Quantum Hall effects in a Weyl semimetal: Possible application in pyrochlore iridates

Yang, Kaiyu; Lü, Yuan; Ran, Ying

doi:10.1103/physrevb.84.075129

Cited by 857 publications

(624 citation statements)

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“…More recently, the research on topological states has been extended to three-dimensional (3D) semimetal systems. [8][9][10][11][12] These systems could demonstrate many fascinating phenomena, such as Weyl fermion quantum transport and various Hall effects, [13][14][15][16] consequently become the rising stars of the field. Up to now, three kinds of topological semimetals have been discovered, i.e., 3D Dirac semimetal (DSM), 12,[17][18][19][20][21] Weyl semimetal (WSM), 8,9,22,23 and node-line semimetal (NLS).…”

Section: Introductionmentioning

confidence: 99%

CaTe: a new topological node-line and Dirac semimetal

Du¹,

Tang²,

Wang³

et al. 2017

npj Quant Mater

115

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Combining first-principles calculations and effective model analysis, we predict that CaTe is a topological node-line semimetal in the absence of the spin-orbit coupling. Using a slab model, we obtain the nearly flat drumhead surface state near the Fermi level. When the spin-orbit coupling is included, three node lines will evolve into a pair of Dirac points along the M−R line. These Dirac points are robust and protected by the C 4 rotation symmetry. Once this crystal symmetry is broken, the Dirac points will be eliminated, and the system becomes a strong topological insulator.npj Quantum Materials (2017) 2:3 ; doi:10.1038/s41535-016-0005-4 INTRODUCTIONTopological insulator (TI) has attracted broad interest in the past 10 years. [1][2][3][4][5][6][7] The unique property of TI is that it is an insulator in the bulk but has exotic metallic surface states due to the topological order. More recently, the research on topological states has been extended to three-dimensional (3D) semimetal systems. [8][9][10][11][12] These systems could demonstrate many fascinating phenomena, such as Weyl fermion quantum transport and various Hall effects, [13][14][15][16] consequently become the rising stars of the field. Up to now, three kinds of topological semimetals have been discovered, i.e., 3D Dirac semimetal (DSM), 12,[17][18][19][20][21] Weyl semimetal (WSM), 8,9,22,23 and node-line semimetal (NLS). [24][25][26][27][28][29] The 3D DSM has four-fold degeneracy point, which can be viewed as the kiss of two Weyl fermions with opposite chiralities in the Brillouin zone (BZ). Protected by the crystal symmetry and time reversal symmetry, 3D DSMs can be robust against external perturbations. Several materials have been theoretically predicted to be 3D DSMs 12,17-21 and some of them have already been confirmed by experiments. [30][31][32][33] If one breaks the time reversal symmetry 8,22,23,34 or the inversion symmetry, 35-38 the 3D DSM will evolve into WSM. Very recently, the predictions about WSM state in TaAs family 37,38 have been confirmed experimentally. [39][40][41][42] Unlike DSM and WSM whose band crossing points distribute at separate k points in the BZ, for a NLS the crossing points around the Fermi level form a closed loop. Several compounds have been proposed as NLSs, including Mackay-Terrones crystals, 25 Bernal graphite, 43 hyperhoneycomb lattices, 44 and antiperovskite Cu 3 PdN 26,27 and Cu 3 NZn. 27 In the absence of spin-orbit coupling (SOC), time reversal symmetry together with inversion or mirror symmetry will guarantee the occurrence of node line in 3D BZ for systems with band inversion. [25][26][27]37,45,46 Same with TI and WSM, NLS also has a characteristic surface state, namely, drumhead-like state. 24-29 Such a 2D flat band surface state may become a route to achieve high temperature superconductivity. 47,48 As a result, it is of great impetus to search new NLS.In this study, based on first-principles calculations and effective model analysis, we propose that CaTe in CsCl-type structure is a NLS with drumhea...

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Section: Introductionmentioning

confidence: 99%

CaTe: a new topological node-line and Dirac semimetal

Du¹,

Tang²,

Wang³

et al. 2017

npj Quant Mater

115

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“…In recent years, there has been an increased interest in the study of 5d transition metal oxides where these energy scales are all comparable. Iridium based oxides such as the square-lattice materials (Sr,Ba) 2 IrO 4 1-3 , the perovskites SrIrO 3 and Sr 3 Ir 2 IO 7 4 , the pyrochlore materials A 2 Ir 2 O 7 (A = Y,Eu,Lu,Sm) [5][6][7] , the honeycomb-lattice materials A 2 IrO 3 (A = Na,Li) [8][9][10] , and the hyperkagome-lattice material Na 4 Ir 3 O 8 11,12 have been materials of intensive recent investigations. The 5d transition metal oxides are expected to be wide-band weakly correlated metals due to large spatial extent of their d-orbitals.…”

Section: Introductionmentioning

confidence: 99%

Fragile magnetic order in the honeycomb lattice IridateNa2IrO3revealed by magnetic impurity doping

2015

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We report the structure, magnetic, and thermal property measurements on single crystalline and polycrystalline samples of Ru substituted honeycomb lattice iridate Na2IrxRu1−xO3 (x = 0, 0.05, 0.1, 0.15, 0.2, 0.3, 0.5). The evolution of magnetism in Na2IrxRu1−xO3 has been studied using dc and ac magnetic susceptibility, and heat capacity measurements. The parent compound Na2IrO3 is a spin-orbit driven Mott insulator with magnetic order of reduced moments below TN = 15 K. In the Ru substituted samples the antiferromagnetic long range state is replaced by a spin glass like state even for the smallest substitution suggesting that the magnetic order in Na2IrO3 is extremely fragile. We argue that these behaviors indicate the importance of nearest-neighbor magnetic exchange in the parent Na2IrO3. Additionally, all samples show insulating electrical transport.

