Current research interests include how thermal and/or fluid-mediated processes alter the microstructure and physical properties of rocks and (other) ancient materials.

All Publications

  • On the evolution of the elastic properties of organic-rich shale upon pyrolysis-induced thermal maturation GEOPHYSICS Allan, A. M., Clark, A. C., Vanorio, T., Kanitpanyacharoen, W., Wenk, H. 2016; 81 (3): D263-D281
  • The rock physics and geochemistry of carbonates exposed to reactive brines JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH Clark, A. C., Vanorio, T. 2016; 121 (3): 1497-1513
  • Metallic Coulomb blockade thermometry down to 10 mK and below REVIEW OF SCIENTIFIC INSTRUMENTS CASPARIS, L., Meschke, M., Maradan, D., Clark, A. C., Scheller, C. P., Schwarzwaelder, K. K., Pekola, J. P., Zumbuehl, D. M. 2012; 83 (8)


    We present an improved nuclear refrigerator reaching 0.3 mK, aimed at microkelvin nanoelectronic experiments, and use it to investigate metallic Coulomb blockade thermometers (CBTs) with various resistances R. The high-R devices cool to slightly lower T, consistent with better isolation from the noise environment, and exhibit electron-phonon cooling [proportional] T(5) and a residual heat-leak of 40 aW. In contrast, the low-R CBTs display cooling with a clearly weaker T-dependence, deviating from the electron-phonon mechanism. The CBTs agree excellently with the refrigerator temperature above 20 mK and reach a minimum-T of 7.5 ± 0.2 mK.

    View details for DOI 10.1063/1.4744944

    View details for Web of Science ID 000308406500044

    View details for PubMedID 22938310

  • Method for cooling nanostructures to microkelvin temperatures REVIEW OF SCIENTIFIC INSTRUMENTS Clark, A. C., Schwarzwaelder, K. K., BANDI, T., Maradan, D., Zumbuehl, D. M. 2010; 81 (10)


    We propose a new scheme aimed at cooling nanostructures to microkelvin temperature based on the well established technique of adiabatic nuclear demagnetization: we attach each device measurement lead to an individual nuclear refrigerator, allowing efficient thermal contact to a microkelvin bath. On a prototype consisting of a parallel network of nuclear refrigerators, temperatures of ∼1 mK simultaneously on ten measurement leads have been reached upon demagnetization, thus completing the first steps toward ultracold nanostructures.

    View details for DOI 10.1063/1.3489892

    View details for Web of Science ID 000283753400031

    View details for PubMedID 21034099

  • Influence of Ortho-H-2 Clusters on the Mechanical Properties of Solid Para-H-2 JOURNAL OF LOW TEMPERATURE PHYSICS Clark, A. C., Cheng, Z. G., Bowne, M., Lin, X., Chan, M. H. 2010; 158 (5-6): 867-881
  • Heat Capacity Peak in Solid He-4: Effects of Disorder and He-3 Impurities (vol 102, 125302, 2009) PHYSICAL REVIEW LETTERS Lin, X., Clark, A. C., Cheng, Z. G., Chan, M. H. 2009; 103 (25)
  • Heat Capacity Peak in Solid He-4: Effects of Disorder and He-3 Impurities PHYSICAL REVIEW LETTERS Lin, X., Clark, A. C., Cheng, Z. G., Chan, M. H. 2009; 102 (12)


    Heat capacity measurements with significantly improved resolution find the presence of a peak in a solid 4He sample in coexistence with liquid. With improved crystallinity, the peak decreases in height and moves to lower temperature. A hysteretic heat capacity signature consistent with 3He-4He phase separation, not detected in an earlier work is clearly observed.

