Observation of the chiral magnetic effect in ZrTe 5

The chiral magnetic effect is the generation of electric current induced by chirality imbalance in the presence of magnetic field. It is a macroscopic manifestation of the quantum anomaly 1,2 in relativistic field theory of chiral fermions (massless spin 1 / 2 particles with a definite projection of spin on momentum) – a dramatic phenomenon arising from a collective motion of particles and antiparti-cles in the Dirac sea. The recent discovery 3–5 of Dirac semimetals with chiral quasi-particles opens a fascinating possibility to study this phenomenon in condensed matter experiments. Here we report on the first observation of chiral magnetic effect through the measurement of magneto-transport in zirconium pentatelluride, ZrTe 5 . Our angle-resolved photoemission spectroscopy experiments show that this material’s electronic structure is consistent with a 3D Dirac semimetal. We observe a large negative magnetoresistance when magnetic field is parallel with the current. The measured quadratic field dependence of the magnetoconductance is a clear indication of the chiral magnetic effect. The observed phenomenon stems from the effective transmutation of Dirac semimetal into a Weyl semimetal induced by the parallel electric and magnetic fields that represent a topologically nontrivial gauge field background. The recent discovery of three dimensional (3D) Dirac semimetals and Bi enables experimental studies of the quantum dynamics of relativistic field theory in condensed matter systems. Relativistic theory of charged chiral fermions in three spatial di-mensions possesses so-called chiral anomaly 1,2 – non-conservation of chiral charge induced by the external gauge fields with non-trivial topology, e.g. by parallel electric and magnetic fields. The existence of chiral quasi-particles in Dirac and Weyl semimetals opens the possibility to observe the effects of the chiral anomaly 6 . Of particular interest is the chiral magnetic effect (CME) 7 – the generation of electric current in an external magnetic field induced by the chirality imbalance, see 8 for a recent review and additional references. This phenomenon is currently under intense study in relativistic heavy ion collisions at Relativistic Heavy Ion Collider and at the Hadron Collider where it was predicted 9 to induce the fluctuations in hadron charge asymmetry with respect to the reaction plane. The experimental data from the STAR 10 Collaboration at RHIC and ALICE 11 Collaboration at LHC indicate the fluctuations consistent with the theory expectations. Closely related phenomena are expected to play an important role in the Early Universe, possibly causing the generation of primordial magnetic fields 12–16 . However, the interpretation in all these cases is debate lack of control chirality

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