Radio Frequency Tunable Oscillator Device Based on a ${\mathrm{SmB}}_{6}$ Microcrystal

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Radio Frequency Tunable Oscillator Device Based on a ${SmB}_{6}$ Microcrystal

Alex Stern, Dmitry K. Efimkin, Victor Galitski, Zachary Fisk, and Jing Xia

Phys. Rev. Lett. 116, 166603 – Published 20 April 2016

Abstract

Radio frequency tunable oscillators are vital electronic components for signal generation, characterization, and processing. They are often constructed with a resonant circuit and a “negative” resistor, such as a Gunn diode, involving complex structure and large footprints. Here we report that a piece of ${SmB}_{6}$ , $100 μ m$ in size, works as a current-controlled oscillator in the 30 MHz frequency range. ${SmB}_{6}$ is a strongly correlated Kondo insulator that was recently found to have a robust surface state likely to be protected by the topology of its electronics structure. We exploit its nonlinear dynamics, and demonstrate large ac voltage outputs with frequencies from 20 Hz to 30 MHz by adjusting a small dc bias current. The behaviors of these oscillators agree well with a theoretical model describing the thermal and electronic dynamics of coupled surface and bulk states. With reduced crystal size we anticipate the device to work at higher frequencies, even in the THz regime. This type of oscillator might be realized in other materials with a metallic surface and a semiconducting bulk.

Received 12 January 2016

DOI:https://doi.org/10.1103/PhysRevLett.116.166603

Physics Subject Headings (PhySH)

Topological insulators

Coupled oscillators Diodes

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Alex Stern¹, Dmitry K. Efimkin², Victor Galitski², Zachary Fisk¹, and Jing Xia¹

¹Department of Physics and Astronomy, University of California, Irvine, California 92697, USA
²Joint Quantum Institute and Condensed Matter Theory Center, University of Maryland, College Park, Maryland 20742-4111, USA

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Vol. 116, Iss. 16 — 22 April 2016

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Figure 1
A 32 MHz ${SmB}_{6}$ oscillator. (a) Representative oscillation outputs at frequencies of 29.6, 30.6, and 32.2 MHz in ascending order, with dc bias currents of 0.47, 1.56, and 2.42 mA. Inset shows a false-color electron microscope image of the device with platinum wires colored in yellow and ${SmB}_{6}$ crystal in white. The oscillator circuit consists of dc current flowing across the crystal and a capacitor (either an external capacitor or from the self-capacitance in ${SmB}_{6}$ ) in parallel. An oscilloscope is then used to measure the output waveform. (b) FFT of the data in (a).
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Figure 2
Scaling of frequency with crystal size. (a) Center frequency of oscillator devices plotted against the crystal surface area. Insets are images of 29 MHz and 250 Hz devices. The colors of the markers on this graph match the colors in (b)–(e). (b)–(e) Output waveforms of the 25 Hz, 250 Hz, 1 kHz, and 29 MHz devices, respectively. The output of the 32 MHz device is illustrated in Fig. 1. (f) The range of external capacitance values we used for each device. No external capacitors are needed for the two highest frequency (smallest) devices.
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Figure 3
Modeling the oscillation. (a) The regime diagram of the phenomenological model. The limit cycle regime supports nonlinear oscillations of temperature and currents. The red saltire symbol denotes the parameter set ( $i_{0} = 1.0$ , $Ω = 0.46$ ), for which time dependencies of the surface current and temperature, (c) and the corresponding vector flow plot (b) for the model, described by the system (1), are presented. (d) Four phases of oscillations in order, which are described in the main text: Joule heating, discharging capacitor, cooling, and charging capacitor. The arrows represent the flow of current.
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Figure 4
Comparing the model with experimental results. Red curves are predictions from the model. Blue dots are measured valued from sample 5. The raw experimental data are shown in the Supplemental Material, Fig. S3. (a) and (b) Amplitude, $Δ V$ and frequency $ν$ of the voltage oscillations on capacitance $C$ for fixed dc bias current $I_{0}$ through the sample. Blue dotted points correspond to $I_{0}^{\exp} = 0.55 mA$ , while red lines correspond to $I_{0}^{fit} = 0.76 mA$ . (c) and (d) Amplitude $Δ V$ and frequency $ν$ of the voltage oscillations on dc bias current $I_{0}$ , through the sample for fixed capacitance $C$ . The blue dots correspond to $C^{\exp} = 2.2 μ F$ , while red lines correspond $C^{fit} = 1.5 μ F$ .
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Physical Review Letters

Radio Frequency Tunable Oscillator Device Based on a SmB6 Microcrystal

Alex Stern, Dmitry K. Efimkin, Victor Galitski, Zachary Fisk, and Jing Xia

Phys. Rev. Lett. 116, 166603 – Published 20 April 2016

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Radio Frequency Tunable Oscillator Device Based on a ${SmB}_{6}$ Microcrystal