Influence of electron doping on the ground state of(Sr1−xLax)2IrO4

Abstract

The evolution of the electronic properties of electron-doped (Sr1−xLax)2IrO4 is experimentally explored as the doping limit of La is approached. As electrons are introduced, the electronic ground state transitions from a spin-orbit Mott phase into an electronically phase separated state, where long-range magnetic order vanishes beyond x = 0.02 and charge transport remains percolative up to the limit of La substitution (x ≈ 0.06). In particular, the electronic ground state remains inhomogeneous even beyond the collapse of the parent state's long-range antiferromagnetic order, while persistent short-range magnetism survives up to the highest La-substitution levels. Furthermore, as electrons are doped into Sr2IrO4, we observe the appearance of a low temperature magnetic glass-like state intermediate to the complete suppression of antiferromagnetic order. Universalities and differences in the electron-doped phase diagrams of single layer and bilayer Ruddlesden-Popper strontium iridates are discussed.

Sign reversal of magnetoresistance in a perovskite nickelate by electron doping

“…At higher temperatures (T > 10 K), larger thermal energy suppresses the positive cusp, resulting only in negative MR that is quadratic in field. Signatures of such a low temperature spin glass like state have been seen in MR and magnetization measurements in other correlated oxides such as iridates 54 . The field scale of ∼ 3.5 T obtained in our experiments is consistent with the hopping energy in VRH regime which is ∼ 0.5 meV, thus signifying the role of spin correlations that govern the low temperature transport.…”

“…Though it is well known that rare earth nickelates exhibit antiferromagnetic order at low temperatures, the precise magnetic structure is complex with proposals of collinear and non-collinear magnetic structures from neutron 52 and soft x-ray scattering studies 18 and canted antiferromagnetic state from magnetic susceptibility measurements 53 . Our measurements at low temperatures (T 5 K) yield a positive cusp in the MR signifying the presence of interacting spins that are frozen as seen in systems exhibiting spin glass phase 54,55 . An application of finite field (∼ 3.5 T) destroys the frozen spin state leading to enhancement in spin scattering resulting in negative MR. At such large fields, the spin are polarized enhancing spin fluctuations and hopping rate of carriers resulting in a decrease in resistance with increase in field.…”

Crystal growth and intrinsic magnetic behaviour of Sr2IrO4

“…The growth sequence of Sr214#2 and Sr214#3 are modifications of Sr214#1 and Sr214#4, respectively. Note that our growth is performed in much lower temperature ranges than used in most of the earlier works 23,28,30 . In Fig.…”

“…La-doped Sr 2 IrO 4 single crystals have only become available in the last couple of years [21][22][23] , but angle-resolved photoemission studies on them 21,22 do not fully reproduce the observations made via the in situ doping method 12,16 . While it is unclear at the moment what leads to such differences between the two doping methods, we note that a well-defined quasiparticle peak is absent for any doping level in La-doped samples, indicating suppressed coherent motion of doped electrons presumably due to disorder created by chemical doping.…”

“…Moreover, we note that previous studies on the parent Sr 2 IrO 4 and its sister compounds have shown significant variations in the magnetic properties even without doping, likely reflecting different defect concentrations 2,4,18,[22][23][24][25][26][27][28][29] . For example, the sizable c-axis component of the uniform magnetic susceptibility is not understood and seems incompatible with the known magnetic structure of Sr 2 IrO 4 .…”