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Engineering thermal conductance using a two-dimensional phononic crystal.

Zen N, Puurtinen TA, Isotalo TJ, Chaudhuri S, Maasilta IJ - Nat Commun (2014)

Bottom Line: Controlling thermal transport has become relevant in recent years.Traditionally, this control has been achieved by tuning the scattering of phonons by including various types of scattering centres in the material (nanoparticles, impurities, etc).We perform the experiments at low temperatures below 1 K, which not only leads to negligible bulk phonon scattering, but also increases the wavelength of the dominant thermal phonons by more than two orders of magnitude compared to room temperature.

View Article: PubMed Central - PubMed

Affiliation: 1] Nanoscience Center, Department of Physics, University of Jyväskylä, P. O. Box 35, FIN-40014 Jyväskylä, Finland [2].

ABSTRACT
Controlling thermal transport has become relevant in recent years. Traditionally, this control has been achieved by tuning the scattering of phonons by including various types of scattering centres in the material (nanoparticles, impurities, etc). Here we take another approach and demonstrate that one can also use coherent band structure effects to control phonon thermal conductance, with the help of periodically nanostructured phononic crystals. We perform the experiments at low temperatures below 1 K, which not only leads to negligible bulk phonon scattering, but also increases the wavelength of the dominant thermal phonons by more than two orders of magnitude compared to room temperature. Thus, phononic crystals with lattice constants ≥1 μm are shown to strongly reduce the thermal conduction. The observed effect is in quantitative agreement with the theoretical calculation presented, which accurately determined the ballistic thermal conductance in a phononic crystal device.

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Superconducting tunnel junction thermometer characteristics.(a) Measured subgap current–voltage characteristics of a typical superconductor-insulator-normal metal-insulator-superconductor (SINIS) thermometer (2RT=43 kΩ) at different bath temperatures in log-linear scale. Horizontal dashed lines correspond to bias currents 450 pA and 8 pA. (b) Measured voltage-bath temperature response of the SINIS thermometer in (a) with two different values of bias current, 8 pA (blue circles) and 450 pA (red circles) (same values as the lines in (a)). Solid lines were calculated using the single-particle tunneling theory, Equation 2. Bath temperature was measured with a calibrated RuO thermometer.
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f6: Superconducting tunnel junction thermometer characteristics.(a) Measured subgap current–voltage characteristics of a typical superconductor-insulator-normal metal-insulator-superconductor (SINIS) thermometer (2RT=43 kΩ) at different bath temperatures in log-linear scale. Horizontal dashed lines correspond to bias currents 450 pA and 8 pA. (b) Measured voltage-bath temperature response of the SINIS thermometer in (a) with two different values of bias current, 8 pA (blue circles) and 450 pA (red circles) (same values as the lines in (a)). Solid lines were calculated using the single-particle tunneling theory, Equation 2. Bath temperature was measured with a calibrated RuO thermometer.

Mentions: The second SINIS junction pair was used as a sensitive thermometer because of their highly non-linear and temperature-dependent current–voltage (I–V) characteristics at sub-Kelvin temperatures242643. In practice, the measurement is usually performed in a constant current bias mode by measuring the temperature-dependent voltage response. When current biased, the SINIS thermometer voltage is a sensitive function of temperature only, and this dependence is typically fully understood by the single-particle tunnelling theory242643 with all parameters (tunnelling resistance of the junctions RT, the superconducting gap Δ and the effective broadening of the superconducting DOS) determined self-consistently from the current–voltage curves of the junctions (Fig. 6a). In practice, we always performed a calibration measurement, where the measured SINIS voltage was compared with the bath temperature given by a calibrated RuO thermometer while the refrigerator temperature was varied, without the electrical heating of the heater junctions (Fig. 6b). This way, any possible non-equilibrium effects (where electron temperature of the devices differs from the lattice temperature) due to the junction bias and external heat loads are self-consistently corrected for. The upper limit for a SINIS thermometer is set by the critical temperature of the superconductor, which means that for Al structures it can operate up to ~1 K.


