Determination of the local structure of Sr 2−x M x IrO 4 (M = K, La) as a function of doping and temperature
K. Terashima, E. Paris, E. Salas-Colera, L. Simonelli, B. Joseph, T. Wakita, K. Horigane, M. Fujii, K. Kobayashi, R. Horie, J. Akimitsu, Y. Muraoka, T. Yokoya, N. L. Saini
DDetermination of the local structure of Sr − x M x IrO (M = K, La) as a function ofdoping and temperature K. Terashima, ∗ E. Paris, † E. Salas-Colera,
3, 4
L. Simonelli, B. Joseph, T. Wakita, K. Horigane, M. Fujii, K. Kobayashi,
1, 7
R. Horie, J. Akimitsu, Y. Muraoka,
1, 7
T. Yokoya,
1, 7 and N. L. Saini Research Institute for Interdisciplinary Science, Okayama University, Okayama, 700-8530, Japan Dipartimento di Fisica, Universit´a di Roma “La Sapienza” - P. le Aldo Moro 2, 00185, Roma, Italy Instituto de Ciencia de Materiales de Madrid, ICMM-CSIC,Sor Juana In´es de la Cruz 3, 28049 Madrid, Spain Spanish CRG BM25 Spline, ESRF - The European Synchrotron, 71 avenue des Martyrs, 38043 Grenoble, France CELLS - ALBA Synchrotron Radiation Facility,Carrer de la Llum 2-26, 08290, Cerdanyola del Valles, Barcelona, Spain ELETTRA, Sincrotrone Trieste, Strada Statale 14, Km 163.5, Basovizza, 34149 Trieste, Italy Department of Physics, Okayama University, Okayama, 700-8530, Japan
The local structure of correlated spin-orbit insulator Sr − x M x IrO (M = K, La) has been inves-tigated by Ir L -edge extended x-ray absorption fine structure measurements. The measurementswere performed as a function of temperature for different dopings induced by substitution of Srwith La or K. It is found that Ir-O bonds have strong covalency and they hardly show any changeacross the N´eel temperature. In the studied doping range, neither Ir-O bonds nor their dynamics,measured by their mean square relative displacements, show any appreciable change upon carrierdoping, indicating possibility of a nanoscale phase separation in the doped system. On the otherhand, there is a large increase of the static disorder in Ir-Sr correlation, larger for K doping thanLa doping. Similarities and differences with respect to the local lattice displacements in cupratesare briefly discussed. I. INTRODUCTION
Transition-metal oxides have been one of the majorresearch subjects in condensed matter physics for last fewdecades, stimulated by large electron-electron correlationin 3 d -electron systems. Recently, 5 d -electron systems areacquiring enormous attention in the field since the spin-orbit interaction energy in these is comparable to theCoulomb interaction and transfer integral energy scaleand hence novel phenomena are expected to emerge dueto their interplay .Among 5 d -electron systems, Sr IrO is an insulatorwith an antiferromagnetic order at T <
240 K . Recently,the electronic structure of Sr IrO has been reported tobe well described by J eff = 1/2 ground state , and itsinsulating behavior has been realized due to the split-ting of J eff = 1/2 band into lower and upper Hubbardband. This material has been regarded as an analogueof 214-type cuprate superconductors ( s = 1/2) in severalaspects, such as K NiF -type crystal structure , antifer-romagnetic magnetic ordering, and correlated insulatingbehavior. In the crystal structure, the Ir-O octahedra iselongated along c -axis and further rotated by ∼
11 degreearound c -axis and the material forms a canted antiferro-magnetic ordering . Although there has been no reportson the temperature dependence of local structure, an x-ray diffraction study has argued that the temperaturedependence of resistivity may be related with atomic co-ordinates of Ir and O atoms .For the carrier-doped Sr IrO system, the emergenceof superconductivity has been predicted theoreticallyin the context of the analogy with cuprates . Al- though superconductivity in this class of material hasnot been reported to date, angle-resolved photoemis-sion studies have reported that the electronic struc-ture in lightly carrier-doped samples are similar withcuprates in several aspects. Furthermore, the existanceof anisotropic excitation gap reminiscent of pseudogaphave been reported .In doped Mott insulators such as the cuprates, notonly the spin but also the lattice degree of freedom havebeen investigated, leading to the conclusion that thestrong