Physica B 316–317 (2002) 513–516 Influence of impurities on two-level systems in amorphous ice $ N.I. Agladze*, A.J. Sievers Laboratory of Atomic and Solid State Physics, Center for Radiophysics and Space Research, Cornell University, C17 Clark Hall, Ithaca, NY 14853-2501, USA Abstract High-density amorphous (HDA) ice has a two-level system (TLS) optical density of states with a strength comparable to that found in many conventional glasses, whereas for the low-density amorphous (LDA) phase the TLS strength is at least 30 times smaller. Isotopic substitution resulting in 50% of the molecules having lower symmetry fails to change this strength ratio suggesting that the observed difference is not due to a breaking of the tetrahedral selection rule in the HDA phase. By doping the samples with different concentrations of LiCl, methanol, HF, NaCl, LiOH, and NaOH we have explored both the defect-induced TLS optical density of states and the glass transition characteristics in the LDA ice phase. r 2002 Elsevier Science B.V. All rights reserved. Keywords: Two-level systems; Amorphous ice; Glass transition The discovery of the irreversible production of an amorphous phase of ice by pressure at low temperature makes possible the measurement of bulk amorphous samples [1,2]. The high-density amorphous (HDA) form is produced by the compression of regular ice at 77 K. Upon heating to B120 K it transforms to the low-density amorphous (LDA) form. At still higher tempera- tures B150 K it transforms to the cubic crystalline phase I c and then at 225 K to I h the hexagonal crystalline phase [3]. So it is possible to make optical and thermal measurements on a variety of phases with a single sample [4]. In this paper, low-temperature far infrared absorption by two-level systems (TLS) is studied in both amorphous ice phases. We find that HDA ice has a TLS optical density of states with strength comparable to that found in many conventional glasses whereas for the LDA phase the TLS strength is at least 30 times smaller. Upon isotopic substitution resulting in 50% of molecules having lower symmetry (HOD) this strength ratio was unchanged suggesting that the observed difference is not due to a breaking of the tetrahedral selection rule in the HDA phase. The lack of an isotope effect also severely limits what exactly can be tunneling to produce the TLS spectrum. By doping the samples with different concentrations of LiCl, methanol, HF, NaCl, LiOH, and NaOH we have explored both the TLS optical density of states and the calorimetric characteristics of the glass transition in the LDA ice phase. For LiCl and methanol we find that the doping significantly changes the TLS optical density of states and the glass transition tempera- ture T g while for other impurities studied the $ Work supported in part by NSF-DMR and by NASA. *Corresponding author. Fax: +16-072-55-6428. E-mail address: agladze@ccmr.cornell.edu (N.I. Agladze). 0921-4526/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0921-4526(02)00558-6