Quasiparticle interference in ZrSiS: Strongly band-selective scattering depending on impurity lattice site

Abstract

Scanning tunneling microscopy visualizations of quasiparticle interference (QPI) enable powerful insights into the k -space properties of superconducting, topological, Rashba and other exotic electronic phases, but their reliance on impurities acting as scattering centers is rarely scrutinized.Here we investigate QPI at the vacuum-cleaved (001) surface of the Dirac semimetal ZrSiS. We find that interference patterns around impurities located on the Zr and S lattice sites appear very different, and can be ascribed to selective scattering of different sub-sets of the predominantly Zr 4d-derived band structure, namely the m = 0 and m = ±1 components. We show that the selectivity of scattering channels requires an explanation beyond the different bands' orbital characteristics and their respective charge density distributions over Zr and S lattices sites. Importantly, this result shows that the usual assumption of generic scattering centers allowing observations of quasiparticle interference to shed light indiscriminately and isotropically upon the q-space of scattering events does not hold, and that the scope and interpretation of QPI observations can therefore be be strongly contingent on the material defect chemistry. This finding promises to spur new investigations into the quasiparticle scattering process itself, to inform future interpretations of quasiparticle interference observations, and ultimately to aid the understanding and engineering of quantum electronic transport properties.2

Surface termination dependent quasiparticle scattering interference and magneto-transport study on ZrSiS

“…This explains why it is easier to observe Zr atoms than S or Si atoms in STM topographic images and confirms the previous impurities study of ZrSiS by STM and DFT study [17]. The simulated STM images also support this view [17]. A dip exists at E∼0.6 eV in PDOS calculation and is also observed in tunnelling spectrum at E∼0.74 eV, which could be related to the change in energy dispersion as indicated by black and The diamond-shaped surface band at G (indicated by the orange arrow in (d)) is separated from the bulk bands.…”

“…To better compare the theoretical calculation with STM and ARPES measurements, we also carry out a slab calculation and the resultant band structure with the surface component is shown in figure 1(d). By comparing the electronic structure of ZrSiS from the bulk and slab calculations, we find the surface states with linear dispersion around X at E F , and this is consistent with previous ARPES [9][10][11][12][13] and STM [17] experiments. Interestingly, we also find that the SOC opens a gap of ∼100 meV (orange circles in figures 1(b) and (c)) on the Dirac crossings around E∼0.6 eV and a surface state emerges to connect the top of inner Dirac band and the bottom of conduction bands (orange arrow along GM in figure 1(d)).…”

“…The measured tunnelling spectra appear to be in excellent agreement with our orbital-projected density of states (PDOS) calculation, as displayed in figure 2(f), in which Zr-d orbital dominates the LDOS near E F over S-p and Si-p orbitals on the surface. This explains why it is easier to observe Zr atoms than S or Si atoms in STM topographic images and confirms the previous impurities study of ZrSiS by STM and DFT study [17]. The simulated STM images also support this view [17].…”

“…Indeed, recent ARPES studies on ZrSiS revealed the existence of non-symmorphic symmetry protected line nodes [9][10][11][12][13], which was first predicted by Kane and Young in 2015 [15]. In addition, there also exist a Dirac surface band at X and a diamond-shaped Dirac band at G from ARPES [9][10][11][12][13]16] and scanning tunnelling microscope (STM) study [17,18]. Both Dirac bands are also shown to disperse linearly up to few hundred meV even above E F by quasiparticle scattering interference (QPI) imaging [17,18], from which ZrSiS exhibits strongly band-selective scattering depending on impurity lattice site [17].…”

“…In addition, there also exist a Dirac surface band at X and a diamond-shaped Dirac band at G from ARPES [9][10][11][12][13]16] and scanning tunnelling microscope (STM) study [17,18]. Both Dirac bands are also shown to disperse linearly up to few hundred meV even above E F by quasiparticle scattering interference (QPI) imaging [17,18], from which ZrSiS exhibits strongly band-selective scattering depending on impurity lattice site [17]. Moreover, transport measurements revealed extremely large, non-saturated and anisotropic magnetoresistance (MR) in ZrSiS [16,[19][20][21].…”