interaction among phonons, spin fluctuations, andthe electronic structure should play a role for the emer-gence of high- T c superconductivity . It has beenalso found that the charge/spin density wave is likelyto commonly exist in the pseudogapped underdoped re-gion of cuprates . Among the lattice-sensitive experi-mental methods, extended x-ray absorption fine struc-ture (EXAFS) is a unique technique to resolve localatomic displacements that turned out to be sensitive tothe occurance of a charge ordering in cuprates . Onthe other hand, the corresponding work of temperature-dependent local lattice displacements has not been re-ported in Sr IrO series although there are several signa-tures of the pseudogap in the system. Furthermore,the bilayer compound Sr Ir O with Ruddlesen-Popperstructure has been found to show an indication of a pos-sible charge order . In Sr Ir − x Rh x O also, optical sec-ond harmonic generation and neutron diffraction mea-surements have indicated a symmetry lowering below acertain temperature due to an emergence of an orderedphase, where both the spatial inversion and rotationalsymmetries of the tetragonal lattice are broken . This a r X i v : . [ c ond - m a t . s t r- e l ] O c t state has been interpreted as a loop-current ordered statethat was initially proposed as an explanation for thepseudogap state in cuprates. Possible existence of a spindensity wave (SDW) state has been also reported . De-spite these similarities with cuprates, there have beenno report of superconductivity yet in Sr IrO upon dop-ing. Therefore, a further systematic study on how thelattice degree of freedom reacts upon doping in the sys-tem should provide important information in clarifyingthe metallization process of correlated spin-orbit insula-tor Sr IrO .In this study, we report doping- as well as temperature-dependence of the local structure around Ir atom in bothhole- and electron-doped Sr − x M x IrO (M = K, La),aiming to find out possible coupling between local lat-tice degrees of freedom with the ordering of spin includ-ing antiferromagnetism. The work is also aimed to findpossible signature of ordering involving local lattice likecharge density wave as has been seen in cuprates. Here,the carriers were introduced by a partial substitution forSr atom in the Sr-O block layer for both type of doping.By a systematic study, we have found that the in-planeIr-O bond has a strong covalency resulting in an Einstein-frequency as high as 800 K, and the bond is hardly af-fected by carrier doping nor the occurance of magneticorder in the system as a function of temperature. We didnot find marked signature of formation of ordered statein the lattice response within experimental uncertainties,while we do see a substantial change in the Ir-Sr correla-tions, affected more by hole-doping than electron-doping.The observed local lattice response against doping differsfrom that of cuprates, indicating that a manipulation ofhard local mode of in-plane Ir-O bond may have some keyrole for possible superconductivity in these materials. II. EXPERIMENTAL
Polycrystalline samples of Sr − x M x IrO (M = La, K)were prepared by conventional solid-state reactions. Amixture of SrCO , K CO , La O and IrO was groundand further mixed by planetary ball-milling (Fritsch, P-7) at a rotation rate of 400 rpm for 3 h with 15 (5 mm-diameter) and 10 (10 mm-diameter) ZrO balls. Theresulting powders were calcined in air at 1150 ◦ C for 15min . Nominal values of substituting atoms of La forSr − x La x IrO was 0.075. The amount of K atoms inSr − x K x IrO samples were determined to be x = 0.04and 0.055 by energy dispersive x-ray spectrometry mea-surements. Hereafter we call those samples as parent,La, K0.04, K0.055. Phase purity of samples were exam-ined by x-ray diffraction measurements (shown in sup-plemental information). N´eel temperature ( T N ) wereevaluated for all the samples by measuring their mag-netization curve, and obtained values are 240 K, 200 K,235 K, and 225 K for parent, La, K0.04, and K0.055, re-spectively (see also supplemental information for magne-tization curve and resistivity). Judging from the amount of dopant atom and T N value, the doping amount ofLa- and K-doped sample of the present study would cor-respond to the samples where excitation-gapped statehas been observed by ARPES , and the La amountis close to the sample where a signature of SDW statehas been observed . The hole doping amount of ourK-doped samples would also be in the regime where asymmetry-broken state has been observed in hole-dopedSr Ir − x Rh x O .Ir L -edge ( E ∼