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Section: D Bulk Propertiesmentioning

confidence: 99%

“…For example, the Hall conductivity of a Weyl-SM having only a pair of WPs at ±k 0 = (0, 0, ±k 0 ) is given by σ xy = e 2 h 2k 0 2π , where 2k 0 is the distance between two WPs. 14,28,29 To understand the relation between the AHE and the distribution of WPs, it is convenient to introduce a Chern vector C = (C x , C y , C z ), which is defined as…”

Section: D Bulk Propertiesmentioning

confidence: 99%

“…According to the recent theoretical studies of the lattice Hamiltonian, 23,25,26 it is shown that when the quadratic-SM is the non-magnetic ground state, the local Coulomb interaction can give rise to the AIAO type magnetic ground state, 2π , where 2k 0 is the distance between two WPs. 14,28,29 To understand the relation between the AHE and the distribution of WPs, it is convenient to introduce a Chern vector C = (C x , C y , C z ), which is defined as2πh ijk C k where ijk is the fully-antisymmetric tensor with 123 = 1. 28,30 Therefore, for a pair of WPs located at ±k 0 = (0, 0, ±k 0 ), the corresponding Chern vector would be C = (0, 0, 2k 0 ) and the location of the two Weyl points are at k = ± 1 2 C. As the distance between the two Weyl points increases, the Hall conductance of the system grows until the two Weyl points are pair-annihilated at the zone boundary.…”

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confidence: 99%

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Emergent Topological Phenomena in Thin Films of Pyrochlore Iridates

Yang

Nagaosa

2014

Phys. Rev. Lett.

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Two quintessential ingredients governing the topological invariant of a system are the dimensionality and the symmetry of the system. Due to the recent development of thin film and artificial superstructure growth technique, it is possible to control the dimensionality of the system, smoothly between the two-dimensions (2D) and three-dimensions (3D). In this work we unveil the dimensional crossover of emergent topological phenomena in correlated topological materials. In particular, by focusing on the thin film of pyrochlore iridate antiferromagnets grown along the [111] direction, we demonstrate that it can show giant anomalous Hall conductance, which is proportional to the thickness of the film, even though there is no Hall effect in 3D bulk material. In addition, we uncover the emergence of a new topological phase, whose nontrivial topological properties are hidden in the bulk insulator but manifest only in thin films. This shows that the thin film of topological materials is a new platform to search for unexplored novel topological phenomena. Dimensionality and symmetry of a system govern the topological nature of a band insulator. [1][2][3][4] For instance, in two dimensional (2D) electronic systems with broken time reversal symmetry (TRS), band insulators can be classified by the quantized Hall conductance, which generally has the form of σ xy = e 2 h N where e is the elementary charge and h is the Planck constant. 5 Since N can be any integer number, there are infinite number of ways distinguishing band insulators. However, when 2D and three dimensional (3D) electronic systems obey TRS, there are only two different ways to discern band insulators based on the Z 2 topological index. [6][7][8][9][10][11] On the other hand, if 3D electronic systems break TRS, there is no way to differentiate band insulators since one insulator can always be deformed to the other insulator adiabatically. Considering such an intimate relationship between the topological property of band insulators and the dimensionality (and also the symmetry), one natural question is how the dimensional crossover from 2D to 3D limit occurs in a thin film structure.In fact, it is recently proposed that in systems with TRS, if we make a thin film by stacking 2D topological insulators, the topological nature of the film dramatically changes depending on the parity of the number of stacked 2D layers. Such an oscillating topological property of the film eventually gives rise to a topologically nontrivial insulator in the 3D bulk limit. 12 The main purpose of this work is to establish such a fundamental relationship between the dimensionality and the topological nature of a system in correlated topological materials.In particular, we focus on the evolution of topological properties of a transition metal oxide (TMO) with strong spin-orbit coupling in its thin film form. The motivation to study TMO with large spin-orbit coupling is two-fold. At first, in this system, due to the strong spinorbit coupling and the resultant enhanced electron cor...

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Quantum Hall effects in a Weyl semimetal: Possible application in pyrochlore iridates

Cited by 857 publications

References 33 publications

CaTe: a new topological node-line and Dirac semimetal

CaTe: a new topological node-line and Dirac semimetal

Fragile magnetic order in the honeycomb lattice IridateNa2IrO3revealed by magnetic impurity doping

Emergent Topological Phenomena in Thin Films of Pyrochlore Iridates

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