Engineering thermal conductance using a two-dimensional phononic crystal.

Zen N, Puurtinen TA, Isotalo TJ, Chaudhuri S, Maasilta IJ - Nat Commun (2014)

Superconducting tunnel junction thermometer characteristics.(a) Measured subgap current–voltage characteristics of a typical superconductor-insulator-normal metal-insulator-superconductor (SINIS) thermometer (2RT=43 kΩ) at different bath temperatures in log-linear scale. Horizontal dashed lines correspond to bias currents 450 pA and 8 pA. (b) Measured voltage-bath temperature response of the SINIS thermometer in (a) with two different values of bias current, 8 pA (blue circles) and 450 pA (red circles) (same values as the lines in (a)). Solid lines were calculated using the single-particle tunneling theory, Equation 2. Bath temperature was measured with a calibrated RuO thermometer.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3973070&req=5

f6: Superconducting tunnel junction thermometer characteristics.(a) Measured subgap current–voltage characteristics of a typical superconductor-insulator-normal metal-insulator-superconductor (SINIS) thermometer (2RT=43 kΩ) at different bath temperatures in log-linear scale. Horizontal dashed lines correspond to bias currents 450 pA and 8 pA. (b) Measured voltage-bath temperature response of the SINIS thermometer in (a) with two different values of bias current, 8 pA (blue circles) and 450 pA (red circles) (same values as the lines in (a)). Solid lines were calculated using the single-particle tunneling theory, Equation 2. Bath temperature was measured with a calibrated RuO thermometer.
Mentions: The second SINIS junction pair was used as a sensitive thermometer because of their highly non-linear and temperature-dependent current–voltage (I–V) characteristics at sub-Kelvin temperatures242643. In practice, the measurement is usually performed in a constant current bias mode by measuring the temperature-dependent voltage response. When current biased, the SINIS thermometer voltage is a sensitive function of temperature only, and this dependence is typically fully understood by the single-particle tunnelling theory242643 with all parameters (tunnelling resistance of the junctions RT, the superconducting gap Δ and the effective broadening of the superconducting DOS) determined self-consistently from the current–voltage curves of the junctions (Fig. 6a). In practice, we always performed a calibration measurement, where the measured SINIS voltage was compared with the bath temperature given by a calibrated RuO thermometer while the refrigerator temperature was varied, without the electrical heating of the heater junctions (Fig. 6b). This way, any possible non-equilibrium effects (where electron temperature of the devices differs from the lattice temperature) due to the junction bias and external heat loads are self-consistently corrected for. The upper limit for a SINIS thermometer is set by the critical temperature of the superconductor, which means that for Al structures it can operate up to ~1 K.

Bottom Line: Controlling thermal transport has become relevant in recent years.Traditionally, this control has been achieved by tuning the scattering of phonons by including various types of scattering centres in the material (nanoparticles, impurities, etc).We perform the experiments at low temperatures below 1 K, which not only leads to negligible bulk phonon scattering, but also increases the wavelength of the dominant thermal phonons by more than two orders of magnitude compared to room temperature.

View Article: PubMed Central - PubMed

Affiliation: 1] Nanoscience Center, Department of Physics, University of Jyväskylä, P. O. Box 35, FIN-40014 Jyväskylä, Finland [2].

ABSTRACT
Controlling thermal transport has become relevant in recent years. Traditionally, this control has been achieved by tuning the scattering of phonons by including various types of scattering centres in the material (nanoparticles, impurities, etc). Here we take another approach and demonstrate that one can also use coherent band structure effects to control phonon thermal conductance, with the help of periodically nanostructured phononic crystals. We perform the experiments at low temperatures below 1 K, which not only leads to negligible bulk phonon scattering, but also increases the wavelength of the dominant thermal phonons by more than two orders of magnitude compared to room temperature. Thus, phononic crystals with lattice constants ≥1 μm are shown to strongly reduce the thermal conduction. The observed effect is in quantitative agreement with the theoretical calculation presented, which accurately determined the ballistic thermal conductance in a phononic crystal device.

Show MeSH