11 keV) x-ray absorption measurementswere carried out at the Spline beamline of the Euro-pean Synchrotron Radiation Facility where Si(111) dou-ble crystal monochromator was used to obtain the energyresolution ∆ E/E of 1.4 × − . The powder samples weremixed with cellulose matrix and then pelletized for trans-mission measurements, to reach the desired thickness forthe absorption jump to be ∼ -edge. Fluo-rescence signals of samples and Pt L edge of Pt film forenergy reference placed at down stream of the beam wererecorded simultaneously (not shown). Several absorptionscans were acquired at each temperature to ensure spec-tral reproducibility for each sample and to estimate thestatistical error. Both of the statistical error and the er-ror coming from the correlation between parameters weretaken into account for the error bars of obtained physicalparameters. k (A -1 ) χ ( k ) * k | F T { χ ( k ) * k } | Distance (A)Sr IrO LaK0.04K0.055
Ir- S rIr- O p / O a LaK0.04K0.055Ir L -edge T = 20 K Sr IrO FIG. 1. Fourier transform magnitudes of Ir L -edgeEXAFS ( k -weighted) measured on Sr IrO (solid line),Sr . La . IrO (dotted dashed line), Sr . K . IrO (dot-ted line), and Sr . K . IrO (dashed line) samples at 20K. Here, the data are not corrected by the phase shifts. Insetshows the corresponding EXAFS oscillations of χ ( k ) ∗ k . III. RESULTS AND DISCUSSION
Figure 1 shows the magnitude of Fourier transformsof Ir L -edge EXAFS oscillations extracted from the x-ray absorption spectra on parent Sr IrO and La, K0.04, IrO | F T { k * χ ( k ) } | Bond distance (A)Sr K IrO Sr K IrO Sr La IrO (a) (b) (c) (d) T (K) = 3002802502302001801004520150300280250230200180954520140 300280250230200180954520140 3002802502302001801004520150 Ir O p O a Srabc(e)
FIG. 2. Temperature dependent Fourier transform magnitudes of Ir L -edge EXAFS for Sr . K . IrO (a), Sr . K . IrO (b), Sr IrO (c), and Sr . La . IrO (d) after phase shift correction. Red dots represent experimental data, while blue linesshow the model fits considering three shells namely Ir-O p and Ir-O a , and Ir-Sr. (e) Structural image of Sr IrO . and K0.055 samples at T = 20 K. The Fourier transformswere obtained using a Gaussian window ( k -range 3.1-16˚A − ) and are not corrected for the phase shifts thus rep-resent raw data. The first peak appears around 1.8 ˚Acorresponds to the bond distances between Ir and in-plane oxygen (Ir-O p , ∼ a , ∼ ∼ k -weighted χ ( k )EXAFS oscillations for each sample at the same tem-perature. All spectra show overall correspondence eachother and signals tend to be damped at higher k -regionbeyond ∼
14 ˚A − . Next we take into account the phaseshift correction to quantify local atomic displacements.Figure 2 shows the temperature dependent Fouriertransforms of k -weighted Ir L -edge EXAFS after phaseshift correction. Spectra in (a)-(d) are shown in the samevertical scale with the same amount of offset for a real-istic comparison. It is clear from the figure that withincreasing temperature, the spectral intensity ∼ ∼ > . Namely, the bond distancesand the mean square relative displacement (MSRD) ofthe absorber-backscatterer pair of atoms are obtained.The EXCURVE 9.275 code was used for the modelfits. The model fits are displayed by solid lines in Fig.2. As starting values for the fit, we have used the struc-tural parameters reported at room temperature for theparent compound . The present analysis is modelled bythree shells, namely Ir-O p and Ir-O a , and Ir-Sr, wherethe photoelectron phase shifts for each bond is takeninto account. In the model fit, the passive electrons re-duction factor S is set to 0.95. The number of neigh-boring atoms N i are 4 for Ir-O p , 2 for Ir-O a , and 8 forIr-Sr. The photoelectron energy zero ( E ) was fixed af-ter fit trials on different scans. Six parameters, namelythe bond distances and MSRDs of Ir-O p , Ir-O a , and Ir-Sr bonds are varied in the