Condensed Matter seminars

Disordered Weyl semimetal: a global phase diagram and chiral superuniversality

by Vladimir Juricic (Nordita)

112:028 (Nordita South)


Nordita South

Weyl semimetal (WSM), besides manifesting chiral anomaly and Fermi arc surface states, exhibits a quantum-phase transition into a diffusive metallic phase at strong disorder. The existence of this phase transition has been established in the case of a most common disorder represented by charge impurities. However, other types of disorder are also inevitably present in the experimental samples, such as random asymmetric shifts in the chemical potential between the Weyl cones, giving rise to an axial potential disorder. Motivated by this physical situation, I will consider a minimal lattice model for a WSM and study generic phase diagram in the presence of eight possible types of disorder. I will show that emergent chiral symmetry plays a fundamental role in determining universality classes of the disorder-driven transitions in a WSM. Chiral-symmetric disorders exhibit superuniversality – chiral superuniversality – the correlation-length exponent (v) and the dynamical critical exponent (z) are independent of the type of disorder as long as the chiral symmetry is preserved [1]. These are equal to z=3/2 and v=1 to the one-loop in the expansion either about lower critical dimension or about the critical disorder distribution. Our numerical results for the average density of states strongly support emergent chiral superuniversality. On the other hand, chiral-symmetry breaking disorders lead to the quantum-critical lines where the critical exponents depend on the location at the line. To establish a global phase diagram of a WSM, I will also discuss WSM-insulator transition and in particular effects of disorder on the quantum-critical anisotropic semimetal separating WSM and insulator. Finally, I will show how various types of disorder leave an imprint in the scaling of some numerically and experimentally relevant observables, such as optical conductivity [2]. [1] B. Roy, R.-J. Slager, and V. Juricic, arXiv: 1610.08973. [2] B. Roy, V. Juricic, and S. Das Sarma, Scientific Reports 6, 32446 (2016).