Electrically tunable transport in the antiferromagnetic Mott insulator ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$

Electrically tunable transport in the antiferromagnetic Mott insulator ${Sr}_{2} {IrO}_{4}$

C. Wang, H. Seinige, G. Cao, J.-S. Zhou, J. B. Goodenough, and M. Tsoi

Phys. Rev. B 92, 115136 – Published 18 September 2015

Abstract

Electronic transport properties of the antiferromagnetic Mott insulator $S r_{2} Ir O_{4}$ have been investigated under extremely high electric biases. Using nanoscale contacts, we apply electric fields up to a few MV/m to a single crystal of $S r_{2} Ir O_{4}$ and observe a continuous reduction in the material's resistivity with increasing bias, characterized by a reduction in the transport activation energy by as much as $16 %$ . Temperature-dependent resistivity measurements provide a means to unambiguously retrieve the bias dependence of the activation energy from the Arrhenius plots at different biases. We further demonstrate the feasibility of reversible resistive switching induced by the electric bias, which is of interest for the emerging field of antiferromagnetic spintronics. Our findings demonstrate the potential of electrical means for tuning electronic properties in $5 d$ transition-metal oxides and suggest a promising path towards development of next-generation functional devices.

Received 10 July 2015

DOI:https://doi.org/10.1103/PhysRevB.92.115136

Authors & Affiliations

C. Wang^1,2, H. Seinige^1,2, G. Cao³, J.-S. Zhou², J. B. Goodenough², and M. Tsoi^1,2

¹Physics Department, University of Texas at Austin, Austin, Texas 78712, USA
²Texas Material Institute, University of Texas at Austin, Austin, Texas 78712, USA
³Center for Advanced Materials, Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506, USA

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Vol. 92, Iss. 11 — 15 September 2015

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Figure 1
Current-voltage characteristics of SIO point contacts measured at $T = 77 K$ . (a) Voltage $(V)$ vs current $(I)$ characteristics of 11 point contacts with zero-bias resistances ranging from 13 to $27 k Ω$ are shown in different colors. The inset shows schematically a point contact between a sharpened Cu tip (top light gray) and the crystal (dark gray) on a Cu back electrode (bottom light gray). (b) Resistance $(R = V / I)$ vs current $(I)$ plots for the same 11 point contacts. (c), (d) Analysis of $R$ vs $I$ (c) and $V$ (d); measured characteristics (black) are shown together with fits by different models: Joule heating (dashed cyan), Poole-Frenkel (dashed green), space charge limited currents (dashed dark yellow), tunneling barrier (dashed pink), and field-effect model (red).
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Figure 2
The crystal structure of SIO and field-induced distortions. (a) Each $Ir O_{6}$ octahedron rotates $11.8^{\circ}$ about the $c$ axis. The Ir, Sr, and O atoms are shown in red, blue, and green, respectively. (b) Zoom into four $Ir O_{6}$ octahedrons. (c) The four $Ir O_{6}$ octahedrons with oxygen ions displaced along the $c$ axis. (d) Schematic illustration of the distortion of the Ir-O-Ir bonding due to an oxygen ion (green) displacement. Undistorted bonds are shown in gray.
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Figure 3
Effects of electric field on the resistance of SIO point contacts. (a) Normalized contact resistance $[R (E) - R (0)] / R (0)$ as a function of electric field $E$ . Different colors represent data from different contacts with resistances ranging from 11 to $24 k Ω$ . Dashed gray lines are the boundary $(10 %)$ fits of the field-effect model.
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Figure 4
Temperature dependence of the point-contact $R (I)$ characteristics. (a) Measured $R (I)$ curves (black) at temperatures from 83 to 166 K together with the field-effect model fits (red). The temperature dependencies of $A, Δ_{0}$ , and $B$ fitting parameters are shown in panels (b)–(d), respectively.
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Figure 5
Characterization of the activation energy Δ from temperature-dependent resistivity measurements. (a) Experimental data of $R$ vs $T$ (open triangles) with an exponential fit (black curve). The inset shows the same data as $ln (R)$ vs $1 / T$ (straight lines are guides for eye). (b) Temperature dependence of $Δ$ as extracted from the slope of $ln (R)$ vs $1 / T$ in (a). (c) The bias dependence of $Δ$ at $T = 167 K$ extracted from the $ln (R)$ vs $1 / T$ dependencies at different bias currents (not shown).
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Figure 6
Resistive switching in point-contact $R (I)$ characteristics. (a) A typical $R (I)$ curve with up- (gray) and down- (black) sweeps of $I$ . The switching current is indicated by $I_{c}$ and arrow. (b) The magnitude of critical current $I_{c}$ vs applied magnetic field is shown with open circles (solid dots) for up- (down-) sweep of magnetic field. (c) Variations in the zero-bias resistance (magnetoresistance ratio) as a function of the applied magnetic field. All measurements were done at $T = 77 K$ . (d) Magnitude of the critical (switching) field vs contact size. Open (solid) symbols are for switching events at positive (negative) biases.
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Physical Review B

covering condensed matter and materials physics

Electrically tunable transport in the antiferromagnetic Mott insulator ${Sr}_{2} {IrO}_{4}$

C. Wang, H. Seinige, G. Cao, J.-S. Zhou, J. B. Goodenough, and M. Tsoi

Phys. Rev. B 92, 115136 – Published 18 September 2015

Abstract

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Physical Review B

covering condensed matter and materials physics

Electrically tunable transport in the antiferromagnetic Mott insulator Sr2IrO4

C. Wang, H. Seinige, G. Cao, J.-S. Zhou, J. B. Goodenough, and M. Tsoi

Phys. Rev. B 92, 115136 – Published 18 September 2015

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Electrically tunable transport in the antiferromagnetic Mott insulator ${Sr}_{2} {IrO}_{4}$