model fit. The R -range forthe model fits is 1.5-4.0 (∆ R = 2.5) while the k -rangeis 3.1-16.0 (∆ k = 12.9) with the number of independentparameters (2∆ R ∆ k / π ) being about 20. In the modelfit, an attempt was made to include two different Ir-O a bonds as suggested by a second harmonic light reflectionmeasurement , however, we did not find any evidence ofsuch bond distances in our studied system.Figure 3 shows temperature dependence of bondlengths of Ir-O p , Ir-O a , and Ir-Sr in K0.055, K0.04, par-ent, La samples, obtained by the EXAFS model fits. TheMSRDs of each bond are shown in Fig. 4. The dashedlines in Fig. 4 denote the fit result of MSRD by the cor-related Einstein-model ; σ = σ + σ ( T ) where σ de-notes static part and σ ( T ) stands for the dynamic part.The vertical dotted lines in Fig. 3 and 4 indicate T N estimated from magnetization measurments for all thesamples. We found that the local structural parametersdetermined in the present study for the parent compoundare consistent with those reported by neutron diffractionexperiments (see also supplemental information forthe comparison with the structural parameters reportedearlier). We have also found that within the experimen-tal uncertainties, neither local bond distance nor MSRDshow any evident response against the formation of mag-netic ordering in all the samples. The mean value ofIr-O p bond distance tend to decrease by K-substitutionand increase by La-substitution. On the contrary, themean value of Ir-O a bond distance tend to increase byK-substitution and decrease by La-substitution. Thesetendencies are consistent with the earlier XRD report onBa − x M x IrO (M = K, La) . Regarding the tempera-ture dependence of bond length, it is commonly observedin all the samples that the thermal expansion of Ir-O p bond seems to be smaller than that of Ir-O a bond, in-dicating the strong covalency between Ir and planar Oatom. The presence of strong covalency in Ir-O bondis also consistent with almost temperature-independentbehavior of MSRD in Fig. 4 and estimated Einstein tem-perature is more than 800 K. Interestingly, the strong co-valency and high Einstein temperature of Ir-O p bond isnot altered by the nature of carrier doping (electron andhole). σ of Ir-O p remained as small as ∼ forall the samples. Ir-O a bond seems to have slightly higher σ value than Ir-O p by ∼ with similarly highEinstein temperature, and the bond remained also unaf-fected by carrier doping although it should be mentionedthat the experimental uncertainty of Ir-O a is larger thanthat of Ir-O p due to the proximity of those two bondlengths. On the other hand, we have found notable in-crease of MSRD value of Ir-Sr bond in doped samples,that is mainly attributed to the increase of static part( σ ). The dynamical part ( σ ( T )) of Ir-Sr bond is muchless affected resulting in almost unchanged Einstein tem-peratures in doped samples ( ∼
240 K for all). Judgingfrom σ values, the degree of static disorder remainedthe same in two K-doped samples, although T N valuesand K amounts are different. There is a tendency thatthe increase in static disorder at K-doped samples arehigher than that at La-doped sample, which can be at-tributed to the larger difference of ionic radius betweenSr (1.31 ˚A) and substituent atoms, namely ionic ra-dius of K + is 1.55 ˚A while that of La is 1.216 ˚A in9-coodination .Let us attempt to understand possible implications ofthe present findings. Our current observation of negli-gible softening in Ir-O p bond with high Einstein tem-perature suggests that the high covalency in Ir-O maynot permit charge doping in the IrO sublattice to ob-tain mobile carriers, as it is discussed to happen in nick-elate heterostructures . Therefore the carriers dopedby the substitution in Sr-O layer would tend to local-ize, which may cause a nano-scale spatial phase separa-tion. In fact, there are scanning tunneling spectroscopy Sr IrO Ir-O p Ir-O a Ir-Sr 100 200 3001.952.002.052.103.303.353.40 B ond d i s t a n ce ( A ) Temperature (K) 100 200 300100 200 300 100 200 300
K 0.04 LaK 0.055 (a) (b) (c) (d)
FIG. 3. Temperature dependence of bond length around Iratom derived from model fit shown in Fig. 2. Vertical dottedlines denote T N for each sample.
