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Near-field photonic cooling through control of the chemical potential of photons


Photonic cooling of matter has enabled both access to unexplored states of matter, such as Bose–Einstein condensates, and novel approaches to solid-state refrigeration1,2,3. Critical to these photonic cooling approaches is the use of low-entropy coherent radiation from lasers, which makes the cooling process thermodynamically feasible4,5,6. Recent theoretical work7,8,9 has suggested that photonic solid-state cooling may be accomplished by tuning the chemical potential of photons without using coherent laser radiation, but such cooling has not been experimentally realized. Here we report an experimental demonstration of photonic cooling without laser light using a custom-fabricated nanocalorimetric device and a photodiode. We show that when they are in each other’s near-field—that is, when the size of the vacuum gap between the planar surfaces of the calorimetric device and a reverse-biased photodiode is reduced to tens of nanometres—solid-state cooling of the calorimetric device can be accomplished via a combination of photon tunnelling, which enhances the transport of photons across nanoscale gaps, and suppression of photon emission from the photodiode due to a change in the chemical potential of the photons under an applied reverse bias. This demonstration of active nanophotonic cooling—without the use of coherent laser radiation—lays the experimental foundation for systematic exploration of nanoscale photonics and optoelectronics for solid-state refrigeration and on-chip device cooling.

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Fig. 1: Principle and experimental set-up.
Fig. 2: Detection of contact and quantification of cooling.
Fig. 3: Measured cooling power, radiative heat conductance and negative luminescence, and their comparison to theory.
Fig. 4: Modelling of spectral and modal properties, and predicted cooling power for a photodiode without cladding.

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Data availability

The data that support the findings of this study are available from the corresponding authors on reasonable request.


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E.M. and P.R. acknowledge support from DOE-BES award no. DE-SC0004871 (Scanning Probe Development and Analysis) and from the Army Research Office award no. FO42860 (Instrumentation and Nanopositioning Tools). We acknowledge the Lurie Nanofabrication Facility for facilitating the fabrication of devices.

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Nature thanks P. Bharadwaj, Y. De Wilde and J. Saenz for their contribution to the peer review of this work.

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Authors and Affiliations



E.M. and P.R. conceived the work. L.Z. and A.F. performed the experiments. L.Z. performed the calculations and polished the photodiodes. D.T. and R.M. fabricated the calorimeter devices. The manuscript was written by L.Z., E.M. and P.R. with comments and inputs from all authors.

Corresponding authors

Correspondence to Edgar Meyhofer or Pramod Reddy.

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The authors declare no competing interests.

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Extended data figures and tables

Extended Data Fig. 1 Fabrication of the calorimeter.

a, Step 1: a double-bonded silicon-on-insulator wafer from which the calorimeter is fabricated. Step 2: doping at the surface via phosphorus diffusion. Step 3: removing the phosphosilicate glass (PSG) layer that is formed during doping using a buffered hydrofluoric acid solution. Step 4: RIE to form a mesa feature. Step 5: patterning of the platinum serpentine thermometer. Step 6: RIE to form the footprint of the suspended device. Step 7: etching the silicon handle wafer using deep RIE to suspend the device. b, A representative scanning electron microscope image of a fabricated calorimeter device.

Extended Data Fig. 2 Characterization of the frequency response and the thermal conductance of the calorimeter, and the surface roughness for the calorimeter mesa and the photodiode.

a, A schematic of the measurement approach employed for obtaining the data shown in b and c. b, Frequency response of calorimeter, showing the normalized temperature increase of the calorimeter as a function of the frequency of heating. c, Measured relation between the power input into the suspended region of the calorimeter and the temperature increase. The black line represents a linear fit to the experimental data. d, AFM image of the calorimeter mesa, showing particles for which the largest height is around 55 nm. e, AFM image of the photodiode after polishing and cleaning, featuring a peak-to-peak roughness of around 25 nm.

Extended Data Fig. 3 Averaging scheme for measuring the cooling power.

a, Schematic depiction of the voltage bias applied to the diode. The diode is periodically biased for a duration of 4 s at a periodicity of TP = 8 s. b, Schematic depiction of the lock-in voltage output, Vf, (measured using an SR830 lock-in amplifier, Stanford Research Systems) across the platinum serpentine resistor of the calorimeter in response to a high-frequency (f = 2,534 Hz) sinusoidal current of amplitude If.

Extended Data Fig. 4 Schematic for measuring the radiative conductance GNFRHT.

a, Schematic of the set-up for measuring radiative conductance. The emitting area of the photodiode is located below the n-InAs layer. b, Effective thermal resistance network illustrating the major heat transfer pathways. The calorimeter has a power input (Qcal) due to a current supplied to the platinum resistor. The calorimeter has two major heat dissipation pathways, including heat conduction through the beams with thermal conductance Gbeams, and radiative heat exchange with the diode via a radiative conductance GNFRHT. c, d, Simultaneously recorded displacement and calorimeter temperature change (∆Tcal) during a GNFRHT measurement.

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This file contains Supplementary Text and Data, Supplementary Figures 1-12 and Supplementary References.

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Zhu, L., Fiorino, A., Thompson, D. et al. Near-field photonic cooling through control of the chemical potential of photons. Nature 566, 239–244 (2019).

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