Metallic magnetic calorimeters. Andreas Fleischmann Heidelberg University

Transcription

1 Metallic magnetic calorimeters Andreas Fleischmann Heidelberg University

2 metallic magnetic calorimeters paramagnetic sensor: Au:Er 300ppm, Ag:Er 300ppm M detector signal: T main differences to calorimeters with resistive thermometers no dissipation in the sensor no galvanic contact to the sensor

3 Magn. Susceptibility magnetic susceptibility of Au:Er E Er 3+, J = 15/2 spin-glas 15 K B paramagnetic range with spin-spin-interaction (RKKY) Temperature

4 Magnetization M [A/m] Specific heat C [10 4 J mol 1 K 1 ] signal size thermodynamical properties of interacting spins (RKKY) are well understood Au:Er 300 ppm Au:Er 300 ppm Inverse Temperature T 1 [K 1 ] Temperature T [mk] Signal size can be calculated with confidence Numerical optimization of detector design

5 readout of magnetic calorimeters T = 50 mk T = K room temperature paramagnetic sensor Detector Amplifier SQUID magnetometer two-stage SQUID setup with flux locked loop to linearize the first stage SQUID allows for: low noise large bandwidth / slewrate small power dissipation on detector SQUID chip (voltage bias)

6 sensor geometries for micro-fabrication

7 noise contributions fluctuations of energy between sub-systems C abs C spins (optimum for C abs = C spins ) flux noise of SQUID-magnetometer S F = 2 L, required: 100 magnetic Johnson noise - thermal currents in the metallic components - marginal in all present detectors sensor magnetic 1/f noise S F ~ N Er SQUID S F ~ 1/f, S m 1Hz m Er2 /Hz temperature independent (20mK 4K) LTD-13

8 maxs-20: 1 8 array for soft x-rays 1 8 x-ray absorbers 250μm 250 μm, 5 μm thick gold 98% 6 kev electroplated into photoresist mold mech/therm contact to sensor by stems to prevent loss of initially hot phonons Temperature sensors: sputtered Au: 166 Er 300ppm Meander shaped pickup coils 2.5 μm wide Nb lines, I c 100mA On-chip persistent current switch (AuPd) 250 mm Au:Er on Nb meander

9 signal rise not affected by stems between absorber and sensor rise time: mk, as expected for the spin-electron-relaxation from Korringa-constant of Er in Au

10 magnetic flux signal decay decay time adjusted by sputtered thermal link (Au) here: 3 30 mk nearly single exponential decay On-chip thermal bath time

11 maxs-20 operated at 20mK in dry dilution fridge 55 Mn DE FWHM = kev DE FWHM = kev

12 maxs-20 operated at 20mK in dry dilution fridge 55 Mn DE FWHM = kev DE FWHM = kev

13 Counts per 3 ev Counts per 3 ev maxs-20 exposed to x-rays and gammas of 241 Am 241 Am/ 237 Np Energy [kev] Nuclear transition Nuclear transition Nuclear transition Nuclear transition Energy [kev]

14 maxs-20: no saturation up to 60 kev 241 Am non-linearity: 60 kev as expected from thermodynamical properties smooth, quadratic dependence DE FWHM = 60 kev in reach! E/DE FWHM > 30,000!

15 Erbium in Silver: simpler pulse shape at T < 30mK Ag:Er vs. Au:Er: Larger RKKY interaction nuclear spin < 1 smaller response no nuclear el. quadrupole moment strongly reduced hyperfine splitting marginal nuclear heat capacity no first decay as in Au:Er at T < 30mK Au:Er T = 45 mk Au:Er T = 10 mk Ag:Er Au:Er T = 6 mk

16 maxs-20/30/200: 8 8 arrays for x/g-ray-spectroscopy for photons up to 20/30/200 kev with DE FWHM = 2/5/30 ev read out by 32 two-stage dc-squids 2/4/8 mm Dry dilution fridge (Bluefors, FI)

17 First maxs-30 recently yielded 8 8 absorbers for photons up to 30 kev each 0.5mm 0.5 mm 15 mm thick gold

18 Rayleigh-polarimeter for soft x-rays using the polarization dependence on the coherent x-ray scattering pioneered by the NASA-GSFC group

19 MOCCA: 4k-pixel molecule camera to study reaction cross sections of molecular ions in cold interstellar plasmas in the cryogenic storage ring CSR at MPI-K, HD Position and energy resolved detection of neutral molecular fragments after neutralizing with an electron in the e-cooler Heidelberg University, MPI-K Heidelberg, Columbia Astro Lab NY MOCCA: 45mm 45mm pixels resolution: DE FWHM 100 ev T < 10K operated at T = 20 mk 16 two-stage SQUIDs to read-out 64 rows 16 two-stage SQUIDs to read-out 64 columns

20 MOCCA s 2048 pickup coils Failure tolerant design Yield benefits from MLA-150 (Heidelberg Instruments) Thermal links between sensor and absorber Thermal link to the heat bath

21 MOCCA s 4096 absorbers Filling factor > 99.3% (2mm ion-milled gaps)

22 a spectrometry KRISS, IBS Korea Au:Er Gold foil absorber

23 ECHo aims for a direct neutrino mass determination Requires 1k to 1M detectors implanted with 163 Ho First 64-pixel chips with fully integrated micro-wave SQUID MUX (18 layer process)

24 Dedicated / Integrated dc-squids PTB-Berlin, UNM, Star-Cryoelectronics, Heidelberg Univ. Particularly important for MMCs with sub-ev resolution! (small inductances) e.g. SQUIDs with meander-shaped inductance and sensor from UNM / Star-Cryoelectronics

25 MMC light/heat detectors for scintillator-based 0n2b search KRISS, IBS Korea Heidelberg Univ., KRISS, IBS Korea, CEA Saclay patchable detectors used in integrated, highly segmented sensors 5 detector modules of AMoRE-pilot to improve timing and DE in AMoRE, LUMINEU... MMC

26 Summary metallic magnetic calorimeters combine in a unique way time resolution energy resolution linearity micro-fabrication works channel-count and complexity increase variety of applications is growing