100 200 300Temperature (K)100 200 300100 200 300100 200 300 M S R D ( A - ) a Ir-O p (a) (c) (d)(b) Sr IrO K 0.04 LaK 0.055
FIG. 4. Mean square relative displacement of Ir-O p , Ir-O a ,and Ir-Sr bond distance as a function of temperature. Dashedlines show the Einstein model fit for each bond. For Ir-O a ,typical magnitude of error is put only for 300 K data for bettervisualization of data, avoiding error bars to highly overlapeach other and mask other data. Vertical dotted lines denote T N for each sample. studies reporting a signature of phase separation betweenlarge-gap (Mott gap) state and small-gap state . Re-cent ARPES studies also report the coexistence of lowerHubbard band and in-gap band, which can be also rec-onciled by the possible phase separation . In case ofcuprates, the in-plane Cu-O bond tend to be softer , al-lowing the doped charges to be mobile in CuO plane.It should be noted that cuprates are strongly affectedby the Jahn-Teller distortion that can locally relax withdoping, while such a distortion of IrO octahedra is muchless in Sr IrO . We also note that in case of sister com-pound Sr Ir O , the system also shows phase separationat lightly doped regime but becomes metal when La isdoped more than 4 %, while Sr IrO does not in a simi-lar doping level. Such a difference can be caused by thedifference of the band width and the dimensionality ofthe parent material . Apart from such other factors, acontrol of covalency in in-plane Ir and O atoms may beimportant to induce superconductivity in Sr IrO sys-tem.It is worth recalling that the formation of excitation-gapped state has been observed in the electronic struc-ture of both hole- and electron-doped systems byARPES . The existence of symmetry-broken statehas been observed by second harmonic light reflection and neutron diffraction techniques in hole-dopedSr Ir − x Rh x O , where this state has been discussed inrelation with the excitation-gapped state . In addition,recent magnetic resonant x-ray scattering measurementon Sr − x La x IrO has suggested the presence of SDWstate . In the current EXAFS study of Ir-O and Ir-Sr lo-cal lattice response, we did not observe any significant in-fluence of the formation of such or any other ordered statein the temperature dependence within available dopingrange. This is in constrast to the cuprate case, where theformation of a charge-ordered state triggers a character-istic softening in the in-plane Cu-O bond as revealedby polarized EXAFS. Although no indication of such re-sponse of the local structure has been seen in the currentstudy with certain experimental uncertainty (enhancedby the proximity of Ir-O p and Ir-O a bond lengths), fur-ther detailed study of polarized EXAFS using single crys-tals as well as in wider doping range should be helpful toobtain bond-resolved information on the local structure. IV. CONCLUSIONS
In summary, doping- and temperature-dependence ofatomic displacements around Ir atom are studied by IrL EXAFS in Sr − x M x IrO (M = K, La). We have foundthat Ir atoms form strong covalent bond with O atomswith high Einstein-frequency, which does not get alteredby electron or hole doping. The configurational disor-der in Ir-O layer seems to remain unaffected by dopingwhile it is different for Ir-Sr. The former observation isin contrast to the cuprate case, where doped charge in-duces softening in in-plane lattice displacement, and thisdifference may be one of the intervening factors for theoccurance of superconductivity in Sr IrO system. ACKNOWLEDGMENTS
