Abstract
Quantum spin-liquids are strongly correlated phases of matter displaying a highly entangled ground state. Due to their unconventional nature, finding experimental signatures of these states has proven to be a remarkable challenge. Here we show that the effects of local impurities can provide strong signatures of a Dirac quantum spin-liquid state. Focusing on a gapless Dirac quantum spin-liquid state as realized in NaYbO$_2$, we show that single magnetic impurity coupled to the quantum spin-liquid state creates a resonant spinon peak at zero frequency, coexisting the original Dirac spinons. We explore the spatial dependence of this zero-bias resonance, and show how different zero modes stemming from several impurities interfere. We finally address how such spinon zero-mode resonances can be experimentally probed with inelastic spectroscopy and electrically-driven paramagnetic resonance with scanning tunnel microscopy. Our results put forward impurity engineering as a means of identifying Dirac quantum spin-liquids with scanning probe techniques, highlighting the dramatic impact of magnetic impurities in a macroscopically entangled many-body ground state.
Highlights
Quantum spin liquids (QSL) [1,2,3] are exotic magnetic phases of matter, characterized by strong quantum fluctuations and frustration [4], lacking magnetic order even at zero temperature [5]
We have shown that individual magnetic S = 1/2 impurities coupled to a Dirac quantum spin-liquid state, as realized in NaYbO2, give rise to a divergent spinon density of states at zero frequency
The emergence of such zero modes is associated with the low-energy Dirac nature of the spinon excitations and as a result provides a simple spectroscopic signature distinguishing Dirac spin liquids from generic gapless Dirac liquids with a finite Fermi surface
Summary
Quantum spin liquids (QSL) [1,2,3] are exotic magnetic phases of matter, characterized by strong quantum fluctuations and frustration [4], lacking magnetic order even at zero temperature [5]. Other paradigmatic examples are carbon vacancies [36,51,52,53,54,55,56] and hydrogen ad-atoms [57,58] in graphene, giving rise to a divergent density of states [36,52] and magnetism [37,53,58] Along this line, recent experimental advances have demonstrated the possibility of single-atom manipulation in a variety of systems by means of scanning probe techniques [59,60,61,62,63,64,65,66,67,68,69,70,71,72,73].
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