Radio Frequency Tunable Oscillator Device Based on aSmB6Microcrystal

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 μm 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.

Direct observation of surface-state thermal oscillations in SmB6 oscillators

“…Due to the simplicity of the proposed model, it is not surprising to observe some deviation in the waveform shapes between the model and experimental data. The theoretical model and its regime diagram have been discussed in details in our previous paper [15]. Here we briefly outline fitting of the current and temperature time dependencies, presented in Fig.…”

“…It is proposed to form a strongly interacting version of a Topological Insulator [9][10][11][12][13], with a Kondo Gap in the bulk and a gapless states on the surface that seems to be protected by time-reversal symmetry [7]. The lack of impurity conduction in the bulk has allowed the realization of a radio frequency oscillator device [15] based on SmB 6 micro-crystals, where a small DC current drives the SmB 6 crystal into an oscillating state and generates large oscillating voltages.…”

“…The lack of impurity conduction in the bulk has allowed the realization of a radio frequency oscillator device [15] based on SmB 6 micro-crystals, where a small DC current drives the SmB 6 crystal into an oscillating state and generates large oscillating voltages. This behavior was explained by a theoretical model [15], which utilized a coupling between two conduction channels, namely, metallic surface conduction and thermally activated bulk conduction which result in significant differences in sample heating under an applied current. While this Letter will focus on the verification of this model in a proposed topological Kondo insulator, a general seiconducting sample with metallic channels with electrical and thermal coupling can be described equally well.…”

“…Since the design of higher frequency oscillator up to THz [15] relies on the validity of above model, it is vitally important to verify experimentally the other key component of the model, the oscillating surface temperature. The difficulty in observing these thermal oscillations is multifaceted.…”

“…The crystal of this size was chosen due to the desire to measure low frequency thermal oscillations, which have been shown to arise only in large single crystals. [15] Single crystals of SmB 6 were grown using an aluminum flux method described in previous work. [5] Thermometry was performed via four probe resistance measurements of a RuO 2 thermometer mounted to a single surface of the studied crystal via thermally conducting varnish separated by a thin electrically insulating layer.The Vishay RuO 2 thermometer, as depicted in Fig.1b is primarily constructed from an alumina substrate with electrodes capping two ends that allow for electrical contact with the RuO 2 film which is protected by a thin epoxy layer.…”