We thank ESRF staff for support in the EXAFS datacollection. K. T. and T. W. would like to acknowledgethe hospitality at the Sapienza University of Rome. Thisresearch was partially supported by the Program for Pro-moting the Enhancement of Research University fromMEXT, the Program for Advancing Strategic Interna-tional Networks to Accelerate the Circulation of TalentedResearchers from JSPS (R2705), and JSPS KAKENHI(Grants Nos. 2704, 25000003, 26247057, and 15H05886).This work is a part of the executive protocol of thegeneral agreement for cooperation between the SapienzaUniversity of Rome and Okayama University, Japan. ∗ [email protected] † Research Department Synchrotron Radiation and Nan-otechnology, Paul Scherrer Institut, CH-5232 Villigen PSI,Switzerland M. Imada, A. Fujimori, and Y. Tokura,
Rev. Mod. Phys. ,1988, , 1039. G. Jackeli and G. Khaliullin,
Phys. Rev. Lett. , 2009, ,017205. M. K. Crawford, M. A. Subramanian, R. L. Harlow, J. A.Fernandez-Baca, Z. R. Wang, and D. C. Johnston,
Phys.Rev. B , 1994, , 9198. B. J. Kim, H. Jin, S. J. Moon, J.-Y. Kim, B.-G. Park, C.S. Leem, J. Yu, T. W. Noh, C. Kim, S.-J. Oh, J.-H. Park,V. Durairaj, G. Cao, and E. Rotenberg,
Phys. Rev. Lett. ,2008, , 076402. B. J. Kim, H. Ohsumi, T. Komesu, S. Sakai, T. Morita, H.Takagi, and T. Arima,
Science , 2009, , 1329. I. M. Bhatti, R. Rawat, A. Banerjee, and A. K. Pramanik,
J. Phys.: Condens. Matter , 2014, , 016005. F. Wang and T. Senthil,
Phys. Rev. Lett. , 2011, ,136402. Y. K. Kim, N. H. Sung, J. D. Denlinger, and B. J .Kim,
Nat. Phys. , 2016, , 37. A. de la Torre, S. McKeown Walker, F. Y. Bruno, S. Ricc´o,Z. Wang, I. Gutierrez Lezama, G. Scheerer, G. Giriat, D.Jaccard, C. Berthod, T. K. Kim, M. Hoesch, E. C. Hunter, R. S. Perry, A. Tamai, and F. Baumberger,
Phys. Rev.Lett. , 2015, , 176402. Y. Cao, Q. Wang, J. A. Waugh, T. J. Reber, H. Li, X.Zhou, S. Parham, S.-R. Park, N. C. Plumb, E. Rotenberg,A. Bostwick, J. D. Denlinger, T. Qi, M. A. Hermele, G.Cao, and D. S. Dessau,
Nat. Commun. , 2016, , 11367. K. Terashima, M. Sunagawa, H. Fujiwara, T. Fukura, M.Fujii, K. Okada, K. Horigane, K. Kobayashi, R. Horie, J.Akimitsu, E. Golias, D. Marchenko, A. Varykhalov, N. L.Saini, T. Wakita, Y. Muraoka, and T. Yokoya,
Phys. Rev.B , 2017, , 041106(R). B. Keimer, S. A. Kivelson, M. R. Norman, S. Uchida, andJ. Zaanen,
Nature , 2015, , 179. A. Lanzara, P. V. Bogdanov, X. J. Zhou, S. A. Kellar, D.L. Feng, E. D. Lu, T. Yoshida, H. Eisaki, A. Fujimori, K.Kishio, J.-I. Shimoyama, T. Noda, S. Uchida, Z. Hussain,and Z.-X. Shen,
Nature , 2001, , 510. G.-H. Gweon, T. Sasagawa, S.Y. Zhou, J. Graf, H. Takagi,D.-H. Lee, and A. Lanzara,
Nature , 2004, , 187. W. Tabis, Y. Li, M. Le Tacon, L. Braicovich, A. Kreyssig,M. Minola, G. Dellea, M. J. Veit, M. Ramazanoglu, A. K.Goldman, T. Schmitt, G. Ghiringhelli, N. Barisic, C. J.Dorow, G. Yu, X. Zhao, B. Keimer, and M. Greven,
