Photon Factory Activity Report 2017 #35 (2018)

BL-28A/2016G079

Angle-resolved photoemission study on (Sr,La)2IrO4Kensei TERASHIMA1,*, Masonori SUNAGAWA2, Hirokazu FUJIWARA2, Kazumasa
HORIGANE1, Masanori FUJII2, Rie HORIE1, Kaya KOBAYASHI1,2, Jun AKIMITSU1, Kanta ONO3,Hiroshi KUMIGASHIRA3, Yuji MURAOKA1,2, and Takayoshi YOKOYA1,2
1
Research Institute for Interdisciplinary Science, Okayama University, 3-1-1, Okayama, 700-8530,
Japan
2
Department of Natural Science and Technology, Okayama University, 3-1-1 Okayama, 700-8530,
Japan
3
High Energy Accelerator Research Organization (KEK), Photon Factory, Tsukuba, Ibaraki 3050801, Japan
1 Introduction
5d electron system is acquiring attention of thecondensed matter field as a system where the energy scaleof spin-orbit coupling is as large as those of Coulombinteraction and transfer integral, to produce possible
novel phenomena. Among them, Sr2IrO4 has been
regarded as a promising candidate for superconductor
since it has been proposed that the insulating behavior of
the sample is originating from the splitting of Jeff=1/2
band due to strong correlation [1]. The sample isisostructural to one of cuprates La2CuO4 and shows anTheantiferromagnetic order below TN = 240 K.
emergence of superconductivity in doped system has been
predicted by theoretical studies [2] although there has
been no corresponding experimental report so far.
Nevertheless, it has been reported that K-doped sample
surface shows peculiar electronic structure withanisotropic excitation gap [3] reminiscent of pseudogap incuprates. The existence of similar electronic state has
been also reported recently in the cleaved sample surfaceof Sr2-xLaxIrO4 [4]. Further detailed investigation of thispseudogap-like state in electron-doped iridates has beenhighly anticipated.
In this work, we have performed angle-resolved
photoelectron spectroscopy on Sr2-xLaxIrO4 (x = 0, 0.08).
We have measured electronic structure at temperatures
both below and above TN of crystals, in order to find out
how the pseudogap reacts by raising temperature.
2 ExperimentSingle crystals of Sr2IrO4 and Sr1.92La0.08IrO4 weresynthesized by flux method.
ARPES mesurements were perfomed at BL-28A,Photon Factory. The energy resolution was set at 30meV. We used circulary polarized light of hν = 100 eV toexcite photoelectrons. The Fermi energy of the sample
was referenced to that of gold which had electronic
contact with samples.
3 Results and Discussion
We show in Fig. 1(a) ARPES intensity plot
Sr1.92La0.08IrO4 as a function of two dimensional wave
vector at binding energy of 50 meV, taken at T = 100 K.
We have observed electron-like dispersion centered at Γpoint, which forms the circle-shaped remnant Fermi
surface. As shown in Fig. 1(f), the leading edge ofphotoemission energy distribution curve (EDC) lies
below EF, indicating the presence of an excitation gap
near the X point at T = 100K in Sr1.92La0.08IrO4. This
excitation gap seems to be closed by raising temperature
up to T = 260 K, although spectra has broadened (Fig.
1(c) and 1(e)) considerably partially because of possible
aging. Further study with higher vacuum should benecessary to conclude the temperature dependence ofexcitation gap in doped iridates.

Fig. 1: (a) ARPES intensity plot of Sr1.92La0.08IrO4 as afunction of two dimensional wave vector atbinding energy of 50 meV, taken at T = 100 K. (b)ARPES intensity plot along ΓX direction at T =100 K. (c) same as (b) at T = 260 K. (d) and (e)second derivative of (b) and (c). (f) EDCs taken at
k-point indicated by an arrow in (b).
References[1] B. J. Kim et al., Phys. Rev. Lett. 101, 076402 (2008).
[2] F. Wang et al., Phys. Rev. Lett. 106, 136402 (2011).
[3] Y. K. Kim et al., Nat. Phys. 12, 37 (2016).
[4] A. de la Torre et al., Phys. Rev. Lett. 115, 176402(2015).
* k-terashima@cc.okayama-u.ac.jp