Anomalous optical response in TiN LEKIDs

Transcription

1 Anomalous optical response in TiN LEKIDs SRON Juan Bueno, J. Baselmans TUD/Kavli P. J. Coumou, G. Zheng, P. J. de Visser, T. Klapwijk Cardiff S. Doyle, P. Ade CEA/INAC - E. F. C. Driessen

2 Motivation Promising material for LEKIDs Figure of merit M M = aq it R s N 0 V 2

3 Non-homogeneity of TiN Tunnel spectroscopy measurements showed the TiN is a disordered superconductor and has an inhomogeneous energy gap (Sacepe et al., PRL 101, (2008)) 3

4 How to experimentally probe this Use a TiN film with relatively low disorder homogeneous But still with a high resistivity/kinetic inductance 4

5 Disordered TiN (I) Model with a disorder-dependent pair breaking parameter (Coumou et al., PRB 88, (R) (2013)) Disorder broadens the density of states (Driessen et al., PRL 109, (2012)) Increasing disorder 5

6 Disordered TiN (II) Tunnel spectroscopy measurements 6

7 Disordered TiN (II) Tunnel spectroscopy measurements Small disorder No local variations 7

8 Disordered TiN (II) Tunnel spectroscopy measurements Small disorder No local variations Large disorder Local variations 8

9 Experimental setup (I) Box in a box setup Band-pass filter centered at 350GHz 9

10 Experimental setup (II) Thickness = 45nm T c = 3.1K R s = 41.5 W L s = 16.5 ph LEKID design Linewidth = 24mm Line separation = 60mm Area = 1200x986mm F res = 3.4GHz Q c = 7x

11 Absorption planar absorber Cryogenic FTS down to 1K R s = 50W R s = 60W R s = 45W 11

12 TiN responsivity to 350GHz radiation Increasing temperature Responsivity increases with bath temperature 12

13 TiN NEP for 350GHz radiation NEP at 100Hz at 250mK NEP decreases as loading power increases Opposite observed in Al and NbTiN/Al KIDs, and predicted by BCS theory TiN - 13

14 TiN NEP for 350GHz radiation NEP at 100Hz at 250mK NEP decreases as loading power increases Opposite observed in Al and NbTiN/Al KIDs, and predicted by BCS theory NbTiN/Al - APL 103, (2013) TiN - 14

15 TiN NEP for 350GHz radiation NEP at 100Hz at 250mK NEP decreases as loading power increases Opposite observed in Al and NbTiN/Al KIDs, and predicted by BCS theory NbTiN/Al - APL 103, (2013) TiN - TiN/Ti/TiN APL 106, (2015) 15

16 Landscape conjecture D = 475meV dd = 0.1D = 47.5meV 16

17 Landscape conjecture D = 475meV dd = 0.1D = 47.5meV k B T = 9meV (at 100mK) still see the effect of the non-homogeneity 17

18 Landscape conjecture D = 475meV dd = 0.1D = 47.5meV k B T = 9meV (at 100mK) still see the effect of the non-homogeneity k B T = 22meV (at 250mK) smearing of the inhomogeneity 18

19 19

20 Absorption planar absorber Cryogenic FTS down to 1K Resistivity measurement: R s = 41.5W Fitted data Best fit: R s = 50W Worst fit high R s : R s = 60W Worst fit low R s : R s = 45W 20

21 350 GHz TiN response Phase response Non-monotonic Important chip heating Dominated by TLS at low temp Amplitude response Monotonic response Response increases with bath temperature Contribution of s 2 at high temp Response(s 2 ) >> Response(TLS) not reached Phase Amplitude 21

22 TiN responsivity Phase responsivity Not to be trusted due to important chip heating TLS contribution needs to be subtracted Amplitude responsivity Monotonic Responsivity increases with bath temperature Phase not to be trusted Amplitude 22

23 TiN noise spectrum Noise taken at 250mK to avoid TLS issue Noise independent of loading power Cross-correlation analysis done and no sign of photon noise found Roll-off due to Q factor Phase Amplitude 23

24 TiN NEP NEP at 100Hz at 250mK NEP decreases as loading power increases, opposite observed in Al and NbTiN/Al KIDs, and predicted by BCS theory Dark NEP way off optical NEP 24

25 TiN vs NbTiN/Al NEP at 100Hz at 250mK NEP decreases as loading power increases, opposite observed in Al and NbTiN/Al KIDs, and predicted by BCS theory Dark NEP way off optical NEP TiN - NbTiN/Al - APL 103, (2013) 25

26 TiN vs TiN/Ti/TiN NEP at 100Hz at 250mK NEP decreases as loading power increases, opposite observed in Al and NbTiN/Al KIDs, and predicted by BCS theory Dark NEP way off optical NEP TiN - TiN/Ti/TiN APL 106, (2015) 26

27 Disordered dependent pair-breaking parameter model Thickness = 45nm T c = 3.1K R s = 41.5 W L s = 16.5 ph D 0 = 475 mev a/d 0 =

28 Landscape conjecture (I) Bath temperature dependence D = 475meV hw = 1.15meV 350GHz photon energy dd = ad = 0.1D = 47.5meV disordered film k B T = 9meV at 100mK hw k B T dd D 28

29 Landscape conjecture (II) Bath temperature dependence D = 475meV hw = 1.15meV 350GHz photon energy dd = ad = 0.1D = 47.5meV disordered film k B T = 22meV at 250mK smearing of the inhomogeneity hw k B T dd D 29

30 Landscape conjecture (III) Loading power dependence D = 475meV hw = 1.15meV 350GHz photon energy dd = ad = 0.1D = 47.5meV disordered film Low photon flux quasiparticles cannot escape low energy depressions hw k B T dd D 30

31 Landscape conjecture (IV) Loading power dependence D = 475meV hw = 1.15meV 350GHz photon energy dd = ad = 0.1D = 47.5meV disordered film High photon flux low energy depressions full quasiparticles can move hw k B T dd D 31

32 Conclusions Relatively low disordered ALD TiN measured, which can be modelled using a disorder-dependent pair breaking parameter model FTS measurements showed that TiN absorbs power Strong TLS contribution in the phase response Responsivity increases as loading power increases (opposite to Al and NbTiN/Al KIDs, and BCS theory prediction) Noise independent of loading power, and no photon noise observed NEP decreases as loading power increases (opposite to Al and NbTiN/Al KIDs, and BCS theory prediction) Dark NEP much smaller than optical NEP 32