Nat.Commun. , 2014, , 5875. N. L. Saini, A. Lanzara, H. Oyanagi, H. Yamaguchi, K.Oka, T. Ito, and A. Bianconi,
Phys. Rev. B , 1997, , N. L. Saini, H. Oyanagi, T. Ito, V. Scagnoli, N. Filippi, S.Agrestini, G. Campi, K. Oka, and A. Bianconi,
Eur. Phys.J. B , 2003, , 76. H. Chu, L. Zhao, A. de la Torre, T. Hogan, S. D. Wilson,and D. Hsieh,
Nat. Mat. , 2017, , 200. L. Zhao, D. H. Torchinsky, H. Chu, V. Ivanov, R. Lifshitz,R. Flint, T. Zi, G. Cao, and D. Hsieh,
Nat. Phys. , 2016, , 32. J. Jeong, Y. Sidis, A. Louat, V. Broute, and P. Bourges,
Nat. Commun. , 2017, , 15119. X. Chen, J. L. Schmehr, Z. Islan, Z. Porter, E. Zoghlin, K.Finkelstein, J. P. C. Ruff, S. D. Wilson,
Nat. Commun. ,2018, , 103. K. Horigane, M. Fujii, H. Okabe, K. Kobayashi, R. Horie,H. Ishi, Y. F. Liao, Y. Kubozono, A. Koda, R. Kadono,and J. Akimitsu,
Phys. Rev. B , 2018, , 064425. G. R. Castro,
J. Synchrotron Rad. , 1998, , 657. B. Ranjbar, and B. J. Kennedy,
J. Solid State Chem. , 2015, , 178. G. Bunker,
Introduction to XAFS , Cambridge UniversityPress, 2010. S. J. Gurman,
J. Synchrotron. Rad. , 1995, , 56. D. H. Torchinsky, H. Chu, L. Zhao, N. B. Perkins, Y.Sizyuk, T. Qi, G. Cao, and D. Hsieh,
Phys. Rev. Lett. ,2015, , 096404. E. Sevillano, H. Meuth, and J. J. Rehr,
Phys. Rev. B , 1979, , 4908. Q. Huang, J. L. Soubeyroux, O. Chmaissem, I. Natali Sora,A. Santro , R. J. Cava, J. J. Krajewski, and W. F. PeckJr.,
J. Sold State Chem. , 1994, , 355. T. Shimura, Y. Inaguma, T. Nakamura, M. Itoh, and Y.Morii,
Phys. Rev. B , 1995, , 9143. F. Ye, X. Wang, C. Hoffman, J. Wang, S. Chi, M. Matsuda,B. C. Chakoumakos, J. A. Fernandez-Baca, and G. Cao,
Phys. Rev. B , 2015, , 201112(R). H. Okabe, M. Isobe, E. Takayama-Muromachi, N.Takeshita, and J. Akimitsu,
Phys. Rev. B , 2013, ,075137. R. D. Shannon,
Acta Cryst. , 1976, , 751. M. N. Grisolia, J. Varignon, G. Sanchez-Santolino, A.Arora, S. Valencia, M. Varela, R. Abrudan, E. Weschke, E.Schierle, J. E. Rault, J.-P. Rueff, A. Barth´el´emy, J. Santa-maria, and M. Bibes,
Nat. Phys. , 2016, , 484. X. Chen, T. Hogan, D. Walkup, W. Zhou, M. Pokharel,M. Yao, W. Tian, T. Z. Ward, Y. Zhao, D. Parshall, C.Opeil, J. W. Lynn, V. Madhavan, and S. D. Wilson,
Phys.Rev. B , 2015, , 075125. I. Battisti, K. M. Bastiaans, V. Fedoseev, A. de la Torre, N.Iliopoulos, A. Tamai, E. C. Hunter, R. S. Perry, J. Zaanen,F. Baumberger, and M. P. Allan,
Nat. Phys. , 2017, , 21. V. Brouet, J. Mansart, L. Perfetti, C. Piovera, I. Vobornik,P. LeF`evre, F. Bertran, S. C. Riggs, M. C. Shapiro, P.Giraldo-Gallo, and I. R. Fisher,
Phys. Rev. B , 2015, ,081117(R). T. Hogan, Z. Yamani, D. Walkup, X. Chen, R. Dally, T.Z. Ward, M. P. M. Dean, J. Hill, Z. Islam, V. Madhavan,and S. D. Wilson,
Phys. Rev. Lett , 2015, , 257203. A. Yamasaki, H. Fujiwara, S. Tachibana, D. Iwasaki, Y.Higashino, C. Yoshimi, K. Nakagawa, Y. Nakatani, K. Ya-magami, H. Aratani, O. Kirilmaz, M. Sing, R. Claessen, H.Watanabe, T. Shirakawa, S. Yunoki, A. Naitoh, K. Takase,J. Matsuno, H. Takagi, A. Sekiyama, and Y. Saitoh,
Phys.Rev. B , 2016, , 115103. Supplemental Information
I. SAMPLE PROPERTIES
Figure S1(a) show powder x-ray diffraction patterns of Sr − x M x IrO (M = La, K, x = 0.075 for La and 0.055for K), measured using a conventional x-ray spectrometer with a graphite monochromator (RINT-1100, Rigaku).The parent sample showed tiny impurity peak (2 θ ∼
