Detecting quantum spin liquid on Kitaev model through a superconducting junction
A. R. Moura, L. V. Santos
TL;DR
The paper addresses the challenge of identifying Quantum Spin Liquids, specifically Kitaev QSLs hosting itinerant Majorana fermions coupled to a $Z_2$ gauge field, by proposing a spintronic probe. It develops a framework for spin current injection from a superconducting metal into a Kitaev QSL and evaluates the current via linear-response theory, focusing on spin-flip scattering at the SC/Kitaev interface. The analysis links the injected spin current to Majorana excitations and contrasts Kitaev-based interfaces with conventional magnonic junctions, revealing distinctive spin-current signatures. The work offers a viable experimental route to detect QSLs and facilitates integration of topological quantum materials with superconducting platforms for quantum technologies.
Abstract
The Kitaev model belongs to an unconventional class of two-dimensional spin systems characterized by anisotropic, bond-dependent interactions that give rise to Quantum Spin Liquid (QSL) states. These exotic phases, marked by the absence of magnetic ordering even at zero temperature, support fractionalized excitations and emergent gauge fields. A particularly compelling feature of the Kitaev model is its exact solvability, which reveals low-energy excitations in the form of itinerant Majorana fermions-quasiparticles that obey non-Abelian statistics and are of central interest in topological quantum computation due to their inherent robustness against local perturbations and decoherence. Despite extensive theoretical advancements, the experimental identification of QSLs remains challenging, as conventional magnetic probes fail to detect their defining properties. In this work, we present a theoretical investigation of spin current injection from a superconducting metal into a Kitaev quantum spin liquid. By employing a spintronic framework, we derive the dynamics of the injected spin current and demonstrate how its signatures can be traced back to the underlying Majorana excitations in the spin liquid phase. Superconductivity plays a pivotal role in this context, not only as a source of coherent quasiparticles but also as a platform with potential for interfacing with topological quantum devices. Our analysis contrasts the Kitaev-superconductor interface with conventional ferromagnetic junctions, where spin transport is carried by magnons, and highlights distinctive features in the spin current response. These findings open new directions for the detection of QSLs and contribute to the broader effort of integrating topological quantum materials into scalable quantum technologies.