High PDMR contrast in single NV centres and related photocurrent properties

Abstract

This paper aims to extend the understanding of the mechanism of photo-electrical detection of magnetic resonance (PDMR) in nitrogen-vacancy (NV) centres. This technique is particularly important for development of solid-state quantum computing platforms. In particular, we report on the new insight in the photocurrent (PC) generation and charge cycling in the single NV centre, which is related to PDMR contrast reaching 50\% and above. We develop a technique to locate PC related features. We find that electrons generated at the NV centre are stored in interface trap levels and establish that the interface states serve as an amplifier that can be driven by introducing a second laser into our confocal setup. We show that controlling these interface states allows one to significantly enhance the PDMR contrast. We develop a model that consistently explains observed amplification effects even without the application of a bias voltage.

Figures (8)

• Figure 1: The scheme for photocurrent (PC) mapping used in this work. The position of the laser focus alters between the scanned pixel and the NV centre for which the PC mapping is performed. The PC is recorded one second after the focus is moved to a pixel and one second after the focus moved to the NV centre. The focus is moved to the NV centre immediately after the PC from pixel is recorded. Then the focus is moved to the next pixel in some time ($\tau$) after the PC from the NV spot is recorded. Laser light is blocked by an acousto-optic modulator (AOM) during focus movement. $\tau$ is not a fixed time, rather it is a time until a certain PC threshold is reached, at which point the measurement conditions for the next pixel are considered to be reset, as discussed in the text. The PC threshold is chosen individually for each NV. Examples of the resulting maps as well as the standard PC map for comparison are demonstrated. We call the map of the PC from pixels - the ’Reset PC scan’, and the map of the PC from the NV spot - the ’PC reaction scan’, discussed in the text.
• Figure 2: (a) Energy level scheme of NV centre, showing photon absorption, photon generation ($I$), and electron generation ($G$). Only transitions relevant for the discussion are depicted. The green circles are photons, the blue circle is an electron. (b) PC and PL electron spin contrast for different laser powers measured on Sample M. PC contrast repeats the general trend of the PL contrast, while staying significantly higher. (c) PC as a function of the charge generation rate. The dependence is non-linear, which leads to the difference in PL and PC contrast. $20\%$ ODMR contrast translates to $20\%$ contrast in $G$, which, in turn, translates to $50\%$ PDMR contrast. In (b) such ratio between ODMR and PDMR contrast is observed at 2 mW laser power.
• Figure 3: (a) The Reset PC scan of the surface (xy-scan) around the electrodes of the Sample G. (b) The Reset PC scan of the surface (xy-scan) around the NV centre. No additional PC is detected with NV in focus compared to the PC in the vicinity. As a reference, the inset depicts the result of a standard PC scan around the NV centre. Multiple single NV centres are in the vicinity, which makes the map look irregular. (c) The Reset PC depth scan (yz-scan, where z is the coordinate perpendicular to the diamond surface) around a graphite electrode. The dashed lines here and in (a) mark the intersection of these two perpendicular scans. The PC is originating form a single point 50 μm below the surface (after correction for refraction). Note that due to the cone shape of the beam, single points appear as cone shapes on depth scans (see SI). (d) The PC as a function of time before and after illumination of a pixel in (a), (b) or (c). The PC decays to 0 pA after 30 seconds. The NV would need to be illuminated again to restore the PC from the pixel.
• Figure 4: (a) Beam shapes after optical objective and the corresponding graphite electrode illumination pattern. (b) Reset PC scans of the sample surface (see Methods) with respective beam shapes from (a). The scans are made under 0V bias. The electrodes on the surface are marked grey. The scans with the antisymmetric beam profile show that the electrode, which is illuminated stronger exhibits a stronger PC profile around it. (c) Reset PC scans with symmetric beam profile under bias voltage. The general pattern shape is preserved, while a PC offset is added in the direction of the voltage.
• Figure 5: (a) The PC reaction depth scan (yz-scan) around a graphite electrode. The PC drops significantly after illuminating the intersection of diamond, electrode and air, which results in the dark spot in that area of the scan. (b) The PC as a function of time before and after illumination of the dark spot in (a). The NV PC drops significantly after the illumination of the dark spot but slowly rises back once the NV is back in focus. (c) Current-voltage characteristic of a Source before and after illumination of NV centre. Laser power is 3mW. Bridge population is supposedly zero before NV illumination and non-zero after illumination.