Microkelvin investigations (µKI)
Different subsystems of matter may have very different temperatures at the same time, though they may be spatially inseparable. Fascinating examples of this are the assemblies of nuclear spins and conduction electrons in metals. Experiments on condensed matter well below 1 mK can be performed routinely in a carefully designed cryostat, combining a powerful dilution refrigerator and an adiabatic nuclear demagnetization stage.
Group leader
Dr. Juha Tuoriniemi
Research
Experiments on condensed matter well below 1 mK can be performed routinely in a carefully designed cryostat combining a powerful dilution refrigerator and an adiabatic nuclear demagnetization stage.
Systems still thermally active at such low temperatures include most nuclear spin ensembles, fermion fluids (pure and dilute He-3), and some conduction electron systems, which fail to develop superconductivity or magnetic ordering at higher temperatures.
µKI Group currently focus to two main lines of research: to the search of superfluidity of He-3 in dilute mixtures of the helium isotopes and to the study of helium crystals. These subjects were earlier studied by two separate groups: YKI and Interface, correspondingly.
The past achievements include the observations of spontaneous long range magnetic ordering of the nuclear spin systems in copper, silver, and lithium. Experiments at negative absolute temperatures have been performed in silver and rhodium. The lowest temperature ever achieved was recorded in 1999 - the spin temperature of nuclei in rhodium metal was reduced to about 0.000 000 000 1 K = 100 pK by a cascade nuclear demagnetization technique.
World record in low temperatures
The search of superfluidity of He-3 in dilute mixtures of the helium isotopes
We develop a new method for cooling helium mixtures by a so-called adiabatic melting technique. The micro-Kelvin capacity of our cryostat will be used to cool pure He-3 into the superfluid state prior to letting it mix with pure He-4. The isotope separation in the experimental chamber at ultra low temperatures will be achieved by the solidification of He-4 due to applied pressure, which, once released, will lead to melting of the He-4 crystal, mixing of the isotopes, and consequent dilution cooling. The cooling ratio by dilution of the thermally isolated helium mixture increases dramatically as the initial temperature of pure He-3 is decreased below its superfluid transition point. This way, temperatures far below 0.1 mK, which is the practical limit for cooling helium mixtures by conventional techniques, should become achievable.
The study of helium crystals
Helium crystals present a beautiful model system in which general properties of crystalline surfaces such as the equilibrium crystal shape, surface phase transitions (roughening) and elementary mechanisms of the crystal growth can be studied over a wide temperature range, in principle down to absolute zero. In addition, helium crystals reveal several exceptional phenomena like crystallization waves which are the melting-freezing waves on the superfluid-solid interface and which are due to quantum properties of liquid and solid helium at low temperatures.
In the current project the shape and growth dynamics of He-3 and He-4 crystals has been studied at ultra low temperatures. For imaging the crystals we used a unique low-temperature Fabry-Pérot interferometer, which is built inside the nuclear demagnetization cryostat and which allows simultaneous observations of the global shape of the crystals as well as fine details of the liquid-solid interface. In past several original results were obtained, as the discovery of a multitude of different types of facets (smooth flat faces) on He-3 crystals and the accurate measurements on the growth dynamics of He-3 crystals along the melting curve down to 0.0005 K. In future the effect of a magnetic field on the properties of the liquid-solid interface of He-3 will be investigated.
Eleven different types of facets observed on the surface of helium-3 crystals.
Facilities
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Stanford Research Systems Sr560 low-noise preamplifier (× 3)
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Stanford Research Systems 830 amplifier (× 1)
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Tenelec TC 243 amplifier (× 1)
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Ithaco 3961B two-phase lock-in amplifier (× 1)
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Agilent 4263B LRC-meter (× 1)
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Andeen-Hagerling 2500A capacitance loss bridge (× 2)
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Linear Research LR-700 resistance bridge (× 1)
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RV-Elektroniikka AVS-46 resistance bridge (× 1)
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RV-Elektroniikka AVS-47 resistance bridge (× 1)
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TEL-Atomic TEL-UCS30-1K multichannel analyzer (× 1)
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Leiden Cryogenics dilution refrigerator (× 1)
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Precision Cryogenic Systems PVS-633 helium dewar (× 1)
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Balzers HLT 160 leak detector (× 1)
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BGZ0800 helium leak detector (× 1)
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Alvetec 12 su-qa-700-1 acceleration sensor (× 1)
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RV-elektroniikka PLM-4 Pt-temperature sensor (× 2)
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Pfeiffer Vacuum MaxiGauge vacuum multigauge controller (× 1)
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Bronkhorst F-111C-HA-33-V mass flow meter for gases (× 1)
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HP 33120A function generator (× 1)
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Agilent Technologies function generator (× 2)
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Protherm PTF 16/38/250 tube furnace (× 1)
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Melles Griot 05-LPH-141 laser (× 1)
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Limab 90082-Ic5I HeNe laser (× 1)
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Applied Physics Systems DC SQUID magnetometer (× 1)
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Bartington MAG O1h magnetometer (× 1)
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Cryomagnetics superconducting magnet (× 1)
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Magnicon DAQ SQUID-sensor (× 1)
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Magnicon XXF-1-6/3 noise sensor (× 1)
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Kinetic Systems vibration damper (× 1)
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Agilent 54641A oscilloscope (× 1)
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Tektronix TDS 310 oscilloscope (× 1)
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HP 34401A multimeter (× 4)
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HP 3478A multimeter (× 1)
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Oxford IPS120-10 power supply (× 2)
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HP 6628a power supply (× 1)
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HP 3325b power supply (× 1)
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RV-Elektroniikka Tvl-10 power supply (× 2)
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Finn Metric BOP20-10m power supply (× 2)
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Tenelec TC 948 high voltage power supply (× 1)
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Alcatel ATP80 turbo molecular high vacuum pump (× 1)
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Alcatel ATP100 turbo molecular high vacuum pump (× 2)
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Alcatel Adixen 5081 turbo molecular high vacuum pump (× 1)
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Alcatel 2005 rotary vane vacuum pump (× 1)
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Alcatel 1015 rotary vane vacuum pump (× 1)
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Alcatel 2015 rotary vane vacuum pump (× 1)
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ALC 201541 centrifugal pump (× 1)
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Edwards EH-1200 blower roots vacuum booster pump (× 2)
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Edwards 18B4 vapour diffusion pump (× 1)
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Edwards E2M80 rotary vane pump (× 2)
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Leybold Z92 00010 gate valve (× 1)
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Varian SH-110 scroll pump (× 1)
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Cheos Star-1 Camera Controller Video filming equipment (× 1)
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Hamamatsu C7500-51CCD CCD camera (× 1)
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Photometrics Star 1 video camera head (× 1)
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Photometrics digital CCD video camera system (× 1)