Magnetic interactions in a proposed diluted magnetic semiconductor (Ba
 
 1−
 x
 
 K
 
 x
 
 )(Zn
 
 1−
 y
 
 Mn
 
 y

Yang, Huan-Cheng; Liu, Kai; Lu, Zhong-Yi

doi:10.1088/1674-1056/27/6/067103

Cited by 50 publications

(68 citation statements)

References 51 publications

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“…WSM can be divided into two types: type-I Weyl semimetal (WSM1) with vanishing density of states (DOS) at the Weyl node and type-II Weyl semimetal (WSM2) with finite DOS contributed by electron and hole pockets separated by the Weyl node. The earlier proposals for candidate materials of WSM are all WSM1 [1][2][3] . In case that Lorentz invariance is broken, the Weyl cones may be tipped over and transformed into WSM2.…”

Section: Introductionmentioning

confidence: 99%

Global phase diagram of disordered type-II Weyl semimetals

Liu

Jiang

et al. 2017

Phys. Rev. B

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With electron and hole pockets touching at the Weyl node, type-II Weyl semimetal is a newly proposed topological state distinct from its type-I cousin. We numerically study the localization effect for tilted type-I as well as type-II Weyl semimetals and give the global phase diagram. For disordered type-I Weyl semimetal, an intermediate three-dimensional quantum anomalous Hall phase is confirmed between Weyl semimetal phase and diffusive metal phase. However, this intermediate phase is absent for disordered type-II Weyl semimetal. Besides, near the Weyl nodes, comparing to its type-I cousin, type-II Weyl semimetal possesses even larger ratio between the transport lifetime along the direction of tilt and the quantum lifetime. Near the phase boundary between the type-I and the type-II Weyl semimetals, infinitesimal disorder will induce an insulating phase so that in this region, the concept of Weyl semimetal is meaningless for real materials.

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Section: Introductionmentioning

confidence: 99%

Global phase diagram of disordered type-II Weyl semimetals

Liu

Jiang

et al. 2017

Phys. Rev. B

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“…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].…”

Section: Introductionmentioning

confidence: 99%

Surface States in Holographic Weyl Semimetals

et al. 2017

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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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“…One celebrated example in three dimensions is the zero-dimensional Weyl point [7][8][9][10][11][12][13][14][15][16][17][18] described by the Weyl Hamiltonian, which has been long sought-after in particle physics but only experimentally observed in condensed matter materials [19][20][21]. Such a Weyl point can be viewed as a magnetic monopole [22] in the momentum space and possesses a quantized Chern number on a surface enclosing the point.…”

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confidence: 99%

Weyl Exceptional Rings in a Three-Dimensional Dissipative Cold Atomic Gas

2017

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Three-dimensional topological Weyl semimetals can generally support a zero-dimensional Weyl point characterized by a quantized Chern number or a one-dimensional Weyl nodal ring (or line) characterized by a quantized Berry phase in the momentum space. Here, in a dissipative system with particle gain and loss, we discover a new type of topological ring, dubbed Weyl exceptional ring consisting of exceptional points at which two eigenstates coalesce. Such a Weyl exceptional ring is characterized by both a quantized Chern number and a quantized Berry phase, which are defined via the Riemann surface. We propose an experimental scheme to realize and measure the Weyl exceptional ring in a dissipative cold atomic gas trapped in an optical lattice.Recently, condensed matter systems have proven to be a powerful platform to study low energy gapless particles by using momentum space band structures to mimic the energy-momentum relation of relativistic particles [1,2] and beyond [3][4][5][6]. One celebrated example in three dimensions is the zero-dimensional Weyl point [7][8][9][10][11][12][13][14][15][16][17][18] described by the Weyl Hamiltonian, which has been long sought-after in particle physics but only experimentally observed in condensed matter materials [19][20][21]. Such a Weyl point can be viewed as a magnetic monopole [22] in the momentum space and possesses a quantized Chern number on a surface enclosing the point. Another example is the one-dimensional Weyl nodal ring [3,[23][24][25], which has no counterpart in particle physics. It can be regarded as the generalization of zero-dimensional Dirac cones in two-dimensional systems, such as in graphene, to three-dimensional systems. Such a nodal ring has a quantized Berry phase over a closed path encircling it but does not possess a nonzero quantized Chern number. This leads to a natural question of whether there exists a topological ring exhibiting both a quantized Chern number and a quantized Berry phase in the momentum space.So far, studies on those gapless states focus on closed and lossless systems. However, particle gain and loss are generally present in natural systems. Such systems can often be described by non-Hermitian Hamiltonians [26][27][28][29], which are widely applied to many different systems [30][31][32][33][34][35][36][37][38][39][40]. Due to the non-Hermiticity, eigenvalues of the Hamiltonian are generically complex unless the PT symmetry [41] is conserved and the imaginary part of energy is associated with either decay or growth. Another intriguing feature of a non-Hermitian system is the existence of exceptional points (EPs) [26][27][28][29] at which two eigenstates coalesce and the Hamiltonian becomes defective, leading to many novel phenomena, such as lossinduced transparency [30], single-mode lasers [36,37], and reversed pump dependence of lasers [33].In this paper, we investigate a system of Weyl points in the presence of a spin-dependent non-Hermitian term and find a Weyl exceptional ring composed of EPs. In stark contrast to a Weyl nodal ...

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Magnetic interactions in a proposed diluted magnetic semiconductor (Ba _{1−
x} K _x )(Zn _{1−
y} Mn _y

Cited by 50 publications

References 51 publications

Global phase diagram of disordered type-II Weyl semimetals

Global phase diagram of disordered type-II Weyl semimetals

Surface States in Holographic Weyl Semimetals

Weyl Exceptional Rings in a Three-Dimensional Dissipative Cold Atomic Gas

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Magnetic interactions in a proposed diluted magnetic semiconductor (Ba 1− x K x )(Zn 1− y Mn y

Cited by 50 publications

References 51 publications

Global phase diagram of disordered type-II Weyl semimetals

Global phase diagram of disordered type-II Weyl semimetals

Surface States in Holographic Weyl Semimetals

Weyl Exceptional Rings in a Three-Dimensional Dissipative Cold Atomic Gas

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Product

Resources

About

Magnetic interactions in a proposed diluted magnetic semiconductor (Ba _{1−
x} K _x )(Zn _{1−
y} Mn _y