[Paper Review] Intrinsic chiral magnetic effect in Dirac semimetals due to dislocations

M. N. Chernodub, M. A. Zubkov|arXiv (Cornell University)|Jul 31, 2015

Topological Materials and Phenomena3 citations

TL;DR

This paper proposes that dislocations in Dirac semimetals induce an intrinsic chiral magnetic effect via emergent magnetic flux, leading to a chiral fermion mode along the dislocation axis. When an external electric field is applied parallel to the dislocation, spectral flow pumps axial charge, and the intrinsic magnetic field generates a longitudinal electric current, enhancing conductivity in transport measurements.

ABSTRACT

A dislocation in a Dirac semimetal carries an emergent magnetic flux parallel to the dislocation axis. We show that due to the emergent magnetic field the dislocation accommodates a single fermion massless mode of a corresponding low-energy one-particle Hamiltonian. The mode is propagating along the dislocation with its spin directed parallel to the dislocation axis. In agreement with the chiral anomaly observed in Dirac semimetals, an external electric field to the spectral flow of the one-particle Hamiltonian by pumping the fermionic quasiparticles out from vacuum and creating a nonzero axial (chiral) charge in the vicinity of the dislocation. In the presence of the chirality imbalance, the intrinsic magnetic field of the dislocation generates an electric current along the dislocation axis. We point out that this effect – which is an intrinsic analogue of the chiral magnetic effect – may experimentally reveal itself through transport measurements in Dirac semimetals via enhanced conductivity when the external electric field is parallel to the dislocation axis.

Motivation & Objective

• To investigate the emergence of chiral fermion modes in Dirac semimetals due to dislocations.
• To understand how the emergent magnetic flux from dislocations leads to axial charge pumping under external electric fields.
• To demonstrate that the intrinsic magnetic field of the dislocation generates a longitudinal electric current via the chiral magnetic effect.
• To propose a measurable transport signature—enhanced conductivity—when the external electric field is aligned with the dislocation axis.

Proposed method

• Modeling the dislocation as a source of emergent magnetic flux parallel to the dislocation axis in the low-energy effective Hamiltonian.
• Analyzing the one-particle Hamiltonian to identify a single propagating massless fermion mode along the dislocation.
• Applying an external electric field to induce spectral flow, which pumps quasiparticles from vacuum and creates axial (chiral) charge.
• Calculating the resulting current generated by the intrinsic magnetic field of the dislocation in the presence of chiral imbalance.
• Using symmetry and topological considerations to link the chiral anomaly to the emergence of a net current along the dislocation.
• Predicting experimentally observable signatures through transport measurements in Dirac semimetals.

Experimental results

Research questions

• RQ1 How do dislocations in Dirac semimetals give rise to emergent magnetic flux and associated chiral fermion modes?
• RQ2 What is the role of the chiral anomaly in enabling axial charge pumping via spectral flow under an external electric field?
• RQ3 How does the intrinsic magnetic field of the dislocation generate a net electric current along its axis?
• RQ4 What measurable transport response can be expected when the external electric field is parallel to the dislocation?
• RQ5 In what way does this effect represent an intrinsic analogue of the chiral magnetic effect?

Key findings

• Dislocations in Dirac semimetals host a single chiral fermion mode propagating along the dislocation axis with spin aligned parallel to the axis.
• The emergent magnetic flux from the dislocation leads to a chiral anomaly, enabling spectral flow under an external electric field.
• Axial charge is pumped into the vicinity of the dislocation due to the chiral anomaly, creating a chiral imbalance.
• The intrinsic magnetic field of the dislocation generates a net electric current along the dislocation axis in response to the chiral imbalance.
• Enhanced longitudinal conductivity is predicted when the external electric field is applied parallel to the dislocation axis.
• The effect provides a distinct transport signature for detecting intrinsic chiral magnetic effects in Dirac semimetals.