Strain-induced chiral magnetic effect in Weyl semimetals

We study the surface states of a strongly coupled Weyl semimetal within holography. By explicit numerical computation of an inhomogeneous holographic Weyl semimetal, we observe the appearance of an electric current restricted to the surface in presence of an electric chemical potential. The integrated current is universal in the sense that it only depends on the topology of the phases showing that the bulk-boundary correspondence holds even at strong coupling. The implications of this result are subtle and may shed some light on anomalous transport at weak coupling. INTRODUCTIONWeyl semimetals (WSMs) are novel gapless topological states of matter with electronic low-energy excitations behaving as left-and right-handed Weyl fermions [1][2][3][4][5][6][7]. These quasiparticles are localized around Weyl nodes in the Brillouin zone, points where, in band theory, valence and conduction bands touch at the Fermi energy. The Nielsen-Ninomiya theorem [1] states that left-and right-handed Weyl nodes appear in pairs. The existence of these nodes requires either inversion or time reversal symmetry to be broken. In the latter case, Weyl nodes of opposite chirality are separated spatially in the Brillouin zone. Weyl nodes can be characterized as monopoles of Berry flux with charge ±1 which reflects the chirality of the excitations. As such, Weyl nodes represent topological objects in the Brillouin zone and are stable under most perturbations, including interactions. As in topological insulators, the existence of surface states is guaranteed by topology. Moreover, it has been shown [2] that the surface states of a WSM form so-called Fermi arcs connecting the projections of the Weyl nodes onto the surface Brillouin zone.The transport properties of WSMs are tightly bound to the axial anomaly of quantum field theories with Weyl fermions. This leads to anomaly-related phenomena in WSMs such as the anomalous Hall effect [8][9][10][11][12], the chiral magnetic effect [13,14] and related effects like the negative magnetoresistance [15,16]. Furthermore, it has been predicted that lattice deformations couple to the fermionic low-energy excitations with different signs, giving rise to effective axial gauge fields [17,18]. Such lattice deformations naturally arise at the surfaces of a WSM, inducing localised axial magnetic fields in their vicinity. Moreover, it was shown that the Fermi arcs can be understood from this perspective as zeroth Landau levels generated by these fields [19].It is important to remark that in the strong coupling regime the description in terms of bands, or even correlation functions, cannot be applied and therefore it is compelling to study to which extent the weak coupling intuitions can be extrapolated. In Refs. [20,21], the authors addressed the question whether the properties of a (homogeneous and infinite) WSM can be found in the strong coupling regime. To this end, they presented a holographic model which exhibits a topological phase transition from a trivial phase to a non-trivial WSM phase. In this letter...

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“…Analogous situations were recently studied at weak coupling using a tight binding model in Refs. [26,27]. Strictly speaking, Eq.…”

Section: The Modelmentioning

confidence: 99%

Surface States in Holographic Weyl Semimetals

et al. 2017

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“…However, the resulting spectral quantization is approximate and restricted to energies near the Dirac point. Non-uniform strain has also been discussed for Weyl semimetals, but controlled effects are again restricted to the low-energy part of the spectrum [9][10][11].…”

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confidence: 99%

Strain-Induced Landau Levels in Arbitrary Dimensions with an Exact Spectrum

et al. 2016

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Certain non-uniform strain applied to graphene flakes has been shown to induce pseudo-Landau levels in the single-particle spectrum, which can be rationalized in terms of a pseudo-magnetic field for electrons near the Dirac points. However, this Landau level structure is in general approximate and restricted to low energies. Here we introduce a family of strained bipartite tight-binding models in arbitrary spatial dimension d and analytically prove that their entire spectrum consists of perfectly degenerate pseudo-Landau levels. This construction generalizes the case of triaxial strain on graphene's honeycomb lattice to arbitrary d; in d = 3 our model corresponds to tetraxial strain on the diamond lattice. We discuss general aspects of pseudo-Landau levels in arbitrary d.

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“…Indeed, in Weyl materials, b 0 and b correspond to energy and momentum-space separations between the Weyl nodes, respectively. Strain-induced axial (or, equivalently, pseudoelectromagnetic) fields are described byÃ 5 ν , which is directly related to the deformation tensor [26][27][28][29][30]33]. As is easy to check, the consistent electric current, i.e.,…”

Section: The Consistent Chiral Kinetic Theorymentioning

confidence: 99%

“…For example, as shown in Refs. [25][26][27][28][29][30], static mechanical strains applied to Weyl semimetals generate pseudomagnetic fields. As in graphene, the corresponding effective gauge fields capture the corrections to the kinetic energy of quasiparticles caused by unequal modifications of hopping parameters in a strained crystal.…”

Section: Introductionmentioning

confidence: 99%

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Chiral magnetic plasmons in anomalous relativistic matter

et al. 2017

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The chiral plasmon modes of relativistic matter in background magnetic and strain-induced pseudomagnetic fields are studied in detail using the consistent chiral kinetic theory. The results reveal a number of anomalous features of these chiral magnetic and pseudomagnetic plasmons that could be used to identify them in experiment. In a system with nonzero electric (chiral) chemical potential, the background magnetic (pseudomagnetic) fields not only modify the values of the plasmon frequencies in the long-wavelength limit, but also affect the qualitative dependence on the wave vector. Similar modifications can be also induced by the chiral shift parameter in Weyl materials. Interestingly, even in the absence of the chiral shift and external fields, the chiral chemical potential alone leads to a splitting of plasmon energies at linear order in the wave vector.

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Strain-induced chiral magnetic effect in Weyl semimetals

Cited by 131 publications

References 36 publications

Surface States in Holographic Weyl Semimetals

Surface States in Holographic Weyl Semimetals

Strain-Induced Landau Levels in Arbitrary Dimensions with an Exact Spectrum

Chiral magnetic plasmons in anomalous relativistic matter

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