Evidence for the chiral anomaly in the Dirac semimetal Na ₃ Bi

Abstract

In a Dirac semimetal, each Dirac node is resolved into two Weyl nodes with opposite "handedness" or chirality. The two chiral populations do not mix. However, in parallel electric and magnetic fields ( E: || B: ), charge is predicted to flow between the Weyl nodes, leading to negative magnetoresistance. This "axial" current is the chiral (Adler-Bell-Jackiw) anomaly investigated in quantum field theory. We report the observation of a large, negative longitudinal magnetoresistance in the Dirac semimetal Na3Bi. The negative magnetoresistance is acutely sensitive to deviations of the direction of B: from E: and is incompatible with conventional transport. By rotating E: (as well as B: ), we show that it is consistent with the prediction of the chiral anomaly.

Nernst and magnetothermal conductivity in a lattice model of Weyl fermions

“…Another route which can result in the experimental verification of the novel WSM phase is to first realize a 3D Dirac semimetal and then break time reversal symmetry by applying a magnetic field, which will split a Dirac cone into a pair of Weyl nodes. Na 3 Bi and Cd 3 As 2 were recently proposed to be Dirac semimetals 27,28 , and also have been confirmed experimentally by a series of experiments [29][30][31][32][33][34][35][36][37] . In Bi 1−x Sb x for x ∼ 3 − 4% also the Dirac semimetal phase has been predicted [38][39][40] , and experimental signatures of realizing a WSM phase by breaking TR have been reported 41 .…”

“…Cd 3 As 2 , and Bi 1−x Sb x with x ∼ 3 − 4% were recently proposed 27,28,[38][39][40] , and also realized experimentally to be Dirac semimetals [29][30][31][32][33][34][35][36][37]41 . This has paved the way to realizing a TR broken WSM phase, which has been so far verified by a few experimental signatures 24,37,41,42 .…”

“…an imbalance of charge between two distinct species of chiral fermions in the presence of non-orthogonal applied electric and magnetic fields. Several transport signatures have been proposed to test chiral anomaly such as negative longitudinal magenoresistance 16,21,60,61 and chiral magnetic effect 16,62,63 of which the former has been recently claimed to be observed in experiments 24,37,41,42 .…”

Topological semimetals with helicoid surface states

“…The nontrivial topology gives rise to anomalous bulk properties of topological semimetals such as the chiral anomaly [3][4][5]. Several classes of topological semimetals have been theoretically proposed so far, including Weyl, [2,[6][7][8][9][10][11][12][13], Dirac [14][15][16][17] and nodal line semimetals [7,[17][18][19][20][21][22][23][24][25][26][27][28][29][30], some among which have been experimentally observed [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47].Surface states of topological semimetals have attracted much attention. On the surface of a Weyl semimetal, the Fermi surface consists of open ar...…”

Intra-cone transition effect to magnetoconductivity in Dirac semimetal

“…This has led to the theoretical predictions [6,7] and experimental observations of gapless three dimensional Dirac semimetals such as N a 3 Bi and Cd 3 Se 2 [8][9][10][11][12]. There are several papers which report the unusual magnetoresistance in Weyl semimetals [13,14] and Dirac semimetals [15][16][17]. It would be interesting to compare the experimental observations to theoretical predictions.…”