    View details for DOI 10.1103/PhysRevLett.102.125302

    View details for Web of Science ID 000264632100037

    View details for PubMedID 19392292

  • Thermal history of solid He-4 under oscillation PHYSICAL REVIEW B Clark, A. C., Maynard, J. D., Chan, M. H. 2008; 77 (18)
  • Effect of He-3 impurities on the nonclassical response to oscillation of solid He-4 PHYSICAL REVIEW LETTERS Kim, E., Xia, J. S., West, J. T., Lin, X., Clark, A. C., Chan, M. H. 2008; 100 (6)


    We have investigated the influence of impurities on the possible supersolid transition in 4He by systematically enriching isotopically pure samples with 3He. The addition of 3He broadens the onset of nonclassical rotational inertia and shifts it to higher temperature, suggesting that the phenomenon is correlated with the condensation of 3He atoms onto the dislocation network in solid 4He.

    View details for DOI 10.1103/PhysRevLett.100.065301

    View details for Web of Science ID 000253238400044

    View details for PubMedID 18352487

  • Probable heat capacity signature of the supersolid transition NATURE Lin, X., Clark, A. C., Chan, M. H. 2007; 449 (7165): 1025-1028


    Liquid 4He enters the superfluid state and flows without friction below 2.176 K. Thin liquid films adsorbed on solid substrates undergo the same transformation, although at a lower temperature. When the substrate is subjected to oscillatory motion a portion of the film, known as the superfluid fraction, decouples from the oscillation. A similar phenomenon has been observed in solid 4He, in which a fraction of the solid seems to decouple from the motion of the surrounding lattice. Although this observation has been replicated in various laboratories, no thermodynamic signature of the possible supersolid transition has been seen. Here we report the finding of a heat capacity peak that coincides with the onset of mass decoupling. This complementary experimental evidence supports the existence of a genuine transition between the normal solid and supersolid phases of 4He.

    View details for DOI 10.1038/nature06228

    View details for Web of Science ID 000250395000046

    View details for PubMedID 17960238

  • Nonclassical rotational inertia in helium crystals PHYSICAL REVIEW LETTERS Clark, A. C., West, J. T., Chan, M. H. 2007; 99 (13)


    It has been proposed that the observed nonclassical rotational inertia (NCRI) in solid helium results from the superflow of thin liquid films along interconnected grain boundaries within the sample. We have observed NCRI in large (4)He crystals grown at constant temperature and pressure, demonstrating that the superfluid grain boundary model cannot explain the phenomenon.

    View details for DOI 10.1103/PhysRevLett.99.135302

    View details for Web of Science ID 000249786700049

    View details for PubMedID 17930606

  • Search for superfluidity in solid hydrogen PHYSICAL REVIEW LETTERS Clark, A. C., Lin, X., Chan, M. H. 2006; 97 (24)


    A torsional oscillator study of solid para-hydrogen has been carried out down to 20 mK in a search for evidence of superfluidity. We found evidence of a possible phase transition, marked by an abrupt increase in the resonant period of oscillation and onset of extremely long relaxation times as the temperature was raised above 60 mK. In contrast to solid 4He, the change in the period for para-hydrogen is not a consequence of irrotational superflow. The long relaxation times observed suggest the effect is related to the motion of residual ortho-hydrogen molecules in the solid.

    View details for DOI 10.1103/PhysRevLett.97.245301

    View details for Web of Science ID 000242888700040

    View details for PubMedID 17280295

  • Specific heat of solid helium International Symposium on Quantum Fluids and Solids (QFS 2004) Clark, A. C., Chan, M. H. SPRINGER/PLENUM PUBLISHERS. 2005: 853–58
  • Quartz crystal microbalance study of superfluid He-4 films on gold and porous gold surfaces 13th International Symposium on Quantum Fluids and Solids Hieda, M., Clark, A. C., Chan, M. H. SPRINGER/PLENUM PUBLISHERS. 2004: 91–96
  • The growth of intermetallic compounds at Sn-Ag-Cu solder/Cu and Sn-Ag-Cu solder/Ni interfaces and the associated evolution of the solder microstructure Annual Meeting of the TMS Zribi, A., Clark, A., Zavalij, L., Borgesen, P., Cotts, E. J. SPRINGER. 2001: 1157–64