18 deg) while no such intensity was observed in La and K0.055samples, indicating high phase purity of samples. Figs. S1(b) and (c) show the temperature dependence of theresistivity and the magnetic susceptibility of samples. The electrical resistivity was measured by a conventional dcfour-probe method. The magnitude of the resistivity was reduced by both type of doping but samples remainedinsulating. Magnetic susceptibility measurements were performed using a superconducting quantum interferencedevice magnetometer (Quantum Design MPMS-R2). Both of the N´eel temperature and the magnetic moment ofsamples were reduced by La or K substitution for Sr. -1 I n t e n s it y ( a r b . un it s ) θ (deg) (b) R e s i s ti v it y ( Ω c m ) (c) LaparentK 0.055 parentLaK 0.055 parentLaK 0.055K 0.04 S u s ce p ti b ilit y ( - e m u / g ) Temperature (K) Temperature (K)
FIG. S1. x-ray diffraction patterns (a) and temperature dependence of resistivity of Sr IrO , Sr . La . IrO , andSr . K . IrO samples. (c) Temperature dependence of the magnetic susceptibility of Sr IrO , Sr . La . IrO ,Sr . K . IrO , and Sr . K . IrO samples. II. COMPARISON OF STRUCTURAL PARAMETERS WITH THOSE OF EARLIER REPORTS
Figure S2 shows Ir-O p (a), Ir-O a (b), and Ir-Sr (c) bond distances of parent Sr IrO taken from literature including neutron diffraction, x-ray diffraction and EXAFS, as well as those from present study. It turned out thatin the parent compound, the local structural parameters deduced in the current study show a good correspondencewith the averaged structural parameters reported by neutron diffraction studies. FIG. S2. Comparison of Ir-O p (a), Ir-O a (b), and Ir-Sr (c) bond distances of parent Sr IrO between the present study andearlier reports . ∗ [email protected] † Research Department Synchrotron Radiation and Nanotechnology, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland M. K. Crawford, M. A. Subramanian, R. L. Harlow, J. A. Fernandez-Baca, Z. R. Wang, and D. C. Johnston,
Phys. Rev. B ,1994, , 9198. Q. Huang, J. L. Soubeyroux, O. Chmaissem, I. Natali Sora, A. Santro , R. J. Cava, J. J. Krajewski, and W. F. Peck Jr.,
J.Sold State Chem. , 1994, , 355. T. Shimura, Y. Inaguma, T. Nakamura, M. Itoh, and Y. Morii,
Phys. Rev. B , 1995, , 9143. F. Ye, S. Chi, B. C. Chakoumakos, J. A. Fernandez-Baca, T. Qi, and G. Cao,
Phys. Rev. B , 2013, , 140406(R). F. Ye, X. Wang, C. Hoffman, J. Wang, S. Chi, M. Matsuda, B. C. Chakoumakos, J. A. Fernandez-Baca, and G. Cao,
Phys.Rev. B , 2015, , 201112(R). M. V. Rama Rao, V. G. Sathe, D. Sornadurai, B. Panigrahi, and T. Shripathi,
J. Phys. Chem. Solids , 2000, , 1989. I. M. Bhatti, R. Rawat, A. Banerjee, and A. K. Pramanik,
J. Phys.: Condens. Matter , 2014, , 016005. B. Ranjbar, and B. J. Kennedy,
J. Solid State Chem. , 2015, , 178. H. T. Yu, S. L.Kiu, B. Li, H. Y. Wang, J. Cheng and Z. H. Wang,
Europhys. Lett. , 2017, , 27007. J. Cheng, C. M. Zhu, S. L. Liu, B. Li, H. Y. Wang, Y. Wang, and W. Xu,
Mater. Res. Bull. , 2017, , 1. J. Cheng, P. Dong, B. Li, S. L. Liu, X. Wang, Y. Wang, and X. Li,
J. Synchrotron. Rad. , 2018,25