[Paper Review] The Realization and Dectection of Weyl Semimetals in Cold Atomic Systems

Wen‐Yu He, Shizhong Zhang+1 more|arXiv (Cornell University)|Jan 10, 2015

Cold Atom Physics and Bose-Einstein Condensates3 citations

TL;DR

This paper proposes a scheme to realize 3D Weyl semimetal phases in ultracold atomic systems by coupling multilayers of honeycomb optical lattices via Raman lasers, which induce Chern insulator behavior in each layer. Finite interlayer coupling closes the bulk gap at specific momenta due to Raman-assisted tunneling, enabling the emergence of Weyl points; experimentally tunable coupling strength realizes one or two pairs of Weyl points, and Landau-Zener tunneling is proposed as a detection method with enhanced transition probability at Weyl points.

ABSTRACT

In this work, we describe a method to realize 3D Weyl semimetal by coupling multilayers of honeycomb optical lattice in the presence of a pair of Raman lasers. The Raman lasers render each isolated honeycomb layer a Chern insulator. With finite interlayer coupling, the bulk gap of the system closes at certain out-of-plane momenta due to Raman assisted tunnelling and result in the Weyl semimetal phase. Using experimentally relevant parameters, we show that both one and two pairs of Weyl points can be realized by tuning the interlayer coupling strength. We suggest that Landau-Zener tunnelling can be used to detect Weyl points and show that the transition probability increases dramatically when Weyl point emerges.

Motivation & Objective

• To propose a realistic quantum simulation platform for 3D Weyl semimetals using ultracold atoms in optical lattices.
• To demonstrate how interlayer coupling and Raman lasers can close the bulk gap at specific momenta, leading to Weyl semimetal phases.
• To show that Weyl point number and position can be tuned via interlayer coupling strength.
• To propose Landau-Zener tunneling as a detectable signature for the presence of Weyl points.

Proposed method

• Couple multilayers of two-dimensional honeycomb optical lattices to form a 3D system.
• Apply a pair of Raman lasers to each layer, inducing a Chern insulating state with nontrivial quantum Hall effect.
• Introduce finite interlayer tunneling via Raman-assisted hopping, breaking inversion symmetry and enabling gap closure at specific out-of-plane momenta.
• Use experimentally feasible parameters to tune the interlayer coupling strength and control the number of Weyl points.
• Model the system using a tight-binding Hamiltonian with Raman-induced complex hopping terms.
• Propose Landau-Zener tunneling as a probe: transition probability increases sharply when Weyl points are present.

Experimental results

Research questions

• RQ1 Can 3D Weyl semimetal phases be realized in ultracold atomic systems using coupled optical lattices?
• RQ2 How does interlayer coupling strength influence the number and location of Weyl points?
• RQ3 What role does Raman-assisted tunneling play in closing the bulk gap and enabling Weyl semimetal behavior?
• RQ4 Can Landau-Zener tunneling serve as a detectable signature for Weyl points in this system?
• RQ5 Is it possible to experimentally tune between one and two pairs of Weyl points using realistic parameters?

Key findings

• Weyl semimetal phases emerge due to bulk gap closure at specific out-of-plane momenta when interlayer coupling is finite.
• One or two pairs of Weyl points can be realized by tuning the interlayer coupling strength, with experimentally feasible parameters.
• Raman-assisted tunneling is essential for gap closure and the formation of Weyl nodes in the 3D band structure.
• Landau-Zener tunneling transition probability increases significantly when a Weyl point is present, indicating a detectable signature.
• The system realizes a topologically nontrivial phase with robust Weyl points under realistic experimental conditions.