Weyl points have been well studied in SOC FF superfluids [24], and here we focus only on the novel structured Weyl points. (iii) We also discuss how the structured W...

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Anisotropic Weyl Fermions from the Quasiparticle Excitation Spectrum of a 3D Fulde-Ferrell Superfluid

Cited by 68 publications

References 62 publications

Thermodynamic properties of Rashba spin-orbit-coupled Fermi gas

Thermodynamic properties of Rashba spin-orbit-coupled Fermi gas

Weyl Superfluidity in a Three-Dimensional Dipolar Fermi Gas

Structured Weyl Points in Spin-Orbit Coupled Fermionic Superfluids

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