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Heat conduction by photons through superconducting leadsPowerPoint Presentation

Heat conduction by photons through superconducting leads

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Heat conduction by photons through superconducting leads

W.Guichard

Université Joseph Fourier and Institut Neel, Grenoble, France

M. Meschke, and J.P. Pekola

Low Temperature Laboratory, Helsinki University of Technology, Espoo, Finland

Thermal conductance

T2

T1

Heat flow

Thermal conductance

Heat flow (T1 > T2)

What conducts heat in a solid ?

Electrons (important for metals)

Phonons (lattice vibrations)

Q

T

T +T

Quantum of thermal conductance

and what about photons ?

Measurement of quantized thermal conductance

Quantized electronic thermal conductance

2DEG in a GaAs-AlGaAs heterostructure

Molenkamp et al. Phys. Rev. Lett 68 (1992)

Quantized phonon thermal conductance

Silicon nitride membrane

K. Schwab et al. , Nature 404 (2000)

Energy relaxation in a submicron metal island

Pex

In thermal equilibrium:

Electron-electron collissions

Electron-phonon collisions

Pep

M.Meschke et al.

Energy relaxation in a submicron metal island

Pex

Pe

In thermal equilibrium:

Electron-electron collisions

Electron-phonon collisions

Pep

+Electron-photon „radiative“ relaxation ?

M.Meschke et al.

Heat transported between two resistors

Ge= ?

Voltage noise emitted by resistor Ri:

1D Black body radiation

R1,T1

R2,T2

Net heat flow from hot to cold resistor:

Quantum of thermal

Conductance:

Schmidt et al.,Phys. Rev. Lett., 93 (2004)

Typical experimental set-up

Island size:

6.6 mm x 0.8 mm x 20 nm

SQUID junction size:

3 mm x 0.1 mm

SINIS junction size:

3 mm x 0.1 mm

Electrical circuit

Ib

Iheat

V

Actual experimental configuration: tunable impedance between the resistors

Electrical Model I

L0

L0

L0

Transmission line:

C0

C0

C0

Here:

R2

R1

L0

L0

L0

C0

C0

C0

L~30 μm

Tunable inductance:

R2

R1

SINIS thermometer

Probes electron temperature of N island

(and not of S!) in the case of T/Tc<0.4

Low leakage of junctions

Measured variation of island temperature:variation of bath temperature

Flux Φ0

Ic=20nA

CSQUID=15fF

R1=R2=200

P1=1fW

P2=0

Measured variation of island temperature:amplitude of modulation

Conclusion

- -First observation of the crossover from phonon relaxation to radiative photon relaxation at temperatures of about 100 mK
- Thermal and electrical model explain quite well the measured data
- Implications on:
- performance of bolometers (sensitivity): coupling to the heat bath
- removing excessive heat from devices at milli-kelvin range

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