Tuning the semimetallic charge transport in the Weyl semimetal candidate Eu₂Ir₂O₇ (111) epitaxial thin film with an all-in-all-out spin structure

Abstract

We report the stoichiometric epitaxial growth of the Eu2Ir2O7 (111) thin film on YSZ substrate by a two-step solid phase epitaxy (SPE) method. An optimized post-annealing environment of the SPE was superior over the conventional air annealing procedure to get rid of the typical impurity phase, Eu2O3. The thickness-dependent structural study on Eu2Ir2O7 (111) thin films suggests a systematic control of Ir/Eu stoichiometry in our films, which is otherwise difficult to achieve. In addition, the low-temperature electrical resistivity studies strongly support the claim. The power-law dependence analysis of the resistivity data exhibits a power exponent of 0.52 in 50 nm sample suggesting possible disorder-driven semimetalic charge transport in the 3D Weyl semimetallic candidate Eu2Ir2O7 . In addition, the all-in-all-out/all-out-all-in antiferromagnetic domains of Ir4+ sublattice is verified using the field cooled magnetoresistance measurements at 2 K. Hall resistivity analysis indicate semimetallic hole carrier type dominance near the Fermi level up to the measured temperature range of 2-120 K. Altogether, our study reveals the ground state of stoichiometric Eu2Ir2O7 (111) thin film, with an indirect tuning of the off-stoichiometry using thickness of the samples, which is of interest in the search of the predicted 3D Weyl semimetallic phase.

Berry curvature induced spontaneous and topological-like Hall effect in magnetic Weyl semimetallic Nd2Ir2O7 (111) thin films

“…23 The low temperature (2-55 K) resistivity data signify that the ground state is non-metallic (dρ/dT < 0) in nature 25 and probably lies in the semimetallic region. 27,33 To check the magnetic field (H) induced modification of the charge dynamics, temperature-dependent longitudinal resistivity (ρ xx ) measurements were performed under the application of 140 kOe of the magnetic field along [111] direction in both "zero-field cooled" and "field-cooled" conditions. In Fig.…”

“…30 The sample fabrication protocol is kept the same as in the earlier report. 27 The crystallinity of post-annealed Nd 2 Ir 2 O7 thin films was characterized using a Rigaku SmartLab high-resolution four-circle x-ray diffractometer (XRD) with Cu-K α1 radiation. The electrical and magnetotransport properties were measured in Dyna-Cool physical property measurement systems (PPMS) (Resistivity option, Quantum Designs) on a Hall bar by the four-probe method.…”

“…At H = 0, both the A and B domains will be present in equal proportion in the sample. 27 In the B-domain, the Ir 4+ 5d moments will order in the AOAI structure, whereas the Nd 3+ 4 f moments will order in the AIAO structure, as shown in Fig. 3(c).…”

“…24 These observations suggest widely different ground states in Nd 2 Ir 2 O7, from charge-gaped insulators to zero gap semimetals or metals, which might arise due to slight Nd/Ir offstoichiometry in Nd 2 Ir 2 O7, like other pyrochlore iridates. [25][26][27] A recent study by Kim et al on Nd 2 Ir 2 O7 (111) thin films indicates semimetallic charge transport down to the lowest measured temperature of 2 K. 17 Furthermore, a single crystal study by Udea et al on Nd 2 Ir 2 O7 under an applied hydrostatic pressure shows stabilization of the WSM phase within a few Kelvin of the temperature region just below the AIAI/AOAI AFM ordering temperature T N . 18 The abovementioned observations imply that below T N , the AFM ordering of Ir 4+ can stabilize topological electronic phases with a number of Weyl nodes in momentum space.…”